Abstract: The scenario of exposure of paddy fields and surface water in Dongtiaoxi watershed was reconstructed for test of a modified RICEWQ-EXAMS model in aquatic eco-risk assessment and healthy risk assessment of the application of pesticides in rice paddy fields in Dongtiaoxi Watershed. RICEWQ-EXAMS model has been extensively adopted in assessment of exposure of paddy field-surface water in countries the world over. Now it is independently modified by the research group and tested in this project. Results show that among all the ten kinds of pesticides commonly used in paddy fields of this region, herbicide trifluralin showed a high risk of acute toxicity to green algae, insecticide endosulfan, both a high risk of acute toxicity and a risk of chronic toxicity to fish, avermectins a high risk of acute toxicity to daphnia, and hexaflumuron both a high risk of acute toxicity and a risk of chronic toxicity to daphnia, the other pesticides are quite low in risk of either acute or chronic toxicity to fish, daphnia and algiae. As to the healthy risk assessment of the 10 pesticides, identical conclusions are reached whether using the traditional method or the risk assessment model that the 10 pesticides do not pose risk to human health when used properly in paddy fields. The results of the assessment tally quite well with the actual situation. Therefore, it could be concluded that the develoed scenario and the modified model can quite effectively be used in risk assessment of the application of pesticides in paddy fields in Dongtiaoxi watershed.

Key words: Dongtiaoxi River, rice paddy, pesticide, risk assessment, model, scenario