Twenty Two hydroelectric reservoirs are either under consideration or construction in Canada and 90 per cent of these projects have the potential of exposing indigenous populations to increased levels of neurotoxin methylmercury, a new study has warned.
The study by researchers at Harvard University is published in journal of Environmental Science and Technology and it claims that 90 per cent of proposed new Canadian hydroelectric projects are likely to increase concentrations of the methylmercury in food webs near indigenous communities.
Scientists explain that the microbes convert naturally occurring mercury in soils into potent methylmercury when land is flooded – as is the case when dams are built for hydroelectric projects. This neurotoxin moves up the food chain and poses a risk to people living near the areas where the projects are being constructed. The reason is that indigenous people tend to have diet comprising of locally available resources including fish. Marine animals tend to consume the neurotoxin in tiny proportions as their consume their food. In small quantities methylmercury isn’t that huge a risk, but as it moves up the food chain its concentration increases and by the time it reaches indigenous people, the levels are high enough to cause serious damage.
To understand how methylmercury impacts human populations, the Harvard team studied three Inuit communities downstream from the proposed Muskrat Falls hydroelectric facility in Labrador. The project will require the flooding of land bordering the Churchill River, upstream from an estuarine fjord called Lake Melville. The team has been working in this region since 2012 during which a multi-pronged investigation into how methylmercury accumulates in the ecosystem and how it may impact communities who rely on the ecosystem for food and resources has been carried out.
Based on the data collected through extensive measurements, researchers built a framework to understand how different forms of mercury cycle through this ecosystem and formalized a mathematical model to forecast post-flooding methylmercury levels in the Churchill River and downstream estuary. They then used measurements of levels of methylmercury in the food web and unique chemical tracers for where each food item, such as salmon or trout, obtained its methylmercury to project levels of the toxin in different species of fish and wildlife. Finally, the team studied the diets and baseline methylmercury exposures of more than 1000 Inuit who live on Lake Melville’s shore to understand how changes in their food would affect individual exposures.
The team found that while there were large differences in exposure to methylmercury across the population, on average exposure to the toxin will double after the upstream area is flooded. While some people are still below the U.S. Environmental Protection Agency’s reference dose for methylmercury, any increase in exposure is associated with increased risks of cardiovascular disease and neurodevelopmental delays among children
The people at the highest risk of mercury exposure are those who eat locally caught wildlife nearly every day, especially river fish, where the increase of methylmercury is expected to be highest.