Thyroid gland lesions in organohalogen contaminated East Greenland polar bears (Ursus maritimus)

Abstract

Thyroid gland histology was examined in 20 organohalogen contaminant (OHC)-exposed East Greenland polar bears (Ursus maritimus). OHC concentrations measured in subcutaneous adipose tissue were between 3556 and 28,670 ng g−1 lw for polychlorinated biphenyls (ΣPCB51), 9 and 3403 ng g−1 lw for the sum of organochlorine pesticides (hexachlorocyclohexanes, hexachlorobenzene, chlordanes, dichlorodiphenyltrichloroethanes, and dieldrin), and from 21 to 130 ng g−1 lw for polybrominated diphenyl ethers. Histological examinations revealed that 12 of the bears (10 males aged 3–19 years and two females aged 4–7 years) had normal thyroid tissue while eight bears (40%) of varying ages and genders (three males aged 3–9 years and five females aged 4–25 years) showed clear histological lesions including parafollicular C-cell proliferation, nodular hyperplasia, and interstitial fibrosis. No significant differences were found in prevalence of thyroid gland lesions between males and females. Similarly, no marked difference was found in mean age between individuals with and without lesions. There was no significant difference in OHC mean concentrations between males and females or between individuals with and without lesions. Despite no documented relationship to OHC concentrations in adipose tissue, it is worth noting that the lesions were similar to that of OHC exposed lab and wildlife contaminated mammals. Since the lesions were not associated with age or gender, other environmental factors such as energetic stress and autoimmunity/genetic predisposition also need to be considered. It is therefore possible that OHCs, in combination with other environmental and intrinsic factors described in the literature, may interfere with the hypothalamic–pituitary–thyroid axis (HPT axis) resulting in endocrine perturbations in East Greenland polar bears.