International Journal of Applied Science and Engineering Research

Uncontrolled industrialization and urbanization coupled with improper disposal of effluents have become the leading cause for accumulation of metals in soil beyond permissible limits and in turn affects the soil quality and inhabiting invertebrate populations. In this study we aimed to assess the impact of sewage effluents on metal concentrations in agricultural soil and its indirect effect on non target organisms like earthworms by measuring the magnitude of heavy metal contamination and physico-chemical characteristics of soils. The heavy metal concentrations in effluents fed irrigated soils were found to have copper (Cu), zinc (Zn), iron(Fe), nickel (Ni), magnesium(Mg), Total chromium (Cr), lead (Pb) and manganese (Mn) which were determined at four sampling sites along Vrishabhavathi valley where wastewater was used to irrigate agricultural fields for growing vegetables for at least 10–15 years. Total heavy metal concentrations (mg/kg) in soils of pH 3.5 to 7.1 from all sites ranged from 15.3 to 149 mg/kg for Cu, 5.3 to 15.84 mg/kg for Zn, 28.1 to 79.5 mg/kg for Fe, < 0.1 to 0.28 mg/kg for Pb, 0.12 to mg/kg for Cr, 0.05 to 1.02 mg/kg for Ni, 0.7 to 7.0 mg/kg for Mg and 0.46 to 1.35 mg/kg for Mn. The concentrations had increased significantly in the agricultural fields compared with control soils. Continued use of sewage polluted water for irrigation purpose would result in increased metal concentrations in soils exceeding their permitted limits, depending on location. This has also resulted in altered behaviour in non target organisms like earthworms which exhibited changes in burrowing patterns, burrow length, and surface migration in laboratory spiked soils. It was concluded that the use of wastewater in urban and periurban agricultural practices may lead to bioaccumulation and bio-transformation of enriched heavy metals that may pose potential environmental and health risks in the long-term.