WHO updates fact sheet on Mercury and Health (9 March 2017)

The World Health Organization (WHO) has updated its fact sheet on mercury and health.

Key Messages:

Mercury is considered by WHO as one of the top ten chemicals or groups of chemicals of major public health concern.

Mercury is a naturally occurring element that is found in air, water and soil.

Mercury exists in various forms:

  • elemental (or metallic) and inorganic (to which people may be exposed through their occupation); and
  • organic (e.g., methylmercury, to which people may be exposed through their diet).

These forms of mercury differ in their degree of toxicity and in their effects on the nervous, digestive and immune systems, and on lungs, kidneys, skin and eyes.

Human activity is the main cause of mercury releases, particularly

  • coal-fired power stations,
  • residential coal burning for heating and cooking,
  • industrial processes,
  • waste incinerators and
  • as a result of mining for mercury, gold and other metals.

Once in the environment, mercury can be transformed by bacteria into methylmercury. Methylmercury then bioaccumulates (bioaccumulation occurs when an organism contains higher concentrations of the substance than do the surroundings) and biomagnifies.


People may be exposed to mercury in any of its forms under different circumstances.

However, exposure mainly occurs through

  • consumption of fish and shellfish contaminated with methylmercury and
  • through worker inhalation of elemental mercury vapours during industrial processes.

Cooking does not eliminate mercury.

Exposure to mercury – even small amounts – may cause serious health problems, and is a threat to the development of the child in utero and early in life.

Factors that determine whether health effects occur and their severity include:

  • the type of mercury concerned;
  • the dose;
  • the age or developmental stage of the person exposed (the foetus is most susceptible);
  • the duration of exposure;
  • the route of exposure (inhalation, ingestion or dermal contact).

Health Effects

Mercury may have toxic effects on the nervous, digestive and immune systems, and on lungs, kidneys, skin and eyes.

Methylmercury exposure in the womb can result from a mother’s consumption of fish and shellfish. It can adversely affect a baby’s growing brain and nervous system.

The primary health effect of methylmercury is impaired neurological development. Therefore, cognitive thinking, memory, attention, language, and fine motor and visual spatial skills may be affected in children who were exposed to methylmercury as foetuses.

The inhalation of mercury vapour can produce harmful effects on the nervous, digestive and immune systems, lungs and kidneys, and may be fatal.

The inorganic salts of mercury are corrosive to the skin, eyes and gastrointestinal tract, and may induce kidney toxicity if ingested.

Neurological and behavioural disorders may be observed after inhalation, ingestion or dermal exposure of different mercury compounds.

Symptoms include

  • tremors,
  • insomnia,
  • memory loss,
  • neuromuscular effects,
  • headaches and
  • cognitive and motor dysfunction.

Mild, subclinical signs of central nervous system toxicity can be seen in workers exposed to an elemental mercury level in the air of 20 μg/m³ or more for several years. Kidney effects have been reported, ranging from increased protein in the urine to kidney failure.

How to reduce human exposure from mercury sources

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

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

Phase out use of 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 (including some types of light bulbs)
  • dental amalgam (for dental fillings)
  • skin-lightening products and other cosmetics
  • pharmaceuticals.

Mercury use in vaccines and pharmaceuticals

Mercury, such as thiomersal (ethylmercury), is used in very small amounts as a preservative in some vaccines and pharmaceuticals.

Compared to methylmercury, ethylmercury is very different.

Ethylmercury is broken down by the body quickly and does not accumulate.

WHO has closely monitored scientific evidence relating to the use of thiomersal as a vaccine preservative for more than 10 years, and has consistently reached the same conclusion:

Ethylmercury used as a preservative in some vaccines does not pose a health risk.

Useful Links:

Link to the updated fact sheet:


Link to WHO page on ten chemicals of major public health concern:


Link to WHO leaflet on top ten chemicals of public health concern (English) [PDF]:


Link to WHO question and answer page on thiomersal:


Link to WHO information sheet on thiomersal:


Link to WHO question and answer page on thiomersal in vaccines:


Link to Global Vaccine Safety Reports on Thiomersal and vaccines:


Link to WHO page on mercury:



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