Nanosized plastics are an emerging concern in freshwater ecosystems, raising the question whether they put freshwater ecological processes at risk. Litter decomposition is a major ecological function in forested streams which is mainly driven by aquatic hyphomycetes. Here we investigated whether increasing concentrations (up to 102.4 mg/L) of nanosized polystyrene plastics (NPPs; 100nm) affect litter decomposition by five widely distributed species of aquatic hyphomycetes. Results showed that average litter decomposition decreased by 8% relative to the control when exposed to 102.4 mg/L NPPs. Aquatic hyphomycete species differed in their sensitivity to NPPs. The greatest inhibition of litter decomposition was found with Tetracladium marchalianum, where it dropped from 37 (control) to 16% (102.4 mg/L of NPP). Overall our study highlights the emerging risks and potential dangers of NPPs to freshwater ecosystem functioning. It also indicates that the impact of NPPs may be species specific.
