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Heavy Metals in Sediments and Runoff Waters in Argentina’s Soils 13

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Heavy Metals in Sediments and RunoffWaters in Soils of the Matanza

River Basin, Argentina

M. De Siervi and A. F. de Iorio

Catedra de Quımica Analıtica, Facultad de Agronomıa UBA, Ciudad

Autonoma de Buenos Aires, Argentina

C. I. Chagas

Catedra de Manejo y Conservacion de Suelos, Facultad de Agronomıa

UBA, Ciudad Autonoma de Buenos Aires, Argentina

Abstract: Soil profiles near watercourses that drain rural areas with agricultural lands

and pastures, as well as recreational zones and densely populated industrial centers, are

directly influenced by human activities. Therefore, these soils condition the contami-

nation dynamics of the aforementioned watercourses in a remarkable way. The

present study deals with soils belonging to a first order subbasin. Pedons representative

of positive areas located in slopes (B) and of alkaline sites close to the alluvial plane (T)

were selected as study sites. In both cases, the land is used for extensive farming.

Composite samples of the upper 5 cm of both soil types were treated either with vermi-

compost or phosphate fertilizer to study the effect of the addition of these elements on

the runoff dynamics of heavy metals. Experiments using a rainfall simulator that

formed drops on runoff microplots containing soil samples were carried out under lab-

oratory conditions. The runoff obtained was analyzed for lead (Pb), zinc (Zn), cadmium

(Cd), and nickel (Ni), both dissolved and particulate, following the Community Bureau

of Reference (BCR) adaptation of the sequential extraction procedure. From these

results, it was concluded that the use of high amounts of organic amendment

produced important effects on the surface condition of the soils that determine a

highly significant reduction in the delivery of suspended solids to watercourses.

Amendments, however, may release heavy metals that flow through runoff avenues

either as particulate or dissolved forms. Most of the heavy metal concentration is

Received 7 November 2003, Accepted 14 January 2005

Address correspondence to Marcelo De Siervi, Catedra de Quımica Analıtica,

Facultad de Agronomıa UBA, Av. San Martın 4453, Ciudad Autonoma de Buenos

Aires 1417, Argentina. E-mail: marcelodesiervi@yahoo.com

Communications in Soil Science and Plant Analysis, 36: 1–12, 2005

Copyright # Taylor & Francis, Inc.

ISSN 0010-3624 print/1532-2416 online

DOI: 10.1080/001036205002507421

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represented by the sediments produced by the runoff and not by the concentration of

dissolved elements in runoff waters.

Keywords: Heavy metals, rainfall simulator, sediment, runoff waters

INTRODUCTION

The soil profiles close to watercourses that drain rural areas with agricultural

lands and pastures, as well as recreational zones and densely populated indus-

trial centers, are directly influenced by human activities. Because of this

reason, such soils condition the contamination dynamics of the aforemen-

tioned watercourses in a remarkable way. The accumulation and persistence

of many heavy metals produce an important ecological problem (Andreu

1993). Because the soil is a key element in the control of heavy metals in

the environment, it is essential to understand its behavior in this system.

It is generally assumed that metallic ions remain stationary in agricultural

soils (McBride 1995); however, the effect of factors that favor their mobility

may result in an increased absorption by plants or runoff in their infiltration to

the water table. Such factors include the properties of the metals in question,

the quantity and type of absorption sites, pH, concentration of complexing

anions (organic and inorganic), and the cations with which they compete in

solution within soils (Tyler and McBride 1982).

The Matanza-Riachuelo River Basin extends over 2240 km2, including

areas that belong to the Capital City and 11 districts of the province of

Buenos Aires. The population (approximately 2,720,000 inhabitants) is

densely concentrated in the districts of Avellaneda, Lanus, Lomas de

Zamora, and Buenos Aires City.

The Matanza-Riachuelo River receives the inflow of a great number of

watercourses, streams (open and piped), and pluvial drainages. The main

river course is 64 km long, which represents a distance of 85 km from its head-

waters down to its mouth in de La Plata River. The present study is focused on

the upper basin of the river, where activities are predominantly agricultural.

Although many works have dealt with marine and estuarine sediments at a

global scale, very few studies have been carried out on the speciation and

mobilization of heavy metals in river sediments that are not influenced by

mining activities. So far, there is little published information on the

chemical forms of heavy metals in the sediments of the Matanza River

Basin (Rendina 2002).

Great efforts have been made worldwide toward the knowledge and

interpretation of the importance of the flow of contaminants of rural, indus-

trial, and urban origin in surface waters washed to watercourses (Ongley

1997; Mosley and Peake 2001). However, the use of rainfall simulators and

runoff microplots is a new experience in the study of the dynamics of heavy

M. De Siervi, A. F. de Iorio, and C. I. Chagas2

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metals in runoff waters, both in Argentina and worldwide (Loch et al. 1995;

Singh et al. 1999).

The main goal of our project was the evaluation of the inflow of heavy

metals into a watercourse, produced by the runoff of a subbasin of the

Matanza-Riachuelo River used for agriculture and cattle farming.

MATERIALS AND METHODS

The present study deals with the soils of a first-order subbasin located in the

headwaters of Morales Stream (348 500 S, 598 000 W), main tributary of the

Matanza River (Figure 1). The study area belongs to “Los Grillos Ranch,”

General Las Heras District, located at the intersection of the roads 200 and

6. The sampling sites were selected on 1:50000 INTA (Instituto Nacional

de Tecnologıa Agropecuaria) maps of the area (INTA 1997). Pedons repre-

sentative of positive areas located in slopes (Brandsen Series and/or

Canuelas Series, Typic Argiudoll) were selected under the denomination of

“Backslope” (B). Also pedons representative of alkaline soils occurring in

the complex occupied by the alluvial plane of Morales Stream (Typic

Natracualf) were selected under the denomination of “Toeslope” (T). In

both cases, the land use corresponds to extensive cattle farming in this

sector of the Matanza River Basin.

Composite samples of the top 5 cm of the soil were treated either with vermi-

compost or phosphate fertilizer to study the effects of the addition of these

elements on the runoff dynamics of heavy metals. Physical and chemical

Figure 1. Map showing the location of the study area.

Heavy Metals in Sediments and Runoff Waters in Argentina’s Soils 3

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properties of the studied soils shown in Table 1 were determined by following

standard procedures (Klute 1986; Page 1982). Table 2 shows the total average

concentrations of the studied elements in the vermicompost and the phosphate

fertilizer.

Experiments using a rainfall simulator that formed drops on runoff micro-

plots containing soil samples were carried out under laboratory conditions

(Irurtia and Mon 1994; Kamphorst 1987). The energy applied to the soil by

this device was 12 J per kg of simulated rainfall. The soil samples were pre-

viously disturbed, mixed with vermicompost or fertilizer, and finally saturated

with water during a whole week before starting the rainfall simulation

following the methodology proposed by Sharpley (1985). The surface

runoff obtained was analyzed to determine the heavy metals [cadmium

(Cd), leaf (Pb), zinc (Zn), and nickel (Ni)] contained in the dissolved

(,0.45mm) and particulate fractions (.0.45mm). Such chemical analysis

was carried out according to the Community Bureau of Reference (Commis-

sion of the European Communities 1992) adaptation of the sequential extrac-

tion procedure in the particulate fraction.

Exchangeable, oxides and carbonates, organic matter and sulfides, and

residual fractions were obtained by following this methodology. Comparison

between these concentrations and the dissolved form for each metal were

made. Quotients smaller than 1 indicated that the concentration of the

dissolved form was higher than the particulate one.

Statistical Analysis

The results were statistically analyzed through ANOVA. Treatment mean

comparisons were made by Tukey test (Snedecor and Cochran 1980).

Table 1. Physical and chemical properties

measured in the two types of soils compared

Variable Backslope Toeslope

Sand (%) 32.40 21.25

Silt (%) 43.80 50.00

Clay (%) 23.80 28.75

Organic carbon (%) 1.70 1.60

Conductivity (ds m21) 0.28 0.98

Ca2þ (meq/100 gr) 8.00 6.21

Mg2þ (meq/100 gr) 8.50 5.87

Naþ (meq/100 gr) 1.85 43.48

Kþ (meq/100 gr) 0.29 6.54

pH (H2O, 1 : 2.5) 5.39 9.10

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RESULTS AND DISCUSSION

The total concentration of sediments in runoff water are shown in Table 3. Soil

loss for treatments with vermicompost were significantly lower than those for

the fertilizer or the control soils. These results show that the vermicompost can

be very effective in controlling soil losses. The lowest sediment concentration

was observed for the toeslope soil treated with the organic compost. Complex

interactions between detachment and transport processes at the soil surface

can be responsible for the obtained results (Nearing et al. 1990), particularly

for weak structured topsoils like the toeslope soil.

Lead

Figure 2 shows that Pb content in the sediments (particulate fraction) of

backslope soils was 16 times higher than the concentration of dissolved

lead in the control (BC), 20 times higher than in the fertilized plot (BF),

and 47 times higher than in the plot with vermicompost amendment (VL).

The values obtained in the latter plot contrast with control and fertilized

plots and emphasize the fact that the concentrations of dissolved metals

Table 2. Total average concentration of Pb, Ni, Zn,

and Cd in the organic amendment and in the fertilizer

Variable Vermicompost Phosphate fertilizer

Lead 49.25 11.0

Nickel 17.50 10

Zinc 915.00 20

Cadmium 2.13 1.4

Table 3. Concentrations of sediments in

runoff waters

Treatmenta Concentration� (g L21)

BC 23.99 ab

BV 15.78 c

BF 27.77 a

TC 23.20 ab

TV 9.60 d

TF 23.33 b

aB, backslope; T, toeslope; C, control;

V, vermicompost; F, fertilizer.�Means followed by the same letter are

not significantly different (p . 0.05).

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were much lower in plots with vermicompost amendment owing to the great

quantity of functional groups of humic substances, which trap metals in

solution, thus reducing their concentration to a minimum. On the other

hand, it is also evident that the amount of sediments measured in the treat-

ments with organic amendment was always lower than in the other two

cases (Table 2), because this treatment would favor the structural stability,

with the lead concentration in this particulate material (in mg Pb g21

sediment) higher.

In the case of plots of toeslope soils, the trend observed was similar, but

its magnitude was much lower. The total lead in the particulate fraction was

lesser because of the lower concentration of sediments, whereas the concen-

tration of the dissolved form did not differ significantly from the measure-

ments in backslope soils.

Exchangeable Pb attached to the particulate fraction appears in a lower

concentration than dissolved Pb (Figure 2). In the plot of backslope with

vermicompost amendment, the conditions that explain the total concentration

are repeated: the content calculated in the sediment is higher and the concen-

tration of the dissolved form is much lower.

From the results obtained on the oxides and carbonates fractions in

toeslope soils and the organic matter and sulfide fraction in backslope, it

can be concluded that the origin of the high proportions of Pb in these

fractions depend on the differential capacities of both soils types to adsorb

the metal in the inorganic fraction.

There is scientific evidence of the speciation of heavy metals that confirm

these results. Carapeto and Purchase (1999) found that in sediments of a

channel near London, Pb was chiefly in the organic fraction (53–72% of

total Pb) and in the exchangeable fraction (1–10%). Although such magnitudes

are similar to the values obtained in the present work, the lower percentage

of Pb in the organic fraction may obey the lower content of organic matter

Figure 2. Concentrations of Pb expressed in mg Pb L21 of runoff water.

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in these soils (3.5%) compared to the sediments sampled (13%). Cabral and

Lefevbre (1998) reported similar proportions of Pb in the organic fraction

of soils with similar percentages of organic matter (2.3%).

Nickel

The total content of Ni in the sediments washed by the runoff water seems to

have much higher magnitudes than the dissolved forms. There was a trend

determined by the concentrations of sediments (in g L21): in the control the

total content of Ni was 73 times higher in the particulate fraction than in its

dissolved form. In the plot with vermicompost amendment, this coefficient

was over 100, whereas in the fertilized plot it dropped down to 30. The

content of dissolved Ni in runoff water was more than twice the value in the

control plot, probably owing to the metal contributed by the fertilizer and not

because of its natural content in the soil. This can be supported by the fact

that the Ni concentration in the phosphate fertilizer (Table 2) is 10mg g21,

and it is very probable that the metal exist in the form of soluble salts.

The concentrations of exchangeable Ni, measured in the sediments and

converted into mg Ni L21 of runoff water, seem to have a defined and

different behavior depending on the characteristics of the soil. In backslope,

the results in mg L21 may be considered similar, but the magnitudes can be

very different compared with the concentrations of the dissolved forms.

This depends undoubtedly on the different concentrations of the metal in

question in the different plots. The concentration of the dissolved form in

the control has an intermediate value between the low concentration of the

treatment with vermicompost (because of the aforementioned reasons) and

the higher concentration of the fertilized plot (owing to the concentration of

Ni contributed by the addition of soluble fertilizer) (Table 4).

The magnitudes calculated in the case of the plots of toeslope soils

showed a very different relationship, but their trend was similar to the first

case: the plot with vermicompost presented higher values than the control

and the fertilized plots (Figure 3).

Table 4. Concentrations of dissolved Pb, Ni, Zn, and Cd in runoff waters

TreatmentaLead

(mg L21)

Nickel

(mg L21)

Zinc

(mg L21)

Cadmium

(mg L21)

BC 59.7 7.5 148.8 3.3

BV 15.2 3.0 49.2 1.5

BF 53.0 18.8 106.7 2.7

TC 92.6 37.1 315.7 4.9

TV 16.3 2.0 52.9 0.9

TF 58.2 22.2 263.3 2.2

aB, backslope; T, toeslope; C, control; V, vermicompost; F, fertilizer.

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However, in this case, the concentrations (in mg L21) differ. In TC and

TF, the concentrations of Ni in the dissolved form were higher than in the

exchangeable fraction contained in the washed sediments. Again, the expla-

nation can be found in the elevated concentration contributed by the fertilizer

(Table 2) and in the high concentration of soluble and readily available forms

of Ni in the original plot of toeslope soil.

Zinc

Some important facts are apparent in the case of zinc. In backslope soils, the

zinc content of the residual fraction, expressed in mg L21 of runoff water, did

not differ significantly among treatments (p , 0.05).

Influenced by the high concentration of Zn in the vermicompost

(900 ppm), the treatments where the amendment was applied showed a high

total concentration of this metal, mainly in the exchangeable fractions,

oxides, and carbonates. The addition of organic amendment probably

increased the number of adsorption sites by raising the ECC; thus, the

excess of available Zn contributed by the amendment would take its place

in these new sites (Figure 4).

Cadmium

The concentrations of cadmium measured in the different fractions clearly

reflect the differences among treatments, revealing a decrease in the

residual fraction when plots of both soil types were amended with vermicom-

post (Figure 5). Although the amendment and the fertilizers do not contain

high concentrations of Cd (2 and 20mgmg21, respectively), the effects of

Figure 3. Concentrations of Ni expressed in mg Ni L21 of runoff water.

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the treatment were not evident. The reduction in the total concentration in the

treatment with organic amendment, in both backslope and toeslope soils, was

mainly due to its physical action but also to its chemical effect. On one hand,

the amendment reduced the output of sediments (Table 2); on the other hand,

these sediments had different texture, content, and type of organic matter.

Carapeto and Purchase (2000), Q1in their study on the speciation of the

heavy metals of sediments from a dredged channel, found that 9 of 10

samples had greater proportions of Cd in the residual fraction (54–65% of

total Cd), followed by the organic (26–37%), and the exchangeable

fractions (6–18%).

The present study corroborates such results, because the percentages of

the residual fraction with respect to the total concentration are even higher,

except for the plots treated with vermicompost, where the higher percentages

corresponded to exchangeable and oxide and carbonate fractions for both soil

types (Table 5).

Figure 5. Concentrations of Cd expressed in mg Cd L21 of runoff water.

Figure 4. Concentrations of Zn expressed in mg Zn L21 of runoff water.

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Boruvka et al. (1997) found that 33.7–40.5% of the total Cd was in the

exchangeable phase and within a range of 1.7–11% in the organic fraction

in the case of contaminated soils of the alluvial planes of the river Litavka.

Those values are significantly higher than the ones obtained in the present

study. A high concentration of heavy metals in the exchangeable phase may

derive from different initial forms of the metals originated from different

sources, as well as from the possible saturation of adsorption sites when

metal concentrations are very high (Carapeto and Purchase 1999).

pH Influence

The amendment with large amounts of Zn2þ (vermicompost) could have

produced a reduction in the sediment pH because the detachment of Hþ

Table 5. Concentrations of Pb, Ni, Zn, and Cd in the different particulate fractions

(exchangeable, oxides and carbonates, organic matter and sulfides, and residual)

expressed in micrograms of metal in suspended solids per liter of runoff water

Metal TreatmentaExchangeable

(mg L21)

Oxides

(mg L21)

Organic matter

(mg L21)

Residual

(mg L21)

Total

(mg L21)

Pb BC 28.8 220.7 210.0 488.3 947.8

BV 54.8 206.3 131.5 325.6 718.2

BF 36.9 251.9 206.6 596.8 1,091.4

TC 39.4 336.5 83.1 281.2 740.2

TV 41.2 150.8 167.6 110.8 470.3

TF 34.3 376.3 223.0 24.3 657.8

Ni BC 28.8 132.0 232.0 154.3 547

BV 33.6 120.0 185.9 10.9 350

BF 44.4 174.1 283.8 72.5 574

TC 23.2 85.9 282.4 235.1 626

TV 32.0 91.4 137.1 11.1 271

TF 12.4 80.9 266.9 293.0 653

Zn BC 223.9 431.9 160.0 1,523.6 2,339

BV 1,925.7 3,903.9 315.7 826.1 6,971

BF 166.6 370.2 216.1 1,700.1 2,453

TC 92.8 510.5 212.8 1,649.3 2,465

TV 1,142.5 2,373.6 114.2 368.4 3,998

TF 124.3 653.1 233.3 1,516.2 2,526

Cd BC 1.6 4.8 0.2 28.9 35.5

BV 4.4 7.8 5.4 7.9 25.6

BF 4.4 5.2 0.8 11.8 22.2

TC 3.9 12.3 0.7 24.6 41.5

TV 13.0 4.6 0.4 0.1 18.0

TF 4.7 5.3 1.3 30.2 41.5

aB, backslope; T, toeslope; C, control; V, vermicompost; F, fertilizer.

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from the cation exchange complex into the soil solution made by the high

concentration of this metal.

However, in the vermicompost treatment in both soils, the pH results

lower because of the contribution of the high organic matter concentration

with its functional groups. With lower pH, the heavy metals were adsorbed

to the cation exchange complex, and this could have been the cause of

reduction in the delivery of soluble metals in the runoff waters.

CONCLUSIONS

The herein obtained results allow us to conclude that the use of high amounts

of organic amendment (i.e., vermicompost) produce important effects on the

surface condition of the soil, which in turn, determine a highly significant

reduction in the emission of suspended solids to watercourses.

Despite the high level concentrations of the studied heavy metals in the

vermicompost, the use of this organic amendment would not contribute

with these elements that reach the runoff ways either as particulate or

dissolved form.

Most of the heavy metal concentration is represented by the sediments

produced by the runoff and not so much by the concentration of dissolved

elements in runoff waters; therefore, the use of this kind of management

practice would be widely recommended for the heavy metal dynamics in

soil, and its influence over the pollution of watercourses by runoff.

In all of the studied metals, the treatment with vermicompost produced a

noticeable decrease in the concentrations of dissolved metals in runoff waters,

presumably owing to the effect of the organic compounds supplied by the

amendment, which trap the metals in their particulate fraction.

ACKNOWLEDGMENTS

Funding for this project was provided by the Agencia Nacional de Promocion

Cientıfica y Technologica (ANPCyT) included in the Programa de Moderniza-

cion, Contrato Prestamo BID 1201/OC-AR-PICT 15028. This project has

been also supported by a grant from the Oniversidad de Buenos Aires,

UBACyt G033.

REFERENCES

Andreu, V. (1993) Contenido y Evolucion de Cd, Co, Cr, Cu, Ni, Pb y Zn en Suelos deLas Comarcas de L’Horta y La Ribera Baixa (Valencia); Servei de Publicacions,University of Valencia: Valencia, Spain.

Boruvka, L., Kristoufkova, S., Kozak, J., and Chan, H.-W. (1997) Speciation ofcadmium, lead and zinc in heavily polluted soils. Rostlinna Vyroba, 43: 187–192.

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