Public Health and Environment (PHE)

Frequently asked questions: mercury and health

October 2011

1. What is mercury?

Mercury and its compounds comprise one of the top ten groups of chemicals of major public health concern according to WHO. WHO has identified these chemicals as highly hazardous, and more action is needed to prevent adverse health impacts. Mercury is a naturally occurring element that is found in air, water and soil. It exists in several forms – elemental (also known as metallic mercury), inorganic and organic, all of which have different toxic effects. Mercury is a known toxic substance that is harmful to humans, especially pregnant women, infants and children.

2. What are the main sources of human exposure to mercury?

Mercury releases in the environment result mainly from human activity. Burning of coal for power and heating is by far the major source of mercury. Coal contains mercury which is emitted when the coal is burned. Almost half of mercury emissions to air are from coal fired power plants, industrial boilers and household use for heating and cooking. Other main sources of mercury emissions are industrial processes, waste incinerators and as a result of mining for mercury, gold and other metals. Because mercury is an element that naturally occurs in the environment, it is also released as result of volcanic activity and weathering of rocks.

3. In what manufactured products can mercury be found?

Mercury can be found in varying amounts in many products: including batteries; measuring devices such as thermometers and barometers; electric switches and relays in equipment; lamps, including energy-saving household lightbulbs; dental amalgam; cosmetics; and pharmaceuticals. Mercury may be found in skin-lightening products, however such products are widely banned.

Proper care is important when using and disposing of mercury-containing products.

4. In what ways is mercury harmful to human health?

People are mainly exposed to methylmercury when they eat fish and shellfish that contain methylmercury. Almost all people have at least trace amounts of methylmercury in their tissues, reflecting methylmercury’s widespread presence in the environment and people’s exposure through the consumption of fish and shellfish. People may be exposed to mercury in any of its forms under different circumstances.

For fetuses, infants, and children, the primary health effect of methylmercury is impaired neurological development. Methylmercury exposure in the womb, which can result from a mother's consumption of fish and shellfish that contain methylmercury, can adversely affect a baby's growing brain and nervous system. Impacts on cognition , memory, attention, language, and fine motor and visual spatial skills have been seen in children exposed to methylmercury in the womb.

5. How does mercury enter the food chain?

As mercury moves through environmental media (in air, sediments, water), it undergoes complex transformations. Once deposited, the chemical form of mercury can be methylated in soils and sediments, largely through metabolism by bacteria. Methylmercury, which is the most toxic form of mercury, biomagnifies in food webs, especially the aquatic food web (such as in fish species higher in the food chain). Methylmercury bioaccumulates (higher concentration than the surroundings) in marine and fresh water fish and mammals. The older the fish or mammal, the higher the methylmercury concentration. It also biomagnifies, that is, the higher the organism is in the food chain, and the higher its methylmercury concentration. Therefore, bigger predatory fish are more likely to have higher levels of methylmercury, but smaller fish in particularly contaminated areas may also have high levels of mercury.

6. What can be done to reduce the risks to human health?

Promote the use of clean energy sources that do not burn coal.

Burning of coal for power and heating is by far the major source of mercury and is a major public health issue. Almost half of mercury emissions to air are from coal fired power plants, industrial boilers and households. Coal contains mercury which is emitted when the coal is burned. Other hazardous air pollutants are also emitted, for example PM10 particles, which are particles of 10 micrometers or less, can penetrate into the lungs and may enter the bloodstream and are very harmful to health. Substantial health co-benefits can be achieved by switching to clean energy sources.

Eliminate mercury mining, and use of mercury in gold extraction and other industrial processes.

Mercury is an element that cannot be destroyed, therefore mercury already in use can be recycled for remaining essential uses; primary mercury mining is no longer needed. Mercury use in chlor-alkali and vinyl chloride monomer production is being phased out. Mercury use in artisanal and small-scale gold mining is particularly hazardous, and health impacts for vulnerable populations are significant. Tackling small scale informal mining is challenging, requiring multi-stakeholder input, as communities are often on the poverty line.

Switch to non-mercury fever thermometers and sphygmomanometers in health care.

Mercury thermometers and sphygmomanometers are no longer needed in health care. Validated and affordable alternatives to mercury are available.

Phase out use on non-essential mercury-containing products and implement safe handling, use and disposal of remaining mercury-containing products.

Mercury is contained in many products: including batteries; measuring devices such as thermometers and barometers; electric switches and relays in equipment; lamps; dental amalgam; skin lightening products and other cosmetics; and pharmaceuticals. A range of actions are being taken to reduce mercury levels in products, or to phase out products. In health care, dental amalgam is used in almost all countries. A 2009 WHO Expert Consultation concluded that a global near term ban on amalgam would be problematic for public health and the dental health sector, but a phase down should be pursued by promoting disease prevention and alternatives to amalgam; research and development of cost-effective alternatives; and education of dental professionals and raising public awareness. Mercury use in some pharmaceuticals, such as thiomersal (ethyl mercury) used as a preservative in some vaccines, is very small by comparison with other mercury sources and is essential. There is no evidence that suggests a possible health hazard with the amounts of thiomersal currently used in human vaccines. Inorganic mercury is also added to skin lightening products in significant amounts. Many countries have banned mercury-containing skin lightening products because they are hazardous to human health.

7. What specific actions is WHO taking to reduce the risks?

WHO's core function is to is to establish the scientific basis for the sound management of chemicals, and to strengthen national capabilities and capacities for chemical safety. This helps the WHO Member States to focus their actions on the most effective way to prevent, or reduce health risks. WHO's task is to review and analyze the accumulated scientific evidence, and use expert advice to draw conclusions, and to identify effective interventions.

WHO publishes evidence about the health impacts of the different forms of mercury, guidance on identifying populations at risk from mercury exposure, tools to reduce mercury exposure, guidance on the replacement of thermometers and sphygmomanometers in health care. WHO leads projects to promote the sound management and disposal of health care waste and has facilitated the development of an affordable validated non-mercury blood pressure measuring device. WHO is assisting countries to phase out the use of mercury thermometers and shpygmomanometers in health care.

8. What is the Intergovernmental Negotiating Committee to prepare a global legally binding instrument on mercury?

In February 2009, the Governing Council of UNEP agreed on the need to develop a global legally binding instrument on mercury to address risks to human health and the environment as a consequence of anthropogenic mercury releases.

The work to prepare this instrument is undertaken by an intergovernmental negotiating committee convened by UNEP. The goal is to complete the negotiations before the twenty-seventh regular session of the Governing Council/Global Ministerial Environment Forum in 2013.

Participation in the intergovernmental negotiating committee (INC) is open to all Governments. Intergovernmental organizations and representatives from the civil society may also take part as observers.

9. What is the role of WHO in the treaty negotiations?

WHO, as a specialized agency of the United Nations, has observer status in the INC. The role of WHO is to provide independent authoritative information in line with the available evidence on each of the issues, and to assist in collecting further information where appropriate.

10. What are the implications of the globally binding treaty on Mercury and how will it effect the health sector?

The treaty is an important opportunity for governments and other stakeholders to take action to reduce mercury exposure. The major sources of mercury exposure need to be addressed meaningfully in order to achieve public health objectives. The different uses and emissions vary widely in their potential to impact on human health. There are two types of issues for the health sector measures needed to reduce human exposure to mercury to benefit public health; and reducing uses of mercury in health care.