Unveiling Mixed Microplastics and Organic Contaminants of Different Classes Affection: Dual-Phase Partitioning and...

Microplastics (MPs) act as vectors for organic contaminants, but how polymer type, size, and pollutant hydrophobicity jointly steer biodegradation remains unclear. Here, triclosan (TCS, a hydrophobic antimicrobial, log K_ow ∼ 4.8) and sulfamethoxazole (SMX, a hydrophilic antibiotic, log K_ow ∼ 0.89) were selected owing to their distinct nature and were spiked at low and high concentrations into batch systems containing polyethylene (PE) or polypropylene (PP) MPs (10 and 50 μm). At low levels, both pollutants were rapidly biodegraded (>95%), irrespective of MPs. At high levels, TCS was strongly sorbed, lowering aqueous bioavailability and inducing dense biofilms on PP-10 μm that enriched Enterobacteriaceae and Pseudomonas, yet degradation slowed to 24-32%. For hydrophilic SMX, MPs served as extra colonizable surfaces, with PP-10 μm boosting the removal to ∼70%. Sorption kinetics confirmed faster TCS uptake on smaller, moderately polar PP-MPs compared to SMX. Physiochemical analysis of MPs revealed pronounced surface oxidation and cracking, especially on PP-10 μm, correlating with enriched plastic degraders. In-depth microbial analysis identified Gammaproteobacteria as TCS biomarkers and Alphaproteobacteria for SMX. Overall, MPs act as conditional regulators: enhancing biodegradation at realistic doses, but at high concentrations, PP-10 μm becomes a potent sink and microreactor, retarding TCS degradation yet accelerating its own weathering.