Research On Surface Water Exposure Predicting Technique For Pesticides Used On Upland Crops

Pesticide ecological risk assessment is an important part of pesticide registration and plays an important role in pesticide environmental safety management. Pesticide ecological risk assessment includes four major steps: problem formulation, exposure assessment, effect assessment and risk characterization. Among the four steps,exposure assessment is the most key and difficult step, exposure assessment mainly studies the spatial and temporal distribution of pesticides in the ecological environment and the process from the source to the receptor, with the aim of obtaining the pesticides' exposure level in the environment. At present, models are important tools to conduct the exposure assessment,but model can't run without the specific environment in which pesticides are used, including local climate, soil,hydrology, crop cultivation and etc., all of these constitute an exposure scenario.Therefore, the construction of exposure scenarios is the basis for exposure simulation and ecological risk assessment.China has a vast territory,and upland crops are distributed throughout the country.The high diversity of the upland crops, and the high occurance of the diseases and pests determine the high usage of pesticides. Therefore, the pollution of surface water caused by the extensive use of pesticides on upland crops should not be underestimated. And surface water risk assessments for pesticides used on upland crops are necessary.In this paper, progresses on pesticide upland crop-surface water risk assessment of EU and U.S. were reviewed, including the risk assessment procedures, the exposure models, the scenarios and etc. Meanwhile, the current situation and problems of risk assessment in China was summarized and analysised. Then, on the basis of the development methods of exposure scenario of EU, the national standard upland crop-surface water exposure scenarios were developed. Finally, the aquatic risks of pesticides used on wheat were predicted by using the scenarios developed. The research contents and results of this paper were as following:(1) Investigation of Ecological risk assessment progresses of upland crop-surface waterBy consulting the relevant literatures, the latest status of pesticide ecological risk assessment of upland crop-surface water was investigated. The results showed that:USEPA and EU had developed a number of exposure assessment models, and had built a large number of upland crop-surface water scenarios. In USEPA, the first I level model was GENEEC, which was specially developed for aquatic ecological risk assessment; the first II level model was PRZM/VVWM, which was integrated into the latest PWC platform. And the latest upland crop-surface water modelling platform--PWC includes 69 standard scenarios and 55 non-standard scenarios. In EU,the STEPS ONE TWO model had been developed for the first and second levels,and the SWASH shell had been developed for the third level exposure assessment. As to the scenarios, 10 upland crop-surface water scenarios had been developed, six of which are drainage scenarios, and the other four are run-off scenarios. In addition,Norway, Germany and some other countries have developed several exposure assessment models for their country. Currently, in China, the Pesticide Risk Assessment Exposure Simulation Shell (PRAESS) has been developed by Nanjing Institute of Environmental Science to carry out the exposure assessment of pesticides.In PRAESS,PRZM/EXAMS model was used,and two typical upland crops-surface water scenarios were developed.(2) Development of upland crops-surface water pesticide exposure scenario system for China Upland crop-surface water pesticide exposure scenario system for China was developed under the principle of "the realistic worst case" and the method established. Firstly, according to the temperature and precipitation, five scenario zones were divided in China by GIS, they were: north-east district, north-west district, north of China, Yangtze River basin, south of China; Then overlayed the county distribution map and the upland crops distribution map to get the county map with upland crops distribution; Then collected the soil organic matter data and precipitation data of each county with upland crops, and calculated the percentile and the protection degree, the sites of which the conditions meet the above conditions were regarded as alternative scenario sites. Finally, eight scenario sites were determined from the alternative ones according to the soil texture, slope and etc..And the protection degree of these sites were about 95th percentile. The scenario sites were: Jilin Yitong, Henan Xinan, Shandong Laizhou, Shanxi Zhouzhi, Zhejiang Jinhua, Jiangxi Hukou, Guangdong Xinyi and Hainan Danzhou. Then, parameters for each site were collected to form the scenario files.(3) The integration of upland crop-surface water exposure predicting platformAfter determining the site, the weather, soil, water and crop data were access through field research and query information. Converting scenario data into a particular format required by the model, then added to the shell. Creating a new crop, soil and water file in the scenario manager, and make the corresponding changes;meteorological parameters directly generated DVF format files on the C drive PRAESS directory. After the scenario file is generated, the PRAESS platform can be used for the integration of upland crops - surface water scenrio files.(4) Application of PRAESS in predicting the aquatic risk of pesticides used on wheat After integrating the scenarios developed into PRAESS, PRAESS was used to assess the aquatic risk of pesticides used on wheat. Firstly, frequently-used pesticides list was obtained through investigation, 34 pesticides were selected for simulation; .Then the physi-chemical properties,the efate in upland and aquatic environment,the application informations and aquatic toxicity data of these pesticides were collected to carry out the exposure modelling and effect assessment. Finally, the pesticides were ranked according to the risk quotients (RQs) derived by dividing the environmental exposure concentrations (EECs) with the predicted no effect concentrations (PNECs). The results showed that: of the 34 pesticides simulated,there were 12 pesticides with unacceptable risk to fish; and 24 pesticides with unacceptable risk to daphnia; the chronic risks to algae of all the pesticides simulated were acceptable.