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Researchers: Mercury Converted To Its Most Toxic Form In Ocean Waters

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EDMONTON, Alberta -- University of Alberta-led research has confirmed that a relatively harmless inorganic form of mercury found worldwide in ocean water is transformed into a potent neurotoxin in the seawater.

After two years of testing water samples across the Arctic Ocean, the researchers found that relatively harmless inorganic mercury, released by human activities like industry and coal burning, undergoes a process called methylation and becomes deadly monomethylmercury. Methylation, in this case, is the addition of a methyl group to heavy metals catalyzed by certain enzymes.

Lead U of A researcher Igor Lehnherr says the greatest exposure to monomethylmercury for humans is through the consumption of marine-based foods. "Unlike inorganic mercury, monomethylmercury both bio-accumulates and bio-magnifies, meaning its toxic effects are amplified as it progresses through the food chain," said Lehnherr. "Humans are at the top of the food chain, so we're getting the highest content of this neurotoxin through contaminated seafood."

Lehnherr, who just last week was awarded his PhD in biological sciences, says the data collected in the Arctic Ocean paints a disturbing picture. "The conversion of inorganic mercury to monomethyl mercury accounts for approximately 50 per cent of this neurotoxin present in polar marine waters," said Lehnherr. "Those high levels could also account for a significant amount of the mercury found in Arctic marine organisms."

For the study, Lehnherr's research group incubated seawater samples, collected from the Canadian Arctic Archipelago, with stable inorganic mercury. Lehnherr found that the relatively harmless inorganic mercury was converted, through methylation, into the neurotoxin monomethylmercury. "We believe the methylation process is happening in oceans all over the world," said Lehnherr.

The researchers say this is the first direct evidence that inorganic mercury is methylated in seawater. The research team is now going to look at how the process works.

"We're 90 per cent sure that the methylation process is carried is carried out by microbial life forms in the ocean like algae," said Lehnherr.

The research was published earlier this month online in Nature Geoscience.

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