Reckoning with the U.S. Role in Global Ocean Plastic Waste (2022) / Chapter Skim
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4 Physical Transport and Pathways to the Ocean
4 Physical Transport and Pathways to the Ocean
Pages 73-88
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From page 73... ...
These include urban, coastal, and inland stormwater outfalls; treated wastewater discharges; atmospheric deposition; direct deposits from boats and ships; beach and shoreline wastes; and transport from inland areas by rivers and streams (Dris, Gasperi, and Tassin 2018)
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From page 74... ...
WATERBORNE PATHWAYS Waterborne pathways of plastic waste include river flows, stormwater discharge, wastewater treatment plant effluent, and beach and shoreline wastes (see Figure 4.2)
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From page 75... ...
are major pathways for plastic waste entering the ocean from a variety of sources including littering (intentional or accidental) , illegal dumping, and landfill leakage, as well as stormwater outfalls, combined sewer overflows, wastewater treatment plant effluent, and atmospheric deposition, which are described as pathways in more detail in subsequent sections (Williams and Simmons 1997, Windsor et al.
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From page 76... ...
. Quantitative global estimates of transport of plastic debris by rivers to the ocean come from modeling studies that use proxies including population density and mismanaged plastic waste generation rates to predict debris fluxes, which were then evaluated against available published data from a small number of individual rivers (Lebreton et al.
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From page 77... ...
Such information will be valuable not only to better understand local sources and transport dynamics but also to build and validate models used for process studies and for regional or global budgeting studies. Stormwater Runoff Urban and suburban stormwater can be substantial and important contributors of plastic waste, especially microplastics from land to rivers and nearshore areas (Sutton et al.
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From page 78... ...
. Wastewater Discharges Wastewater entering treatment plants can be highly contaminated with quantities of mostly fine microplastics, particularly fibers shed from clothing and other textiles (Carr, Liu, and Tesoro 2016)
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From page 79... ...
The importance of onsite sewage disposal systems as microplastic sources, and associated groundwater discharge of microplastics to waterways and the ocean, is presently uncertain. Beach and Shoreline Waste Beach and shoreline waste may be deposited as locally generated litter (accidental or intentional)
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From page 80... ...
. Larger, denser particles tend to accumulate locally near river and stormwater outfalls, because stream velocities diminish in open water.
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From page 81... ...
Microplastics in soil, on roads, and at the ocean surface that are large enough to be entrained into the atmosphere and small enough to be elevated into the atmospheric planetary boundary layer can be subject to long-range transport and may have residence times up to 1 week (Brahney et al.
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From page 82... ...
. In analyses of particle pathways, research has demonstrated that microplastic transport can occur on regional scales (>100 km; see Allen et al.
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From page 83... ...
. The San Francisco Bay region also has a lengthy history of collecting trash data from beaches and inland shorelines during volunteer beach cleanups.
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From page 84... ...
. that achieving this goal will require effective monitoring methods by which to measure progress, the California State Water Resources Control Board and San Francisco Estuary Institute recently published the California Trash Monitoring Playbook in an attempt to help standardize data collection (S.
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From page 85... ...
This work can be used as a guide for interventions that target these sources. Shoreline Debris from Community Science In addition to the studies discussed above, the San Francisco Bay region has a decades-long record of community science efforts to capture data on beach and inland shoreline debris through volunteer beach cleanup efforts.
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From page 86... ...
. For analysis of microplastics, specifically, one must select an extraction protocol to remove particles from tissues, organic matter, or sediment, as well as a method for chemical identification of some or all suspected plastic particles (Hidalgo-Ruz et al.
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From page 87... ...
PHYSICAL TRANSPORT AND PATHWAYS TO THE OCEAN 87 FINDINGS AND CONCLUSION Finding 8: Although the transport of plastic waste to the ocean in the United States cannot be comprehensively estimated from available data, individual studies show a sizeable transport of microplastics and macroplastic wastes along a variety of waterborne and airborne paths as well as direct inputs from shorelines and maritime activities. Finding 9: Plastic waste discharge to the ocean varies greatly with location and over time, reflecting variability in plastic waste gen eration by source, effectiveness of waste collection, and variability in transport processes such as river and stream flows; ocean waves, currents, and tides; and winds.
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