Biodegradable and conventional microplastics as vectors of extracellular ARGs in WWTP effluents: Mechanistic and differential global health risk

Microplastics (MPs) in wastewater treatment plant (WWTP) effluents created a unique microenvironment for extracellular antibiotic resistance genes (eARGs) within extracellular DNA (eDNA). However, the micro-scale mechanisms governing the association of eARGs with biodegradable versus non-biodegradable MPs—and the resulting health risks—in WWTP effluents remained poorly understood on a global scale. In this study, the first comprehensive characterization of eARGs bound to biodegradable (polylactic acid, polyhydroxyalkanoates, and poly (butylene succinate)) and non-biodegradable (polyethylene, polystyrene, and polyvinyl chloride) MPs in WWTP effluents was presented, alongside an evaluation of the contributions of key environmental factors. The findings revealed that MPs selectively adsorbed eDNA fragments, with biodegradable MPs exhibiting markedly higher loading capacities. MPs underwent heterogeneous aggregation with effluent eDNA and low-molecular-weight environmental molecules via van der Waals interactions and hydrogen bonding; Ca 2+ and Mg 2+ ions further facilitated eDNA adsorption through cation bridging. Conversely, disinfection by-products, dissolved organic matter (DOM), and antibiotics (ANT) attenuated eDNA adsorption via steric hindrance. However, DOM and ANT could co-adsorb onto MP surfaces, indirectly amplifying the health risks of MP-associated eARGs. A global health risk assessment of eARG-laden MPs in WWTP effluents identified high-risk regions such as Morocco, Vietnam, Denmark, Portugal, South Korea, and India spanning Western, Central, and Southern Europe, Western Asia, and Africa. Therefore, while global efforts focus on restricting or banning non-biodegradable plastics and promoting biodegradable alternatives, the health risks associated with biodegradable MPs carrying eARGs should be a priority concern. Furthermore, the molecular-level mechanisms driving the association of eARGs with MPs elucidated in this study can provide theoretical foundations and references for the development of risk control technologies targeting the transmission of MPs and ARGs in WWTP effluents. • Attraction between MPs and eDNA mainly depends on hydrogen bonds and van der Waals • Ca 2+ and Mg 2+ promote MPs' eDNA carrying via bridging interactions significantly more • MPs indirectly carry abundant eDNA via heteroaggregation with dissolved organic matter • Compared with non-biodegradable MPs, biodegradable MPs carrying eDNA pose higher risk • MPs in WWTPs effluent with ARGs show a high total health risk index in W/S Europe, Asia, & Africa