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      River plastic emissions to the world's oceans

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          Abstract

          Plastics in the marine environment have become a major concern because of their persistence at sea, and adverse consequences to marine life and potentially human health. Implementing mitigation strategies requires an understanding and quantification of marine plastic sources, taking spatial and temporal variability into account. Here we present a global model of plastic inputs from rivers into oceans based on waste management, population density and hydrological information. Our model is calibrated against measurements available in the literature. We estimate that between 1.15 and 2.41 million tonnes of plastic waste currently enters the ocean every year from rivers, with over 74% of emissions occurring between May and October. The top 20 polluting rivers, mostly located in Asia, account for 67% of the global total. The findings of this study provide baseline data for ocean plastic mass balance exercises, and assist in prioritizing future plastic debris monitoring and mitigation strategies.

          Abstract

          Rivers provide a major pathway for ocean plastic waste, but effective mitigation is dependent on a quantification of active sources. Here, the authors present a global model of riverine plastic inputs, and estimate annual plastic waste of almost 2.5 million tonnes, with 86% sourced from Asia.

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          Microplastic pollution in the surface waters of the Laurentian Great Lakes

          Neuston samples were collected at 21 stations during an ~700 nautical mile (~1300 km) expedition in July 2012 in the Laurentian Great Lakes of the United States using a 333 μm mesh manta trawl and analyzed for plastic debris. Although the average abundance was approximately 43,000 microplastic particles/km², station 20, downstream from two major cities, contained over 466,000 particles/km², greater than all other stations combined. SEM analysis determined nearly 20% of particles less than 1 mm, which were initially identified as microplastic by visual observation, were aluminum silicate from coal ash. Many microplastic particles were multi-colored spheres, which were compared to, and are suspected to be, microbeads from consumer products containing microplastic particles of similar size, shape, texture and composition. The presence of microplastics and coal ash in these surface samples, which were most abundant where lake currents converge, are likely from nearby urban effluent and coal burning power plants.
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            Microplastics profile along the Rhine River

            Microplastics result from fragmentation of plastic debris or are released to the environment as pre-production pellets or components of consumer and industrial products. In the oceans, they contribute to the ‘great garbage patches’. They are ingested by many organisms, from protozoa to baleen whales, and pose a threat to the aquatic fauna. Although as much as 80% of marine debris originates from land, little attention was given to the role of rivers as debris pathways to the sea. Worldwide, not a single great river has yet been studied for the surface microplastics load over its length. We report the abundance and composition of microplastics at the surface of the Rhine, one of the largest European rivers. Measurements were made at 11 locations over a stretch of 820 km. Microplastics were found in all samples, with 892,777 particles km −2 on average. In the Rhine-Ruhr metropolitan area, a peak concentration of 3.9 million particles km −2 was measured. Microplastics concentrations were diverse along and across the river, reflecting various sources and sinks such as waste water treatment plants, tributaries and weirs. Measures should be implemented to avoid and reduce the pollution with anthropogenic litter in aquatic ecosystems.
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              The Danube so colourful: A potpourri of plastic litter outnumbers fish larvae in Europe's second largest river

              1 Introduction Plastic, the lightweight and long-lived material, has become a serious environmental hazard (Thompson et al., 2009). The annual global production of the organic polymer has rapidly increased from 1.7 to 280 million tonnes within the last 60 years (Plastics Europe, 2012) resulting in the accumulation of plastic litter in virtually all habitats (Browne et al., 2011). Marine systems are sinks for pre- and post-consumer plastic and the multifaceted negative impacts of plastic pollution on wildlife (reviewed in Cole et al., 2011; Derraik, 2002; Oehlmann et al., 2009) as well as several aspects of debris composition, distribution and abundance have been described here (reviewed in Ryan et al., 2009). Although accumulation of plastic in the ocean is prevalent, there is scarce data on plastic inputs in the oceans (Law et al., 2010). Marine plastics originate from ship or land-based sources (Coe and Rogers, 1997) with the latter to be of greater relevance (Andrady, 2011). A significant portion of the terrestrial plastic is transported to the seas by rivers. Nevertheless, quantifications of plastic loads in rivers found in primary literature are minimal (Moore et al., 2011). Realistic estimations of the plastic flow from rivers to oceans are very important in helping to raise the awareness of the sources of plastic debris and ultimately to drive measures to reduce it. In this article, we present results from a two-year (2010, 2012) survey on plastic litter transport in Europe's second largest river, the Danube. The main aim of the study was to categorize and to quantify drifting plastic items. In a second step we compare plastic abundance and plastic mass in the river with those of ichthyoplankton (drifting fish larvae and juveniles). Adverse health effects may arise when small fish confuse plastic particles with food items (zooplankton, fish eggs) and ingest them (Carpenter et al., 1972). Finally we give a rough estimate of the input of plastic litter via the River Danube into the Black Sea. To our knowledge, this is the first report on plastic transport in a large river. The whole study was embedded in a scientific project that highlights larval dispersal and the conservation of riverine fish populations. All sacrificed individuals were handled according to applicable regulations and used for comprehensive analysis (Lechner et al., 2013b). 2 Methods 2.1 Study site The study was conducted in a free flowing stretch of the Austrian Danube between Vienna and Bratislava. All sampling sites were situated within the “Danube Alluvial Zone National Park” which preserves the last remaining major wetlands environment in central Europe (http://www.donauauen.at). Here, the average river width is 350 m and the discharge at mean flow is 1930 m3 s−1. Featuring the world's most international river basin (19 countries, 800.000 km2, 81 million people), the Danube is a special case study regarding conservation and management issues (Sommerwerk et al., 2009). As the main tributary (input of 6444 m3 s−1 at mean flow) and major nutrient pathway, the Danube directly affects the Black Sea (BSC, 2009). Beside eutrophication, the vulnerable ecosystems of this continental water face an increasing threat of plastic litter pollution (Topcu et al., 2013). Inputs from land-based sources have gained less attention but are supposed to be high, especially via the Danube River System (Lebreton et al., 2012). 2.2 Sampling The sampling procedure has been accurately described elsewhere (Lechner et al., 2013b). Briefly, we utilized stationary conical driftnets (0.5 m diameter, 1.5 m long, 500 μm mesh) that were fixed to iron rods driven into the riverbed and sampled the top 0.5 m of the water column. Nets covered 60% of the water column in more than 75% of all cases. The mesh size we used is in the range of other studies that quantified suspended plastics (reviewed in Hidalgo-Ruz et al., 2013). A flowmeter (2030R, General Oceanics®, Miami) was attached to the lower third of each net entrance to measure the volume of filtered water. In this volume-reducing approach, the filtered sample (containing plastics, fish larvae, organic debris and other items) is collected in a jar attached to the net-end and can be taken to laboratory for further processing. Duplicates (2010) and triplicates (2012) of driftnets were simultaneously exposed at three (2010) to four (2012) sampling stations along both river margins with maximum distances of 1 km between the single stations and 25 m between the shoreline and driftnets. In 2010, we sampled circadian (24 h) periods with hourly intervals between single sample events. In 2012, sampling started 2 h before sunset (according to ephemeris) and was continued in hourly intervals until midnight. Collecting day and night samples was essential in consideration of realistic comparisons between ichthyoplankton and plastics abundance: larval fish drift is known to exhibit a distinct diurnal rhythm with nocturnal peaks in individual numbers (Pavlov et al., 2008). Therefore, exclusive daytime sampling would have underestimated fish densities by far. The sampling period (Apr–Jul) was chosen to comprise the entire drift season (Lechner et al., 2013a). Before preservation in 96% alcohol, all fish were overdosed (500 mg/l) with the anesthetic tricaine methanesulfonate. 2.3 Sampling processing In the laboratory, plastic items and fish larvae were separated from the samples in a two-step process. Each sample was suspended in a water bath and a density separation (buoyant plastic particles and larvae with intact swim bladders were removed), was followed by a careful visual sorting of the remaining material by the naked eye. 2.4 Characterization and quantification of plastics All plastic pieces and larvae were counted. A subsample (n = 500) of fish larvae was taken and all individuals were weighed to the closest 0.01 g (moist mass). Each plastic particle was allocated to one of the categories shown in Fig. 1. Pellets, spherules and flakes characterize different types of industrial raw material that serve as precursors for plastics production. The category “others” encapsulates all other pieces and fragments of plastic consumer products. A subsample (n = 500) of each category was taken and all containing items were weighed to the closest 0.01 g and measured to the closest 0.01 mm (Zeiss® Axio Imager M1 with Axio Vision 4.8.2 software for image analysis). Referring to the size-ranges of the defined groups, the collected plastic may be termed mesodebris (2–20 mm; pellets, flakes, big spherules, others) or microdebris ( 5 cm), which did not enter driftnets through the small gap between net-frame and water surface. But especially large material contributes to the plastic mass in oceans (Lattin et al., 2004). 3) Compared to Germany and Austria, all other neighbouring countries of the Danube feature lower standards in their wastewater and sewerage treatment (http://www.icpdr.org). Their potentially higher contributions to the Danube's plastic load should considerably cumulate and increase the average input at the mouth. Plastic is the dominant debris in the Black Sea with a high percentage of items (47%) sourcing in neighbouring countries (among them several of the Danube basin), potentially introduced by river currents (Topcu et al., 2013). There is rare information about land based litter sources and the “Development and improvement of the existing monitoring system to provide comparable data sets for pollutant loads (from direct discharges and river inputs)” is a high priority task of the “Black Sea Strategic Action Plan” (BSC, 2009). Giving first answers on abundance and composition of plastic litter in the river Danube we hope to serve the cause and help to strengthen the enforcement of national and international regulations on land-based pollution sources (i.e. Operation Clean Sweep®, http://www.opcleansweep.org) Furthermore, our results shall give impetus to continuative studies on freshwater plastic pollution. All harmful consequences of plastic contamination described in marine systems (ranging from ingestion of plastic particles by a wide range of organisms to introduction of alien species which raft plastic litter) may operate in rivers and lakes and deserve closer attention.
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                Author and article information

                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group
                2041-1723
                07 June 2017
                2017
                : 8
                : 15611
                Affiliations
                [1 ]The Ocean Cleanup Foundation , Martinus Nijhofflaan 2, Delft 2624 ES, The Netherlands
                [2 ]The Modelling House , 66b Upper Wainui Road, Raglan 3297, New Zealand
                [3 ]HKV Consultants , PO Box 2120, Lelystad 8203 AC, The Netherlands
                [4 ]Department of Chemical and Biomolecular Engineering, North Carolina State University , Campus Box 7905, Raleigh, North Carolina 27695, USA
                Author notes
                Article
                ncomms15611
                10.1038/ncomms15611
                5467230
                28589961
                22e1e0b9-99e0-4bda-8e72-b1b5450ac2b0
                Copyright © 2017, The Author(s)

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                History
                : 27 October 2016
                : 11 April 2017
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