Stereoselective degradation pathway of amide chiral herbicides and its impacts on plant and bacterial communities in integrated vertical flow constructed wetlands

This study demonstrates the stereoselective degradation patterns and biodegradation mechanisms of metolachlor (MET) and napropamide (NAP) in integrated vertical flow constructed wetlands (IVCW). The higher interphase transferability of NAP resulted in higher degradation rates of 90.60 +/- 4.09%. The enantiomeric fraction (EF) values of 0.38 +/- 0.02 and 0.54 +/- 0.03, respectively, recorded for the enantiomers S-MET and R-NAP, with higher herbicidal activities, demonstrated their highly selective biodegradation patterns. The antioxidant enzyme activities and fluorescence parameters of plants showed positive correlations with the degradation efficiency and enantioselectivity of MET and NAP. Adaptive regulations by plants promoted the proliferation of microbial genera like Enterobacter and unclassified_Burkholderiales, which could facilitate plant growth. Moreover, enrichment of the herbicide-degrading functional bacteria Terrimonas (5.10%), Comamonas (4.05%) Pseudoxanthomonas (4.49%) and Mycobacterium (1.42%) demonstrably promoted the preferential degradation of S-MET and R-NAP. Furthermore, the abundance of Ferruginibacter favored the use of R-NAP as carbon source to achieve co-removal of R-NAP and NO3--N.

Automated summary

This study reveals the stereoselective degradation patterns and biodegradation mechanisms of metolachlor and napropamide in integrated vertical flow constructed wetlands. The higher interphase transferability of napropamide leads to higher degradation rates, while the enantiomers of metolachlor and napropamide demonstrate highly selective biodegradation patterns. The antioxidant enzyme activities and fluorescence parameters of plants are positively correlated with the degradation efficiency and enantioselectivity of the pesticides. Adaptive regulations by plants promote the growth of microbial genera and the enrichment of specific herbicide-degrading bacteria, facilitating the degradation of the pesticides. The presence of Ferruginibacter contributes to the co-removal of napropamide and NO3--N.