EDMONTON -- Alberta Health has issued a health warning on eggs from two northern lakes downstream from the oilsands after dangerous levels of mercury were discovered in them.

James Talbot, chief medical health officer, has advised people to restrict their consumption of gull and tern eggs from Lake Athabasca and Mamawi Lake in the Peace-Athabasca delta. Children and pregnant women are at higher risk, he said.

"The developing brain is the one that's most at risk from mercury."

Talbot said the Nunee Health Authority in Fort Chipewyan has been informed of the advisory.

The levels of mercury, a potent neurotoxin, were first discovered last September by federal researchers monitoring the environmental impact of the oilsands.

But concerns about mercury in the environment dates back at least to 2010, when an Environment Canada study found mercury in the eggs of water birds downstream from oilsands development seemed to have grown by nearly 50 per cent over the three previous decades.

Alberta Health has previously issued consumption advisories for fish from area lakes.

Talbot said he's asked the monitoring program to put more emphasis on health issues. Scientists could look at more commonly eaten eggs, such as those from ducks or geese, or larger animals that are part of the traditional diet, such as moose or deer.

"Anything that's part of the traditional diet, it's worth assuring people that it's safe to eat," said Talbot.

"Given the mandate for the monitoring agency, a health perspective on what's there could result in timely information."

Talbot said surveys suggest that gull and tern eggs aren't commonly eaten. But he acknowledged that information may be incomplete.

"Those studies may be flawed if they missed people who are living a more traditional lifestyle and not available to answer surveys," Talbot said.

The amount of mercury in the eggs is still low enough to allow pregnant women to eat three eggs a week from Lake Athabasca and five from Mamawi, although Talbot points out gull and tern eggs are much smaller than chicken eggs.

Talbot said the source of the mercury hasn't been identified.

Mercury is commonly released from large-scale land disturbances such as dams or industrial developments. It can also drift in from sources such as coal-fired power plants, of which Alberta has several.