Plastics in the environment are gradually fragmented into weathered debris distinguished from original plastics by the integrative action of influencing factors (e.g., UV light, heating and physical abrasion). As artificial carbon-source substrates in aquatic ecosystems, plastics are swiftly colonized by biofilms for growth and utilization. To investigate the influences of weathering of plastics on the colonized biofilms, and reveal the environmental fate of weathered plastics colonized by biofilms, freshwater from the Yangtze River (Nanjing, China) were collected for biofilm incubation. Denser biofilms with higher biomass and carbon metabolic capacity were observed on photoaged polyethylene plastics than those on original plastics. The effects of plastic surface properties on biofilm characteristics were revealed by the analysis of partial least squares regression (PLSR). Roughness was the principal influencing factor, while rigidity had the opposite effect to it. 16S rRNA gene high-throughput sequencing results indicated the high relative abundance of environmental and biological harmful microorganisms (e.g., Cyanobacteria, Flavobacterium) on photoaged plastics. The microbial functional profiles (KEGG) predicted by Tax4Fun showed that the functions (e.g., membrane transport, energy metabolism, etc.) of biofilm on photoaged plastics were dissimilar with those on original ones. These findings suggested that the distinct microbial community and the adverse functional changes in biofilms on photoaged plastics potentially enhanced their environmental risks. On the other hand, biofilms on original low-density polyethylene (LDPE) films were dominated by Exiguobacterium. The potentials of this microorganism in rapidly accommodating to a hydrophobic substrate and degrading plastics were both worthy of attention. Therefore, it is necessary to consider the weathering of plastics in exploring the environmental behavior of plastics and the "plastisphere", and to give further insights into the double-edged nature of the "plastisphere".

Impacts of weathering of polyethylene plastics on the colonized biofilms: The simulation in freshwater microcosms

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