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ADSORPTION AND MOBILITY OF PESTICIDES AND TRACE METALS WITH SOILS
AND CLAYS
RESUME
THESIS SUBMITTED FOR THE DEGREE OF
IN CHEMISTRY
BY
Miss. NUSRAT IQBAL M. Sc. M. Phil.
DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY
ALIGARH (INDIA)
July, 1987
RESUME
RESUME
Pesticides and chemical fertilizers are now being
extensively employed in India and abroad to achieve self suffi
ciency in food crops. It has been revealed that the extensive
use of chemical fertilizers containing several unwanted heavy
metals are posing health hazard to human beings. It has also
been realized in recent past that a voluminous amount of work has
been reported on the use of sewage and industrial waste applica
tion to agriculture land. It has been recognised that these
materials contain heavy metals such as Pb, Cd, Ni, Ag, Hg etc.
A great danger is involved due to the indiscriminate use of
these chemicals, a very little work has been done and, therefore,there
is a need to understand the specific role of these chemicals to
produce a healthy growth of plants and microbial activities in soil.
Pesticides and heavy metals show a variable adsorption in
soil as a result of variation in the environmental factors, such
as climatic influences, texture, clay mineral composition, moisture
level, alkalinity, salinity and pH etc. Therefore, it has been
established that the nature and extent of adsorption with soils
and clays affect their persistence, degradation, leaching and
translocation in soil environment which in turn control soil fer
tility, plant growth, environmental pollution and soil behaviour.
(il)
The distribution of pesticides in soils after irrigation of rain
fall is impoirtant as its effectiveness is dependent on its position
in soil profile. Their persistence and leachability in soils play
a vital role in determining their efficiency potential for crop
damage and environmental pollution. Therefore, it is important to
carry out investigations on some important pesticides and heavy
metals with clays and soils with a particular view to understand
their mechanism of adsorption and mobility to assess their effi
ciency potential for their proper utilization and to avoid the risk
of soil pollution.
In view of this, it was considered worthwhile to undertake
studies on the "Adsorption and mobility of pesticides and trace
metals with soils and clays". The investigations reported in thesis
have been divided into the following chapters:
I, Studies on the mobility of some heavy metals through soil
by thin layer chromatography as influenced by organic
acids and bases,
II. Studies on the mobility of some pesticides as affected by
their chemical characteristics and some soil properties,
III, Adsorption of Cu , Pb * and Zn ^ with Ca- saturated
illite.
IV. Studies on the adsorption of methyl,2-benzimidazole car
bamate (MBC) with clays as affected by various soil para
meters.
(iii)
A concise account of the results achieved on the plan
mentioned above are as follows:
Chapter-I deals with the mobility of some heavy metals
namely, Pb, Cd, Ni, Hg and Ag in Aligarh soil in terms of R^-values
by soil thin layer cliromatography (soil TLC), The influence of
organic acids and their sodium salts, amino acids and organic bases
on mobility were studied.
It was found that the organic acids i.e.^fonnic, acetic and
oxalicj amino acids i.e, glycine, alanine and valine have increased
the mobility of heavy metals. However, no marked influence could
be observed in the case of organic bases i.e.^nicotine and pyridine.
The results have been explained on the basis of reaction mechanism
of complex formation, their stability, molecular size, pH and the
nature of the heavy metals in soil solutions,
Chapter-II deals with the mobility of some pesticides i,e,,
Fluchloralin, Formothion, Malathion and Thiometon through 3akit
sandy loam and Itwa silt loam soils have been studied by using
soil thin layer chromatography. The effect of soil organic matter
and their fractions (HA & FA), clay mineral, free sesquioxide
(AlpO, & Fe20v), soil pH and exchangeable cations was also under
taken as their mobility factor.
It was found that the pesticides moved in the order:
Thiometon Maiathion> Formothion>Fluchloralin, The effects of
(iv)
all parameters studied have been found to decrease the pesticide
mobility to a considerable extent except the malathion which showed
an increase in its mobility upon the addition of humic acid to soils.
The results have been explained on the basis of chemical character
istics of pesticide molecule and their adsorption characteristics
over soil colloids,
2+ 2+ 2+ Chapter-Ill deals with the adsorption of Cu , Pb and Zn
on Ca- saturated illite using the adsorption isotherms, Freundlich
equation and thermodynamic parameters. These results reveal that o o o
the binding strength of these ions follow the order Cu '*'>Pb '*'>Zn •*•
over Ca- illite surface and the adsorption decreases with rise in
temperature. From the Freundlich constants the adsorption capacity
(K) supports the above conclusions for the order of their preference
while the intensity factor (1/n) shows the reverse order of adsorp
tion capacity of the metal ions. The thermodynamic parameters i.e.
AG, AH and AS"were also calculated which also confirmed our
earlier results,
Chapter-IV deals with the studies on the adsorption of
methyl,2-ben2imida2ole carbamate (MBC) at 30°C with Na- form of
montmorillonite, synthetic montmorillonite, illite, kaolinite and
dickite as affected by various soil parameters. The adsorption
isotherms were 'S' type in the case of Na- montmorillonite and Na-
synthetic montmorillonite and 'L' type for other clays under study
The adsorption isotherms were well represented by Freundlich
(v)
equation. The adsorption of MBC was in the order: Na- montmori-
llonite > Na- synthetic montmorillonite > Na- illite>Na- kaolinite>
Na- dickite. The values of adsorption capacity (K) is found to
decrease in the same order as in the case of adsorption isotherms
while the adsorption intensity (1/n) of MBC over montomorillonite
and synthetic montmorillonite is about half of the intensity for
kaolinite and dickite. It is suggested that there is strong compe
tition for adsorption sites in montmorillonite and synthetic mont
morillonite.
The adsorption was found to increase with increase in soil
organic matter, AlpO, and FepO^ contents and decrease with increase
in pH values and amount of sand contents.
ADSORPTION AND MOBILITY OF PESTICIDES AND TRACE METALS WITH SOILS
AND CLAYS
THESIS SUBMITTED FOR THE DEGREE OF
IN
GHBMLISTRY
BY
Miss. NUSRAT IQBAL M. Sc. M. Phil.
DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY
AUGARH (INDIA)
July, 1987
^ c ^ ^ ^556.p"
• 2 m 19W
T3443
DEDICATED TO MY
RESPECTED PARENTS
•>>. \*>i l t i t -
A L I G A R H M U S L I M U N I V E R S I T Y
M. Se. Ph. D.
Rcf. No
CHEMISTRY SECTION Z. H. COLLEGE OH ENGG. & TECH.
A. M. U. ALIGAKH.2020O1
Dated... 2§..7., 1987..
This i s to certify that the thesis
entitled,"Adsorption and mobility of pesticides
and trace metals with soi ls and clays" i s an
original work don© by Miss Nusrat Iqbal xinder my
supervision and i s suitable for submission for
the degree of Doctor of Philosophy .In Chemistry.
r-
3 ,11 ku^ ( SAMIULLAH KHAN )
Supervisor
ACKNOWLEDGEMENT
With utmost regard I express my deepest sense of
gratitude to Dr. Samiullah Khan, Reader, Chemistry Section,
Z.H, College of Engineering and Technology, Aligarh Muslim
University, Aligarh, for his valuable guidance, keen and
tireless assistance during the course 6f this work. 1 also
express my gratefulness to Professor A.U. Malik, Chairman,
Chemistry Section, Z.H. College of Engineering and Technology,
Aligarh Muslim University, Aligarh and Professor M.S. Ahmad,
Chairman, Department of Chemistry, Aligarh Muslim University,
Aligarh for providing research facilities,
I also wish to thank my colleagues and well wishers
for their cooperation and friendly behaviour.
( Nusrat Iqbal )
C O N T E N T S
Page
Goieral Introduction 1
Chapter - I : Studies on the mobility of some heavy metals through soi l by thin layer chromatography as influenced by organic acids and bases.
Introduction 57
Esqperimental 58
Results and Discussion - - — - - - - - - 65
References - - - - - - - - - - 83
Chapter - II: Studies on the mobility of some pesticides as affected by their chvnical characteristics and some soi l properties.
Introduction - - - - - - - - - - 85
Experimental - - - - - - - - - - 86
Results and Discussion - - - - - - - - - - 92
References - - - - - - - - - - 109
Chapter - III: Adsorption of Cu^*, Pb^* and Zn^* with Ca- saturated i l l i t e .
Introduction - - - - - - - - - - 110
Eacperimental — 111
Results and Discussion - - - - - - - - — 116
References - - - - - - - - - - 125
Chapter - IV: Studies on the mobility of methyl, 2-benzimidazole carbamate (MBC) with clays as affected by various soil parameters.
Introduction - - . - - • . - - - - - 127
Experimental - - - — . . . . . . 127
Results and Discussion . . . . - „ . - . . 131
References 151
List of Papers 152
GENERAL INTRODUCTION
GENERAL INTRODUCTION
Soil is a product, resulting from disintegration and
decomposition of rocks, plants and animal materials. It possess
es a distinct morphological, mineralogical and phyaicochemical
properties, resulting from certain inheritance, from its unique
position on the surface of the earth and from the environmental
factors existing at that position. However, according to Joffe
(1936) the soil may be defined as a natural body, differentiated
into horizons of mineral and organic constituents, usually un
consolidated, of variable depth, which differs from the parent
material below in morphology, physical prope:rties and constitution,
checmial properties and composition and biological characteristics.
COMPOSITION OF SOIL
Soil is very complex in nature and consists of mainly five
important constituents namely mineral matter, organic matter,
soil water, soil air and living organisms.
MINERAL MATTERS:
The mineral matter is a product of physical and chemical
weathering of rocks consists of particles of varying sizes; those
in the finer state of subdivision 0.002 mm form the clay frac
tion. The crystal structure of clay minerals have been discussed
2
in considerable detail by Grim,(1953); Marshall, (1964);
Van Olphen, (1963). Extensive studies of X-ray diffraction
patterns have revealed that clay is crystalline in nature and
composed of few simple building units (Donahue, 1977). The
first is a tetrahedron of four oxygen atoms surrounding a central
cation (usually Si * or Al ) and the second unit consists of
octaiiedron of six oxygens (or hydroxyls) around a large cation
3+ 2+ 2+ 3+
wiiich is most commonly Al , Mg , Fe or Fe combination of
these structural units gives rise to the structure of the clay
minerals. Various types of clay minerals are made up of some basic
arrangements of tetrahedra and octahedra namely, 1:1 and 2:1
arrangements. Some important and most frequently found clay
minerals are: montmorillonite, illite, vermiculite, chlorite,
kaolinite and amorphous clays. Structures of some important clay
minerals are given in Figs, 1 and 2^ The cation exchange, surface
areas and basic unit arrangements of the clay minerals and amor
phous materieils are given in Table-I,
Montmorillonite:
Montmorillonites are swelling and sticky clays. They have
2:1 arrangement in which a single tetrahedral layer joined to each
side of the octahedral layer in sandwitch fashdon by sharing of
oxygen atoms. Some important references associated with the
investigations on the montomorillonite are: Hofmann et al, (1933);
SILICA SHEET W^m^^Mi
Si02
02 (OH)
(OH)
EXTERNAL ADSORPTIVE SURFACES
SILICA SHEET
ALUMINA SHEET'W
i.
CRYSTAL UNIT 7.1
DISTANCE FIXED LITTLE OR NO ADSORPTION
CRYSTAL UNIT
I (a l DIAGRAMMATIC EDGE VIEW OF KAOLlNITt SHOWING TWO COMPLETE LAYERS. THE RESPECTIVE CfSTAL UNITS ARE BOUND TO EACH OTHER TIGHTLY BY AN OXYGEN-HYDROXYL LINKAGE, THEREBY GIVING A RESTRICTED AND NON-EXPA^JDING LATTICE. THE ADSORPTIVE CAPACITY IS LIMITED.
'2(0ft)j
LXTERNAL ADSORPTIVE
SURFACES
510,
H j O
SiO,
^ ' ^2 SILICA SHEET
A, ^ ^ Z ^ A L U M I N A S H E E T ; ^ ^
SILICA SHEET
i+EXCHANGEABLE .S JCAIiONS l.._
SILICA SHEET
^ALUMirJA SHEET/
SILICA SHEET T I I
. . .1- -
I I
1(c ) ILLITE HAS THE SAME GENERAL STRUCTURAL ORGANIZATION AS MONTMORIL-LONITE EXCEPT IN RESPECT TO THE LINKAGES BETWEEN THE CRYSTAL UNITS. HERE K ATOMS SUPPLY ADDITIOhJAL CONNECTING LINKAGES BETWEEN THE CRYSTAL UNITS, THUS SUPPLEMENTING THE OXYGEN BONDING. THE EXPANSlOfJ IS SHARPLY LESSENED BY K LINKAGES AND ADSORPTIVE CAPACITY OF THE CLAY LOWERED,
CRYSTAL UNIT 9.3 A
DISTANCE VARIABLE INTERNAL ADSORPTIVE SURFACES
CRYSTAL UNIT
K b ) DIAGRAMMATIC EtXiE Vl tW OP MONTMORILLONITE SHOWING TWO COMPLETE LAYERS. THE RESPECTIVE CRYSTAL UtJITS ARE LOOSELY BOUfJD TO ONE ANOTHER BY WEAK OXYGEN LINKAGES WHICH ALLOW WIDE EXPANSION OF THE LATTICE. THERE IS HIGH INTLRNAL AUSORPTION OF WATER AND CATIONS,
FIG. I
o o o o
TETnAHEDRAL SILICON SHLET
W /r /' ^'K J''^
OCTAHEDRAL GIBBSITE LHEET
c-axis I I I I I I
OCTAHEDRAL SHEET
TETRAHEDRAL SHEET
HYDROGEN BONDING
— 6
+ 12
y \ y \ ^ (y 6 "^ Xf ^ ^ 4 0 + 2 (OH) - l O
b-axis"*
? ' ' 0 KAOLINITE. A I 1 LAYER SILICATE MINERAL
4 Si
6 0
NET CHARGE
+ 16
- 1 2
4,~c^ u' ' W ^ -
n H^o EXCHANGEADLE CATIONS
2 ( c ) ILLITE STRUCTURE IS SIMILAR TO ? (b ) EXCEPT THAT THE ELECTRICAL IMBALANCE IS SET RIGHT OY THE PRESENCE OF K lOrJS SITUATED QETWtEtJ ADJACENT LAURS LO THAT THE NET CHARGE IS O.
14 A°
I I Tl/AMI !>RAl
sHt i r
c-axis OCTAHEDRAL
SHEET
TETRAHEDRAL SHEET
OC) O O ^ , ^ 0 -
.uir b - a x i b - *
6 0 4 (Si,
4 0 + 2
4 ( A I ,
4 0 + 2
4 SI 6 0
Al)
(OH)
Ft.Mrf)
(OH)
NET CHARGE
- 1 2 + 16
- 1 0
+ 12
- 1 0
+ 16 - ( 2
0
or
or
or
l 2 S S
less
lc^>0 (2 Q
2(b) MONTMORILLONITE, A FREELY EXPAtJSlOLE 2-1 LAYER MINERAL. THE INTER-LAYER CATIONS ARE FREELY EXCHANGEABLE
F I G 2
3
Marshall (1935); Maegdefrali and Hofmann (1957); Hendricks
(1942); Schramm and Kwak (1984); Keren (1979); Barshad (I960);
and Brown and Miller (1971) etc, who contributed in ascertaining
the physico-chemical behaviour of the clay mineral vis a vis its
structure, Marshall (1935) and Hendricks (1947) showed that
montmorillonite always differs from its theoretical formula
(0H)^SiQA1^02Q.nH20 because of substitution within the lattice
of Al by Mg, Fe, Zn and Cr etc. and Si by Al giving a series
of group minerals. X-ray studies have shown the stacking of
silica-alumina-silica units in the C-direction, layer being conti
nuous in a- and b- direction with the result that these exert a
weak bond and an excellent cleavage between them, V/ater and other
polar molecules can easily penetrate between the unit layers
causing the lattice to expand in the c- direction. The dimension
of c axis is, therefore, not fixed but varies from 9.6 A to
substantially complete separation of the individual layers in some
cases. The cation exchange capacity of this mineral is high and
varies from 80-120 mecj/lOO g clay,
Illite;
I t has been well established (Grim et a l . , 1937; Bolt
e t a l . J 1963) tha t i l l i t e has very s imilar s t ruc ture to t ha t of
montmorillonite having 2:1 type of basic un i t s t r uc tu r a l arrange
ment. However, i t has large number of potassium ions between the
4
silica sheets of two successive units that act as a bridge in
holding adjacent layers together so tightly that water can not
penetrate between these layers. The size of the unit cell is 0
10 A . Amorphous substitution is possible within the lattice
resulting in a wide variation in their composition. Because of
illite's close structural similarity to primary mica, it is
considered to be a member of mica group. The cation exchange
capacity of illite varies from 20-40 meq/lOOgclay.
Vermiculite:
This mineral is similar to that of illite in its structure
(Gruner, 1934; Hendricks and Jefferson, 1938) but the layers held
more weakly together by hydrated magnesium (6 water molecules in
octahedral coordination with Mg) rather than tightly bound together
by l{'"ions, Venniculite has more swelling property than illite
but not as much as montmorillonite.
Chlorite;
It is often called 2:2 type clay (Donahue et al. 1977)
because its layer has two silica tetraliedra, an alumina tetrahed
ron and a magnesium octahedron. It is similar to the unit lattice
of vermiculite except that the hydrated magnesium in vermiculite,
is a firmly bonded magnesium hydroxide octahedral sheet in chlo
rite. Chlorite do not swell when wetted with water and have low
cation exchange capacity varying from 10-40 meq/lOOg clays.
s
Kaolinite;
Kaolinite is a hydrous aluminium silicate of approximate
composition AlpO,.2Si02.2H2O, The structure of this mineral was
suggested by Pauling (1930) and further work on the structure
rapidly followed by Gruner (1932). Kaolinite, Nacrite, Hallocite
and Dickite are the isomers of kaolin group. Kaolinite is 1:1
type clay having only one sheet of silica tetrahedra per sheet of
3 + alumina octahedra per layer. Almost no substitution of Al for
4+ 2+ 3+ Si or Mg for Al has occurred in kaolinite, so the net
negative charge is zero and thus the cation exchange capacity is
low. However each layer has one plane of oxygens replaced by
hydroxyls which result in strong hydrogen bonding between the
oxygen and hydroxyl layers of ad;jacent units. Because of such
strong hydrogen bonding, kaolinite do not allow water to penetrate
between the layers and have almost no swelling property. The size
of unit cell is 7.2A . The cation exchange capacity of this
mineral varies from 3-15 meq/IOOg clay.
Amorphous clays;
These are the mixture of crystalline and amorphous oxides
and hydroxides of silica, iron, aluminium and other elements which
are also exist in soils (Schwertmann and Fischer, 1973; Bigham
et al.^1978; Koon et al.^1980; Adam and Kassim, 1984; Mehlich,
1962;Basila, I962) in varying proportion. A very little research
G
TABLE - I
C.vl\OJ UXCi NlGE C^PhClTI, SURi- ACE AREA, AND BASIC UNIX AliR^^CiK-
,..:i\xo O/ V..RI0U3 CLAY InlkER/vLS Al^ Al-iORHIOUS MATERIALS.
i-iineral ma t t e r
Phys ica l p r o p e r t i e s
Cat ion Surface exchange a rea capac i t y (3^^ ^^^^^^ (meq/100g) p e r gram)
Bas ic u n i t arrangement
K a o l i n i t e
Montfflori l lonite
l l l i t e
Ve rmicu l i t e
C i a o r i t e
3-15
10-Ao
10-40
7-30
80-150 600-800
65-100
100-150 60O-8OO
2 5 - ^
1:1
2:1
2:1
2:V
2:2
a
Oxides and nydrox ides
2-6 100-800
* From Ba i ly and V/hite (1964) .
D i f f e r e n c e witii montmor i l lon i t e :
a ) A l a r c e number of K ions Detween s i l i c a sheet;j of two succe^ive
u n i t s and ajuorphouj s u b s t i t u t i o n i s p o s s i b l e .
b ) S imi l a r t o i l l i t e but has tiie l a y e r s he ld more weakly t o g e t n e r
by hydratod mac,nosium r a t n e r than K i o n s .
7
has been done on these materials regarding their physical and
chemical properties and their contribution to soil characteris
tics. Hsu and Bates (1963) have reported that these amorphous
clays have positive charge and ijiay contribute significantly to
anion exchange capacity of the soil that depends upon the pH of
the soil solution.
SOIL ORGANIC MATTER
The soil organic matter (SOM) or humus may be defined as
the organic residue left behind after microbial decomposition of
plant and animal remains, frequently dark coloured and possessing
certain characteristics physical and chemical properties
(Waksman, 1936), Its synthesis and degradation constitutes a
dynamic process and depends largely on soil environment. In
general, humus may be divided into two main groups as follows:
1. liunio Substances; Transformed products bearing little or no
resemblance to the anatomical stiMctures from which they are derived,
2. Nonhumic Substances: Unaltered remains of plant and animal
tissues and also organic compounds that have definite character
istics.
The humic substances can further be subdivided into three
main subgroups (Banerjee, 1979) according t6 their solubility in
alkali and acids, namely:
8
(i) Humic acid; Soluble in alkali and insoluble in acids.
(ii) Fulvic acid; Soluble in both alkali and acids,
(iii) Huciin; Insoluble in both alkali and acids.
Accumulation patterns of humic and fulvic acid fractions have
been studied by various workers (Goh et al, 1976; Schnitzer and
Khan, 1972; Syers et al. 1970; Kilham and Alexander, 1984) to
sliow that the humic acid concentrated principally in the surface
or inimediately below the surface horizon v/hile fulvic acid
fraction extends to much lower depth and is hardly precipitated
from an alkaline extract by acid because of its more functional
groups (Sclinitzer and Khan, 1972; Stevenson and Goh, 1971).
The chemistry of humic substances has extensively been
studied in recent years (Ghosh and Schnitzer, 1980; V/ilson, I98I;
V/ilson and Goh, 1983; Wilson et al,, 1983; Newman and Tate, 1984)
to characterize their composition and properties in soil. The
kind of 30il and its environment and the method of extraction
have been considered (Tan, 1978) as the conflicting factors to
affect the nature and characteristics of t]ie huiaic substances.
The need to standarize the method of extraction is, therefore,
stressed (Flaig et al. 1975; Burgej, I966) as it influence tlio
chemical behaviour of these substances. For example. Tan (1978)
extracted humic substance with UaiP^^Y ^"^ ' ' ^ ^^ study the
changes in IR spectra. It was reported that Na^PpO^ yield HA
with better resolved spectra than NaOH, and allowed to observe
9
the difference in Ha specti'a between soil (groups. The structure
of humic materials extracted from marine environments are highly
aliphatic and, from terristorial environments range highly
aromatic to higlily aliphatic (Wilson & Goh, 1983).
In general, humic acid molecules are composed of an
aroiuatic and aliphatic parts v/iiich are linked together (Zunino
and Martin, 1977), Hurnic acid consists of phenolic and other
aromatic units witii amino acids, peptides, polysacharides etc.
Tue functional ciiemical analysis revealed that the major functional
groups in hvunic acid are carboxylic, phenolic, alcoholic, conju
gated ketonic, carbonyl, raethoxy, amino (-NHp), secondary amino
(-KH-) and ring nitrogen. All these groups are electron donar,
hence can coordinate metal ion which behave as electron acceptor.
The presence of large concentration of oxygen containing groups
(-COOH, -OH, and -C=0) in humic materials tend to mai e them
hydrophilic. V/hile the aromatic rings, fatty acids, esters and
aliphatic carbons provide them a hydrophobic nature. Thus, the
humic materials are considered to have a simultaneous hydrophilic
as well as hydrophobic nature and hence capable of adsorption of
hydrophouic and hydrophilic substances on its surfaces.
On the basis of numerous analysis made on hunic and fulvic
acids, the main differences between model HA and FA v/ere r('porL.-;d
(Sciinitzer and Ghosh, 1y79) as follows: Total acidity, alcoholic
Oh, and CCOH content of the FA are appreciably higher than liA
10
'.viiile the nuiubcr ol' phenolic <JH, total C- 0 and -OGII-,- t roups
are a .proxiwately same in both the substances. The hii:,her E,/E^
ratio of FA than that of h^ indicates the lower particle size
of FA.
The macromolecular structure of humic and fulvic acids
has been studied by various workers (FiUkherjee and Lahiri, 1958;
Visser, 1964; Flaig and BeutaloSpacher, I968) and the concepts of
•Sphero-colloid' and Flexible linear configuration'put forward.
It v/;is shovm tiiat the hA and FA benave like 'Sphero-colloid' at
high sample concentration, low pH, or in presence of sufficient
neutral salt concentration wnile they are Flexible linear colloid
• in normal conditions (Ghosh and Schnitzer, 1980) that are pre
vailing in soils. The chemical structure and reactions of hiMic
substances have been a subject of researches of nearly two cen
turies, yet much remains to understand about these substance.
Considering various aspects of reported literature, Schnitzer and
Ghosh (1979) proposed a model of partial chemical structure of FA
as shown in Fig. 3. The molecular arrangement may account for a
significant position of the fulvic acid structure. Besides the
Vunder IVaals inLeraction and TV-A" bonding, attraction betwen n
Liie building blocks is also likely, mainly tiirough hydrogen bond
ing which luaicuo Lhe i;LniCture flexible ponnitting building blocks
Lo aggregate and disporso reversibly depending upon the environ
ment, viz. pK, ionic strength and nature of metal ions present
etc.
U
X u °xP
=o^.
g <
>
3 LL.
o-u u-o ^ ^ ' o o /
1 /
' X / o _ o u=o X V /
-= -<0-s ^ ) — ( X / \ X
o o N
^ ^ '^
\ j O
U-o UJ cc 3 H O 3 a: CO
<
o UJ
_J < 1— a: <
11
Humin is a fraction of aoil huiiius which is strongly bound
to clay minerals after the usual alkali extraction of humic acids
and is known to resist the extraction. Khan (1945) and Zyrin
(19^8) reported that a part of humic substance known as humin,
consists of humic and fulvic acids, but the only difference is
that the humic acid extracted from humin freiction contains lower
percentage of oxygen and hydrogen than that extracted from the
decalcified soil. Besides, the humic and fulvic acid content,
hymatomelanic acid has also been reported to be present in humin
fraction (Benerjee and Mukherjee, 1972).
SOIL WATER
Soil water is an important constituent of soil which helps
to control soil air, soil temperature, evapotranspiration require
ment and supply of nutrients to growing plants (Brady, 1974),
The soil water content vary with the soil texture and vary from
5.1 to 11.9 percent (Donahue, 1977).
In a study of water retention in soils, Ali and Biswas
(1968) determined the relationship between the nature and amount
of clay in soil and vi ater retention capacity. It was found that
the water retention and release v;ere maximum in bentonite clay
followed by illite and then kaolinite. The amount of available
water in soil was also found to be related with silt (Abrol and
Bhumbla, 1966) and organic matter content (Ali, 1965).
12
Water niovi ment in soils ia an another Important ajipect
of soil water relationship since it decides the amount of water
stored in the root zone, or the depth to which applied v/ater v/ill
move or whether the soil will percolate salt to prevent the deve
lopment of soil salinity. The movement of water in soil is
influenced by the location, extent, and physical characteristics
of the different horizons.. Since a major portion of water either
from rainfall, or from irrigation moves under unsaturated condi
tions, it is important to determine the hydraulic conductivity
under unsaturated conditions. The references associated with the
work on the subject are Luxmoore et al. (1977); McNeal (I968);
Lagerwerff (1969); Sojka et al. (1977); Clothier et al. (1977)
and Nakano (1977) etc.
SOIL iilR
The soil air mainly consists of oxygen, carbon dioxide,
nitrogen and nitrous oxide etc. It has been observed that the
composition of soil air varied with the climate conditions
(Russell and Appleyard, 1915) as well as with the nature of the
ijoil (Jonc, 1981).
Using various analytical methods i.e. IR spectroscopy,
Gas chromatO[j,raphy etc., nitro/j,on and nitrous oxide gases have
been measured in soils (Arnold, 1954; Dowdell and Smith, 1974)
which may be a cause of nitrogen losses under an aerobic condi
tions due to denitrification processes. The other physiologically
13
active gases like ethylene, methane, hydrogen sulphide, volatile
latty acids, alcohols, ketones and aldehydes have been reported
to be ibrmed in water logged soils by microorganisms (Smith,
1977).
MICROBIALS AND THgJR ACTIVITIES IN SOIL
Small living things are biologically classified as
plant (microflora) or animal (microfaiina) and are considered to
be present in the soil surface or in top few inches of the soil
Having their population in billions per gram of soil (Donahue,
1977). It is a universally knov/n truism that these microorganisms
affect and influence the properties of soil.
Soil microfaunae primarily comprises of:
(i) Protozoa
They are primitive, unicellular microscopic animals tiiat
feed mainly on bacteria and hence are believed as a controlling
factor upon tae abundance of bacteria. Thus influence micro
biological populations and hastens the recycling of plant nutri
ents. The main protozoan groups are amoebae^ flagellates and
ciliates,
(ii) Nematodes
Nematodes are microscopic, unsegmeixted, thread l i k e woniiS
and may oe c lasni f ied according to t h e i r feeding hab i t s . Omnivo-
14
rous , prcdaceous and p a r a s i t i c nematodes are common in s o i l s .
So i l microi'lorae consis ts of bac te r i a , fungi, ac t ino-
mycetes and algae which occur in almost a l l s o i l samples.
( i ) Bacteria
Bacteria are most abundant groups usually present in soils.
These are unicellular and include spore forming and nonspore-
forming rods, cocci vibro and spirills. They vary considerably
in shape, size and in their energy requirements (aerobic and
anaerobic), energy utilization (autotrophic and hetrotrophic) and
xn relation to plaxits and animals (Saprophytic and parasitic).
Some specific autotrophic soil bacteria can oxidize aimaonia to
nitrites and then to nitrates. Some other bacteria can also
oxidize sulphur, iron, manganese, hydrogen and carbon monoxide.
Another autotrophic bacteria may reduce the nitrates to inert
nitrogen gas. While hetrotrophic bacteria includes both nitrogen
fixing and nonnitrogen fixing kinds, Clastridium (more abundant
in poorly drained acid joils) and Azatobacter (more abundant in
well drained neutral soil) could fix atmospheric nitrogen into
soils.
(ii) Fungi
Fungi caii be classified according to their nutritive process
and are parasitic, apropiiytic or symbiotic. Parasitic fun^i de
composes resistant cellulose, lignins and gums resulting holes in
15
soil and cause plant diseases. Saprophytic funfii obtain their
energy from decomposition of organic matter while symbiotic fungi
live Oi. the roots of certain plants in a dependent relationship
in v/iiicli both fungus and plant are mutually benefitted,
(iii) Actinomycetes
Actinomycetes are ctiaracterized by branched mycelia
similar to fungi (Nocradia genera), and resembles bacteria when •
the mycelia break into fragments (genera streptomyces and micro-
juonospora), Actinomycetes vary greatly in their biochemical pro
perties in relation to higher plants and animals and in their
effects on soil bacteria.
(iv) Algae
Soil algae are microscopic, chlorophyll bearing organisms.
Tlie main groups are the green, blue green, yellow green and
diatoms. They develop tha t in moist f e r t i l e s o i l s . Certain blue
green algae have demonstrated the a b i l i t y t o f ix ni trogen from
atmosphere. Tiie species of these type of algae genera are nostoc,
Gcytonema and anabaena (Cameron and i?\iller, I96O; Mayland et ol .^
1966).
(v) Vj ruses
Viruses are noncellular organisms and are composed of
specific nucleic acid surrounded by a coat of protein. They can
multiply and grow only jaside living cells.
I n 0
The microbial activities in soil are largely responsible
for the maintenance of coil fertility as well as soil properties
(Russell, 1973). A nuij.ber of biochemical transformation viz.
amiuonification, nitrification, denitrification, symbiotic and non
symbiotic Np- fixation etc., soilre^iration sulphur, phosphorus
and other trace metal transfonnation have been reported to occur
as a result of microbial activities in soil (Parr, 1974; Gov/da
et al. 1976; Bollag and Henninger, 1976; Vlassak, 1975; Gaur et al.
1977) etc. Microbials mineralize (Reich and Bartha, 1977);
oxidize (Pepper and Miller, 1978) and reduce elements in soils and
indirectly influence their solubilities. Pesticides are consider
ed to alter the number of activities of microorganism in soils
(V/ainwright, 1978), Atmospheric pollution is also considered by
v'/ainwright (1980) as a factor to effect the microbial activities.
Studies on the nitrogen fixation by root nodule bacteria
and Rliizobium have been a subject of considerable research (Reddy
and Patrick, 1979; Charyulu and Rao, 1979). The nodulating bac
teria of various legunies are mostly those of the cowpea group
which is very well represented in India and the tropics. The pea
(R, Leguminosarum), and bean (R, Phaseoli) groups are represented
by few legume hosts. Nitrogen fixation by root nodule bacteria
is influenced by many factors, such as, nitrogen status of the
soil, supply of nutrient elements like phosphorus and molybdenum
etc.
17
ORGA?:iG COMPOUNDS IN SOIL
A number of organic cheiaicals are reported to exist in
soils, 'The transformation of organic compounds occurs mostly
throu^u biochemical processes caused by the action of micro
organisms, particularly of their enzyme systems. The organic
compounds which are generally found in soils are:
(a) Aliphatic acids
A large number of organic acids are intermediates of
metabolism of plants and microorganisms or can be derived from
them. Some are products of oxidative degradation of organic subs
tances (Yoshida and Nakadate, 1964). The amounts of formic and
acetic acid depend upon the soil conditions in which they exist.
The level of formic acid and acetic acid ranges from 0.5 to 0,9
and 0.7 to 1.0/g of soil respectively.
Many Organic acids occur in the aqueous systems of both higher
and lower fonns of plant life. Aliphatic acids of conmion occurrence
in plants include the lower members of the fatty acid series:
formic, acetic, propionic, butyric. Of equa].ly wide distribution
are the following acids: oxalic, glycolic, lactic, tartaric.
Other acids are citric, succinic, malic acids are found
in many fruits and leaves. In poorly drained soils the conditions
for the formation of aliphatic acids by microorganisms are more
favourable than in aerobic soils. For instance Takijima (19^1)
has reported the accumulation of acid in soils are in the order
18
a c e t i o b u t y r i c >t'ormic >fumaric, propionic, va l e r i c , succinic
and l a c t i c acids in .somo cases.
Some work has been reported on the influence of acids on
LLa crovrth of p lan ts and concluded both favourable and unfavour
able e f fec ts . Organic acids are also involved in the so lub i l i za
t i o n , and t ranspor t of the mineral pa r t of t-he s o i l s , Schwartz
e t a l , (1954) have been f i r s t to use modem chromatographic tech
niques for character izing a l ipha t i c organic acids in aerobic
s o i l s ,
(b) Amino acids and Proteins
About 20 to 50 percent of the organic bound nitrogen is in
the form of amino acids in soils (Bremner, 1965). The total amount
does not exceed 2 pg per g soil. The composition of the amino
acids from decomposing plant material, microbial synthesis or
exudation by roots, seems to have no such influence on the compo
sition of proteins in soil (Stevenson, 1956). But characteristic
differences occur when organic substances are decomposed by selec
tive groups of organisms (Cheshire et al,^1965). In soil hydro-
lysates, leucine and iscleucine, lysine,, alanine, glycine, valine
and sulphur corrtaining amino acids are found mostly in larger
quantities than the other aniino acids.
(c) Carbohydrates
The dead Vcocfc^tive mat^jrial contr ibutes the major par t of
carboiiydrates to so i l organic matter in the form of di f ferent
19
polyiiier saccharides, especially cellulose and horaicellulose.
The microorgc^nisms synthesize polysaccharides and other carbo
hydrates and furthemiore they also decoiLpose the polysaccharides
from plant material. The approximate content of carbohydrates in
soil organic matter is 5 to 16 percent isolated by various pro
cedure (Cheshire and hundie, 1965; Donnaar, 1967; Gupta and
Sov/den, 1963).
Gupta (1967) listed some of the different carbohydrates
v/.iich have been found in soils as;
(i) Monosaccharides
Hexoses : glucose, glactose, mannose, fructose.
Pentoses: arabinose, xylose, ribose, fucose, rhamnose,
(ii) Disaccharides
Sucrose, cellubiose, gentiobiose,
(iii) OliKosaccha'rides
Cellotriose.
(iv) Polysaccharides
Cellulose, hemicellulose.
(v) Amino sugars
Glucosamine, glactosaiaine, n-acetyl - D glucosamine.
20
(v i ) Sugar alcohols
Manitol, inosi tol*
( v i i ) Sugar acids
Glacturonic, Glucoronic acid,
(viii) hethylated sugars
2,0-methyl-D-xylose, 2,0-methyl-D-arbinose, 2,0-
methylrhamnose, 4,0-methyl glactose,
(d) I^ionocyclic phenolic compounds
Phenolic compounds in soils can be derived from phenolic
plant constituents such as flavones, flavanols, catechines,
phenolcarbonic acids and others formed by microbial synthesis.
(e) Organic phosphates
Soi l organic matter contains a small port ion of organic
phospnates. The cons t i tu t ion of the compounds iden t i f i ed so far
allows the assumption tha t they are derived from nucleic acids ,
i n o s i t o l phosphates and the phospholipids. Some of them come
in to the so i l by plant mater ia l , otiiers are synthesized by
microbes.
21
PESTICIDES
Pesticides are chemicals used for controlling the pests
like fungi, insects, herbs or other animal pests that attack crop resources
food ii other useful to man. The general definition for pesti-
cides was given by Ware (1978) as "Any substcince used for con
trolling, preventing, destroying, repelling or mitigating pests
is known as pesticide ",
Pesticides can broadly be classified into various classes
according to their use such as herbicides, fungicides and insec
ticides. There are also rodenticides, nematocides, molluscacides,
acaricides, and weedicides etc.
Herbicides
Herbicides are those chemicals which are used to destroy
or supress the growth of unwanted herbiceous and weed plant with
out injuring others. Organic chemicals which exhibit herbicidal
and plant grov;th regulator properties are numerous and varied
from biological, physical and chemical standpoints. They can be
subclassified into following groups:
(i) S-Triazines; These herbicides conform to the general
formula;
R;
N
N
22
'R.
wht re R and R^ refers to the N-substituted with lower alkyls
and X to CI, OCH^, and SCH, etc. for extensively used S-triazine.
oome of the commonly used S-triazine herbicides are: Simazine,
Atrazino, Atratone, Prometone, Ainetryne. Frometryne etc,
(ii) Substituted ureas; The substituted ui-ea class of herbi
cides contain a number of widely used compounds such as fenuron,
diuron, monuron, linuron, norea, chloroxuron, fluometuron and
S-iduron etc. Various new herbicides of this group are being eva
luated. These are used at high concentration rates as soil steri-
lants and at low rates as selective pre- and post- emergence her
bicides in crop production.
(iii) Phenoxyalkanoic acid; The members of this class of her
bicides are used primarily as foliar applied treatments. Some
of the important phenoxy alkanoic acid herbicides are;
2,4,5-T; I'iCP; LCPA; Dichloroprop and Silvex etc. They are gene
rally empolyed as pre- emergence treatment in conjuQction with
other herbicides because of their sliort residual life.
23
(iv) Carbanilates: Many types of carbanilates snow herbicidal
actions. Some of the most extensively used compounds of this
^roup includes swep, propham, chloropropham and bahban etc,
Sv/ep, propham and chloropropham are used as pre- anergence her
bicides, while banban is used as post- emergence control of wild
oat in cereals. These compounds are readily degradable by micro
organisms. They are lost through volatilization if they are
applied to wet soil,
(v) Chlorinated Aliphatic acids; Various chlorinated aliphatic
acids such as 2,2-dichloropropionic acid (dalapan); trichloroace
tic acid (TCA) and 2,2-dicl:aoroisobutyric acid (FV/-450) etc, have
been used as herbicides,
(vi) /ynitrole; It is a substituted triazole (3-amino-1,2,4-
triazole) herbicide which is used primarily due to its resisti
vity towards microorganism (Ashton, I96I), However, it was later
obuorved that ciiemical as well as microbial degradation both may
be experienced by this compound.
Besides tiie above most extensively used herbicides, there
are many otiier compounds which are also used as herbicides. They
include: Pyridine, N-aliphatic carbamates, Dipyridyls and many
others.
Fungicides
Fungicidoc are those chemicals which are used to control
24
various fungi and fungus bom diseases like mil.dew, blights,
smuts, rusts, scab, spot, rot etc. Fungi are pathogaiic organisms
which may be present on foliage surface as powdery mildews, they
may remify through plant tissues.
Fungicides are of two main types;
(i) Surface fungicides: These fungicides are used to apply to
foliage as sprays or dusts. They do not enter the plant tissues
but kill the fungus and the surface spores. They include:
Bordeaux mixture, lime sulphur, preparations containing Cu, Zn,
Mg, As, S and other natural plant extractions.
The organic surface fungicides are: orgejiic mercury, alkyl
mercury and phenyl mercury. They are appeared to cause wide
spread environmental hazards due to much toxic mercury metal
(Dix, 1981), The organic thiocarbamates such as thiram, ziram,
zineb and Maneb etc. and phenolic compounds such as dinitrophenol,
dlnocap and many others have been used as organic surjPace fungi
cides to replace organic mercury ccmpounds.
(ii) Systemic fungicides: These fungicides are absorbed into the
plant through leaves, roots and seeds and are translocated within
the plant tissues. Consequently this group is more effective than
the surface fungicides. However, newer systemic fungicides are
continuing to be developed, benomyl, MBC, TBZ, thiophanates, dowco,
triarimol, and carboxiin etc, are in common use. All organic fungi-
cides have low toxicity to plants, birds and mammals, so they are
25
not potentially hazardous in the short term. Some products contain
ing metal that are known to accumulate in food chains, may pose
some health hazards.
Insecticides
Insecticides are those chemicals which are used to kill or
control various insects. They can be applied directly to soil or
as sprays or dusts to foliage plants. Pests such as wire-worms,
chafer grubs and root maggots in soil are extremely difficult to
be controlled due to their relatively inactive nature. Volatile
insecticides are more beneficial as they can permeate the soil
crevices and reach the inactive stages of the pests such as eggs
or pupae. In general, insecticidal chemicals may be classified in
to follov/ing groups:
(i) 0rganochlorines; Among various organochlorine insecticides,
the most important and best known is DDT, it was followed by BHC
(1942), Within a very short period, a range of these insecticides
were developed as chlordane (19^5), heptachlor (1945), toxaphene
(1947), methoxychlor (1948), aldrin (19^8), dieldrin (19^8),
endrin (1951), and endosulfan (1956) etc. and are used as insecti
cides. In general, these are wide spectrum insecticides used to
kill a great variety of pests.
(ii) Or^anophosphorus: The organophosphorus insecticides
includes: Parathion (1944), diazinon (1952), trichlorophon (1952),
26
phorate (1954), carbophenothion (1955), disulfoton (1956),
dimethoate (1956), fenthion (1957), thionaz:Ln (1959), menazone
(1961), difXonatG (I966), chlorfen vinphos (1963) and others like
malathion, phosphamidon, dichlorvos etc, Tlie organophosphates
are much more soluble in v/ater, but their volatility is nearly-
equal to that of organochlorines. These insecticides are less
persistent in comparison to organochlorines.
(iii) Carbamates; Some carbamate compounds have also been used
as insecticides. They include CHyiC, carbofuron, bendiocarb,
aminocarb, metabal etc. Most of the carbamates act on insects in
a similar way to the organophosphorus compounds. They persist much
less than organochlorines but longer than organophosphorus compounds
With increasing use of pesticide in agriculture, these
chemicals are harmful for environment, Rachael Carson (1965) was
one of the first, v/ho recognize the dangers of pesticide pollution.
She produced evidence of toxic effects upon wild life and potential
hazard to man. Since then, a number of workers have carried out
experiments on various aspects of environmental pollution caused
by pesticides (Heuper and Conway, 1964; Mellanby, 1972a,b).
Some pesticides are described as stable and persistent in
soil for varying period of time, Watter and Grussendorf (I969)
showed that organo-chlorine insecticide deposits on the walls of
stores might be a source of residue in grains. Few organochlorine
and organocarbamate insecticides are feebly systemic and are
27
adsorbed by roots or leaves, metabolized, and translocated in
noninsecticidal amounts to leave persistent and undesirable
residues at harvest. Duggan (1968) showed that oil containing
seeds may concentrate these to one tenth of the original content
in soil,
Menzie (I969) has classified the possible biotransfomia-
tion of pesticides in plants and soils. These include; oxidation,
dehydration, dehydrohalogenation, reduction, conjugation, hydro-
lytic reaction, exchange reaction and isomerization. The factors
including the presence of residues may be artificial or natural.
The natural factors are-more sobtle in their effect on residues
in plants. They include the plants (Stoller, 1970); soil
(Harris and Sans, 1969); Weather (Li-nkson et al, 1965); penetra
tion (Frank, 1967; Frank, 1970); absorption (Hulpke, 1970);
translocation (Nash and Beall, 1970) and diffusion. Animals and
humans absorb these chemicals from their food,and accumulate them
in specific body organs until it reaches a lethal threshold dosage
for species. In general, the harmful effects of pesticides can
directly be related to their persistence and accumulation in the
environment, as well as within the body tissues of animals and
humans.
Various aspects of pesticide residues have been studied
by many workers. Some of those include; persistence (Robinson,
1970); pesticide in peoples (Waasherman et al,, I967); transloca
tion (Helling, 1971; Wain and Carter, 1967); residues in feed,
food and fibre plants, and tobacco (Finlayson and MacCarty, 1965).
28
TRACE METALS
Sixteen elements are knovm to be essential for plant
growth and microbial activities in soils. Of these some are
needed by plants in larger amounts and are called major nutri
ents v/hilc others that are required in smaller amounts are known
as micro or trace elements. These are iron, manganese, zinc,
copper, boron, chlorine and molybdenum, A part from these, some
other elements such as Pb, Cd, Cr, Ni, Ag, Hg, As, Se, V and Ba
etc. are also knovm to be present in soil in trace quantities,
however-, they are not essential for plant or animal growth and
found to be toxic to men and animals and produce undesirable
effects (Singh and Singh, 1977; Dijkshoorin et al,j1979;
Lauwerys et al.^1979j Schmitt, et al,_,1979 etc.). Forbes et al,
(197' ) have reported that the adsorption of heavy metal cations
on solid solution interface, is not simply an electrostatic but
consider (i) as a function of properties of the solid surface
and the adsorbing species, (ii) the ability of the adsorbing metal
ions to hydrolyse in solution in determining their affinities for
the surface of soil minerals.
In recent years, man has utilized the sewage and indus
trial v astes as a source of micronutrients in most of the deve
loping countries like India, Large population centres producing
tremendous amount of sev/age sludge and rapid ::Lndustrialization
29
incorporating many heavy metals, however, aroused the concern
over tiieir possible use in agriculture. Composition of different
sludge and industrial wastes has been studied by various worKers
(Stover et al.^1976; Anderson and Nilson, 1972), It was found
that heavy metals constitute a major part of its composition, Thej
are accumulated in soils because of their excessive use and causes
a hazardous problem to plant and animal life.
In most of the studies, it has been shown that the metals
added to soil remain in the upper few inches (Williams et al,_,
1980; Page and Chang, 1975) because of various immobilizing i|;iecha-
nisms like precipitation of specific adsorption on oxides, clay
minerals and organic matter. Considering the sludge as a complex
mixture of organic and inorganic species, various forms of trace
metals in soil could be understood (Gregson and Alloway, 1984;
Tills and Alloway, 1983).
The chemical behaviour of trace metals has extensively
been studied in relation to soils and clays (Bowman et al,j1981;
Hodgson, 1963; Tiller et al,^1979). It has been observed that
Pb may form soluble inorganic complexes with Einionic groups like
hydroxyl, chloride, sulphide, phosphate and carbonate according
to soil pH, and acidity of interacting ions, Richard and Nriagu
(1978) observed that Pb remains as carbonate species, particularly, 2
Pb(C0,)2" ^'^ P^ ^" between 6 and 8, while at pH-<6 and in absence 2+ +
of carbonate, Pb , PbCl , and PbClp v/ere predominant inorganic
30
spec ies . Santillan-Medrano and JurinaK(1975) reported the for
mation of PbCO , Pb(0H)2, ^^3(^0^)2, Pb^(PO^),OH, and/or
Pb,0(1^^)2 species at pH in between 7.5 and 8,0 , Pb has also
been observed to complex with sulphur based amino acid, cystein
and fulvic acid (S i l l en and k a r t e l l , 1964; Schnitzer and Skinner,
1967). Gregson and Alloway (1984) studying the Pb speciat ion in
heavi ly pol luted s o i l , reported tha t Pb occurs as both high and
low molecular v/eight organo-Pb-complex depending upon the i n i t i a l
pH. In a potentiometric study of metal-HA complexes, Stevenson
(1977) reported tha t there are two or more binding s i t e s in Pb-HA
complex formation. Thus, 2:1 and 1:1 Pb-HA complex are formed to
give a chain l i ke s t ruc ture by displacing H ions from exchange
s i t e s or by releasing proton from hydration water of metal ion.
In comparison to other heavy metals , the order of s t a b i l i t y cons
t a n t for metal - HA complex i s as follows:
C u > Pb§> C d > Z n
Bittel and Miller (1974) studied the adsorption behaviour of Pb
on luontmorillonite, kaolinite and illite to show that the adsorp
tion sites were all alike and there was little or no interaction
between adsorbed ions. On geothite, Pb was reported to be speci
fically adsorbed and its distribution between solid and liquid
phase is pH dependent (Forbes et al., 197V). It was reported
(Forbes et al., 1976) that for each Pb ion adsorption, nearly tv/o
moles of H ions are displaced from interface which was in the
31
direct contrast of the mass action approach of Grimme (1968). 2 +
Again, the Pb has hydrolysable nature, its adsorption could be
considered to occur via the adsorption of PbOH and Pb(OH)p
species at higher pli values (James and Healy, 1972).
Cadmium is accumulated in soils , mainly through continuous
application of sewage sludge; (Anderson and Nilsson, 197^) on the
soil colloids is a major factor influencing the distribution of Cd
between aqueous and solid phase in soil water system. Lagerwerff
and Brewer (1972) investigated the exchange behaviour of cadmium
with Al and Ca treated soils. It was found that cadmium adsorp
tion decreased with increasing AlCl^ or CaClp and decreasing NaCl
concentration in soil solution. The effect of exchangeable cations
on the Cd sorption by montmorillonite was studied by Garcia-Mira-
gaya and Page (1977) who observed the following decreasing order:
Na->K - > Ca -•> Al-mon-tmorillonite.
Jarvis and Jones (1980) found that the cadmium strongly sorbed
by soils when added in the amount comparable to that added through
sewage sludge or phosphatic fertilizers. They also observed that
various cations are capable of disorbing Cd from soil in the order:
Pb > Zn > Cu > Mn > Ca
Nickel is another phytotoxic (Foronghi et al., 1976; Ormrod, 1977)
and zootoxic element , especially to marine life (NRC, 1975; Toth,
32
1968). It causes carcinogenesis (NRC, 1975). Nickel is generally-
accumulated in soils through industrial and municipal wastes.
It is introduced into human and animal food
chain mainly through water and food plants via soils. Thus, the
availability of Ni in soil solution and its absorption by plants
is an important process which is governed by its chemistry in
soils, Sadiq and Enfield (198A) studied the solid phase formation
and chemistiy of Ni in soils. It was observed that nickel behaves
in several ways depending upon the pH of soil solution. In Fe
dominated soils, nickel ferrite (NiFe^O,) and Ni(PO.)2 are preci
pitated depending upon the availability of Fe in soils. Nickel
oxides and hydroxides have been identified in soils having pH
greater than 9. Other species which are reported to precipitate
are carbonate, sulphate, phosphate, chloride, hydroxy complexes
like NiCOH)"*", Ni "*", NiSO^ , NiHPO° etc. Bromo-, chloro-, iodo-
and nitrocomplexes etc.
In general, it has been pointed out that atmospheric fall
out from ore smelter contributes significantly to soil contamina
tion with heavy metals (Goodman and Roberts, 1972; Cartwright et
al., 1977; Franzin et al., 1979). They exist in soil as bound
species with carbonate, oxide, organic matter and as exchangeable
or incorporated in crystal lattice (McLaren and Crawford, 1973;
Gibbs, 1977). Mattigod and Sposito (1977) reported the sulphate
complex species of these trace metals at low pH values, which dec
reased with increasing pH due to their complexation with organic
matter.
33
Glnzburg (I96O) reported that the preferential uptake
of metal cations followed the order Pb > Cu > C a > B a > Mg >• Hg
on montmorillonite and that the capacity of the heavy pietals
to replace the Ca on Kaolinite is in the order Pb > Cu >Hg.
ADSORFTION
The term adsorption was first used by Kayser (1881) at
the suggestion of E-du Boise-Raymond and refers strictly to the
existence of higher concentration of any par-ticular component at
the surface of liquid or solid phase than is present in the bulk.
In general, adsorption may be classified into two types
namely physical and chemical. The physical adsorption occurs
mainly due to weak forces, like ion-dipole, dipole-dipole, polari
zation or induced dipole, and Vander Waal's forces etc. It
involves usually lesser heat changes of the order of 0.5 to 2 KCal
or less (Adams, 1973; Glasstone, I960). This phenomenon is more or
less non-specific, reversible and temporary in character. While
chemical adsorption is due to the formation of chemical bond
between the adsorbent and adsorbate molecules. It is characteri
zed by a large heat change as 5-20 KCal, In some cases, the value
of the heat of adsorption has been reported to be in the range of
15 to 50 KCal per mole. (Adamson, I96O; Biggar and Cheung, 1973;
Gregg and Singh, 1967). Thus, the chemical adsorption is a speci-
34
fie, non-reversible and permanent surface phenomenon.
Adsorption of inorganic and organic components have gained
considerable importance in the field of soil chemistry. In
recent years, Khan and Bansal (1980); Joshi (1986); Goodman (1986);
Cline and Oconnor (1984); o'Connor et al. (1983); Kuo and Baker
(1980); Ellioott and Huang (1979); Curtin et al, (1980); Reddy
et al. (1987); Rick et al, (1987); and others have studied the
adsorption phenomena in relation to soil and clays in various
aspects.
The clay minerals as well as crystalline and amorphous
obcide.s and hydroxides both having a capacity for adsorption due to
coulombic, and/or physical forces. Organic pesticides adsorb on
both organic and inorganic surfaces depending upon the chemical
properties of adsorbent and adsorbate (Weber, 1972), The organic
matter has been reported to have a highest cation exchange capa
city (200 to 400 meq/100 g) and surface area (500 to 800 sq. m.
per gram) which are comparable to montmorillonite and vermiculite
(Bailey and White, 1964), Basic pesticides were reported to be
adsorbed strongly on soil organic matter (Weber et al,,1969) and
expanding lattice clay minerals (Weber, I966; Weber, 1970), Acidic
pesticides were adsorbed in moderate amounts on organic matter
and relatively low amounts on clay minerals and hydrous metallic
oxides (Carringer & Weber, 1974; Scott & Weber, 1966; Weber, 1972).
While non-ionic pesticides were considered to adsorb in greatest
amount by organic matter but their adsorption by clay mineral was
35
also important for organophosphate and several other pesticide
families (Weber, 1972), In addition, it has been reported that
carbamate and organophosphate insecticides were adsorbed by soil
organic matter (Leenheer and Ahlrichs, 1971). The physico-
chemical nature of adsorbate which controls the role of the mole
cules may be summarized as follows: (i) Chemical character, shape
and configuration, (ii) Acidity or basicity of the molecule, (iii)
Vater solubility, (iv) Charge distribution on the organic cations,
(v) Polarity, (vi) Molecular size and (vii) Polarizability.
Adsorption of inorganic cations with soils has extensively
studied by a number of workers as Curtin (1980); Kuo and Baker
(1980); Graffin and Au (1977) etc. and generally found in the
following order.
. + H''>Al^"*">Ba^-'>Sr^*>Ca^-'>Mg^"*">K'">Na''>Li
The property of adsorption plays an important role in
holding water and plant nutrients and keeps them available for the
use of growing plants. Fertilizers in the form of soluble subs
tances, are retained on the surface of the soil colloid due to
their adsorption and indurate for leaching.
Adsorption equations
An adsorption isotherm represents the functional relation
ship between adsorbed phase concentration (X/m) and solution con
centration (Ce) at constant temperature. Generally, two types of
3 r» 0
isotherm equation namely Freundlich and Langmuir equations, have
most frequently been used to describe the adsorption behaviour of
various species in soils,
(a) Freundlich equation; In Freundlich type of adsorption iso
therm, the concentration of solute species in adsorbed phase is
given by the equation:
Vn x/m = KCe
or ln ( x/m) = InK + ^^n inCf
where, "x/m is the amount of solute adsorbed (X) per mass of
adsorbent ("m ), the constants K and 1/n represents the adsorption
capacity and intensity, respectively, Ce is the equilibrium concen
tration of solute in solution.
If In (x/m) is plotted against InCe , a straight line is
obtained whose intercept and slope represents the constant K and
1/n respectively. Using the value of K as a measure of adsorption,
the adsorption capacity of various adsorbent may be compared while
1/n measure the non-linearity of the process. If 1/n is unity, the
process is said to be linear.
(b) Langmuir equation; The Langmuir equation may be written as:
./ ABCe X/m = 1 + BCe
37
where, A = adsorption maxima (^g/g ) ; B = coefficient that
reflects the relative rates of adsorption and desorption at
equilibrium and, thus, an affinity term (ml//ag); x/m and Ce are
the same as in Freundlich equation.
The linear transformation of the above equation can be
written as:
C e A . Ce ^ ^ / /^ A BA
The slope and intercept of the plot (Ce/x/m "vs. Ce)
gives the value of constants, 1/A and 1/BA respectively. The
adsorption capacity of adsorbent (A), depends upon the specific
surface area, surface charge characteristic etc. The constant
B is a measure of the adsorption energy.
Classification of Adsorption isotherm
Giles et al. (196O) studied the adsorption from aqueous
solution of a variety of solutes and developed a classification of
adsorption isotherms into S,L,H & C tj^es depending upon the ini
tial slope.
S -Type;
The S-type isotherms are common when solid had a high
affinity for the solvent. This type of isotherm indicates a ten
dency for large adsorbed molecules to associate rather than to
38
remain as isolated units. In the S-type curve the slope initia
lly increased witii increase in concentration due to cooperative
adsorption. At the saturation point where no site remained
vacant slope fill. Such type of isotherms occurred when the ac
tivation energy for desorption of solute was concentration depen
dent and or was markedly reduced by large negative contribution
of the solvent,
L-Type;
TiiG L-type of isotherm was formed when the sol id had
a liigh af f in i ty for the so lu te , or the adsorbed solute molecule
were not ve r t i ca l l y oriented. This curve showed tha t as more
s i t e s in the substrate were f i l l e d up i t became increasingly
d i f f i c u l t for a bombarding solute molecule to find a vacant
s i t e . In L-type curve, the solid possessed fev/ s i t e s which were
-/ideiy separated and had large hydrophobic region. This type
of isotherms was reported by Weber (1966) and Bailey et a l ,
(1^j6n) in studying the adsorption of t r i a z i n e pes t i c ides .
H -Type;
Tlie li-type curve was rare and obtained when the solute
has a very high affinity for substrate or there was no measurable
amount of solute left in the solution. The initial part of H-
type isotherm was vertical. This type of curve along v/ith a
platean was obtained in case of chemisorption of fatty acids,
39
(Smith and Puzek, 19^), nanatocides such as telOMe(Singhal and
Kumar, 1976) and ionic micilles or polymeric molecules. The
length o£ plateau indicated the difficulty of formation of second
leiyer.
g-Type;
The C-type isotherm, was obtained when new sites became
available as the solute molecules were adsorbed from the solution.
It represented penetration of substrate micropores by solute with
or without solvent. The small solute molecules were found to be
accompanied by water while the larger were with or without water.
Such type of isotherms were found by Greenland et al, (1962) and
Singhal et al, (1976) in case of amino acid and necaatocide adsorp
tion respectively,
MOBILITY OF PESTICIDES AND TRACE MSTALS IN SOILS
The movement of chemical substance in soil may influence
ootli its effectiveneas and potential as a contaminant in adjacent
soil, V)fater or air. The substance moves predominantly in vertical
direction in the zone of aeration above the water label (Jordan
et al, 1970), The chemical substance in soil may translocate due
to two general processes namely, mass transfer and diffusion. Any
movement to a considerable distance is said to be occurred by mass
transfer i,e, flow or convection. It is caused by water percolat-
40
ing downward or absorption upward through soil pores. Further
more, the soils have pores of various sizes, therefore, the
mobility of a particular substance in soils varies with the
particle size. The movement through diffusion may be described
by Pick's law which is;
j _ D ^ and > ^ = D ( - ^ 2 )
It shows that the rate of movement (J) of a chemical substance over
a distance of X at time t is directly proportional to its diffusion
coefficient, D and concentration, C, The diffusion coefficient, D
determines whether the chemical diffuse through air or water.
According to Goring (1967), the chemicals with water/air ratios 4
under 1x10 diffuse primarily through air while those with their
ratios higher than this diffuse through water. It is also obser
ved that most of the pesticidal chemicals have their water/air
4 ratio more than 3x10 and hence, their movement in soil occurs in
aqueous solutions (Helling, 1970).
Interaction with the soil itself is a highly significant
factor v/hich retards the movement of chemicals in soil. Various
other factors which affects the mobility have been reported by
Builey and V/hite (I96A) and others (Rhodes et al,, 1970; Schreiber
et al., 1971). Some important parameters influencing the move
ment of chemical substances includes their adsorption, formulation
and their solubility in water, flov; rate, amount of v/etting events,
41
r- e of their application and degradation etc. Some other
iactors like nature of chemical substance and soil colloids,
soil pH, exchangeable cations and anions etc, have also been
reported (Singhal and Bansal, 1978; Khan and Khan, 1986;
G-rover, 1973; Singiial et al,, 1977) etc. to affect the trar^oca-
tion process in soil.
To evaluate the movement of chemical substance in soil,
various methods have been used. In which column chromatographic
iiietiiods and soil tiiin layer are considered as powerfull tools.
Yariouo conventional columns have been used by various workers e.g.
aluminium'rings (Harris, 1957), sectioned monel metal pipes
(Upchurch and Pierce, 1957), stove pipe sections (Rodgers, 1968),
staked time cans (Sheets, 1958), perforated teflon (Kay and Elrick,
1967), rectangular plastic paper (Horowitz, I968) etc. The chemi
cal substance is analysed in various sections of the column.
Direct analysis of column effluent (Davidson and Santelmann, I968;
Rodgers, 1968) has been carried out for highly mobile substances.
Soil Tnin Layer Chromatography; Thin layer chromatography is an
inexpensive,sensitive, selective and rapid tool of analytical
chemistry used for the separation and identification of inorgaiiic
and organic compounds (Ludwick et al., 1977; Pribyl et al., 1977;
Krahneet al., 1977). Soil thin layer chromatography is an adsorp
tion chromatography using a thin layer of soil as adsorbent or
stationary phase. While the mobile phase being liquid (generally
42
water) percolate throu iti the stationary phase. This technique
was i'irst successi'uliy used by Helling and Turner (1968). It is
aualo ;oua to conveniioual Tl£ v/ith substitution oi" soil as the
adsorbent phase. Later, this technique was successfully applied
to study the movement oi" various pesticides (Rhodes et al. , 1970;
Helling, 1971a,b,c,- Abdel-Kader et al., 1984; Dedek et al., 1985);
or -anics (Singhal and Bansal, 1978; Krishnamurthy, 1983; Shannon
et al., 1985); and tracemetals (Singhal et al., 1977; Singh et al.,
1985).
The preparation of soil TLC plates is carried out by
spreading a uniionn thin layer of aqueous soil slurry with the
help of an applicator. It is then allowed to stand overnight for horizontal , .
drying in , position (Bremner et al., 1961). The thick-
nesG of tiie layer on soil TLC plates in the range of 0.15 to 2.0 mm,
is unimportant with respect to R . for diagnostic or qualitative
work (Helling, 1971).
The amount of substance applied, depends upon tiie layer
thickness and the v isua l iza t ion method which are inversely pro
por t iona l to each other . The substance to be studied i s normally
applied by touching the t i p of a f i l l e d cap i l l a ry , micropipette
or microburette to the adsorbent layer . The sample i s placed or
spotted about j> cm above the bottom end of the p l a t e so tha t the
solvent level wi l l be at l eas t one cent'^imeter below the centre
o i' the spot. The diameter of the spot should not exceed 0.5 cm and
should be as small as poss ib le . These p la te s were then developed
43
in developing solution (usually water), air dried, and the spot
is detected by various methods like chanicai reagents, fluore
scence and iodine vapours etc., but the substance with which the
ccMnponent reacts chemically must not be used. The mobility is then
estimated as R^-values which is the ratio of the distance travelled
by the substance under study to the distance travelled by the
solvent (Helling, 1971). The substance detection on the developed
plate is an important step of this technique and must be made very
clear as it characterizes the adsorption behaviour of that substance
and adsorption capacity of the soil. It was observed (Helling, 1970)
that highly mobile compound without any significant tailing, is
adsorbed linearly on to the soil surface. While in the case of
compounds with lesser mobility exhibiting tailing, shown a non
linear adsorption. Thus, soil thin layer chromatography provides a
very large field of application for investigating problems in various
applied or non-applied fields.
THE PROBLEM
The application of pesticides, sewage and industrial waste
to soil are finding a great importance in modem agricultural
practices. Their presence in soils may influence the growth of
plants and soil microorganisms. They are also posing some undesir
able effects on our flora and found due to the indiscriminate use
of pesticides and heavy metals. In India, various food plants have
44
been studied to analyse the presence of pesticides and heavy
metals such as Pb, Cd, Ni, Hg, Ag and many otherso It has been
observed that their concentration exceeds the maximuia permissible
limit in food plants.
Pesticide residues in soil may originate from accidental
or incidental contamination, as from spoilage, from pesticides
in adhering particles of treated soil, by volatilization of pesti
cides from treated soil or from dusts or sprays drifted by wind,
^hile sewage sludge and industrial wastes and many other processes
like atmospheric fallout, auto ejdiaust, fertilizer impurities,
have produced tlje heavy metal contamination of soils and plants.
Due to the great importance attached with the heavy metals
and pesticides, it was considered worthwhile to undertake investi
gations along the follov/ing lines which constitute the subject
matter of this thesis entitled, "Adsorption and mobility of pesti
cides and trace metals with soils and clays".
1. Studies on the mobility of some heavy metals through soil by thin layer chromatography as influenced by organic acids and bases.
2. Studies on the mobility of some pesticides as affected by their chemical characteristics and some soil properties.
^. Adsorption of Cu "*", Pb " and Zn "*" with Ca- saturated illite.
4. Studies on the adsorption of methyl, 2-benzimidazole carbamate (MBC) with clays as affected by various soil parameters.
45
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CHAPTER - I
THE IKrLUEKCE OF ORGANIC ACIDS AND BASES ON TliE MOBILITY
OF SOME HEAVY MET'ALS THROUGH ALIGARH SOIL BY
SOIL THIN LAYER CHROMATOGRAPHY
57
INTRODUCTION
Among various organic compounds, carboxylic acids
(Schwartz et al„,l954), amino acids (Rending, 1951; Sowdens, 1956)
and organic bases like nicotine (Shtompel, 1981; Hanks et al<, 1980
and pyridine (Hanks et al., 1980; Vasil'Chenko et al.-1975;
Martin, 1977) have been found to occur or used in soils.
These organic compounds are found to interact with soil
colloids (Smith, 1934; Greenland et al,jl962; Brindley and Moll,
1965; Khan and Singhal, 1967; Theng, 1974) which may affect the
metal translocation and influence their availability to plants.
However, their specific role in the translocation of heavy metals
has not yet been attempted. Recently Khan et al, (1982) have re
ported that the heavy metals translocate in the soil as metal-soil
organic matter (SOM) complexes and emphasized the importance of
organic compound in the translocation of heavy metals. The purpose
of this study is to understand the role of certain organic com
pounds e.g. carboxylic acids, amino acids and organic bases in the
mobilization of certain heavy metals like Pb, Cd, Ni, Hg and Ag which
are of polluting nature using soil thin layer chromatography. The
present study may be useful in understanding the behaviour of other
organic chemicals having similar functional groups in the metal
translocation through soils.
58
EXPERIMENTAL
(A) DETERMINATIOn OF MECHANICAL COMPOSITION OF THE SOIL
The mechanical composition of the Aligarh soil was deter
mined by International pipette method (Piper, 1950). For this,
a 10g soil sample (passed through 7 mesh BSS sieve), was dispers
ed in water after treatment with 30? 2^P ^° remove any organic
matter and 0.2N HCl and 50 ml sodium oxalate (8g/ litre) as dis
persing agent. The percentage of coarse, medium and fine sand
was calculated from the weight of residue left behind on 25, 72
and 200 mesh sieves (BSS), The suspension was diluted to 500 ml
and transferred to a graduated boiling tube which was immersed in a
constant temperature water bath at 25 + 1 C throughout the course
of pipetting. A 10 ml sample was pipetted out carefully at speci
fied intervals of time from a depth of 10 cm. It was dried and
weigiied. Tlie percunLage of medium silt, fine silt and clay
were then calculated from the weights of residues. The percentage
of coarse silt was calculated by substracting the sum of the per
centage of all the fractions given above from hundred. The
results of mechanical analysis are: Sand: 60,^YQ, Silt: 25,5% and
clay:M'/o
(B) DETERMINATION OF pH
The pH of the soil was determined with Elico pH meter,
model L.-10, with glass and saturated calomel electrodes assembly.
5!)
A 1:2,5 soil: water ratio suspension was used for measuring
the pH of the soil. The pH of the soil was found to be 8.8,
(C) PETERlVilNATION OB' ELECTRICAL CONDUCTIVITY
The electrical conductivity of the soil was measured with
Phillips conductivity bridge and dip type cell at 30 + 1 C.
A 1:2.5 soil: water ratio was use for the measurement. The
-4 -1 electrical conductivity of soil was 4.8 x 10 mhos cm .
(D) DETERMINATION OF ORGANIC MATTER
The soil organic matter content of the soil was detennined
by the method of Walkley (1947) as follows:
Reagents required
1N pot*assium dichromate, cone, sulphuric acid, 85% sulphuric acid and
phosphoric acid, 1% diphenylaniine indicator in^ water . N/2
ferrous ammonium sulphate solution.
Procedure
A 2 g of soil sample was taken in 500 ml conical flask,
10 ml of N potassium dichromate solution and 20 ml of conCo sul
phuric acid were added. The flask was shaken gently several
times and allov/ed to stand for 30 minutes and thereafter 200 ml
of distilled water, 10 ml of phosphoric acid, and 1 ml of di-
phenylaudne indicator were added to it. The amount of unreacted
60
potassium dichromate was titrated against standard N/2 ferrous
ammonium sulphate solution till the violet colour change to pur
ple, and finally to green. Reagents blank determination was
also carried out in the same manner. From the volume of dichro
mate solution used for oxidation, organic carbon was calculated
by the expression:
Organic carbon = (Blank litre - Actual litre} x 0,003 x M weight of dry soil in g.
wiiere M is concentration of ferrous ammonium sulphate. The value
of organic carbon was converted to organic matter by multiplying
witij the factor 1,724. The organic matter content of Aligarh
soil was found to be 0,4o%,
(E) DETERMINATION OF CATION EXCHANGE CAPACITY
Tlio cation exchange ca[)acity of the soil was determined
by the method of Jackson (1958).
Reagents required
0.05N hydrochloric acid, IN sodium acetate (pH 5), 1N
calcium cixloride solution, EDTA solution, ^% solution of erio-
chrome black 'T' in ethanol, buffer (pH 10), 2% sodium cyanide
solution.
Procedure
A 5g soil sample was taken in a 100 ml conical flask and
61
tlie soluble salts were washed out by treating the soil with
0.05N HCl and finally with distilled water. It was furtiier
treated with 1N sodium acetate of pH 5 for 30 minutes with inter
mittent stirring. This acidified sample was given five washings
with 1N standard calcium cliloride solution„ The excess salt was
removed by washing with 80% aqueous acetone solution untill the
excess CaClp is removed, as indicated by a negative AgNO^ test
for chloride ion in the final washing. The calcium ions were
exchanged from Ca saturated soils by means of exchanging it with
a neutral 1N sodium acetate solution. The washings were collected
and utilized in the determination of exciianged Ca by titrating
it with a standard EDTA solution, using 10 ml of the NH^Cl-NH^OH
buffer of pH-10 and eriochrome black 'T' indicator with 1 ml of
2/0 NaCN solution as masking agent for interfering ions, A reagent
blank was also run simultaneously to avoid any error due to impu
rities. The blank readings were substracted from the readings of
calcium determination. From the volume of the EDTA used, the
values of cation exchange capacity was calculated by using the
expression:
„ , .. V X N X 100 Exchange capacity = — r - r z — T - r , T^—: ( in meq. per weight of the so i l m g. 100 g so i l )
where, V is the volume of EDTA, N is the normality of EDTA solu
tion used. The cation exchange capacity of Aligarh soil was deter
mined to be 16.3 meq per 100 g soil.
62
(F) DETEmiNATION OF EXCHANGEABLE CATIONS
A 50 g air dried soil sample was taken intp a 250 ml
conical flask and a 100 ml of 1N NH^OAc was added to it. The flask
was covered with a stopper and was shaken for 20 minutes and then
allowed to stand overnight. The contents of the flask were then
transferred into a buckner funnel in which a moist Whatman filter
paper (no. 42) had been seated by gentle suction. The soil was leach
ed with an additional 400 ml of NH^OAc, The filtrate containing
NHiOAc extract of soil was evaporated to dryness on a steam plate.
If the residue is dark in colour (indicating organic matter), it is
again treated with 2 ml of 30j6 JLOg and 2 ml of 6N HNO, and heated
to dryness on a steam plate» The dried residue was dissolved in 10
ml of 6N H:I and diluted with distilled water. It was filtered
through Whatman filter paper (no. 42) and the volume was made upto
100 ml.
Exchangeable calcium plus magnesium was estimated in the
known volume of filtrate by EDTA titration with eriochrome black
•T' indicator. Calcium was also estimated separately by using mu-
rexide indicator with 10J KOH as recommended by Jackson (1958). The
volume of EDTA for magnesium was calculated by substracting the
volume for calcium from the volume of calcium plus magnesium used.
The exchangeable sodium and potassium were estimated in
solution by using 'Systronicks' flame photometer. Standard curve
for sodium (0»50 fig) and potassium {0-^ /ug) were drawn (Fig. 4)
and the amounts of Na and K in solution were estimated by using
these curves. The exchangeable Ca "*", Mg '*', Na"*" and K* were found
tOOr
c
o
0 [0 20 20 40 SO Concentt^ation oF Sodium In ppm
1 I I I L \0 ZO 30 40 50
concentration of Potassium in ppm
FIG.4-STANDARD CURVES FOR SODIUM AND POTASSIUM BY FLAME PHOTOMETER.
63
to be 3.5, 1.2, 3.0 and 0,5 meq. per 100 g soil respectively.
(a) MOBILITY (Rf.) DETERMINATION BY SOIL THIN LAYER CHROMATOGRAPHY
Apparatus and reagents
TLC applicator with adjustable thickness_,uniform glass
plates (20x20 cm), glass chambers with cover, glass sprayer,
100 mesh sieve (BSS).
A 0.1M nitrate solutions of lead, cadmium, nickel, mercury
and silver in distilled water, 0.5% (w/v) ethanolic solution of
haematoxylene, dimethyl glyoxioe, and 1% (w/v) dithizone solu
tion in CCl, etc.
Preparation of plates
For the measurement of R^ values, the soil samples were
ground and passed through 100 mesh sieve (BSS) to obtain a homo
geneous particle size ( 150 ju).
A slurry of prewashed soil sample (free from soluble salts)
was prepared in distilled water with a soil water ratio of 1:2
in each case. Glass plates were cleaned with detergent solution,
water and with 50% methanol-water acidified with hydrochloric
acid, and finally the plates were wiped with cotton soaked with
hexane. These glass plates were coated with slurries of soil
sample to a thickness of 0,5 mm with the help of TLC applicator.
64
Tile prepared plates were kept on a rack and were allowed to dry
in the air at room temperature overnight. Two lines at 3 cm and
13 cm above the base were scribed so that the standard development
distance of 10 cm was used on all the plates,
APPLICATION OF SAMPLE AND DEVELOmENT OF PLATES
k 6 pi nitrate solution (O.IM) of heavy metals was applied
on the base line of TLC plate in a single application with the
help of micropipette. The plates were then developed with distill
ed water or amended distilled water upto the upper line on the
plates in a closed glass chambers by ascending chromatography.
To prevent disintegration of soil in contact with water, wet
strips of filter paper about 2,5 cm wide were wrapped around the
bottom of the plate before the development,
DRYING AND DETECTION OF CHROMATOGBLAMS
The developed plates were air dried at room temperature
(30 C). Visualization of heaA/y metals i,e, Pb, Hg and Ag; was
made by spraying 0,% (w/v) ethanolic solution of haematoxyiene
as a violet colour spot of metal-haematoxyiene complex which
remained stable for about 10 hours. While Ni, and Cd were detected
as red colour spots of Ni-glyoxime, and Cd- dithizonate complexes
by spraying dimethyl glyoxime and ^% (w/v) dithizone in CCl/
respectively.
65
MEASUREMENT OF Rf - VALUES
The frontal R^- values (mobility) was measured by the
relation:
Value - ^^o^'tal distance moved by the metal^ ^ ~ ~ Frontal distance moved by the developer
FOR THE EFFECT OF ORGANIC MATTER
The soil was treated with :5CS ^J^2 ^° decompose soil
organic matter (SOM) according to the method of Jackson (1958).
The soil sample with and with decomposed SOM were used as static
phase on the TLC plates and distilled water as developer. The
results are given in Table-II.
FOR THE EFFECT OF ORGANIC ACIDS AND BASES
The calculated volume of aqueous solutions of different
acids like formic acid, acetic acid, oxalic acids and their
aqueous salt solution, Glycine, Alanine and Valine; Nicotine and
Pyridine were taken in jars. These solutions were used as
developer while natural soil as static phase. The results are
given in Table -III to XIII and Fig. 5-7.
RESULTS AND DISCUSSION
An examination of Table-II shows that the mobility of
heavy metals through soil with and without organic matter (30';o H2O2
66
t reatment) follows the order, Ni>Cd>Hg>Ag>Pb, The r e s u l t s
are in accordance with the e a r l i e r view of Khan et a l , (1982) and
Lund et a l . (1976) tha t the heavy metals move as t h e i r soluble
metal-SOM complexes in so i l according to t h e i r ion s ize (Table-I l )
and complexing nature . The decomposition of so i l organic matter
enhances the heavy metal mobili ty to subs tant ia te the clay-metal-
SOM in te rac t ions (Theng, 1974).
The effect of carboxylic acids on the mobility of heavy
metals i s given in Table- I l l to V and Fig, 5 which shows tha t the
mobil i ty increases with increase in the concentration of ac ids .
The heavy metal mobility in different acid media follows the order
f o r m i c > a c e t i c > o x a l i c acids which may be a t t r ibu ted to the solu
b i l i t y of metal carboxylate (Table- I I ) , The r e l a t i v e order of t h e i r
mobili ty in the acid medium was Ni>Cd>Hg>Ag>Pb except in the
case of ace t ic acid in which the order being Hg>Cd>Ni>Ag>Pb
which i s in the reverse order of the i n s t a b i l i t y constants of t h e i r
ace ta te s a l t s . Thus the ion s i ze , i n s t a b i l i t y constants and solu
b i l i t y of metal carboxylates seem to determine the extent of t h e i r
mobil i ty tlrirough s o i l .
The r e s u l t s were further ver i f ied with the sodium carboxy
l a t e systems (Table VI to VIII and Fig, 6) which show tha t the
addi t ion of sodium carboxylates enhances the heavy metal mobility
approximately equal to tha t of carboxylic ac ids . The t r ans loca
t i o n in presence of organic acids and t h e i r s a l t s could be explain
ed by considering the re lease of heavy-metals from adsorptive
67
sites of soil colloids due to the preferential adsorption of + +
H or Na resulting the formation of metal carboxylates which
may move through soil. The probable reaction mechanism can be
given as follows:
The carboxylic acids or their sodium salts ionize to
give:
Hm X -- ^ mH^ + X ""
Na^ X ^ - m Na" + x" "
The H or Na replaces the heavy metal ions from soil colloids
as:
+ \ . „u / M \ „ .,n+/ MCH^O) - Yn + nH"*" (or Na ) ::^=^ "H (or Na) -Y + IT'^ili^O)
In acid systems, the pH of the s o i l decreases from 8,8 tovxN3,0.
The heavy metals remain in t h e i r ionic form and combines with
carboxylate ions as
m
mM "" + n X° - : ; r - r ^ /"MmXn 7 ° I I
mM'"*- + ( n + 1 ) x " ' - ^ i z ^ /-MmX(n + i ) 7"*" H I
The metal-carboxylatcs (I to I I I ) so fonned moved tiirough
t h e s o i l . Moreover, the increased concentration of carboxylate
•« <^
'_ TN
t -•r
l^
c 1 -
'x r. • ^ H O ' 0
• - T 1 < — 1
a o s H rO
i f3 • "H
S f l U rj4
o H H >H
H
' a W H >-J rQ
m o r J
^ w K EH
#—* O
S E-i EH • i ; • . • *
o M / • — «
• j ;
Q a: o ^A H O CO
ft, o GH
P ft^ rt< rq f : [:: EH
I 1
)
» \
« W H •C
^ X O
(5 0
^ a w u: EH
f n 0
>H
H a M
m 3 8 1
j i (O EH
^ H CO
0
> H
EH
a H
^ EH : 0
^ Hi
- — « r -
1 UO 0 0 T—
t.O
^
ii •H
>> -P •H H •H
H 0 CO
cu •p
i H Cd CO r-) P C\] <U X
•J: 0
01 p
ra - p - p (U 0 0
a oJ
CO
H cU
3g cu 0
A * H
0) 4->
•H <U H - P 0
cU-P H -P w cti to G - p 0 0 <D
M 0 a
N +3 0 •H (!)
w goo a 0
C fn ^ 0 cd
M a x
to 0) :3
H
rt >
t
1 tH
cd
•P 3 0
- p •H 0 •^•r\ U
n a p • r i bD-P 0 (u « j .
CO 0 e
A H
-P •H 0 : 5 - H ?H
d QJ H ro -P •H bO-P 0 fn c
CO 0 a
CO
•p 0) Q
p cS 0) Li
<u H ^ :3 H 0 to
fl i - l
• VO V -
0) H
H 0
CO
vo T -0
• 0
VO
C\J N^
» 0
CO r -
• 0
H 0)
^ 0
•r1 4 H
t ^ r<^
0 0
• 0
0) I-J
E?^ (1) 0
> CO
H
0) 0 > CO
C--•V-
0 0
« 0
i n
cr» CM
• 0
c^ T—
• 0
g 3 •H
^ 03 0
(U H ,Q :3 H 0 to
« M
l A
• 0
• 0
cr> 1 0 T -
X try I S
• m
l A
ITN CNJ
• 0
l A r -
• 0
>>. U 3 0
u QJ
»
\o X-
8 0
• 0
« l A
-J-
• r -
CO t A
0 •
0
<h
l A
— •
0
s •
0
T^ cd Q) •-J
-4-^ A 0 0 •
0
CM 0
• 0
1
r A CO r -
•
0
r A
T -
CNJ
• 0
r A r -
• 0
U 0)
> H •H
CO
-— MD VO cr> V -
N _ *
0 • d
g g Q)
ri<
• d
JH
<u to cu
•H ^1
Cx<
1
a
cr\ LA
cr. r -•—X
> 0)
• . --"x H VO • a vO to C7> cd V-
> ^ t 3 S
ro H (U
to TJ
•H c3 0 •r4 -P to to
p td 0 (U
>H :^:
1 1
p 0
68
69
TABLE - I I I
EFFECT OF FORMIC ACID ON THE MOBILITY (R^-VAIUES) OF HEAVY METALS THROUGH AUGARH SOIL.
R^-valuea Heavy ^ metals Formic acid 0.0 0,1 0.5 1.0 1.5 2.0
(moles/ l i t r e )
Nickel 0 .18 0.44 0.72 0.85 0.92 0.95
Cadmium 0.17 0.40 0.69 0.81 0.90 0.94
S i l v e r 0.13 0.31 0.51 0.58 0.65 0.71
Mercury 0.15 0.25 0.56 0.66 0.74 0.84
Lead 0.08 0.18 0.32 0.39 0.43 0,45
70
TABLE - IV
EFFECT OF ACETIC ACID ON THE MOBILITY (R -VAIXJES) OF HEAVY METALS THROUGH AUQARH SOIL.
R--value3 Heavy metals Acetic acid 0.0 0.1 0.5 1.0 1.5 2.0
(moles / l i t r e )
Nickel 0.18 0.57 0.63 0.76 0.77 0.78
Cadmium 0.17 0.56 0.66 0.79 0.82 0.85
S i l v e r 0.13 0.47 0.42 0.44 0.A6 0.50
Mercury 0.14 0.43 0.70 0.81 0.84 0.87
Lead 0,08 0.21 0.34 0.4o 0.46 0.48
71
TABLE - V
EFFECT OF OXALIC ACID ON THE MOBIUTY (Rj «VAUUE3) OF HEAVY METALS THROUGH ALIGARH SOIL,
R^-va lues Heavy ^
metals oxal ic acid 0.00 0.05 0,10 0.25 0.50 (moles/ l i t r e )
Nickel 0.18 0.19 0.24 0.35 0.41
Cadmium 0.17 0.15 0.18 0.33 0.4o
S i l v e r 0.13 0.12 0.17 0.25 0.31
Mercury 0.15 0.17 0.26 0.29 0.35
Lead 0.08 0.10 0.20 0.27 0.28
72
TABLE - VI
EFFECT OF SODIUM FDRHATE ON THE MOBILITY (R^-YALUSS) OF HEAVY
METALS THROUGH ALIGARH SOIL.
Heavy m e t a l s
R^ - va lues
Sodium formate 0 .0 0 ,1 0 . 5 1.0 1,5 2 .0 ( m o l e s / l i t r e )
Nicke l 0 .18 0,23 0,49 0.71 0.82 0 .88
Cadmium 0.17 0.26 0 .45 0 .64 0,70 0,77
S i l v e r 0 .13 0.17 0 .30 0.35 0.42 0 .54
Mercury 0.15 0 .15 0.23 0.27 0.20 0.22
Lead 0.08 0.09 0 .14 0.19 0 .24 0 .30
73
TABLE - VII
EFFECT OF SODIUM ACETATE ON THE MOBIUTY (R^-VAIUES) OF HEAVY METALS THROUGH AUGARH SOIL.
Heavy metals
R^- values
Sodium aceta te 0,0 0.1 0,5 1.0 1,5 (moles/ l i t r e )
Nickel 0.18 0.32 0.66 0.80 0,86
Cadmium 0.17 0.25 0.61 0,79 0,87
S i l v e r 0.13 0.24 0.37 0.44 0.43
Mercury 0.15 0.17 0.20 0.25 0.31
Lead 0.08 0.14 0.24 0.36 0.46
74
TABLE - VIII
EFFECT OF SODIUM OXALATE ON THE MOBILITY (R -VAUUES) OF HEAVY METALS THROUGH ALIGARH SOIL.
Heavy metals
Rj^-values
Sodium oxalate o.OO 0.05 0.10 0.25 0.50 (moles / l i t r e )
Nickel 0.18 0.2? 0.38 0.55 0,73
Cadmium 0.17 0.16 0.18 0.24 0.37
S i l v e r 0.13 0.11 0.12 0.15 0.11
Mercury 0,15 0.13 0,11 0.12 0,11
Lead 0.08 0.07 0.09 0.13 0.16
75
TABLE - IX
EFFECT OF GLYCINE ON THE MOBILITY (R -VALUES) OF HEAVY METALS THROUGH ALIGARH SOIL.
Heavy metals
R*-values
Glycine 0,00 0.01 0.05 0.10 (moles / l i t r e )
Nickel
CadmivuD
S i l v e r
Mercury
Lead
0.18
0.17
0.13
0.15
0.08
0.42
0.17
0.19
0.20
0.07
0.60
0.15
0.25
0.20
0.07
0.70
0.20
0.30
0.25
0.08
76
TABLE • X
EFFECT OF DL» ALANINE ON THE MOBILITY (R -VALUES) OF HEAVY METALS THROUGH ALIGARH SOIL.
R^-values Heavy * metals Dl- Alanine 0.00 0.01 0.05 0.10
(moles / l i t r e )
Nickel 0.18 0.52 0.80 0.89
Cadmium 0.17 0.17 0.18 0.21
S i l ve r 0.13 0.15 0.30 0.35
Mercury 0.15 0.15 0.3A 0.35
Lead 0.08 0.09 0.09 0.09
77
TABLE -
EFFECT OF VALINE ON THE MOBIUTY THROUGH ALIGARH SOIL.
Heavy metals y^ixne 0.00
(moles / l i t r e )
Nickel 0.18
Cadmium 0,17
S i l v e r 0.13
Mercury 0,15
Lead 0.08
XI
(R -VALUES) <
R--values
0.01
0.53
0.17
0.21
0.15
0.10
DF HEAVY
0.05
0.83
0.16
0.24
0.29
0.09
METALS
0.10
0.93
0.20
0.35
O.Ao
0.09
78
TABLE - XII
EFFECT OF NICOTINE ON THE MOBILITY (R -VALUES) OF HEAVY METALS THROUGH ALIGARH SOIL.
Heavy metals
R^- values
Nicotine 0.000 0.002 0.008 0.050 (moles / l i t r e )
Nickel 0.18 0.17 0.14 0.15
Cadmium 0.17 0.11 0.11 0.10
S i l v e r 0.13 0.09 0.08 0.08
Mercury 0.15 0.09 0.09 0.09
Lead 0.08 0.08 0.08 0.08
79
TABLE - XIII
EFFECT OF PYRIDINE ON Th£ MOBILITY (R^-VAIUES) OF HEAVY KETAL3 THROUGH ALIGARIi SOIL. ^
Heavy ^f " va lues m e t a l s
P y r i d i n e Q.OOG 0.002 0.008 0.050 m o l e s / l i t r e
Nicke l
Cadmium
S i l v e r
M ercury
Lead
0.18
0.17
0 .13
0 .15
0.08
0.17
0.16
0.11
0 .13
0.09
0.17
0.16
0 .11
0.11
0 .10
0.15
0.16
0.11
0.10
0 .10
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80
ions favour the formation of -vely charged metal carboxylate (III)
which lowers the adsorption of these species over the -ve sites of
soil colloids and hence increased the mobility. The density of
the surface -ve charge on soil colloids is also enhanced due to
the adsorption of carboxylate ions over reactive sites as in the
case of other anions (Ra^jan and Fox, 1975).
While in the case of salt systems, the pH increased from
8.8 to 9.2. Most of the metal ions may be considered to remain
in the form of MOH (monovalent), MOH"^ and/or M(0H)2 (divalent)
which can form their respective metal carboxylates as
0 //
R - C - 0 ... H - 0 Ml
(IV)
R - C ^
0
(V)
H
I 0
M
and/or R - C y- H
0 .. H -0 -
0
M
(VI)
The hydrated metal-carboxylates (IV to VI) so formed move through
the soil. But as the salt concentration increased, the -vely
charged species (Vl) may favourably be formed which causes a lower
preference over the soil colloids and thus enliance the mobility.
81
The effect of some amino acids is given in Table-IX to
XI and Fig, 7 which shows that the mobility of heavy metals
generally increases with increase in the concentration of amino
acids. The order of heavy metal mobility in soils was found to
be valine >-alanine >. glycine which is in accordance with their
own mobility in soil (Singhal et al,, 1978) while the relative
order of the mobility of the heavy metals in soil was Ni>Hg>Ag>
Cd>Pb except in the case of glycine where the order being Ni
A-g>Hg>Cd>Pb, As the pH of the soil solution was alkaline
(8.3), the amino acids may be expected to remain in their anionic
forms (Theng, 1974) because pH •;> pi (isoelectric point). These
anionic forms of the amino acids may combine with the heavy metals
as H
0 .0''
R-CHNH - C + M(OH)'*' > R-CHNH - C 0
0" 0 M
(VII)
The instability constant of these metal-araino acid
complexes were reported (Yatsimirsku & Vasil'ev, 1959) in the
reverse order of the mobility. The larger molecular size of
amino acid restricts the adsorption of its metal complex on the
interlemeller surfaces(Talibuddin, 1955) and mobilize it faster.
Thus, the stability and size of heavy metal amino acid complex
(VII) decide the mobility of these metals in the soil environ
ment.
82
The effect of organic bases such as nicotine and pyridine
on the mobility of heavy metals is given in Table-XII and XIII.
It is evident that the nicotine and pyridine have no marked
influence on the heavy metal translocation in soils. However, a
slight decrease in the mobility is observed in some cases which
may be attributed to the metal-base soil/clay complex formation.
As the pH of the system upon the addition of these bases remains
above 7 (8,3 in our case), the lone pair of nitrogen may attract
the heavy metals through hydrogen bonding (Singhal and Singh,
1972) as follows:
-N: + H O ,., H-OH-M-Yn 1 ^
1 -N ... H-O^-Yn + H2O
I (VIII)
(Where - N : = Q ) o r Q ^ - ^ ^ ^
heavy metal with n charge)
soil colloids and M is
Thus, the complexation of metal with bases and soil colloids
immobilized the heavy metals in soil.
83
REFERENCES
BRINDLEY, G.W. and MOLL, W.F. ( J r . ) ; Am. M i n e r a l o g i s t , 50 , 1355 (1965) .
FREISER, H. and FERNANDO, Q^; ' I o n i c e q u i l i b r i a i n a n a l y t i c a l c h e m i s t r y ' . New York, Wiley (196b) .
GREENLAND, D . J . , LABY, R.H. and QUIRK, J * P . ; T r a n s . Farad. S o c . , 5 8 , 829 (1962) .
HANKS, A.R., SCHRONK, L.R. and ARNST, T .C . ; . J . Liq . Chromat. , 3 ( 7 ) , 1087 (1980) .
c JACKSON, M.L.; ' S o i l Chemical A n a l y s i s ' , P r i n t i c e - H a l l , Englewood
C l i f f s . , N J . (1958) ,
KHAN, S . , NANDAN, D. and KHAN, N.N.; Environ. P o l l u t . (Se r . B ) , 4 ( 2 ) , 119 (1982) .
KHAN, S. and SINGHAL, J . P . ; S o i l S c i . , 104, 427 (1967) .
LUND, L . J . , PAGE, A.L. and NEI^ON, C O . ; J . Environ, Q u a l . , 5 , 330 (1976) .
MARTIN, F . , SAIZ-JIMENEZ, C. and CART, A.; S o i l S c i , Soc. Am. J . , 4 1 ( 6 ) , 1114 (1977) .
PIPER, C . S . ; ' S o i l and P lan t Ana lys i s ' Uny Adelaide Aust . (1950) .
RAJAN, S . S . S . and FOX, R.L . ; Proc . S o i l S c i . Soc, Am. 39 , 846 (1975) .
RENDING, V.V.; So i l S c i . , 7 1 , 253 (1951) .
SCHWARTZ, S.M., WARNER, J . E . and MARTIN, W.P.; S o i l S c i . Soc. Am. P r o c , 18, 174 (1954) .
SHTOMPEL, Ya.A., MURZINOVA, I . I . £md KOTSYUBA, M.A.; Agrokhimiya, 3 , 99 (1981) .
84
SINGHAL, J . P . , KHAN, S. and BANSAL, V.; P roc . I nd i an N a t l . S c i . Acad., Vf(5) , 267 (1978) .
SINGHAL, J . P . and SINGH, R . P . ; Ind ian J . Chem., 10, 1100 (1972) .
SMITH, C.R.; J . Am. Chem. S o c . , 56, 1561 (1934) .
SOVTOENS, F . J . ; S o i l S c i . , 82 , 491 (1956) .
TALIBUDDIN, 0 . ; Trans Farad. S o c , 5 1 , ^82 (1955) .
THENG, B.K.G.; The chemistry of c lay organic r e a c t i o n s (1 s t e d n . ) , London, Adam. Hi lge r (1974) .
VASIL'CHENKO, V . F . , ABRAMOVA, K.A., DUBR0V3KAYA, A.A. and II'NITSKAYA, L . P . ; Simp, S t r a n . Chlenov. SEV. I 0 t h , 2, 34 (1975) .
WALKLEY, A.; i b i d . , 63 , 251 (1947) .
WEAST, R.C., and SELBY, S.M.; Handbook of chemistrv and physics. (47th edn.). Ohio, Chemical Rubber Co, (1966)0
YATSIMIRSKU, K.B. and VASIL'ev, V.P.; Instability constants of complex compoundSo New York, Consultants Bureau Enterprises, Inc. (1959).
CHAPTER . I I
THE MOBIUTY OF PESTICIDES IN SOILS AS AFFECTED BY
THEIR CHEMICAL CHARACTERISTICS AND
SOME SOIL PROPERl'IES
85
INTROOJCTION
The study of pesticide mobility In so i l s i s an Important
phenomenon in understanding I t s effectiveness for bloactlvity in
so i l (Kurlekar and Khuspe, 1984)«, Various soil pax^umeters such
as soil organic matter and the i r fractions i«e humlc and fulvic
acids; nature of exchangeable cations over clay surfaces, clay
contents, soil pH and free metal oxides e tc . have been found to
influence the translocation of oirganic pesticides in soi ls
(Bailey and White, 1964j Neazpass, 1971; Singhal and Bansal, 1978).
I t has been observed that adsorption and desorption of organic
chaaicals in soi l are greatly influenced by the molecular s t ruc
ture of the compound(Hortland, 1970),
Among pesticides selected for the study, Formothlon,
Malathion and Thiometon are organophosphorus Insecticides \fbich
are used for controlling the insect borne diseases in various
crops (Ghos, 1979; Deshmukh et a l . , I960; Thimmaiah and Thippes
Wamy, 1980). Whilst, Fluchloral.ln i s an halogen containing her
bicide (Raghavaiah et a l . , 1980). The work on the translocation
of these chemicals as influenced by the i r chaaiical characterist ics
and soi l properties i s lacking in l i t e ra tu re . Therefore, i t was
thought worthwhile to conduct some experiments on the i r t rans lo
cation in relation to soi l pollution caused by the i r indiscrimi
nate use in agriculture.
86
EXPERIMENTAL
Two soil samples are used for the study of the mobility
of pesticides. The soils were dried, crushed and sieved through
100 mesh sieve.
1. Itwa silt loam (Aerie Ochraquelf) - Varanasi
2. Sakit sandy loam (Typic Natrustalf) - Etah
The physicochemical properties of these soils were deter
mined as described in Chapter - I. The results are given in
Table - XIV.
The pesticides used for the study are organophosphorus and
chlorinated. The chemical name, structure and other properties are
given in Table - XV,
DETEfMINATION OF R^-VALUES BY SOIL THEN-LAYER CHROMATOGRAPHY(TLC);
Mobility of the selected pesticides in terms of their Re
values in soils was determined by soil thin layer chromatography as
follows;
Apparatus; TLC applicator with adjustable thickness, uniform glass
plates of 20x4 cm size and glass t,anks 25x10 cm and a glass sprayer.
Preparation of solutions and soil samples
Solution of pesticides;
A 10% solutions of Thiometon, Malathion, Formothion and
Fluchloralin were prepared in ethanol.
87
Detector: A 0.59 AgNO, solution was prepared in a solvent
mixture containing acetone and water in the ratio of 3:1,
For the effect of organic matter? Two sets of experiments were
conducted to study the effect of soil organic matter and their
fractions i.e. humic acid and fulvic acid on the mobility of
pesticides.
In one set of experiments, two soil samples were used to
study the effect of organic matter by taking (1) as natural soil
containing organic matter and (2) the soil sample after removal
of organic matter by 309 2^2 ^^^^ there was no effervescence.
The results are reported in Table-XVI.
In other set of experiments, the organic matter was
extracted from the two soils namely Itwa silt loam and Sakit sandy
loam soils by the method of Desai and Ganguli (1979) and frac
tionated into humic and fulvic acid; and then purified as follows:
Extraction of soil organic matter (30M): The soil samples were
slurried, sieved through 100 mesh sieve (BSS) and digested with
0.2N NaOH + 0,2N Na2C0, mixture (taking solid, water-alkali
mixture ratio as 1:10 wt/wt) for 6 hours at 80 C under continuous
stirring condition. It was then allowed to stand overnight. The
supernatant liquid was collected by siphoning and the residue was
again treated in the same way for several times for complete
extraction, Supernatants were pooled together and centrifuged at
5500 rpm and the residue rejected, A portion of the centrifugate
88
was purified by dialysis till the dialyzate was free of alkali.
It was again filtered through 0*22 mm membrane filter and kept
for electrodialysis.
Separation of humic acid (HA) and fulvic acid (FA)t The centri-
fuged extract was acidified with hydrochloric acid to pH-2 to
precipitate HA and then allowed to stand overnight. The yellow
coloured supernatant (FA) was siphoned off and collected. The
HA coagulated was centrifuged and the supernatant was mixed with
FA solution.
Purification of HA and FA; The HA was treated wi-tti ammonia
under slightly warm condition, allowed to stand overnight, centri
fuged and the residue re^jected as it contains prefuse quantities
of Al and Fe, The HA was then precipitated from st4>ematant,
centrifuged and supernatant solution discarded. This process was
repeated several times till no residue was obtained on centrifU-
gation of ammonical supernatant. Again, the HA was dissolved in
ammonia and the solution was passed through 0*22 um membrane
filter and then purified by dialysis and electrodialysis.
In case of FA, it was tre£ited with ammonia, a bulky white-
brown precipitate of Al (OH)a> if appeared; was removed by fil-
tration (over Whatman filter paper no, 1), The pH of the filtrate
was brought back to 2 with HCl centrifuged and the supernatant made
ammonical again, allowed to stand overnight and then filtered
through membrane filter. The process was repeated several times
till no white precipitate was obtained upon the addition of ammonia.
89
The FA solution was concentrated by evaporation under an IR lasep
at 60 C, filtered through membrane filter and the filtrate was
brought back to pH 2 for dialysis and electrodialysis.
Dialysis and electrodialYsia; The solutions of HA and FA were
placed in central compartment of the electroanalysis cell and the
platinum electrode compartments were filled with doubly distilled
water and was changed intennittendly with stirring the HA and FA
solution in central compartment. It was continued till the water
in electrode compartment did not lahow the presence of chloride
ions. Again, the process was speeded ixp with the help of pro
gressively increased d,c, voltage fr<Mn an initial 5 volts to 200
volts. The care was taken to replace the water from electrode
compartments. This process was continued till the conductance of
the water in the cathode compartm^it was equal to that of distill
ed water.
The SOM, humic and fulvic acid thus prepared and purified
were stored in well cleaned glass reagent bottles. These com
pounds (SOM, HA and FA) were then added to their respective soils
in known quantities. The amended soil samples were used to pre
pare TLC plates for Rx.-values determination. The results are
reported in Table-XVII to XIX and Fig. 8.
For the effect of clay content; The clay mineral contents of the
soils (Itwa and Sakit) were separated as follows:
90
The so i l samples were a i r dr ied, broken ijqp in a morter using
rubber covered p e s t l e , and passed through 7 mesh sieve (BSS) to
ranove gravel por t ions . I t was then washed with d i s t i l l e d water
t o remove soluble s a l t s and t h a i t r ea ted with 30% H^Op solut ion t o
deccmpose s o i l organic matter ( t i l l no effervescence). Excess of
hydrogen peroxide was decomposed by gently warming the mixture
for few minutes. The cooled mixture was then covered with water and
s o i l dispersed with sodium oxalate solut ion (8 g m / l i t r e ) . The
mixture was shaken vigorously by an e l e c t r i c a l s t i r r e r for a few
hours . The col lo ida l suspension thus obtained was paissed through a
two layer sheet of Whatman f i l t e r paper no, 1 placed in the bowl
of In te rna t iona l Chemical Centrifug;e a t a speed of 3»500 rpm. The
res idue l e f t over in the bowl was again s t i r r e d with d i s t i l l e d
water and centrifuged as above. The process was repeated th ree or
four times to get suff ic ient clay suspensions which were a i r dried
and clay mineral was s tored.
The separated clay minerals were added to t h e i r respect ive
s o i l s which were used to prepare TL:^ p l a t e s for mobili ty determi
na t ions . The r e s u l t s are reported in Table-XX and Fig, 9.
For the effect of pH: The effect of pH on the mobil i ty of
p e s t i c i d e s was studied using the s o i l samples a t various pH values
adjusted with 0.01N HNO or NaDH, These s o i l samples were coated
on the TLC p la tes for the mobility determinations. The r e s u l t s
a re given in Table-XXI,
91
For the effect of exchangeable cationsi The soil samples were
saturated with various cations i.e. H*, K*, Ca "*" and Hg "*" in the
sane manner as described in Chapter » I of the thesis* The
results are reported in Table-XXII,
For the effect of sesguioxides (AI2O, and FegO,)! The soil
plates were prepared by the addition of varying amount of AlpO,
and Fe^O,, The results are reported in Table-XXIII A XXIV and
Fig. 10.
Preparation of TLC plates: The glass plates (20x 4 cm) were
coated with soil or amended soil samples as described in Chapter-I
of this thesis.
Application of samples: A 0.006 ml of pesticide solution per
spot in single application was applied with a micropipette on the
base line at a height of 3 cm.
Develoiment of plates: The coated plates with soil sample were
developed in distilled water as described in Chapter I of this
thesis.
Drying and detection: The developed plates were air dried at room
temperature. Visualization of pesticides on the chromatogram was
made by spraying Ammonical AgNO, solution with the help of spray
bottles on exposure of these sprayed plates to sunlight for five
minutes. The Malathion, Thiometon and Fonnothion developed a yellow
colour spot which becomes bluish in about five minutes, while
92
Pluchloralin developed a distinct dark yellovr colour spot.
The colour so developed remain stable for about a week. The
mobility of pesticides in different soils was evaluated in terms
of R^-values as described in Chapter-I of this thesis,
RESULTS AND DISCUSSION
The mobility (R^-value) of ionic (Fluchloralin) and non
ionic (Formothion; Malathion and Thiometon) pesticides are report
ed in Table-XVI, It shows that the pesticide mobility is greater
in sandy loam as compared to silt loam soil which has a large
available surface to bind the pesticide molecules. The order of
their mobilities in both soils ia Thiometon>Malathion>Formothion>
Fluchloralin, Considering the chemical structure of these pesti
cides, it could be said that the ionic nature and the polarity of
the compound play a significant role in its movement through soil.
The least mobility of Fluchloral;Ln could be understood by its
relatively high affinity for the adsorption sites of soil colloids
as reported for ionic pesticides (Singhal and Kumar, 1976j Maqueda
et al,, 1983).
Among organophosphorus pesticides Thiometon has a reactive
sulphur atom attached with a hydrophobic ethyl group which inhi
bits its interaction with soil colloid surfaces and hence shows a
highest mobility than the other two (i,e. Malathion and Formothion),
Whilst, in the case of Malathion and Formothion, both of which have
93
two carbonyl groups with o-atoms available for interactions with
soil colloids through hydrogen bonding and/or Vander Waal's
forces. The higher mobility of Malathion than Pormothion could be
due to a greater steric hinderance caused by two bulky ethyl groups
in the structure of former. The N-atom in Fonnothion may also pro
vide another binding site for its interaction with soil colloide
and hence additional restriction slows down its mobility in soil,
Table-XVI shows that the mobility of all the pesticides
increases as the soil organic matter (SOM) is decomposed with H2O2
(30?6), It is obvious as the decomposition of SOM reduces the
binding sites in the soil colloid and hence increased the mobility.
This was again examined by adding SOM extracted from the same soil.
The resvats reveal (Table-XVII to XIX and Fig, 8) that on addition
of 0,5% SC*1, HA and FA to its respective soil, decreased the mobi
lity of pesticides to about 0.2o to 0,35 R^ units. However, in the
case of Malathion, addition of 0,59 HA increased its mobility to
0.09 R^-units. It may be seen from the Table-XVlII that HA incre
ased the malathion mobility, the corresponding decrease by FA goes
upto 0,58 and 0,61 R^-units in two soils and its average mobility
(with HA & FA) remains around the same as in the case of 0,5%
addition of SOM, However, some other factors such as mineralogical
properties and pH etc, may also contribute in restricting or en
hancing the mobility of pesticides. Thus results could not be
explained quantitatively due to the complexity of the soil syat&n
unless the specific work is carried out on each aspect which is
beyond the scope of the sub;3ect of this chapter.
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98
TABLE - XVI
MOBILITY (R.^- VALUES) OF PESTICIDES THROUGH SOILS
Mobility (R^-values)
Itv/a s i l t loam Sakit sandy loam Pest ic ides
V/ith organic V/ithout With organic Without organic matter organic matter matter
matter
Fluchloral in 0.78 0.87
Formothion 0.80 0.84
Malathion 0.90 0.92
Thiometon 0.95 0.96
0.81
0.86
0.91
0.94
0.84
0.88
0.93
0.97
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2>niEA-^y
ITWA SILT LOAM
0-4 0-6 0 0-2
Metal oxidB adde<) (7o) 0-4 0-6
Fig. 10. Effect of metal oxide (AI2O3 & FC2O3 ) on the mobility
of pesticidei; (•) F luchloro l in^ (x ) Formothion,
(o) Molathion, (A) Thiometon.
105
Table-XX and Fig, 9 show that on addition of clay minerals
to respective soil decreases the pesticide mobility to about 17
to 25 R^-units in Itwa silt loam and 29 to 34 Rj^units in Sakit
sandy loam soil. This decrease may also be attributed to increased
binding sites in the soil colloids due to the addition of clay
fractions. The greater reduction in pesticide mobility in Sakit
sandy loam than in Itwa silt loam could be explained on the basis
of the nature of clay mineral added. As the separated clay from
Sakit sandy loam soil contains chlorite mineral with mica and has
a higher CEC values in ccmparison to the other clay separated
(Kaolinite with mica) from Itwa silt loam. The addition of clay in
the former soil increased its CEXJ values from 123 meq Kg to 141
meq Kg soil in comparison to the later soil which becomes 117
-1 -1
meq Kg from 116 meq Kg by adding 5% soil clays. The pesticide
mobility order ronained the same in both the cases showing the
importance of their reactivity in soil colloids,
Table-XXI indicates that the highest pesticide mobility
was found around the neutral pH and decreased in both the acid
as well as alkailine pH range. It could be due to a fixation of
H ions over adsorption sites which may bind the pesticide mole
cules through hydrogoi bonding to restrict the mobility in acid
soils. Whilst, in the case of alkaline medium, the soil organic
matter gets solublized and also the cations on the exchange sites
of mineral surfaces gets hydrolyzed. These hydrolyzed cations
presumably adsorb the pesticide molecules through hydrogen bonding.
The possible interaction could be vritten. as follows:
In acid medium
adsorption ^ ^ ^ ^ ^^ sixes
pesticide molecule
In alkaline medium
si?e?^^''''^*-°" * °-^
pesticide molecule
106
adsorption sites ^ H * . . . 0 -
^J^^^*^^°^!1*.0H . . . 0-X
Table-XXII shows that the pesticide mobility in cation
saturated soi ls follows the orderj Unamended soi l>H-30i l>
Ca-soil>Mg-soil>K-soil , in both the soi ls under study. Various
authors (Singhal et a l . , 1978| Khan and Bansal, 1980) have repor
ted that the pesticide molecules adsorbed onto the cation satura
ted soi l surface through the cations and hence hydrated cation
s ize could be a important factor in deciding the pesticide adsorp
t ion order. The hydrated size of H i s largest and K being
smallest (Table-OCXII), Thus, the greater hydration of H -ions
in H-saturated soil than other ions, prevents the interaction
b-etween pesticide and soi l colloids. However, the role of pH of
the H-saturated soi l which i s decreased from 10,5 to 7,9 and 6,6
to 3,2 in Sakit sandy loam soi l and Itwa s i l t loam soil respective
ly , could not be ruled out.
107
However, in the case of Ca- and Mg- soil, the lower value
of ionic index (Zi /r) for Ca (4.04) than Mg •*" (6,15) seems to
be a reason for their lesser interaction (Nieboer and Richardson,
1980) with pesticide molecules and hence a higher pesticide mobility
was observed in Ca- soil than Mg- soil.
Table XXIII & XXIV and Figure 10 show that the mobility of
pesticides decrease with the addition of Al^O, and FopO, in both
the soils. It may be explained on the basis of increased binding
sites due to the interactions of precipitated Al and Fe hydroxide
(Khan and Khan, 1986) species.
108
REFERENCES
BAILEY, G.W. and WHITE, J.L.; J. Agric, Food Chem., 12, 324 (1964).
DESAI, M.V.M. and GANGULY, A,K,; J, Indian Chem. Soc., 56, 1167 (1979).
DESHMUKH, S.D., AKHARE, M.D. and BORLE, M.N.; Indian J, Plant Prot., 7, 66 (1980).
GHOS, M.R.; Pesticides, 13, 9 (1979).
JACKSON, M.L.; Soil chemical analysis. Englewood Cliffs, NJ, Prentice Hall (1958),
KHAN, S.U. and BANSAL, V.; J, Colloid and Interface Sci,, 78, 554 (1980).
KHAN, S.U., KHAN, N.N. and IQBAL, N.; J, Indian Soc. Soil Sci., 33, 779 (1985).
KHAN, S.U. and KHAN, N.N.; Soil Sci,, 142, 214 (1986).
KURLEKAR, V.G. and KHUSPE, V.S.; Pesticides, 18, 11 (1984).
MAQUEDA, C , PEREZRODRIGUEZ, J.L., KARTIN, F., and HOSIN, H.C; Soil Sci., 136, 75 (1983).
MORTLAND, M.M.; Adv. Agron., 22, 75 (1970).
NEARPASS, D.C.; Soil Sc i . Soc. Am. P r o c , 35, 64 (1971).
NIEBOER, E, and RICHARDSON, H.S. ; Environ. Po l lu t , (Ser, B), 1,3 (1980).
RAGHAVAIAH, C.V., BABU, M.S. and RAO, M.S.; Pes t i c ides , 14, 32 (1980).
SINGHAL, J . P . and BANSAL, V.; Soil S c i . , 126, 36o (1978),
SINGHAL, J . P . , KHAN, S.U. and BANSAL, O.P.; Aust. J . Chem., 31 , 2151 (1978).
109
SINGHAL, J . P . , and KUMAR, D.; So i l S c i , , 121, 156 (1976).
THIMMAIAH, G. and THIPPESWAMY, C ; Pes t i c ides , 14, 7. (1980).
CHAPTER - III
ADSORPTION OF Cu "*'. Pb " AND Zn '*' ON
Ga- SATURATED ILLITE
no
INTRODUCTION
Accumulation of certain heavy metals such 2+ 2+ 2+ - continuous
as Cu , Pb and Zn in soil, due to 'application of chemical
fertilizers and sewage sludge (Anderson and Nilsson, 1972; Dutta
and Mookheroee, 1980) is posing serious concern to soil pollution.
Several attempts have been made to understand the basic chemistry
of adsorption and desorption processes of these metals over soil
colloids in recent years (Joshi and Shanna, 1986; Chatterjee and
Mandel, 1985) which provides informations on their availability
to plants. Copper (II) and Zinc (II) are considered as soil nutri
ents and neeeded for healthy crops growth (Joshi et al., 1981,1982)
while lead (II) is toxic metal (Walker et al., 1977j Nakos, 1979)
and not required for plant growth. Adsorption and interaction of
these metals over soil colloids is found to depend largely on
several factors such as nature of saturated cations (Dhillon et al, and 'fada
1984; Abd Elfattah,^1981), soil pH (Maguire et al., 1981; Robert
et al,, 1983), type and extent of clay minerals, soil organic matter
(SOM) contents etc, (Petruzzelli et al,, 1981; Jahiruddin et al,,
1985).
The present work deals with the adsorption of Cu "*", Pb "*"
and Zn through adsorption isotherms, Freundlich equation constants
and thermodynamic parameters such as AG, As and A H so as to get
some valuable information on the degree of their interaction over
illite surfaces saturated with Ca ions which is most common in
calcareous soils.
I l l
EXPERIMENTAL
The clay mineral used in these investigations was illite,
obtained from Ward's Natural Scien,ce Establishment Inc., Rochester
(USA). It was broken up in a mortar using a rubber covered pestle.
A <2 yuni fraction was obtained by dispersion in distilled water and
subsequently passing it through the sheets of Whatman filter paper
No. 1 fitted, in the bowl of 'International Chemical Centrifuge'
at a speed at 3500 rpm. The organic impurities were decomposed by
30% ^2^2 ^^'^ ^^® •'•• ^^ suspended in distilled water for further
use.
PREPARATION OF SODIUM SATURATED ILUTS
The clay suspension was treated with 2N sodi\m chloride
solution several times. The mixture was then shaken each time for
about half an hour and allowed to settle down. The supernatant salt
solution was removed from the clay by decantion. The clay is washed
with distilled water till it was free from Cl~ ions (negative AgNO,
test) and the conductivity of the suspension was almost equal to
that of distilled water. The clay suspension was then stored in
bottles for use.
PREPARATION OF Ca- SATURATED ILLITES
The Ca- illite was prepared from Na- illite by treating it
with 2N calcium chloride solution in the same manner as described
112
above fo r t h e p r e p a r a t i o n of Na- i l l i t e . The C a - s a t u r a t e d i l l i t e
sample was then s t o r ed i n s toppered g l a s s b o t t l e s fo r u s e ,
DETERMINATION OF CONCSI TRATION OF TEE. Ca- ILLITE
The concen t r a t i on of t h e Ca- i l l i t e was determined by evapo
r a t i n g 10 ml of t h e suspension i n p e t r i d i s h of known weight and
dry ing t h e r e s i d u e a t 105 C and f inia l ly determining t h e weight of
r e s i d u e l e f t . The concen t r a t i on of Ca- i l l i t e was found 22.8 g/
l i t r e .
DETERMINATION OF THE CATION EXCHANGE CAPACITY OF THE Ca- ILLITE
The c a t i o n exchange capac i ty (CEC) of t h e Ca- s a t u r a t e d
i l l i t e was determined by t h e ammonium a c e t a t e method (Jackson, 1958)
as desc r ibed i n Chapter - I of t h i s t h e s i s . The c a t i o n exchange capa
c i t y fo r calcium i l l i t e was found t o be 31 .5 meq/lOO g c l a y ,
ADSORPTION EXPERIMENT
The adsorp t ion experiments of Cu "*", Pb "*" and Zn "*" were
conducted by t ak ing 5 ml of t h e Ca- i l l i t e suspensions i n a l a r g e
number of g l a s s s toppered t ubes and adding varying amounts of 0.01N
of Cu (NO,)p, Pb(N0,)2 °^ 2ii(N0^)2 s o l u t i o n i n s e p a r a t e s e t s and
a d j u s t i n g t h e mixture t o a cons tan t volume (25 ml) wi th d i s t i l l e d
wa te r and shaking t h e s e tubes a t 30 C i n t h e f i r s t s e t of e x p e r i
ments and a t 60 C i n t h e second s e t for 12 hours i n each c a s e .
m The suspensions v/ere then cen t r i fuged and t h e r e s i d u a l Cu, Pb and
Zn ions were es t imated by s t andard EDTA s o l u t i o n ( R e i l l e y e t a l , ,
1959) . The d i f f e r ence between metal ion concen t r a t i on added minus
t h e amount of metal ions i n superna tan t l i q u i d s gave t h e amount
of metal adsorbed by t h e c l a y . The de te rmina t ion of Cu "*", Pb "*"
and Zn '*' a re made as fol lows and r e s u l t s a r e given i n Table XXV t o
XXVII and F i g . 11 .
DETERMINATION OF COPPER (Cu "*")
The amount of copper (Cu ) was es t imated i n equ i l ib r ium
s o l u t i o n by EDTA t i t r a t i o n method us ing PAN as i n d i c a t o r .
REAGENTS REQUIRED; The chemicals used fo r t h i s experiment were
of BDH a n a l y t i c a l grade and t h e i r s o l u t i o n a r e p repared as fo l lows:
S tandard EDTA s o l u t i o n : A 0.01N EDTA s o l u t i o n was prepared i n
d i s t i l l e d wate r .
PAN / ~ 1 - ( 2 - P y r i d y l a z o ) - 2 - N a p t l : i o i y s o l u t i o n : A 0,1% s o l u t i o n of
PAN was p repa red in methyl a l c o h o l .
Buf fe r s o l u t i o n (pH 4 ) : Buffer s o l u t i o n of pH 4 was p repared by
mixing 180 ml of N/5 sodium a c e t a t e and 820 ml of N/5 a c e t i c ac id
s o l u t i o n .
Procedure; A 5 ml of superna tan t l i q u i d v/as talcen in a b r e a k e r ,
t r e a t e d wi th 5 ml bu f f e r of pH 4 and t h r e e drops of PAN i n d i c a t o r .
114
The contents were then titrated with standard EDTA solution. From the
values EDTA solution used up minus the blank reading, the amount of
Cu "''adsiartied by Ca- illite was calculaited.
DETSRI4INATI0N OF LEAD (Pb " )
The amount of lead (Pb "*") was also estimated in equilibrium
solution by EDTA titration method using xylenol orange as an indi
cator as follows:
Standard EDTA solution; A 0.01N EDTA solution was prepared in
distilled water and standardized with standard CaClp solution using
eriochrome black 'T' as indicator and buffer solution of pH 10,
Buffer solution (pH 5.5); A 41,0 g sodium acetate trihydrate was
dissolved in distilled water and 30 ml of glacial acetic acid was
added to it. The volume was made to 500 ml with distilled water.
Indicator solution; A 0.1 g of xylenol oriange indicator was weighed
and dissolved in 10 ml of methyl alcohol.
Procedure; A 5 ml portion of supernatant liquid was taken in a
beaker and 10 ml of buffer solution (pH 5.5} was added to it. The
mixture was wanned to 50 C, 2 drops of xylenol orange indicator is
added and titrated with standard EDTA solution to a light yellow
end point. From the volume of EDTA used minus the readings of re-
agent blank, the amount of Pb "*" adsorbed by Ca- illite was calculated.
115
DETERMINATION OF ZINC (Zn^"^)
The amount of zinc (Zn ; was estimated in equilibrium
solu t ion by EDTA t i t r a t i o n using ammonium fluoride solut ion as mask
ing agent for calcium (Reil ley et a l , , 1959) and eriochrome black
•T' as ind ica to r .
REAGENTS RaaUIREDt The chemical used for t h i s are prepared as
follows:
Standard EDTA solut ion: A 0.01N EDTA solut ion was prepared in
d i s t i l l e d water.
Buffer solut ion (pH 10); Dissolve 54 g of ammonium chloride in
200 ml of water then add 350 ml of 25% ammonium hydroxide and d i l u t e
t o one l i t r e in d i s t i l l e d water.
Procedure: A 5 ml port ion of supernatant l iquid was taken in a
beaker, add 5 ml of Ammonium fluoride solut ion and then t r e a t e d with
5 ml of a buffer pH 10 and three drops of eriochrome black 'T ' i n d i
ca to r . The contents were then t i t r a t e d with standard EDTA solut ion
t o a blue end point . From the values of EDTA solut ion used minus
t he blank reading, the amount of Zn adsorbed by Ca- i l l i t e was
ca lcu la ted .
lis
RESULTS AND DISCUSSION
The results of adsorption of Cu "*", Pb "*" and Zn "*" experiments
at 30°C and 6o°C over Ca- illite are reported in Tables-XXV to
XXVII and Fig, 11. It is observed that the adsorbed amount of
these metals en to the illite surface decreases with the rise in
temperature. It has been a general observation in adsorption pro
cess (Bartell et al., 1951) that the kinetic energy of the inter
acting ions increases and therefore the electrostatic attraction of
these species decreases which results a decrease in their adsorp
tion with the rise in temperature.
The adsorption isotherms (Fig, 11) show that the adsorption
of the heavy metal ions over Ca- saturated illite follow the order
Cu>Pb>Zn at 30° and 60°C. This sequence is indicative of the
retention affinity of the metal ions or their calcium replacing
power over the exchangeable sites of the illite surfaces. Similar
view has also been observed by Forbes et al. (1976) working on
geothite.
The adsorption data conformed to Freundlich equation. The
relative binding stren,-,th between clay siirface and the cations,
could be obtained easily by Freundlich equation constants (Table-
XXVIII). Freundlich adsorption equation may be written as:
/ „ Vn x/m = KC
or In x/m = InK + Vn InC
117
where x/jjj g the amount adsorbed by mass 'm' of the adsorbent,
K andVn are constants and depend upon the nature of the adsorbent,
adsorbate and temperature and C is the equilibrixim concentration
(/ig/ml) in solution. A plot of In x/j against InC is shov/n in
Fig, 12, The value of K which is a measure of adsorption capacity
was calculated by extra polating the curve to zero equilibrium con
centration (C = 0). The value of V n which is a measure of adsorp
tion intensity was determined from the slope of the Freundlich
adsorption isotherms (Fig, 12), The calculated values of these
constants are reported in the Table-XXVIII, The adsorption capacity
(K) of these ions follows the same order Cu ''•>Pb "*">Zn "*". The
values are found to decrease with the increase in temperature which
confirm our earlier deduction for the adsorption order and tempera
ture effect. However the values of 1/n shows the reverse order of
their adsorption capacity (K), These values indicate that there is
an inverse relationship between adsorbent capacity and intensity
of adsorption.
The thennodynamic parameters such as equilibrium constant
(KQ) , ree energy {C^Q ), enthalpy (AH ) and entropy (AS ) asso
ciated with the metal ions adsorption on Ca- illite surface at 30
and 60 C were calculated according to .
the following relationship:
TABLE - XXV
118
ADSORPTION OF Cu^"^ ON Ca- I LUTE AT 30°C AND 60°C.
Concen t ra t ion of c l ay suspension =
Volume of
S t r e n g t h <
c l ay suspension t aken =
Df Cu(N0^)2 sol^"^^®"
T o t a l volume of mixture
Volume of t i t r a t e d
Volume of 0.01N Cu(N0^)2 added
(ml)
At ^O^Z
0 . 5 1.0 2 . 0 3 .0 4 . 0 5.0 7 . 0
10.0
At 60°C
0 . 5 1.0 2 . 0 3 . 0 4 . 0 5.0 7 .0
10.0
=
=
superna tan t s o l u t i o n =
Volume of 0.01N EDTA used
(ml)
0 .04 0.09 0.18 0.33 0.42 0.57 0 .88 1.32
0 .05 0.10 0.19 0 .35 0.45 0.62 0.93 1.39
Amount of
22 .8 g / 1
5 ml
0.01 N
25 ml
5 ml
Cu2+ Amount of Cu^ in equ i l ib r ium adsorbed s o l u t i o n
(meq/1)
0 .016 0 .036 0 .072 0.132 0 .168 0 .228 0.352 0 .528
0 .020 0 .040 0.076 0 .140 0 .180 0 .248 0 .372 0.556
(i oieq/lOOg c l ay )
2 .63 4.82 9 .65
11.84 16.66 18.86 22.80 29.82
2 .19 4.39 9.21
10.96 15.35 16.66 20.61 26.75
119
TABLE - XXVI
ADSORPTION OF Pb^"^ ON Ca- ILLITE AT 30^C AND 60^C.
Concen t ra t ion of c lay suspensior:
Volume of c l ay suspension t aken
S t r e n g t h of
T o t a l volume
Pb(N0,)2 sol^'^^io^
; of mixture
Voliome of supen ia tan t s o l u t i o n t i t r a t e d
Volume of 0.01N Pb(N0,)2 added
(ml)
At 30°C
0 .5 1.0 2 . 0 3 . 0 4 .0 5 .0 7 . 0
10 .0
At 60°C
0 . 5 1.0 2 . 0 3 . 0 4 .0 3,0 7 . 0
10.0
Volume of 0.01N EDTA used
(ml)
0 .05 0.11 0.19 0.35 0.47 0.63 0.97 1.44
0.06 0.13 0.19 0.37 0 .49 0.63 0.99 1.53
L = 2 2
=
= 0.
=
=
Amount of i n , e q u i l i t s o l u t i o n
(meq/1)
0.020 0 .044 0.076 0.140 0.188 0.252 0.388 0.576
0.024 0.052 0.076 0.1^8 0.196 0.252 0.396 0.612
U8 g/ ]
5 ml 01 N
25 ml
5 ml
Pb^* irium
Amount of Pb "*" adsorbed (raeq/ 100g c l ay )
2 .19 3 .95 9.21
10,96 14.47 16.22 18.86 24.56
1.75 3.07 9.21
10.09 13.59 16,22 17.98 20.61
120
TABLE - XXVII
ADSORPTION OF Zn "*" ON Ca- ILUTE AT 30°C AI^ 6Q°C
Concent ra t ion of c lay suspension =
Volume of c lay suspension t aken =
S t r e n g t h of Zn(NO,)p s o l u t i o n
T o t a l volume of mixture
Volume of t i t r a t e d
Volume of 0.01N Zn(N0^)2 added
(ml)
At 30°C
0 . 5 1.0 2 .0 3 .0 4 . 0 5 .0 7 .0
10 .0
At 60°C
0 . 5 1.0 2 . 0 3 .0 4 . 0 5 .0 7 .0
10 .0
=
superna tan t s o l u t i o n =
Volume of 0.01N EDTA used
(ml)
0.06 0.13 0 .20 0.38 0.52 0 .68 1.02 1.54
0.06 0.13 0.21 0.39 0.53 0.71 1.07 1.57
Amount of
22 .8 6 /1 5 ml
0.01 N
25 ml
5 ml
•7 2 + Zn i n equ i l ib r ium
s o l u t i o n (meq/1)
0.024 0.052 0.080 0.152 0.208 0.272 0.408 0.616
0.024 0.052 0.084 0.156 0.212 0.284 0.428 0,628
Amount of Zn "*" adsorbed (me jq/100g c l a y )
1.75 3.07 8.77 9 .65
12.28 14.03 16.66 20.17
1.75 3.07 8.33 9.21
11.84 12.72 14.47 18.86
ni
TABLE - XXVIII
2+ _ 2 + 2. FREUNDLICH CONSTANTS FOR Cu " . Pb " AI^ Zn'""*' ADSORPTION
ON Ca- ILLITE AT 3Q°C AND 60°C,
Meta l ions Temperature Freundl ich Cons tan ts
(°K) • K V n
Copper
Lead
Zinc
303 333
303 333
303 153
50.5 46.3
41.8 40.8
35.8 30.9
0.69 0.73
0.71 0.78
0.75 0.79
22
TABLE - XXIX
THERMODYNAMIC PARAMETERS FOR CU ' , Pb^"^ AND TJ?"^ ON Ca- ILLITE SURFACE
Thermodynamic Parameters M e t a l T emp er at ur e
/0v^ ? T ^ ^ " AG^ AH° AS° ( K) brium
constants (KQ) (Calmole"'') (Calmole"^ )(Caldeg"''mole"''
Copper 335 24.0 -2103 "^99 4^2
X ^^o ^ u ^ '^-^. • - 1 0 : ? ^ 77-7 3 . 7
Zinc ^^^ ^)i'7, -^^n:; -74 5.8
303 333
303 333
303 333
26.6 24.0
23.1 20,6
20.6 20.4
-1977 -2103
-1892 -2002
-1824 -1997
0-40 0-50 0-60 0-65 Equilibrium concentration (nneq/l)
2+ 7+ 7+ FIG.11 Adsorption isothernns of Cu, Pb and Zn
on Ca-i l l i te .
W/x Ul
o
I TJ
U c o
+ N c
M • D C 03
+ n Q_
^ -
o
o in
E i_ Ci)
SI o I/)
c o
o •D *TJ
H u
c D
cn
iZ
12 0
A G ° = - RTlnKo
m ^02 I inKo = -AH°/R ( " Y - - - f - )
and AS° = ( A H ° - A G ° ) / T
(where a l l the symbols have t h e i r usual meanings).
The calculated values for K Q , A G ^ , A H and AS^ are reported in
Table-XXIX.
The negative free energy change ( AG°) (Table-XXIX) in a l l
the case ind ica tes t h a t the adsorption of metal ions over Ca--2+ ^^ 2-1
i l l i t e surface follows the order: Cu > Pb ^ Zn, The free energy
change which i s a measure of the driving force for a react ion to
occur, decreases with r i s e in temperature in a l l the cases show
t h a t the adsorption decreases at higher temperature. The exchange
r eac t ions were therefore spontaneous and there was a higher p re fe -
rence of the heavy metal ions over i l l i t e surfaces than for Ca 4+ At 4+ j-t
ion . The data confirms the s e l ec t i v i t y order C u > Pb >• Zn > C a over i l l i t e surface.
The negative values of standard enthalpy change ( A H ) in
a l l cases during the exchange react ion show tha t the react ion i s
exothermic and the heavy metal ions are more t i g h t l y bound on the
exchange s i t e s of the i l l i t e surfaces as compared to the calcium
ions and the adsorption decreases as the temperature increases .
124
The above conclusions are supported "by entropy (AS ) gain
during the Cu , Pb and Zn "*" exchange with Ca- i l l i t e . The +ve
values of the entropy change indicate tha t the system becomes more
disordered in the adsorption process of Cu "*", Pb "*" and Zn " over
Ca- i l l i t e . This i s possibly due to the breaking of the s t ruc ture
of the adsorbed water layer with a concomitant change in the hydra
t i o n s ta tus of the cation t ransfer red from clay solut ion phase
(Van Bladel and Menzel, 1969).
m REFERENCES
AbD-ELFATTAH, A. and WADA, K.: J , Soi l S c i . , 32(2), 271 (1981).
ANDERSSON, A.^and NILSSON, K.O.; Ambio, 1, 176 (1972).
BARTELL, F.E. , THDMAS, T.L. and YING, Pu; J . Phy, Colloid Chem., 55, 1456 (1951). .
BIGGAR, J.W. and CHEUNG, M.W,; So i l Sci , Soc. Am. Proc . , 37, 863 (1973).
CHATTERJEE, A.K. and MANDEL, L.N.; J , Indian Soc. So i l S c i . , 33(3) , 669 (1985).
DHELLON, S.K. and DHILUON, K.S.; J . Indian Soc, Soi l S c i . , 32(2), 250 (1984),
DUTTA, I . and MOOKHERJEE, A.; Indian Environ, Health, 22, 220 (1980),
FORBES, E.A., POSNER, A.H. and QUIRK, J . P . ; J , So i l S c i , , 27(2), 154 (1976),
JACKSON, M.L.; 'So i l Chemical Analys is ' , Prent ice-Hal l , Englewood C l i f f s . , N.J. (1958).
JAHERUDDIN, M., 'IIVESEY, N.T, and CRESSER, M.S.; Commun, Soi l Sci , Plant Anal . ,16(8) , 909 (1985).
JOSHI, D.C., DHIR, R.P. and GUPTA, B .S . ; J . Indian Soc. So i l S c i . , 29, te (1981).
JOSHL, D.C., DHIR, R.P. and GUFTA, B.S . ; J . Indian Soc. Soi l S c i . , 30, 547 (1982).
JOSHI, D.C. and SHARWA, B.K.; J . Indian Soc, Soi l S c i . , 34, 257 (1986).
MAGUIRE, M., SALVEK, J . , VIMPANY, I . , HIGGINSON. F.R. and PICKERING, W.F.; Aust, J , So i l Res , , 19(3), 217 (1981).
120
NAKOS, G.; Plant and So i l , 53, 427 (1979).
PETRUZZELLI, G., GUIDI, G. and UJBRANO, L.; Heavy Met. Environ., I n t . Conf. 3rd, 866 (1981).
REILLEY, C.N., SCmiD, R.W. and SADEK, F .S . ; J . Chem. Educ., 36, 555" (1959).
ROBERT, D. HARTER; Soi l Sc i . Soc. Am. J . , 47, 47 (1983).
VAN-BLADEL, R. and MUNZEL, R.; Proc. In te rn . Clay Conf., Tokyo, 619 (1969).
WALKER, W.M., MILLER, J .E . and HASSETT, J . J . ; So i l S c i . , 124, 145 (1977).
CHAPTER - I V
STUDIES ON THE ADSORPHON OF METHYL. 2-aENZIMIDA20LE
CARBAMATE (MBC) WITH CLAYS AS AFFECTED
BY VARIOUS SOIL PARAMETERS
127
INTRODUCTION
Methyl, 2-Benzimidazole Carbamate (MBC) is a systemic
fungicide used to control a wide spectrum of fungal diseases
(Ram and Vir, 1984; Sandhu and Gill, 1982). It has been shown
that it can interact with soil colloids because of its persis
tence in soil with a half life period of several months
(Baude et al,, 1974), Adsorption studies on MBC have been carried
out by various workers (Aharonson and Kafkafi, 1975; Khan and
Khan, 1986; Khan et al,, 1987) to show that the nature of its
interaction with clays and soils differ significantly depending
upon the soil constituent, soil properties and pH etc. However,
studies on its adsorption over various type of clays as influenced
by some soil parameters such as soil organic matter, sesquioxide
and soil pH have been lacking in literature.
The present chapter reports the influence of the nature
of clay minerals, soil organic matter, sand, free Al- and Fe-oxides
and soil pH on the adsorption of MBC which might be useful to
understanding its behaviour in various types of soils containing
these clays.
EXPERIMENTAL
The clay minerals used in these investigations were
montmorillonite, synthetic montmorillonite, illite, kaolinite and
128
dickite which were obtained from Ward's Natural science establish
ment, Rochester, NY (USA ). A ^ 2/um fraction of the clays were
separated by dispersion and centrifugation, taking care to remove
most of the sand and dark coloured silt. The organic matter was
decomposed by treatment with 30% HpOp and then the suspensions were
converted into Na- clays as follows:
PREPARATION OF SODIUM SATURATED CLAYS
Na- clays were prepared by the same method as given in
Chapter- III of this thesis.
DETERMINATION OF CATION EXCHANGE CAPACITY
The CEC values of Na- form of clays were determined by
ammonium acetate method (Jackson, 1958) as described in Chapter-I
of this thesis. The CEC values for Na- forms of montmorillonite,
synthetic montmorillonite, kaolinite and dickite clays were found
to be 118.5, 110.0, 38.80, 12.5, 10.8 meq per 100 g clay respec
tively,
DETERMINATION OF SURFACE AREA
Surface area of clay samples were determined by Hendricks
and Dyal's method (1950). For this, weighed samples of Na- clays
were taken in small aluminium boxes of known weights. The samples
were sprayed evenly over the bottom of the boxes. The boxes,
12!}
without lid were placed in a dessicator over 250 g of PpOc. The
samples were then dried to a constant weight. They were then
wetted with ethylene glycol added from a pipette dropwise and
warming. The samples were then placed in a dessicator and allowed
to stand at room temperature (30 C). Weights of the samples were
recorded after every sixteen hours interval and drying continued
till two successive weights agreed upto tenth of a milligram.
Surface area was then calculated from the equation:
Wg A =
Ws X 0.00031
2 where A » surface area in m /g; Wg = weight in grams of
glycol retained by samples, Ws = weight in grams of the samples
on PpO^ dried basis and 0.00031 is the Dyal Hendricks value for 2
the grams of glycol required to form a monolayer on one m of
surface area. The surface area of Na- forms of montmorillonite,
synthetic montmorillonite, illite, kaolinite, and dickite clays
2
were found to be 808,5, 710,5, 114,0, 35.5 and 30.5 m /g respec
tively.
DETERMINATION OF MBC
Methyl, 2-Benzimidazole carbamate (MBC) concentration in
supernatant liquid was determined by UV spectrophotometer against
reagent blank at 280 nm wavelength (Chiba, 1977). The standard
curve for MBC is shown in Fig, 13,
130
ADSORPTION EXPERIMENTS
In a duplicate set of experiments, 0,5 g of each clay
minerals were taken into 500 ml conical flask and varying amounts
of MBC (0 to 1000/ig) in 0.01M NaCl solution were added to it.
The total voliime of the suspension made to 250 ml with distilled
water. The suspensions were equilibrated in a electric driven
shaker and the temperature was made constant at 30 + 1 C, It was
centrifuged after 8 hours (equilibrium time of MBC adsorption)
for 20 mts at 10,000 rpm. The concentration of MBC in supernatant
liquid was determined as described earlier. The amounts of MBC
adsorbed over clay minerals were calculated from the amount of MBC
added minus the amount of MBC remaining in the supernatant solution.
The results are given in Table-XXX to XXXIY and Fig. 14.
Effect of Soil Organic Matter;
To study the effect of soil organic matter on the adsorption
of MBC, two sets of experiments were carried out with a low
(aoO^g MBC/g clay) and high (2000/Ug MBC/g clay) amount of added
MBC, The soil organic matter was extracted from a peat soil by the
method of Desai and Ganguli (1979) and added to the above experi
ments in varying amounts. The incubation, centrifugation and ad
sorption was carried out in the same manner as in the case of
adsorption experiments. The results are shown in Table-XXXVI and
XXXVII and Fig. 16(a).
131
Effect of Sand content;
For studying the effect of sand on the adsorption of
FiBC, varying amount of sand with a particle size ,85 nun were
added to the adsorption reaction vessel. The method for the
adsorption of MBC remained the same as above. The results are
recorded in Table-XXXVIII and XXXIX and Fig. 16(b).
Effect of Free Al20^ and Fe20,;
The effect of free Al- and Fe-oxides on the adsorption of
MBC was studied by adding varying amount of AlpO, and 620^ to
the adsorption reaction vessel. The results are reported in
Table- XL and XLI and Fig. 16(c).
Effect of Suspension pH;
The effect of suspension pH on the adsorption of KBC was
studied by varying the suspension pH to 3,6,9 and 12 with the
help of 0.01N HNO, or NaDH, The experiments were carried out in
the same manner as described above. The results are reported in
Table-XUIandXLLII and Fig. 16(d).
RESULTS AND DISCUSSION
An examination of adsorption isotherms (Fig, 14) shows that
the adsorption of MBC over montmorillonite and synthetic montmori-
132
llonite in their Na- form conform to class 'S' and that on illite,
kaolinite and dickite, conform to class 'L' according to the cla
ssification of Giles et al, (I96O). It suggests that the MBC
adsorption vary with the nature of clay mineraHs under study. Since
the clay minerals were all in their Na- form, hence the structural
difference among the clays play an important role in MBC adsorp
tion. As the montmorillonite clays are swelling clays, the MBC
molecules meet strong competition with solvent water molecules for
the adsorption sites while in the case of illite, kaolinite and
dickite which have decreasing swelling properties, MBC molecules
does not meet any competition with the water molecules.
The order of MBC adsorption for various clay minerals
is as follows: montmorillonite >synthetic montmorillonite>
illite >• kaolinite •> dickite which obeys the values of their CBC
and surface area.
The adsorption data were fitted in Freundlich equation
in its linearized form (Murali and Aylmore, 1983).
Vn x/m = KC or log x/m = log K + 1/ ^ log C
where x/m is the amoimt of MBC adsorbed per 'm* mass adsorbant,
C is the equilibrium MBC concentration; K and Vn are constants.
A plot of log x/m Vs log C gave a straight line (Fig, 15).
The values of adsorption capacity (K) and intensity (1/n) were
TABLE - XXX
in
ADSORPTION OF MBC ON Na-MONTMORILLONITE
Amount of Na-montmori l loni te t aken
Concen t ra t ion of MBC s o l u t i o n added
T o t a l volume of
Volume of MBC s o l u t i o n added
(ml)
2 . 5
5.0
10.0
20 .0
30 .0
40 .0
6 0 . 0
80 .0
100.0
120.0
t h e suspension
Absorbance a t
280 nm
0.005
0.013
0.026
0.045
0.055
0.086
0.145
0.201
0.268
0.318
..
B
m
0 .5
10
g
ppm
250 ml
. Amount of MBC i n equ i l ib r ium suspension
Oug/ ml)
0.061
0.150
0.286
0.503
0.618
0.962
1.608
2.238
2.980
3.539
Amount of MBC adsorbed
(Aig/ ml)
19.50
25.00
57.00
1A8.50
291.00
319.00
396,00
481.00
510.00
630.50
m
TABLE - XXXI
ADSORPTION OF MBC ON Na-SYNTHETIC MONTMORILLONITE
Amount of Na-
Concentration
syn, montmorillonite taken =
of KBC solut ion added =»
Total volume of the suspension
Volume of MBC Absorbance solut ion added a t
(ml) 280 nm
2 .5
5.0
10.0
20.0
30.0
^ . 0
60.0
80.0
100.0
120.0
0.005
0.014
0.028
0.0A8
0.067
0.092
0.151
0.215
0.272
0.335
~
Amount of MBC i n equilibrium suspension
( ^g /ml )
0.063
0.155
0.309
0.529
0.7A0
1.020
1.678
2.390
3.020
3.720
0.5 g
10 ppm
250 ml
Amount of MBC adsorbed
(yUg/g )
18.50
22.50
45.50
135.50
230.00
290.00
361.00
405.00
490.00
540.00
133
TABLE - XXXII
ADSORPTION OF MBC ON Na- ILUTE
Amoxmt of Na- i l l i t e t aken = 0 . 5 g
Concen t ra t ion of MBC s o l u t i o n = 10 ppm added
T o t a l volume of t h e suspension = 25o ml
Volume of MBC so lu t ion added
(ml)
2.5
5.0
10.0
20.0
30.0
AO.O
60.0
80.0
100.0
120.0
Absorbance a t
280 nm
0.006
0.015
0.027
O.OAS
0.084
0.110
0,163
0.231
0.277
0.339
Amount of MBC i n equilibrium suspension
(^g / ml)
0.070
0.163
0.297
0.538
0.929
1.223
1.809
2.569
3.078
3.770
Amount of MBC adsorbed
(MS/g )
15.00
18.50
51.50
131,00
135.50
188,50
295.50
315.50
461,00
515.00
13G
TABLE - XXXIII
ADSORPTION OF MBC ON Na- KADUNITE
Amount of Na- kao l in i t e taken = 0,5 g
Concentration of MBC solut ion = 10 ppm added
Total volume of the suspension = 250 ml
Volume of iVlBC s o l u t i o n added
(ml)
2 . 5
5.0
10.0
20 .0
3 0 . 0
^ . 0
6 0 . 0
80 .0
100.0
120.0
Absorbance a t
280 nm
0.008
0.017
0.052
0.062
0.096
0.127
0.191
0.254
0.319
0.377
Amount of MBC i n equ i l ib r ium suspension
(/Ug/ml )
0.089
0.184
0.359
0.689
1.069
1.410
2.120
2.820
3.549
4.190
Amount of MBC adsorbed
( / i g /g )
5.50
8 .00
20 .50
55,50
65 .50
95 .00
140,00
190,00
225,50
305.00
137
TABLE - XXXIV
ADSORPTION OF MBC ON Na- DICKITE
Amount of Na- dickitetaken = 0.5 g
Concentration of MBC solution = 10 ppm added
Total volume of the suspension = 250 ml
Volume of MBC so lu t ion added
(ml)
2 .5
5.0
10.0
20.0
30.0
40.0
60.0
80.0
100.0
120.0
Absorbance at
280 nm
0.008
0.017
0.033
0.063
0.097
0.128
0.196
0.257
0.323
0.385
Amount of MBC i n equilibrium suspension
(Aig/ml)
0.092
0.188
0.364
0.699
1.078
1.420
2.179
2.858
3.590
4.276
Amount of MBC adsorbed
( jug /g )
4.00
6.00
18.00
50.50
61.00
90.00
110.50
171.00
205.00
261.00
138
TABLE - XXXV
FREUNDLICH CONSTANTS FOR THE ADSORPTION OF MBC ON
N a - CLAYS AT 30^C.
Type of Na- clays Freundlich constants
« Vn
Na- montmorillonite 239.25 0.931
Na- synthetic 199.35 0,932 montmorillonite
Na- illite 155.22 0.933
Na- kaolinite 63.62 1.o67
Na- dickite 53.62 1,115
13^
TABLE - XXXVI
EFFECT OF SOIL ORGANIC MATTER (SOM) ON THE ADSORPTION ON Na- MONmORILLONITE.
Amount of Na- montmor i l lon i t e taken
Concen t ra t ion of MBC s o l u t i o n added
T o t a l volume of t h e suspension
Volume of MBC s o l u t i o n added
(ml)
AO
100
40
100
40
100
40
100
40
100
40
100
Amoiont of SOM added
0 .1
0 . 2
0 . 4
0 .6
0 .8
1.0
Absorbance a t
280 nm
0.079
0.248
0.072
0.234
0,059
0.220
0.051
0.212
0.043
0.206
0.038
0.200
= 0 . 5
10
OF MBC
g
ppm
=» 250 ml
Amount of MBC i n equ i l ib r ium suspension
(Aig/ml)
0.879
2.760
0.800
2.603
0.660
2.449
0.563
2.356
0.A80
2.289
0.419
2.223
Amount of MBC adsorb ed
(^ig/g )
360.50
620.00
400.00
698.50
470.00
775.50
518.50
822.00
560.00
855.50
590.50
888.50
140
TABLE - XXXVII
EFFECT OF SOIL ORGANIC MATTER (SOM) ON THE ADSORPTION OF MBC ON Na- ILLLTE.
Amount of Na- i l l i t e t aken = 0 , 5 g
Concen t ra t ion of MBC s o l u t i o n = 10 ppm added
T o t a l volume of t h e suspension = 250 ml
Volume of MBC Amount of Absorbance Amount of Amount of s o l u t i o n added SOM added a t MBC i n MBC adsorb-
(ml) (%) 280 nm equ i l i b r ium ed suspension ( ^ g / g )
( ^g /ml )
AO
100
4o
100
40
100
40
100
40
100
40
100
0.1
0.2
0.4
0.6
0 .8
1.0
0.108
0.269
0.103
0.262
0.095
0.248
0.086
0.237
0.079
0.227
0.073
0.220
1.199
2.990
1.1A9
2.910
1.050
2.755
0.960
2.630
0.876
2.520
0.809
2.440
200.50
505.00
225.50
545.00
275.00
622.50
320.00
685.00
362.00
740.00
395.50
780.00
TABLE - XXXVIII
EFFECT OF SAND ON THE ADSORPTION OF MBC ON Na- MONTMORILLONITE
Amount of Na- montmorillonite taken
Concentration of MBC solution added
Total volume of the suspension
0,5 g
10 ppm
250 ml
Volume of MBC solution added
(ml)
Amount of sand added
(g/g)
Absorbance Amount of MBC Amount of at in equilibrixim MBC adsorb-
280 nm suspension ed (Aig/ml) (Aig/g)
40
100
40
100
40
100
40
100
40
100
40
100
0.01
0.02
0.04
0,06
0.08
0.10
0.088
0.272
0.090
0.275
0.092
0.281
0.095
0.287
0.097
0.292
0.099
0.297
0.980
3.025
0.995
3.060
1,024
3.123
1.055
3.184
1.080
3.241
1.103
3.295
310.00
488.50
302,50
470,00
288,00
438,50
272.50
408.00
260,00
379,50
248.50
352,50
U2
TABLE - XXXIX
EFFECT OF SAND ON THE ADSORPTION OF MBC ON Na- ILUTE.
Amount of Na- i l l i t e taken Concentration of MBC solut ion added Total volume of the suspension
0.5 g 10 ppm
250 ml
Volume of Amount of MBC solution sand added added
(ml) (g/g)
Absorbance Amount of MBC Amount of at in equilibrium MBC adsorb-280 nm suspension ed
(Mg/ml) (/ug/g )
40
100
40
100
40
100
40
100
40
100
40
100
0.01
0.02
0.04
0.06
0.08
0.10
0.112
0.286
0.115
0.292
0.119
0.500
0.121
0.507
0.124 .
0.514
0.127
0.520
1.249
5.180
1.275
5.240
1.519
5.550
1.544
5.410
1.580
5.489
1.410
5.555
175.50
410.00
162.50
580.00
140.50
555.00
128,00
295.00
110,00
255.50
95.00
222.50
H:I
TABLE - XL
EFFECT OF ADDED AI2O, AND Fe203 ON THE ADSORPTION OF MBC ON
Na- MONTMORILLONITE.
Amount of Na- montmorillonite taken • 0.5 g Concentration of MBC solution added = 10 ppm Total volume of the suspension « 250 ml
Volume of MBC Amount of Absorbance Amount of MBC Amount of solution metal oxide at in equilibrium MBC adsorb-added added 280 nm suspension ed
(ml) {%) (Mg/ml) (Aig/g )
ALUMINIUM OXIDE (Al20^)
AC
100
40
100
40
100
40
100
40
100
40
100
0.1
0.2
0.4
0.6
0.8
1.0
0.081
0.261
0.077
0,256
0.070
0.247
0.065
0.239
0.062
0.232
0.060
0.229
0.899
2.903
0.850
2,844
0.775
2.740
0.720
2.655
0.689
2.583
0.670
2.540
350.50
548.50
375.00
578,00
412.50
630.00
440.00
672.50
455.50
708.50
465.00
730.00
w
TABLE - XL (Contd.)
Volume of Amount of Absorbance Amount of MBC Amount of MBC solution metal oxide at in equilibrium MBC adsorb-added added 280 nm suspension ed
(ml) (%) (Mg/ml) (Aig/g )
IRON OXIDE
40
100
40
100
40
100
40
100
40
100
40
100
(Fe203)
0 .1
0 .2
0 . 4
0 .6
0 . 8
1.0
0.076
0.255
0.070
0 . 2 ^
0.061
0.236
0.054
0.226
0.051
0.221
0.049
0.217
0.840
2.835
0 .775
2.756
0.680
2.619
0.599
2.516
0.570
2.450
0.543
2.409
380.00
582.50
412.50
622.00
460,00
690,50
500.50
742.00
515.00
775.00
528.50
795.50
Hil
TABLE - XLI
EFFECT OF ADDED Al^O, AND Fe^O, ON THE ADSORPTION OF MBC ON
Na- ILLITE.
Amount of Na- illite taken
Concentration of MBC solution added
Total volume of the suspension
0.5 g 10 ppm
250 ml
Volume of Amount of Adsorbance MBC solution metal oxide at added added 280 nm
(ml) W
Amount of l C Amount of in equilibrium MBC adsorb-suspension ed
(Aig/ml) (Aig/g)
ALUMINIUM OXIDE (AI2O,)
40
100
40
100
40
100
40
100
40
100
40
100
0.1
0.2
0.4
0.6
0.8
1.0
0.108
0.272
0.106
0.268
0.103
0.261
0.101
0.257
0.099
0.253
0.097
0.251
1.199
3.026
1.175
2.979
1.l4o
2.900
1.119
2.850
1,104
2.809
1.080
2.789
200.50
487.00
212.50
510.50
230.00
550.00
240.50
575.00
248.00
595.50
260.00
605.50
lis
TABLE - XLI (Contd.)
Volume of Amount of Absorbance Amount of MBC Amount of MBC solution metal oxide at in equilibrium MBC adsorb-added added 280 nm suspension ed
(ml) (%) (Aig/ml) (Aig/g)
IRON OXIDE
40
100
AO
100
40
100
40
100
40
100
40
100
(Fe203)
• 0.1
0 . 2
0 . 4
0 .6
0 . 8
1.0
0 .104
0.266
0.100
0.260
0.094
0.250
0.092
0.243
0.090
0.239
0.088
0.237
1.160
2.955
1.109
2.890
1.04o
2.779
1,020
2.7O0
1.004
2.655
. 0.980
2.633
220.00
522.50
245.50
555.00
280.00
610.50
290.00
650.00
298.00
672.50
310.00
683.50
147
TABLE - XLII
EFFECT OF pH ON THE ADSORPTION OF MBC ON Na- MONTMORILLONITE
Amount of Na- montmorillonite taken » 0,5 g
Concentration of MBC solution added = 10 ppm
Total voliome of the suspension = 250 ml
Volume of MBC solution added
(ml)
pH of the suspension
Absorbance Amount of MBC Amount of at in equilibrium MBC adsorb-
280 nm suspension ed ( /ml) ipg/g)
ho
100
40
100
40
100
40
100 12
0.077
0.229
0.086
0.241
0.093
0.250
0.097
0.259
0.860
2.539
0.960
2.680
1.030
2.779
1.080
2.880
370.00
730.50
320.00
660.00
285.00
610.50
260.00
560.00
TABLE - XLIII
EFFECT OF pH ON THE ADSORPTION OF MBC ON Na «ILLITE
Amount of Na- i l l i t e taken
Concentration of MBC solut ion added
0.5 g
10 ppm
Total voliome of the suspension = 250 ml
HH
Volume of MBC solution added
(ml)
Ao
100
40
100
40
100
40
100
pH of the suspension
3
6
9
12
Absorbance a t
280 nm
0.109
0.272
0.118
0.303
0.125
0.316
0.126
0.320
Amoxmt of MBC i n equilibrium suspension (pg/ml)
1.210
3.020
1.316
3.369
1.390
3.509
1.401
3.550
Amount of MBC adsorb, ed
( ^ i g / g )
195.00
490.00
142.00
315.50
105.00
245.50
99.50
225.00
2.0 4-0 6-0 8'0 10.0 U-O
Co-ncC/^j/rwlJ-^
FIG. 13. STANDARD CURVE OF MBC
700 r
0
;Na-Montmori l loni te -•-* No-Synthetic Montmorillonite -«- iNa- IU i te -x-iNa-Kaolini'te -A-;Na-Die kite
1-0 2-0 3-0 A'O 5-0 Equil ibrium concentration (/jg/ml)
FIG-14. ADSORPTION ISOTHERMS OF MBC ON No-CLAYS AT 30°C.
3-0 r
2-5
2-0
X
^ V 5
1-0
0-5 -
0
r'lUonite etic Montmrillonite
ite A - } HQ- Dicki tc
-2 -1 log C
FIG.15 FREUNDLICH ADSORPTION ISOTHERMS OF MBC OVER Na-CLAYS AT 30°C.
900
800
700
600
500
_ ^0 0 en
^ 3 0 0
200
100 -XI
o
o o ^ 8 0 0
0 700
D GOO O
1 500
Z,00
300
200
100
r-
^
'fy' - / ' . < ^
y y
- /3 y
/
.^^ * ^X-
> •)<•
1 1
(a ) ^^^^
^^^'^
. / ' y*
^ - o ' ' ' ^
yO-
.^ ^ ^ ^¥r
^ ^ ^
1 1 1
0-2 0-4 0-6 0-8 1-0 S0M(7o) added
J>-^'
- _ . ^ . ^ o _ - - o __-o--2
t-;-^^' . _ _ - ^ — - ) ^ — • > t - - i
Curves 1 to 4 for AI2O3
Curves 5 to 8 for Fe203
J I I 1 1
0 0-2 0.4 0-6 0-8 1-0 Sesquloxide(7o) added
(b)
MBC, 800 >jg/g clay MBC,2000>jg/g clay
"»«---. - . -^ - - »
^ - - - ) f - _
0 0-02 0 0 6 010 Sand added (g/g)
(d)
^vL--^ °''---. 0 ~
"^^
- X - ^ _
0 6
PH 12
F16.1G INFLUENCE OF (o) SOIL ORGANIC MATTER (b) SAND (c) FREE A l - i Fe OXIDES AND (d) SUSPENSION pH ON THE ADSORPTION OF MBC ON {-o- ) MONTMORILLONITE AND ( - M - ) ILLITE SURFACES.
149
estimated from the intercept and slope of the curves respectively
and are given in Table- XXX V . It shows that the values of K
decrease in the same order as found in the case of adsorption iso
therms. While the adsorption intensity of MBC over montomorillonite
and synthetic montmorillonite is about half of the intensity for
other clays. These results again confirm the earlier observation
from adsorption isotherm that there is a strong competition for
adsorption sites in montmorillonite and synthetic montmorillonite
than the other clays under study.
The effect of soil organic matter on the adsorption of MBC
is shown in Table-XXXVI and XXXVII and Fig. 16(a). It is evident
that an addition of SOM to the clay mineral increases the MBC adsorp
tion. It may be due to the increase in adsorption sites as well as
in surface area of the clay due to SOM-clay complexation. This
also shows that the order of MBC adsorption between two clays studi
ed remained the same as montmorillonite >• illite. While in the case
of sand addition to clay minerals, MBC adsorption reduced (Table-
XXXVIII and XXXIX Fig. I6b) due_ to the physical barrier created thereby
blocking the MBC particle toYeach adsorption sites.
Table- XL and XLI and Fig,l6c show that the addition
of Al- and Fe- oxides increased the MBC adsorption over clay mine
rals due to increased adsorption sites(Lindsay, 1979). It may be
explained as Free oxides of Al- and Fe- added to clay suspension,
get hydrolyzed and coordinate with MBC molecules through hydrogen
150
bonding and/or Vander Waal's forces according to the suspension
pH, However, the interaction of AlpO^ or Fe^O, with clay minerals
can not be ruled out. Hence, there is a possibility of blocking
of adsorption sites of the clay particles which is evident from
the slow increase in the MBC adsorption (Fig, l6c).
Table-XLH&XLHL and Fig, 16(d) show that the effect of
suspension pH on the adsorption of MBC on to the clay surfaces. It
shows that the MBC adsorption decreases with increase in suspension
pH at both the levels of added MBC, At low pH values, the MBC gets
protonated to become a positively charged molecules and their sub
sequent adsorption over clay surfaces may be plausible e:q)laination
for its increased adsorption in acidic pH range (Aharonson and
Kafkafi, 1975) while at high pH values, the MBC adsorption decreases
due to their hydrolysis. However, the decrease in adsorption is
slow, but even at pH 12, the adsorption was observed. This suggests
the involvement of hydrogen bonding, Vander Waal's forces and/or
coordination through cations etc, in adsorption process (Khan and
Bansal, 1980).
iSj
REFERENCES
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CHLBA, M.j J. Agric. Food Chem,, 25(2), 368 (1977).
DESAI, M.V.M. and GANGULI, A.K,; J. Indian Chem. Soc, 56, 1167 (1979).
GILES, C.H., McEWAN, T.H., NAKHWA, S.N. and SMITH, D,; J. Chem. Soc, 3973 (1960).
HENDRICKS, S.B, and DYAL, R.S.; Trans. 4th Inter. Congr. Soil. Sci., 2, 71 (1950).
JACKSON, M.L.; 'Soil Chemical Analysis', Prentice Hall, Englewood Cliffs, NJ, p. 57 (1958).
KHAN, S. and BANSAL, V.; J. Colloid Interface Sci., 78, 554 (1980).
KHAN, S. and KHAN, N.N.; Clay Research (1986).
KHAN, S., KHAN, N.N. and KHAN, F.A.; Clay Research (1987).
LINDSAY, W.L.; 'Micronutrients in Agriculture', Soil Sci. Soc. Am. Madison (1972).
MURALI, V. and AYLMORE, L.A.G.; Soil Sci., 135, 203 (1983).
RAM, V. and VIR, D.j Pesticides, 18, 65 (1984).
SANDHJ, K.S. and GILL, S.P.S.; Pesticides, 16, 17 (1982).
152
PAPERS FUBUSHED AND CX)MMUNICATED
1. The Influsnce of organic acids and bases on the mobility
ot some heavy metals through Aligarh so i l .
Indian Soc, Soil Sc i , , 33, 779-784 (1985),
2. Pesticide mobility in soi ls as affected by the i r chemical
characterist ics and some soil properties.
Environ. Pollut. (Revised and communicated).
3 . Adsorption of Cu *, Pb * and Zn * with Ca-saturated
i l l i t e .
Clay Research (Commuxiicated).
A. Studies on the adsorption of methyl, 2-benzimidazole
carbamate (MBC) with clays as affected by various soi l
parameters.
Soil Science. (Communicated).
Influence of Organic Acids and Bases on the Mobility of Some Heavy Metals in Soil
SAMIULLAH KHAN, N . NAZAR KHAN AND NUSRAT IQBAL
Chemistry Section, Z.H. College of Engineering and Technology, Aligarh Muslim University, Aligarh, Uttar Pradesh, 202001
Abstract: The influence of organic acids and their sodium salts, amino acids and organic bases on the mobility of some heavy metals through the soil was examined by using thin layer chromatography. The organic acids, i.e., formic, acetic and oxalic ; and amino acids i.e., glycine, alanine and valine have increased the mobility of heavy metals. However, no marked influence could be observed in the case of organic bases, i.e., nicotine and pyridine. The results have been explained on the basis of reaction mechanism of complex formation, their stability, molecular size, pH and the nature of the heavy metals in soil solutions. (Key words : Heavy metals, influence, mobility in soil, organic acids and bases, thin layer chromatography)
Among various organic compounds, carboxylic acids (Schwartz et al. 1954), amino acids (Rending 1951 ; Sowden 1956) and organic bases like nicotine (Shtompel et al. 1981 ; Hanks et al. 1980) and pyridine (Vasil'chenko et al. 1975 ; Martin et al. 1977) have been found to occur or were used in soils. These organic compounds were found to interact with soil colloids (Smith 1934; Greenland et al. 1962; Brindley & Moll 1965 ; Khan & Singhal 1967 ; Theng 1974) and afifect the metal ion translocation in soil and consequently their availability to plants. However, their specific roles in the translocation of heavy metals have not yet been studied. In
another paper from this laboratory (Khan et al. 1982), it has been reported that the heavy metals translocate in soil as metal-soil organic matter (SOM) complexes. The purpose of the present study was to understand the role of carboxylic acids, amino acids and organic bases in the mobilization of certain heavy metals like Pb, Cd, Ni, Hg and Ag, using soil thin layer chromatography.
Materials and Methods
The soil used in these investigations was an illitic fine sandy loam (depth 0-30 cm) from Aligarh district in Uttar Pradesh. Its physicochemical properties
J. Indian Soc. Soil Sci Vol. 33 : 779-84,1985
no JOtJRNAI. OF TbB INblAl) SOtlEtY OF SOlL SClEKefi (Vol. 3S
were as follows: sand 33.4% ; organic matter 0.40% ; pH 8.8 (1 : 2.5 soil: water); EC 4.8x10-4 mhos/cm; CEC 16.3 m.e./ 100 g ; exchangeable Ca 3.5, Mg 1.2, Na 1.0, K0.5m.e/100g.
The soil was dried and ground to pass through a 100 mesh sieve. It was slurried with distilled water and coated on glass plates (20x20 cm) with the help of a conventional TLC applicator to give a uniform layer of 0.5 mm thickness in each case. The plates were then air dried at room temperature (30°C). Two lines were scribed at 3 and 13 cm from the base so that a 10 cm distance could be used for development in all cases. A 0.1 M solution of metal nitrate was applied at the base line of TLC plates as a single spot (0.006 ml) with the help of a micropipette. The plates were wrapped with a wet strip of filter paper at the bottom of the plates (about 2.5 cm) to prevent disintegration of soil and then developed with distilled water or amended solutions in closed chambers. The developed plates were air-dried at room temperature (30°C) and the heavy metals, Pb, Ag and Hg were detected by spraying 0.5% (w/v) ethanolic solution of haematoxylin, which gave a violet coloured spot. Ni and Cd were visualised as red spots by spraying dimethylglyoxime and 1% (w/v) dithizone in CCI4 respectively. The heavy metal mobility was measured in terms of R/ values.
To study the effect of organic acids and their Na-salts, and of amino acids and organic bases, an aqueous solution of each of them with varying concentrations was taken and used as developer, the soil being the static phase.
Results and Discussion
An examinat'on of table 1 shows that the mobility of heavy metals through soil with and without organic matter (3o% H2O2 treatment) follows the order : Ni>Cd>Hg>Ag>Pb. The results are in accordance with the earlier observations of Lund et al. (1976) and Khan et al. (1982) that the heavy metals move as their soluble metal-SOM complexes in soil according to their ion size (Table 1) and compbxing nature. The decomposition of soil organic matter enhances the heavy metal mobility, thereby substantiating the clay-metal-SOM interactions (Theng 1974).
The effect of carboxylic acids on the mobility of heavy metals is given in fig. 1, which follows the order : fo rmioace t io oxalic acids; which may be attributed to the solubility of metal carboxylates (Table 1). Further the mobility increases with increase in the concentration of acids. The relative order of the mobility of metals in the acid medium was: Ni>Cd>Hg>Ag>Pb;except in the case of acetic acid, with which the order was: Hg>Cd>Ni>Ag>Pb, the order being inversely related to the instability constants of their acetate salts. Thus, the ion size, instability constants and solubility of metal carboxylates seem to determine the extent of their mobility in soil.
The results were further verified by using the sodium carboxylate systems (Fig. 2). The translocation in presence of organic acids and their salts could be explained by considering the mobilization of heavy metals in soil as a result of formation of metal carboxylates. The heavy
1985] M6ilLITY OF HfeAVV METALS iJ* SOtti m
Table 1. ^ffect of organic matter on the mobility of heavy metals in soil; metal ion size*, instability constants^ and solubility' of the metal carboxylate
Heavy metals
Nickel
Cadmium
Mercury
Lead
Silver
R/ value
S.ilwitb organic maiter
0.18
0.17
0.15
0.08
0.13
Soil \vi tiout organic matter
0.32
0.29
0.25
0.15
0.21
Ion size parameter >< 10'cm
6
5
5
4
3
Instability constant of metal acetate
0.016
0.0017
3.75x10-'
0.038
0.183
Solubility in water (g/iOO g)
Mttal formate
Soluble
Very soluble
0.4
1.6
...
Metal aceta e
16.6
Very soluble
0.75
45.61
0.72
Metal oxalate
Insoluble
0 00337
Insoluble
0.00016
0.0034
o-Preiser and Fernando (1966) 6—Yetsimirsku and Vasil'ev (1959) c—Weast and Selby (1966)
Ni, »Cd, oHg, * Ag. xPb
OXALIC ACID
0 8
0.0 0 5 1.0 15 2.0 0 0 0.5 1.0 15 20 0 0 0.10 0.25
Concentration of Car boxy lie acids (mole/I it re)
Fig. I Effect of some carboxylic acids on the mobility of heavy metals in soil
0.50
7«2 JOURNAL OP THE INDIAN SOCIBTV OF SOIL SCIBNCB £Vol. 3i
N i , »Cd , o Hg, t A 5 , K P!>
' O r FORMATC
0 :
OG
0 4
0 2
I
I 0 0
. /
-o^
O X A L A T E
0 0 0 5 •>- i S 2 0 c 0 0 : 10 15 2 ' 0 0 0 01 ^1 p" r \!t^CT of Sod i jmcarbo\y l3 te5(mol»s / l i t re )
Fig 2 Effect of sodium salts of orgaoic acids on the mobility of metals in soil
0 50
metal ions combine with carboxylate ions as follows:
mM»++(n-l)X'»- :^ [M« X,,.!,]"-* ...I
mM»++n X"*- ;;i [M„ X„lf> .II
mM»+(n+1) X*"- ;;± [M„ X(„+i,]»- ...III
Increased concentration of carboxylate ions favours the formation of negatively charged metal carboxylate (III) which lowers the adsorption of these species over the negatively charged sites of soil colloids and hence increases the mobility.
In the case of salt systems, the pH increased from- 8,8 to 9.2. Most of the metal ions may be considered to remain in the form of MOH (monovalent), MOH+ and/or M(0H)2° (divalent) which can form
their respective metal carboxylates as
( / r . \R-C-O. . .H-OM/
0... /
- c \
H 1 0 1
.(IV)
.(V)
O M
and/or
R - O ,0...H- -O'
\ O . . . H - 0 - M y .,.(VI)
As the salt concentration increases, the negatively charged species (VI) may be formed thereby enhancing its mobility against the negatively charged soil colloids.
The effect of some amino acids is shown in table 2. The mobility of heavy metals generally increases with increase in the
1985] MOBILITY OF HEAVY METALS IN SOILS 783
Table 2. Effect of amino acids on mobility {Rf values) of some heavy metals in soil
Heavy metal
Nickel
Cadmium
Sil-er
Mercury
Lead
Glycine (moles/litre)
0.0
0 !8
0 17
013
0 15
0.08
0.01
0.42
0.17
0.19
0.20
0 07
0.05
0.60
0.15
0 25
0.20
0 07
0.10
0.70
0.20
0.30
0.25
0 08
Alanine (moles/litre)
00
0.!8
0.17
0.13
0.15
0 08
0.01
0.32
0.17
0.15
0.15
0 09
0 05
0.80
018
0.30
0.34
0.09
0.!0
0.89
0.21
0.35
0 35
0.09
Valine (rnoles/litre)
0.0
0.18
0.17
0.13
0.15
0.08
0.01
0.53
0.17
0.21
0.15
0.10
0.05
0.83
0.16
0.24
0.29
0.09
0.10
0.93
0 20
0.35
0.40
0.09
concentration of amino acids. The order of heavy metal mobility in soil is found to be: valine>alanine>glycine, which is in accordance with their own mobilities in soil (Singbal et al. 1978), while the relative order of the mobility of heavy metals in soil was : Ni>Hg>Ag>Cd>Pb; except in the case of glycine, where the order is : Ni>Ag>Hg>Cd>Pb As the pH of the soil solution becomes alkaline (,8.3), the amino acids are expected to remain in their anionic forms (Theng 1974), because pH>pI (isoelectric point). These anionic forms of the amino acids may combine with the heavy metals as follows:
R - C H N H - C C -|-M(OH)+-^
R-CHNH—C<^
H I
o o I
O—M
...(VII)
The instability constant of these metal-amino acid complexes were reported (Yatsimirsku & Vasil'ev 1959) in the reverse order of the mobility. The larger molecular size of amino acid restricts the
adsorption of its metal complex on the interlamellar surfaces (Talibudeen 1955) and, therefore mobilises it faster. Thus, the stability and size of heavy metal amino acid complex (VII) decide the mobility of these metals in the soil environment.
The effect of organic bases such as nicotine and pyridine on the mobility of heavy metals is shown in table 3. It is evident that nicotine and pyridine have no marked influence on the heavy metal translocation in soil. However, a slight decrease in the mobility is observed in some cases, which may be attributed to the metal-base soil complex formation. As the pH of the system upon the addition of these bases remains above 7 (8.3 in this case), the lone pair of nitrogen may attract the heavy metals through hydrogen bonding (Singhal &. Singh 1972) as follows :
I —N: -l-H.O . H-OH—M-Y„
-> —N...H—0-M-Y„-fH20 ...(VIII) I
where, Y=soil colloids and M is heavy metal with n+ charge.
^84 JOURNAL OF tHE INDIAN SOCIETY OF SOIL SCIENCE [Vol.33
Table 3. Effect of organic bases on the mobility (J?/ values) of heavy metals in soil
Heavy metal
Nickel
Cadmium
Silver
Mercury
Lead
Nicolir
0 00
0.18
0 17
0.13
015
0C8
le (moles/litre)
0 002
0.17
0.11
0.09
0.09
0 08
0 008
0.14
0.11
('.08
0.09
0 08
0 050
015
0.10
0.08
0.09
0 08
Pyridine
0.00
0.18
0.17
0.13
0.15
0.08
fmol.s/iitrc)
0.0C2
0,(7
0.16
0.11
0.13
0,09
0.008
0.17
0.16
0.11
0.11
O.IO
0.050
0.15
0.16
0.11
0.10
0.10
Thus, the complexation of heavy metal with bases as well as soil colloids immobilize them in soil.
Acknowledgement
The financial support from Indian Council of Agricultural Research (ICAR), New Delhi, is thankfully acknowledged.
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Brindley, G.W. & Moll, W.F. (Jr.) (1965) Am. Miner. 50, 1355.
Preiser, H. & Fernando, Q.( 1966)/ortic Equilibria 'n Analytical Chemistry, John Wiley, New York.
Greenland, D.J., Laby, R H. & Quirk, J.P. (1982) Trans. Farad. Soc.SS,i29.
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Vasil'chenko, V.F,, Abramova, K.A., Dubrovskaja, A.A. & II'Nitskaya, L.P. (1975) Simp. Siran-chelnov. SEV 10th 2, 34.
Weast, R.C. & Selby, S.M. (1966) Handbook of Chemistry and Physics (47th ed.), Chemical Rubber Co., Ohio.
Yatsimirsku, K.B. & Vasil'ev, V.P. (1959) Instability Constants of Complex Compounds, Consultants Bureau Enterprises, Inc., New York.
{Received November 1983, A ccepted September 1985)
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