Research Article: Two decades of biomonitoring polar bear health in Greenland: a review

Date Published: February 24, 2012

Publisher: BioMed Central

Author(s): Christian Sonne, Robert J Letcher, Thea Ø Bechshøft, Frank F Rigét, Derek CG Muir, Pall S Leifsson, Erik W Born, Lars Hyldstrup, Niladri Basu, Maja Kirkegaard, Rune Dietz.

http://doi.org/10.1186/1751-0147-54-S1-S15

Abstract

We present an overview of studies of anthropogenic pollutants in East Greenland polar bears over the period of 1999-2011. East Greenland polar bears are among the most polluted species, not just in the Arctic but globally, and represent an excellent biomonitoring species for levels and effects of global pollution in an apex predator. Therefore, an international multidisciplinary team joined to monitor and assess the patterns and concentrations of contaminants and their potential negative impact on polar bears. The review showed that East Greenland polar bears are exposed to a mix of chlorinated, brominated and fluorinated organic compounds as well as mercury which are all known to have endocrine, immune and organ-system toxic properties. For example, the concentrations of PCBs (polychlorinated biphenyls) in blubber ranged approximately 800-21,000 ng/g lw while mercury concentrations in liver and kidney ranged 0.1-50 μg/g ww. Regarding health endpoints, bone density seemed to decrease as a function of time and OHC (organohalogen compound) concentrations and further T-score for adult males indicated risk for osteoporosis. .The size of sexual organs decreased with increasing OHC concentrations. In the lower brain stem, mercury-associated decreases in NMDA-receptor levels and DNA-methylation was found The present review indicated that age was one of the major drivers for liver and renal lesions, although contaminants and infectious diseases may also play a role. Lesions in thyroid glands were most likely a result of infectious and genetic factors and probably, together with endocrine disrupting chemical (EDCs), the reason for disturbances/fluctuations in blood plasma thyroid hormone concentrations. Except for bone density reductions and neurological measures, all findings were supported by case-control studies of Greenland sledge dogs exposed long-term orally to similar combinations of contaminant concentrations. The studies of sledge dogs also indicated that the mixture of contaminants and fatty acids in the blubber of prey similar to that of polar bears induces cellular as well as humoral immune toxic changes. These controlled studies using model species for polar bears indicate that the correlative findings between health endpoint and contaminants in polar bears could be a cause-and-effect relationship. Physiologically based pharmacokinetic (PBPK) modelling showed that the risk quotients were ≥1 for ΣPCB, dieldrin and PFOS, which indicate an increased risk of prenatally reproductive pathology. In conclusion polar bears are susceptible to long-range transported chemicals that may have various adverse effects on multiple organ systems such as the reproductive and immune system.

Partial Text

The use of East Greenland polar bears (Ursus maritimus) as a biomonitoring key species for measuring exposure to OHCs (organohalogen compounds) and Hg (mercury) was initiated in Scoresby Sound in 1983 and is now the most comprehensive time trend studies of pollution on this species [1-7]. In addition, museum samples of skin and skulls collected since year 1892 have been included for Hg analysis and various patho-morphological and toxico-pathological density analyses [4,6-11].

Chlorinated legacy contaminants (PCBs and OC pesticides), brominated flame retardants (PBDEs), perfluoroalkyl contaminants (PFCs) and Hg have been analyzed in brain, adipose tissue, liver, kidney, blood and hair samples from East Greenland polar bears. The range of contaminant concentrations used in relation to health endpoints during the period 1999-2002 are seen in Table 1. Concentrations increase in the order: PBDEshttp://doi.org/10.1186/1751-0147-54-S1-S15