FATE OF HEAVY-METALS IN A LAND TREATMENT SYSTEM - IRRIGATED WITH MUNICIPAL WASTE-WATER

The fate of heavy metals (Cd, Cu, Hg, Pb, and Zn) in a rice paddy slow rate land treatment system (SR-LTS) has been studied. The SR-LTS was d esigned to dispose of wastewater from west Shenyang city, in northeast P.R. China, where various industries are located. Soil samples from 4 different soil depths (0-100 cm) and rice (roots, leaves, grain) were collected and analyzed for heavy metals by ICP and AAS. As expected, the highest concentrations were detected in the top layer of the soil. Copper, lead and zinc were considerably more mobile (50-80%) than eit her cadmium or mercury in the SR-LTS soil profile. Heavy metals measur ed in rice leaves and rice grain were significantly lower than in the roots, which contained high amounts of Cd, Pb, Cu, and Zn correspondin g to the soil burden. Overall, this study suggests that the content of cadmium (0.24 mg kg-1) in the rice grain should be assessed for risks to human health.