Toxic chemicals in penguins
2008-05-10 08:24
Washington - The pesticide DDT,
banned decades ago in much of the world, still shows up in
penguins in Antarctica, probably due to the chemical's
accumulation in melting glaciers, a sea bird expert said on
Friday.
Adelie penguins, known for their waddling gait and a habit
of nesting on stones, have long shown evidence of DDT in their
fatty tissues, although not in enough concentration to hurt the
birds, according to Heidi Geisz of the Virginia Institute of
Marine Science.
But researchers were surprised to see that the level of the
pesticide in Adelies' fat had not declined, even after DDT was
banned for exterior use in the 1970s in the United States and
elsewhere.
First noted in 1964, while the chemical was still widely
used, the amount of DDT found in Adelie penguins rose in the
1970s and has stayed stable since then, Geisz said in a
telephone interview.
In findings published in the journal Environmental Science
& Technology, Geisz and her colleagues noted that persistent
organic pollutants like DDT accumulate and become concentrated
in the Antarctic ecosystem.
"DDT, along with a lot of other of these organic
contaminants, actually travel through the atmosphere ...
toward the polar regions by a process of evaporation and then
condensation in cooler climates," Geisz said, explaining this
is how the pesticide got deposited in Antarctic glaciers.
DDT declined dramatically in Arctic wildlife over the last
decade, while the amount of the chemical in Antarctic Adelies
stayed stable, the study said.
DDT was easily detectable in glacier melt water, Geisz
said.
Food chain
Adelies feed off tiny creatures called krill that live in
melted glacier water, and DDT is transmitted up the food chain
directly to the penguins.
There is not enough of the chemical to harm the birds, but
it is measurable in samples of penguin corpses and their
abandoned eggs, Geisz said.
Some kinds of birds that ingest DDT, especially birds of
prey like the American bald eagle, produce eggs with extremely
thin shells which are easily crushed by adult birds. Geisz said
this has not been demonstrated to be the case with sea birds.
A more pressing issue for the Adelie penguins that breed on
the Antarctic Peninsula is encroaching climate change, she
said. The peninsula, which stretches north toward South
America, has been warming much faster than the rest of the
continent.
Warming on the peninsula means "we see more snow and more
moisture and these (Adelie) eggs end up getting soaked and
frozen", Geisz said. "It allows opportunities for people like
me to study the eggs, but it's not necessarily ideal for the
penguins."
Originally developed as a powerful multi-species pesticide,
DDT was used in World War Two to clear South Pacific islands of
malaria-causing insects for US troops and in Europe as a
de-lousing powder. The United States banned the chemical in
1972. The World Health Organisation approved it in 2006 for use
indoors to fight malaria.