Distribution and Extraction of Heavy Metals in Soil and Their Accumulation in Brassica oleracea L. after Long Term Wastewater Irrigation

Abstract

Wastewater irrigation has become a common practice especially in third world countries. Over the period of time population growth has resulted in increased domestic and industrial wastes. People produce huge quantities of vegetables and crops yields with wastewater irrigation without knowing its effects on soils, plants and ultimately on consumers. Therefore, a study was carried out to compare accumulation of heavy metals (Fe, Cu, Pb, Zn, and Cr) in wastewater irrigated soils with rain fed soils. Water soluble, and total extractable heavy metals were determined. The contents of water soluble, exchangeable and total plant essential elements (K, Ca, and Mg) were also determined. Soil samples from three different layers (0-30 cm, 30-60 cm and 60-100 cm depth) were collected from both wastewater irrigated field and rain fed field. Results indicated that water soluble heavy metals varied in soil in order Fe> Cr > Pb > Zn > Cu irrespective of the depth and irrigation management. Total heavy metals in all layers of soil were noted as Cr > Zn > Pb > Cu > Fe for wastewater irrigated field and Cr > Zn > Pb > Fe > Cu for rain-fed field. On the other hand the concentrations of water soluble essential elements varied as K > Mg > Ca for both rain-fed and wastewater irrigated soils. The study clearly indicated that wastewater irrigation caused heavy metal accumulation in both soils and plants. The use of wastewater for agriculture may be economically productive due to abundance of nutrients present in it but have adverse effects on soil, plant and ultimately its consumers. Although heavy metals in plant were found within the standard limits, however, continuation of such practices for a longer period of time may escalate their levels beyond the safe limits.