The wind and water currents carry mercury into the Arctic, where it eventually works its way into the food web. Over time, as one animal consumes the next, the heavy metal, a potent neurotoxin, builds up in top predators, such as seal and whale.

The World Health Organization considers mercury to be one of the top ten health concerns. While we are all exposed to a certain amount of mercury, some people are regularly exposed to high levels, including those who rely on subsistence fishing. Mercury can affect the brain development of fetuses and of children and lead to cardiovascular problems in adults.

Elsie Sunderland, of the Harvard School of Public Health, studies how heavy metals and other contaminants cycle through the environment and what effect they have on human and ecological health. Her research recently took her team to a community in Nunatsiavut, the first autonomous region in Canada governed by the Inuit, that lies downstream of an 824MW hydroelectric project on the lower Churchill River, in Labrador.

To mitigate global warming many governments are opting for hydroelectric power instead of coal-fired power plants. But these developments release mercury into the waterways, which can build up in fish and other marine animals, warns Sunderland.

Inuit groups in Canada recently called for an expansion of a federal research program that studies industrial pollutants, including mercury. They fear that the rapid changes to the land, ice and wildlife in the Arctic could lead to negative health impacts.

Sunderland: Methylmercury in the Arctic comes increasingly from artisanal gold mining

Elsie Sunderland: Microbes produce methylmercury from inorganic mercury, so the question really is “What are the sources of inorganic mercury in the Arctic?” It’s a combination of natural and anthropogenic sources. Mercury is a naturally occurring metal found in soils and in the marine environment, as well as in rivers and lakes. But it also comes from coal-fired power plants and artisanal gold mining. Coal-fired power plants were once the largest source – and they are still a very large source – but artisanal and small-scale gold mining are the largest global source now. It is not that those activities have grown so much, but it’s just that we didn’t have data before. [Editor’s note: Coal burning and artisanal and small-scale gold mining account for 24 percent and 37 percent, respectively, of total anthropogenic emissions according to the United Nations Environment Programme’s Global Mercury Assessment 2013.]

A large fraction of the mercury emitted to the atmosphere is in a stable, long-lived form that is transported long distances before being deposited in remote locations like the Arctic. The Arctic receives mercury emitted from the global anthropogenic sources and natural sources, such as volcanoes. The Arctic can also receive mercury that is transported in large-scale oceanographic circulation from the North Atlantic and North Pacific, although our recent research suggests the Arctic Ocean is a net exporter of mercury to the North Atlantic.

In the Arctic, there is a very interesting atmospheric chemistry phenomenon during the polar sunrise that triggers a chemical reaction called a bromine explosion that scavenges all the elemental mercury out of the atmosphere and deposits it onto the snow and ice.

Arctic Deeply: How are the people who live in the north affected by methylmercury exposure?

Elsie Sunderland: Methylmercury is a neurotoxin and has been associated with impaired cardiovascular health in adults, and there is emerging evidence that it also affects the endocrine and immune systems. The communities in the Arctic tend to be very highly exposed. You do see much, much higher levels of exposure to mercury because you get those very high fish consumers and marine mammal consumers. There are also broader ranges of exposure in those communities, because people eat variable amounts of fish.

Arctic Deeply: Can you tell me more about your recent study, which looked at the potential impact of a hydroelectric project in Labrador?

Elsie Sunderland: The issue we were looking at there was not increases in inorganic mercury inputs to the system, but at the changes in the geochemistry of the system that increased the production of methylmercury.

If you have a flowing river and you flood a large region around it for hydroelectric development, you create the perfect tasty environment for happy microbial activity to convert mercury to methylmercury.

We talk about hydroelectric power as green power and the shift away from coal. In Canada, 60 percent of the country’s electricity comes from hydropower. The whole country benefits, but the costs, which are tremendous, are borne by these communities where the development is taking place. It is a huge environmental justice issue.

Many places are not being given standing within that dialogue. At most, the environmental impact assessment concludes that increased monitoring should take place. They’re told that if there is a big methylmercury problem, then dietary advisories will be issued. That is not really acceptable, in this case in particular, because these northern communities don’t have great grocery stores.

The question of risk is more complicated when you consider the co-benefits of otherwise healthy marine foods. In this case, the risk-benefit calculation has to consider also the benefits of micronutrients and protein in the food, and the cultural and social benefits associated with harvesting country foods. In this case, you could instead consider the reductions of nutritional benefits of those foods rather than a health risk. When methylmercury levels reach very high levels, such as in larger predatory fish and older seals and whales, then the risks of these foods likely outweighs the benefits, although it needs to be evaluated on a regional basis and depends, in part, on the amounts of marine foods being consumed.

Arctic Deeply: How does climate change affect the input of mercury in the Arctic?

Elsie Sunderland: The cracks in the sea ice during the polar spring are the source of these bromine explosions. As the seasonality of the sea ice changes, the timing of that phenomenon may change. The other thing the sea ice does is it caps the mercury – it keeps it in the ocean. Without the sea ice it can evade back to the atmosphere. So, decreasing sea ice could potentially reduce the burden of mercury in the Arctic ocean.

But I think that will be more than compensated for by the changes in the terrestrial environment. There you have massive rivers that are exceptionally important in the Arctic and we are starting to see a large increase in dissolved trace metals flowing into the ocean and an increase in freshwater discharges. The permafrost contains mercury in these soil reserves that have been deposited for millennia that have been completely immobile because they are frozen, and then all of a sudden you melt them and heat them up and the microbes go nuts. These massive changes in the terrestrial environment are now the largest source of mercury into the Arctic Ocean. It’s going to swamp those other effects.

Arctic Deeply: How quickly can we expect to see mercury levels decline following the push to phase out coal-fired power plants?

Elsie Sunderland: It depends on what you are looking at. For fish fish born in the past year, it can happen very quickly. For a 25-year-old polar bear, it is going to take a little while to see the change. For a person, it depends on how much fish they eat and what they eat. It can decline incredibly quickly if they shift not the quantity of fish or seafood they eat, but what exactly they’re eating. A lot of communities are harvesting opportunistically, like seal, and if they pick very young animals, they have very low concentrations of bio-accumulated contaminants. They are, in a way, protecting themselves. The selection of foods plays a huge role on the individual level of exposure.

The problem is that most people want a simple message: it’s safe or it’s not safe. But the message is really, try to eat more of this and a little bit less of that. That is a pretty effective way to manage exposures. Even eating just a little bit of the seal or whale that they like, it really depends on the ecosystem too, but there is a way to maintain diets that can minimize the burdens if people are open to that information, so that becomes more of an effective communication message.

Arctic Deeply: What are the best targets for regulation and policy?

Elsie Sunderland: The regulation of emissions from coal-fired power plants is still number one on the agenda. The technology is there to do this very effectively and there are a lot of other co-benefits in terms of other air pollutants, so it is just a matter of will. People have to buy into this.

The other one is in the context of small-scale gold mining. The issue there is that it is often an illegal industry. One quick fix is to legalize it, because then the government can start to have oversight. There are also some simple technologies that can reduce by orders of magnitude the amount of mercury that needs to be consumed to keep that mining activity going. We need to recognize that it is going to happen in these very poor communities, where there is a huge economic incentive to do it, and ask how can you do it more safely and in a way that has global benefits. I’m not sure the global benefits to the Arctic by reducing small-scale gold mining in Peru are clear to the average person, but that is kind of a cool … because you can see a global signature.

Arctic Deeply: What changes could be made to reduce exposures in communities near hydroelectric projects?

Elsie Sunderland: First of all, I think having a very aggressive monitoring program for impacts is a no-brainer. The second thing is to clear the reservoir before flooding, because the microbial activity is stimulated by the presence of organic matter and the decomposition of that organic matter. The more organic material that you can remove prior to flooding, the lower the magnitude and duration that pulse of mercury should be. They often remove trees, but not bushes. I think the big one would be to remove the organic topsoil. It is worse to remove trees and leave behind sticks and brush, because you have a more labile organic source. It sounds like a huge effort, but the investment in these infrastructure projects is enormous. If I just tell you a dollar number, it might sound really large, but it should be more considered in the cost of the overall project.

Arctic Deeply: What gaps remain? What questions still need to be answered?

Elsie Sunderland: The biggest gap we have in our knowledge right now relates to the terrestrial environment, the changes that are about to occur and the magnitude of the impacts. All of a sudden, we’ll get a big pulse of mercury as everything melts.

I was at an Arctic Circle meeting recently and a lot of what people were talking about, outside of the group of scientists who think about things like geochemistry, were issues related to infrastructure. Many permafrost areas are collapsing and it is affecting buildings and airports and communities. But they are not thinking about neurodevelopment, it is not as clearly visible. People are also thinking that when you talk about human health and well-being in the Arctic, you’re talking about food security and the availability of physicians for remote communities. But they’re not thinking about exposures to these global contaminants.

It is very important that they become part of the dialogue. We have a responsibility to these communities, globally, and we have a preview of what can happen if mercury levels continue to rise. Everything is accelerated in the Arctic.

This interview has been edited for clarity and length.

Top image: Muskrat Falls is the site of an 824 MW hydroelectric project in Labrador that is scheduled to generate its first power in 2018. Inuit living downstream of the dam are concerned that mercury levels will soar. (Amina Schartup)