Temporal monitoring of liver and kidney lesions in contaminated East Greenland polar bears (Ursus maritimus) during 1999-2010

Abstract

Organohalogen contaminants bioaccumulate to high concentrations in tissues of polar bears (Ursus maritimus). The exposure levels are in the order to be toxic to inner organs like liver and kidney. We therefore investigated the temporal development of lesions in liver (n=115) and kidney (n=122) samples from East Greenland polar bears taken over the 12 year period from 1999 to 2010. Seven liver and seven kidney lesions were observed of which six were age-related. Controlling for this, the analyses showed that hepatic steatosis and renal cell infiltrations, glomerular sclerosis and tubular hyperplasia decreased over the investigated time period (all p<0.05). Similarly, hypertrophy of hepatic Ito cells, renal glomerular capillary wall thickening and interstitial fibrosis increased over the study period (all p<0.05). Regarding contaminant, concentrations of polybrominated diphenyl ethers in adipose tissue were negatively associated with hepatic mononuclear cell infiltrations (p=0.05) and a similar trend was found for Hg (p=0.09). Hexachlorobenzene was positively associated with portal cell infiltrations and hepatic lipid granulomas, while polychlorinated biphenyls were negatively associated with the prevalence of steatosis (both p<0.05) and a similar trend was found for hexachlorocyclohexanes (p=0.08). Mercury was positively correlated with the frequencies of hypertrophic Ito cells (p=0.002) and a similar trend was found for perfluorooctanesulfonic acid (p=0.07). In renal tissue, hexachlorocyclohexanes were positively associated with medullar hyaline casts (p=0.03) and a similar trend was found for cell infiltrations (p=0.08). There was a trend of trans-nonachlor being positively associated with glomerular sclerosis (p=0.06) while dichlorodiphenyltrichloroethanes were negatively associated with tubular hyperplasia (p=0.02). These results suggest that specific liver and renal lesions have decreased or increased over time and that long-range transported organohalogen contaminants and mercury may be among the co-factors responsible for these observations. These relationships are important to take into account when biomonitoring health and pollution in wildlife species such as polar bears.