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Christian Sonne,^1,2 Rune Dietz,¹ Erik W. Born,³ Frank F. Riget,¹ Maja Kirkegaard,¹ Lars Hyldstrup,⁴ Robert J. Letcher,⁵ and Derek C. G. Muir⁶

¹National Environmental Research Institute, Department of Arctic Environment, Roskilde, Denmark; ²Department of Basic Animal and Veterinary Sciences, Royal Veterinary and Agricultural University, Frederiksberg, Denmark; ³Greenland Institute of Natural Resources, Nuuk, Greenland, Denmark; ⁴University Hospital of Hvidovre, Hvidovre, Denmark; ⁵Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario, Canada; ⁶National Water Research Institute, Environment Canada, Burlington, Ontario, Canada

Abstract
We analyzed bone mineral density (BMD) in skulls of polar bears (Ursus maritimus) (n = 139) from East Greenland sampled during 1892-2002. Our primary goal was to detect possible changes in bone mineral content (osteopenia) due to elevated exposure to organochlorine [polychlorinated biphenyls (PCBs) , dichlorodiphenyl trichloroethane (DDT) and its metabolites, chlordanes (CHLs) , dieldrin, hexacyclohexanes, hexachlorobenzene] and polybrominated diphenyl ether (PBDE) compounds. To ensure that the BMD value in skull represented the mineral status of the skeletal system in general, we compared BMD values in femur and three lumbar vertebrae with skull in a subsample. We detected highly significant correlations between BMD in skull and femur (r = 0.99 ; p < 0.001 ; n = 13) and skull and vertebrae (r = 0.97 ; p < 0.001 ; n = 8) . BMD in skulls sampled in the supposed pre-organochlorine/PBDE period (1892-1932) was significantly higher than that in skulls sampled in the supposed pollution period (1966-2002) for subadult females, subadult males, and adult males (all, p < 0.05) but not adult females (p = 0.94) . We found a negative correlation between organochlorines and skull BMD for the sum of PCBs (PCB ; p < 0.04) and CHL (p < 0.03) in subadults and for dieldrin (p < 0.002) and DDT (p < 0.02) in adult males ; indications for PBDE in subadults were also found (p = 0.06) . In conclusion, the strong correlative relationships suggest that disruption of the bone mineral composition in East Greenland polar bears may have been caused by organochlorine exposure. Key words: BMD, bone mineral density, chlordane, DDT, dieldrin, endocrine disruption, osteoporosis, PCBs, polar bear, polychlorinated biphenyls, Ursus maritimus. Environ Health Perspect 112:1711-1716 (2004) . doi:10.1289/ehp.7293 available via http://dx.doi.org/ [Online 13 September 2004]

Address correspondence to C. Sonne, National Environmental Research Institute, Department of Arctic Environment, Frederiksborgvej 399, DK4000 Roskilde, Denmark. Telephone: 45-46-30-19-54. Fax: 45-46-30-19-14. E-mail: csh@dmu.dk

We thank J. Brønlund and local hunters for organizing sampling in East Greenland, the Zoological Museum of Copenhagen for skull maceration and preparation support, and P.M. Lind and three anonymous reviewers for their comments on the manuscript.

Financial support was provided by the Danish Cooperation for Environment in the Arctic and the Commission for Scientific Research in Greenland.

The authors declare they have no competing financial interests.

Received 28 May 2004 ; accepted 13 September 2004.