posts: 24889
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| 24889 | Where does our plastic accumulate in the ocean? | untitled-reusable-block-29 | wp_block | publish | <!-- wp:columns --> <div class="wp-block-columns"><!-- wp:column --> <div class="wp-block-column"><!-- wp:paragraph --> <p>The world now produces more than <a href="https://ourworldindata.org/plastic-pollution#how-much-plastic-does-the-world-produce">380 million tonnes</a> of plastic every year, which could end up as pollutants, entering our natural environment and oceans.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>Of course, not all of our plastic waste ends up in the ocean, most ends up in landfills: it’s estimated that the share of global plastic waste that enters the ocean is around 3%.{ref}Jambeck, J. R., Geyer, R., Wilcox, C., Siegler, T. R., Perryman, M., Andrady, A., … & Law, K. L. (2015). <a href="http://science.sciencemag.org/content/347/6223/768">Plastic waste inputs from land into the ocean</a>. <em>Science</em>, 347(6223), 768-771.{/ref} In 2010 – the year for which we have the latest estimates – that was around 8 million tonnes.{ref}The estimates for this figure range from around 4 to 12 million tonnes, with 8 million as a midpoint. In the context of this discussion, the uncertainty in this value is less important: the difference between ocean plastic inputs and observed plastic in surface ocean waters are orders of magnitude – rather than multiples – apart.{/ref}</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>Most of the plastic materials we produce are less dense than water and should therefore float at the ocean surface. But our best estimates of the amount of plastic afloat at sea are orders of magnitude lower than the amount of plastic that enters our oceans in a single year: as we show in the visualization, it’s far lower than 8 million tonnes and instead in the order of 10s to 100s of thousands of tonnes. One of the most widely-quoted estimates is 250,000 tonnes.{ref}Eriksen, M. et al. <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0111913">Plastic pollution in the world’s oceans: more than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea</a>. <em>Plos One</em> 9, e111913 (2014).{/ref}</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>If we currently pollute our oceans with millions of tonnes of plastic each year, we must have released tens of millions of tonnes in recent decades. Why then do we find at least 100 times less plastics in our surface waters? </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>This discrepancy is often referred to as the ‘missing plastic problem’.{ref}Lebreton, L., Slat, B., Ferrari, F., Sainte-Rose, B., Aitken, J., Marthouse, R., … & Noble, K. (2018). Evidence that the Great Pacific Garbage Patch is rapidly accumulating plastic. <em>Scientific Reports</em>, <em>8</em>(1), 4666. Available at:<a href="https://www.nature.com/articles/s41598-018-22939-w"> https://www.nature.com/articles/s41598-018-22939-w</a>.{/ref} It’s a conundrum we need to address if we want to understand where plastic waste could end up, and what its impacts might be for wildlife, ecosystems and health.</p> <!-- /wp:paragraph --></div> <!-- /wp:column --> <!-- wp:column --> <div class="wp-block-column"><!-- wp:paragraph --> <p> </p> <!-- /wp:paragraph --> <!-- wp:image {"id":24884,"sizeSlug":"full"} --> <figure class="wp-block-image size-full"><img src="https://owid.cloud/app/uploads/2019/09/Pathway-of-plastic-to-ocean.png" alt="" class="wp-image-24884"/></figure> <!-- /wp:image --></div> <!-- /wp:column --></div> <!-- /wp:columns --> <!-- wp:heading {"level":4} --> <h4>The ‘missing plastic problem’</h4> <!-- /wp:heading --> <!-- wp:paragraph --> <p>There are several hypotheses to explain the ‘missing plastic problem’. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>One possibility is that it is due to imprecise measurement: we might either grossly overestimate the amount of plastic waste we release into the ocean, or underestimate the amount floating in the surface ocean. Whilst we know that tracking ocean plastic inputs and their distribution is notoriously difficult{ref}Cressey, D. (2016). <a href="https://www.nature.com/news/bottles-bags-ropes-and-toothbrushes-the-struggle-to-track-ocean-plastics-1.20432">Bottles, bags, ropes and toothbrushes: the struggle to track ocean plastics</a>. <em>Nature News</em>, <em>536</em>(7616), 263.{/ref} the levels of uncertainty in these measurements are much less than the several orders of magnitude that would be needed to explain the missing plastic problem.{ref}Lebreton, L., Egger, M., & Slat, B. (2019). <a href="https://www.nature.com/articles/s41598-019-49413-5">A global mass budget for positively buoyant macroplastic debris in the ocean</a>. <em>Scientific reports</em>, <em>9</em>(1), 1-10.{/ref} <br><br>Another popular hypothesis is that ultraviolet light (UV) and mechanical wave forces break large pieces of plastic into smaller ones.These smaller particles, referred to as microplastics, are much more easily incorporated into sediments or ingested by organisms. And this is where the missing plastic might end up.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>One proposed ‘sink’ for ocean plastics was deep-sea sediments; a study which sampled deep-sea sediments across several basins found that microplastic was up to four orders of magnitude more abundant (per unit volume) in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean than in plastic-polluted surface waters.{ref}Woodall, L. C., Sanchez-Vidal, A., Canals, M., Paterson, G. L., Coppock, R., Sleight, V., … & Thompson, R. C. (2014). <a href="http://rsos.royalsocietypublishing.org/content/1/4/140317">The deep sea is a major sink for microplastic debris</a>. <em>Royal Society Open Science</em>, 1(4), 140317.{/ref}<br><br>But, new research may suggest a third explanation: that plastics in the ocean break down slower than previously thought, and that much of the missing plastic is washed up or buried in our shorelines.{ref}Lebreton, L., Egger, M., & Slat, B. (2019). <a href="https://www.nature.com/articles/s41598-019-49413-5">A global mass budget for positively buoyant macroplastic debris in the ocean</a>. <em>Scientific reports</em>, <em>9</em>(1), 1-10.{/ref} </p> <!-- /wp:paragraph --> <!-- wp:heading {"level":4} --> <h4>Plastics persist for decades and accumulate on our shorelines</h4> <!-- /wp:heading --> <!-- wp:paragraph --> <p>To try to understand the conundrum of what happens to plastic waste when it enters the ocean, Lebreton, Egger and Slat (2019) created a global model of ocean plastics from 1950 to 2015. This model uses data on global plastic production, emissions into the ocean by plastic type and age, and transport and degradation rates to map not only the amount of plastic in different environments in the ocean, but also its age.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>The authors aimed to quantify where plastic accumulates in the ocean across three environments: the shoreline (defined as dry land bordering the ocean), coastal areas (defined as waters with a depth less than 200 meters) and offshore (waters with a depth greater than 200 meters). They wanted to understand where plastic accumulates, and how old it is: a few years old, ten years or decades? </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>In the visualization I summarized their results. This is shown for two categories of plastics: shown in blue are ‘macroplastics’ (larger plastic materials greater than 0.5 centimeters in diameter) and shown in red microplastics (smaller particles less than 0.5 centimeters). </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>There are some key points we can take away from the visualization:</p> <!-- /wp:paragraph --> <!-- wp:list --> <ul><li>The vast majority – 82 million tonnes of macroplastics and 40 million tonnes of microplastics – is washed up, buried or resurfaced along the world’s shorelines.</li><li>Much of the macroplastics in our shorelines is from the past 15 years, but still a significant amount is older suggesting it can persist for several decades without breaking down.</li><li>In coastal regions most macroplastics (79%) are recent – less than 5 years old.</li><li>In offshore environments, older microplastics have had longer to accumulate than in coastal regions. There macroplastics from several decades ago – even as far back as the 1950s and 1960s – persist. </li><li>Most microplastics (three-quarters) in offshore environments are from the 1990s and earlier, suggesting it can take several decades for plastics to break down.</li></ul> <!-- /wp:list --> <!-- wp:paragraph --> <p>What does this mean for our understanding of the ‘missing plastic’ problem?</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p><strong>Firstly</strong>, is that the majority of ocean plastics are washed, buried and resurface along our shorelines. Whilst we try to tally ocean inputs with the amount floating in gyres at the centre of our oceans, most of it may be accumulating around the edges of the oceans. This would explain why we find much less in surface waters than we’d expect. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p><strong>Secondly</strong>, accumulated plastics are much older than previously thought. Macroplastics appear to persist in the surface of the ocean for decades without breaking down. Offshore we find large plastic objects dating as far back as the 1950s and 1960s. This goes against previous hypotheses of the ‘missing plastic’ problem which suggested that UV light and wave action degrade and remove them from the surface in only a few years. </p> <!-- /wp:paragraph --> <!-- wp:image {"id":24886} --> <figure class="wp-block-image"><img src="https://owid.cloud/app/uploads/2019/09/Where-does-plastic-accumulate-800x396.png" alt="" class="wp-image-24886"/></figure> <!-- /wp:image --> <!-- wp:heading {"level":4} --> <h4>How much plastic will remain in surface oceans in the coming decades?</h4> <!-- /wp:heading --> <!-- wp:paragraph --> <p>The study by Lebreton, Egger and Slat challenges the previous hypotheses that plastics in the surface ocean have a very short lifetime, quickly degrade into microplastics and sink to greater depths. Their results suggest that macroplastics can persist for decades; can be buried and resurfaced along shorelines; and end up in offshore regions years later. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>If true, this matters a lot for how much plastic we would expect in our surface oceans in the decades which follow. The same study also modelled how the mass of plastics – both macro and micro – in the world’s surface waters might evolve under three scenarios:</p> <!-- /wp:paragraph --> <!-- wp:list {"ordered":true} --> <ol><li>we stop emitting any plastics to our oceans by 2020;</li><li>‘emissions’ of plastic to the ocean continue to increase until 2020 then level off;</li><li>‘emissions’ continue to grow to 2050 in line with historic growth rates.{ref}Under growth scenarios, the authors assume annual growth rates continue in line with the average increase in global plastic production over the decade from 2005-2015.{/ref}</li></ol> <!-- /wp:list --> <!-- wp:paragraph --> <p>Their results are shown in the charts.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>The scenarios of continued emissions growth are what we’d expect: if we continue to release more plastics to the ocean, we’ll have more in our surface waters. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>What’s more striking is that even if we stopped ocean plastic waste by 2020, macroplastics would persist in our surface waters for many more decades. This is because we have a large legacy of plastics buried and awash on our shorelines which would continue to resurface and be transported to offshore regions; and existing plastics can persist in the ocean environment for many decades.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>The amount of microplastics in our surface ocean will increase under every scenario because the large plastics that we already have on our shorelines and surface waters will continue to breakdown. And, any additional plastics we add will contribute further. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>This also matters for how we solve the problem of ocean pollution.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>If we want to rapidly reduce the amount of both macro- and microplastics in our oceans, these results suggest two priorities:<br><br> <em>Number one</em> — we must stop plastic waste entering our waterways as soon as possible. Most of the plastic that ends up in our oceans does so because of <a href="https://ourworldindata.org/plastic-pollution#mismanaged-plastic-waste">poor waste management</a> practices – particularly in <a href="https://ourworldindata.org/plastic-pollution#what-determines-how-much-mismanaged-waste-we-produce">low-to-middle income countries</a>; this means that good waste management across the world is essential to achieving this.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>But this ambitious target alone will not be enough. We have many decades of legacy waste to contend with.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>This makes a <em>second priority</em> necessary— we have to focus our efforts on recapturing and removing plastics already in our offshore waters and shorelines. This is the goal of Slat, Lebreton and Egger – the authors of this paper – with their <a href="https://theoceancleanup.com/">Ocean Cleanup</a> project.</p> <!-- /wp:paragraph --> <!-- wp:html --> <iframe src="https://ourworldindata.org/grapher/macroplastics-in-ocean"></iframe> <!-- /wp:html --> <!-- wp:html --> <iframe src="https://ourworldindata.org/grapher/microplastics-in-ocean"></iframe> <!-- /wp:html --> | {
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"text": "To try to understand the conundrum of what happens to plastic waste when it enters the ocean, Lebreton, Egger and Slat (2019) created a global model of ocean plastics from 1950 to 2015. This model uses data on global plastic production, emissions into the ocean by plastic type and age, and transport and degradation rates to map not only the amount of plastic in different environments in the ocean, but also its age.",
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2019-09-24 06:12:15 | 2022-04-13 14:10:14 | {} |
The world now produces more than [380 million tonnes](https://ourworldindata.org/plastic-pollution#how-much-plastic-does-the-world-produce) of plastic every year, which could end up as pollutants, entering our natural environment and oceans. Of course, not all of our plastic waste ends up in the ocean, most ends up in landfills: it’s estimated that the share of global plastic waste that enters the ocean is around 3%.{ref}Jambeck, J. R., Geyer, R., Wilcox, C., Siegler, T. R., Perryman, M., Andrady, A., … & Law, K. L. (2015). [Plastic waste inputs from land into the ocean](http://science.sciencemag.org/content/347/6223/768). _Science_, 347(6223), 768-771.{/ref} In 2010 – the year for which we have the latest estimates – that was around 8 million tonnes.{ref}The estimates for this figure range from around 4 to 12 million tonnes, with 8 million as a midpoint. In the context of this discussion, the uncertainty in this value is less important: the difference between ocean plastic inputs and observed plastic in surface ocean waters are orders of magnitude – rather than multiples – apart.{/ref} Most of the plastic materials we produce are less dense than water and should therefore float at the ocean surface. But our best estimates of the amount of plastic afloat at sea are orders of magnitude lower than the amount of plastic that enters our oceans in a single year: as we show in the visualization, it’s far lower than 8 million tonnes and instead in the order of 10s to 100s of thousands of tonnes. One of the most widely-quoted estimates is 250,000 tonnes.{ref}Eriksen, M. et al. [Plastic pollution in the world’s oceans: more than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0111913). _Plos One_ 9, e111913 (2014).{/ref} If we currently pollute our oceans with millions of tonnes of plastic each year, we must have released tens of millions of tonnes in recent decades. Why then do we find at least 100 times less plastics in our surface waters? This discrepancy is often referred to as the ‘missing plastic problem’.{ref}Lebreton, L., Slat, B., Ferrari, F., Sainte-Rose, B., Aitken, J., Marthouse, R., … & Noble, K. (2018). Evidence that the Great Pacific Garbage Patch is rapidly accumulating plastic. _Scientific Reports_, _8_(1), 4666. Available at:[ https://www.nature.com/articles/s41598-018-22939-w](https://www.nature.com/articles/s41598-018-22939-w).{/ref} It’s a conundrum we need to address if we want to understand where plastic waste could end up, and what its impacts might be for wildlife, ecosystems and health. <Image filename="Pathway-of-plastic-to-ocean.png" alt=""/> ## The ‘missing plastic problem’ There are several hypotheses to explain the ‘missing plastic problem’. One possibility is that it is due to imprecise measurement: we might either grossly overestimate the amount of plastic waste we release into the ocean, or underestimate the amount floating in the surface ocean. Whilst we know that tracking ocean plastic inputs and their distribution is notoriously difficult{ref}Cressey, D. (2016). [Bottles, bags, ropes and toothbrushes: the struggle to track ocean plastics](https://www.nature.com/news/bottles-bags-ropes-and-toothbrushes-the-struggle-to-track-ocean-plastics-1.20432). _Nature News_, _536_(7616), 263.{/ref} the levels of uncertainty in these measurements are much less than the several orders of magnitude that would be needed to explain the missing plastic problem.{ref}Lebreton, L., Egger, M., & Slat, B. (2019). [A global mass budget for positively buoyant macroplastic debris in the ocean](https://www.nature.com/articles/s41598-019-49413-5). _Scientific reports_, _9_(1), 1-10.{/ref} Another popular hypothesis is that ultraviolet light (UV) and mechanical wave forces break large pieces of plastic into smaller ones.These smaller particles, referred to as microplastics, are much more easily incorporated into sediments or ingested by organisms. And this is where the missing plastic might end up. One proposed ‘sink’ for ocean plastics was deep-sea sediments; a study which sampled deep-sea sediments across several basins found that microplastic was up to four orders of magnitude more abundant (per unit volume) in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean than in plastic-polluted surface waters.{ref}Woodall, L. C., Sanchez-Vidal, A., Canals, M., Paterson, G. L., Coppock, R., Sleight, V., … & Thompson, R. C. (2014). [The deep sea is a major sink for microplastic debris](http://rsos.royalsocietypublishing.org/content/1/4/140317). _Royal Society Open Science_, 1(4), 140317.{/ref} But, new research may suggest a third explanation: that plastics in the ocean break down slower than previously thought, and that much of the missing plastic is washed up or buried in our shorelines.{ref}Lebreton, L., Egger, M., & Slat, B. (2019). [A global mass budget for positively buoyant macroplastic debris in the ocean](https://www.nature.com/articles/s41598-019-49413-5). _Scientific reports_, _9_(1), 1-10.{/ref} ## Plastics persist for decades and accumulate on our shorelines To try to understand the conundrum of what happens to plastic waste when it enters the ocean, Lebreton, Egger and Slat (2019) created a global model of ocean plastics from 1950 to 2015. This model uses data on global plastic production, emissions into the ocean by plastic type and age, and transport and degradation rates to map not only the amount of plastic in different environments in the ocean, but also its age. The authors aimed to quantify where plastic accumulates in the ocean across three environments: the shoreline (defined as dry land bordering the ocean), coastal areas (defined as waters with a depth less than 200 meters) and offshore (waters with a depth greater than 200 meters). They wanted to understand where plastic accumulates, and how old it is: a few years old, ten years or decades? In the visualization I summarized their results. This is shown for two categories of plastics: shown in blue are ‘macroplastics’ (larger plastic materials greater than 0.5 centimeters in diameter) and shown in red microplastics (smaller particles less than 0.5 centimeters). There are some key points we can take away from the visualization: * The vast majority – 82 million tonnes of macroplastics and 40 million tonnes of microplastics – is washed up, buried or resurfaced along the world’s shorelines. * Much of the macroplastics in our shorelines is from the past 15 years, but still a significant amount is older suggesting it can persist for several decades without breaking down. * In coastal regions most macroplastics (79%) are recent – less than 5 years old. * In offshore environments, older microplastics have had longer to accumulate than in coastal regions. There macroplastics from several decades ago – even as far back as the 1950s and 1960s – persist. * Most microplastics (three-quarters) in offshore environments are from the 1990s and earlier, suggesting it can take several decades for plastics to break down. What does this mean for our understanding of the ‘missing plastic’ problem? **Firstly**, is that the majority of ocean plastics are washed, buried and resurface along our shorelines. Whilst we try to tally ocean inputs with the amount floating in gyres at the centre of our oceans, most of it may be accumulating around the edges of the oceans. This would explain why we find much less in surface waters than we’d expect. **Secondly**, accumulated plastics are much older than previously thought. Macroplastics appear to persist in the surface of the ocean for decades without breaking down. Offshore we find large plastic objects dating as far back as the 1950s and 1960s. This goes against previous hypotheses of the ‘missing plastic’ problem which suggested that UV light and wave action degrade and remove them from the surface in only a few years. <Image filename="Where-does-plastic-accumulate.png" alt=""/> ## How much plastic will remain in surface oceans in the coming decades? The study by Lebreton, Egger and Slat challenges the previous hypotheses that plastics in the surface ocean have a very short lifetime, quickly degrade into microplastics and sink to greater depths. Their results suggest that macroplastics can persist for decades; can be buried and resurfaced along shorelines; and end up in offshore regions years later. If true, this matters a lot for how much plastic we would expect in our surface oceans in the decades which follow. The same study also modelled how the mass of plastics – both macro and micro – in the world’s surface waters might evolve under three scenarios: 0. we stop emitting any plastics to our oceans by 2020; 1. ‘emissions’ of plastic to the ocean continue to increase until 2020 then level off; 2. ‘emissions’ continue to grow to 2050 in line with historic growth rates.{ref}Under growth scenarios, the authors assume annual growth rates continue in line with the average increase in global plastic production over the decade from 2005-2015.{/ref} Their results are shown in the charts. The scenarios of continued emissions growth are what we’d expect: if we continue to release more plastics to the ocean, we’ll have more in our surface waters. What’s more striking is that even if we stopped ocean plastic waste by 2020, macroplastics would persist in our surface waters for many more decades. This is because we have a large legacy of plastics buried and awash on our shorelines which would continue to resurface and be transported to offshore regions; and existing plastics can persist in the ocean environment for many decades. The amount of microplastics in our surface ocean will increase under every scenario because the large plastics that we already have on our shorelines and surface waters will continue to breakdown. And, any additional plastics we add will contribute further. This also matters for how we solve the problem of ocean pollution. If we want to rapidly reduce the amount of both macro- and microplastics in our oceans, these results suggest two priorities: _Number one_ — we must stop plastic waste entering our waterways as soon as possible. Most of the plastic that ends up in our oceans does so because of [poor waste management](https://ourworldindata.org/plastic-pollution#mismanaged-plastic-waste) practices – particularly in [low-to-middle income countries](https://ourworldindata.org/plastic-pollution#what-determines-how-much-mismanaged-waste-we-produce); this means that good waste management across the world is essential to achieving this. But this ambitious target alone will not be enough. We have many decades of legacy waste to contend with. This makes a _second priority_ necessary— we have to focus our efforts on recapturing and removing plastics already in our offshore waters and shorelines. This is the goal of Slat, Lebreton and Egger – the authors of this paper – with their [Ocean Cleanup](https://theoceancleanup.com/) project. <Chart url="https://ourworldindata.org/grapher/macroplastics-in-ocean"/> <Chart url="https://ourworldindata.org/grapher/microplastics-in-ocean"/> | {
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"content": "\n<div class=\"wp-block-columns\">\n<div class=\"wp-block-column\">\n<p>The world now produces more than <a href=\"https://ourworldindata.org/plastic-pollution#how-much-plastic-does-the-world-produce\">380 million tonnes</a> of plastic every year, which could end up as pollutants, entering our natural environment and oceans.</p>\n\n\n\n<p>Of course, not all of our plastic waste ends up in the ocean, most ends up in landfills: it\u2019s estimated that the share of global plastic waste that enters the ocean is around 3%.{ref}Jambeck, J. R., Geyer, R., Wilcox, C., Siegler, T. R., Perryman, M., Andrady, A., \u2026 & Law, K. L. (2015). <a href=\"http://science.sciencemag.org/content/347/6223/768\">Plastic waste inputs from land into the ocean</a>. <em>Science</em>, 347(6223), 768-771.{/ref} In 2010 \u2013 the year for which we have the latest estimates \u2013 that was around 8 million tonnes.{ref}The estimates for this figure range from around 4 to 12 million tonnes, with 8 million as a midpoint. In the context of this discussion, the uncertainty in this value is less important: the difference between ocean plastic inputs and observed plastic in surface ocean waters are orders of magnitude \u2013 rather than multiples \u2013 apart.{/ref}</p>\n\n\n\n<p>Most of the plastic materials we produce are less dense than water and should therefore float at the ocean surface. But our best estimates of the amount of plastic afloat at sea are orders of magnitude lower than the amount of plastic that enters our oceans in a single year: as we show in the visualization, it\u2019s far lower than 8 million tonnes and instead in the order of 10s to 100s of thousands of tonnes. One of the most widely-quoted estimates is 250,000 tonnes.{ref}Eriksen, M. et al. <a href=\"https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0111913\">Plastic pollution in the world\u2019s oceans: more than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea</a>. <em>Plos One</em> 9, e111913 (2014).{/ref}</p>\n\n\n\n<p>If we currently pollute our oceans with millions of tonnes of plastic each year, we must have released tens of millions of tonnes in recent decades. Why then do we find at least 100 times less plastics in our surface waters? </p>\n\n\n\n<p>This discrepancy is often referred to as the \u2018missing plastic problem\u2019.{ref}Lebreton, L., Slat, B., Ferrari, F., Sainte-Rose, B., Aitken, J., Marthouse, R., \u2026 & Noble, K. (2018). Evidence that the Great Pacific Garbage Patch is rapidly accumulating plastic. <em>Scientific Reports</em>, <em>8</em>(1), 4666. Available at:<a href=\"https://www.nature.com/articles/s41598-018-22939-w\"> https://www.nature.com/articles/s41598-018-22939-w</a>.{/ref} It\u2019s a conundrum we need to address if we want to understand where plastic waste could end up, and what its impacts might be for wildlife, ecosystems and health.</p>\n</div>\n\n\n\n<div class=\"wp-block-column\">\n<p> </p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" width=\"3326\" height=\"2043\" src=\"https://owid.cloud/app/uploads/2019/09/Pathway-of-plastic-to-ocean.png\" alt=\"\" class=\"wp-image-24884\" srcset=\"https://owid.cloud/app/uploads/2019/09/Pathway-of-plastic-to-ocean.png 3326w, https://owid.cloud/app/uploads/2019/09/Pathway-of-plastic-to-ocean-150x92.png 150w, https://owid.cloud/app/uploads/2019/09/Pathway-of-plastic-to-ocean-400x246.png 400w, https://owid.cloud/app/uploads/2019/09/Pathway-of-plastic-to-ocean-768x472.png 768w, https://owid.cloud/app/uploads/2019/09/Pathway-of-plastic-to-ocean-800x491.png 800w\" sizes=\"(max-width: 3326px) 100vw, 3326px\" /></figure>\n</div>\n</div>\n\n\n\n<h4>The \u2018missing plastic problem\u2019</h4>\n\n\n\n<p>There are several hypotheses to explain the \u2018missing plastic problem\u2019. </p>\n\n\n\n<p>One possibility is that it is due to imprecise measurement: we might either grossly overestimate the amount of plastic waste we release into the ocean, or underestimate the amount floating in the surface ocean. Whilst we know that tracking ocean plastic inputs and their distribution is notoriously difficult{ref}Cressey, D. (2016). <a href=\"https://www.nature.com/news/bottles-bags-ropes-and-toothbrushes-the-struggle-to-track-ocean-plastics-1.20432\">Bottles, bags, ropes and toothbrushes: the struggle to track ocean plastics</a>. <em>Nature News</em>, <em>536</em>(7616), 263.{/ref} the levels of uncertainty in these measurements are much less than the several orders of magnitude that would be needed to explain the missing plastic problem.{ref}Lebreton, L., Egger, M., & Slat, B. (2019). <a href=\"https://www.nature.com/articles/s41598-019-49413-5\">A global mass budget for positively buoyant macroplastic debris in the ocean</a>. <em>Scientific reports</em>, <em>9</em>(1), 1-10.{/ref} <br><br>Another popular hypothesis is that ultraviolet light (UV) and mechanical wave forces break large pieces of plastic into smaller ones.These smaller particles, referred to as microplastics, are much more easily incorporated into sediments or ingested by organisms. And this is where the missing plastic might end up.</p>\n\n\n\n<p>One proposed \u2018sink\u2019 for ocean plastics was deep-sea sediments; a study which sampled deep-sea sediments across several basins found that microplastic was up to four orders of magnitude more abundant (per unit volume) in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean than in plastic-polluted surface waters.{ref}Woodall, L. C., Sanchez-Vidal, A., Canals, M., Paterson, G. L., Coppock, R., Sleight, V., \u2026 & Thompson, R. C. (2014). <a href=\"http://rsos.royalsocietypublishing.org/content/1/4/140317\">The deep sea is a major sink for microplastic debris</a>. <em>Royal Society Open Science</em>, 1(4), 140317.{/ref}<br><br>But, new research may suggest a third explanation: that plastics in the ocean break down slower than previously thought, and that much of the missing plastic is washed up or buried in our shorelines.{ref}Lebreton, L., Egger, M., & Slat, B. (2019). <a href=\"https://www.nature.com/articles/s41598-019-49413-5\">A global mass budget for positively buoyant macroplastic debris in the ocean</a>. <em>Scientific reports</em>, <em>9</em>(1), 1-10.{/ref} </p>\n\n\n\n<h4>Plastics persist for decades and accumulate on our shorelines</h4>\n\n\n\n<p>To try to understand the conundrum of what happens to plastic waste when it enters the ocean, Lebreton, Egger and Slat (2019) created a global model of ocean plastics from 1950 to 2015. This model uses data on global plastic production, emissions into the ocean by plastic type and age, and transport and degradation rates to map not only the amount of plastic in different environments in the ocean, but also its age.</p>\n\n\n\n<p>The authors aimed to quantify where plastic accumulates in the ocean across three environments: the shoreline (defined as dry land bordering the ocean), coastal areas (defined as waters with a depth less than 200 meters) and offshore (waters with a depth greater than 200 meters). They wanted to understand where plastic accumulates, and how old it is: a few years old, ten years or decades? </p>\n\n\n\n<p>In the visualization I summarized their results. This is shown for two categories of plastics: shown in blue are \u2018macroplastics\u2019 (larger plastic materials greater than 0.5 centimeters in diameter) and shown in red microplastics (smaller particles less than 0.5 centimeters). </p>\n\n\n\n<p>There are some key points we can take away from the visualization:</p>\n\n\n\n<ul><li>The vast majority \u2013 82 million tonnes of macroplastics and 40 million tonnes of microplastics \u2013 is washed up, buried or resurfaced along the world\u2019s shorelines.</li><li>Much of the macroplastics in our shorelines is from the past 15 years, but still a significant amount is older suggesting it can persist for several decades without breaking down.</li><li>In coastal regions most macroplastics (79%) are recent \u2013 less than 5 years old.</li><li>In offshore environments, older microplastics have had longer to accumulate than in coastal regions. There macroplastics from several decades ago \u2013 even as far back as the 1950s and 1960s \u2013 persist. </li><li>Most microplastics (three-quarters) in offshore environments are from the 1990s and earlier, suggesting it can take several decades for plastics to break down.</li></ul>\n\n\n\n<p>What does this mean for our understanding of the \u2018missing plastic\u2019 problem?</p>\n\n\n\n<p><strong>Firstly</strong>, is that the majority of ocean plastics are washed, buried and resurface along our shorelines. Whilst we try to tally ocean inputs with the amount floating in gyres at the centre of our oceans, most of it may be accumulating around the edges of the oceans. This would explain why we find much less in surface waters than we\u2019d expect. </p>\n\n\n\n<p><strong>Secondly</strong>, accumulated plastics are much older than previously thought. Macroplastics appear to persist in the surface of the ocean for decades without breaking down. Offshore we find large plastic objects dating as far back as the 1950s and 1960s. This goes against previous hypotheses of the \u2018missing plastic\u2019 problem which suggested that UV light and wave action degrade and remove them from the surface in only a few years. </p>\n\n\n\n<figure class=\"wp-block-image\"><img loading=\"lazy\" width=\"800\" height=\"396\" src=\"https://owid.cloud/app/uploads/2019/09/Where-does-plastic-accumulate-800x396.png\" alt=\"\" class=\"wp-image-24886\" srcset=\"https://owid.cloud/app/uploads/2019/09/Where-does-plastic-accumulate-800x396.png 800w, https://owid.cloud/app/uploads/2019/09/Where-does-plastic-accumulate-150x74.png 150w, https://owid.cloud/app/uploads/2019/09/Where-does-plastic-accumulate-400x198.png 400w, https://owid.cloud/app/uploads/2019/09/Where-does-plastic-accumulate-768x380.png 768w\" sizes=\"(max-width: 800px) 100vw, 800px\" /></figure>\n\n\n\n<h4>How much plastic will remain in surface oceans in the coming decades?</h4>\n\n\n\n<p>The study by Lebreton, Egger and Slat challenges the previous hypotheses that plastics in the surface ocean have a very short lifetime, quickly degrade into microplastics and sink to greater depths. Their results suggest that macroplastics can persist for decades; can be buried and resurfaced along shorelines; and end up in offshore regions years later. </p>\n\n\n\n<p>If true, this matters a lot for how much plastic we would expect in our surface oceans in the decades which follow. The same study also modelled how the mass of plastics \u2013 both macro and micro \u2013 in the world\u2019s surface waters might evolve under three scenarios:</p>\n\n\n\n<ol><li>we stop emitting any plastics to our oceans by 2020;</li><li>\u2018emissions\u2019 of plastic to the ocean continue to increase until 2020 then level off;</li><li>\u2018emissions\u2019 continue to grow to 2050 in line with historic growth rates.{ref}Under growth scenarios, the authors assume annual growth rates continue in line with the average increase in global plastic production over the decade from 2005-2015.{/ref}</li></ol>\n\n\n\n<p>Their results are shown in the charts.</p>\n\n\n\n<p>The scenarios of continued emissions growth are what we\u2019d expect: if we continue to release more plastics to the ocean, we\u2019ll have more in our surface waters. </p>\n\n\n\n<p>What\u2019s more striking is that even if we stopped ocean plastic waste by 2020, macroplastics would persist in our surface waters for many more decades. This is because we have a large legacy of plastics buried and awash on our shorelines which would continue to resurface and be transported to offshore regions; and existing plastics can persist in the ocean environment for many decades.</p>\n\n\n\n<p>The amount of microplastics in our surface ocean will increase under every scenario because the large plastics that we already have on our shorelines and surface waters will continue to breakdown. And, any additional plastics we add will contribute further. </p>\n\n\n\n<p>This also matters for how we solve the problem of ocean pollution.</p>\n\n\n\n<p>If we want to rapidly reduce the amount of both macro- and microplastics in our oceans, these results suggest two priorities:<br><br> <em>Number one</em> \u2014 we must stop plastic waste entering our waterways as soon as possible. Most of the plastic that ends up in our oceans does so because of <a href=\"https://ourworldindata.org/plastic-pollution#mismanaged-plastic-waste\">poor waste management</a> practices \u2013 particularly in <a href=\"https://ourworldindata.org/plastic-pollution#what-determines-how-much-mismanaged-waste-we-produce\">low-to-middle income countries</a>; this means that good waste management across the world is essential to achieving this.</p>\n\n\n\n<p>But this ambitious target alone will not be enough. We have many decades of legacy waste to contend with.</p>\n\n\n\n<p>This makes a <em>second priority</em> necessary\u2014 we have to focus our efforts on recapturing and removing plastics already in our offshore waters and shorelines. This is the goal of Slat, Lebreton and Egger \u2013 the authors of this paper \u2013 with their <a href=\"https://theoceancleanup.com/\">Ocean Cleanup</a> project.</p>\n\n\n\n<iframe src=\"https://ourworldindata.org/grapher/macroplastics-in-ocean\"></iframe>\n\n\n\n<iframe src=\"https://ourworldindata.org/grapher/microplastics-in-ocean\"></iframe>\n"
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