Frequently Asked Questions

Mercury is all around us in the environment. It is found in the air, soil, plants, lakes, rivers and oceans. It can get into the air naturally, through events like volcano eruptions and forest fires, or because of human actions like burning coal, mining and incinerating waste. When it gets into lakes and rivers, microbes living in the sediment and water can change it into a form of mercury called “methylmercury”. Plants and animals living in the water and sediments may easily take up methylmercury. The methylmercury levels in living things increase as it moves up the food chain, starting with tiny water-dwelling creatures like plankton to aquatic insects, then to fish, and finally to animals that eat fish. Methylmercury may be dangerous to people if it builds up in high amounts in the body.

Methylmercury is absorbed into the bloodstream after ingestion. Once in the blood, methylmercury moves throughout the body’s tissues and organs, but the greatest concern relates to its accumulation in the liver, kidneys, and brain.

Because methylmercury enters the bloodstream after ingestion, it may also transfer from people who are pregnant to the fetus and/or to an infant during breastfeeding (via umbilical cord blood, placenta, and breast milk).

Methylmercury does not continuously build up in the body. The liver helps to convert methylmercury back into inorganic mercury. Methylmercury and inorganic mercury are constantly eliminated from the body through hair, feces and urine. However, if exposure to methylmercury through ingestion is frequent, the body’s ability to eliminate it may not be able to keep up with the exposure, and the levels of methylmercury in the body may increase. Once exposure from ingestion stops or is reduced, the body’s natural ability to eliminate methylmercury can act to decrease the levels of this substance in the body’s organs and tissues.

Over time, the human body naturally eliminates substances from the body, but in the case of methylmercury, it takes about 2 months before half of it is eliminated in the blood, at least for most people.

At high enough intakes, methylmercury may be harmful to people of all ages. Of particular concern are people who are or who may become pregnant, people who are breastfeeding, and children/youth (18 years and younger).

Developing fetuses, infants and children/youth are believed to be most susceptible to the potential harmful effects of methylmercury. For this reason, methylmercury is of particular concern for people who are or who may become pregnant and/or are breastfeeding. When these people are exposed to methylmercury, it can be transferred from their blood to the developing baby, and/or into breastmilk. The potential health consequences of methylmercury may include negative effects on brain development, which can result in language, memory and attention impacts in children who were exposed in the womb.

Therefore, children/youth, people who are currently, intending to, or who might become pregnant, and/or who are breastfeeding should be especially cautious about methylmercury exposures.

Fish and seal meat are nutritious food choices. They are sources of protein and healthy fats, like omega-3 fatty acids, and are low in saturated fats. However, people may ingest small amounts of methylmercury when they eat fish or seal. So, both the benefits and risks of eating certain types of fish and seal should be considered. Meal sizes, and how often a person eats fish or seal (or other foods containing mercury) can greatly affect how much methylmercury a person may ingest and absorb in their body.

In general, the longest lived and largest fish (and other aquatic organisms such as seals), that are at the top of the food chain (i.e., predatory fish, seals, birds), tend to have the highest levels of methylmercury. Also, mercury tends to be higher in certain organ meats, like seal liver, with seal livers from older seals having much higher mercury concentrations than those from younger seals. This trend has been shown in seals elsewhere in the world.

The Muskrat Falls fish and seal monitoring program has consistently shown that levels of mercury in seal liver are higher than in seal meat and in fish. These higher levels have been measured both before and after project flooding.

Given the known tendency for seal liver to contain high levels of mercury, the MHMOC recommends that people should limit or avoid eating adult seal liver, until further consultation and assessment is completed. This interim recommendation is similar to many areas across the Canadian north. This advice is directed mainly at those people who are potentially most sensitive to the effects of methylmercury (i.e., children/youth, people who are currently, intending to, or who might become pregnant and/or who are breastfeeding).

Each year, about a thousand samples are collected in the Churchill River and Lake Melville to test for mercury in water, fish and seals. Sediment samples are collected and tested every five years. The results of this testing are used to help people make informed decisions about what they eat.

Data and reports can be found at the following websites:

Department of Environment and Climate Change – https://www.gov.nl.ca/ecc/methylmercury-mrf/

NL Hydro –
https://nlhydro.com/about-us/publications/environmental-reports-for-the-lower-churchill-project/

If you would like to support the work of the MHMOC by providing fish and seal samples for mercury analysis from the reservoir, Churchill River, Goose Bay, or Lake Melville, please email the MHMOC at info@mhmoc.com. You can also participate in community discussions, dietary surveys, or monitoring programs when available.

Based on modelling and analyses conducted to date, it is predicted that increases in methylmercury, that are attributed to the Muskrat Falls Project, will occur within the reservoir and immediately downstream of the Muskrat Falls hydroelectric generating facility within the Churchill River. The modelling also predicted that when the Churchill River flows into Goose Bay, it will contain low levels of methylmercury, but this methylmercury will begin to break down, settle on sediments, and be taken up by aquatic organisms. The model results also predicted that the highest increases would occur two to three years after flooding, after which methylmercury levels in water would then begin to return to baseline levels at all locations.

Based on the trend in the water monitoring results for the four years since flooding occurred, the predicted increase has been recorded in the reservoir, the Churchill River and eastern Lake Melville, and is now trending downward. Within Goose Bay and western Lake Melville, the methylmercury concentrations have been lower than those in the reservoir and river, but are decreasing more slowly than at the other monitored locations.

For more information about the water monitoring program, please visit: https://www.gov.nl.ca/ecc/methylmercury-mrf/

Well water near the Churchill River and Lake Melville is very unlikely to be affected by any changes to methylmercury levels in the reservoir, the Churchill River, Goose Bay or Lake Melville. Regardless, in all water sampling locations in the Churchill River and Lake Melville, measured methylmercury results were significantly lower than the Guidelines for Canadian Drinking Water Quality, which includes a Maximum Acceptable Concentration of 0.001 mg/L for all forms of mercury.

No matter where you live, well water should always be tested regularly for bacteria and chemicals that may be present. If local residents have concerns about the safety of their well water, they may contact the nearest Government Service Centre office to request a well water sample bottle for free testing.

To learn more about the MHMOC, please click here.

There will continue to be monitoring and analysis of mercury concentrations in fish, seal meat and seal liver. The MHMOC will also review monitoring results and consult with communities and community elders to inform future recommendations. Communication materials will also be developed for distribution.

Mercury in Canadians – Health Canada, December 2021

Mercury in Fish – Health Canada, November 2019

Environmental Reports for the Lower Churchill Project – Newfoundland & Labrador Hydro (nlhydro.com) – NL Hydro