The pesticides known as chlordanes belong to a class of long-lasting organochlorine pollutants that includes DDT and polychlorinated biphenyl, or PCB. Although Western countries have banned their use, chlordanes applied years ago gradually evaporate and circulate by air as far north as the Arctic.
To pin down the pollutants origins, Terry F. Bidleman of the Meteorological Service of Canada in Downsview, Ont., and his colleagues analyzed air samples collected between 1984 and 1998 from Arctic sites in Canada, Finland, Russia, and Sweden. The researchers found that concentrations of several related chlordanes decreased by half every 5 to 10 years.
Like many organic molecules, each chlordane compound comes in two mirror-image variants called enantiomers, which may break down at different rates in the environment. Using gas chromatography, the researchers measured the relative amounts of both forms of several chlordanes in the various Arctic sites. The bigger the difference in those amounts the older the chlordane.
Based on shifts in the ratio of the enantiomers over time, the researchers determined that recently applied pesticide is responsible for a decreasing fraction of airborne chlordane in the Arctic. However, chlordanes applied to farms and homes in temperate regions years ago are still being released from the soil, drift north into the Arctic, and linger there, the researchers say in an upcoming issue of Environmental Science and Technology.
The finding strongly suggests that release of old pesticides accounts for the chlordanes in Arctic air, agrees Crispin J. Halsall, an environmental chemist at Lancaster University in England.