The first national map to show mercury concentrations across Canada, paints a toxic picture for loons and some types of sport fish in this region.
The map, part of a soon-to-be-published research study in the journal, Environmental Science & Technology, shows Eastern Canada has the highest levels of mercury in the country, posing a risk to fish-eating birds like loons, some freshwater sport fish, like walleye, and other wildlife.
“Our work is showing that Eastern Canada is particularly sensitive for mercury contamination. Even at very low concentrations, atmospheric mercury is creating issues for our wildlife and fish,” said Linda Campbell, an associate professor of Environmental Studies at Saint Mary’s University in Halifax.
Campbell, and Environment Canada scientists Neil Burgess in Newfoundland, and David Depew in Ontario started the research four years ago.
Their findings are based on an analysis of 230,000 yellow perch from lakes and rivers across Canada. Yellow perch are one of the most common species of freshwater fish in Canada and popular prey for wildlife like common loons and walleye, Campbell said in an email interview.
“As a result, yellow perch makes a great indicator for monitoring mercury in the aquatic environment,” said Campbell, also a Saint Mary’s University Fellow in Environmental Sciences.
Mercury is emitted into the atmosphere from industrial processes, as well as the burning of coal and gas for power generation, and deposited into lakes and rivers by precipitation. Once in water, it can be converted into methylmercury, a type of organic mercury, which is more toxic and rapidly taken up by small algae and plankton organisms and transferred along the food chain, Campbell said.
Methylmercury accumulates in living things and over time can reach high concentrations in fish-eating animals such as loons and sport fish.
As it moves from west to east, the colour-coded map shows how Canada’s mercury picture worsens.
Many yellow perch that the researchers analyzed in Eastern Canada were found to have mercury concentrations that“exceed certain tolerance thresholds” for loons and walleye.
“Other studies have shown wildlife starts to demonstrate toxic responses to mercury at those concentrations,” Campbell said.
This research study assessed risk and didn’t look at the actual health of loons or wildlife, but other “studies in southern Nova Scotia and Quebec have already found loon reproductive impacts. Those impacts include lower ability to take care of young, few chicks being hatched and erratic behaviour,” she said.
Campbell calls Eastern Canada “the Goldilocks region” for mercury geochemistry with a “just right” combination of geography and water chemistry to convert atmospheric mercury to methylmercury in lakes.
Eastern Canada’s lakes and soils are more acidic, which promote the conversion to methylmercury. It has forests that accumulate and retain atmospheric mercury and then the leaves, and leaf litter enter the water cycle each year. As well, fish in acidic lakes grow more slowly allowing a longer period for mercury to accumulate in their muscle tissue.
The value of having the national map is to show the variations in mercury concentrations across the country and those areas which need frequent monitoring.
It shows the pressing need to” investigate ways to reduce mercury emissions from industrial processes and coal and gas burning in any way possible,” Campbell said.
The study received funds from Environment Canada and a discovery grant for the Natural Science and Engineering Research Council of Canada.
By Clare Mellor | thechronicleherald.ca