Climate change is boosting levels of banned pollutants such as PCBs and DDT in the atmosphere, Canadian, Chinese and Norwegian scientists have found.

A "wide range" of persistent organic pollutants, or POPs, have been increasingly released into the Arctic atmosphere since the early 1990s, says the study led by Environment Canada scientist Jianmin Ma, "confirming that Arctic warming could undermine global efforts to reduce environmental and human exposure to these toxic chemicals."

What are POPs?

Persistent organic pollutants are a group of chemical compounds that include:

  • Some pesticides such as DDT and hexachlorobenzene
  • Industrial chemicals such as polychlorinated biphenyls (PCBs), which were used as cooling and insulating liquids in electronics.
  • Byproducts such as furans and dioxins.

They are of international concern because they:

  • Are linked to adverse effects on human reproduction, development and behaviour as well as on the nervous, endocrine and immune systems.
  • Are linked to population declines, diseases or abnormalities in a number of wildlife species.
  • Are very stable in the environment and can persist for years without degrading.
  • Tend to accumulate in animal fats, increasing in concentration as they travel up the food chain.
  • Tend to concentrate in colder climates such as Canada’s North.
  • Travel long distances across the globe through the atmosphere. They may become trapped temporarily in water, snow, ice or soil before revapourizing and continuing on their journey when conditions are right.

The United Nations Stockholm Convention on Persistent Organic Pollutants, signed by 92 countries and the European Commission in 1991, banned or severely restricted 12 POPs, including DDT, hexachlorobenzene and PCBs. Another nine were added to the convention in 2009.

The study, published Sunday in Nature Climate Change, links higher summer air temperatures and lower sea ice cover to increasing levels of POPs. That suggests that POPs previously trapped in water, snow and ice could be released back into the air as the ice melts, allowing them to travel long distances through the environment.

The production and use of POPs has been restricted and, in some cases, banned outright under agreements such as the 2001 United Nations Stockholm Convention on Persistent Organic Pollutants. The restrictions were put in place because POPs are linked to negative health and environmental effects. Exposure to PCBs, for example, can cause skin, lung and nervous system problems and a possible increased risk of cancer. POPs also persist in the environment for a long time after their release because they are resistant to degradation and tend to accumulate in the tissues of living organisms.

Because of the international restrictions, levels of POPs have been declining worldwide.

Scientists have long suspected that climate change could help release POPs trapped in ice, the water below sea ice, snow and soil. However, they never had the evidence to back up that suspicion.

Increasing levels of some POPs such as PCBs had previously been measured at air monitoring stations in Svalbard, Norway, and Alert, Canada, but other POPs seem to have been declining.

Ma and collaborators at Environment Canada, the Yantai Institute of Coast Zone Research in China and the Norwegian Institute for Air Research closely examined measurements of POPs taken in Svalbard and Alert between 1993 and 2009, along with surface air temperatures and sea ice cover in different parts of the Arctic. They also compared the data to computer simulations showing how climate change will affect levels of POPs in the atmosphere.

Effects more obvious since 2000

The effects of climate change were unmasked in the data by subtracting off the effect of declining production and use of POPs. The link between higher summer air temperatures, lower sea ice cover and higher POP concentrations in the air became more evident in the past decade as the sea ice melted more quickly, the study said.

In the central Canadian Archipelago of the western Arctic, the increase in a POP called hexachlorobenzene seemed particularly sensitive to decreases in sea ice compared to other areas. The researchers noted that in the 1990s, hexachlorobenzene concentrations in the water there were found to be highest compared with other areas.

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The Arctic Ocean ice pack is retreating farther during summers. (Jonathan Hayward/Canadian Press)

The researchers suggested that based on the study, climate change will alter the ways in which organisms can be exposed to POPs, and consequently the ways in which human health can be affected.

Jordi Dachs, a scientist at the Institute of Environmental Assessment and Water Research in Barcelona said the results mean that POPs could continue to negatively impact the environment and human health far longer than previously believed.

In an analysis accompanying Ma’s article, Dachs noted that the study focused on only a few POPs.

"But there are thousands … that behave in similar ways in the environment," he wrote. "If the mobility of these compounds is increased by climate change, it could have significant implications for ecosystems and human health."