PET plastic used extensively in consumer products has permeated the deep sea water column and entered the food chain

A new study provides direct proof that a potentially large pool of marine microplastics may exist within the largest living space on Earth, the deep-sea water column


                            PET plastic used extensively in consumer products has permeated the deep sea water column and entered the food chain

Polyethylene terephthalate (PET) - a type of plastic commonly used in consumer products, including food and beverage packagings such as single-use drink bottles and to-go containers - have spread throughout the deep-sea, and have entered the food chain, reveals a new study. While plastic waste has been documented in nearly all types of marine environments, the study points to a more extensive reservoir for such waste.

The research - a joint effort by the Monterey Bay Aquarium Research Institute (MBARI) and Monterey Bay Aquarium - provides direct evidence that a potentially large pool of marine microplastics may exist within the largest living space on Earth, the deep-sea water column. According to the research team, while many people have heard of the “Great Pacific Garbage Patch,” a vast area of ocean between California and Hawaii where ocean currents concentrate plastic pollution, this study shows there may also be a lot of plastic far below the ocean’s surface.

The study, published in “Scientific Reports”, also found small ocean animals are consuming microplastic, which introduces the particles into food webs, both at the surface and in the deep. “We did this study because we need a strong baseline understanding of the types and amounts of microplastic present at different depths in the ocean. This study is the first-of-its-kind to sample and inventory microplastic pollution in the deep sea systematically and to then trace that plastic into deep-sea food webs,” Dr. Anela Choy, lead author of the paper, told MEA WorldWide (MEAWW). Choy conducted the research while a postdoctoral fellow at MBARI. She is currently an assistant professor at the Scripps Institution of Oceanography, UC San Diego.

The study in California’s Monterey Bay National Marine Sanctuary is the first systematic look at microplastic, with repeated sampling at the same locations and a range of depths. A total volume of 26,239L of seawater from depths spanning 5 to 1000 meters was sampled and examined for microplastic particles.

The researchers also looked at concentrations of microplastic particles in specimens of two marine species that filter-feed in the water column: Pelagic red crabs and giant larvaceans. They found microplastic in all of the animal specimens they surveyed. The most abundant plastics found were PET, polyamide, and polycarbonate, widely used packaging for foods and beverages.

“PET was the most common plastic identified from all depths of the water column samples (both nearshore and offshore sites), from the gastrointestinal tracts of pelagic red crabs, and discarded larvacean sinkers. Polyamide (PA) was the second most common plastic polymer identified from the three sample types, followed by polycarbonate (PC) and polyvinyl chloride (PVC),” said the paper.

A joint news release by Monterey Bay Aquarium and Scripps Institution of Oceanography said pelagic red crabs and tadpole-like giant larvaceans are critical parts of ocean food webs. “Pelagic red crabs are commonly found in large numbers near the ocean’s surface, where they are consumed by many species of fish, including tuna. Larvaceans create large mucus filters that collect organic material - and microplastic - then discard those filters, which are consumed by other animals as they sink to the ocean floor,” it added.

Equipped with a microscope and a laboratory technique called Raman spectroscopy, researchers from Arizona State University contributed to the study. Most of the microplastic particles the researchers discovered were highly weathered, suggesting they had been in the environment for months or years. The release said even though Monterey Bay is home to commercial fisheries, the team found very few particles of polypropylene or other plastics commonly used in local fishing gear. The researchers also detected more microplastic particles offshore than nearshore.

“This suggests that most of the particles did not originate from local fishing gear. It also suggests that at least some of the microplastic was transported into the area by ocean currents,” said Kyle Van Houtan, chief scientist at the Monterey Bay Aquarium and one of the study’s co-authors, in the release. This finding could indicate that plastic is widely distributed in the deep ocean, and may even be concentrated there.

Microplastic’s Pervasive from the Surface to the Seafloor

Study provides direct proof that a potentially large pool of marine microplastics may exist within the largest living space on Earth, the deep-sea water column. (Source: Image courtesy of Monterey Bay Aquarium Research Institute (MBARI) )

Using MBARI’s underwater robots, equipped with sampling devices designed specifically for this project, the researchers filtered plastic particles out of seawater on multiple occasions at two different locations and at various depths, from five to 1,000 meters below the surface of Monterey Bay, California. Some samples were collected just offshore of Moss Landing Harbor, but the majority were collected about 25 kilometers from shore, in the deep waters of Monterey Canyon.

“The results surprised the team. They found nearly identical concentrations of microplastic particles near the surface and in the deepest waters surveyed. Perhaps more startling, they found roughly four times the concentration of microplastic particles in the mid-water range (200 to 600 meters down) than in waters near the surface,” said the release.

The paper said that as plastic waste generation is predicted to continue to grow, large-scale conservation and mitigation efforts must consider the enormous spatial (both horizontal, and vertical) and ecological scale of the problem that these new findings reveal. “Smart and science-informed policy and regulations around the globe and the plastic production industry, are urgently needed,” Choy told MEAWW. The researchers recommend the use of new monitoring and sampling technologies to access and inventory the full scale of microplastic pollution in the deep sea.