Divergent impacts of conventional and biodegradable microplastics on pesticide fate and toxicity in a soil–chive system, underscoring a soil-plant-microbe disruption

Microplastics (MPs) and pesticides increasingly co-occur in agricultural soils, yet their combined effects on soil biology and plant–soil interactions remain poorly understood. Here we provide the evidence that biodegradable polylactic acid (PLA) MPs, despite their eco-friendly reputation, fundamentally reshape soil microbial and biochemical dynamics under pesticide stress. In a soil–chive system, PLA, but not conventional polyethylene (PE), significantly delayed iprodione (IPR) degradation (up to 7.7-fold), increased the persistence of its toxic metabolite 3,5-dichloroaniline (3,5-DCA), and enhanced plant uptake of 3,5-DCA (up to 59%). Mechanistically, PLA disrupted beneficial bacterial enrichment, altered microbial community composition, and interfered with plant detoxification pathways, notably glutathione metabolism and amino acid biosynthesis. These interactions intensified phytotoxicity, stunted plant growth, and reduced soil–plant resilience. Our findings reveal a previously overlooked ecological trade-off: biodegradable MPs can amplify pesticide risks by destabilizing soil microbial processes and stress-response mechanisms. This work advances understanding of how novel contaminants interact in soils and highlights the importance of integrating soil biological functions into sustainability assessments of alternative plastics.