Abstract

Soil contamination was investigated in the vicinity of Zarshouran gold mine through determination of total concentrations and chemical speciation of As, Cu, Zn, Cd, and Pb. Forty-six surface soil samples at depth of 0–15 cm were collected and analyzed from the mining district. The average concentrations (reported as mg/kg) of As 155.88, Pb 184.22, Cd 8.66, Zn 129.92, Cu 65.06, in the soil samples are much higher than the world average, while Ni and Fe are less than the world average. Examination of the single element distribution plots revealed that enhanced levels of heavy metals are associated with known mineralization zones and depended on the distance from the mine site except for Ni. Geo-accumulation indices and Enrichment Factors performed on the data imply that the collected soils have been significantly influenced by the Au-mining activities. The calculated geoaccumulation values for the soil samples indicated that the surface soils are virtually unpolluted with respect to Fe, and Ni but highly polluted with As and Cd. Enrichment level of Cu and Zn was considerable, while Pb showed very high to extremely high enrichment. The results obtained from the sequential extraction analysis of the metals from all the fine fraction of the soil samples revealed that heavy metals were largely associated with the residual fraction. However, the amounts of metals bound to Fe–Mn oxides and organic matter were relatively higher than those bound to carbonates or those in exchangeable forms. The average speciation percent and risk assessment code (RAC) results revealed that Cd and Pb were mobile in exchangeable phase while As, Pb, Zn and Ni bound to Fe–Mn oxides with a medium risk to the environment.