Heavy metal contents of soils from semiarid Pampa, Buenos Aires Province, Argentina

Heavy metals, such as Cu, Mo, and Zn are needed in small quantities by plants and animals, however they may enter soils in quantities that can pose risks to the health of vegetation, crops and humans. The objective of this work was to determine the concentrations of Cd, Co, Cr, Cu, Mo, Ni, Pb, and Zn in 17 Typic Argiustolls from the semiarid Pampa region (Argentina), where there has been intensive agricultural production. Contents of the readily available, DTPA-extractable, and total forms of these metals were determined. Soil pH varied from acidic to neutral or near neutral. The organic carbon varied between 17 and 45 g kg(-1). All soils had a base saturation > 70%. The particle size data show that silt and clay contents predominate and the soils are mainly clay-loams or loams. The content of all the metals in the soils were higher than the normal levels for soils from loessic parent materials not affected by anthropic activity. The highest total and DTPA-extractable contents of the heavy metals were: Cd: 84 and 42 mg kg(-1); Co: 54 and 12 mg kg(-1); Cr: 98 and 8.7 mg kg(-1); Cu: 145 and 39 mg kg(-1); Mo: 188 and 48.3 mg kg(-1); NI: 44 and 6.3 mg kg(-1) Pb: H 8 and 33.6 mg kg(-1) and Zn: 441 and 114 mg kg(-1). They were all higher than the amounts in the parent materials of the region previously studied by several investigators. This suggests that the accumulation in the Surface soil is mainly anthropogenic. Leaching of carbonates from the surface soils may have caused an increase of heavy metals in the surface soil, despite the continuous uptake by plants. The mobility of heavy metals, deduced from the analytical data, were in the order of Cd > Zn > Pb > MO > CLI > Ni > Cr > Co. Readily available contents of these metals were closely correlated with soil pH. In the case of Cr and Mo the highest soluble contents appeared in the soils with higher pH, whereas for the other metals contents increase with an increase in acidity.