Skull pathology in East Greenland and Svalbard polar bears (Ursus maritimus) during 1892 to 2002 in relation to organochlorine pollution

Abstract

East Greenland and Svalbard polar bears (Ursus maritimus) are heavily polluted with long-range transported organochlorines such as PCBs (polychlorinated biphenyls). To investigate the negative health impacts, a time-trend study of skull pathology was conducted on 269 East Greenland and 241 Svalbard polar bears. The skulls were sampled during 1892-2002 and 1964-1992, respectively. Seven different pathological changes were found: adonti, displacement of teeth, caries, osseous proliferations, exostosis, tooth wear and periodontitis. Only tooth wear and periodontitis was in a prevalence that allowed statistical treatment. The most severe cases of tooth wear and periodontitis were accompanied by a substantial loss of alveolar bone structure. The prevalence of tooth wear and periodontitis increased significantly with age (p<0.001) with incisor wear being more severe than in canines, premolars and molars (p<0.001). No sex difference was found for tooth wear (p=0.22) while a significant difference between sexes was found for periodontitis (p=0.01) with males having higher prevalence than females (odds ratio of 2.5 for males:females). In East Greenland, the prevalence of tooth wear was significantly higher in polar bears collected in the pre pollution period (<1960) than in bears sampled during polluted periods (1960-1980 and 1981-2002) (p<0.001). Regarding periodontitis, the prevalence was not significantly different between pre-pollution and pollution periods (p=0.309). Polar bears from Svalbard had significantly higher prevalence of tooth wear (p<0.001) and periodontitis (p=0.02) than polar bears from East Greenland. The tooth wear and periodontitis odds ratios for Svalbard:East Greenland were 135 and 2.6, respectively. Hence, we found a clear age/sex link and geographical difference but no evidence for an association between skull pathology and exposure to organochlorines in East Greenland and Svalbard polar bears.