The findings, presented Monday in the journal Nature Ecology and Evolution, underscore the idea that different parts of the ocean may be far more interconnected than previously thought - and that risky forms of pollution may be pervasive even in the most remote places.
Alan Jamieson, from Newcastle University in the United Kingdom, and colleagues identified two types of persistent organic pollutants, or POPs in the marine animals: polychlorinated biphenyls (PCBs) and polybrominated diphenyl (PBDEs).
According to USA Today and the Washington Post, Dr. Alan Jamieson, a marine ecologist from Newcastle University, and his colleagues found elevated levels of industrial chemicals a group of tiny shrimp-like crustaceans living at depths of 10,000 meters in the Mariana Trench.
Scientists also discovered polybrominated diphenyl ethers (PBDEs) which were used as flame retardants and are known to reduce fertility.
PCBs were first used as dielectric fluids in the 1930s. Cancer and other health problems in animals have been linked to PCBs, and their manufacture was phased out decades ago. Once there, the carcasses are consumed by a wide range of deep-sea creatures.
Each lander was equipped with special traps created to catch tiny shrimp-like crustaceans called amphipods known to inhabit some of the ocean's deepest and most extreme environments.
PCBs and PBDEs are scary for a couple of reasons.
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"Contaminant levels were considerably higher than documented for nearby regions of heavy industrialization, indicating bioaccumulation of anthropogenic contamination and inferring that these pollutants are pervasive across the world's oceans and to full ocean depth", reads the report.
In the Mariana trench, the world's deepest, the highest PCB levels in samples were 50 times higher than in crabs from paddy fields fed by the Liaohe River, one of China's most polluted.
Just how invasive man-made pollution has become is highlighted by Dr Jamieson, who says he has seen video of a Canadian beer can lying on the sea floor four miles down, off New Zealand, while a friend told him about a raincoat found in the Mariana Trench, intact, at nearly seven miles.
"The high levels of these chemicals in the deepest reaches of the ocean is unexpected, but their presence there should not be surprising to us given the size of the human population and the vast amounts of industrial products we produce". They collected the animals using a "lander" vehicle deployed from a boat over the Mariana and Kermadec trenches. These pollutants are also water-repellent so they tend to cling to plastic waste. The amphipods were contaminated with PCBS (polychlorinated biphenyls), unsafe chemicals utilized for quite a long time in the industry, and additionally other mechanical contaminations known as diligent natural poisons.
The researchers say the most logical explanation for the accumulation of these toxic compounds in such isolated areas is that plastic marine debris and dead animals contaminated at the surface sank through the water column.
Report author Alan Jamieson said: "We still think of the deep ocean as being this remote and pristine realm, safe from human impact, but our research shows that, sadly, this could not be further from the truth".