Environmental geochemistry of agricultural soils and topsoils irrigated by sewage in the south of Torbate Heydarieh city, Khorasan-e-Razavi province, Northeast of Iran

The farmlands area in the south of Torbate Heydariyeh city has been irrigated by sewage for over 30 years. In this study, the chemical composition and physicochemical properties of soils irrigated by sewage and heavy metal concentration of vegetables cultivated in these soils are determined and compared with unpolluted samples. The polluted soils have a lower pH (7.5- 7.8) and higher organic content (more than 2.3%) than other soils (with pH>8 and organic component < 1%). All soil samples show similar major oxide composition and the same rare earth element (REE) patterns indicative similar parental materials. However, the trace elements composition is completely different between polluted and unpolluted soils. The soils irrigated by sewage show intense enrichment of many elements, especially heavy metals. These soils have lower 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 206Pb/207Pb and higher 208Pb/206Pb ratios than other soils which indicate the role of anthropogenic sources in their genesis. The bioavailability values in the polluted soils are very higher than unpolluted samples which led to increasing of transfer factor and heavy metal concentration in the vegetables. The concentration of Cd, Cr, and Pb in the polluted vegetables is more than the maximum permitted concentration.