Heavy Metals in Brown Rice (Oryza sativa L.) and Soil After Long-Term Irrigation of Wastewater Discharged from Domestic Sewage Treatment Plants

A pot experiment was conducted in a plastic film house to evaluate the translocation and uptake of heavy metals (Pb, Cd, Cu, and Zn) into brown rice (Oryza sativa L.) and the heavy metals residues in soils which had previously been irrigated with domestic wastewater for a long time (3 years). The range of Pb, Cd, Cu, and Zn was 5.10 ± 0.01, 0.105 ± 0.017, 5.76 ± 0.42, and 23.56 ± 1.40 mg kg^-1, respectively in the domestic wastewater-irrigated soil, and 0.370 ± 0.006, 0.011 ± 0.001, 0.340 ± 0.04, and 2.05 ± 0.18 mg kg^-1, respectively, in the domestic wastewater-irrigated brown rice. The results indicated that application of domestic wastewater to arable land slightly increased the levels of Pb, Cd, Cu, and Zn in soil and brown rice (P < 0.01). The concentrations of heavy metals in brown rice were lower than the recommended tolerable levels proposed by the Joint FAO/WHO Expert Committee on Food Additives. However, the continuous monitoring and pollution control of hazardous materials from domestic wastewater are needed in order to prevent excessive build-up of heavy metals in the food chain.