The impressive Peregrine falcon, which fought its way off the U.S. endangered species list less than five years ago, may soon be facing a different kind of threat. Findings published in the current issue of the journal Environmental Science and Technology suggest that the creature's eggs may be susceptible to contamination from a popular flame-retardant chemical, which scientists previously thought did not pose a danger to wildlife.

Peter Lindberg of the Swedish Society for Nature Conservation in Stockholm and his colleagues studied three populations of peregrine falcons, two in the wild and one in captivity, between 1987 and 1999. They analyzed the creatures' eggs and found a variety of forms of chemicals known as brominated diphenyl ethers (BDEs), which are widely used as flame retardants. In particular, the team discovered high levels of the so-called deca form of the chemical, which is relatively large and was thought to be too big to cross cell membranes and be taken up into animals. "The fact that we have found [deca] in falcon eggs means that it is in their food, is taken up from the gut and is transferred to the eggs," study co-author Cynthia de Wit of Stockholm University says.

Peregrine falcons in the U.S. were initially endangered by the widespread use of the pesticide DDT, which caused their eggshells to thin and break prematurely. BDEs do not cause such thinning, but previous studies have suggested that the chemicals cause neurobehavioral problems and could interfere with the creatures' hunting abilities. Animals stateside have a higher potential for exposure to the chemicals than those studied in Sweden. "According to statistics from 1999, 24,300 tons of deca were used in the Americas compared to only 7,500 tons in Europe," de Wit notes. "We discovered the DDT problem because bird populations crashed. They still haven't completely recovered from DDT, so new effects could be masked. "