Agricultural films derived microplastics intensify acetochlor toxicity on soil health

Herbicide acetochlor (ACT) is widely used in agricultural production, but it remains unclear whether microplastics (MPs) from agricultural films exacerbate its harmful effects on soil health. Here, a microcosm cultivation experiment was conducted to investigate the impacts of PE (Polyethylene)-MPs and PBAT (polybutylene adipate terephthalate)-MPs with ACT (MPs/ACT) on soil health. Results showed that MPs/ACT treatment caused soil acidification, depletion of organic carbon and ammonium, altered enzyme activities, and influenced greenhouse gas emissions compared to ACT alone. MPs/ACT co-exposure also restructured microbial communities, reducing alpha diversity, increasing co-occurrence network complexity, enriching putative contaminant degraders, and enhancing the relative abundance of key nitrogen-cycling genes, enzymes, and carbon-cycling genes. Notably, PBAT/ACT stimulated nitrification-denitrification processes more than PE/ACT, indicating polymer-specific effects on soil nutrient cycling. Overall, MPs/ACT decreased soil health by 8.89 % - 14.63 %, greater than 8.39 % caused by ACT alone. These results demonstrate that MPs exacerbate the toxic effects of ACT on soil health. Mitigation strategies, such as reducing MP inputs, optimizing herbicide use, and incorporating biochar or microbial amendments, may help to restore soil health and maintain ecosystem stability. This study provides critical insights into the compounded impacts of MPs and herbicides on soil ecosystems.