Modelling the transfer and accumulation of microplastics in a riverine freshwater food web

Microplastics are a pervasive pollutant of aquatic ecosystems and are reported to interact with a wide range of aquatic biota. The complexities of natural food webs means that the transfer and accumulation of microplastics is difficult to assess, and only a handful of studies have attempted to quantify trophic transfer in freshwater biota. Bioaccumulation models can provide a valuable tool to explore the transfer of microplastics along complex food webs, but such approaches have been rarely applied to freshwater ecosystems. Here, a food web accumulation model was implemented to assess the transfer, bioaccumulation and hence biomagnification potential of microplastics along a food web located in the River Slaney catchment in south-east Ireland. Literature feeding values and environmental field data were used to simulate microplastic uptake in benthic macroinvertebrates, with fish and Eurasian otter (Lutra lutra (Linnaeus, 1758)) comprising the higher trophic levels. Microplastic concentrations from the model were used to form a basis of comparison with empirical data for benthic macroinvertebrates and brown trout (Salmo trutta Linnaeus, 1758). Predicted concentrations were greatest in benthic macroinvertebrates and lowest in fish species such as European eel (Anguilla anguilla (Linnaeus, 1758)) and three-spined stickleback (Gasterosteus aculeatus (Linnaeus, 1758)). Biota magnification factors for fish and L. lutra indicate that microplastic accumulation between the specific predator-prey interactions are not expected. To better inform models such as this, and therefore improve their accuracy, it is important to gain a better understanding of microplastic retention times in biota and the interaction between microplastics and resources utilised by benthic macroinvertebrates and fish, such as plant material, allochthonous detritus as well as terrestrial and aerial prey. A bioaccumulation model, used to explore the transfer and possible accumulation of microplastics along a riverine food web, showed that microplastic are not expected to accumulate in the gastrointestinal tracts of higher level biota based on the predator-prey interactions specified.