Exposure to organochlorine chemicals is linked to reduced bone mineral density among polar bears from East Greenland, according to a study published today in the December issue of the peer-reviewed journal Environmental Health Perspectives (EHP). In the study of 139 polar bear skulls, researchers compared 41 samples collected between 1892 and 1932 with 98 samples collected between 1961 and 2002. Bone mineral density in the skulls collected before 1932—considered “pre-pollution” by the researchers—was significantly higher than that in skulls sampled in the “post-pollution” period after 1961, when scientists first began seeing organochlorines and other persistent organic pollutants (POPs) in the fat of polar bears.
The researchers also analyzed a subset of 58 skulls collected between 1999 and 2002 to examine the organochlorine body burden in relation to bone mineral density. In this group, exposure to PCB compounds and to chlordane (a now-banned insecticide) both correlated with low bone mineral density among younger bears. In adult males, concentrations of dieldrin (another banned insecticide) and total DDT residues also correlated with low density.
POPs resist breakdown, store easily in fat, and bioaccumulate through the food chain. Once widely used in agriculture and industry, several types have been classified as probably or possibly carcinogenic to humans, and there are now restrictions or bans related to their application. However, these highly toxic chemicals are very stable over time, and they remain widely present in the environment, where they still pose a serious health threat.
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