Concern over the release of heavy metals to the environment from human activities has existed for decades.
Emissions of lead, along with particulate matter and sulphur dioxide (SO2), from a Canadian smelter were the basis for one of the earliest transboundary disputes (Canada-U.S. International Joint Commissions, 1920's).
When the Canadian Department of the Environment was created in 1971, heavy metals were addressed through federal environmental legislation.
The adverse health effects on native peoples consuming fish caught in the vicinity of mercury chlor-alkali plants led to the promulgation of the Chlor-Alkali Mercury Release Regulations under the then Canadian Clean Air Act (CAA) in the mid-1970s.
Concern over emissions of lead from secondary lead smelters lead to the CAA Secondary Lead Smelter National Emission Standards Regulations limiting emissions of lead from such facilities. These two regulations have been maintained to the present and are now under the Canadian Environmental Protection Act, 1999 (CEPA 1999)
Various heavy metals are target substances in several domestic and international agreements and plans as noted in the sections below. The following heavy metals have now been assessed for toxicity and added to Schedule 1, List of Toxic Substances of the Canadian Environmental Protection Act, 1999 (CEPA 1999):
- Inorganic cadmium compounds
- Hexavalent chromium compounds
- Particulate matter containing metals that is released in emissions from copper smelters or refineries, or from both
- Particulate matter containing metals that is released in emissions from zinc plants
In addition to the early Canadian regulations on heavy metals emissions mentioned above, other CEPA 1999 regulations limiting heavy metal emissions have since been promulgated. Some heavy metals are now being reported annually under the CEPA 1999 National Pollutant Release Inventory (NPRI).
The 1978 Canada-U.S. Great Lakes Water Quality Agreement (GLWQA) identified and set concentration limits in water for ten heavy metals identified as persistent toxic substances of concern in the Great Lakes: arsenic, cadmium, chromium, copper, iron, lead, mercury, nickel, selenium and zinc. Heavy metal releases to the environment continued to receive attention over subsequent years.
Mercury maintains a place at the top of the list of heavy metals of concern. Mercury is emitted largely in the gaseous state and does not adhere to fine particles in emission streams to the extent that other heavy metals do. Due to its long atmospheric residence time, mercury is more mobile than most other heavy metals and can be transported through the atmosphere on a global scale, frequently depositing far from the source.
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