Microplastic in the ocean

While cleaning up files on my computer, I came across this image I put together a few years ago from a trip to New Zealand. It struck me as a great example to use to discuss some of the challenges presented by ocean plastic. Plastic in the oceans is arguably one of the most important and pervasive environmental problems today.

Ocean plastic is problematic for a number of reasons, but primarily because marine animals eat it. Some of the most famous examples are seabirds and turtles, which can starve to death when their digestive tracts fill with toothbrushes, plastic bags, and other material. Creatures like turtles and marine mammals can also become entangled and drown in large items like phantom nets and bags. But even small creatures eat ocean plastic, because by far the largest numerical proportion of ocean plastic falls in small size fractions. Small plastic particles may come from washing clothing, the initial plastic beads used to melt down and create plastic goods called nurdles, or might be fragments of larger plastics that have broken down.

Eating plastic can lead to a number of negative consequences. For instance, zooplankton experimentally offered microplastic beads and algae ate less algae overall, and some retained plastic particles in their guts for longer periods that normal food particles were retained. Similarly, feeding experiments conducted this summer by NSF-sponsored Research Experience for Undergraduate student Eliya Baron-Lopez of UC San Diego and intern Rowan Yelton at the New England Aquarium (NEAq), together with Juanita Urban-Rich of UMass Boston and Randi Rotjan of NEAq showed that corals readily ingest microplastic particles, and can re-ingest particles that are expelled. Thus, animals like corals may be expending energy to ingest, expel, and reingest particles that ultimately provide no nutritional benefit and may prove harmful. Filling up on plastic instead of food can lead to reduced growth, fecundity (reproductive output), or starvation.

Aside from clogging up the digestive tracts of marine life, plastic also has a potentially more sinister side: it tends to adsorb pollutants like PCBs from the water column, thus acting as a potential vector to move pollutants from the water column into the food chain. Aside from potentially devastating effects on marine life, human health may also be compromised. For example, one study found that European consumers could be ingesting approximately 11,000 microplastic particles annually through shellfish consumption, with unknown impacts on human health. Tiny plastics are a huge problem because (1) their high surface-area-to-volume ratio and chemical makeup increases the likelihood of pollutant adsorption, (2) they are ubiquitous and creatures that eat particles in that size fraction tend not to be the brightest on the planet (thus lacking strong discriminatory powers), and (3) there is no known way to clean them up.

So, if we can't realistically clean up the existing plastic pollution without killing everything in the oceans, what's to be done? A recent study found that small particles tended not to disperse very far from their sources on land, possibly due to biofouling and subsequent settling to the bottom. It's therefore clear that the most obvious place to start is not in deploying expensive and failure-prone cleanup devices in the middle of the ocean, but instead preventing plastic pollution at our shores. Mr. Trashwheel is one adorable and effective method to capture macroplastic. Microplastic pollution can be prevented by not using personal care products that use them (you'll have to be a careful consumer if microplastics haven't yet been banned where you live), and wearing fabrics made of natural fibers. That fleece in your closet? Repurpose the fabric in a way that it won't need to be washed anymore and replace it with clothing that doesn't shed fibers, or keep an eye out for new clothes washing technologies that prevent microplastic pollution.

References

Choy, C. A., & Drazen, J. C. (2013). Plastic for dinner? Observations of frequent debris ingestion by pelagic predatory fishes from the central North Pacific. Marine Ecology Progress Series, 485, 155-163.

Cole, M., Lindeque, P., Fileman, E., Halsband, C., Goodhead, R., Moger, J., & Galloway, T. S. (2013). Microplastic ingestion by zooplankton. Environmental Science & Technology, 47(12), 6646-6655.

Van Cauwenberghe, L., & Janssen, C. R. (2014). Microplastics in bivalves cultured for human consumption. Environmental Pollution, 193(6), 5e70.

Wilcox, C., Van Sebille, E., & Hardesty, B. D. (2015). Threat of plastic pollution to seabirds is global, pervasive, and increasing. Proceedings of the National Academy of Sciences, 112(38), 11899-11904.

Woodall, L. C., Sanchez-Vidal, A., Canals, M., Paterson, G. L., Coppock, R., Sleight, V., Calafat, A., Rogers. A. D., Narayanaswamy B. E., & Thompson, R. C. (2014). The deep sea is a major sink for microplastic debris. Royal Society open science, 1(4), 140317.