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.
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