The Skimmer is a new MEAM feature where we review the latest news and research on a particular topic. For our first Skimmer, we’re covering plastic in the ocean and its implications for management. We don’t know about you, but we can barely keep up with the dizzying array of disturbing news on ocean plastic. But since it’s our job to keep up with the news, the Skimmer is here to help out.

Editor’s note: Please be aware that this is NOT a comprehensive review of the literature on plastic in the ocean. This is a roundup of some of what has come out lately – in this case in 2016 and 2017 – primarily in the published literature but with some supplements from popular news reports.

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How much plastic is out there?

  • The first global analysis of all mass-produced plastics ever manufactured estimated that 8,300 million metric tons of virgin plastics have been produced to date. This same study estimated that, as of 2015, approximately 6,300 million metric tons of plastic waste had been generated – of which 9% was recycled, 12% was incinerated, and 79% was in landfills or the natural environment.
  • The research and consulting firm Eunomia pulled together a lot of numbers, both their own and from other sources. These estimates are based on medians of possible ranges and are therefore very rough. But they give an idea of the order of magnitude of plastic flows into and in the ocean. Eunomia estimates:
  • 12.2 million metric tons of plastic enters the oceans every year
  • Over 80% of this comes from land-based sources. This input is largely composed of larger plastic litter such as drink bottles and plastic packaging. Primary microplastics (plastics smaller than 5 mm and manufactured as microbeads, capsules, fibers, or pellets) are a small (<10% by weight) but important component of the total plastic entering the ocean environment.
  • The remainder of plastic entering the ocean is released at sea, primarily from fishing activities (e.g., lost or discarded fishing gear) and shipping activities.

So the plastic entering the ocean from land-based sources, where is it coming from?

  • In a nutshell, most of the plastic entering the ocean is coming from places with large populations and poor waste management. To be more specific, most of it is coming from the Asian continent. (Sorry, Asia.)
  • Eunomia’s number crunching suggests that of the plastic entering the ocean from land-based sources (most of the plastic in the ocean), the bulk is coming from coastal populations (i.e., the plastic featured in the 2015 Jambeck et al. study above) and a smaller portion is coming from inland populations via rivers. Two 2017 studies are helping us to refine numbers for river discharge into the ocean, and, again, Asia is leading the way.

Where does the plastic end up once it is in the ocean?

  • It all ends up in the big garbage patch in the middle of the North Pacific, right? Nope. While there is undoubtedly a lot of plastic in surface waters of the North Pacific gyre (the highest concentration found anywhere on the ocean surface), some recent number crunching suggests that plastic at the surface of the ocean may be a relatively small portion of total plastic in the ocean and most of it may actually be at the bottom of the ocean. In fact, a better question than “where is plastic in the ocean?” would be “where isn’t plastic in the ocean?”
  • Moving north, while plastic debris is scarce or absent in a lot of Arctic waters, there is quite a bit of it in the Greenland and Barents seas, probably due to transfer from the North Atlantic. Further transport from here may be downward, so the seafloor in this area of the Arctic may be collecting a lot of plastic debris and may also be where some of that missing plastic is located.
  • And, finally, one of the most remote islands on earth, Henderson Island in the South Pacific’s Pitcairn Islands, is littered with an estimated 37.7 million pieces of plastic despite being uninhabited by humans.

What happens to plastic once it is in the ocean?

  • We’re not going to dig too deep into this question, but we will offer some quick points from a 2017 article that reviews what is known (and not known) about marine weathering of plastics. Once it is in the ocean, plastic debris is exposed to physical stress (from turbulence, abrasion with other particles, etc.), ultraviolet radiation, changing temperatures, salt, oxidizing conditions and colonization by microorganisms such as phytoplankton, bacteria, and fungi.
  • Plastics break down into progressively smaller bits or “secondary microplastics”, release chemical additives they are manufactured with, absorb and adsorb chemicals from the ambient water, get eaten and potentially passed along in the food chain, move with currents, and, last but not least, sink.
  • These occurrences are definitely not mutually exclusive and can interact in complex ways. For instance, biofouling can increase the density of plastic debris and lead to it sinking. Being eaten by zooplankton may lead to plastic particles being incorporated into fecal pellets which are also relatively dense and sink quickly. Biofouling can increase uptake of plastic particles into the food web and slow the leaching of chemicals into seawater. Sinking lower in the water column or to the seabed can reduce exposure to ultraviolet radiation and physical stress and slow further weathering.
  • In short, the whole thing is complicated, and we have a lot more to learn.

What impacts are plastics having on marine organisms and habitats?

  • We’re all familiar with the distressing photos of sea creatures tangled up in plastic or the stomachs of seabirds filled with plastic bits. Recent years have seen an increase in the roster of animals known to be affected by entanglement with and ingestion of plastic. One recent study used expert elicitation to parse out which plastic trash items were having the greatest impact on seabirds, marine mammals, and sea turtles. The response from experts? Ingestion and entanglement are worse than chemical contamination for these fauna, and fishing gear, balloons, plastic bags, and plastic utensils are the biggest problems.
  • How bad is this for marine animals? Again, it’s unclear, and the answer will undoubtedly be very different for different species and environments. It’s worth bearing in mind, though, that while microplastics are indeed really good at aggregating contaminants in the water, these contaminants were already in the water and potentially being aggregated already by various prey species. So just because animals are eating microplastics with lots of nasty toxins doesn’t mean the animals wouldn’t be exposed to and eating those nasty toxins, at least at some level, anyway…
  • And moving down in size from microplastics, some of the most disturbing recent discoveries relate to nanoplastics (particles smaller than 1 µm). Nanoplastics are produced by industrial processes or the breakdown of microplastics. Very little is known about their distribution in the marine environment because most sampling methods cannot detect nanoplastics.
  • While we are starting to synthesize early research findings on microplastics, nanoplastics are really a new frontier, and very little is known about the impacts of nanoplastics on marine organisms and ecosystems. But early findings suggest that they have the potential to be even more disruptive than larger plastic particles. A very recent study published in Nature found that:

    1. Nanoplastics can get transferred up a food chain, in this case, from algae to zooplankton to fish
    2. Unlike exposure to larger plastic particles, exposure to plastic nanoparticles reduced the survival of zooplankton
    3. Nanoplastics can cross the blood-brain barrier in fish and accumulate in fish brain tissue and, in this study, the fish affected by nanoplastics ate more slowly and explored their surroundings less than unaffected fish.

Tea, anyone?

  • And while most of the literature focuses on the impact of plastics on organisms, plastics can also alter habitats including sandy beaches, salt marshes, mangrove forests, coral reefs, seagrass beds, and oyster reefs. A nice short review of these impacts by habitat is here.
  • In another fascinating bit of news, plastic has also been enabling an extraordinary rafting event in recent years, carrying species-laden debris resulting from the 2011 tsunami in eastern Japan across the Pacific Ocean to North America and Hawai’i. Researchers have documented 289 Japanese coastal marine species arriving alive on eastern Pacific shores, setting new records for transoceanic survival and dispersal of coastal species by rafting. Why this, why now? In large part it is due to the abundance of synthetic materials, including plastic, which float and don’t degrade quickly.

Can we just clean it out of the ocean?

What are we doing to stop plastic from getting into the ocean?

That’s a bummer about marine organisms, but what about me?

  • Well, if you’re eating seafood (or sea salt for that matter), there’s a good chance you are ingesting some amount of plastic (ditto if you are drinking water).
  • Is plasticky seafood bad for you? It’s unclear. While the plastic in seafood is probably not good for you, experts estimate that the amount of chemicals (those added to plastic during manufacture and those adsorbed or absorbed from the environment) from microplastics that a person would ingest from a serving of seafood is negligible. [The consumption of pathogens on microplastics was not considered in this particular analysis, however.]
  • A bigger concern is likely to be nanoplastics which are likely to be passed up the food chain to humans. Unlike microplastics, nanoplastics can leave the digestive system and enter other bodily systems, such as the immune system. So stay tuned on this front.
  • And, of course, the amount of microplastic and nanoplastic in the ocean is expected to increase in coming years. This creates the possibility that the amount of chemicals you get from eating seafood may increase to a more harmful level in the future.

Good for you for making it this far! We’re going to finish up with two big picture questions.

First, what impact is plastic having on marine ecosystems at an ecosystem level?

  • We took the “ask an expert” option on this one and asked this question directly to leading ocean plastics guru Kara Lavender Law. Law is a research professor of oceanography with Sea Education Association in Woods Hole, Massachusetts and was co-lead for the National Center for Ecological Analysis and Synthesis (NCEAS) working group on marine debris from 2011 to 2015. According to Law, “This is one of the biggest questions in plastic marine debris research. Chelsea Rochman led a critical analysis of the literature through 2012 in a paper published in Ecology that asked the question about ecosystem level impacts of debris from evidence presented in the scientific literature. They found only two demonstrated impacts at the ecological level, both affecting the biological assemblage – one due to the addition of debris as artificial habitat, the other to smothering by debris. These impacts are not those most people think about when they think about plastic marine debris. We simply do not know what the ecological impacts are of plastics ingestion or entanglement, for example, on populations or ecosystems. This doesn’t mean there are none, but these are very difficult questions to answer.”

And second, how critical is plastic pollution relative to other ocean threats?

  • I think that by now we’ve all read that horrific estimate that if we keep producing (and not properly disposing of) plastics at predicted rates, there will be more plastic (by weight) than fish in the oceans by 2050. While there is some debate about the accuracy of this estimate, there is undoubtedly a lot of plastic going into the oceans.
  • We took the “ask an expert” option again here and asked Law this question. According to her, “Gauging the ‘importance’ of these impacts relative to other threats to ocean and ecosystem health is entirely dependent on the metrics – what is considered ‘important’? It may be that today some of the other threats, such as ocean warming, ocean acidification, overfishing, eutrophication, etc., are having larger or more immediate impacts on particular cohorts or ecosystems. But the continuing acceleration in global plastics production with no clear ‘best’ management strategy for these materials at their end-of-life is a major cause for concern into the future.”

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