"These chemicals are semi-volatile, meaning they don't stay in the air forever," Hayley H. N. Hung, a scientist at Environment Canada and co-author of the study, told SolveClimate News . "They drop down and get deposited into different materials. The organically rich, cold soil in the Arctic is a good trap for these chemicals, and POPs in the polar oceans are capped by sea ice, which literally puts a lid on the pollutants to keep them in place."
She continued: "When these deposits change — for example, when the sea ice melts — the POPs are 'uncapped' and are free to re-enter the atmosphere."
Predicting Future Trends
Ma and his colleagues then plugged the data of concentrations of POPs into models of three different Arctic-warming scenarios spanning the next five decades. The models showed significant increases in pollutant levels over the next 50 years, demonstrating that as snow pack and sea ice continue to melt in the coming decades, they will continue to discharge these stored POPs.
The re-release of the pollutants could have ripple effects worldwide. Once they are emitted back into the atmosphere, the POPs can catch a ride on the Earth's wind and ocean circulation systems, which can carry them as far south as Mexico and northern Africa.
This isn't just a problem for the Arctic, scientists say. POPs are also trapped in Antarctic snow and sea ice, although in less concentration since the majority of pollutants were emitted in Northern Hemisphere countries. As the Antarctic warms due to climate change, the Southern Hemisphere will likely get a fresh dose of newly unleashed toxics, the research suggests.
If these remobilized pollutants re-enter the food chain and start bioaccumulating once again as they move from one species to the next, the results could be disastrous for wildlife and humans.
The compounds have been shown to cause cancer, allergies, damage to the central and peripheral nervous systems, reproductive disorders and disruption to the immune system, according to the U.S. Environmental Protection Agency and the United Nations Environment Program.
The pesticide DDT, for instance, was present in such high levels in bald eagles in the mid-twentieth century that it thinned their eggshells, resulting in reduced fertility rates and a rapid decline in the species.
Because scientists don't know the actual concentration of POPs in the snow, oceans capped by sea ice and soil of the Arctic, the extent of this re-release remains unknown, said Hung.
"This paper is the beginning of a story," she said. "There were predictions that climate change would have an effect on POPs. Now we've shown that it does. Next, we need to figure out just how much of a change this will cause, both in the amounts being released and the impact it will have."