Rodd Laing

On-site sampling and testing proved to be better than modelling at predicting how mercury will behave in the waters below a planned hydroelectric dam. Photo credit: Rodd Laing

The hazards posed by fluid mechanics exercises are well known and accepted by anyone who engages in this diabolically complex modelling procedure. Nevertheless, when those hazards graduate from mathematical inaccuracies to potential population health risks, attention to detail becomes all the more urgent.

Trevor Bell certainly thought so as he studied plans to dam one end of a 250 kilometre-long estuary on the Newfoundland and Labrador coastline for a hydroelectric generating station at a place called Muskrat Falls, west of Happy Valley-Goose Bay on the Churchill River. The project is already prominently controversial for economic and political reasons, but the Memorial University of Newfoundland geography professor was further concerned about the potential concentration of methylmercury in Lake Melville. This downstream estuary is where Labrador Inuit hunt and harvest animals whose bodies may Proceedings of the National Academy of Sciences contain significant amounts of this compound. 

Nalcor Energy, the St. John’s company that is overseeing the work, had addressed this possibility in a 2011 report, which argued that organic and inorganic forms of mercury travelling over the dam would sink into the lake-bottom sediments where they would remain isolated from plants or animals that could make their way into any human diet. “One of their claims was that Lake Melville is a well-mixed estuary,” says Bell, who wondered if that was the case and subsequently headed up an independent investigation by researchers from Harvard University and the University of Manitoba. “Our results show it’s a highly stratified estuary.” 

A variety of sampling at different depths revealed that, far from being well mixed, the freshwater flowing into the estuary remains on top of a briny mixture, creating a layer many metres in thickness where organic material remains buoyant and active. “There is actually methylmercury production going on there,” Bell says of the Harvard study. “This has never been recognized before, because the assumption was it’s all going on in the reservoir. Once again, measurements and observations trump assumptions.”

Tracking the movement of mercury through a complex biological environment is a daunting task at the best of times, but the potential impact of this element on human health makes it important to take on the challenge. In inorganic forms, mercury can be tolerated in small amounts and ultimately excreted by the human body. If local geochemical conditions conspire to create methylmercury, on the other hand, this compound readily interacts with some of our most vital tissues — including the highly sensitive blood-brain barrier, where it can irreparably damage the nervous system. 

Our civilization’s widespread and growing use of mercury-laden materials such as coal has created abundant opportunities for this threat to arrive in many different parts of the world. Methylmercury formation is promoted by the low oxygen levels established by vegetation decaying in the reservoir behind a dam, where this agent will begin to bioaccumulate — moving up the local food chain in ever higher concentrations from the simplest organisms into plants, then animal predators and finally the human inhabitants. 

The Lake Melville findings were published this spring in a scientific report commissioned by the Nunatsiavut Government, which governs the province’s Inuit region. The proliferation of methylmercury within the estuary was also outlined in an early publication by the study authors in the Proceedings of the National Academy of Sciences. 

“I believe in evidence-based decision-making,” says Bell, who has devoted much of his recent career to work with Inuit on environmental issues affecting Canada’s north. Although hydroelectric energy is often touted as relatively benign “green power,” he argues, a dam and hydro-electrical station at Muskrat Falls will have health consequences borne by Inuit practicing their traditional livelihood downstream in their constitutionally protected territory. “They’re the ones who will experience up to a 1,500 percent increase in methylmercury,” he says. “It’s an example where the precautionary principle must be exercised.”