Search

Arsenic concentrations of 73 soil samples collected in the semi-arid Zimapán Valley range from 4 to 14 700mgAskg−1. Soil arsenic concentrations decrease with distance from mines and tailings and slag heaps and exceed 400mgkg−1 only within 500m of these arsenic sources. Soil arsenic concentrations correlate positively with Cu, Pb, and Zn concentrations, suggesting a strong association with ore minerals known to exist in the region. Some As was associated with Fe and Mn oxyhydroxides, this association is less for contaminated than for uncontaminated samples. Very little As was found in the mobile water-soluble or exchangeable fractions. The soils are not arsenic contaminated at depths greater than 100cm below the surface. Although much of the arsenic in the soils is associated with relatively immobile solid phases, this represents a long-term source of arsenic to the environment. [Copyright &y& Elsevier]