The Great Lakes Executive Committee (GLEC) has determined that sulphates do not meet the criteria to be designated as a Chemical of Mutual Concern (CMC) under the Great Lakes Water Quality Agreement.
The designation is a necessary step before developing binational action plans to address chemical threats to the Great Lakes ecosystem.
Sulphates were nominated for CMC designation following concerns raised by the Great Lakes Indian Fish & Wildlife Commission (GLIFWC), which highlighted the chemical’s role in transforming mercury into methylmercury — its most toxic form. GLIFWC also emphasized the harm sulphates cause to wild rice, a plant of deep cultural and nutritional significance to Indigenous communities in the region.
Sulphate occurs naturally in numerous minerals, but can also be discharged into an aquatic environment from wastes in industries that use sulphates and sulphuric acid, such as mining and smelting operations, kraft pulp and paper mills, textile mills and tanneries. According to Health Canada, distillation systems for sulphate and chloride removal must be capable of reducing an average influent concentration of 800 mg/L to a maximum concentration of 250 mg/L.
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In a related development, the Canadian and U.S. co-leads of the Annex 3 Extended Subcommittee on CMCs have recommended that radionuclides also not be designated as a candidate CMC. GLEC is expected to make a final decision on that recommendation by the end of 2025.
Radionuclides were first nominated in 2016 by more than 100 non-governmental organizations and again in 2022, including a renewed call from GLIFWC. Community and environmental groups across the Great Lakes basin are preparing formal responses to the proposed recommendation over the next two months.
Environmental advocates, including the Canadian Environmental Law Association (CELA) and the Great Lakes Ecoregion Network, have voiced concerns about both the recent decisions and the broader criteria framework used to evaluate CMC nominations. They argue that the current approach may fall short in addressing harmful chemicals that threaten Great Lakes health and the communities that rely on them.
“In assessing whether a substance should be a CMC in the great lakes, it is not good enough to say that currently it isn’t a problem or is only a limited problem,” CELA stated in a January 2025 letter to the GLEC. “Instead, if there are indicators of problems and potential problems, we should list it as a CMC so that we commit to monitor it and [understand] whether its use is increasing, etc., and take preventive measures to avoid creating a worsening situation.”
