Mercury and its compounds are highly toxic to humans, ecosystems and wildlife. Even relatively low doses can have serious neurotoxic effects on adults and children. Initially considered as an acute and local problem, they are now understood to be a global challenge with chronic effects. Some studies also show renal and cardiovascular effects. New epidemiological findings indicate that toxic effects may occur at lower exposure levels then previously considered. Methylmercury can cross the placenta, entering the fetus and accumulating in its brain and other tissues. Hence, exposure of women of childbearing age and children is of the greatest concern.

Owing to the transport of mercury through the environment and its bioaccumulation, the principle source of exposure to methylmercury in the general population is diet, in particular fish consumption. Dental amalgams are the main source of mercury exposure for most people in developed countries. Other sources include cosmetics, thiomersal in vaccinnes, thermometers and other medical devices.

Specific concerns are the potential exposures of population living near contaminated sites, waste and dumping sites, and plants producing mercury-containing products. Identifying such sites, assessing health risks from exposure and developing risk management programmes may have immediate positive health effects on the exposed population, and help to prevent the risk of future exposure.