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1. 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. ( April 2021 , Ecological Applications)

   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), andNeogobius 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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2. Relative exposure to microplastics and prey for a pelagic forage fish

   https://doi.org/10.1088/1748-9326/ac7060  

   Chavarry, J M ; Law, K L ; Barton, A D ; Bowlin, N M ; Ohman, M D ; Choy, C A ( June 2022 , Environmental Research Letters)

   Abstract In the global ocean, more than 380 species are known to ingest microplastics (plastic particles less than 5 mm in size), including mid-trophic forage fishes central to pelagic food webs. Trophic pathways that bioaccumulate microplastics in marine food webs remain unclear. We assess the potential for the trophic transfer of microplastics through forage fishes, which are prey for diverse predators including commercial and protected species. Here, we quantify Northern Anchovy ( Engraulis mordax ) exposure to microplastics relative to their natural zooplankton prey, across their vertical habitat. Microplastic and zooplankton samples were collected from the California Current Ecosystem in 2006 and 2007. We estimated the abundance of microplastics beyond the sampled size range but within anchovy feeding size ranges using global microplastic size distributions. Depth-integrated microplastics (0–30 m depth) were estimated using a depth decay model, accounting for the effects of wind-driven vertical mixing on buoyant microplastics. In this coastal upwelling biome, the median relative exposure for an anchovy that consumed prey 0.287–5 mm in size was 1 microplastic particle for every 3399 zooplankton individuals. Microplastic exposure varied, peaking within offshore habitats, during the winter, and during the day. Maximum exposure to microplastic particles relative to zooplankton prey was higher for juvenile (1:23) than adult (1:33) anchovy due to growth-associated differences in anchovy feeding. Overall, microplastic particles constituted fewer than 5% of prey-sized items available to anchovy. Microplastic exposure is likely to increase for forage fishes in the global ocean alongside declines in primary productivity, and with increased water column stratification and microplastic pollution. 

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3. MICROPLASTIC POLLUTION IN THE TIJUANA ESTUARY BEACHESOF SOUTHERN CALIFORNIA

   Sheppard, Q. ; Gray, S.C. ( February 2022 , Ocean Sciences Meeting)

   no editor. (Ed.)

   The Tijuana River Watershed encompasses 1750 square miles of territory in both Mexico and the United States, culminating at the National EstuarineResearch Reserve. While this area comprises one of the largest undisturbed wetlands in the state, it is one of the most polluted rivers in SouthernCalifornia, draining raw sewage and nonpoint source pollution. Despite extensive research, microplastic pollution along the beaches has not been explored. The objective of this study is to determine how the abundance and morphology of microplastic pollution in beach sediments vary with distance along the littoral cell from the Tijuana River outfall. Twenty samples were collected at 10 sites that span from the Tijuana River outfall to Mission Beach, San Diego. They are characterized as outfall sites, low-visitation beaches near the outfall, and high-visitation beaches further from the outfall. Solutions of 100ml sediment and 400ml hyper-saline solution were mixed and settled for 16 hours before being processed using a vacuum filtration system in a laminar fl ow hood. The microplastics (MP)were counted and classified using light microscopy. Laboratory practices to reduce laboratory contamination were employed and analytical blanks were run for every 3 samples. MPs ranged from 1 to 199/100ml sediment, of which approximately 91% were fibers. The greatest MP abundance occurred at the river outfall sites, but recovery rates were highly variable, and the analytical blanks ranged from 3-63/100ml sediment. The results oft his study suggest that microplastic distribution in sandy beach sediments is patchy but higher near the Tijuana River Outfall, and that future studies should report analytical blanks and employ methods to reduce contamination. Understanding the relationship between watersheds and microplastic distributions may inspire policy change on water quality protections in watersheds. 

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4. Microplastic in riverine fish is connected to species traits

   https://doi.org/10.1038/s41598-018-29980-9  

   McNeish, R. E. ; Kim, L. H. ; Barrett, H. A. ; Mason, S. A. ; Kelly, J. J. ; Hoellein, T. J. ( August 2018 , Scientific Reports)

   Microplastic is a contaminant of concern worldwide. Rivers are implicated as major pathways of microplastic transport to marine and lake ecosystems, and microplastic ingestion by freshwater biota is a risk associated with microplastic contamination, but there is little research on microplastic ecology within freshwater ecosystems. Microplastic uptake by fish is likely affected by environmental microplastic abundance and aspects of fish ecology, but these relationships have rarely been addressed. We measured the abundance and composition of microplastic in fish and surface waters from 3 major tributaries of Lake Michigan, USA. Microplastic was detected in fish and surface waters from all 3 sites, but there was no correlation between microplastic concentrations in fish and surface waters. Rather, there was a significant effect of functional feeding group on microplastic concentration in fish.Neogobius melanostomus(round goby, a zoobenthivore) had the highest concentration of gut microplastic (19 particles fish⁻¹) compared to 10 other fish taxa measured, and had a positive linear relationship between body size and number of microplastic particles. Surface water microplastic concentrations were lowest in the most northern, forested watershed, and highest in the most southern, agriculturally dominated watershed. Results suggest microplastic pollution is common in river food webs and is connected to species feeding characteristics. Future research should focus on understanding the movement of microplastic from point-source and diffuse sources and into aquatic ecosystems, which will support pollution management efforts on inland waters.

    

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5. What You Net Depends on if You Grab: A Meta-analysis of Sampling Method’s Impact on Measured Aquatic Microplastic Concentration

   https://doi.org/10.1021/acs.est.1c03019  

   Watkins, Lisa ; Sullivan, Patrick J. ; Walter, M. Todd ( January 2022 , Environmental Science & Technology)

   Microplastic pollution is measured with a variety of sampling methods. Field experiments indicate that commonly used sampling methods, including net, pump, and grab samples, do not always result in equivalent measured concentration. We investigate the comparability of these methods through a meta-analysis of 121 surface water microplastic studies. We find systematic relationships between measured concentration and sampled volume, method of collection, mesh size used for filtration, and waterbody sampled. Most significantly, a strong log−linear relationship exists between sample volume and measured concentration, with small-volume grab samples measuring up to 104 particles/L higher concentrations than larger volume net samples, even when sampled concurrently. Potential biasing factors explored included filtration size (±102 particles/L), net volume overestimation (±101 particles/L), fiber loss through net mesh (unknown magnitude), intersample variability (±101 particles/L), and contamination, the potential factor with an effect large enough (±103 particles/L) to explain the observed differences. On the basis of these results, we caution against comparing concentrations across multiple studies or combining multiple study results to identify regional patterns. Additionally, we emphasize the importance of contamination reduction and quantification strategies, namely that blank samples from all stages of field sampling be collected and reported as a matter of course for all studies. 

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