Scientists have found “extraordinary” levels of persistent organic pollutants 10km deep in the Mariana Trench in the Pacific Ocean. This means that oceans and marine life have been contaminated at full ocean depth. The Mariana Trench—located in the western Pacific Ocean–is the deepest part of the world’s oceans and is 2,550 kilometres long with an average width of 69 kilometres.
These trenches are ‘likely sinks for contaminants that enter the marine environment’ and are far from pristine say researchers in an article published in Nature Ecology & Evolution. The oceans comprise the largest biome (naturally occurring flaura and fauna) on the planet and these toxic man-made pollutants are threatening their survival.
The Mariana trench is located close to the industrialized regions in the Northwest Pacific and the infamous Great Pacific Garbage Patch. Since it is located beneath a vast accumulation of plastic debris, the toxic Polychlorinated biphenyls PCBs sink to depths of the ocean.
Persistent organic pollutants (POPs) are of particular concern for the researchers. POPs are released into the environment due to industrial accidents and discharges, leakage from landfills, or incomplete incineration. 1.3 million tonnes of POPs were manufactured from 1930s to the 1970s before they were banned. 65 percent of these toxic pollutants are thought to be still contained in landfills or within electrical equipment; the remaining 35 percent is in coastal sediments and open oceans.
POPs accumulate in the fat of organisms and are known to wreak havoc on endocrine system. An organism’s reproductive success is also severely hindered. Polychlorinated biphenyls (PCBs) one kind of POP is linked with the low reproductive success of female orcas (killer whales) and has threatened the specie’s survival. POPs are invulnerable to degradation—they cannot be broken down naturally.
Last year, the NOAA Office of Ocean Exploration and Research in their Deepwater Exploration of the Marianas found a plastic bag, food container and a beer can deep in the trench.
What is even more alarming is that the highest levels of PCBs were “fifty times more contaminated than crabs from paddy fields fed by the Liaohe River, one of the most polluted rivers in China”. The only Northwest Pacific location as polluted as the current state of the Mariana is Suruga Bay (Japan), one of the world’s most heavily industrialised areas.
It’s not just Mariana, 7,000km away in the Kermadec trench which is also believed to be 10km deep also finds itself facing a similar situation.