The Study Of Health Risk Assessment On Heavy Metals Of Crops In City Reclaimed Water Irrigation Area

With the increase of water shortage and water pollution in China, the lack of agricultural irrigation water becomes an important factor which hampered China's agricultural production. The municipal reclaimed water is an important alternative source of water for irrigation. It is an effective method to use city reclaimed water to resolve water shortage in agriculture, but heavy metals in the water may be absorbed by human body through food chain; the excessive amount of them will be harmful, and ultimately affect human health. So it is necessary to use risk assessment technology to evaluate the impacts on human's health caused by heavy metals in reclaimed water, and then provide the theoretical basis for the using of municipal reclaimed water.This research was based on the demonstrative engineering of municipal reclaimed water for irrigation of farmland in Wuqing District, Tianjin. Corn and wheat were chosen as the experimental crops in the experiment. The impact on soil and crops caused by heavy metals in the reclaimed water irrigation area was analyzed. Monte Carlo method was used to calculate human health risk probability distribution about the heavy metals in crops, then health risk assessment was made, and the key risk factors were decided. The results will contribute to provide referenced basis for the safe use of reclaimed water for irrigation of farmland.The main conclusions will be draw as following:(1) During the experiment, the heavy metals in soil do not show obvious residue; the heavy metal proportion in plant irrigated by municipal reclaimed water is higher than that in control area, but the difference was not significant; seven kinds of heavy metals in the crops were lower than corresponding food hygiene standards and national food hygiene standards, the content of heavy metal is always higher in wheat than in corn, so it is necessary to evaluate the risks.(2)Through the compared among enrichment coefficient of different metals, certain crop has different enrichment capacity of different kinds of metal. Different crops have different enrichment capacity to a certain metal; wheat has stronger enrichment capacity to heavy metal than corn.(3)The health risks analysis of heavy metals in crops:In accordance with international standards, harmful heavy metals could be divided into two kinds: one is chemical carcinogenic metal; the other is non-chemical carcinogenic metal. Lifetime carcinogenic risks of arsenic, cadmium, chromium and lead are less than maximum acceptable level of risk recommended by the International Commission on Radiological Protection (ICRP). Each of the non-carcinogenic heavy metals in the lifetime risks is less than the maximum acceptable level of risk recommended by British Royal Society, the Swedish Environmental Protection Agency and the Netherlands Ministry of Environment. For the individual carcinogenic risk and non-carcinogenic risk of heavy metals, the risk of wheat is higher than that to corn. Based on the assumption that a variety of chemical pollutants have additive risks to human health, the total risk of heavy metal carcinogenic risk and heavy metal non-carcinogenic risk is less than the recommended maximum acceptable level of risk; The total risk of wheat is higher than that of corn, and chromium carcinogenic risk of the total cancer risk is over 70 percent.