Abstract: 【Objective】 Degradation of pesticide residue (chlorpyrifos and fipronil) in rice from farm to dining table and risk assessment for human health were studied to reveal the magnitude of the risks faced by different populations having interest in rice, and to provide a guiding line for application of pesticide in field, and to refine and update the human health risk assessment data while helping to determine a MRL value and harvest interval. 【Method】 A field trial was designed following the protocol of NY/T788-2004, and residues in harvested rice were monitored by GC. Residue levels of post-harvest-applied chlorpyrifos and fipronil during storage, exposure to sunlight, washing and cooking processes (boiled rice) of brown rice were investigated; Several perimeters of evaluation model of dietary exposure evaluation model (DEEM) was employed to estimate the acute and chronic risk faced by different populations of interest, POR (percent of RfD ) and MOE (Margin of the exposure) were included. 【Result】 A positive correlation was found in pesticide residue betweon harvested rice and treatment of pesticide in field, residue presented in harvested rice raised with the raising application rate and treatment times. The concentration of pesticide residue decreased as a function of time during rice storage and preparing and cooking processes. The pesticide residues decreased by 91.16% and 96.16% at the end of the experimental period. The boiling process had a significant effect on the major degradation of pesticides. Risk assessment to human health showed that chlorpyrifos residue in rice should be concerned, and dietary exposures from eating food crops treated with chlorpyrifos exceeded the level of concern for the entire population. Chronic dietary risk from food alone showed that dietary exposures from eating food rice treated with fipronil was below the level of concern for the entire population, including children. Acute dietary (food only) risk estimate for chlorpyrifos as percent of aPAD (acute population adjusted dose) over 100% frequently when the treatment rate and times raised, the result showed that risk faced by boys under the age of 14 was higher than the girls at the same age, and the risk level reversed for the subpopulation at the age above 14. The risk faced by population of rural residential region was more serious than the risk faced by population of urbanite with rice as thceir food, the most sensitive population subgroup, children and male in population of countryside faced higher acute dietary risk than the other subpopulation groups. Thus acute dietary risks from food (rice) alone are of concern. Re-identification of harvest interval found to be the critical point and most important measure to mitigate risk to all population for rice safe eating. The results showed that all risk level of trials for human health decreased to acceptable range when the harvest interval extended to 14 days. 【Conclusion】 Risk quotients indicate that multiple application and double rate of chlorpyrifos increase the risks to entire population and prolong exposures to toxic concentrations. To address these risks, a number of measures including reduced application rates (should not be doubled at single application), increased retreatment intervals (longer than 7 days), extended interval of harvest (at least 14 days) will be needed. Concerning about the toxicity of fipronil to fish, bees and aquatic invertebrate specie, MRL of fipronil in rice is suggested being 0.01 mg?kg-1, which followed the Codex regulation.

Key words: rice, risk assessment, pesticide residue, chlorpyrifos, fipronil