Hydroelectric dams shown to increase neurotoxins in surrounding soil
Hydroelectric dams have been found to increase the level of the neurotoxin methylmercury in the surrounding soil, according to Harvard University researchers.
The study focused on 22 hydroelectric reservoirs under consideration or construction in Canada and claimed that 90 per cent of them are likely to increase concentrations of the neurotoxin.
The study did, however, also suggest ways to mitigate the increased levels of the harmful compound by using methods such as removing the top layer of soil before flooding.
“The human and ecological impacts associated with increased methylmercury exposures from flooding for hydroelectric projects have only been understood retrospectively, after the damage is done,” said Elsie Sunderland, senior author of the study.
“This paper establishes a prospective framework for forecasting the impacts of proposed hydroelectric development on local communities.”
The reason for the increase is due to the actions of microbes that live in the soil and convert naturally occurring mercury into potent methylmercury when land is flooded, such as after the construction of hydroelectric dams.
The methylmercury moves into the water and animals, magnifying as it moves up the food chain. This makes the toxin especially dangerous for indigenous communities living near hydroelectric projects because they tend to have diets rich in local fish, birds and marine mammals, such as seals.
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 team collected extensive measurements of how different forms of mercury cycle through this ecosystem and formalized a mathematical model to forecast post-flooding methylmercury levels
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.
“After collecting all of this information, we can rapidly see how all these people’s exposures will change with the increased methylmercury levels in local wildlife and who will be most affected in this population,” said Ryan Calder who worked on the project.
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 US 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.
“For population that relies heavily on locally caught food, the increase in exposure is drastic,” said Calder.
“We see substantial fractions of this population whose pre-flooding methylmercury exposure is at or below regulatory thresholds and post-flooding are pushed way above them without mitigation measures.
“What our study allows is time to consider mitigation measures that will reduce these potential exposures for the most vulnerable people.”
In September Myanmar announced it was going to construct a large number of hydro-electric facilities in order to solve its energy crisis and move away from its dependence on coal.
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