May 5, 2008 -- Although use of the pesticide DDT was banned in the Northern Hemisphere in the 1970s, and DDT levels in the Arctic have declined steadily since then, new measurements show that DDT levels in Antarctic Adélie penguins have remained constant.
"These levels are not high enough to be of concern," said lead researcher Heidi Geisz of the Virginia Institute of Marine Science in Gloucester Point, Va. But the presence of DDT suggests that other contaminants, some of which might have greater effects on seabirds, might be moving in the environment in similar ways, she added.
The researchers blame melting glaciers for the continuing supply of DDT -- deposited in the ice in past decades -- to the environment, where it is taken up by phytoplankton and moves up the food chain, accumulating in the fat of animals at the top, such as Adélie penguins.
"There wasn't any DDT coming in on the air, or in the snow, or in the sea ice," Geisz said of other team members' environmental measurements, "but when they looked at the melt water, it was easily detectable there."
The team measured DDT levels in the fat of 12 penguins they found dead and in 27 eggs found ruined at two study sites in the Antarctic. They compared these findings with measurements from the 1960s and 1970s and found no statistical change in the combined levels of DDT and its breakdown product, DDE.
"It's not conclusive, given our sample size," Geisz noted, "but it appears that these levels aren't declining."
Some of the penguins died of trauma, not starvation, and the eggs were ruined for various reasons, so the researchers believe the measurements reflect the population at large.
Still, if glacial melt is the source of DDT in the Antarctic, why are levels declining in the Arctic, where plenty of melting is going on?
Geisz suggests that DDT levels are simply much higher in the north, where most of the use occurred: "It would likely be the same in the Arctic, with melting of the glaciers releasing DDT," she said. "But these changes are overwhelmed by the levels already in the system," which are declining.
Although DDT is still used in parts of South America and its use is growing in Africa, DDT levels are a small fraction of what they were before they were banned.
Because Adélie penguins don't migrate, they provide an indication of DDT levels in the Antarctic alone.
"They are picking up these background levels, because they aren't migrating anywhere where there are point sources," Geisz said.
"It didn't come as much of a surprise that there is still DDT in penguins in Antarctica," environmental chemist Frank Wania of the University of Toronto Scarborough told Discovery News after reviewing the findings. There are only a few historical data points for the researchers to compare with, he noted, which makes it difficult to conclude too much from the findings.
Still, "it is surprising that it wouldn't have declined since the 60s or 70s," he said.
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Discovery News blog: Earth Impacts