The idea that the deep ocean is a pristine place safe from the unwanted impacts of human activities does not seem true as scientists find evidence of high levels of toxic pollution in animals thriving in what is considered as the most remote place on Earth: the Mariana Trench.
Crustaceans From World's Deepest Trenches Contaminated With Toxic Chemicals
For the study published in the journal Nature Ecology and Evolution, researchers used a deep-sea lander and traps to collect tiny crustaceans from two of the deepest marine trenches in the world: the Mariana Trench in the Pacific Ocean and the Kermadec Trench near New Zealand.
Analyses showed that the tiny crustaceans that thrive in the dark waters of these trenches are contaminated with toxic chemicals that have already been banned decades ago.
POPs: Toxic Chemicals Banned Decades Ago
Alan Jamieson, from Newcastle University in the UK, and colleagues identified two types of persistent organic pollutants, or POPs in the marine animals: polychlorinated biphenyls (PCBs) and polybrominated diphenyl (PBDEs). POPs are highly toxic industrial chemicals that were banned in the late 1970s but do not break down in the environment.
The pollutants have earlier been detected at high levels in marine animals in Western Europe and the Inuit people in the Canadian Arctic.
How POPs Contaminate Marine Animals In The Deepest Parts Of The Ocean
The findings suggest that POPs infiltrate the deepest parts of the ocean as particles of plastic and dead animals fall downward. The toxic chemicals accumulate in fat and are concentrated in organisms up the food chain. These pollutants are also water-repellent so they tend to cling to plastic waste.
Jamieson explained that the bottom of these deep trenches is inhabited by scavenging animals and these organisms devour organic materials that fall down.
Researchers said that while finding some POPs in the deepest parts of the ocean is not unexpected, what actually surprised them were the high levels of contamination in animals.
Higher Level Of PCB Contamination In Mariana Trench Crabs
Analysis showed that the crustaceans in the Mariana Trench were contaminated with PCBs 50 times greater than the crabs in one of the most polluted rivers in China. PCBs were once used in electrical equipment before they were banned in the United States over environmental and health concerns.
"These data clearly indicate that potent anthropogenic contamination and bioaccumulation has occurred in a dominant macrofaunal group inhabiting the complete depth range of two of the deepest marine trenches," the researchers wrote in their study.
The researchers also found that the concentration of PCB was higher in the Mariana Trench than in Kermadec, which could be attributed to the proximity of the former to an industrialized region and the Great Pacific Garbage Patch.
The researchers said that large-scale ocean currents can transport the particles contaminated by chemicals over long distances. Earlier studies also showed that contaminants that start out on the surface of the ocean can sink deep in the waters sticking to garbages and bodies of dead animals.