How Microplastics Are Contaminating Our Oceans

Kristin Osika

An average of eight million metric tons of plastic waste enter our oceans every year. Making up about 27% of total plastic waste annually, the amount of plastic ending up in the ocean is enough to cover every foot of every coastline on the planet. Plastic waste is harming ecosystems on both land and water. Ingestion or entanglement of plastic debris has been recorded in 47% of all marine mammals, including sea turtles, crustaceans, and sea birds. Entanglement with marine life and the accumulation of macroplastics into large garbage patches in ocean gyres are major threats to our ecosystems, but the bigger problem is physically much smaller. The biggest threat to the marine ecosystem and even to ourselves is the presence of microplastics, both in shallow waters and thousands of feet under the surface.


Microplastics are particles of plastic measuring less than 5 millimeters, and end up in our oceans from a number of different sources. Microplastics can be formed from the breakdown of larger, macroplastics, like plastic water bottles, or washed into our oceans as a part of personal care products containing micro-beads. The micro-beads in products like face wash and toothpaste ultimately end up in the ocean, where it appears they never fully break down. Recently, legislation was passed that banned the use of micro-beads less than 5 millimeters in products in an effort to reduce microplastic waste.


Recent research shows evidence of microplastics in deep ocean basins, a region so remote that scientists previously thought it could not be harmed by human pollution. Studies conducted on deep-sea organisms prove, however, that plastics have even infiltrated areas of the ocean isolated from human activity.


In May 2016, researchers tested nine organisms collected from ocean basins in the mid-Atlantic and the Southwest region of the Indian Ocean. They found plastic microfibers in six of the nine organisms, the first evidence ever recorded of plastic ingestion by deep-sea marine life. Microplastics were found in organisms from three different phyla, Cnidaria, Echinodermata, and Arthropoda. Each of these phyla have different feeding mechanisms, suggesting that a diverse group of deep-sea organisms can and will ingest microplastic.




Organisms found to have ingested microfibers; (a) blue microfiber from mouth area of sea pen polyp; (b) sea pen; (c) example sea pen polyp; (d) black microfiber embedded in surface of zoanthid; (e) zoanthids on bamboo coral skeleton; (f) blue microfiber on feeding maxilliped of hermit crab; (g) hermit crab with symbiotic zoanthid; (h) sea cucumber



Organisms that live deep in ocean basins rely heavily on organic detritus from the euphotic zone, small particles that sink from areas near the surface exposed to sunlight. These particles, often called “marine snow”, resemble microplastic in size and shape. The confirmation of ingestion of microplastic into deep-sea organisms suggests that microplastics are becoming integrated into marine snow, an issue particularly relevant for organisms in deep ocean ecosystems.


There is no conclusive research that points to the final fate of microplastics in the ocean. Because they are already broken down into minuscule particles, it is possible that microplastics will remain intact through generations of ingestion by many organisms. Research conducted in the ocean basins confirms what scientists have already feared; microplastics are entering organisms at the bottom of the food chain and have the potential to travel upwards.


How can this microplastic problem affect us in the future?


Microplastics resemble marine snow as well as plankton, which are ingested by large filter feeders. Microplastics can absorb high levels of pollutants, and can settle in sediment on the sea floor or remain suspended in the water column. When organisms from anywhere in the ocean ingest these poisonous microfibers, the toxins can be passed into them and subsequently into their predators. As humans, we are the top predator and therefore at risk. The final factor of this research examines whether microplastics will be transferred up the food chain, and eventually into fish that become a part of our diet. Specific consequences of this potential ecological disaster are still unknown, but scientists hypothesize that with the continued build up of microplastics in the ocean, this man made toxic waste will ultimately end up in the food we eat.


This past summer I had the opportunity to conduct field research on microplastics at the Island School, on Cape Eleuthera in the Bahamas. Working with a research intern at the Cape Eleuthera Institute, we studied the concentration and nature of microplastics in the Exumas, a deep area of ocean off the coast of Eleuthera. We set up a trawl, a small net designed to catch plastics on the surface of the water as it trailed behind the boat. Once we collected the trawl, we were able to identify microplastics by their size and properties; small pieces of sediment will sink in a test tube of water while plastic will float. Although the ocean around us appeared to be pristine, there was a high concentration of microplastics on the surface alone. The threat microplastics present is relevant to both marine organisms and ourselves, and it’s clear that the conservation of our oceans is vital to a healthy environment and functioning ecosystem.


Caroline Petrow-Cohen ’18



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