Acetochlor promotes the aging of mulch-derived microplastics in soil by altering the plastisphere microbial community

Although many studies have already highlighted the effects of mulch-derived microplastics (MDMPs) on adsorbing and spreading organic pollutants, the ecological risks of MDMPs co-contaminated with herbicide and the interaction between them have not been clarified. In this study, the interactions between MDMPs from virgin and aged low-density polyethylene (LDPE) films and the herbicide acetochlor in soil were investigated by microcosmic experiments. Results showed that acetochlor in soil was significantly enriched on the surface of MDMPs, with higher concentration on aged-MDMPs compared to virgin-MDMPs. Acetochlor significantly accelerated the fragmentation of aged-MDMPs, leading to more oxygenated functional groups and promoting biofilm development. Acetochlor also notably altered plastisphere microbial community, with Pseudomonas dominating for an extended period in acetochlor-treated samples. This suggests that Pseudomonas may facilitate the aging of MDMPs, likely due to its dual ability to degrade both acetochlor and polyethylene. Additionally, acetochlor initially increased microbial diversity and interaction complexity in the plastisphere, but decreased them in later phase, resulting in a more specialized community. These findings reported here broaden our understanding of interactions between MDMPs and herbicide in soil and offer insights for improved farmland management practices.