Seasonal and Distributional Changes in the Composition and Flux of Anthropogenic Microparticles in the Surface Waters of the Charles River, Massachusetts, United States

Plastic is a growing global environmental problem. While much of the focus of anthropogenic microparticles has focused on microplastics and their occurrence in marine systems, anthropogenic microparticles are found in freshwater systems. The Charles River is a highly impacted and historically important river within Massachusetts and runs for 80 miles within the state of MA through a variety of land uses. Microparticle concentrations were found to vary along the length of the river and ranged in concentrations from 1–19 pieces/L, with generally higher concentrations downstream. Microfibers were the dominant (72%) type of microparticles found, and the majority (avg 76%) of microparticles were synthetic. The highest estimated flux of microparticles occurred in May, with an estimated flux of 2 billion microparticles per day via the Charles River into the Boston Harbor. The average annual concentration of microparticles was correlated with land use, with higher concentrations occurring in regions with higher impervious coverage and in areas designated as industrial or high-density residential. Polyester, polypropylene, and polyamides were the dominant plastic polymers. However, seasonal changes in the relative importance of each polymer, along with changes in the abundance and flux rates, indicate that there would be seasonal variability in the type of microparticles exported. Changes in composition occurred between stations and between the head and mouth of the river, suggesting particle retention due to either deposition, degradation, or biological consumption.