Development And Application Of Surface Water Exposure Assessment Scenarios System For Pesticides Used In Rice Paddy

Rice is the largest grain crop in China,accounting for about thirty percent of the food crop area.Rice grows in seasons with high temperature and precipitation which could cause high occurrence of diseases,pests and weeds because of the high humidity of the paddy environment.In addition,the paddy water needs to be discharged into the surrounding surface water for the requirement of rice cultivation practice.So the risk of pesticide pollution to surface water caused by rice production is quite high.The risk assessment of pesticide can provide scientific basis for decision-making of pesticide environmental management.However,the research of pesticide risk assessment technology in China is still relatively weak,especially in the exposure assessment of the scenario sysyem is not perfect,which cannot meet the requirement of risk management.In this paper,in view of the current lack of exposure assessment scenarios in China,a scenario system for rice-surface water exposure assessment was established,and the established scenario system was applied to assess the aquatic ecological risk of pesticides commonly used on rice in China.As a result,a list of pesticides needing to be concerned was put forward,which could provide scientific basis for pesticide environmental safety management.The research contents and results are as follows:(1)Research on models and scenarios of pesticide rice-surface water exposure assessment in the worldThe existing models of surface water exposure assessment for pesticide application in rice paddy were studied,including RICEWQ,Tier I Rice Model and PFAM of the United States,MED-RICE and SWAGW of the European Union,Aquatic PEC,PADDY series and PCPF series of Japan,TOP-RICE and PRAESS platform of China.The differences of models were compared from the aspects of model principles,formula,input parameters and output results,prediction accuracy,simulation scale,and the existing scenarios included in each model are deeply analyzed.On this basis,the emphasis of future research in China was put forward,that is,to improve the scenario system of rice paddy-surface water exposure assessment,to strengthen the validation and comparison of different models,and to develop the large-scale simulation model for basins.(2)Scenario site selection of surface water exposure assessment for pesticide application in rice paddyAccording to the "realistic worst case" principle and the specific principles of scenario sites selection,site selection was carried out for rice-surface water exposure assessment.On the basis of the existing rice paddy scenario zones,the annual average precipitation,soil organic matter data,rice planting data and other basic data of all counties in each scenario zone were collected.The 80 percentile precipitation and 20 percentile soil organic matter content of each scenario zone were calculated,and the sites which could meet the above conditions at the same time were selected as alternative scenario sites.At last,according to the protection degree,rice planting areas,soil texture,soil species distribution and other factors of each site,eight scenario sites for rice-surface water exposure assessment were finally determined,which are located in Shenyang,Langxi,Liyang,Xinhua,Yichun,Sanming,Huiyang and Qiongshan.(3)Development of scenario system for rice-surface water exposure assessment of pesticidesField survey,data search and expert consultation were used to collect four types of scenario parameters of weather,soil,water and crop in eight scenario sites.The meteorological information includes daily average data of five meteorological elements from 1971 to 2000;Soil information includes soil texture,bulk density and etc.;Water body information includes data of ten factors such as sediment content and flow rate etc.;Crop information includes data on nearly twenty elements such as planting time,irrigation and drainage practice and etc.Basing on the collected scenario information,the compilation of three types of scenario files(meteorology,water body and crop files)were completed,the scenario system finally constructed eight seenario points and twenty specific scenarios.Finally,the established scenario files are integrated into the rice-surface water exposure assessment model and PRAESS(Pesticide Risk Assessment Exposure Simulation Shell)platform.Thus,a pesticide simulation tool with rice-surface water scenarios covering the national rice cultivation areas and the national rice planting condition in China was developed.(4)Aquatic ecological risk assessment of pesticides used in rice paddyTwenty pesticedes commonly used in rice paddy in China were selected to carry out aquatic ecological risk assessment.Application of the developed scenario system of rice-surface water exposure assessment and exposure simulation tool to for exposure assessmen.Through simulation,the predicted exposure concentration(PEC)values of these pesticides in all scenarios were obtained.Then the aquatic effect data of these pesticides were collected to calculate the predicted no effect concentration(PNEC)value.Finally,the risk quotient values which could demonstrate the risks were obtained by dividing the predicted exposure concentration(PEC)with the predicted no effect concentration(PNEC).According to the risk characterization results,ten pesticide varieties that need attention are proposed,of which four varieties(chlorpyrifos,butachlor,triazophos and carbendazim)belong to special focus on pesticides,there are three pesticides(malathion,etofenprox and acetochlor)are focused on pesticides,and two pesticides(abamectin and tebuconazole)are needed pay attention to pesticides.