Toxic Water = Deadly Food
Communities all over Canada have iron-bound ties to fishing, whether it be remote northern communities who have long relied on fish for their subsistence or the millions of Canadians who fish recreationally, regardless of the season. Many people are aware of the risks of consuming too much tuna sushi – high levels of mercury accumulate in the tissues of large fish and can have health effects on humans. But in the Canadian context, consumers of freshwater fish from our own lakes sometimes must be cautious of elevated levels of mercury due to the pollutant’s global footprint.
Although many may think of mercury as a silvery liquid metal, it also exists as a gas in the earth’s atmosphere. It gets there naturally from sources like volcanoes, but human activities have increased the amount in the air by between 2 and 3 times; the largest human sources are currently from smallscale gold mining and coal burning for power generation. This mercury in the air comes back to the Earth’s surface in rain and snow and is also taken up by plants. Once in the soil, it is slowly released via the decomposition of organic matter, such as leaves and wood, and is moved in water through watersheds into streams and lakes. It can then be turned into a form of mercury (methylmercury) that can be taken up by and accumulated in living organisms. There are consumption advisories for fish in lakes across Canada because of mercury, even in northern lakes far away from any industry. These advisories in the north present a major concern to the food security of these communities, where fish are an important traditional source of protein and food from the south is very expensive.
Brian Branfireun and his research group in the Department of Biology at Western University are investigating the landscape processes that take mercury from the atmosphere, process it through organic matter cycling, and finally export it to streams, rivers, and lakes. His work on the processes that affect mercury movement in watersheds is linked to fish and other aquatic organisms through collaborative partnerships with other researchers, government agencies and local communities.
"Mercury isn’t just emitted from smokestacks and then falls from the sky into lakes”, says Branfireun – the microbes in soils that interact with mercury play a central role in determining the form of mercury entering a lake, and thereby the levels in fish. To make matters even more complex, changing climates have profound effects on these processes; higher temperatures in the north are not just warming the air, but are also changing amounts of snowfall and the rate of permafrost thaw. Permafrost is especially important because it contains trapped mercury and soil carbon which are potentially released as the rates of permafrost thaw increase.
The Branfireun group is contributing data that will allow for the development of predictive landscape models to help assess in which watersheds fish will be more susceptible to mercury accumulation, now and into the future, guiding policies about mercury risk in the multitude of lakes found in Canada’s north.