New measurements have shown that DDT levels in Antarctic Adelie penguins have remained constant, contrary to the reports that it had declined steadily since the 1970s, when the pesticide was banned in the Northern Hemisphere.
According to a report in Discovery News, though these levels are not high enough to be of concern, 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.
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 Adelie penguins.
"There wasn't any DDT coming in on the air, or in the snow, or in the sea ice, but when they looked at the melt water, it was easily detectable there," said lead researcher Heidi Geisz of the Virginia Institute of Marine Science in Gloucester Point.
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, but it appears that these levels aren't declining," said Geisz.
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.
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 Adelie 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," said Geisz.
"It didn't come as much of a surprise that there is still DDT in penguins in Antarctica," according to environmental chemist Frank Wania of the University of Toronto. "Still, it is surprising that it wouldn't have declined since the 60s or 70s," he added.