The Degradation By Microorganism And Earthworm Detoxification Mechanism Of Typical Chiral Amide Fungicide Mandipropamid

The substantial and frequent application of fungicides in agricultural production has led to the persistent residues in soil,causing serious threats to the soil ecological environment.The soil microbial degradation and the detoxification metabolisms of soil animals have important implications for fungicidepolluted soil remediation.In this study,a typical amide chiral fungicide,mandipropamid,was selected as the target compound.According to its recommended use dose and application frequency,the degradation characteristics of both the mandipropamid enantiomers and the changes in the potential degradative microbial bacteria were studied in the eight repeated treatments with mandipropamid enantiomers.At the same time,the detoxification metabolisms of earthworms to mandipropamid enantiomers were investigated in artificial soil.The main results are as follows:1.The mandipropamid enantiomers were separated using the high-performance liquid chromatography method.The residual analysis of mandipropamid enantiomers in natural soil,artificial soil,and earthworms was established using a Qu ECh ERS-UPLC-MS/MS detection.2.With increasing treatment frequency and intial concentration,the degradation half-life of mandipropamid in soil increased significantly.Besides,the R-enantiomer is preferentially degraded in non-sterilized soil.Specifically,the degradation half-lives of mandipropamid are 10.4-101.9 d(Racmandipropamid),10.2-79.2 d(R-mandipropamid)and 10.4-130.5 d(S-mandipropamid),respectively.3.Repeated treatments of mandipropamid enantiomers significantly changed the soil microbial community.Compared to the S-enantiomer treatment,the relative abundances of Proteobacteria in the Renantiomer treatment significantly increased,and its relative abundances showed a significant upward trend with increasing treatment frequency and initial concentration.Nine bacterial genera were identified as the potential degradative bacteria associated with the degradation of both the enantiomers at the genus level,which might be the main reason for the preferential degradation of mandipropamid enantiomers in soil.The relative abundances and increased rates of the six potential degradative bacteria genera,Burkholderia,Paraburkholderia,Hyphomicrobium,Methylobacterium,Caballeronia and Ralstonia,in soil treated with R-enantiomer were significantly higher than those in soil treated with S-enantiomer;the relative abundances and increased rates of the three potential degradative bacteria genus,Haliangium,Sorangium and Sandaracinus,in soil treated with S-enantiomer were significantly greater than those in soil treated with R-enantiomer.4.Repeated treatments of mandipropamid enantiomers significantly changed the soil microbial community functional diversity.The relative abundances of six microbial metabolic pathways,Cell motility,Cellular community-prokaryotes,Membrane transport,Signal transduction,Xenobiotics biodegradation and metabolism,and Environmental adaptation,at the level 2 increased by 0.9%-70.9%(R-enantiomer treatment)and 0.5%-54.8%(S-enantiomer treatment)compared to the control treatment,respectively.Moreover,the relative abundances of these six microbial metabolic pathways increased with increasing treatment frequency and initial concentration.Furthermore,the contribution percentages of the dominant bacteria Burkholderia,Paraburkholderia,Hyphomicrobium and Methylobacterium to these six microbial metabolic pathways in soil treated with R-enantiomer were greater than those in soil treated with S-enantiomer;the contribution percentages of the dominant bacteria Haliangium to these six microbial metabolic pathways in soil treated with R-enantiomer were lower than those in soil treated with S-enantiomer.5.No significant difference was found in the degradation of mandipropamid enantiomers in artificial soil.However,the accumulated residues of enantiomers in earthworms showed significant difference as the accumulation rate of S-enantiomers(0.054 mg/(kg?d))was significantly higher than that of Renantiomer(0.049 mg/(kg?d)).The three main detoxification enzymes in earthworms exhibited different detoxification activities to mandipropamid enantiomers.The activities of carboxylesterase and cytochrome P450 increased significantly,while the activity of glutathione transferase was inhibited,and the effect of S-enantiomer was significantly greater than that of R-enantiomer.The transcriptome sequencing results revealed that many detoxification and metabolism pathways such as bile secretion metabolic pathway were significantly enriched after exposure to both the mandipropamid enantiomers.The results of expression trends of related functional genes in earthworms using the q RT-PCR were consistent with the transcriptome sequencing results.The results above indicated that earthworms showed different detoxification and metabolism to mandipropamid enantiomers by regulating the expression of detoxification related functional genes and the detoxification metabolism-related pathways as well as by altering the different detoxification enzyme activities.