Mercury is a naturally occurring element found in the earth's crust, with natural deposits generally found as a vermilion red ore called cinnabar. Mercury exists in three different forms: elemental, inorganic and organic. In the environment, microorganisms (bacteria and fungi) and natural processes can change mercury from one form to another. Mercury is persistent, and builds up, or bioaccumulates, in living organisms.
Mercury is released into the air, water and soils from a range of natural sources. Mercury is mobilized in the environment by natural weathering processes, forest fires and flooding. Human (or "anthropogenic") sources are also adding to natural sources of mercury in the environment. About half of the mercury currently released into the atmosphere comes from human activity, such as the burning of fossil fuels (particularly in coal-fired power plants), mining and base metal smelting, the production of chlorine and sodium hydroxide in the mercury-cell chlor-alkali industry, cement production, and municipal and medical waste incineration. In addition, the improper disposal of products that contain mercury such as fluorescent light bulb tubes, high-intensity discharge lamps, mercury vapor lamps, mercury fever thermometers and thermostats, dental amalgam waste, and mercury switches in older car models can lead to the release of mercury from municipal landfills, steel recycling, or other end-of-life disposal methods. The Government of Canada has taken actions together with provinces and territories to remove or minimize some of these risks.
Mercury released to the environment, either through natural processes or human activities, can be transformed by microorganisms and bacteria into a highly toxic organic substance called methyl mercury. Methyl mercury builds up in living organisms through their surrounding environments and becomes more concentrated as it transfers up the food chain. Decreasing emissions and deposition of mercury would be expected to prevent increases in methyl mercury concentrations in the environment.
Methyl mercury can also be generated by bacterial activity in submerged soil (for example, at new hydroelectric dam sites) and from other flooded areas, and subsequently released to drainage systems.
While elemental mercury can be absorbed through breathing and inorganic mercury through ingestion, by far the most common route of exposure in humans is through the eating of fish containing methyl mercury. Methyl mercury is toxic and has the ability to pass the blood-brain barrier and affect the central nervous system; recent results also indicate that methyl mercury may have a significant impact on the reproductive capacity of specific fish populations and can affect the reproduction and behavior of fish-eating wildlife like loons and otters. Methyl mercury exposure can have a wide array of health effects on humans, ranging from depression of the immune system to neurological disorders, depending upon the level of exposure. Populations of particular concern include high fish-eating communities, pregnant women, women of child-bearing age and young children in those communities.
Canada continues to reduce the use and release of mercury. Mercury releases have declined since the 1980s because of anti-pollution measures and Canada-wide standards and regulations. Because mercury is transported globally through the atmosphere, Canada continues its active role in regional and international efforts to reduce mercury in the environment around the world.
Mercury is currently on the List of Toxic Substances under the Canadian Environmental Protection Act, 1999 (CEPA 1999). However, there are sufficient significant global adverse impacts to warrant international action to reduce the risks to human health and/or the environment arising from the release of mercury and its compounds into the environment. Therefore, the Government of Canada is proposing to amend the List of Toxic Substances to include mercury and its compounds. This will enable the Government of Canada to move forward on Canada's proposed actions to manage mercury and compounds containing mercury. This Notice was published on June 12, 2010 and will be followed by a 60-day public comment period (from June 12, 2010 to August 11, 2010).
Being informed is the best protection. Find out more about mercury through Health Canada's It's Your Health - Mercury and Human Health fact sheet, and the Health Canada document entitled, Mercury - Your Health and the Environment. Information on mercury may also be found on Environment Canada's Management of Toxic Substances Mercury Web page, and Mercury and the Environment Web page.
Health risks for any substance depend on the hazard (its potential to cause health effects) and the dose (the amount to which you are exposed).