Current and potential risks of microplastics in global surface waters

Microplastics are a persistent and ubiquitous environmental contaminant in global marine and surface waters. Microplastics can harm wildlife who ingest them by inhibiting food assimilation and can potentially translocate into tissue. Mismatches between particle sizes captured by field sampling and those used for toxicity experiments make direct comparisons of lab and field data challenging. While tools for overcoming this 'non-alignment problem' exist – which account for mismatched sizes using probability distributions and restrict bioaccessible particles by effect mechanism, and frameworks for assessing harm to ecosystems have been recently developed, these tools have not yet been applied to global surface water concentrations. Therefore, we assessed the risk of floating microplastics (1 µm - 5 mm) in marine and freshwater ecosystems globally, by comparing occurrence concentrations with ecotoxicity data. We estimated that 37.0% of marine environments currently exceed a conservative risk threshold protective of 95% of species (food dilution-based), while 0.5% of marine environments currently exceed least conservative risk thresholds protective of 90% of species (tissue translocation-based). By 2030 and 2040, these fractions may increase to 43.4% and 47.4%, respectively, under a business-as-usual scenario for future plastic discharge into aquatic ecosystems; and 33.6% and 26.5%, respectively, under a system change scenario in which waste is reduced through reductions in plastic demand, substitution by alternative materials, and increased recycling rates. Our results demonstrate spatial heterogeneity of microplastics contamination, with hotspots identified in the Mediterranean Sea, the Yellow Sea, and in the oceans gyres close to the Northern and Southern Tropics. Also see: https://micro2022.sciencesconf.org/421551/document