There is no corner of the world safe from the destructive shadow cast by human pollution, a recent study published in Nature Ecology and Evolution has found — not even the darkest depths of the sea.

Marine scientists studied crustaceans taken from two of the deepest ocean trenches in the world, the Mariana Trench located in the North Pacific nearby Guam, and the Kermadec Trench, found in the South Pacific off the eastern coast of New Zealand. Looking specifically for persistent organic pollutants (POPs), a type of pollution that only very slowly degrades and causes serious health problems in many life forms, they were taken aback by what they saw. All the critters studied had "extraordinary levels" of POPs, even higher than what's typically found in the surrounding sea life of places known for hosting factories and other abundant sources of pollution.

The findings, the researchers wrote, contradict the perception of the deep sea being a "pristine," untouched environment, and suggest that even pollution we had stopped creating decades ago is still harming marine life.

In the food chain, POPs accumulate in organisms' fat in higher and higher levels as animals eat contaminated prey. The researchers theorize that the cycle starts over in the deep sea when these carcasses or other sources of POPs sink down to the bottom of the ocean and are scavenged by the kinds of animals they studied.

"The very bottom of the deep trenches like the Mariana are inhabited by incredibly efficient scavenging animals, like the 2cm-long amphipods we sampled, so any little bit of organic material that falls down, these guys turn up in huge numbers and devour it," lead author Alan Jamieson told the Guardian.

Other scientists have discovered everything from discarded Spam tins to Budweiser beer cans at different depths of the Mariana Trench, which reaches down as far as 7 miles at its deepest point. The samples in the current study were taken from as far deep as 10 kilometers, or just over 6 miles.

One particular type of POPs found by Jamieson's team, called polychlorinated biphenyls (PCBs), have largely been banned from use in manufacturing since the 1970s. But though two-thirds of the 1.3 million tons of PCBs that were created from the 1930s until they were banned are contained in landfills or existing electrical equipment — the rest are suspected to be found in our oceans and coasts. Their appearance in the Trench not only signals their continued effect on the environment, but also forebodes how difficult it will be to clean up other still-common causes of ocean pollution like plastic.

His team next hopes to document how exactly POPs are affecting the deep ocean life. Research elsewhere has shown they can disrupt hormone production, cause cancer, and even muck with fertility in humans.

This article originally appeared at Our old pollution is poisoning the deepest depths of the sea.