Study On The Stereoselective Environmental Behaviors Of Phenylpyrazole Chiral Pesticides In Aquatic Organisms And Pollution Remediation

Pesticides are routinely applied for agricultural, industrial, and home use to control or prevent invasive insects, diseases, and unwanted plant growth. For the last two decades’pesticide use has been increasing for the high productivity in agriculture About thirty percent of known registered pesticides are chiral including the most frequently used pyrethroid insecticides, phenoxypropionic acid herbicides and organophosphorus insecticides and so on. Most of chiral pesticides have been applied to agriculture as racemic forms. Flufiprole and Fipronil is phenylpyrazole insecticide developed by Aventis, which has been used for control against a wide range of soil and foliar insects, such as rice grasshoppers, rice skippers, vine weenil, termites and black ants in agriculture, forestry and urban environmentsThe chiral separation of two chiral metabolites enantiomers of fipronil,RPA200766 and MB200761 was performed on (R, R) Whelk-O1 chiral column (pirkle type), CHIRALCEL OD-H chiral column, CHIRALPAK IB chiral column by high-performance liquid chromatography (HPLC). Chromatographic conditions such as mobile phase composition and column temperature were optimized. The thermodynamic parameters such as entropy and enthalpy were calculated based on the van’t Hoff equation. Baseline separation was obtained with both metabolites enantiomers under optimized chromatographic conditions.Three kinds of freshwater organisms as well as alga were employed to evaluate the aquatic toxicity of flufiprole, fipronil and metabolites. The acute toxicity of flufiprole and fipronil shows a certain degree of enantioselectivity:for 4 species of alga, the acute toxicity of R-form is higher than that of S-enantiomer; on the contrary, the toxicity of R-form to Anodonta woodiana and loach was lower than its antipode. The toxic of metabolites was higher than parent compound.To examine the influence of the microorganisms in the sediment on transformation, two water-sediment ecosystems were designed:water with natural sediment (WS1) and water with sterile sediment (WS2). In the water-sediment ecosystem (WS1), the half-life of fipronil in water was approximately 11.8 days, and about 62% degraded during the total exposure period of 90 days. The EF values in water changed gradually from the initial 0.49 to 0.44 after 90 days. In the sediment, a rapid distribution of fipronil during the first 16 days was found, and the highest concentration of fipronil detected in the sediment was 86.5 ng g-1, after that, a decline tendency was observedIn the water-ssdiment-L.minor-A.woodianas ecosystem, the half-life of fipronil in the water was determined to be approximately 4.6 days and more than 90%loss were observed after a total exposure period of 90 days. It was the best ecosystem for the remediation fipronil residue in water because of a combination contribution of sediment, L.minor and A,woodianas. EFs in water increased from 0.5 to 0.55 showing slight enantioselectivity. In the sediment, a rapid distribution of fipronil during the first 7 days was observed, and the highest concentration reached 106 ng g-1 at days 21. The EF was 0.57 at the end of the exposure, which was lower than that in WS1. The possible reason was that A.woodiana released S-fipronil into sediment. Fipronil was also accumulated in L.minor, and approximate 9.2 ng g-1 of fipronil was detected after 7 days exposure. EFs in L.minor increased from the initial 0.49 to 0.72 at the 11th day, and after that, the EFs gradually indicating a significant in L.minor. In A.woodiana, fipronil was accumulated reaching a maximum concentration 214 ng g-1 at the 21th day. Thereafter, it gradually declined. Eventually, the concentration decreased to 30 ng g-1 at the end of the experiment. It was found S-fipronil was preferentially accumulated and R-fipronil was degraded by A.woodiana, with EF values of 0.35 at the end of the exposure..The enantioselective bioaccumulation and elimination of fipronil in Anodonta woodiana (A.woodiana) and loach were studied and the main metabolites fipronil desulfinyl, fipronil sulfide and fipronil sulfone were determined. In the bioaccumulation process, fipronil in A.woodiana and loach reached equilibrium after 11 days and the enantiomeric fraction (EF) values showed that the bioaccumulation was enantioselective with enantioenrichment of S-fipronil. The degradation of fipronil in A.woodiana and loach fitted first-order kinetics model with half-lives of the enantiomers were 5.8 d for R-fipronil and 7.6 d for S-fipronil, and the EF values decreasing from 0.5 gradually indicating the R-enantiomer was preferentially degraded. The degradation of single enantiomers was also performed and the results revealed a fast conversion of R-fipronil to S-fipronil by A.woodiana. The three metabolites were all detected in A.woodiana-water system, in which fipronil sulfone and fipronil sulfide had higher concentration levels. According to the 72-h LC50 values, S-fipronil was much more toxic than the racemate and R-fipronil. Moreover, the metabolites were more toxic than the parent fipronil. The results suggested the individual enantiomers of chiral pollutants and the metabolites should be considered in the risk assessments..The adsorption of flufiprole and fipronil by biochar were determined. The results showed that biochar displayed a good effect of removed the flufiprole and fipronil in water. The toxicity of flufiprole and fipronil against loach by biochar were also studied. The results revealed the biochar could decrease the toxicity of flufiprole, fipronil and metabolites. The potential risks of fipronil and the metabolites on the aquatic system warrant further research and the environmental risk assessment should take the enantioselectivity into consideration.