Geochemical and environmental investigation of sewage-irrigated soils and crops of Sabzevar, NE of Iran

Abstract

The present study identifies the effects of sewage irrigation on the surface soils geochemistry and the concentration of heavy metals in plants of Sabzevar area, which were irrigated for a long time by wastewater. This study shows that the sewage irrigation has led to decreasing pH and increasing organic matter, and also it makes the accumulation of P2O5, high-field-strength elements (Ga, Ta, Th, U and Y) and heavy metals (Cd, Co, Cu, Pb, Sn and Zn) in contaminated soils. Likewise, the concentration of rare-earth elements (REE) in contaminated soils is more than background samples with moderate enrichment of light REE compared with high REE in REE pattern diagram (mean LaN/LuN = 5.77). The calculated transfer factor and enrichment factor indexes in plants grown on the polluted soils are significantly higher than the control samples which show the heavy metal enrichment in the contaminated samples. Although the cultivated crops on this area (maize, beet, alfalfa, barely) are used only for animal feed, the heavy metal analysis indicated that the concentration of Cr, Cu, Ni and Pb in these plants, especially alfalfa and maize, is more than the maximum permitted levels defined in different standards.