Exploring Methods for Understanding and Quantifying Plastic-Derived Dissolved Organic Matter

Plastics have accumulated in the environment to become a globally significant pool of organic carbon (Stubbins et al., 2021) and a contaminant of ecological concern (McLeod et al., 2021). Most studies still report plastics in terms of counts (i.e., pieces of plastics) though some report masses of plastics, and even fewer report plastic carbon. In a recent review, we assumed plastics to be 83% carbon by mass based on data for oceanic microplastics (Zhu et al., 2020; Stubbins et al., 2021). This overly simplistic conversion allows plastics to be placed in a carbon cycle context, a context critical to plastic-derived dissolved organic carbon (DOC; Figure 1). However, this conversion should be improved to account for variations in the carbon content of different polymers. To make these improvements, studies should report data for sizes, masses, and types of base polymer of plastics collected. These data would allow comparison among studies and facilitate improved accounting for plastics and their fates in the environment. Reporting masses of specific polymers would make conversion from plastics to carbon more accurate and provide a common chemical unit for comparison among plastic polymer types (i.e., we could use carbon as we do biomass).