It’s hard to find a part of the Earth that hasn’t been impacted by human existence these days. Even the most remote beaches of the tropics will often see its share of washed up plastic waste. But surely, if there was any place on this planet that has yet been touched by man, it should be the deepest parts of our oceans at the Mariana Trench. At least that’s what one group of scientists futilely hoped for when they found “extraordinary” levels of polychlorinated biphenyls (PCBs) and other pollutants in tiny crustaceans living in the world’s deepest ocean trench, the Mariana Trench.
“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,” says lead author on the study, Dr. Alan Jamieson.
He continued by comparing the recorded levels against other industrial waters: “In fact, the amphipods we sampled contained levels of contamination similar to that found in Suruga Bay, one of the most polluted industrial zones of the northwest Pacific.”
The same team also found PCBs in creatures living in the Kermadec Trench about 1,500km north of New Zealand, meaning the pollutants aren’t limited to just one place. They report their findings in the journal Nature Ecology and Evolution.
Starting in the 1930s through the 70s when the chemicals were banned, PCBs were used as electrical insulators and flame retardants. They’re just one of a whole slew of persistent organic pollutants (POPs) humans used to produce for manufacturing and agricultural purposes which got out into the environment through industrial leaks and deliberate dumping. It’s thought 1.3 million tonnes of the chemical were produced before they were banned.
The problem with these organic compounds is that they don’t break down easily and persist in animals as they move through the food chain. The PCBs in the trenches could have accumulated over time through falling plastic or as dead sea creatures fell to the sea floor. Despite their remote locales, we’re now finding the deep ocean can act as a sink with higher concentrations of pollutants than ocean surfaces.
More research is needed to find out exactly how the pollutants impact the wider ecosystem, Dr. Jamieson stated.
As surprising as it is to find chemicals from the 70s in high concentrations, we still continue to dump chemicals into the oceans today.
Take, for instance, the practice of mountaintop removal mining in the eastern U.S. To get at underground coal seams, companies will literally blast off the tops of mountains and dump the debris into local valleys where streams and rivers will transport the heavy metal by-products into the ocean.
And then there’s the global practice of allowing nitrate-enriched fertilizer to run off agricultural fields and into waterways where they skew marine ecologies and create life-sucking algae blooms.
Dr. Jamieson warned of the dangers of using the ocean as a dumping ground: “We’re very good at taking an ‘out of sight out of mind’ approach when it comes to the deep ocean but we can’t afford to be complacent.
“This research shows that far from being remote the deep ocean is highly connected to the surface waters and this means that what we dump at the bottom of the sea will one day come back up in some form another.”