Common coastal best management practice materials are a microplastic source

Coastal development has led to a reframing of shoreline protection best management practices (BMPs), which use geotextiles for erosion control and shoreline stabilization. One risk of geotextile use in dynamic coastal environments is degradation into microplastics. This preliminary study quantified microplastic release from such degradation. Two common BMP geotextiles, black silt fence and green mesh geomat, were exposed to simulated estuarine conditions in mesocosms that included wave action as well as ambient ultraviolet radiation and temperatures. Water from the mesocosms was sampled, sieved, and analyzed through a combined approach of visual counting and laser direct infrared (LDIR) analysis. Visual counts revealed elevated synthetic particles in both treatments, with black particle concentrations 8.8x higher in the black silt fence treatment and green particle concentrations 5.1x higher in the green mesh geomat treatment. LDIR verification indicated elevated polypropylene concentrations from first exposure "wash-off" (5600 particles m^-2 day^-1 for the black silt fence and 20,000 particles m^-2 day^-1 year for the green mesh geomat). Shedding rates generally increased after the second sampling to a maximum rate of 140 and 230 particles m^-2 day^-1 for the green mesh geomat and black silt fence, respectively, at 48 days. Results indicate these geotextiles will release microplastics for far longer time scales than was monitored in this project, suggesting a need for a reassessment of current BMP materials and their management to better mitigate microplastic pollution in coastal environments.