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Mercury is a naturally occurring element that is a liquid at room temperature.  Mercury is released naturally from rocks, soil and volcanoes. Mercury is also used in, and released from, a variety of industrial processes and commercial products. These human activities have boosted levels of mercury in the atmosphere.
Is mercury a health hazard?
Liquid elemental mercury, commonly found in household thermometers, thermostats and barometers, quickly forms a poisonous, colourless and
odourless vapour when spilled. If inhaled, this vapour is rapidly absorbed through the lungs. Children are especially at risk because mercury
vapours, which are heavier than air, often linger near the floor where children crawl and play.
At higher concentrations, mercury vapour can cause damage to the mouth, respiratory tract and lungs, and can lead to death from respiratory failure. Long-term exposure to low concentrations causes symptoms similar to those of methyl mercury.
Inorganic mercury can cause kidney failure and gastrointestinal damage. Mercury salts are irritating and can cause blisters and ulcers on the lips and tongue. Rashes, excessive sweating, irritability, muscle twitching, weakness and high blood pressure are other symptoms of elevated exposures.
Organic mercury (methyl mercury)
Some types of bacteria and fungi can change mercury into its most toxic form, methyl mercury. Methyl mercury tends to accumulate to some degree in all fish, but especially in predatory fish such as shark, swordfish, certain species of tuna (which are generally sold fresh or frozen), escolar, marlin and orange roughy, as well as in marine mammals. Predatory freshwater fish such as pike, bass and
walleye may also have elevated methyl mercury levels.
Methyl mercury is absorbed through the digestive tract and distributed throughout the body. It readily enters the brain, where it may remain for a long period of time. In a pregnant woman, it can also cross the placenta into the fetus, building up in the fetal brain and other tissues. Methyl mercury can also be passed to the infant through breast milk. 
Tips to protect your family: 
  • When dental fillings need repair, consider a product that does not contain mercury.
  • Pregnant women, people allergic to mercury and those with impaired kidney function should avoid mercury fillings.
  • Whenever possible, amalgam fillings should not be removed when you are pregnant because the removal may expose you to mercury vapour. When appropriate, the primary teeth of children should be filled with non-mercury materials.
  • Follow Health Canada's fish consumption advice in order to enjoy the health benefits of eating fish while controlling exposure to mercury.
  • Certain groups (young children, women who are or may become pregnant) should also limit their consumption of canned albacore (white) tuna.
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