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1. Hitchhiking into the Deep: How Microplastic Particles are Exported through the Biological Carbon Pump in the North Atlantic Ocean

   https://doi.org/10.1021/acs.est.2c04712  

   Galgani, Luisa; Goßmann, Isabel; Scholz-Böttcher, Barbara; Jiang, Xiangtao; Liu, Zhanfei; Scheidemann, Lindsay; Schlundt, Cathleen; Engel, Anja (November 2022, Environmental Science & Technology)

   Understanding residence times of plastic in the ocean is a major knowledge gap in plastic pollution studies. Observations report a large mismatch between plastic load estimates from worldwide production and disposal and actual plastics floating at the sea surface. Surveys of the water column, from the surface to the deep sea, are rare. Most recent work, therefore, addressed the “missing plastic” question using modeling or laboratory approaches proposing biofouling and degradation as the main removal processes in the ocean. Through organic matrices, plastic can affect the biogeochemical and microbial cycling of carbon and nutrients. For the first time, we provide in situ measured vertical fluxes of microplastics deploying drifting sediment traps in the North Atlantic Gyre from 50 m down to 600 m depth, showing that through biogenic polymers plastic can be embedded into rapidly sinking particles also known as marine snow. We furthermore show that the carbon contained in plastic can represent up to 3.8% of the total downward flux of particulate organic carbon. Our results shed light on important pathways regulating the transport of microplastics in marine systems and on potential interactions with the marine carbon cycle, suggesting microplastic removal through the “biological plastic pump”. 

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2. Constraining the atmospheric limb of the plastic cycle

   https://doi.org/https://doi.org/10.1073/pnas.2020719118  

   Janice Brahney, Natalie Mahowald (April 2021, Proceedings of the National Academy of Sciences of the United States of America)

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   Microplastic particles and fibers generated from the breakdown of mismanaged waste are now so prevalent that they cycle through the earth in a manner akin to global biogeochemical cycles. In modeling the atmospheric limb of the plastic cycle, we show that most atmospheric plastics are derived from the legacy production of plastics from waste that has continued to build up in the environment. Roads dominated the sources of microplastics to the western United States, followed by marine, agriculture, and dust emissions generated downwind of population centers. At the current rate of increase of plastic production (∼4% per year), understanding the sources and consequences of microplastics in the atmosphere should be a priority. 

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3. Plastic rain in protected areas of the United States

   https://doi.org/10.1126/science.aaz5819  

   Brahney, Janice; Hallerud, Margaret; Heim, Eric; Hahnenberger, Maura; Sukumaran, Suja (June 2020, Science)

   Eleven billion metric tons of plastic are projected to accumulate in the environment by 2025. Because plastics are persistent, they fragment into pieces that are susceptible to wind entrainment. Using high-resolution spatial and temporal data, we tested whether plastics deposited in wet versus dry conditions have distinct atmospheric life histories. Further, we report on the rates and sources of deposition to remote U.S. conservation areas. We show that urban centers and resuspension from soils or water are principal sources for wet-deposited plastics. By contrast, plastics deposited under dry conditions were smaller in size, and the rates of deposition were related to indices that suggest longer-range or global transport. Deposition rates averaged 132 plastics per square meter per day, which amounts to >1000 metric tons of plastic deposition to western U.S. protected lands annually. 

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4. The “plastic cycle”: a watershed‐scale model of plastic pools and fluxes

   https://doi.org/10.1002/fee.2294  

   Hoellein, Timothy J; Rochman, Chelsea M (April 2021, Frontiers in Ecology and the Environment)

   Research on plastics in global ecosystems is rapidly evolving. Oceans have been the primary focus of studies to date, whereas rivers are generally considered little more than conduits of plastics to marine ecosystems. Within a watershed, however, plastics of all sizes are retained, transformed, and even extracted via freshwater use or litter cleanup. As such, plastic litter in terrestrial and freshwater ecosystems is an important but underappreciated component of global plastic pollution. To gain a holistic perspective, we developed a conceptual model that synthesizes all sources, fluxes, and fates for plastics in a watershed, including containment (ie disposed in landfill), non‐containment (ie persists as environmental pollution), mineralization, export to oceans, atmospheric interactions, and freshwater extraction. We used this model of the “plastic cycle” to illustrate which components have received the most scientific attention and to reveal overlooked pathways. Our main objective is for this framework to inform future research, offer a new perspective to adapt management across diverse waste governance scenarios, and improve global models of plastic litter. 

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5. A fish tale: a century of museum specimens reveal increasing microplastic concentrations in freshwater fish

   https://doi.org/10.1002/eap.2320  

   Hou, Loren; McMahan, Caleb D.; McNeish, Rae E.; Munno, Keenan; Rochman, Chelsea M.; Hoellein, Timothy J. (July 2021, Ecological Applications)

   Abstract Plastic is pervasive in modern economies and ecosystems. Freshwater fish ingest microplastics (i.e., particles <5 mm), but no studies have examined historical patterns of their microplastic consumption. Measuring the patterns of microplastic pollution in the past is critical for predicting future trends and for understanding the relationship between plastics in fish and the environment. We measured microplastics in digestive tissues of specimens collected from the years 1900–2017 and preserved in museum collections. We collected new fish specimens in 2018, along with water and sediment samples. We selected four species: Micropterus salmoides (largemouth bass), Notropis stramineus (sand shiner), Ictalurus punctatus (channel catfish), and Neogobius melanostomus (round goby) because each was well represented in museum collections, are locally abundant, and collected from urban habitats. For each individual, we dissected the digestive tissue from esophagus to anus, subjected tissue to peroxide oxidation, examined particles under a dissecting microscope, and used Raman spectroscopy to characterize the particles' chemical composition. No microplastics were detected in any fish prior to 1950. From mid‐century to 2018, microplastic concentrations showed a significant increase when data from all fish were considered together. All detected particles were fibers, and represented plastic polymers (e.g., polyester) along with mixtures of natural and synthetic textiles. For the specimens collected in 2018, microplastics in fish and sediment showed similar patterns across study sites, while water column microplastics showed no differences among locations. Overall, plastic pollution in common freshwater fish species is increasing and pervasive across individuals and species, and is likely related to changes in environmental concentrations. Museum specimens are an overlooked source for assessing historical patterns of microplastic pollution, and for predicting future trends in freshwater fish, thereby helping to sustain the health of commercial and recreational fisheries worldwide. 

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