Microplastic contamination of river beds significantly reduced by catchment-wide flooding

Microplastic contamination of the oceans is one of the world’s most pressing environmental concerns. The terrestrial component of the global microplastic budget is not well understood because sources, stores and fluxes are poorly quantified. We report catchment-wide patterns of microplastic contamination, classified by type, size and density, in channel bed sediments at 40 sites across urban, suburban and rural river catchments in northwest England. Microplastic contamination was pervasive on all river channel beds. We found multiple urban contamination hotspots with a maximum microplastic concentration of approximately 517,000 particles m−2. After a period of severe flooding in winter 2015/16, all sites were resampled. Microplastic concentrations had fallen at 28 sites and 18 saw a decrease of one order of magnitude. The flooding exported approximately 70% of the microplastic load stored on these river beds (equivalent to 0.85 ± 0.27 tonnes or 43 ± 14 billion particles) and eradicated microbead contamination at 7 sites. We conclude that microplastic contamination is efficiently flushed from river catchments during flooding.

Rachel Hurley, Jamie Woodward, James J. Rothwell, Nature Geoscience,

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The influence of exposure and physiology on microplastic ingestion by the freshwater fish Rutilus rutilus (roach) in the River Thames, UK

Microplastics are widespread throughout aquatic environments. However, there is currently insufficient understanding of the factors influencing ingestion of microplastics by organisms, especially higher predators such as fish. In this study we link ingestion of microplastics by the roach Rutilus rutilus, within the non-tidal part of the River Thames, to exposure and physiological factors. Microplastics were found within the gut contents of roach from six out of seven sampling sites. Of sampled fish, 33% contained at least one microplastic particle. The majority of particles were fibres (75%), with fragments and films also seen (22.7% and 2.3% respectively). Polymers identified were polyethylene, polypropylene and polyester, in addition to a synthetic dye. The maximum number of ingested microplastic particles for individual fish was strongly correlated to exposure (based on distance from the source of the river). Additionally, at a given exposure, the size of fish correlated with the actual quantity of microplastics in the gut. Larger (mainly female) fish were more likely to ingest the maximum possible number of particles than smaller (mainly male) fish. This study is the first to show microplastic ingestion within freshwater fish in the UK and provides valuable new evidence of the factors influencing ingestion that can be used to inform future studies on exposure and hazard of microplastics to fish.

Alice A. Horton, Monika D. Jürgens, Elma Lahive, Peter M. van Bodegom, Martina G. Vijver, Environmental Pollution, Volume 236, May 2018, Pages 188–194

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Macroplastic and microplastic contamination assessment of a tropical river (Saigon River, Vietnam) transversed by a developing megacity

Both macroplastic and microplastic contamination levels were assessed for the first time in a tropical river estuary system, i.e. the Saigon River, that traverses a developing South East Asian megacity, i.e. Ho Chi Minh City, Vietnam. The analysis of floating debris collected daily on the Nhieu Loc – Thi Nghe canal by the municipal waste management service shows that the plastic mass percentage represents 11–43%, and the land-based plastic debris entering the river was estimated from 0.96 to 19.91 g inhabitant−1 d−1, namely 350 to 7270 g inhabitant−1 yr−1. Microplastics were assessed in the Saigon River and in four urban canals by sampling bulk water for anthropogenic fiber analysis and 300 μm mesh size plankton net exposition for fragment analysis. Fibers and fragments are highly concentrated in this system, respectively 172,000 to 519,000 items m−3 and 10 to 223 items m−3. They were found in various colors and shapes with smallest size and surface classes being predominant. The macroplastics and fragments were mainly made of polyethylene and polypropylene while the anthropogenic fibers were mainly made of polyester. The relation between macroplastic and microplastic concentrations, waste management, population density and water treatment are further discussed.

Lisa Lahens, Emilie Strady, Thuy-Chung Kieu-Le and al., Environmental Pollution, Volume 236, May 2018, Pages 661–671

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Assessment of debris inputs from land into the river in the Three Gorges Reservoir Area, China

Riverine debris in the Three Gorges Reservoir Area (TGRA) poses a threat to electricity generation, ship navigation, and water environment. Quantifying riverine debris inputs from land into the river is a foundation for modeling of the transport and accumulation of floating debris on the water surface in the TGRA. However, this has not been researched to date. In this study, debris inputs from land into the river in the TGRA were assessed according to the response relationship between debris inputs and surface runoff. The land-based debris inputs in the TGRA were estimated using simulated surface runoff which was simulated by the Soil and Water Assessment Tool (SWAT) model. Results showed that 15.32 × 106 kg of land-based debris was inputted into the main channel of the TGRA in 2015 which accounted for 9.74% of total debris inputs (the monitoring data of river-sourced and land-sourced debris inputs was 157.27 × 106 kg). Debris inputs varied seasonally and peaked in the summer season (July to September). Compared with monthly measured data, the average relative errors in 2015 were below 30%. In addition, areas with higher debris pollution inputs were mainly located in the upper section of the TGRA, between the Tang River Basin and the Long River Basin. The proposed method was tested and determined to be reliable; thus, it can be used to quickly estimate debris inputs from land into the river by surface runoff of the outlets in a river basin. Moreover, this method provides new insight into the estimation of land-based debris inputs into rivers.

Jing Wan, Yonggui Wang, Meiling Cheng, Bernard A. Engel, Wanshun Zhang, Hong Peng, Environmental Science and Pollution Research, , Volume 25, Issue 6, pp 5539–5549

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Gallatin Microplastics Initiative

The Gallatin River carries the mountains to the sea. It carries our communities and our livelihoods. It carries our stories and dreams. And this river also carries something more ominous in its waters: Our garbage.

In a pilot survey of five sites along the Gallatin River, microplastic particles were found in every sample, some in startlingly high numbers. With this knowledge, we launched the Gallatin Microplastics Initiative to study the abundance and types of microplastics in the Gallatin Watershed. This is an expansion of the Worldwide Microplastics Project.

​In each year of the Gallatin Microplastics Initiative, 60+ volunteers will return four times to their assigned sites on the main Gallatin and its tributaries, gathering an in-depth picture of plastic pollution from 70 sites in the watershed. This information will help us understand the extent of the problem and how to resolve it.

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Microplastic Effect Thresholds for Freshwater Benthic Macroinvertebrates

Now that microplastics have been detected in lakes, rivers, and estuaries all over the globe, evaluating their effects on biota has become an urgent research priority. This is the first study that aims at determining the effect thresholds for a battery of six freshwater benthic macroinvertebrates with different species traits, using a wide range of microplastic concentrations. Standardized 28 days single species bioassays were performed under environmentally relevant exposure conditions using polystyrene microplastics (20–500 μm) mixed with sediment at concentrations ranging from 0 to 40% sediment dry weight (dw). Microplastics caused no effects on the survival of Gammarus pulex, Hyalella azteca, Asellus aquaticus, Sphaerium corneum, and Tubifex spp. and no effects were found on the reproduction of Lumbriculus variegatus. No significant differences in growth were found for H. azteca, A. aquaticus, S. corneum, L. variegatus, and Tubifex spp. However, G. pulex showed a significant reduction in growth (EC10 = 1.07% sediment dw) and microplastic uptake was proportional with microplastic concentrations in sediment. These results indicate that although the risks of environmentally realistic concentrations of microplastics may be low, they still may affect the biodiversity and the functioning of aquatic communities which after all also depend on the sensitive species.

Paula E. Redondo-Hasselerharm, Dede Falahudin, Edwin T. H. M. Peeters, and Albert A. Koelmans, Environ. Sci. Technol., Article ASAP, January 16, 2018

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Export of plastic debris by rivers into the sea

Abstract ImageA substantial fraction of marine plastic debris originates from land-based sources and rivers potentially act as a major transport pathway for all sizes of plastic debris. We analyzed a global compilation of data on plastic debris in the water column across a wide range of river sizes. Plastic debris loads, both microplastic (particles <5 mm) and macroplastic (particles >5 mm) are positively related to the mismanaged plastic waste (MMPW) generated in the river catchments. This relationship is nonlinear where large rivers with  population-rich catchments delivering a disproportionately higher fraction of MMPW into the sea. The 10 top-ranked rivers transport 88–95% of the global load into the sea. Using MMPW as a predictor we calculate the global plastic debris inputs form rivers into the sea to range between 0.41 and 4 × 106 t/y. Due to the limited amount of data high uncertainties were expected and ultimately confirmed. The empirical analysis to quantify plastic loads in rivers can be extended easily by additional potential predictors other than MMPW, for example, hydrological conditions.

Christian Schmidt, Tobias Krauth, and Stephan Wagner, Environ. Sci. Technol., 51 (21), pp 12246–12253, 2017