Poisonous chemicals that had been locked in ice for decades are now being released as climate change melts Antarctic glaciers, researchers report.
The chemicals, including the pesticide DDT, are seeping into the polar ecosystem and finding their way into wildlife populations.
Scientists made the discovery when studying the levels of pollutants in the fat and eggs of Adélie penguins.
DDT has been banned or severely restricted since the 1970s because it and other so-called volatile organic compounds were shown to cause reproductive ailments in animals.
In birds, for example, DDT breaks down into DDE, which can block calcium absorption and cause the birds to lay eggs with thinner shells.
With the chemical no longer in widespread use, scientists expected to find lower levels in Adélies.
"We were surprised to find that levels had not declined but had stabilized," said Heidi Geisz, a researcher at the Virginia Institute of Marine Science.
What's more, a small amount of the chemical had not yet been broken down by the animals' metabolism, which suggested that a fresh source of DDT was somehow finding its way into the penguins' guts.
Locked in Ice
To solve the mystery, Geisz and colleagues began to search for the pathways that contaminants might have traveled.
Like their emperor penguin cousins, Adélies don't migrate out of Antarctica, so Geisz knew the birds must be encountering pollutants locally. (See an interactive map of Antarctica.)
She first measured the environment for DDT from Africa, where the pesticide is still used in some countries to control malaria-infected mosquitoes.
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