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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. Related Links: Discovery News blog: Earth Impacts |
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