Microplastics inhibit oxytetracycline degradation in soils: Insights into biofilm-enhanced adsorption and microbial community shifts

Microplastic (MP) pollution and antibiotic contamination are increasingly recognized as global environmental challenges. However, the mechanisms by which microplastics (MPs) influence oxytetracycline (OTC) degradation in soil remain poorly understood. This study examined the effects of MPs on OTC degradation in organic fertilizer-amended paddy soil using microcosm incubations, MP biofilm cultivation, and adsorption experiments. Results showed that polyethylene (PE) and polylactic acid (PLA) MPs significantly inhibited OTC degradation, lowering degradation rates by 11.1 %-20.2 %. Adsorption isotherms followed the Freundlich model, with biofilm-associated MPs exhibiting K values 7.52-8.23 times higher than those of pristine MPs. In adsorption kinetics, biofilm formation increased the equilibrium adsorption capacity of MPs for OTC by 5.52-6.53 times. Polylactic acid addition (1.50 %) selectively enriched Kitasatospora and Actinoallomurus, increased the abundance of aerobic and Gram-positive bacteria, and reduced bacteria with Gram-negative traits or potential pathogenicity. These microbial shifts further suppressed OTC degradation in soil. Collectively, our findings demonstrate that MPs hinder OTC degradation in paddy soils and may intensify environmental risks by enhancing antibiotic adsorption and reshaping soil microbial communities.