Learning About Mercury Contamination in Thunder Bay Harbour

Mercury. It is scientifically documented that mercury accumulates in the bodies of fish as well as humans. In humans mercury causes particularly harmful neurological effects. Minamata disease is the term used to describe the impacts of mercury poisoning, first detected in the residents of Minimata Bay, Japan in 1956.

Across Ontario, several areas are dealing with mercury contamination from the pollution of years past. Grassy Narrows First Nation is one such location, as is Thunder Bay Harbour. Within the northern portion of the harbour (near the mouth of the Current River and just in front of the former Cascades Fine Paper mill) approximately 400,000 cubic metres of mercury-contaminated pulp and sediment lies suspended in the water. The contamination covers an area several football fields in size and is up to four meters thick.

Mercury-contaminated pulpy material collected by DST Consulting during field studies to determine the extent of the contaminated sediment within the Thunder Bay Harbour.

Cleanup Options

In 2006 an investigation by North/South Consulting, found the level of mercury in certain spots was more than 5 times the Provincial Sediment Quality Guideline’s Severe Effect level (2 ug/g d.w.). In 2014, Cole Engineering presented a number of options to the public for remediating this contaminated sediment. Disposal options included placing the material in a secure landfill, in a new on-site Confined Disposal Facility (CDF), or disposal at the existing Mission Bay CDF adjacent to Chippewa Park.


Understanding Mercury

If you are a little older you might recall mercury, a silver, liquid metal, you may have rolled around in your hand in high school chemistry class. Since that time, the toxicity of mercury has been extremely well documented. Mercury is an element which can neither be created nor destroyed, although it can “speciate” or “cycle” between various forms. In fact, mercury is a natural constituent in many substances, including soil, vegetation like trees, and coal.

When coal is combusted, in power plants for example, mercury is a by-product of the combustion process. Mercury moves up the smokestack and is then transported through the atmosphere, falling out on land, rivers and lakes. The atmospheric deposition of mercury is by far the largest source of mercury in the environment and the leading contributor to consumption advisories for fish in Ontario’s lakes. Almost every lake within the Superior watershed, including Lake Superior itself, has consumption advisories for mercury, mainly due to atmospheric deposition.


More Toxic Forms of Mercury

Understanding mercury in the environment, along with its impacts, is far from a linear process and involves many factors. The process of “methylation”, whereby bacteria in the aquatic ecosystem transforms inorganic mercury into much more toxic methylmercury, depends on a variety of environmental factors.  It is important to remember that the rates of methylation vary widely and can differ even on the same site. Methylation rates in the Thunder Bay situation are not well documented. Additional research is needed to better understand the local impacts and risks of mercury-contaminated sediment in Thunder Bay, as well as how these risks are perceived, understood and communicated.

Protecting our natural waters is an important part of Canada Water Week. We encourage you to learn more about the mercury contamination in Thunder Bay Harbour at rap.infosuperior.com/northharbour


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Celebrate Canada Water Week in Thunder Bay – March 20 to 26, 2017.


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Samuel Pegg is a Masters of Environmental Studies – Northern Environments and Cultures student at Lakehead University. His research focuses on risk communication and public relations with respect to the remediation of complex environmental issues such as the Thunder Bay North Harbour.

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