Biodegradable microplastics exacerbate the risk of antibiotic resistance genes pollution in agricultural soils

The widespread emergence of antibiotic resistance genes (ARGs) poses a severe global health threat, exacerbated by agricultural practices such as fertilization and plastic mulch use. While biodegradable plastics are promoted as environmentally friendly alternatives to conventional plastics, their ecological impact on soil ARGs remains poorly understood. This study conducted incubation experiments using soils with distinct long-term fertilization histories (no fertilization CK, chemical fertilizer CF, and pig manure PM) collected from 14-year field experiment sites at Changshu National Agro-Ecosystem Observation and Research Station. The soils were exposed to four types of microplastics (conventional: polyethylene [PE] and polyvinyl chloride [PVC]; biodegradable: polylactic acid [PLA] and polybutylene adipate terephthalate [PBAT]), and the ARGs and mobile genetic elements (MGEs) were quantified using high-throughput quantitative PCR, targeting 329 ARG subtypes and 34 MGEs. Results revealed that PM soil exhibited the highest ARGs abundance, and exposure to biodegradable microplastics (PLA and PBAT) further enriched ARGs by 21.5 % and 47.9 %, respectively. Microplastic exposure enhanced horizontal gene transfer potential by strengthening ARG-MGE co-occurrence, and altered bacterial communities by promoting the proliferation of generalist taxa (e.g., Proteobacteria) identified as key hosts of risk ARGs. These findings challenge the assumption of biodegradable plastics as environmentally friendly, demonstrating their potential to exacerbate ARGs pollution in agricultural soils. This study provides critical insights into the interactive effects of fertilization and microplastic exposure on the soil resistome, with implications for plastic management and ARGs risk control in agroecosystems.