Bacteria may play role in producing far more toxic version in northern lakes

Scientists seek key to mercury mystery


RESOLUTE BAY – Arctic char in Resolute Lake contain amounts of methyl-mercury that exceed what Health Canada considers safe to eat regularly.

The fresh fish is still probably far healthier for most people to eat than frozen pizza and other processed foods sold at the co-op, although pregnant women may want to use caution. Mercury is a neurotoxin, and when it builds up to dangerous levels it's believed to cause serious health problems, such as brain damage and heart disease, in unborn children.

How the unusually high levels of this form of mercury got in the char of Resolute Lake remains a puzzle to scientists.

What's already well known is that mercury is released into the air by industrial pollution, particularly the burning of coal. This mercury is carried by air currents from southern regions to the Arctic, where the mercury falls to the ground in rain and snow.

But this takes the form of "inorganic" mercury, which is fairly harmless compared to the far more nasty methyl-mercury found in northern lakes.

Something in northern lakes is changing the mercury. To better understand how this happens, Igor Lehnherr and Jane Kirk, two PhD students from the University of Alberta, spent July at Lake Hazen on northern Ellesmere Island, conducting tests on several small lakes and ponds.

While it will be a long time before they're finished analyzing samples in their lab back in Alberta, under the supervision of their professor, Vincent St-Louis, the two suspect that certain bacteria, which reside in the mud of northern lakes and breathe different types of salt the same way we breathe air, may be transforming the inorganic mercury into methyl-mercury.

"These little ponds are just pouring out methyl-mercury," said Kirk.

The methyl-mercury found in northern Ellesmere's lakes aren't believed to be much of a risk to the animals that live there, such as Arctic terns that feed on mercury-rich zooplankton in the small ponds.

But mercury causes more harm as it moves up the food chain. Char eat zooplankton. Ringed seals eat char. And polar bears, the Arctic's top predator, feast on the blubber of seals, which studies have shown hold growing amounts of mercury.

Lehnherr and Kirk chose the ponds near Lake Hazen because they're easy to study. No rivers pass through them, and at 81.5 degrees north, they're far away enough from people that there are few complicating factors.

Despite being the most remote lakes and ponds in Canada, Lehnherr and Kirk have been surprised by how much life flourishes in the water they study.

"They're amazing, the kind of life you can see in such a small pond – tadpoles, shrimp," said Lehnherr.

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