Traditional and biodegradable plastics host distinct and potentially more hazardous microbes when compared to both natural materials and planktonic community

Microplastic particles are persistent micropollutants that provide a substrate for the growth of bacterial biofilms, posing a threat to the environment. This study explores the changes in commercially available food containers made of conventional (polypropylene PP, polyethylene terephthalate PET), innovative biodegradable (Mater-Bi) and natural (wood and cellulose) materials, when introduced in the surface waters of Lake Maggiore for 43 days. Spectral changes revealed by FT-IR spectroscopy in PET and Mater-Bi, and changes in thermal properties of all human-made material tested indicated a degradation process occurred during environmental exposure. Despite similar bacterial richness, biofilms on PET, PP, and Mater-Bi differed from natural material biofilms and the planktonic community. Human-made material communities showed a higher proportion of potential pathogens, with PET and PP also exhibiting increased abundances of antibiotic resistance genes. Overall, these findings stress the need for dedicated strategies to curb the spread of human-made polymers in freshwaters, including innovative materials that, due to their biodegradable properties, might be perceived less hazardous for the environment. Microplastic particles (MPs) are massively discharged in aquatic ecosystems, posing risks to animals and, potentially, to humans. In addition to their intrinsic properties, MPs can possibly serve as a refuge for allochthonous antibiotic-resistant and pathogenic bacteria, making them further concerning not only as chemical but also as microbiological emerging pollutants. The role of MPs in the spread of pathogens and antibiotic resistance genes in freshwaters is far from being assessed. This study aims to improve our understanding of whether and how MPs facilitate the persistence and possible dissemination of pathogenic bacteria within freshwater microbial communities.