Exposure assessment of heavy metals resulting from farmland application ofwastewater sludge in Tianjin, China: The examination of two existing national standards for soil and farmland-used sludge

Land application is one of the major methods of managing municipal sludge i n China. The sludge is used for fertilizing and conditioning soil, but due to the high concentration of heavy metals and other chemicals that it conta ins, improper use of sludge will lead to the contamination of farmland soil . To provide guidance on the application of sludge in China, the Control St andards for Pollutants in Sludge for Agricultural Use (CSPSAU) were enacted , and implemented in 1985. Afterwards, the National Environment Quality Sta ndards for Soil (NEQSS) were also formulated and put into effect in 1996. I n this article, these two national standards were examined by means of expo sure assessment. The main exposure pathway to humans that was considered wa s dietary intake of crops grown on the sludge-applied farmland. Five major types of agricultural crops (rice, wheat, tuber roots, vegetables, and frui ts) and three groups of exposure population (the urban individual group, th e rural sludge-applying individual group, and the rural sludge nonapplying individual group) were assessed. This case study in Tianjin, China, shows t he necessity of reexamining the national standards of the CSPSAU and the NE QSS in the context of risk assessment. More comprehensive surveys and monit oring programs assessing heavy metals contained in farmland soils and crop tissues will be necessary for examining the risks to human health.