Microplastics stimulating polycyclic aromatic hydrocarbon biodegradation via cometabolism in historically...

Microplastics (MPs) are widely documented to inhibit the biodegradation of various organic pollutants in artificially spiked soils; however, their influence in naturally aged, field-contaminated soils remains poorly understood. In this study, we investigated the effects of biodegradable and conventional MPs (BMPs and CMPs) on polycyclic aromatic hydrocarbon (PAH) biodegradation in an agricultural soil with 16-year coking contamination. After 90 days of incubation, both BMPs and CMPs significantly enhanced biodegradation of Σ16PAHs (the total 16 priority PAHs) by 31.5% and 8.7%, respectively, with BMPs showing 3.6-fold greater efficiency than CMPs. The enhanced PAH biodegradation was attributed to the enriched copiotrophic microbes (e.g., Actinobacteriota, Bacteroidota, and Ascomycota), the increased fungal alpha diversity, and the improved bacterial-fungal metabolic coordination. BMPs specifically promoted the biodegradation of low-molecular-weight PAHs by 36.3%, largely through enriching the bacterial genus Dongia, while both MP types comparably enhanced medium- and high-molecular-weight PAH degradation. Polyethylene MP-treated soil accumulated more released additives than polylactic acid MP-treated soil, confirming BMPs outperformed CMPs in promoting cometabolism with PAHs. Additionally, PAH biodegradation in BMP treatments showed lower reliance on microbial cooperative networks than it did in CMP treatments. These findings reveal the unexpected potential of BMPs as bio-stimulating agents for enhancing PAH degradation in historically contaminated soils.