The impacts of polystyrene microplastics on development, energy transfer and nutrient cycling of biofilms: A comprehensive chronic toxicity study

The escalating prevalence of microplastics (MPs) in aquatic ecosystems is anticipated to exert a significant impact on the growth and development of aquatic biota. Nonetheless, the current body of research on the mechanisms through which microplastics influence biofilm colonization in freshwater systems remains insufficiently elucidated. To address this research gap, we investigated the impact of polystyrene microplastics (PS-MPs) on biofilm growth and development, with a particular focus on their effects on functional metabolism in freshwater environments. Using controlled long-term experiments, we explored the influence of PS-MPs at concentrations of 1, 10, and 100 mg/L over 52 days on microbial community structure, alpha and beta diversity and functional potential. The results showed a concentration-dependent inhibition of biofilm biomass and chlorophyll a content, with the most severe reduction (43.5% in biomass, 31.4% in chlorophyll a) occurring at 100 mg/L PS-MPs. LDH activity, indicative of oxidative stress, significantly increased under PS-MPs exposure, especially during early biofilm development, suggesting acute cellular stress. In addition, PS-MPs likely disrupt carbon and nitrogen cycling within biofilms, as evidenced by the increased relative abundance of Pseudomonas and Cyanobacteria under high PS-MPs concentrations, indicating microbial community adaptation to environmental stressors. Functional prediction analyses further revealed altered expression in key metabolic pathways, such as those involved in antioxidant synthesis, nitrogen metabolism, and purine biosynthesis. The findings provide critical insights for understanding the ecological risks posed by MPs and underline the necessity of developing targeted strategies for pollution mitigation and ecological restoration in freshwater systems. • PS-MPs inhibits the growth and development of biofilms. • PS-MPs induced oxidative damage of biofilms. • PS-MPs change the colonization process of biofilms. • PS-MPs alter the species composition of biofilms • The toxicity of PS-MPs to biofilms is a form of chronic toxicity