Enantioselective Bioaccumulation And Toxicity Effects Of Several Chiral Pesticides On Scenedesmus Obliquus And Rana Nigromaculata Tadpoles

Pesticides play an important role in repelling pests, preventing disease and guaranteeing grain security on agriculture. However, the abuse of pesticides leads to environmental pollution and pesticide residue, which threatens the ecosystem and human health seriously. In the process of production or use, chiral pesticides can enter into aquatic ecological system causing toxic effect on aquatic organisms. And the enantiomers may exhibit different environmental behaviors during their absorption, transport, and degradation processes. Therefore, the study of chiral pesticides environmental behaviors on enantiomer level can help to evaluate environmental safety of chiral pesticides more accurately and reliably, provide basic theory for solving problems of aquatic ecological system caused by pesticides,and it plays an important role in protecting the environment. Previous toxicology research on the aquatic ecosystem shows that algae and amphibians are very sensitive to poison in water, and they are easy to artificial cultivation, which have been designated as indicator organisms for aquatic system bioassays. As primary producers in the food web, algae is the first step for pesticide entering into the food web. And because algae has a greater specific surface area, it can be easier to enrich pesticide, so study the effects of pesticides on the algae is an important part of the study of pesticides influence on high trophic level and even the human beings. Development and metamorphosis of tadpoles is very similar with other vertebrates in utero pregnancy development, hence study the effects of pesticides on tadpoles can be used to estimate pesticide effects on humans and other vertebrates. In the present work, we selected seven chiral pesticides as research objects, measured the differences in toxicity and biochemical impacts of their individual enantiomers in Scenedesmus obliquus and Rana nigromaculata tadpoles, studied their bioaccumulation and degradation behaviors in the experimental organisms. Furthermore, we studied the bioaccumulation and degradation behaviors of the enantiomers in food chain of algae-tadpole, and evaluated the risk of chiral pesticides for ecological environment.In the studies of enantioselective behaviors of chiral pesticides in Scenedesmus obliquus, we exposed the algae to chiral fungicides benalaxyl, hexaconazole, triadimefon and its metabolite triadimenol respectively, results showed that toxicity of enantiomers of benalaxyl, triadimenol and hexaconazole are different, and the enantiomers performed different effects on chlorophyll content, SOD and CAT activities and MDA content. Experiments further indicated that S-benalaxyl was preferentially degraded and the more toxic enantiomer resude in the algae, resulting potential toxicity of scenedesmus. For triadimefon,the R-enatiomer was preferentially degraded in the algae, resulting more less toxic1S2S-triadimenol as transformation.In the studies of enantioselective behaviors of chiral fungicides benalaxyl, triadimefon and its metabolite triadimenol, chiral insecticides alpha-cypermethrin and fipronil, chiral herbicide metolachlor in Rana nigromaculata tadpole, results showed that cis-cypermethrin was highly toxic to tadpoles and its enantiomers can affect the growth rate of the tadpoles. Fipronil performed medium toxicity on tadpoles and it can cause apparent deformity. Other pesticides were slightly toxic to the tadpoles. The enantiomers performed different effects on MDA content, and SOD, CAT and GST activities. And results further indicted that tadpoles were preferentially bioaccumulated lR,2S-triadimenol and R-(-)-fipronil rather than their respective enantiomers during the exposed experiment. That more toxic enantiomer resdue in the tadpoles may lead to high potential chronic poisoning effects.According to the results of algae and tadpole studys above, we choose three chiral pesticides benalaxyl, triadimefon and fipronil exposed to the organisms to study their enantioselective behaviors in the food chain, measured their enntioselective bioaccumulation and degradation behaviors. Results showed that algae exposed to pesticide was more potential to accumulate the pesticides, and ingested by tadpoles do not performed biological maginification effect, but ingestion is an important role of pesticides enrichment in tadpoles. Pesticides may influence the higher trophic organisms through the food chain. Benalaxyl enantiomers perform opposite enantioselectivity in Scenedesmus obliquus and Rana nigromaculata tadpoles bioaccumulation. Fipronil enantiomers residue in algae almost the same, but enantioseletively bioaccumulated in tadpoles. These results indicated that different organisms may have different capacities to absorb and metabolize chiral pesticides. Above studies can provide some reference data for environment safety and human health risk assessment of these pesticides.