Comparison of pristine and aged poly-L-lactic acid and polyethylene terephthalate as microbe carriers in surface water: Displaying apparent differences.

Microplastics (MPs) in water environment are potential carriers for many substances. In this study, pristine degradable poly-L-lactic acid (PLLA) and non-degradable polyethylene terephthalate (PET) MPs and their UV-aged counterparts were exposed to the Yuhangtang River (Y-River). The results showed that the surface morphology and structure of all MPs markedly changed after exposure. Oxygen-containing functional groups and hydrophilicity of aged MPs were higher compared with their pristine counterparts, and further increased after river exposure. The content of extracellular polymers (EPS) of biofilms on MPs increased with the exposure time, and was higher on aged MPs than on pristine ones. Similar results were obtained for most antibiotic resistance genes (ARGs) between pristine and aged MPs, and ARGs were positively related to pathogens. Dominant bacteria on all MPs were Proteobacteria (51.3 %-81.1 %), Chloroflexi (5.2 %-20.9 %) and Firmicutes (0.4 %-15.9 %), which markedly differed from the Y-River community. Aged MPs could enrich more microbes but relatively fewer bacterial species than pristine MPs, and higher enrichment and species diversity were observed on PLLA compared with PET. This study demonstrates that MPs are highly effective carriers for microbes, and the results provide valuable insights for evaluating the potential impact of bio-MPs on aquatic ecological environment.