Can Microplastics from Personal Care Products Affect Microbial Decomposition of Plant Litter in Streams? An Insight to the Mixed Effects of Microplastics and Silver Nanoparticles

Microplastics (MPs) are emerging contaminants of a great concern due to their abundance and persistence over time in aquatic environments. However, studies on their impacts on freshwater organisms are scarce. In resemblance, silver nanoparticles (Ag-NPs) are incorporated into textiles and personal care products and are also classified as emerging contaminants. We used the plant litter decomposition model system to investigate the effects of MPs from commercially used personal care product, alone or in mixture with Ag-NPs, on the diversity and activities of aquatic microbial decomposers. We exposed stream microbial communities associated with plant litter to increasing concentrations of MPs (polyethylene extracted from a personal care product; 100 µg L -1 to 1 g L -1 ; 5 levels) for 27 days in the absence or presence of Ag-NPs (0.1 mg L -1 and 1 mg L -1 ). The exposure to MPs, alone or in mixture with Ag-NPs, decreased the activities of aquatic fungi and plant litter decomposition. Mixtures of MPs with Ag-NPs (at higher concentrations) had stronger impacts on enzymatic activities and sporulation of fungal communities. The community structure of sporulating fungi changed under exposure to increasing concentrations of MPs; moreover, the shifts in fungal community were more pronounced in the mixtures with Ag-NPs at the highest exposure concentration. Also, species richness and diversity of aquatic fungal spores were negatively affected by increasing concentrations of the contaminants. Our study provided evidence of the potential harmful effects of MPs, alone or in mixtures with Ag-NPs, on the activities of aquatic fungi and on a key ecosystem process, determinant to organic matter turnover in streams.