Research On Exposure Assessment Technology In Pesticide Groundwater Risk Assessment

Pesticides play an important role in controlling crop pests and smothering and ensuring high crop yield. But pesticide is a double-edged sword which simultaneously brings huge economic benefits to people and creates a serious threat to ecological environment. The pesticides that enter into the environment may generate significant adverse effects to groundwater, surface water and environmental organism. Therefore how to avoid and mitigate the adverse effects caused by pesticide application has become a major environmental problem concerned widely and be solved. Ecological risk assessment has been paid more and more attentions in pesticide environmental safety management in recent years and become a strong technical support of pesticide environmental safety management of many countries.Groundwater is an important part of water resources and an important source of water in people’s lives and industrial and agricultural water. Groundwater is more difficult to be contaminated than surface water. But once contaminated, it is difficult to eliminate the adverse consequences. Pesticides can enter into groundwater body by Rainfall and leaching after they used in field, which lowers the groundwater quality and affects groundwater function. The application of technology of groundwater risk assessment could predict or assess the hazard and effect of pesticide application on groundwater and can provide technical support for pollution prevention. Therefore, it is significant to carry out groundwater risk assessment technical research.Pesticide groundwater risk assessment is different from surface water risk assessment. The ecological receptors of surface water risk assessment consist of humans and a variety of environmental organisms while groundwater risk assessment only focuses on human health currently. Therefore exposure assessment technology is the key point of groundwater risk assessment technology. This thesis centered on the groundwater exposure assessment and carried out the following researches:(1) Research on screening of exposure assessment modelsAnalyzed and compared different tier groundwater exposure assessment models developed by U.S., EU and other countries, including tier Ⅰ screening models (SCI-GROW and Tier Ⅰ Eco-Risk Calculator by U.S., MACRO, PEARL, PELMO and PRZM_GW by EU) and tier Ⅱ exposure assessment models (PRZM3(PRZM+VADOFT) and ADAM by U.S.). After compared the input parameters, simulated behaviors, assessment results and assessment tiers of each models, finally screened out SCI-GROW as tier Ⅰ screening model and PRZM3-ADAM as tier Ⅱ exposure assessment model adapted Chinese actual conditions. SCI-GROW requires less input parameters and these four parameters consider the mobility and degradation of pesticides and application rate and number of applications, which can directly reflect the exposure concentrations of pesticides in groundwater. Therefore it is suitable as tier Ⅰ screening model. PRZM and ADAM consider many factors and are more complicated and they predict results are finer. PRZM mainly simulates the pesticide behaviors after applied in dryland crops in the crop root zone. ADAM mainly simulates the dilution, partitioning, persistence and transport of pesticide in aquifer. Therefore PRZM-ADAM coupled model can predict the pesticide behaviors and residual concentrations in aquifer after applied in dryland crops. Therefore it is suitable as tier Ⅱ exposure assessment model.(2) Establishment of Chinese standard pesticide groundwater scenario system frameworkPresently China has not a set of complete standard pesticide exposure scenario. This thesis established a set of dryland-groundwater scenarios in China for the first time."The realistic worst case" principle is the principle for scenario establishment, which means should choose some real," the worst" features as much as possible in determining the properties of the factors contained in the scenario, namely properties which could easily lead to pesticide contamination. On the basis of the principle, firstly divided the whole country into5scenario zones based metrological conditions, then determine a certain number of scenario sites in each scenario zone. Finally established Chinese dryland-groundwater scenarios system, including5scenario zones (Northeast, Northeast, North China, Yangtze River Basin and Southeast),10scenario sites (Shaanxi Yulin, Inner Mongolia Tongliao, Liaoning Shenyang, Henan Nanyang, Shandong Heze, Jiangsu Fengxian, Jiangxi Ganzhou, Anhui Anqing, Hubei Huanggang and Hainan Danzhou) and totally6scenario crops (corn, wheat, peanut, rapeseed, cotton and sugar cane).(3) Construct and verification/validation of groundwater exposure simulation shellIn order to conduct higher tier pesticide risk assessment in China, Pesticide Risk Assessment Exposure Simulation Shell was co-developed by the company with U.S. Waterborne Environmental Inc.. The model applied in groundwater exposure assessment in PRAESS is PRZM-ADAM model. Combined PRZM-ADAM coupled model with groundwater scenario, the exposure concentration of pesticide in groundwater can be predicted. OAT (One factor at a time) method was used in this thesis to perform sensitivity analysis to the major input parameters of PRZM-ADAM. The results showed that the order of the relative sensitivity of each parameter is:Soil DT50(or application rate)> application rate (or Soil DT50)> Koc> DT50in groundwater. Meanwhile the verification and validation of shell program were performed and finally the validation of PRAESS was verified.(4) Research on application of groundwater exposure assessment technology (screening of pesticide with high contamination risk)Established scenario and shell program were used in this thesis to assess the acute and chronic risks of contamination for groundwater caused by pesticide varieties commonly used in China. Firstly applied PRAESS to get the exposure concentration of pesticide in groundwater, and then calculated the guidance value of a pesticide on the basis of the method recommend by World Health Organization. Divided the predicted peak concentration and annual concentration by the guidance value respectively and judge the acute and chronic risk level of pesticides causing groundwater contamination according to the calculated risk quotients. At last listed the lists of pesticide varieties may result in acute and chronic high contamination risk to groundwater and provided some references for the use of pesticide in the areas that is vulnerable to be contaminated in groundwater caused by pesticide application.The research on groundwater exposure assessment is a significant work. This thesis has done some preliminary works aimed to lay a certain foundation to carrying out the research work on groundwater exposure assessment in China.