Paper: Woodall, L. C., Sanchez-Vidal, A., Paterson, G. L. J., Coppock, R., Sleight, V., Calafat, A., … Thompson, R. C. (2014). The deep sea is a major sink for microplastic debris. Royal Society Open Science, 1, 140317.
Whether you live right on the beach or in the middle of a landlocked area, you’ve definitely heard that our oceans are filling up with plastic. Pictures of birds with stomachs full of plastic and turtles caught in soda rings with deformed shells have been all over the Internet. There’s no denying that plastic trash in the ocean is a huge problem. However, most people don’t know that large pieces of trash likes those just mentioned are only part of the problem. There’s a far more insidious side to the marine plastics story, and that side is microplastics.
Microplastics are just what they sound like – tiny tiny tiny pieces of plastic, so small they can’t been seen without a microscope. They come from three main places: consumer products (like body wash with exfoliating beads), the breakdown of larger plastics from wave action or UV rays, or synthetic fibers that break off our clothes when they get washed.
For a while, microplastics were not a big issue. No one really knew they were there, or if they did, they didn’t think they would cause a big impact on marine environments. But, years of environmental surveys have indicated that even though there’s a ton of trash in the ocean as it is, there doesn’t seem to be enough trash consistent with the amount of trash people are throwing away. In short, there was missing trash, and scientists had to find out where it was going, and these researchers had a hunch it was sinking into the deepest parts of the ocean.
These researchers conducted a large-scale and long-term study of microplastics in the deep sea by analyzing sediment cores collected by remotely operated vehicles (ROVs). From 2001-2012, they went on seven research cruises in three different oceans to collect samples, then brought the cores back to the lab to see just how much plastic was in all that dirt.
To do that, they employed two different techniques called extractions. The first involves filtering the sample over and over again with salt water and fine mesh filter, not unlike making coffee. Filtering the sample caused the natural dirt to filter out, while the only particles remaining in the filter were the microplastics. The second technique involved using a centrifuge and a filter to separate the plastics from the dirt.
To make sure that what they found were microplastics, they analyzed all the particles with a machine called a spectrometer: it uses light to identify what kids of molecules are present in the sample. They compared the results from the particles to known samples of microplastics to make sure they matched up.
Even though a previous study indicated that there weren’t that many microplastics in deep sea sediments, this study used more vigorous methods to determine that in fact, there are a lot of microplastics in deep sea sediments. Most of the microplastics were of the third type, the kind that comes off our synthetic clothes (like polyester) when we wash them. They saw as many as 40 pieces of microplastic in 50 mL of sediment, which is equal to 1/5 of a cup.
The most abundant type of microplastic found was rayon, making up 56.9% of all the plastics seen. Rayon is used mostly in cigarette filters and in fabrics as an alternative to the most expensive cotton – check your shirt to see if it has rayon fibers in it! Technically, though, rayon is only semi-synthetic, meaning that it’s part plastic but also part natural. For that reason, it was excluded from the data.
The most abundant and completely synthetic fiber was polyester, followed by other hard plastics, and acrylic. Those plastics are found in clothing, packaging, and electronics.
Because these microplastics were found in every single sample in every ocean in every location they sampled, it’s reasonable to conclude that these microplastics are everywhere in the deep sea. And, because they found a variety of plastics, the contaminants are coming from a large variety of sources, both domestic and industrial.
Usually, plastic surveys in the ocean focus on larger pieces of plastics along the coasts, so this study is a good reminder that there are other habitats and other sources of plastic that need to be monitored to fully understand how polluted our oceans are. Most of these fibers that the researchers found are negatively buoyant, which means that they’re naturally going to sink in the ocean, rather than float.
So, next time you’re at the store or doing your laundry, check your clothing labels! You might be wearing more plastic than you realized, and that plastic is definitely ending up at the bottom of the ocean.