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Microbiological degradation of the racemic mixture, the enantiopure R- and S-fipronil was examined under both aerobic and flooded conditions in three Chinese paddy soils. The degradation kinectics and enantiomer fraction (EF) were determined by means of high-performance liquid chromatography (HPLC) with chiral Chiralcel OD-H column, while desulfinyl, sulfone and sulfide derivatives were monitored by reversed phase HPLC with diode array detection (DAD). The degradation/transformation of enantiomers of fipronil in the three live soils under aerobic and flooded conditions generally complied with the first-order kinetics (R2 > or = 0.94). The calculated t1/2 values of the enantiomers of fipronil ranged between 21 and 34 days for aerobic incubation experiments and between 8 and 19 days under flooded conditions incubation, respectively. The calculated EF values of fipronil during the incubation time were all close to 0.5, indicating that the degradation/transformation of fipronil was almost nonenantioselective. The main metabolites of fipronil formed in the incubation experiments were sulfone and sulfide derivatives by oxidative and reductive processes, respectively. The oxidative pathway seemed more active. Under flooded conditions, S-fipronil was preferentially degraded in the three soil samples used. The main metabolite was determined as fipronil sulfide. In control experiments, almost no removal of enantiomers of fipronil was observed indicating that the degradation of fipronil in the paddy soil used was attributed to microbial mediated processes under both aerobic and flooded conditions. In addition, no enantiomerization of fipronil was observed in the soil samples examined under both aerobic and flooded conditions. These results for major differences in the degradation of the enantiomers as well as the formation of toxic metabolites may have some implications for better environmental and ecological risks assessment for chiral pesticides.

Spinosad is an insect control agent that is derived from a naturally occurring soil bacterium, and is effective on several classes of insects, especially Lepidoptera larvae. Spinosad consists mainly of a mixture of spinosyns A and D and is registered for uses on a variety of crops in many countries including China. In order to understand the residue behavior of spinosad and to evaluate the dietary risk of spinosad residue in food in China, a number of residue studies were conducted on cotton, Chinese cabbage and eggplant. Residue detection methods using high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection have been validated for the detection of spinosad and its metabolites in cotton, Chinese cabbage and eggplant. The proposed definition of the residue for the estimation of spinosad dietary intake is the sum of spinosyns A and D. According to existing Chinese residue studies, the Supervised Trials Median Residues (STMRs) for cotton seed, Chinese cabbage and eggplant were less than 0.010, 0.103 and 0.045 mg/kg, respectively. Daily intake of spinosad residue in food was calculated by multiplying the pertinent Chinese food consumption data with the STMRs. Establishment of spinosad acceptable daily intake (ADI) of 0-0.02 mg/kg bw was based on a No Observed Adverse Effect Level (NOAEL) of 2.4 mg/kg bw per day and a 100-fold safety factor. Therefore, only 2% of the spinosad ADI is occupied by spinosad dietary daily intake in the Chinese population. The proposed maximum residue limits (MRLs) for spinosad on cotton seed, Chinese cabbage and eggplant are 0.01, 2 and 0.5 mg/kg, respectively. Although the STMRs for cotton and Chinese cabbage are lower or equal to STMRs used by Codex, no STMR for eggplant was used by Joint Meeting on Pesticide Residues (JMPR) when dietary risk assessment was carried out for spinosad. If these Chinese residue studies were considered during the Codex risk assessment process, the International Estimate Daily Intakes (IEDIs) of spinosad in the five Global Environment Monitoring System (GEMS) regional diets would be 2-30% of the ADI (0-0.02 mg/kg bw). In conclusion, spinosad is unlikely to pose any public health issues not only in China but also in global community, if it is applied according to the good agriculture practices (GAPs) established by each countries.

This study was carried out to assess the risk of lambda-cyhalothrin to aquatic organisms used in paddy field, and to provide assistance in the ecological risk management of lambda-cyhalothrin. The acute toxicities of five individual formulations of lambda-cyhalothrin to four aquatic species were investigated in the laboratory, as well as in a simulated paddy field-pond ecosystem, and the results implicated that lambda-cyhalothrin is highly toxic to fish, and to a greater extent to shrimp. There were differences in the toxicities to each aquatic organisms among different formulations. lambda-Cyhalothrin degraded rapidly in the environment, with half-lives of different formulations in paddy field water (0.23-0.53 days), pond water (0.38-0.63 days), and paddy field soil (0.96-7.35 days), respectively. The water overflow from the paddy field following a simulated rainstorm 12h after application of lambda-cyhalothrin did not cause injury to fish, clam or crab, but was severely hazardous to shrimp. Additionally, no injury to shrimp was found when simulated overflow occurred 4 days after application. These results suggest that the environmental risk of lambda-cyhalothrin to aquatic organisms can be reduced by (1) developing a relatively safe formulation such as a suspension concentrate, and/or (2) controlling the drainage time of the paddy field.