Can nature-based biochar and biochar nanoparticles diminish the impacts of silver nanoparticles and microplastics on microbially-driven stream detrital ecosystem?

• Impacts of Ag-NPs and MPs on stream microbial decomposer communities were tested. • Ag-NPs and MPs reduced fungal diversity, reproduction, and leaf-litter decomposition. • Nature-based products (NBPs), biochar and biochar-NPs, did not show any ecotoxicity. • Biochar-NPs stimulated aquatic fungal reproduction and leaf-litter decomposition. • NBPs alleviated the adverse effects of Ag-NPs and MPs on stream detrital ecosystems. Elevated concentrations of emerging contaminants (ECs), such as silver nanoparticles (Ag-NPs) and microplastics (MPs), are of great concern to aquatic environments. These ECs are released into freshwaters due to improper waste management and may pose risk to freshwater biota and associated ecosystem processes. Conversely, biochar (BC) and biochar nanoparticles (BC NPs) are nature-based products (NBPs), reported to remove some contaminants from environmental samples, particularly soil. However, knowledge about their impacts on freshwater ecosystems, alone or in the presence of emerging contaminants, is lacking. We investigated the impacts of Ag-NPs and MPs (polyethylene) on stream-dwelling microbial communities involved in leaf-litter decomposition, as it is a key ecosystem process, sensitive to water quality. Also, the impacts of the nature-based products, BC and BC NPs, were assessed in the absence and presence of Ag-NPs or MPs. Both, Ag-NPs and MPs had negative effects on aquatic fungal communities, reducing reproduction, species richness, and altering species contribution, as well as on leaf-litter decomposition in a concentration-dependent manner. Neither larger particles nor nanoparticles of biochar showed any adverse effects on microbial decomposition at any of the concentrations, suggesting their eco-compatible nature in freshwaters; rather, BC NPs stimulated fungal sporulation and leaf-litter decomposition. Moreover, the presence of these NBPs attenuated the negative effects of the tested ECs in a concentration-dependent manner, with more pronounced effects against MPs. BC NPs showed greater alleviation efficiency than BC in aquatic ecosystems. This study emphasizes the importance of stream detrital ecosystem in ecotoxicological assessments and potential role of nature-based resources to deal with emerging contaminants.