A review of microplastics categorization schemes to facilitate source apportionment: Implications for North American freshwaters

, Yu Jasmine T., Helm Paul A., Diamond Miriam L..

Microplastics, a widespread pollutant in freshwater systems, have numerous sources which are not well understood. Part of source reductions efforts requires knowledge of sources which is based on confident categorization and characterization. A literature review was conducted to compare the categories used for reporting types of microplastics found in North American freshwater environments. Analysis showed that categorization schemes for grouping microplastic particles are highly variable, with up to 17 different categories used across 32 studies. In some studies, pellets and microbeads are used interchangeably and grouped in a single category or assigned separate categories. Similar observations were seen with the fiber and line categories. Fragments are commonly a ‘catch-all' category to describe irregularly shaped particles. Although uncommon, some studies have included source-specific categories such as tire wear, commercial fragments, paint, and irregular microbeads. While there is no universally accepted categorization framework for characterizing microplastics, harmonization would help with source identification. The broad range of categories across studies to report microplastic types creates ambiguity in determining key sources and their contributing load in freshwater environments. Source apportionment efforts would benefit from using particle morphology to assign microplastics to source-specific categories. This will help facilitate cross-study comparisons of microplastic types and help target management and reduction strategies in North America.

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