Research by Virginia Institute of Marine Science graduate student Heidi Geisz and colleagues shows that DDT and its breakdown products persist within the tissues of Adélie penguins, three decades after use of the powerful pesticide was banned in most countries.
The researchers contend that as Antarctic glaciers melt, an accumulated store of DDT within their ice is flowing into the nearby ocean, where it can readily build up within penguin fat and eggs. Penguins are apex predators atop the short polar food chain, making them particularly vulnerable to the accumulation of environmental contaminants.
The scientists caution that accelerated melting due to global warming could lead to a further increase in contaminant input to Antarctica's coastal waters. Average winter temperatures on the Antarctic Peninsula have increased 10°F in the last 30 years, more than five times the global average.
Although there is little evidence that current DDT levels are sufficient to impact penguin health, Geisz says that DDT tends to occur with other "persistent organic pollutants" in nature, raising concerns about the potential cumulative effects of these compounds on penguins and other Antarctic predators.
Persistent organic pollutants, or POPs, are chemicals found in insecticides, pesticides, industrial wastes, and flame-retardants. As their name implies, these compounds resist breakdown, and thus persist in the environment, where they tend to accumulate in the fatty tissues of organisms high up the food chain. Many, including DDT and PCBs, are highly toxic.
POPs accumulate in the Antarctic and Arctic via repeated cycles of evaporation and condensation as they move poleward through the atmosphere from the tropical and temperate zones where most are released.
Geisz's discovery of persistent DDT levels in Adélie penguins runs counter to trends seen in studies of Arctic seabirds, whose falling DDT levels reflect the worldwide decline in DDT usage since worldwide regulations began in the 1970s. Current worldwide use of DDT is less than 10 per cent what it was in the 1960s.
Geisz and colleagues attribute the difference to input from melting glaciers. Says Geisz, "We didn't see a decline of overall DDT in penguin tissues, and we didn't find any DDT or DDT byproducts in air, snow, ice, or seawater. But we did find DDT in glacial meltwater." The team analyzed samples from two widely separated sites in Antarctica.
Geisz, the paper's lead author, is a Ph.D. student in the College of William and Mary's School of Marine Science at VIMS. She is advised by co-authors Rebecca Dickhut and Hugh Ducklow. Professor Dickhut is chair of the Physical Sciences Department at VIMS. Ducklow, now with the Marine Biological Laboratory in Woods Hole, Massachusetts, heads the Long-term Ecological Research site at Palmer Station, one of three U.S. research stations in Antarctica. The remaining co-authors are VIMS technician Michele Cochran and Bill Fraser of the Polar Oceans Research Group.
The research headlines the current online issue of Environmental Science & Technology. It is scheduled to be published in an upcoming print version of ES&T, a leading journal in the field of environmental sciences.
For more information on the Virginia Institute of Marine Science, see www.vims.edu.