Microplastics in San Francisco Bay: Abundance, Transport, Fate, and Policy Recommendations

Abstract:

Microplastics are a diverse class of persistent contaminants that have been observed in water, sediment, and wildlife worldwide. Microplastics and other microparticles were characterized in San Francisco Bay and the adjacent Cordell Bank, Greater Farallones and Monterey Bay National Marine Sanctuaries to determine abundance, sources, pathways, and loadings of these contaminants in a densely populated urban environment. Field staff collected samples of stormwater runoff, wastewater effluent, open Bay and Sanctuary surface waters, Bay sediment, as well as two species of prey fish and two species of bivalves. All samples were analyzed for microparticles using visual techniques; a subset of the particles was examined via Raman or Fourier-transform infrared (FTIR) spectroscopy to identify whether they were composed of plastic polymers or other materials. Levels observed in Bay surface waters and sediment were some of the highest recorded globally to date. Most samples of Bay biota contained microparticles, particularly fibers. Urban stormwater was identified as the predominant pathway for discharge of microplastics relative to wastewater. Black rubbery fragments were a dominant particle type within stormwater, and vehicle tires were indicated as one likely source. The concentrations of microplastics and other microparticles observed in the Bay were used to validate a process-based particle transport model for the Bay and Sanctuaries that can be used to predict the transport and fate of microplastics in the region. Findings further informed a collaborative, multi-stakeholder process to develop data-driven, region-specific policy recommendations to reduce microplastic pollution.