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25 June 2007
Mercury (Hg)  

Introduction

Mercury is a hazardous chemical and is a naturally occurring element found in air, water and soil with little amount. It can exist in three forms, including elemental (metallic) mercury, inorganic mercury compounds and organic mercury compounds. Elemental mercury is a shiny, silver-white liquid metal and easy to vapourize at room temperature. Inorganic mercury compounds take the form of mercury salts, which are generally in white powder or crystals, with the exception of mercuric sulfide (cinnabar) which is red. Microorganisms can convert inorganic mercury into organic mercury compounds, such as methylmercury which is the most common organic form of mercury found in the environment.

Mercury is used widely in measuring instruments (thermometers and blood pressure instruments), electrical and electronic appliances (thermostats), dental amalgam, and the manufacture of chlorine and caustic soda. It was formerly used in cosmetics, traditional medicines, pesticides and the extraction of gold.

Exposure Sources

  • Occupational
    • Manufacturers of equipment that contains mercury (such as electrical switches, thermometers and blood pressure instruments); and
    • Dentists and their assistants that may be exposed to metallic mercury from breathing in mercury vapour released from improper amalgam filling procedure.
  • Non-occupational
    • Inhalation of odourless and colourless mercury vapour due to accidental breakage of mercury thermometer, blood pressure barometers or thermostats in indoor environment;
    • Application of mercury contaminated beauty creams or traditional medicines; and
    • Ingestion of mercury contaminated foodstuffs (especially contaminated predatory fish).

Health effects of mercury

Acute poisoning may result from inhalation of elemental mercury vapour with high amount, or from accidental ingestion of mercury or its salts. Owing to their corrosive nature, it can cause inflammation and necrosis of the oropharynx. Other common symptoms are nausea, vomiting, abdominal pain, bloody diarrhea and renal damage. Exposure of high level of mercury can be fatal.

Chronic exposure to mercury can cause numbness and gradual decreases in the senses of touch, vision, hearing and taste. Progressive loss of memory and balance, insomnia, hand tremors and behavioural changes are common symptoms of its neurological effects. In addition, kidney damage can result in oedema, particularly in the ankles and legs.

Mercury and its compounds are eliminated gradually in urine and faeces. The average half-life of mercury in human is about 60-70 days. However, both elemental and organic mercury can be readily cross the blood-brain barrier and the placenta to foetus, and be excreted in breast milk. In fact, effects of neurological disorder could be irreversible and long lasting. Children and foetuses are more susceptible to mercury poisoning than adults.

How can one reduce the risks of exposure to mercury?

  • Special attention should be paid for using mercury-containing products. They should be kept in safe area and inaccessible to children. These products should be replaced with safer alternatives whenever possible (e.g., using electronic thermometers and blood pressure devices).
  • In case of small mercury spills (one typical thermometer), mercury can be collected with a plain sheet of paper or an eye dropper and then stored in a sealed plastic container (e.g., zip lock bag) for disposal. People should be cautioned to wear gloves before decontamination. Used gloves and used paper or eye dropper should be disposed in the sealed plastic container. Windows and doors should be opened for at least a day to allow good ventilation in the contaminated site. NEVER use a vacuum cleaner to clean up the spill and NEVER clean the contaminated clothes with washing machine. When contamination occurs on non-smooth surface (e.g., carpet or clothes), contaminated materials should be discarded and put into an enclosed plastic bag.
  • For use of cosmetic creams (especially for skin-lightening and freckle removing), the public are recommended to purchase well-established brands from reputable stores. Avoid buying any brands from unknown sources that could be fake and contaminated with mercury.
  • Pregnant women, women of child-bearing age, infants and children are advised not to consume excessive amount of predatory fish such as shark and swordfish. Fishes containing high-quality protein and little saturated fat are good for health. Moderate consumption and a balanced diet are essential to avoid excessive intake of mercury from a small range of food items.

Management of Mercury Poisoning

Laboratory tests are available to measure the amount of mercury in blood or urine. In general, the normal blood or urinary mercury level should be less than 10 g/L. For cases with elevated mercury levels and clinical symptoms and signs, further investigation and in-patient management may be required. Chelating therapy may be indicated in some cases.

For more information

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