Source tracking microplastics in the freshwater environment

Plastics are a frequently observed component of marine debris and there is growing concern about microplastic (MP) ecotoxicity, and the impacts of additives, sorbed hazardous organic contaminants, heavy metals, and biofilm on MP surfaces. The relative importance of MP from different terrestrial and freshwater sources is poorly understood and limits our ability to develop best management practices. This review focuses on evidence and methods for source apportionment of MP in freshwater environments including the use of MP characteristics, mass balance techniques, and surface characteristics. Within-study data indicated some potential for differences in polymer identity and morphology for differentiating select sources, but clear cross-study patterns were lacking. Major challenges identified include technical challenges in accurately identifying polymers, multiple classification schemes for reported MP morphologies, lack of data for several terrestrial sources, poor understanding of differential fate/transport/weathering processes for MP and surface contaminants, and methodological difficulties simultaneously confirming polymers and surface contaminants.