Big hydroelectric dams may excite people as monuments of renewable energy with no harm to the environment in terms of greenhouse gas emissions. But the fact is that they do threaten the health of local human communities.
This was revealed in a new study by Harvard researchers who made the upcoming dams in Canada a case study to suggest that the food chain of indigenous communities is facing the threat of high concentration of neurotoxin methylmercury in the upstream areas.
During dam construction, land gets flooded and bacteria start converting the soil's naturally occurring mercury into methylmercury. This eventually lands up in the food chain of people as they depend on local fish, birds and marine mammals for food.
The study warns that the chemical's impact increases cardiovascular risks and children with high prenatal exposure will suffer from attention deficit and hyperactivity disorder problems.
The findings of the study, published in the ACS journal Environmental Science & Technology also offer some solutions in mitigating the threat.
Mitigation Possible
Among the mitigation measures the study offers includes removal of the upper soil layer before flooding happens. The study predicts a hike in methylmercury levels in all the 22 hydroelectric dams being planned in Canada.
"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.
The Thomas D. Cabot Associate Professor of Environmental Science and Engineering at the Harvard said the paper offers a viable framework for forecasting the impacts of hydroelectric dams on local communities.
Close Observations
To pinpoint the adverse impact of methylmercury on human populations, the team studied three communities downstream at the Muskrat Falls hydroelectric dam in Canada where flooding was imminent from the Lake Melville estuary.
Sunderland's team worked in the region for four years, tracking the methylmercury content that was harming communities linked to the local ecosystem.
They found that the exposure to methylmercury indeed differed across the population and it peaked after flooding in the upstream area.
Ryan Calder, first author of the paper, said information showed how exposures changed with increased methylmercury levels in local wildlife.
Despite some people staying below the U.S. Environmental Agency's threshold on methylmercury, affected cases on cardiovascular disease and hampered neurodevelopment among children were not subsiding.
The risk of exposure was more on the local population who caught wildlife including river fish on a daily basis.
Photo: Gisela Giardino | Flickr