The Metabolic Behavior Of Benalaxyl Enantiomers In Aquatic Environment

As a chiral fungicide, benalaxyl has been widely used on cucumber, tomato, tobacco and many other vegetables and fruit crops to control downy mildew, early blight, and late blight. It has a series of advantages such as high efficiency, low toxicity and long effective period, so the use of benalaxyl is very large for many years. Because of its wide usage and relative long half-life period, benalaxyl could always be detected in the environment. A number of studies have been conducted to evaluate the enantioselective environmental behaviors on an enantiomeric level in soil, animals such as earthworm, rabbit and plants such as cucumber and tomato. However, benalaxyl can enter water system with rainfall, surface runoff and leaching, and then causing water pollution and affect the aquatic organisms. While, few researches have focused on the fate of benalaxyl in the aquatic system yet.In this paper, HPLC methods were developed for the direct enantioseparation of benalaxyl and its main metabolite of benalaxyl acid enantiomers. Residual methods for benalaxyl and its metabolite benalaxyl acid in water and sediment were established. Good linearities were obtained (R>0.99) and recoveries were79%-119%. The environmental behavior and stereoselectivity of the chiral fungicide benalaxyl and its chiral metabolite benalaxyl acid in water, sediment and water-sediment microcosm were studied. The influencing factors such as light and microorganism were also investigated. The results showed that the pollution period of benalaxyl for aquatic environment is long, and benalaxyl had half-lives more than21days in the microcosm system and the metabolite benalaxyl acid could exist in the microcosm more than70days. Benalaxyl was mainly transformed through microbial degradation and thus sediment microorganisms played major role for the dissipation of benalaxyl in the aquatic microcosm. Light could accelerate the degradation of benalaxyl in water indicating that photolysis was also a pathway for the dissipation of benalaxyl. Moreover, the stereoselective behavior of benalaxyl and benalaxyl acid was also investigated, too.(-)-Benalaxyl was preferentially degraded in the microcosm, and (-)-benalaxyl acid was preferentially formed in the microcosm.The paper supplies basis for the further research for effect of benalaxyl in the aquatic environment. Furthermore, the research provides necessary theoretical support for environmental risk of the use of benalaxyl.