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Microplastic contamination in the San Francisco Bay, California, USA
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Researchers measured microplastic abundance across nine sites in San Francisco Bay and in effluent from eight wastewater treatment plants, finding average surface water concentrations of 700,000 particles per km² — higher than other North American urban waterbodies — and noting that tertiary filtration did not meaningfully reduce microplastic discharge compared to secondary treatment.
Despite widespread detection of microplastic pollution in marine environments, data describing microplastic abundance in urban estuaries and microplastic discharge via treated municipal wastewater are limited. This study presents information on abundance, distribution, and composition of microplastic at nine sites in San Francisco Bay, California, USA. Also presented are characterizations of microplastic in final effluent from eight wastewater treatment plants, employing varying treatment technologies, that discharge to the Bay. With an average microplastic abundance of 700,000particles/km(2), Bay surface water appears to have higher microplastic levels than other urban waterbodies sampled in North America. Moreover, treated wastewater from facilities that discharge into the Bay contains considerable microplastic contamination. Facilities employing tertiary filtration did not show lower levels of contamination than those using secondary treatment. As textile-derived fibers were more abundant in wastewater, higher levels of fragments in surface water suggest additional pathways of microplastic pollution, such as stormwater runoff.
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This research identified and quantified the major sources of microplastics entering San Francisco Bay, including stormwater runoff, wastewater treatment plant effluent, and atmospheric deposition. The findings point to urban runoff as a dominant pathway for microplastics reaching this heavily urbanized estuary.
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Sediment samples from San Francisco Bay revealed elevated microplastic concentrations across sites, with polymer types and morphologies consistent with local urban runoff and atmospheric deposition sources.
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Researchers quantified microplastics in urban stormwater runoff from 12 watersheds surrounding San Francisco Bay and found concentrations ranging from 1.1 to 24.6 particles per liter, much higher than typical wastewater treatment plant effluent. The study suggests that stormwater runoff is a major and underappreciated pathway for microplastics and other anthropogenic particles to enter urban waterways.
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Researchers assessed microplastic risk in San Francisco Bay and found that over 75% of water samples exceeded the threshold linked to harming fish and wildlife through food dilution — where animals fill up on plastic instead of real food. Risk was highest in the Central Bay, and actual concentrations were likely even higher than measured.
Microplastic pollution is widely detected in US municipal wastewater treatment plant effluent
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Researchers conducted a wide survey of US municipal wastewater treatment plants and found microplastics widely present in effluent, confirming that conventional treatment does not fully remove microplastics and that treatment plants are ongoing sources of environmental contamination.
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When a large batch of papers lands in the Atlas, we read through it and send a short write-up of what stood out.