Long banned industrial pollutants have recently been found in Earth’s deepest oceanic trenches.
Tiny crustaceans called amphipods collected from the world’s most remote deep sea trenches, the Mariana Trench and the Kermadec Trench, have been found to contain exceedingly high levels of industrial pollutants in their fatty tissue.
A recent study, led by Dr. Alan Jamieson from Newcastle University and published in February in Nature Ecology & Evolution
, reports that the pollutants found include polychlorinated biphenyls (PCBs) and polybrominated diphenyl esters (PBDEs), which are classified as persistent organic pollutants (POP) due to their toxicity and longevity.
PCBs were mainly used in electrical equipment as coolants and insulators, but were discovered to cause cancer and subsequently banned in the 1970s. Unlike PCBs, PBDEs are still in production, despite being linked to adverse health effects including learning and memory impairment, hormone disruption, birth defects and cancer.
"The fact that we found such extraordinary levels of these pollutants in one of the most remote and inaccessible habitats on earth really brings home the long term, devastating impact that humankind is having on the planet," says Dr Jamieson, who is based in the School of Marine Science and Technology at Newcastle University. "It's not a great legacy that we're leaving behind."
How did the chemicals get there?
The Mariana and Kermadec trenches reach depths of up to 11 km and are the world’s deepest trenches—the least explored ecosystems on Earth. The Mariana Trench is located in the North Pacific Ocean, approximately 7,000 km distance from the Kermadec Trench which is located in the South Pacific, near New Zealand. In order to comb the bottom of these trenches, Jamieson’s team employed deep-sea landers capable of withstanding crushing pressures of over 1,000 times sea level.
Given how remote both trenches are, it is surprising that both contain amphipods with abnormally high levels of POPs. However, there were variations in the levels of POPs recorded in amphipods collected from the two trenches.
Amphipods from the Mariana Trench had 15 times
the level of PCBs than those collected from the Kermadec Trench. The researchers speculate that this is due to the Mariana Trench being located nearer large plastic manufacturing locations in Asia, and also to its proximity to the ‘Great Pacific Garbage Patch’—an intense accumulation site for marine debris caused by the convergence of ocean currents that form the North Pacific Gyre. These strong ocean currents might be sucking plastic debris that contain POPs into the deep sea.
In contrast, the Kermadec Trench houses amphipods with PBDEs that were 5 times the concentration in the Mariana Trench, and many times the concentration of PBDEs in the coastal waters off New Zealand’s North Island.
Plastic as magnets for pollution
Finding eye-opening levels of toxic chemicals in remote amphipods is especially worrying as there is no efficient way to clean the oceans of chemical waste.
Every year, a staggering amount of solid and chemical waste is thrown into the sea, with plastic constituting the bulk of the waste. It is well known that plastic debris kills marine animals—approximately 1 million seabirds and more than 100,000 marine mammals, annually.
Common causes of death by plastic include entanglement or choking on plastic bags. Fragmented plastic or tiny plastics like microbeads (found in toothpaste and cosmetic products) can also block the airways or stomachs of marine animals and seabirds if ingested, causing suffocation or starvation.
Another source of danger is the release of toxic chemicals—vinyl chloride, bisphenol A (BPA) and PBDE—by degrading plastics in the sea. Vinyl chloride is associated with reduced fertility and various cancers, while BPA is famous for contributing to an array of health problems including disruption of normal hormone levels, cancer, and negative effects on the brains and behavior of young children. As a result, many plastics are advertised and sold as BPA-free and therefore considered safe for use—though these plastics may have BPA substitutes
such as bisphenol S (BPS) and bisphenol F (BPF), which have similar effects as BPA.
However, once discarded into the ocean, these plastics also pose a third, lesser known threat to marine and human life. Plastic polymers are characteristically hydrophobic and able to attract organic pollutants within seawater. In addition, long exposure to nature and the elements makes plastics fragment and pitted, increasing available surface area. Filamentous algae and biofilms also begin to coat plastic over time.
As a result, plastic debris—including those from biodegradable plastics—not only release chemicals as they degrade, they also act as sponges
, accumulating and concentrating pollutants already within seawater.
This was first demonstrated in a study in 2001 using plastic pellets exposed for 6 days in coastal Japanese waters. Once exposed, these plastic pellets were found to contain concentrated pollutants up to a million times the concentration in surrounding sea water. Shockingly, these pollutants included PCBs and DDE — a breakdown product of the insecticide DDT that was also banned in the US during the 1970s and is credited with the extinction of bald eagles. Several studies have reported similar findings of adsorption of chemicals onto plastics since then.
Coming to a dish near you
These pieces of plastic in the sea can circle the globe in days, traveling on ocean currents until inevitably getting caught in one of the 5 massive ocean gyres — the North and South Pacific gyres, the North and South Atlantic gyres, and the Indian Ocean gyre.
The whirlpools of plastic confetti within the gyres attract deep-sea fish that mistake them for plankton, fish eggs or other food. Just a few meals of chemical-laced plastic can dose the fish with toxic levels of pollutants that accumulate within their bodies, becoming more concentrated with each step up the food chain. Eventually, this results in toxic shrimp, fish and lobsters on our dinner plates.
“We’re all infected with plastic,” says Seattle-based oceanographer Curtis Ebbesmeyer. “Molecules from some kid’s plastic bottle, dropped into the ocean in Asia, are winding up in the food Americans eat.”
This global problem requires a concerted effort to be solved. As consumers, we can help by reducing or eliminating the use of plastic bags, bottles and synthetic materials, soaps with microbeads, and other plastic goods. We can participate in beach cleanups, use reusable bottles and utensils, and donate what we don’t need. Hopefully, such efforts will be enough to reduce our trash while we work on cleaning up what’s already there.
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