Skip to main content

The Globe and Mail

Mackenzie River's fish contaminated with dangerous toxins: scientists

Two people fish on the Mackenzie River in this 2003 photo.New research signals a booming level of dangerous toxins in the river's fish, due to climate change.

JOHN LEHMANN/John Lehmann/Globe and Mail

Scientists studying burbot in the Mackenzie River, one of the country's most pristine rivers, have been surprised to discover that mercury, PCBs and DDT in the fish are rising rapidly, a finding they say is linked to climate change.

The increase in the amount of harmful chemicals has been huge. In the period from the mid-1990s to 2008, PCBs have risen up to six times, DDT by three times, and mercury by 1.6 times in the burbot, a delicacy in the north described as tasting like a freshwater lobster.

Contaminant levels "going up so dramatically was quite surprising," said Gary Stern, a senior scientist with the Department of Fisheries and Oceans and lead researcher on the study, which also involved scientists from the University of Manitoba and Geological Survey of Canada.

Story continues below advertisement

Dr. Stern said the most plausible explanation for the trend is that as temperatures in the Arctic rise due to climate change, snow and ice cover are diminishing, leading to a profusion of algae, zooplankton and other aquatic microscopic life able to absorb pollutants from water.

While this greening of the Arctic environment means there is more for wildlife to eat, it also allows harmful contaminants to enter the food chain in far greater amounts, he said.

The discovery of the rising tally of harmful pollutants in fish in such a remote area of the Northwest Territories was doubly unusual for researchers because contaminant levels should have been going down, based on the declining amount of the chemicals in the general environment. Both PCBs and DDT have been banned for at least the past quarter-century, while mercury concentrations have generally been stable or falling slightly.

Almost no DDT, an insecticide blamed for wiping out bird populations, and PCBs, a transformer fluid linked to cancer and intellectual impairments in children, have been used in the Arctic. Mercury is emitted from coal-fired power plants. But the chemicals have been deposited in the north as air-pollution fallout from heavily industrialized areas.

"What climate change is doing is changing the [biological]availability of PCBs and the DDT that are already in the system," Dr. Stern said .

Among the three pollutants, mercury is the most dangerous to human health because it is a neurotoxin able to undermine brain development in children. The highest levels found were about .44 parts per million in specimens caught in 2006. This placed them under Health Canada's safe maximum of .5 ppm, beyond which authorities advise reduced consumption. Levels in the mid-1990s were around .25 ppm.

A peer-reviewed paper outlining the findings appeared earlier this year in the journal Environmental Science and Technology.

Story continues below advertisement

Dr. Stern said researchers do not know whether contaminants are increasing in fish elsewhere. The burbot were caught near Fort Good Hope, where temperatures have risen an average of 1.9 degrees since the early 1970s. But he has been part of a wider research effort that has found strong hints that warming is driving a rapid increase in biological activity in the north, with the potential to increase harmful chemical residues in animals.

Report an error Editorial code of conduct Licensing Options
As of December 20, 2017, we have temporarily removed commenting from our articles. We hope to have this resolved by the end of January 2018. Thank you for your patience. If you are looking to give feedback on our new site, please send it along to If you want to write a letter to the editor, please forward to