Medical facemask waste alters detritus decomposition and fungal communities in a freshwater pond

Plastic pollution is an ongoing issue in freshwater ecosystems, including that generated from the spike in disposable facemask use during the COVID-19 pandemic. The degradation products of such plastic waste, including plastic leachate compounds and generation of microplastics, have the potential to affect freshwater ecosystem structure and function. We investigated the effects of facemask-derived polypropylene particles of different sizes and their leachates on fungal communities and detritus decomposition in a pond. We further investigated effects of the presence of wood shavings, used to represent a naturally-occurring, highly refractory, organic reference material. Over five weeks, leaf litter mass loss and cotton cellulose tensile strength loss were quantified weekly, and fungal biomass, community composition, and functional gene abundance at two time points. Wood shavings reduced leaf decomposition (-4.4%) relative to controls, while plastics increased decomposition of labile cotton cellulose (+ 6.6%), with the strongest effect from unleached microplastics (+ 22.7%). After 21 days, litter-associated fungal biomass was reduced by the presence of wood shavings (-20.1%) and plastics (-8.6%). Fungal communities differed between wood- and control treatments, and varied widely under plastic exposure. Our findings highlight size- and leachate-dependent effects of facemask-derived plastic particles on freshwater fungal communities and ecosystem functions, which largely contrasted with those of wood.