July 23, 2007 Killer whales hold the gloomy record of being the most-polluted European arctic mammal, says a new study published in the latest issue of Environmental Toxicology and Chemistry. Levels of contaminants measured in whales near Norway were among the highest ever measured in marine mammals, exceeding levels found in harbor seals, polar bears, and white whales.
Killer whales are widely distributed marine mammals capable of surviving on a variety of foods. In this study, blubber samples were taken, using a dart gun, from eight live, free-ranging whales. Contamination levels were six to 20 times higher in killer whales compared to other high-Arctic species, such as white whales.
Very high levels of halogenated organic contaminants (HOCs), including polychlorinated biphenyls (PCBs) and chlorinated pesticides were found in the tissues of killer whales, apparently due to their high concentration in the whales’ primary diet source, herring.
Despite the ban on most PCBs, toxaphene, and DDT, these compounds pose a continuing threat to the health of humans and marine organisms. New HOCs, such as the polybrominated diphenyl ethers (PBDEs) which are used as flame retardants, continue to be released into the environment.
Organisms are particularly vulnerable to HOCs in the marine environment. Because of the low water solubility of these compounds, exposure through the food web leads to the highest concentrations in marine mammals. Several studies have demonstrated adverse effects on the endocrine and immune systems of some marine mammals.
While most HOCs are considered to be poorly metabolized, killer whales in this study had lower levels of certain PCBs, pesticides (chlordane, DDE), toxaphene, and PBDEs than expected, suggesting an ability to metabolize them. This was unexpected, because other marine mammals, such as dolphins and white whales, show a much lower ability to metabolize HOCs.
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