On the need to avoid apple-to-orange comparisons in microplastic research

Summary

Here, we discuss several key issues in the recent microplastic risk assessment conducted by Hataley et al. (2023. Can. J. Fish. Aquat. Scie 80 (10): 1669-1678) for the Great Lakes ecosystem. First, we note that the risk characterizations are incorrect due to errors in parameterizations of the calculations necessary to align exposure and effects data, as well as the corrections for bioaccessibility cutoffs. Second, the lack of quantification of uncertainty in the risk assessment raises concerns. Previous assessments that employed similar methods addressed uncertainties arising from the calculations, revealing that the probabilistic uncertainty inherent in risk characterization can span significant magnitudes. Third, we highlight the problematic use of species sensitivity distributions (SSDs) designed for marine systems in a freshwater context. We emphasize the importance of utilizing SSDs that incorporate relevant freshwater species data, and identify recent studies that provide such data for use in future risk assessments. Based on a previously published assessment, we suggest initiating measures to reduce the release of plastic debris into the watershed and advise research, monitoring, and mitigative strategies to address potential threats to water quality.