Dianshan Lake Ecological Risk Assessment Model And Its Application

With rapid development of the industry and agriculture in recent years, many new chemicals have been created, more and more organic pollutants have been discharged into water through various ways including the emissions of solid, liquid, and gas wastes, precipitation, and runoff. These pollutants, especially with a large amount released via accidental spills within a short period of time, can severely degrade water environment, aquatic ecological integrity and human health. Consequently organic pollution in water has become a major environmental concern. But the current water environment research still mainly focuse on the eutrophication.This study uses USEPA's ecological risk assessment as a framework to develop an approach to assess environmental risk of organic compound in water environment. An ecological toxicity model—AQUATOX was used to simulate dichloromethane concentrations and evaluate its ecological risk in Dianshan Lake. The following are the major results:Organic pollutants, mainly dichloromethane were detected in Dianshan Lake. Routine environmental monitoring showed that the highest concentration of dichloromethane was 0.041mg/l in Qiandengpu in March 2011.AQUATOX toxicological and ecological simulation model of dichloromethane in Dianshan Lake was developed. The model was used to simulate the exposure of the dichloromethane in the water. Using the Hazardous Quotient method, the estimated risk for dichloromethane was 0.3978, indicating that the risk of Dianshan Lake dichloromethane is relatively low but long-term monitoring of the dynamic lake environment and organic pollutants is still required. A sensitivity analysis of the main factors that influence the concentration of dichloromethane in water was performed. Aerobic microbial activity had more effects on the concentration of dichloromethane in water than other physical and chemical factors. Biocumulation of dichloromethane in algae and zooplankton species was also examined and biocumulation in the biota was very low.Finally, a series analysis simulating sudden pollution accidents of dichloromethane in Dianshan lake was performed. The result showed that when the input quality of dichloromethane in Dianshan lake up to 5 ton, the highest concentration of dichloromethane in water will exceed the drinking water standard. When the quality of dichloromethane increases to 100 ton, the time that concentration of dichloromethane decreases to the drinking water standard through the water self-purification will be 45 days, longer than Dianshan Lake's the longest hydraulic retention time in a year. The slow degradation speed may pose environmental risk for Dianshan lake as Shanghai drinking water source. The degradation time of organic in water is decreased significantly, with the rise of temperature. Therefore, pollution accidents occurred in winter will pose higher risk than ones in summer.