Above: La Grande-1 hydroelectric power station in northern Quebec (P199, Wikimedia Commons)

Have you ever heard the expression “mad as a hatter”? Or are you familiar with the Mad Hatter in Alice in Wonderland? Years ago, people who made felt hats worked with mercury nitrate. Many hatmakers also suffered from emotional instability, memory loss and speech problems. Today, doctors might recognize these as symptoms of mercury poisoning. But people back then didn’t make the connection. They just associated these issues with “mad” hatmakers.

In small amounts, mercury isn’t always a bad thing. It occurs naturally and it’s used to make many useful things, like batteries and lightbulbs. But too much mercury can be toxic.

Today, hatmaking is a much safer and felt hats aren’t nearly as popular as they used to be. However, many large hydroelectric dams have been built in recent decades. And these dams are one reason why people today sometimes get exposed to too much mercury.

Did you know? The World Health Organization considers mercury one of the top ten chemicals of major public health concern. Asbestos and lead are also on the list.

Dams and mercury

In 2016, people in Labrador raised concerns about whether the Muskrat Falls hydroelectric project might cause dangerous mercury levels in their water. After all, it wouldn’t be the first time that a problem like this happened in Canada.

The James Bay Project, a series of dams built in Quebec from the 1970s to the 1990s, flooded huge reservoirs. All this water dissolved mercury in the surrounding soil, and some of it was converted to a more toxic form: methylmercury. The fish in the area ended up consuming methylmercury, which was passed on to local people who ate the fish.

Why is methylmercury dangerous?

Methylmercury is mercury (Hg) attached to a methyl group (-CH3). It’s a neurotoxicant, which means it can affect or even damage your nervous system. Your nervous system controls behaviour, movement and emotion. This explains those “mad hatter” symptoms!

Methylmercury can contaminate the brain in many ways. For example, it can cause enzymes to catalyze the wrong reaction. It can also produce oxygen radicals (or oxygen free radicals). Because they’re so reactive, oxygen radicals can damage nearby brain cells. Methylmercury can also harm developing fetuses.

Another big problem with methylmercury is that it bioaccumulates. In other words, it builds up in the organism that consumes it, usually in fatty tissue. Methylmercury also biomagnifies. That means concentrations get higher as it moves its way up the food chain.

For example, a small fish might eat a plant containing methylmercury. Then, a bigger fish eats the smaller one. Even if the smaller fish had low concentrations of methylmercury, the bigger fish might eat several smaller fish every day. And as the bigger fish grows and gets older, methylmercury keeps accumulating in its body. Eventually, a human might eat the bigger fish, consuming a large amount of methylmercury along with it.

People can get rid of methylmercury through their feces (or their breast milk, in the case of nursing mothers). However, this can take a while. Your body would need about 70 days to get rid of just half of what it absorbed. That leaves plenty of time for the methylmercury to harm your health!

Did you know? The treatment for mercury poisoning is chelation therapy. Doctors give the patient a chemical that binds to mercury. The patient then quickly passes the mercury through their urine or feces.

So, should you eat less fish?

It’s no wonder that people living near projects like Muskrat Falls worry about mercury levels. To lower the risk of mercury poisoning, the Canadian government issues advisories for fish caught in certain bodies of water.

For instance, in early 2017, there was a warning about fish from the Star Lake Reservoir in central Newfoundland. Adults were advised to eat no more than one weekly 25-ounce serving. The recommended intake for children and women of childbearing age was less than half that.

Staying safe

By now, you might be wondering whether hydroelectric dams are a terrible thing. Not necessarily. Hydroelectricity can be an environmentally friendly source of energy, especially compared to fossil fuels.

However, hydroelectric dams can also be a cause of mercury poisoning. So if you're a fish lover concerned about mercury levels in your area, keep an eye out for government advisories. They'll let you know how much you can safely eat.

Learn More!

About the health impacts of mercury:

Mercury and health (2016)
World Health Organization

Mercury in the Food Chain (2013)
Environment and Climate Change Canada

Methylmercury Exposure and Health Effects (2012)
Y.S. Hong, Y.M. Kim and K.E. Lee, Journal of Preventative Medicine and Public Health 45

About mercury and hydroelectric dams:

Canada’s Big Dams Produce Clean Energy, and High Levels of Mercury (2016)
I. Austen, The New York Times

Future Impacts of Hydroelectric Power Development on Methylmercury Exposures of Canadian Indigenous Communities (2016)
R.S.D. Calder et al., Environmental Science and Technology 50

Report: Eastmain-1-A and Rupert Diversion hydropower project (2006)
Provincial Review Committee
(This report has information on the James Bay Project.)

Kelly Resmer

Kelly is a chemistry undergraduate laboratory instructor in Halifax.  She loves working with students in the lab, watching chemistry happen! She has a PhD in chemistry and is very interested in studying and learning about bacteria, the good and the bad ones! 

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