Effects of biofilm formation on triclosan adsorption by UV-aged and pristine polystyrene microplastics in aquatic environments

• The biofilms increased the adsorption rate of triclosan but decreased the adsorption capacity. • Adsorption capacity of microplastics for triclosan is proportional to their hydrophobicity. • The adsorption of triclosan on biofilms was dominated by physical adsorption. • The dominant species of biofilm microorganisms were reduced by the presence of triclosan. Microplastics in aquatic environments are readily colonised by microorganisms to form biofilms facilitating the transport of contaminants and attached microbes. We examine the impact of biofilm formation on the physicochemical properties of microplastics and its subsequent effects on the adsorption of organic pollutants. Here, the adsorption of triclosan (TCS) onto polystyrene (PS) microplastics was investigated by comparing pristine PS (O-PS), UV-aged PS (A-PS), and their biofilm-colonised counterparts (O-PS bio and A-PS bio ). The results show that the adsorption rate of TCS by PS after aging decreased by 45 % without a significant effect on the adsorption capacity. The adsorption rate of TCS by the PS biofilm increased by 100 %, whereas the adsorption capacity decreased by 57 %. Based on 16S rRNA analysis, the diversity and richness of biofilm microorganisms were reduced in the presence of TCS, leading to a change in the dominant species of biofilm microorganisms. By accurately assessing the adsorption behaviour of organic contaminants on microplastic biofilms in the laboratory, this study contributes to a deeper understanding of the interactions between microplastics and organic contaminants in real aqueous environments and provides insights into the effects of TCS, as well as the integrated risk of organic contaminants.