May 9, 2008

Melting Glaciers Expose Penguins to DDT

A new study has found that Antarctica's Adelie penguins have recently been exposed to trace levels of the chemical DDT as a result of frozen stores of the pesticide seeping out of the continent's melting glaciers.

The chemical's presence could indicate that other frozen toxins will be released as a result of climate change in the environment, according to Heidi Geisz, a marine biologist at Virginia Institute of Marine Science.  Geisz, who has worked in Antarctica since 1999, led the team that sampled the DDT levels in the penguins as an effort to determine the long-term changes in pollutants found in the continent's seabirds.

She is concerned about the release of a whole cocktail of toxic chemicals, including PCBs and PBDEs, into the ocean.  Such  industrial pollutants have long been linked to various health problems in humans.

"DDT is not the only chemical that these birds are ingesting and it is certainly not the worst," Geisz told New Scientist magazine.

DDT (dichloro-diphenyl-trichloroethane) latches onto tiny airborne particles that then migrate toward the poles. The chemical was first synthesized by chemists in 1874, and began being used as an insecticide in the 1940s.

The United States officially banned the use of DDT in 1972, as did the UK in 1984.  However, it remains in use today by some countries as part of their efforts to fight diseases such as malaria and dengue.  But worldwide, use of DDT has tumbled to 40,000 tons per year in 1980 to 1,000 tons per year today.

A previous study conducted in 1964 had found modest amounts of DDT in the Adelie penguins.  But because of the ban, Geisz and her colleagues had expected levels to have decreased over the past 40 years.  Instead, they were surprised to find that birds living near Antarctica's western peninsula had DDT levels identical to those observed in 1964.  

Geisz explained the process, "As DDT crawls up the food chain, from plankton to krill to penguins, it breaks down into a sister molecule called DDE. The more DDE in an animal, the longer the chemical has been around."

However, the researchers observed low levels of DDE in the penguins, a finding that suggested a new source for the DDT.   

Puzzled by the DDT's origin, Geisz reviewed glacial records dating back several decades, and learned that the continent's glaciers swelled during the 1950s and 60s, something that might have trapped chemicals such as DDT.    As the Antarctic Peninsula's winter temperatures steadily rose 6 degrees Celsius over the past 30 years, the glaciers began melting faster than they swelled.  

Based on her analysis, Geisz estimated that 1 to 4 kg per year of DDT re-enters the ecosystem as a result of glacial runoff from the continent's western ice sheet melts.

Researcher Derek Muir of Environment Canada in Burlington, Ontario, told New Scientist magazine that Arctic glaciers ought to store even more DDT, but the continent's animals seem to be shedding the pesticide.

"The declines in DDT in seals and seabirds in the Canadian Arctic and in polar bears in eastern Greenland suggest it is not having a large impact," he said.

Geisz plans to monitor the flow of other toxins from glaciers to birds to bolster her case for Antarctica.


On the Net:

New Scientist

The study was published in the journal Environmental Science and Technology.  An abstract of the report can be viewed at http://pubs.acs.org/cgi-bin/abstract.cgi/esthag/asap/abs/es702919n.html