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The bucket of water was poured over the stacked sieves. At site eight, the bridge from which collection occurred was too high above the tributary to successfully deploy the pump, so a stainless-steel bucket and winch system were used. With one exception (site eight), an ISCO sampler was used to pump, on average, a total of 100 L of water ( Table S3) from the stream through a foil lid and over two stacked stainless-steel sieves, sized 125 and 355 μm. The field crew timed the collection of the first aliquot to occur at the beginning of the rise of the hydrograph. Once in the water column, the tubing was moved up and down (from just below the surface to just above the stream bed) during sampling. A depth-integrated sample was taken from the center of the tributary with sample tubing secured to a metal pole. During each storm at each sampling site, a composite depth-integrated sample composed of 3–8 aliquots was collected across the hydrograph. Antecedent dry days, total storm rainfall, the maximum 2 h storm intensity, and percent imperviousness of the watershed for each sample are provided in Table S2. Storms were chosen on the basis of strength we sampled during those that were predicted to be sufficiently strong to mobilize contaminants (more than 1.3 cm (cm) of rainfall within 6 h or 1.9 cm within 12 h). We found that the rain garden successfully removed 96% of anthropogenic debris on average and 100% of black rubbery fragments, suggesting rain gardens should be further explored as a mitigation strategy for microplastic pollution.Įach site was sampled once during six storm events from December 2016 to November 2018 ( Table S2). As a case study, we sampled stormwater from the inlet and outlet of a rain garden during three storm events to measure how effectively rain gardens capture microplastics and prevent it from contaminating aquatic ecosystems.
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This suggests that mitigation strategies for stormwater should be prioritized. Fibers and black rubbery fragments (potentially tire and road wear particles) were the most frequently occurring morphologies, comprising ∼85% of all particles across all samples.
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These concentrations are much higher than those in wastewater treatment plant effluent, suggesting urban stormwater runoff is a major source of anthropogenic debris, including microplastics, to aquatic habitats. All stormwater runoff contained anthropogenic microparticles, including microplastics, with concentrations ranging from 1.1 to 24.6 particles/L. Depth-integrated samples were collected during wet weather events. Here, we quantify and characterize urban stormwater runoff from 12 watersheds surrounding San Francisco Bay for anthropogenic debris, including microplastics. Stormwater runoff has been suggested to be a significant pathway of microplastics to aquatic habitats yet, few studies have quantified microplastics in stormwater.