The main way that people are exposed to mercury is by eating fish and shellfish that have high levels of methylmercury, a highly toxic form of mercury, in their tissues. A less common way people are exposed to mercury is breathing mercury vapor. This can happen when mercury is released from a mercury-containing product or device that breaks. Mercury-containing Amalgam fillings, especially when older and brittle, are also a cause of mercury exposure. Through chewing or grinding teeth, the less toxic elemental mercury can be released. When entering the digestive tract, the action of putrefactive bacteria can change elemental mercury to the highly toxic methylmercury.
Mercury exposure at high levels can harm the brain, heart, kidneys, lungs, and immune system of people of all ages. High levels of methylmercury in the bloodstream of babies developing in the womb and young children may harm their developing nervous systems, affecting their ability to think and learn.
Mercury is a known neurotoxin. Exposure symptoms depend on a variety of factors, including:
The effects of mercury exposure can be very severe, subtle, or may not occur at all, depending on the factors above.
Elemental mercury: People may be exposed when they breathe air containing elemental mercury vapors. Vapors may be present in such workplaces as dental offices, smelting operations, and locations where mercury has been spilled or released.
Higher exposures may also cause kidney effects, respiratory failure and death.
Infants in the womb can be exposed to methylmercury when their mothers eat fish and shellfish that contain methylmercury or are exposed to mercury fumes through dental work. This exposure can adversely affect unborn infants' growing brains and nervous systems, affecting cognitive development, memory, attention, language, fine motor skills, and visual spatial skills.
Today's focus on the health impact of exposure to mercury is more on chronic, low or moderate grade exposure—albeit a topic of great controversy—, not high concentration exposure by methylmercury, which caused Minamata disease.