Warming in the Arctic is causing the release of toxic chemicals long trapped in the region's snow, ice, ocean and soil, according to a new study.
Researchers from Canada, China and Norway say their work provides the first evidence that some persistent organic pollutants (POPs) are being "remobilized" into the Arctic atmosphere.
"Our results indicate that a wide range of POPs have been remobilized into the Arctic atmosphere over the past two decades as a result of climate change, confirming that Arctic warming could undermine global efforts to reduce environmental and human exposure to these toxic chemicals," write the scientists, whose analysis was published yesterday in the journal Nature Climate Change.
That's of concern because POPs can travel long distances on air currents, persist in food and water supplies, and accumulate in the body fat of humans and other animals. The pollutants also can be passed from mother to fetus and have been linked to serious health problems in humans and other animals.
Co-author Hayley Hung, a scientist with Environment Canada's Air Quality Division who studies toxic organic pollutants in the Arctic, said that in recent years, researchers had posited that warmer conditions would liberate POPs stored in land, ice and ocean reservoirs back into the atmosphere.
"The chemicals are known to be semi-volatile," Hung said. "They have the ability to evaporate out of storage" -- if temperatures are warm enough.
She and her colleagues began to suspect the phenomenon was already under way when they examined 20 years of air monitoring data collected at a high Arctic monitoring site, Zeppelin Mountain Air Monitoring Station in Norway's Svalbard archipelago.
Toxic blasts from the past
Beginning in the mid-2000s, scientists observed higher levels of certain POPs, including hexachlorobenzene and polychlorinated biphenyls (PCBs), at the Norwegian research station. That stood out, Hung said, because the chemicals' use has been restricted to the point where many POPs are no longer produced. As a result, the level of POPs in Arctic air had been decreasing.
"Stockpiles still exist, but these are limited sources," she said, "and the sources are already known to us. So we were surprised to see concentrations actually coming up at the Svalbard station."
The scientists then examined two decades of monitoring data from the Alert monitoring station in the Canadian province of Nunavut. They saw smaller, though still significant, increases in POPs at the second site.
Hung believes the larger increase at the Svalbard site is caused by its proximity to ocean areas where sea ice has retreated. "This is a sign to us that these chemicals are indeed evaporating out of the ocean," she said.
Still, she noted that all POPs don't react the same way to warming. Hexachlorobenzene and PCBs, the chemicals detected in increasing amounts in Norway and Canada, evaporate more easily than many other POPs, and are harder to dissolve in water. That means they're more prone to re-enter the atmosphere after they're deposited on land or sea.
Jordi Dach, a scientist at the Barcelona, Spain-based Institute of Environmental Assessment and Water Research, said the new study provided convincing evidence of the long-suspected movement of POPs from Arctic reservoirs into the atmosphere.
The new study "demonstrates that climate change can remobilize POPs stored in water, snow, ice and presumably soils -- and that this process is already occurring in the Arctic region," he wrote in an essay accompanying the new study.
Eventually, Dachs said, atmospheric circulation patterns could carry the newly liberated POPs to other parts of the globe.
Oldies, but not goodies
"The remobilization of pollutants generated by our grandparents -- pollutants that were banned decades ago -- are unwanted witnesses to our environmental past that now seem to be 'coming in from the cold," he said.