Investigation of selenium and arsenic in soil samples from a long-term field experiment

Béla Kovács, Éva Széles,József Prokisch, Zoltán Győri

University of Debrecen, Centre of Agricultural SciencesDepartment of Food Science and Quality Assurance

4032 Debrecen Böszörményi str. 138. Hungary

DebrecenBudapest

Nagyhörcsök

Pecs

We have to study the following goals in this research programme

The behaviour of arsenic and selenium in soil:

total concentration,

available concentration,

leaching,

transformation.

Worldwide variation in Se status(Combs, 2001)

0

50

100

150

200

250

300

350

plasma Seng/ml

country

USAUSAChinaChina (urban)(urban)

VenezuelaVenezuela

FinlandFinland

normal level

HungaryHungary

ChinaChina (Keshan dis. areas)(Keshan dis. areas)

CroatiaCroatia

The applied elements and doses in the long-term field experiment (Nagyhörcsök Experimental Station)

Rate (kg/ha) in spring of 1991 Elements

applied 1 2 3 4

Chemicals used

Al 0 90 270 810 AlCl3

As 30 90 270 810 As2O3/NaAsO2 Ba 0 90 270 810 BaCl2

Cd 30 90 270 810 CdSO4

Cr 0 90 270 810 K2CrO4

Cu 0 90 270 810 CuSO4

Hg 30 90 270 810 HgCl2

Mo 0 90 270 810 (NH4)6Mo7O24

Ni 0 90 270 810 NiSO4

Pb 0 90 270 810 Pb(NO3)2

Se 30 90 270 810 Na2SeO3 Sr 0 90 270 810 SrSO4

Zn 0 90 270 810 ZnSO4

Total element contents of soil samples depending on doses (sampling: 1994)

0

50

100

150

200

250

0 150 300 450 600 750

Dose in 1991 (kg/ha)

Co

nce

ntr

atio

n o

f ele

me

nts

(m

g/k

g)

As

Se

Lakanen-Erviö soluble element contents of soil samples depending on doses (sampling: 1994)

010

20304050

607080

90100

0 150 300 450 600 750

Dose in 1991 (kg/ha)

Con

cent

ratio

n of

ele

men

ts (

mg/

kg)

As

Se

Rate of Lakanen-Erviö soluble and total element contents of soil samples depending on doses (sampling: 1994)

0

10

20

30

40

50

60

0 150 300 450 600 750

Dose in 1991 (kg/ha)

Con

cent

ratio

n of

ele

men

ts (

mg/

kg)

As

Se

Concentration of arsenic depending on duration of field experiment and doses in soil samples

0

10

20

30

40

50

60

70

80

90

100

1991 1992 1994 1997 2000

Year of sampling

Co

nce

ntr

atio

n o

f ars

enic

(m

g/k

g)

30

90

270

810

Plot treated with arsenic (4. level)Plot treated with arsenic (4. level)Nagyhörcsök Experimental StationNagyhörcsök Experimental Station

barley (2000)barley (2000)

Concentration of selenium depending on duration of field experiment and doses in soil samples

0

20

40

60

80

100

120

140

1991 1992 1994 1997 2000

Year of sampling

Co

nce

ntr

atio

n o

f se

len

ium

(m

g/k

g)

30

90

270

810

Plots treated with selenium (4. and 3. levels)Plots treated with selenium (4. and 3. levels)

Nagyhörcsök Experimental StationNagyhörcsök Experimental Station

barleybarley (?!) (2000)(?!) (2000)

Selenium content of treated (the highest level) and control plots in different soil layers (2000)

0

2

4

6

8

10

12

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0-30

30-60

60-90

100-130

130-160

160-190

200-230

230-260

260-290

soil layer (cm)

con

cen

trat

ion

of S

e (m

g/k

g)

treated plotcontrol plot

Analysis of selenium standards by IC-ICP-MS instrument100 ppb Se-Meth+100 ppb selenite+100 ppb selenate

Detection limits: 0.01 – 0.05 – 0.1 ppb

0

10000

20000

30000

40000

50000

60000

0 5 10 15 20 25 30

time [min]

ICP

-MS

sign

al [c

ps]

Se-methionine

selenite

selenate

(Se(IV), SeO32-)

(Se(VI), SeO42-)

COOH

CHNH2

CH2

CH2

Se CH3

0

10000

20000

30000

40000

0 5 10 15 20 25

Time (min)

ICP

-MS

sig

na

l (c

ps

)

1991 I/1

1991 I/2

1991 I/3

1991 I/4

selenate

selenite

organic selenium forms

Comparison of contents of selenium forms in 1991(I: 1. repetition, 1, 2, 3, 4 doses: 30, 90, 270 and 810 kg/ha)

Fate of selenite in soil (1:10 water extract)Heavy metal load field experiment: Dr. Imre Kádár, Nagyhörcsök

0

100000

200000

300000

400000

500000

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700000

800000

900000

1000000

0 10 20duration [min]

ICP

-MS

sig

nal [

CP

S]

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10000

15000

20000

25000

0 10 20duration [min]

ICP

-MS

sig

nal [

CP

S]

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5000

10000

15000

20000

25000

0 10 20duration [min]

ICP

-MS

sig

nal [

CP

S]

1993 1993 2003

oxidationselenite

selenate

organic selenium

Conclusion: selenite will be oxidised in soil to selenate selenate more available for plants (it is analogous to sulphate) risk of leaching

selenite

selenate

0

20000

40000

60000

80000

100000

120000

0 5 10 15 20

duration (min)

ICP

-MS

sig

nal

(cp

s)

0-30 cm

30-60 cm

60-90 cm100-130 cm

130-160 cm

160-190 cm

200-230 cm230-260 cm

Comparison of contents of selenium forms in 2000 from different layers

selenite

selenate

organic selenium forms

AcknowledgementsAcknowledgements

• Dr. Imre Kádár (RISSAC)• Hungarian Scientific Research

Fund (OTKA T38450)• István Széchenyi Scholarship

Thank you for your attention!Thank you for your attention!

AsAs

Se As

Se

Separation of selenium ions by High Performance Liquid Chromatography – Inductively Coupled Plasma Mass

Spectrometer hyphenated system (HPLC-ICP/MS)

High Performance Liquid Chromatography (HPLC) column: IC-AN1 anion exchanger

Inductively Coupled Plasma Mass Spectrometer (ICP-MS)

Eluent: Phtalic-acid-Tris buffer

Other information Different levels of the selected metal salts (13) were added

to plots once at starting year (1991) and were mixed into the ploughed layer (0-20 cm)

The treatments were arranged in a split-plot design with replications (2)

These experimental plots are cultivated with commonly used agrotechnics, chemical fertilizers are added yearly to ensure sufficient macronutrient (NPK) supply

Composite soil samples consisting of 20 subsamples are collected yearly from the ploughed layer of each plot

To check the vertical movement of these pollutants, samples are also taken from the subsoil of plots with the highest level of added metal salts in some years (1993, 1996, 2000)

Type of soil in the experiment : calcareous loamy chernozem

Plot treated with cadmium (4. level)Plot treated with cadmium (4. level)Nagyhörcsök Experimental StationNagyhörcsök Experimental Station

Plot treated with lead (4. level)Plot treated with lead (4. level)

Nagyhörcsök Experimental StationNagyhörcsök Experimental Station

Plots treated with molybdenum (1. and 4. levels)Plots treated with molybdenum (1. and 4. levels)Nagyhörcsök Experimental StationNagyhörcsök Experimental Station

Nagyhörcsök Experimental Stationplant and soil samples

- The experiment includes: 4 levels in duplicate, i.e. 8 plots, each with a size of 21 m2.- Experimental plants: maize (1991), carrot (1992), potato (1993), peas (1994), red beet (1995), spinach (1996), wheat (1997), sunflower (1998), sorrel (1999), barley (2000), rape (2001), poppy (2002), wheat (2003), alfalfa (2004), alfalfa (2005)

- Soil sampling and analyses on soil samples: 1991: 0-20 cm soil layer of the plots, 1993: "mobile" fraction in the 0-20, 20-40, 40-60 cm soil layers from plots with the highest level of added metal salts, 1996: "mobile" and "total" fractions in the 0-30, 30-60, 60-90 cm soil layers from plots with the highest level of added metal salts. 2000: As: 0-20, 20-40, 40-60, 60-90 cm soil layers from plots with the highest level of added metal salts, Se: 0-30, 30-60, 60-90, 100-130, 130-160, 160-190, 200-230, 230-260, 260-290 cm from plots with the highest level of added metal salts.

Results considering plant analysesResults considering plant analyses1.Owing to the highest level of arsenic treatment, the quantity of crop of each

applied plant decreased in each year. However arsenic content was not increased in different parts of plants, it was about 1-2 mg/kg concentration range. Arsenic is not mobile in the soil-plant system. From the applied plants, peas and spinach were the most sensitive affected by arsenic. Presumably the applied arsenite (As(III)) is transformed to arsenate (As(V)) which is the more toxic species.2. The destroying effect of Se does not decrease with years, and what is more

the effect of Se increases. Presumably the applied Na-selenite form is transformed to the more toxic Ca-selenate, it is oxidized among those soil conditions. We have to determine the concentration of different selenium species (selenite and selenate) in soil samples during our research. Similarly to Mo, Se is extremely mobile, the plant parts contain many hundreds mg/kg of selenium accompanied toxic symptoms. High applied concentration of selenium destroys even weed-plants recently also.

The arsenic and selenium caused decrease of yield of different plants owing to the fitotoxic effect between 1991-1997: -   maize seed: As and Se -   red beet root: Se -   carrot root: As and Se -   spinach leaf: As and Se -   potato tuber: As and Se -   wheat seed: As and Se -   peas seed: As and Se