Four heavy metals were measured in forty-nine topsoil samples collected from agricultural areas in Siakh-Darengoun, Iran. The goals were to investigate soil spatial distribution patterns of metals; their potential ecological risk; and sources. The Hakanson potential ecological risk index and index of geo-accumulation (Igeo) were used for evaluating the condition of soil heavy metal enrichment and the extent of potential ecological risk. Results demonstrated that the mean concentrations in the agricultural soils were 2.23 mg/kg for Cd, 5.3 mg/kg for Cu, 38.002 mg/kg for Pb, and 13.84 mg/kg for Zn. The average concentrations of Cd and Pb in the agricultural soils were higher than average worldwide soils and for Cu and Zn, values were lower than average worldwide soils. The spatial mapping of the distribution of heavy metals produced by kriging interpolation showed similar patterns for all heavy metals, and higher concentrations of all heavy metals were observed in the western and southern parts of the study area. Our findings demonstrated that in the Siakh-Darengoun plain, natural sources affect the levels of Cu and Zn, however, anthropogenic sources such as chemical fertilizers, especially phosphate fertilizers could be the major sources of Cd and Pb. Hossain Abad agro industry in the west of the study area can be considered as one of the most important heavy metal sources. The geo-accumulation index classified Cu and Zn into no pollution levels, Cd and Pb into unpolluted to moderately polluted level. Cd produced serious ecological risk in agricultural soils and was the main pollutant, while the Cu, Pb and Zn had low ecological risk. Comprehensive potential ecological risk indexes of all metals showed that the soils in Siakh Darengoun were suffering from high level of ecological risk.
