Abstract As global awareness, science, and policy interventions for plastic escalate, institutions around the world are seeking preventative strategies. Central to this is the need for precise global time series of plastic pollution with which we can assess whether implemented policies are effective, but at present we lack these data. To address this need, we used previously published and new data on floating ocean plastics (n = 11,777 stations) to create a global time-series that estimates the average counts and mass of small plastics in the ocean surface layer from 1979 to 2019. Today’s global abundance is estimated at approximately 82–358 trillion plastic particles weighing 1.1–4.9 million tonnes. We observed no clear detectable trend until 1990, a fluctuating but stagnant trend from then until 2005, and a rapid increase until the present. This observed acceleration of plastic densities in the world’s oceans, also reported for beaches around the globe, demands urgent international policy interventions.
Citation: Eriksen M, Cowger W, Erdle LM, Coffin S, Villarrubia-Gómez P, Moore CJ, et al. (2023) A growing plastic smog, now estimated to be over 170 trillion plastic particles afloat in the world’s oceans—Urgent solutions required. PLoS ONE 18(3): e0281596. https://doi.org/10.1371/journal.pone.0281596 Editor: Judi Hewitt, The University of Auckland - City Campus: University of Auckland, NEW ZEALAND Received: January 12, 2022; Accepted: January 26, 2023; Published: March 8, 2023 Copyright: © 2023 Eriksen et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: All data from the Plastic Marine Pollution Global Dataset, Modeling code, and Trend Reversal data are available open source at github.com. https://github.com/wincowgerDEV/ocean_plastic_modeling. Funding: ME received funding from the Baum Foundation to support expeditions and sample collection (http://thebaumfoundation.org/). MT was supported by the European Union’s H2020 research and innovation programme MINKE project (under Grant Agreement No 101008724). These funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.
Introduction Understanding the occurrence and trends of plastic abundance in the world are foundational to assessing current and potential future risks to humans and ecosystems [1]. Modeling plastic pollution’s fate and transport in the ocean surface layer (OSL) is complicated by complex mechanisms of degradation, fouling, and turbulent transport [2]. Fragmentation of large plastic results in micro- and nanoplastics leaving the OSL to shoreline and seafloor compartments, where they may cause harm to organisms through ingestion [3]. While recent modeling efforts suggest rapid export of plastic pollution away from the OSL [4], inputs are likely to continue [5, 6]. Therefore, understanding trends in regional and global plastic pollution mass and abundance is essential to evaluating and mitigating the risks. While challenging, quantifying the global mass of plastics has previously been estimated for the OSL at 93,000 to 578,000 tonnes [7–9]. Spatial and temporal data gaps and variability in station-selection, sample-collection, and analysis make interpreting snapshots in time challenging and make establishing a trend even more difficult for the OSL [10]. Edelson et al. [11] suggested that the wide variability in reported inputs reveals an urgent need for improved monitoring frameworks to facilitate global governance. A few earlier trends offer a perspective of plastic accumulation in the oceans. Archived Continuous Plankton Recorder (CPR) samples show an increasing trend of microfibers since the 1960s [12] and an increasing trend of macroplastic entanglement since the late 1950s [13]. Day and Shaw [14] reported an increase of microplastics in the North Pacific between 1976 and 1985, and Wilcox et al. [15] observed an increasing trend in the western North Atlantic from 1986 to 2015, with a rate of increase paralleling global cumulative plastic production. Although these studies suggest long-term increases, they are only from northern oceans surrounded by the most industrialized countries. In contrast, other studies have found no evidence of a rise in plastic pollution over time [see references in [10]]. Here, we evaluate a global dataset with all available historical data to provide an estimate of the temporal tendencies of plastic concentrations in the global OSL. We also offer a historic overview of international policy measures to reduce plastic inputs; based on that evaluation we call for urgent and effective solutions.
Discussion Our study shows a significant increase since the turn of the century for the global ocean abundance and distribution of plastics in the OSL. The wide confidence intervals from 1979 to 1990 leave no clear detectable trend. From 1990 to 2005, concentrations of plastic fluctuate during this trendless period, followed by a dramatic increasing trend from 2006 onward. These observations may have been influenced by policy interventions, plastic production, fragmentation of existing floating plastic, and/or waste management and trade. Temporal trend The stagnating trend observed prior to 2006 may have benefitted from important policy measures that were implemented during and just before that period (Fig 4). In 1988, MARPOL added Annex V, which established legally-binding agreements among 154 countries to end the discharge of plastics from naval, fishing, and shipping fleets. These interventions were preceded by the United Nations Convention on the Law of the Sea in 1982 and the Convention on the Prevention of Marine Plastic by Dumping of Wastes and other Matter in 1972 [26]. In 1991, the Plastic Industry Trade Association launched “Operation Clean Sweep” with a goal of zero loss of plastic pellets, powders, and flakes from factories [26], with decreasing pellet ingestion in biota observed [27]; however, these and others were voluntary agreements. PPT PowerPoint slide
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TIFF original image Download: Fig 4. International policy interventions and maritime law. A cluster of binding international policy and maritime-law interventions preceding the millennium may have played a role in slowing the increasing trend of plastic waste in the OSL. https://doi.org/10.1371/journal.pone.0281596.g004 The rapid increase from 2005 onwards may reflect exponential growth of plastic production as it relates to inputs [15] or changes in terrestrial waste generation and management [28]. Older macroplastics adrift or stranded on shorelines or in rivers [4] continue to degrade and fragment and contribute to increases in the abundance of microplastics [15]. Despite the observed trends, there is uncertainty in collating data at a global scale. However, the dramatic increase observed herein for oceanic microplastics after 2005 parallels trends estimated for global beaches [29], which are based on completely independent observations. These parallel trends strongly suggest that plastic pollution in the world’s oceans during the past 15 years has reached unprecedented levels. Considerable data exist for the North Pacific and North Atlantic basins, although we lack information for the other ocean basins. More samples are needed in the South Atlantic, South Pacific, Mediterranean, and Indian oceans, all of which remain data-poor regions (see also [29]). In the future, if greater attention is given to the southern hemisphere, and sampling occurs at more-even intervals, models can provide outputs with higher resolution that can better identify spatial and temporal trends. The globalization of raw plastic materials accelerated at the turn of the century [30] leading to rapid increases in import, export, and domestic production of plastic products and packaging and to increases in the amount of plastic waste generated. Simultaneously, plastic recycling, even in countries with highly developed waste-management infrastructure, has historically been low [6]. This lack of recycling has resulted in a flood of plastic products and packaging with dead-end material flows, largely due to the international trade of low-value waste plastics that remain as mismanaged waste in the receiving country [31]. The turn of the century also marked increased emissions of plastic waste from large fishing fleets and artisanal fisheries [32]. Increased international economic activity and the fragmentation and resuspension of degraded macroplastics probably drive the observed increasing trend. These factors have overwhelmed both the natural export mechanisms that transport plastic out of the OSL and any positive impact of those early binding interventions that may have driven the observed decrease toward the end of last century. Limitations The study results are limited by sampling distribution and the unequal distribution of observations (Fig 2 and S4 Fig). The vast majority of samples was collected in the North Pacific and North Atlantic Oceans (Fig 2). Therefore, our results will be biased to observed trends in those ocean basins. The coefficient of variation (S4 Fig) had a wide spread (min = 0.447, max = 10.558, mean = 2.602), which underscores the challenge in modeling time-trends of ocean plastic concentrations accurately. The South Atlantic, Mediterranean, and Indian oceans had the lowest coefficient of variations, but that may be more due to the small number of samples and limited spatial distributions there than having smaller spatial variations. In addition, we recognize limitations in our estimates of particle counts and mass. Particle counts may vary considerably when considering the lower size limit for particles. In terms of mass, and while we used a simple conversion of count to mass [12], new techniques are being developed (e.g., machine learning) to estimate mas and count conversions more accurately [33]. Policy implications The accelerating abundance of plastic in the OSL demands urgent international policy intervention to minimize ecological, social, and economic harm [5]. Without substantial widespread policy changes, the rate at which plastics enter aquatic environments will increase approximately 2.6-fold from 2016 to 2040 [6]. Existing international policies on plastic are fragmented, favor business-oriented solutions [34], lack specificity, and do not include measurable targets [35], with the exception of the 2019 Plastic Waste Amendments to the Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal [36]. Although legally binding, this Convention regulates plastic trade only at the very end of its life cycle, once it becomes waste. International policy interventions after 2005 generally lack robust monitoring frameworks and enforcement mechanisms [34–37]. Because they also are non-binding and voluntary, they are not stemming the tide [38]. For example, the New Global Economy Commitment [39] promotes a set of circular economic principles to ensure the economic viability and meaningful reduction in the production of plastic waste: restrictions on certain products, extended producer responsibility for new and existing products, and waste-reduction targets. They invite stakeholders voluntarily to adopt the goal of making 100% of plastic packaging reusable, recyclable, or compostable by 2025, yet these measures advocate for private-sector self-regulation [34]. Economic barriers to recycled plastic continue to place virgin plastics at a lower cost, as the industries that produce and use plastics resist binding commitments to use recycled plastic and design standards for efficient recyclability, leaving recycling overall to fail expectations [40]. This increased production of virgin plastics will increasingly undermine circular economic principles, including the reuse economy and global policy interventions intended to reduce the most polluting plastic products and packaging [41].
Conclusions Although scientists continue to understand better the environmental fate of plastic pollution, there is consensus that global increases in plastic production result in dramatic increases in plastic pollution as shown herein, underscoring the urgent need for effective global governance. Currently, we are at a turning point in history. Early in 2022, at the United Nations Environmental Assembly 5.2. in Nairobi, all Member States adopted a resolution to end plastic pollution, committing to establish a legally binding global agreement that addresses the full life-cycle of plastic, including its production, design, and disposal, by 2024 [42]. The final outcome of this agreement will be a treaty, but its strength will depend on commitments by the member states and on whether measures are focused on the full life cycle of plastics, from extraction and manufacturing to its end of life [43]. Environmental recovery of plastic has limited merit, so solution strategies must address those systems that restrict emissions of plastic pollution in the first place. Therefore, establishing standardized monitoring frameworks to track global trends and creating binding and enforceable international agreements to prevent the emissions of plastic pollution are the best long-term global solutions.
Supporting information S1 Dataset. These data are available at figshare.com. Plastic Marine Pollution Global Dataset, Modeling code, and Trend Reversal data are available open source On GitHub. The following dataset includes all data points used in our model: https://github.com/wincowgerDEV/ocean_plastic_modeling. https://doi.org/10.1371/journal.pone.0281596.s001 (TXT) S1 Fig. Correcting for non-detects. Correcting for non-detects using the cenros function, we estimated the actual values of the zeros to include in the model (A) observed concentration histogram log+1 transformed. Shows that there is a large gap between the zero observations and the nonzeros which indicates a need to correct non-detects. (B) corrected concentrations are normally distributed in log space. https://doi.org/10.1371/journal.pone.0281596.s002 (TIF) S2 Fig. QQ plots. (A) QQ plots for the initial model fit and (B) the residual model fit. https://doi.org/10.1371/journal.pone.0281596.s003 (TIF) S3 Fig. Global trend based on residuals. Annual global estimates of floating microplastic particles based on residuals from 1979 to 2019 show a period slow decreasing abundance and a steady increase from 2005 onward. Residuals are in log transformed space. The shaded grey area reflects confidence intervals. The “rugplot” at the bottom of the figure provides a line for each sample to show the density of stations. The low number of stations on either end of the figure results in wide confidence intervals. https://doi.org/10.1371/journal.pone.0281596.s004 (TIF) S4 Fig. Coefficient of variation for the datasets for each year. Sampling from year to year and basin to basin has a similar about of relative variability, which is a good thing in terms of fitting models to it. https://doi.org/10.1371/journal.pone.0281596.s005 (TIF) S1 Table. Summary of datasets used in model. The datasets used in the model (126 total). The year (of sample collection), data source, mesh size of net, the ocean basin, and the number of observations in that dataset are summarized. https://doi.org/10.1371/journal.pone.0281596.s006 (XLSX)
Acknowledgments We thank Ocean Missions for data from Iceland and Greenland and thank Ocean Research Project for data from across the Arctic. We also thank the anonymous reviewers for their highly constructive suggestions, which helped to improve this manuscript.