Chemistry of the Great Big Blue: Plastics


From the microscopic to the gigantic, plastic debris has plagued our oceans since its invention. Much of the problem originated initially because we didn’t realize that plastics don’t degrade until after we had dumped tons into the ocean, largely off of ships as trash. WHOI offers a good summary of the history of plastic pollution. Many things changed since that first realization and the nature of plastics in the marine environment has a very different face nowadays.

The plastic is smaller and more widely distributed. There are fairly well-known areas that collect the plastics such as the Great Pacific Garbage Patch.  There are also other areas affected that are closer to shore and where people use marine resources. Plastic often settles in seagrass beds that serve as important nursery habitat and on beaches where turtles and shorebirds mistake them for food and nesting material. Need more details on plastic?

There are three main categories of plastic pollutants: large debris, microplastics, and leachates.

Large debris used to come largely from from ocean dumping but after the 1975 MARPOL V agreement banning such practices, large debris comes from shipping accidents and runoff from land. Many comical stories are chronicled in Tracking Trash, detailing oceanographic insights from thousands of floating rubber duckies and a shoreline littered with escapee sneakers, among others. According to Derraik’s 2002 review article, plastic make up between 37 and 88% of the marine debris washing up along coastlines worldwide. Surprisingly, subantarctic and other remote areas had comparable amounts as populated shorelines. I’ll continue to report some of his choice findings through the rest of this article.

What effect does all this flotsam have on biota? An estimated 86% of turtle species, 43% of seabird species, and 44% of marine mammals have plastics in their gut. You might imagine what plastics do when sitting in a stomach, but they make the animals feel full and otherwise compact their digestive system.  If not eaten, some plastics sink to the seafloor, where in populated places like Tokyo Bay, plastics make up about 85% of the seabed debris. Others continue to float posing an entanglement danger or are used in nesting.

plastic incorporated in nest from

Microplastics form the next category – these are not necessarily visible to the naked eye and are formed either from the degradation of larger pieces or directly discharged into the ocean. Those directly discharged come mostly from hand and facial cleaners – all those ones boasting a clean “scrub” is usually due to small plastics unless specifically labeled “natural” or “apricot”. One of the most well-established threats of these little plastics is that they look like plankton, therefore causing similar ingestion problems at a small scale but also across the globe. These microplastics are largely what the Great Pacific Garbage Patch is made of, and these little plastic balls can float in perpetuity.

microplastics from

Microplastics and small floating debris pieces serve as little floating rafts for potentially invasive species. A leaching piece of plastic is probably not the most hospitable home for marine larvae, and those that survive have many of the indicator attributes of invasive species – like high reproductive output and a long dispersal period. These rafts give enough help to species to expand their dispersal. The effect has been documented across the Tasman Sea, the Caribbean, and even the North Atlantic.

Leachates from both sizes of plastics include the notorious polychlorinated biphenyls (PCBs), bisphenyl A, phthalates, and other plasticizers. Originally designed to give plastic products a desired flexibility, these chemicals have been determined to be toxic to most forms of life.  PCBs have been removed from industrial production for decades, but take centuries to degrade, so will remain an issue in marine food webs. These other chemicals have been established as endocrine disruptor and when impacted in a stomach, can leach enough to stop ovulation and prevent natural steroid hormone production. Whether ambient levels of these chemicals is enough to cause serious effects is still up for debate, but these ambient levels are increasing as is our ability to test for low-level and synergistic effects. Though this article was meant to be informative, I urge you all to think about the plastics involved in your life. Plastics in the ocean and on remote coastlines is only one symptom of a culture dependent on disposable petroleum-based products.

~Bluegrass Blue Crab

Literature Cited:
DERRAIK, J. (2002). The pollution of the marine environment by plastic debris: a review Marine Pollution Bulletin, 44 (9), 842-852 DOI: 10.1016/S0025-326X(02)00220-5


  1. Sam · August 18, 2010

    When I first got my bearded dragon, the pet store recommended that I keep it on crushed walnut shells. So I did. I found that the crushed shells were indigestible and retained their hardness when saturated, and put anything kept on them at an extreme risk of an impaction. I can’t imagine how high the risk of impaction must be for a fish eating in an area with a high concentration of microplastics.

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