Variations in heavy metal accumulation, growth and yield of rice plants grown at different sewage sludge amendment rates

Use of sewage sludge in agriculture is an alternative disposal technique for this waste. The present field study was conducted to assess the suitability of sewage sludge amendment in soil for rice (Oryza sativa L. cv. Pusa sugandha 3) by evaluating the heavy metal accumulation, growth, biomass and yield responses of plants grown at 0, 3, 4.5, 6, 9, 12 kg m−2 sewage sludge amendment (SSA) rate. Sewage sludge amendment modified the physico-chemical properties of soil, thus increasing the availability of heavy metals in soil and consequently with higher accumulation in plant parts. Root length decreased, whereas shoot length, number of leaves, leaf area and total biomass increased significantly when grown under various SSA rates. Yield of rice increased by 60%, 111%, 125%, 134% and 137% at 3, 4.5, 6, 9 and 12 kg m−2 SSA, respectively, as compared to those grown in unamended soil.Sewage sludge amendment rates above 4.5 kg m−2 though increased the yield of rice, but caused risk of food chain contamination as concentrations of Ni and Cd in rice grains were found to be above the Indian safe limits (1.5 mg kg−1) of human consumption above 4.5 kg m−2 SSA and of Pb (2.5 mg kg−1) above 6 kg m−2 SSA. Since aboveground parts of the rice also showed higher concentration than the permissible levels of Ni, Cd and Pb at 4.5 kg m−2 SSA rate, it cannot be used as fodder. The rice husk may be used as bioresource for energy production. Efforts should be made to treat the effluents from small scale industries before discharge into the sewerage system.