Pandemic Legacy: Medical Facemasks as a Potential Source of Marine Microplastic?

Understanding the main sources of microplastic pollution is key towards developing efficient measures to reduce microplastic loadings to marine waters. Yet identifying the main sources of marine microplastic is challenging. Source tracking should be easier in marine bays where inputs are limited. In 2021 we determined the concentrations and characteristics of microplastics > 300 m in surface waters of Placentia Bay, Newfoundland; a bay with negligible river input in an area of low population density, and no plastic processing plants in the vicinity. Microplastics contributed 2-14% to particulate organic carbon (> 300 m), and concentrations ranged from 0.11 to 0.67 particles m-3, a relatively high level given the regions low population density. Microplastic diversity was low; fiber and fragment concentrations dwarfed those of other shapes, and polypropylene (PP) dominated, with transparent PP fibers specifically contributing near 50% to the total microplastic inventory. The overwhelming dominance of transparent PP fibers, as well as the exceptionally high proportion of long fibers, suggest that a distinctive input of large, transparent PP fibers overlaid "background" inputs from other sources. A ballpark estimate indicates that weathering of medical facemasks used during the COVID-19 pandemic are a likely explanation for the dominance of transparent PP fibers in Placentia Bay in 2021. Similar inputs may have affected many other aquatic environments globally, but might not have been observable in systems where other continuous input pathways are high.