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Penguins and Persistent Pollutants

May 30, 2008

Recent research shows that ice preserves more than just Thanksgiving leftovers. Does that mean we’ll see Ted Williams playing baseball again in 2050? Who knows, but it does mean that the DDT we pumped into the environment in the middle of the 20th century is still around.

DDT is best known as a mosquito-killing insecticide used to control the spread of malaria. It was heavily used to control the spread of typhus and malaria during World War II. Then, when the troops came home, farmers used DDT to protect their crops (especially cotton) from insect invasions. DDT was cheap and it was effective—at first. Over time, insects began to build resistance to the toxin and people began to wonder if DDT was too good to be true. It was. DDT can be lethal to crustaceans and fish, but it’s probably best known for its effect on birds of prey. Like other agricultural pesticides, DDT washed into rivers and streams where it contaminated fish that were then gobbled up by birds of prey. After eating the DDT-laced fish, bald eagles, peregrine falcons and brown pelicans (all eventually listed as endangered) suffered a decline in reproductive success because the chemical interfered with their ability to produce strong eggshells.

DDT is a proven animal carcinogen and a possible human carcinogen. The U.S. banned the use of DDT in 1972. Thirty-three other countries have also banned DDT use and 34 countries severely restrict its use.

DDT is one of a dozen or so aptly named persistent organic pollutants (POPs)*. POPs are persistent—obviously. In other words, they never really go away. They build up in an individual’s tissues (bioaccumulate, in science-speak). POPs also biomagnify. That means that they increase in concentration as they travel up the food chain—an animal at the top of the food chain like a bear will have higher concentrations of POPs than a small fish at the bottom of the food chain. And POPs travel long distances, often landing in areas where they were never used—like Antarctica.

Scientists have found DDT in Adelie penguins, a species that spends its entire life in Antarctica. And the levels of DDT in Adelie penguins haven’t changed since the 1970s even though the global DDT use has declined 80% since then.

Huh?

Turns out that, back in DDT’s heyday, the persistent little bugger made it’s way to Antarctica where it became frozen in the Western Antarctic Ice Sheet. Now, thanks to climate change, Antarctic ice is melting. And scientists estimate that, as it melts, the Western Antarctic Ice Sheet releases 2 to 9 pounds of DDT into the seawater each year. Krill (little critters that live in the melt water) take in DDT and when Adelies eat krill (their primary prey) they eat the DDT as well.

While the relatively low level of DDT found in Adelies isn’t likely to wipe out the population, other effects of climate change might. Adelies typically build their nests out of pebbles, but warmer weather has increased snowfall on the Antarctic Peninsula. If they nest while there is snow on the ground, their eggs will become wet and frozen, but if they wait until their nesting area is snow-free, they won’t have enough time to raise their chicks before the krill season ends and it’s time to move south to their wintering grounds.

*Other POPs include brominated flame-retardants (PBDEs), tributyltin (TBT), polycyclic aromatic hydrocarbons (PAHs), aldrin, chlordane, dieldrin, dioxins (PCDDs), endrin, furans (PCDFs), heptachlor, hexachlorobenzene, mirex, PCBs, and toxaphene.

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