Evidence for movement of heavy metals in a soil irrigated with untreated wastewater

Abstract

A Vertisol irrigated for over five decades with an untreated municipal wastewater had elevated levels of DTPA extractable Cd, Co, Cu, Mn, Ni, and Zn in the cultivated layer of the soil as compared to lower layers. Total Co, Ni, and Zn were uniformly distributed in the 150-cm depth of the soil profile, total Cu increased with depth and total than insome deeper layers. Assuming that the added metals had accumulated in the cultivated layer of the soil and assuming uniform distributions of metals in the soil profile at the start of irrigation with wasterwater, the amounts of metals added would have produced increased concentrations in the cultivated layer. These expected differences were not found, except for Mn. This results suggest that the metals Cd, Co, Cr, Cu, Ni and Zn may have migrated downward from the cultivated layer and are now distributed throughout the soil profile or leached below the depth of sampling.