Salt marsh sediments act as sinks for microplastics and reveal effects of current and historical land use changes

Microplastic particles are widespread in marine sediments and the abundance of the different types of particles vary widely. In this paper we demonstrate that salt marshes effectively capture microplastics in their sediments, and that microplastic accumulations increase with the level of urbanization of the land surrounding estuarine areas. We extracted microplastics from sediment cores in salt marshes of SE New England estuaries at different degrees of urbanization and land use intensity. Microplastics were present everywhere, but their abundances increased markedly with the degree of urbanization of the land. Microplastic fragment counts were linked to nearby urbanization and their abundances seemed to be linked to more local, within-watershed inputs. The number of fibers was similar across all sites suggesting that fiber accumulation in these sediments is likely influenced by effective long-distance transport from large-scale areas. The sedimentary record confirmed that microplastics have been accumulating in these estuaries since the early 1950s, and their abundances have increased greatly in more recent years in response to the progressive urbanization of the watersheds and intensification of land uses. Our results highlight the role of salt marsh sediments as sinks for microplastics in the marine environment.