Trophic transfer of microplastics in a model freshwater microcosm; lack of a consumer avoidance response

Microplastics are considered freshwater pollutants of emerging concern. Although microplastics have been identified in a range of taxa, only a limited number of studies have focussed on the trophic transfer of microplastics. The duckweed Lemna minor can act as a microplastic vector in a model freshwater food chain. Here we show for the first time scanning electron microscopy images of 1 μm polystyrene (PS) and 10–45 μm polyethylene (PE) microplastics adsorbed on L. minor surfaces. A feeding test and a novel feeding-choice test were designed to investigate microplastic transfer from freshwater plants to invertebrates. Both tests show that the freshwater amphipod Gammarus duebeni feeds on plant biomass irrespective of the presence of microplastics, indicating lack of avoidance of microplastics. A number of G. duebeni that were fed L. minor with adsorbed PE microplastics had accumulated microplastics in their digestive tracts at the end of the tests. Fragmentation of microplastics transferred via plant feed and using low concentrations was noted for the first time. PE fragments, including particles in the nanosized range, were observed in G. duebeni digestive tracts. Yet, there was no apparent acute negative effect on G. duebeni weight or survival. These findings demonstrate microplastic trophic transfer and fragmentation in a freshwater organism. The finding that novel nanoplastics are found in the gut does show that biological processes are co-determinants of the fate of plastics in the environment and emphasise the importance of nanoplastic impact studies.