Polar Bears In Depth
Management and Conservation
Page 5 of 5
Contaminants. Throughout the 1900s, numerous organic compounds were released into the global environment. Organochlorine pesticides like chlordane, dichlorodiphenyltrichloroethane (DDT), hexachlorocyclohexanes (HCHs), and hexachlorobenzene (HCB) have been used in agricultural areas worldwide and in many undeveloped areas to control mosquitoes and other insects that pose a threat to human health. Many of these compounds are resistant to physical as well as biological degradation and persist in the environment for extended periods. Their persistence allows these compounds to be spread by atmospheric and oceanic circulation, and many have concentrated in the Arctic.
The position of polar bears at the top of the Arctic food chain means they are likely to build up high body burdens of these compounds. Recent studies have verified that likelihood (Norstrom et al. 1998) and raised concerns for health effects of such contamination. The highest concentrations of many chlorinated hydrocarbon compounds have occurred in polar bears of western Russia, Svalbard, and portions of the Canadian High Arctic (Bernhoft et al. 1997; Norstrom et al. 1998). Wiig et al. (1998) hypothesized that environmental contaminants could have caused pseudohermaphroditism by disrupting normal endocrine function of Svalbard polar bears. Although linking contaminants to pseudohermaphroditism remains hypothetical, more recent studies have explicitly linked contaminants to polar bear health. Bernhoft et al. (2000) found significant negative correlations between immunoglobulin (IgG) levels and polychlorinated biphenyl (PCB) and HCB levels in the plasma of Svalbard Polar bears. PCBs and HCB also were negatively correlated with plasma levels of retinal and thyroid hormones in Svalbard polar bears (Skaare et al. 2001). Although specific maladies were not identified, IgG and thyroid hormone levels are associated with a broad variety of health-related systems. Their depression by external contaminants must be of concern. A study nearing completion in summer 2001 provided the strongest evidence yet that pollutants can reduce biological function in polar bears. Wild free-ranging polar bears in Canada, where contamination levels are relatively low, and in Svalbard were captured and vaccinated with harmless viruses. Blood samples collected 5 weeks after vaccination revealed reduced immune system response in the heavily polluted Svalbard polar bears (Skaare et al. 2002).
Although population-level effects of reduced ability to build immunity to disease have yet to be observed, it is clear that organochlorine contamination places polar bears at greater risk to a variety of possible environmental challenges. Use of some of these compounds has been dramatically reduced in recent years, and those reductions may already be reflected in polar bear tissues (Norstrom et al. 1998). Many other chemicals have been introduced in recent years, however, and risks they may cause will continue to create polar bear management uncertainties for decades to come.
The position of polar bears at the top of the Arctic food chain means they are likely to build up high body burdens of these compounds. Recent studies have verified that likelihood (Norstrom et al. 1998) and raised concerns for health effects of such contamination. The highest concentrations of many chlorinated hydrocarbon compounds have occurred in polar bears of western Russia, Svalbard, and portions of the Canadian High Arctic (Bernhoft et al. 1997; Norstrom et al. 1998). Wiig et al. (1998) hypothesized that environmental contaminants could have caused pseudohermaphroditism by disrupting normal endocrine function of Svalbard polar bears. Although linking contaminants to pseudohermaphroditism remains hypothetical, more recent studies have explicitly linked contaminants to polar bear health. Bernhoft et al. (2000) found significant negative correlations between immunoglobulin (IgG) levels and polychlorinated biphenyl (PCB) and HCB levels in the plasma of Svalbard Polar bears. PCBs and HCB also were negatively correlated with plasma levels of retinal and thyroid hormones in Svalbard polar bears (Skaare et al. 2001). Although specific maladies were not identified, IgG and thyroid hormone levels are associated with a broad variety of health-related systems. Their depression by external contaminants must be of concern. A study nearing completion in summer 2001 provided the strongest evidence yet that pollutants can reduce biological function in polar bears. Wild free-ranging polar bears in Canada, where contamination levels are relatively low, and in Svalbard were captured and vaccinated with harmless viruses. Blood samples collected 5 weeks after vaccination revealed reduced immune system response in the heavily polluted Svalbard polar bears (Skaare et al. 2002).
Although population-level effects of reduced ability to build immunity to disease have yet to be observed, it is clear that organochlorine contamination places polar bears at greater risk to a variety of possible environmental challenges. Use of some of these compounds has been dramatically reduced in recent years, and those reductions may already be reflected in polar bear tissues (Norstrom et al. 1998). Many other chemicals have been introduced in recent years, however, and risks they may cause will continue to create polar bear management uncertainties for decades to come.