Land–Sea Connection of Microplastic Fiber Pollution in Frenchman Bay, Maine

This study is the first comprehensive investigation into the extent of microplastic pollution in Frenchman Bay, ME, which is a semi-sheltered coastal bay with some freshwater input making it an ideal location to study the land–sea connection of microplastic pollution. Two sampling campaigns were coordinated for this study, and during the first one, 323 fibers were identified from water samples collected on a weekly basis from the Bay from July through October of 2022. The chemical compositions of a subset of these samples were determined by micro-Raman analysis, identifying the types of microplastic fibers (MPFs) in the Bay. In total, an average of 1.8 fibers/L were found among all sampling locations, from which it was estimated that up to 400 billion MPFs may reside in the upper one meter of Frenchman Bay. A complementary sampling campaign was organized to investigate potential land-based sources of MPF pollution. Grab samples were collected during six sampling events at a variety of rural and urban locations surrounding the Bay. The highest microplastic concentration was from a culvert during a storm, releasing an average of 15.3 fibers/L directly into Frenchman Bay. It is suspected that the MPFs enter Frenchman Bay from regional land-based sources, as the size of the microplastics decreases as the sampling location becomes farther from land, and it appears the color fades in relation to distance from land. This study is the first systematic microplastic sampling campaign of the Bay and can set an example for similar studies in estuary systems that are investigating the land–sea connection.