A 1,500-year correlation between selenium and mercury found in seals and penguins has broken down in the last 50 years. Increased contamination of the Antarctic by mercury and/or other metals may be responsible, but the exact causes remain to be determined. Results from this study are published in the latest issue of Environmental Toxicology and Chemistry, the monthly journal of the Society of Environmental Toxicology and Chemistry.

Past studies have documented that the metalloid selenium interacts with and reduces the toxicity of mercury. Such mercury detoxification has been found in fish, marine mammals, birds and even humans.

Researchers analyzed historic and recent seal hair, as well as seal and penguin excrement. They found a correlation between selenium and mercury over the last 1,500 years—but a lesser correlation in the last 50—suggesting a self-regulating protective mechanism. Every time there was a heavier mercury burden in the animals, more selenium was accumulated from the environment to compensate for and reduce potential mercury toxicity. The researchers suggest this pattern was not restricted to seals and penguins, but probably also applied to fish, plankton and other sea life.

But this pattern of mercury detoxification by selenium has broken down. Mercury levels are higher than they have been in the past, and over the last 50 years, they may have become too high for the self-protection mechanism to work. Increased levels of other metals in the Antarctic may also be a factor. Whatever the causes, this finding raises concern regarding the health of Antarctic ecosystems.

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