Establishment Of Ditch Scenarios For Pesticide Risk Assessment In Surface Water System Of Southern China

Most Pesticides will cause harm to humans, aquatic animals or the eco-system after application inthe field, because they are designated to kill or otherwise adversely affecting weeds and insect pests.Part of pesticides will leakage into soil, water and evaporate into atmosphere, posing a risk toeco-system and human beings. Surface water is the most important origin of drinking and productionwater. In order to prevent and control pesticide pollution of surface water, Pesticide Risk Assessment(PRA) has been carried on in pesticide registration, which is important and useful to regulate therational use of pesticides, ensure the sustainable development of agriculture and keep drinking andproduction water clean. It is scientific and efficient for using exposure models to conduct surface waterrisk assessment of pesticide. Standard scenarios, which represent the realistic worst cases, are importantcomponents of the exposure models.By referencing the EU’s experience and based on the characteristics of the climate, soil andagricultural practice in Yangtze River Basin and South China zones, through the analysis of themeteorological data provided by meteorological stations from1970to2000using expert judgmentmethod, statistical analysis method and spatial analysis technology of GIS, the conclusion of this paperare as following:First, rainfall is the main factor which affects the environmental behavior of pesticides and theimportant driving factor that ditches exposed to. By referencing the EU’s concept of surface waterscenarios and based on the specific climatic, soil and agricultural situations, the vulnerability of paddyfield ditch has been defined. The90thpercentile of vulnerability of ditch scenarios is consists of the90thrainfall and the50thfrequency of overflow.Second, the conceptual model of ditch scenarios was proposed based on the characteristics of theclimate, soil and agricultural practice in Yangtze River Basin and South China zones. The ditches havethe length of750m and the width of2m, the depth fluctuates between1~2m. The ditches are surroundedby30hm2paddy rice field. There aren’t buffer zones between paddy fields and ditches, the distancefrom the last line of paddy rice to the ditch is set to be0.5m. Part of pesticides will enter into ditchesalong with the drainage, runoff and overflow.Third, by the analysis of monthly rainfall data of419meteorological stations in Yangtze RiverBasin and South China zones, the results reveal that time differences of annual rainfall are more obviousthan spatial differences. Through the calculation, the90thrainfall is2020mm in Yangtze River Basin,which is the87thrainfall of Nanchang station in Jiangxi; the90thrainfall is2050mm in South Chinazones, which is the86thrainfall of Shaoguan station in Guangdong. Then, Nanchang and Shaoguan wereselected as the standard scenario spots.The concept of vulnerability of ditch scenarios has been proposed for the first time. The ditchscenarios representing the realistic worst case have been established based on the predecessor’s research.The contents above are the innovative points.The launching of PRA is relatively late in China, but in recent years, the procedures and methodsfor PRA have been established under the joint efforts of pesticide registration and management department and relevant scientific research institutions. There are a lot of work to be done in terms ofPRA in China, such as the development and validation of exposure models, the improvement andsupplement of scenarios spots and databases. It can be predicted that the procedures and methods forPRA will play a more and more important role in pesticide registration.