Risk Assessment Of Heavy Metal Toxicity Through Wheat And Rice Grow In Tianjin Sewage Irrigated Area

Tianjin is one of water-shortage city, in order to maintain the development of agricultural economy and to make up the shortage of water resources in agriculture irrigation.sewage irrigation has become an inevitable way.Because of using sewage irrigation and municipal sludge,soil environmental quality of Tianjin is going downhill,many areas polluted by heavy metal seriously,which the most typical is cadmium pollution.And then lead to rice and vegetables and other crops being polluted,ultimately endanger human health.Many scholar have explored health risk assessment of heavy metals in vegetables,but focus on wheat, rice and other crops with less attention.Risk assessment of heavy metal toxicity through wheat and rice grown in Tianjin sewage irrigated area was studied in this paper. Wheat and rice samples as well as related topsoil were collected,followed by the content of six heavy metals element(Cd,Cu,Pb,Zn,Cr,As,Hg)were exmainated.Level of second grade standard of Tianjin soil environmental quality and second grade standard of Chinese national soil quality were used as the assessment foundation for soils. Chinese National Food Safe Criterion and European Union Food Safe Criterion were used as the foundation for wheat and rice grains. Transfer factor, Daily intake rate and Target hazard quotient were used to assess the potential ecological risk to local population by consumption of wheat and rice grown in the sewage irrigated area soil. The result showed that continuous application of waste water has led to accumulation of heavy metals in the soil and concentrations of Cd, Zn and Hg in soil of Tianjin sewage irrigated area exceeded the permissible limits level of second grade standard of Tianjin soil environmental quality, suggesting they are pollutants. Heavy metals translocation capabilities from soil to edible portion of the plants were different based on their transfer factors, Zn and Cd were more mobile than other metals. The concentration of Pb has crossed the safe limits for human consumption, meaning Pb has ecological risk to human health. Max concentrations of heavy metals such as Cd, Zn, As in part wheat samples and Cu, As in part rice samples exceeded safe limits of Chinese National Standard, suggested that they may have potential ecological risk to human health. Target hazard quotient (THQ) of individual metal was below1, meaning the relative absence of health risks associated with intake of a single heavy metal through consumption of either wheat or rice. THQs of As for wheat and rice would sum up to above1, indicating As may have a risk to the local population by consumption of wheat and rice. Thus regular monitoring of heavy metal contamination in crops grown at waste water irrigated area is necessary and consumption of contaminated crops should be avoided in order to reduce the health risk caused by taking the contaminated crops. The waste water treatment technology should involve steps to remove heavy metals causing risk to human health.