A Near-Synoptic Survey of Ocean Microplastic Concentration Along an Around-The-World Sailing Race
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PLOS ONE RESEARCH ARTICLE A near-synoptic survey of ocean microplastic concentration along an around-the-world sailing race 1☯ 1,2,3☯ 1,4 Toste TanhuaID *, SoÈ ren B. Gutekunst , Arne Biastoch 1 GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, 2 The Ocean Race, Alicante, Spain, 3 SCG Science Consulting±Dr.-Ing, Gutekunst, Koblenz, Germany, 4 Christian-Albrechts-University Kiel, Kiel, Germany ☯ These authors contributed equally to this work. a1111111111 * [email protected] a1111111111 a1111111111 a1111111111 Abstract a1111111111 Litter and plastic pollution in the marine environment is of major concern when considering the health of ocean ecosystems, and have become an important focus of ocean research during recent years. There is still significant uncertainty surrounding the distribution and impact of marine plastic litter on ocean ecosystems, and in particular on the nano- and OPEN ACCESS microplastic fractions that are difficult to observe and may be harmful to marine organisms. Citation: Tanhua T, Gutekunst SB, Biastoch A (2020) A near-synoptic survey of ocean Current estimates of ocean plastic concentrations only account for a small fraction of the microplastic concentration along an around-the- approximated 8 million tons of plastic litter entering the oceans on an annual basis. Here, we world sailing race. PLoS ONE 15(12): e0243203. present the distribution of 100±500 μm microplastic particles within the ocean mixed layer, https://doi.org/10.1371/journal.pone.0243203 covering a significant fraction of the ocean, in a near-synoptic survey. During The Ocean Editor: Erik V. Thuesen, Evergreen State College, Race 2017/2018 edition (formerly known as Volvo Ocean Race), two yachts served as UNITED STATES ships of opportunity that regularly took samples of microplastics on a regular schedule dur- Received: December 4, 2019 ing their circumnavigation. This effort resulted in information on microplastic distribution Accepted: November 17, 2020 along the race track in the ocean's upper, well-mixed, layer. We found concentrations rang- Published: December 8, 2020 ing from 0±349 particles per cubic meter, but with large spatial variability. There was a ten- dency toward higher concentrations off south-western Europe and in the southwest Pacific, Copyright: © 2020 Tanhua et al. This is an open access article distributed under the terms of the and indications of long-range transport of microplastic with major ocean currents. Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All data that were Introduction used for this publication is available from these two public repositories: NOAA NCEI Accession The ocean is on the receiving end of plastic litter and pollution from human populations. 0170967 including further data as pCO2 etc.: Although the majority of litter is disposed of on land, streams and rivers still carry plastic https://data.nodc.noaa.gov/cgi-bin/iso?id=gov. waste into the ocean. It is estimated that roughly 8 million tons of plastic litter enters the ocean noaa.nodc:0170967 EMODnet: https://www. on an annual basis [1]. Currently, the fate of the majority of this plastic is unknown. Only a emodnet-ingestion.eu/submissions/submissions_ small fraction of the plastic input can be accounted for [2] by scaling up observational esti- details.php?menu=39&tpd=232&step=0103_ 001volvo%20ocean%20race The data are public mates to a global scale. Although it is generally assumed that a large fraction of the plastic and can be used without restrictions. With these waste ends up sinking to the bottom of the ocean, there are few estimates of the scale of this data the results in this study can be replicated. pathway and no inventory of plastic in or upon the sediment. However, it is clear that various PLOS ONE | https://doi.org/10.1371/journal.pone.0243203 December 8, 2020 1 / 11 PLOS ONE Microplastic concentration in the world ocean Funding: This study was funded by the Cluster of processes tend to break up large plastic litter to smaller particles that can stay suspended in the Excellence - Future Ocean in Kiel, Germany (project water column for a long time. The effect of plastic litter on marine life and ecosystems is a number CP1756). Volvo Cars provided support to topic of intense research; it is clear that plastics can accumulate in the ingestion systems of purchase instrumentation, and instrumentation developers SubCtech GmbH and bbe Moldaenke larger animals [e.g. 3,4], leading to malnutrition or death [5]. In addition, studies have shown GmbH also provided support. The funders had no that ghost nets can trap animals [6,7]. As the plastic particles get smaller, the potential for role in study design, data collection and analysis, uptake by smaller organisms such as zooplankton and phytoplankton is obvious [8±11]. The decision to publish, or preparation of the long residence time of plastic in the environment also leads to accumulation of plastic particles manuscript. in the food-chain, with an impact on humans through consumption of seafood [12,13]. Competing interests: The authors have read the Plastics constitute a large range of materials composed of a variety of polymer types, with journal's policy and have the following potential microplastics typically defined as particles between 1 μm and 5 mm in size [14,15]. Further- competing interests: the authors received financial more, microplastic comes in many different forms, such as textile fibres made of nylon or par- support from Volvo Cars to purchase ticles e.g. used in cosmetics or for plastic article production. There are two different, principal instrumentation, and they received support from SubCtech GmbH and bbe Moldaenke GmbH in the sources of microplastics in the marine environment: primary and secondary sources. Primary development of instrumentation. This does not sources are defined as small pellets the size of millimetres to centimetres, commonly used, for alter our adherence to PLOS ONE policies on instance, in extrusion or moulding of thermoplastic polymers. Secondary microplastics are sharing data and materials. There are no patents, defined as particles or fibres formed during the decomposition of polymers from, e.g. fishing products in development or marketed products gear or unrecycled polymers. Decomposition is mediated through UV-irradiation, which associated with this research to declare. makes most polymers brittle, as well as wear and friction that creates smaller and smaller pieces, which finally fall into the microplastics category. Most particles eventually decompose into even smaller particles called nanoplastic particles. Nonetheless, polymers generally with- stand eroding or naturally decomposing mechanisms well, contributing to the accumulation of plastic litter in nature [16], although the decomposing rates in the marine environment is often poorly constrained [17]. The distribution of marine plastics in the water column, or at the sea surface, is partially known from a number of studies and reviews [2], although different sampling and measure- ment techniques make direct comparisons difficult [18]. A study of CoÂzar, et al. [19], for instance, combines data from a circumnavigation and modelled distribution of microplastics, finding enhanced concentrations in the subtropical gyres, in general agreeing with model pre- dictions. The purpose of the present study is to provide a snapshot of microplastic distribution in the global ocean mixed layer, sampled and measured in a coherent and near-synoptic man- ner. Here we present observations from two race yachts participating in a race around the world, the 2017/18 edition of The Ocean Race (formerly known as the Volvo Ocean Race). Although this study does not cover all ocean sub-basins, we provide a near-global perspective on pelagic microplastic distribution, utilizing a novel sampling platform and a fast throughput measurement system. Materials and methods For this survey, we utilized two ocean-going race yachts competing in the 2017/2018 edition of The Ocean Race as observation platforms. We installed sampling equipment on two of the 65' one-design yachts known as Volvo Ocean 65s, namely Turn the Tide on Plastic and AkzoNobel. The race started in Alicante, Spain and ended in den Hauge, Netherlands after racing around the world. In addition, we have included data from the pre-race and post-race legs to and from Lisbon, Portugal. The race had port-stops in Lisbon (Portugal), Cape Town (South Africa), Melbourne (Australia), Hong Kong, Auckland (New Zealand), ItajõÂ (Brazil), Newport (Main, USA), Cardiff (UK), Gothenborg (Sweden), and The Hauge (Netherlands). No permission for marine scientific research is required for areas beyond national jurisdiction (i.e. the high seas). The study did not include any endangered species. The boat captains, responsible for technical equipment on the yachts, were adequately trained to minimize environmental impacts caused PLOS ONE | https://doi.org/10.1371/journal.pone.0243203 December 8, 2020 2 / 11 PLOS ONE Microplastic concentration in the world ocean by themselves to their surroundings and were educated on the omnipresence of microplastic particles and the risks of contamination. New filters were positioned next to the sample holder before opening the latch to reduce air exposure. The captains immediately stored the previous samples in aluminium bags, simultaneously installing the new filters in order to minimize exposure time to ambient air. No plastic gloves were used during the process. The time needed to change the filters of one sample in this procedure took less than one minute, on average, and never exceed three minutes. Although the Turn the Tide on Plastic took samples through- out the whole race, AkzoNobel only collected samples for half of the race, after the port-stop in Auckland. See supplementary material for a detailed list of sampling positions. During the race, a total of 96 microplastic samples were taken by filtering seawater through up to three stainless steel filters, although only those within the 100±500 μm size fraction were analysed (S1 Table in S1 File and below).