Heavy metals in soils of Argentina: Comparison

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Heavy metals in soils of Argentina: Comparison between urban and agricultural soils a

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R. S. Lavado , M. B. Rodríguez , J. D. a

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Scheiner , M. A. Taboada , G. Rubio , R. a

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Alvarez , M. Alconada & M. S. Zubillaga

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Departamento de Suelos, Facultad de Agronomía, Universidad de Buenos Aires, Av. San MartÌn 4453, Buenos Aires, 1417, Argentina Version of record first published: 11 Nov 2008.

To cite this article: R. S. Lavado , M. B. Rodríguez , J. D. Scheiner , M. A. Taboada , G. Rubio , R. Alvarez , M. Alconada & M. S. Zubillaga (1998): Heavy metals in soils of Argentina: Comparison between urban and agricultural soils, Communications in Soil Science and Plant Analysis, 29:11-14, 1913-1917 To link to this article: http://dx.doi.org/10.1080/00103629809370081

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COMMUN. SOIL SCI. PLANT ANAL., 29(11-14), 1913-1917 (1998)

HEAVY METALS IN SOILS OF ARGENTINA: COMPARISON BETWEEN URBAN AND AGRICULTURAL SOILS R. S. Lavado, M. B. Rodríguez, J. D. Scheiner, M. A. Taboada, G. Rubio, R. Alvarez, M. Alconada, and M. S. Zubillaga Departamento de Suelos, Facultad de Agronomía, Universidad de Buenos Aires, Av. San MartÌn 4453, 1417 Buenos Aires, Argentina ABSTRACT Trace metals, including heavy metals, can be harmful to the biota and human beings. This leads to study the accumulation of those elements in soils. In the Pampean region (Argentina) this knowledge is scarce. Our objectives were to (i) determine the trace metal concentration in soils of Buenos Aires City and agricultural areas, (ii) start to establish the soil trace metals baseline concentration, and (iii) find relationships between soil properties and those elements Topsoil samples were taken in Buenos Aires City and on farms along an arc 50 to 250 km away from the metropolis. All studied soils were Mollisols. Soil samples were analyzed for their cadmium (Cd), copper (Cu), zinc (Zn), chromium (Cr), cobalt (Co), lead (Pb), and nickel (Ni) contents by acid extraction. Soil properties were determined using standard methods. The soils of Buenos Aires City show the highest average concentrations of Cd, Cu, Pb, and Zn. The further the sampling sites were from Buenos Aires, the lower the metal concentration in the soils. Conversely, there were no differences in Co, Cr, and Ni concentrations from urban to the rural soils. There was a high variability in metal concentrations. We hypothetized that cars are the main source of contamination of Pb and Cd in the urban soils. The measured metals concentrations from rural areas, can be a basis from which to establish the background levels of those soils. Clay content was related to the concentrations of Cd, Cr, Ni. Pb, and Zn in soils. INTRODUCTION Trace metals, including heavy metals, concentration are related to several factors in non-contaminated soils. Among those factors are biogeochemical cycling, parent material, particle-size distribution, soil age, mineralogy, organic matter content, and drainage (Frink, 1993; Lee et al., 1997; Ma et al., 1997). Holmgren et al. (1993) have indicated that concentrations generally follow the degree of weathering. Over those natural processes, man's activities tend to increase the concentration of heavy metals and other trace elements in soils (Dudka, 1992; Dudka, et al. 1995). Those elements can be harmful to the biota, including human beings. This fact leads to the necessity of studying the accumulation of those elements in soils. The extent of soil contamination is generally determined by a comparison with total elemental concentration of soil at an assumed non-contaminated nearby site (Frink, 1996). 1913 Copyright © 1998 by Marcel Dekker, Inc.

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The region of the Pampas (Argentina) is covered mainly by Mollisols, developed from a young parent material (loess-like sediments). The water and temperature regimes vary between udic/thermic in normal relief areas and aquic/thermic in depressions. Most soils do not show significant differences in their genesis (Lavado, 1991). In the region are manufacturing industries and the population is located mainly in the city of Buenos Aires and the outskirts. The region is one of the largest temperate crop production areas of the Southern Hemisphere, but the soils of the area receive no or little mineral fertilizers or organic amenmends like biosolids on urban residues (Lavado, 1991). Mining is not relevant in this area. Soil trace metal concentration has been studied in North America, Europe, and parts of Asia (Ma et al., 1977), but in South America, in general and in the Pampean region in particular, this knowledge is scarce. Llosa et al. (1990) have determinated levels of Pb, Cd, Zn, and Cu in soils in industrial and residential areas of Buenos Aires City. Camilión et al. (1995,1996) determined the Cu, Pb, and Zn contents in agricultural soils located in the south of the city. Comparing local data, the soils of the Buenos Aires City had higher concentrations of Pb, Cu, and Zn than the agricultural soils. However, the degree of contamination and the natural background levels of those metals and several other metals, are still unknown. Our objectives were to (i) determine the trace metal concentration of soils located in the urban area of the Buenos Aires City and agricultural nearby areas, (ii) start to establish the baseline concentration of such metals in eastern Pampean soils, and (iii) find the relationships between several soil properties and these elements. MATERIALS AND METHODS An average of three topsoil (0-20 cm) samples were taken in ten places, two in Buenos Aires Cty and eight on farms along an arc 50 to 250 km away from the metropolis. All studied soils were Mollisols (U.S. Soil Taxonomy): Hapludolls, Argiudolls, and Natraquolls with some differences in clay and organic matter contents, and exchangeable cations. Soil samples were grounded, sieved, and analyzed for their Cu, Zn, Cr, Co, Pb, Cd, and Ni contents. The elements were acid-extracted in a mixture of hydrofluoric, nitric, perchloric, and sulfuric (HF-HNO3-HC1O4-H2SO4) acids (Page et al., 1982). The elements in the extract was determined by inductively couple plasma emission spectrometry (ICP). Clay and organic matter contents and pH were determined in all samples using standard methods (Page et al., 1982). For each sampling site, the average and the standard error was calculated. The soils and sampling sites were grouped according to their distance from Buenos Aires as follows: Distance 0-50 km

Soil Type Vertic Argiudoll (a) Vertic Argiudoll (b)

50-100 km

100-150 km

Location Campus of the Faculty of Agronomy, Buenos Aires City Square at a residential area of the Buenos Aires City

Vertic Argiudoll beheaded(c) Vertic Argiudoll (d)

La Plata County La Plata County

Typic Argiudoll (e) Typic Natraquoll (f) Vertic Argiudoll (g)

S.A. Areco County Cañuelas County San Pedro County


HEAVY METALS IN ARGENTINIAN SOILS

0-50

50-100

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100-150

150-250

Distance from Buenos Aires (km)

FIGURE 1. Average concentration and standard error of Pb, Cd, Cu, and Zn.

• Cr DCo • Ni

0-50

50-100

100-150

150-250

Distance from Buenos Aires (km)

FIGURE 2. Average concentration and standard deviation of Cr, Co, and Ni.

150-250 km

Typic Hapludoll (h) Alberti County Typic Argiudoll (i) Chacabuco County Argiaquic Argiaquoll (j) Chascomús County RESULTS AND DISCUSSION

Concentrations of the metals studied are summarized in Figures 1 and 2. The global distribution of Cd, Cu, Pb, and Zn follow an expected pattern: the soils of Buenos Aires City show the highest average concentrations for these metals. The further the sampling sites from Buenos Aires, the lower the metal concentration in soils. Conversely, there were not differences in the Co, Cr, and Ni concentrations

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Table 1. Correlations between clay content and some elements.


Element

Equation

R2

Cd

y = 15.27 + 23.3 (% clay)

54% (P< 0.06)

Zn

y = 3.54x(%clay)°2 4

50% (P< 0.07)

Cr

y = 10.15 + 0.54 (% clay)

64% (P< 0.05)

Ni

y =15.42+1.4 (% clay)

63% (P< 0.06)

Pb

y = 2.41 + 033 (% clay)

72% (P< 0.03)

from urban to rural soils. There was a high variability in metal concentrations, particularly in the last three soils. This cannot be to attributed to either soil inherent variability or to localized recent contamination. The average concentrations of Cd and Pb in the soils of Buenos Aires City exceeded both the maximum tolerable soil limits (Commision of European Community, 1982) and the maximum level in the range of variation of non-contaminated soils of the World (Frink, 1996). In industrial areas of Buenos Aires City, Llosa et al. (1990) found higher concentrations of Pb but similar Cd levels as we did. The concentrations of both elements in the agricultural soils are around the average world concentrations (Frink, 1996) and the known local values (Camilión et al., 1996). The concentrations of Cu and Zn are below the maximum tolerable thresholds (Kloke, 1983) and do not reach the maximum level in the range of variation of non-contaminated soils of the world (Frink, 1996). However, our Cu level data exceeded those values previously determined in non-contaminated soils of Buenos Aires City (Llosa et al., 1990), and values from other non-contaminated areas elsewhere (Berrow and Reaves, 1984). The concentrations of Zn, however, are lower than those from other local data (Llosa, 1990). There are not previous local data for the elements Co, Cr, and Ni. Our data are shown in Figure 2. Average concentrations of Cr and Ni were below most world data, but those for Co were above (Frink, 19%). Several authors (Frink, 1996; Lee et al., 1997; Ma et al., 1997) have obtained correlations between the concentrations of different heavy metals with particle size fractions. In our case, clay content (data no shown) was only significantly related to the concentrations of Cd, Cr, Ni. Pb, and Zn (Table 1). These correlations coincided with those found in nearby soils (Camilión et al., 1995). There was no relationship between the studied metals and soil pH and the organic matter content. The lack of influence of the latter can be attributed to the large clay content of the soils selected (Lee et al., 1997). In summary, the metal concentration in the studied soils was variable and two factors affected their distribution pattern: the distance from the city and probably to a lesser degree, the one soil characteristic, clay content. For some of the elements, mainly Cd and Pb, their concentrations fell sharply with a distance of 50 km or more from the City of Buenos Aires. With our limited data, it could be hypothetized that

HEAVY METALS IN ARGENTINIAN SOILS

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cars are the main source of contamination for these metals in the urban residential soils. Their total concentrations, particularly those from rural areas, can be taken as a basis to establish the background levels for those soils.


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