Development And Application Of Ground Water Risk Assessment Technology For Pesticides Used In Rice Paddy

Pesticide ecological risk assessment provides scientific basis for pesticide registration and environmental safety management.In rice cultivation,high occurrence of diseases,pests and weeds requires large amount of pesticides to be used frequently over the growing season.Additionally,water is often kept in rice paddies for a relatively long time after pesticide application.All these factors may lead to potential risk to ground water.Therefore,it is important to conduct ground water risk assessment for pesticides used in rice paddy.In this paper,progresses on ground water risk assessment of EU and U.S.for pesticides used in rice paddy were reviewed,including risk assessment procedures,exposure models,scenarios and etc..Current status of ground water risk assessment in China was also summarized and disadvantages were analyzed.Exposure prediction techniques for ground water risk assessment for pesticides used in rice paddy for China were developed.Research contents and results were as following:1.Exposure assessment model screening developing and rice-ground water exposure simulation module couplingBased on the analyzing of Tier I and Tier II rice-ground water models of EU,rice paddy model RICEWQ and PFAM of U.S.,ground water model VADOFT,ADAM and PRZM-GW of U.S..Rice paddy model RICEWQ,ground water model VADOFT and ADAM were selected according to the rice cultivation management situation,the characteristics of ground water pollution and etc..Then rice paddy model and ground water model were coupled to form the rice-ground water exposure simulation module.Finally,module was integrated to Pesticide Risk Assessment Exposure Simulation Shell(PRAESS).2.Development of rice-ground water pesticide exposure scenario system for ChinaRice-ground water pesticide exposure scenario system for China was developed under the principle of "the worst realistic condition".Firstly,according to the weather condition and rice planting status of China,four scenario zones were divided in China by GIS:north-east district,north of Yangtze River basin,south of Yangtze River basin and south of China,which represent the whole rice cultivation area in China,and among these scenario areas,large differences of weather conditions existed.On the bases of the division of scenario areas,eight rice-ground water scenario sites were determined in China according to the precipitation,soil and rice cultivation characteristics of these scenario areas.The scenario sites were:Liaoning Dawa in north-east district,Zhejiang Zhuji,Anhui Langxi and Jiangsu Yixing in north of Yangtze River basin,Fujian Jianyang and Jiangxi Nanchang in south of Yangtze River basin,Guangxi Bobai and Hainan Danzhou in south of China.Weather and soil condition of the scenario sites represented "the worst realistic condition" in their scenario areas,and the total protection level was about 95th.Then,parameters for each site were collected to form the scenario files.3.Development and validation of ground water exposure prediction shellThe rice-ground water exposure simulation module RICEWQ-VADOFT-ADAM and the rice-ground water pesticide exposure scenario system were integrated into PRAESS as scenario file,and update PRAESS to PRAESS1.00.07.Verification and validation of PRAESS 1.00.07 were done.Verification showed that shell run accurately,input document establishing run smoothly,input data and database could be read correctly and output coulddisplayed correct.Preliminary validation showed that the predicting results complied well with monitoring results.4.Application of the developed ground water exposure prediction shellThe developed rice-ground water exposure prediction shell was used to simulate ground water pollution risk for pesticides frequently-used in rice paddies in China.Firstly,frequently-used pesticides list was obtained through investigation;then pesticides frequently-used in rice paddies were predicted by using the developed rice-ground water exposure prediction shell;at meanwhile,risk quotients(RQs)were calculated according to EU's Dringking Water Directive and the WHO's drinking water Guidance Value formula;finally,pesticides which were high risk to ground water were listed by RQs.The resualt showed that,under EU's Dringking Water Directive,there were sixteen pesticides had high acute risk(five herbicides,four insecticides and seven fungicides)and fifteen pesticides had high chronic risk(five herbicides,four insecticides and six fungicides)to ground water in thirty-eight frequently-used pesticides.Under the WHO's drinking water Guidance Value,only simetryn had high acute and chronic risk to ground water in thirty-eight frequently-used pesticides.Simetryn had high acute risk to ground water in Zhejiang Zhuji and Hainan Danzhou,and had high chronic risk to ground water in Hainan Danzhou.Simetryn didn't have high risk in other sites,but its RQs were the highest in all sites.