Note: this overview was based on largely on OCTO‘s excellent edition of The Skimmer from November of 2017.

A history of plastic

Our use of plastic (i.e. malleable) materials began with biologically-derived materials that had intrinsic abilities to bend or properties that allowed folks to mold and conform them into solid and semi-solid objects of various sizes and strengths. Early examples include resins secreted onto trees in India by female Coccoid scale insects (lac bugs, Kerria lacca) being transformed into shellac and the natural gum (chicle) harvested from various South American trees (Manilkara spp.) becoming the basis for our early formulations of chewing gum. The 19th century saw increasing interest in chemically altering of naturally-occurring materials such as rubber, nitrocellulose, and collagen. Soon, chemists were experimenting with tweaks to such naturally occurring compounds to produce compounds like galalite (the product of mixing mammalian milk-derived phosphoproteins with formaldehyde). By the early 1900s, numerous chemists were exploring a wide range of completely synthesized materials that we now recognize as modern, primary petroleum-derived plastics.

A few highlights of our modern, plastic age include:

  • 1855 British chemist Alexander Parkes invents Parkesine, now called celluloid.
  • 1872 German chemist Eugen Baumann polymerizes Polyvinyl chloride (PVC).
  • 1907 Belgian-American chemist Leo Baekeland created Bakelite, the first “real” synthetic that would go on to kick off our modern era of mass-produced plastic (thanks, Leo…).
  • 1945 the end of WWII drives a massive pivot of war-time industry to a consumer-facing, mass-marketed “convenience” era wherein products become increasingly dominated by plastic-containing items.
  • 1968 The Graduate motion picture opens and helps codify a then somewhat amorphous idea burbling through Baby Boomer youth culture at the time which saw love of plastics as “misplaced enthusiasm for an industry that, rather than being full of possibilities, was a symbol of cheap conformity and superficiality.”
  • 1994 the U.S. EPA mandates that all six-pack rings must be biodegradable, culminating 20 years of grass-roots educational campaign focused on attacking the first symbol of coastal and marine plastic pollution.
  • 2015 sea turtle researcher Christine Figgener from Texas A&M films the removal of a single-use plastic straw from the nose of a turtle. The video goes viral and becomes synonymous with the dangers of plastic debris to marine life. As of September 2019, the video has been viewed 37.6 million time on the YouTube platform alone.

An excellent (albeit pro-plastics industry and Euro-centric) timeline of plastic development can be found here.

Categorizing plastic

Today “plastic” is generally taken to refer to synthetic or semi-synthetic polymers (molecules with many repeated subunits), These substances include “pure” plastics with hydrocarbon backbones connected only by carbon-carbon bonds such as…

…and increasingly heterochain polymers (whose backbones are innervated can connected via non-carbon elemental bonds) where much research has centered over past decades:

The Big 8 plastics

What is “microplastic”?

Microplastic (aka “microplastics”) has become a wildly popular term in recent years. Initially this term was used to differentiate smaller, more or less microscopic pieces of polymer (think grains of sand) from the more macroscopic items you can see with the naked eye from some distance away (think plastic straw or plastic bag):

  • Microplastic is typically defined as plastic debris whose maximum dimension is <5 mm. Once we started hunting for microplastic, we quickly recognized yet another broad category of plastic pieces significantly smaller that a few mm. So while “microplastic” is the most universal term, additional terms and modifiers have grown in popularity. Chiefly…
  • Nanoplastic is typically defined as plastic debris whose maximum dimension is between 1 and 100 nm (sensu EFSA 2016).

Most microplastic items we encounter in our monitoring can be readily classified into one of three gross morphological categories:

  • Microspheres (aka microbeads) are machined spheres with constant diameter designed as abrasives in retail products or industrial processes.
  • Microfibers are filamentous or hair-like. These are often the most abundant microplastic items detected on/near continental coastal zones.
  • Microparticles are irregular shaped pieces of plastic often appearing ovoid or trapezoidal when examined under moderate to high magnification.
  • Some research groups distinguish an additional fourth category of nurdles. These are the pre-production plastic pellets used as the feedstock for commercial manufacturing. Indeed, we have seen some huge monitoring campaigns recently designed to detect nurdles in the coastal zone. Regardless, in practice we cannot consistently distinguish weathered nurdles from particles in real-world settings. So while this category is real, we find it not a particularly useful category outside of policy circles and media interviews.

They result from the fragmentation of larger plastic objects (secondary microplastics) and from the direct release of small plastic particles from human activities (primary microplastics). Similarly, [EFSA] European Food Safety Authority. 2016. Presence of microplastics and nanoplastics in food, with particular focus on seafood. EFSA J. 14(6):4501. doi:10.2903/j.efsa.2016.4501.[Crossref], [Web of Science ®] , [Google Scholar]), can be produced by degradation of microplastics or might be released directly from domestic and industrial sources.

Where do we find microplastic?

The short answer is EVERYWHERE. Microplastic has truly become a marker of the anthropocene. Most academic researchers to date have focused on the “Is it here?” questions. Much of effort and argument has now turned to “How much is here?” and related questions. Mostly this has been bogged down in questions of standardized methodologies. We are a key part of this debate and hope to foster consensus and get on with the apples-to-apples sampling and monitoring to answer this question (at least in coastal SoCal, if not across the entire breadth of California).

How much Plastic is in the Ocean

  • 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 widely-quoted 2015 study by Jambeck et al. on plastic waste inputs from land into the ocean estimated that in 2010 alone, 4.8 to 12.7 million metric tons of plastic waste entered the ocean from 192 coastal countries.
  • 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.

What are the sources of coastal and ocean microplastic?

  • 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. And there is A LOT enter the global ocean. One of the most often-quoted stats quotes by the general public is: 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. Regardless of the accuracy of this estimate, it has been quite helpful in bringing pubic attention to the microplastic and marine debris crisis.
  • The 2015 Jambeck et al. study estimated the top 20 contributors of mismanaged plastic waste, considering populations within 50 km of the coast in 2010. Nations on the Asian continent represented 12 of the top 20 countries, with China way out ahead of the pack. The African continent was runner-up with five countries in the mix, and Turkey, Brazil, and the US also made it onto the scoreboard.
  • 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.

Do we have any coastal or ocean plastic sinks?

Once microplastic ends up somewhere, what happens?

  • In short, the whole thing is complicated, and we have barely started to scratch the surface. A few nuggets are beginning to emerge, though.
  • 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.

What type of impacts are we seeing in coastal and marine organisms and communities?

  • 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.
  • But where the marine plastics literature has really been hopping in the past few years is in discovering and synthesizing our understanding of microplastics. Remember those little bitty plastic bits (smaller than 5 mm) we talked about earlier? As we mentioned earlier, they are all over the place, are eaten by lots of different types of marine organisms (coral seem to love them, for example), release lots of potentially toxic chemical additives they are manufactured with, and are really, really good at absorbing and adsorbing contaminants already in the water. (Microplastics have a higher surface to volume ratio than macroplastics which means that plastic debris becomes even more effective at accumulating contaminants as it breaks down.)
  • 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…
  • But so far, exposure to microplastics at the concentrations currently found in the ocean don’t seem to kill most marine organisms. Chronic exposure, however, can change the way marine organisms eat, grow, and reproduce. For a specific example, eating microplastics doesn’t seem to do Pacific oysters and their larvae any favors. And this may mean bigger changes to marine populations, trophic structures, and ecosystems over time.
  • 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.
  • 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.
  • Chelsea Rochman and a crew from NCEAS led a critical analysis of the literature through 2012 in a paper published in Ecology that explored potential ecosystem-level impacts of general marine debris from evidence presented in the scientific literature. They found only two conspicuous, demonstrated ecological impacts, both affecting the biological assemblage. One was due to debris become new as artificial habitat/structures.
    The other was the ubiquitous smothering by debris, known to everyone who grew up in the 1980s from the “cut the ring” campaigns spurred by disturbing six-pack-rings-around-a-pinniped-neck images. Even so, these impacts are not those most people think about when they think about plastic marine debris. 

The policy landscape

  • New initiatives seem to pop up every day, both at the local and state level. Our current state-wide
  • To be sure, other threats, such as overfishing, habitat fragmentation, ocean warming/heat waves, ocean acidification, eutrophication, etc., are having larger, more conspicuous, or more immediate impacts on particular populations or communities. But we are beginning to see a conflating of many of these issues with microplastic waste. In some cases this merging is appropriate, but often this seems more like a political or marketing ploy centering around the fact almost no one is pro-microplastic or pro-marine debris. See for example this very interesting recent discussion on the PBS Newshour wherein a conservative pundit laments that political division can’t even get around the “no brainer” of single-use plastic bans at the federal level. And of course plastic waste is the favorite go-to of folks interested in pushing us to more sustainable lifestyles.