Dinotefuran Enantiomers: Enantioselective Toxicities To Honeybees And Degradation Behaviors In Cucumber And Soil

Enantiomers of chiral pesticides are usually treated as the same compound in traditional researches.However, enantiomers of chiral pesticides may exhibit significant differences in the chiral circumstance.Thus, the traditional researches about chiral pesticides may have certain limits to some extent.Dinotefuran is a novel insecticide which belongs to the third generation of neonicotinoids. It has a chiralcarbon atom and consists of two enantiomers. In order to provide more accurate information for theenvironmental risk assessments of dinotefuran, a series of researches at the level of enantiomers werecarried out in this paper. The main results are as followed.1. Dinotefuran enantiomers were excellently separated by normal-phase HPLC and the elutionorder of the two enantiomers were determined by the online optical rotation detector. The first elutedenantiomer was (+)-dinotefuran and the second eluted one was (-)-dinotefuran. Moreover, a chiralresidue analytical method was established in six kinds of food and environmental matrices. The linearity,accuracy, precision and sensitivity of the method were also investigated. The results showed excellentlinearity of the method with all the R2>0.999. And the average recoveries of dinotefuran enantiomerswere ranging from75.8%to99.4%, with the relative standard deviations of the intra-day and inter-daylower than16.5%. The LOQs were from0.025to0.087mg/kg in different matrices which were muchlower than the current established MRLs.2. The chiral stability of dinotefuran enantiomers were investigated in several organic solvents andpure water. The results showed that dinotefuran enantiomers were configuration stable under the testconditions. No conversion of the enantiomers was observed. Dinotefuran enantiomers showed noobvious degradation under dark and natural light in room during the whole incubation process. However,under the artificial Xenon light (4000lux), dinotefuran enantiomers were fast degraded in organicsolvents and pure water with the half-lives ranging from1.29-3.1h. And there was no enantioselectivitybetween the degradation of dinotefuran enantiomers.3. The acute toxicities of the racemate and two enantiomers of dinotefuran were assayed in thisresearch. Significant enantioselectivity was observed in the acute toxicities of dinotefuran enantiomersto honeybees. In the contact assay, the LD50was0.040、0.021、3.064μg/bee for rac-,(+)-,(-)-dinotefuran. In the oral assay, the LC50was0.322、0.127、4.977mg/L or rac-,(+)-,(-)-dinotefuran.The toxic potency of rac-,(+)-,(-)-dinotefuran was consistent in the contact and oral tests. The toxicorder was (+)-dinotefuran> rac-dinotefuran>(-)-dinotefuran. The acute contact toxicity of(+)-dinotefuran was about145.9times more toxic than its antipode and about2times higher than theracemate. In oral assays,(+)-dinotefuran was about39.1times more toxic than (-)-dinotefuran and15.5times than the racemate.4. Enantioselective degradation of dinotefuran enantiomers were investigated in cucumber and soil.Effect of different application modes of the dinotefuran formulation on the degradation in cucumber wasalso studied. The results showed that enantioselectivity was observed in the degradation process both in cucumber and soil with (-)-dinotefuran preferentially degraded and (+)-dinotefuran more persistent. Andthe half-lives of dinotefuran enantiomers were much longer in soil than in cucumber. One-way ANOAresults showed that the half-lives of enantiomers in cucumber were not significantly different, while insoil the difference was significant.