Environmental Impacts of Reuse of Sewage and Industrial Effluents on Irrigated Farmland

Abstract

Growing population and rapid industrialization has increased the volume of wastewater manifold eventually deteriorating the fresh water resources and surrounding environment due to inappropriate management. In developing countries including Pakistan, industrial wastes and municipal effluents are being used for the irrigation of crops in or near urban centers or discharged into canals, rivers, along roadsides or in the vicinity of industrial establishments. Present study was conducted to evaluate the quality of city sewage effluents being used in agriculture in the vicinity of Lahore for growing vegetables and fodder, and also to document the impacts of wastewater irrigation on agricultural soils and crops. The quality of city sewage effluents was explored under two categories (i) domestic sewage wastewater and (ii) Combine wastewater. Large variations were found in almost all water quality indices with most of the lower values being observed during monsoon season. The irrigation quality of combine wastewater was worst with respect to various parameters including pH, COD, BOD, sulphides and the concentration of heavy metals was also above the FAO limits. There was accumulation of heavy metals in soils receiving wastewater for irrigation. The total metal contents in soil follow the order Mn> Co > Zn > Cr > Ni > Cu > Cd. The sequential extraction procedure developed by Tessier was adopted to demarcate five metal fractions; exchangeable, acid soluble, reducible, oxidizable and residual. Fractionation procedure showed that all the metals except Cd were dominant (>50 %) in the residual fraction. It was observed that the concentration of all studied toxic metals in edible part of the vegetables was above the critical level. The meaningful positive correlation was observed between concentration of metal in vegetable and F1 and F2 fractions, while negative correlation was observed between residual and total metal concentration which indicate the non availability of these fractions. It was observed that the practice of using wastewater in irrigation for growing vegetables and other crops is non-sustainable. In order to study the bioavailability and uptake of Cd, Cr and Ni in silty clay, silt loam and sandy loam soils, with two levels of organic matter by spinach, cabbage and radish field experiments were undertaken. Previous studies showed that the characteristic of soil, such as texture, and organic matter contents affect the mobility of the metal added. The transfer of metals to plants was reported to be higher in sandy soil and differs among plant species. The non essential elements Cd, Cr and Ni can translocate into the edible parts of spinach, cabbage and radish. Of the three plants under study, uptake of metal was highest in spinach followed by radish and least in cabbage.