Adsorption of the antimicrobial triclosan to microplastics impacts biofilm and planktonic microbial communities in freshwater

Microplastics (MPs) are ubiquitous contaminants in freshwater ecosystems that could be hotspots for the interaction of antimicrobial compounds and surface-attached microbial biofilm communities. MPs and antimicrobials are both common in wastewater and urban freshwaters and MPs can adsorb contaminants like antimicrobials to their surface. Within aquatic habitats, MPs also support colonization by microbial biofilms. Therefore, we hypothesized that the adsorption of antimicrobials to MP surfaces would affect microbial communities colonizing MPs, altering their diversity, composition, and antimicrobial resistance. Using a microcosm approach, we assessed the potential for MP fibers to adsorb the common antimicrobial compound triclosan and alter bacterial and algal communities in MP-associated biofilms and in the surrounding water. We exposed acrylic, nylon, and polyester MP fibers to triclosan and measured its adsorption to each, finding that polyester adsorbed the most triclosan (3674 μg g-1) and nylon the least (217 μg g-1). Microcosms containing triclosan-exposed or control fibers of each polymer type were incubated in the lab with water from the Chicago River for 30 days. Analysis of MP-attached and planktonic bacterial and algal communities via high-throughput amplicon sequencing determined that exposure to triclosan significantly changed the taxonomic composition of these communities. These results suggest that widespread MP and triclosan contamination could potentially alter bacterial and algal communities in freshwater habitats. We also used quantitative polymerase chain reaction (qPCR) to measure the abundance of the class 1 integrase gene intI1 as a proxy for the impact of triclosan on resistance, finding no significant difference in intI1 abundance according to triclosan exposure.