Mercury
Environmental Sources
Mercury is a naturally occurring metal which has several forms. Metallic mercury
is a shiny, silver-white, odourless liquid. If heated, it is a colourless,
odourless gas. Mercury combines with other elements, such as chlorine,
sulphur, or oxygen, to form inorganic mercury compounds or “salts,” which
are usually white powders or crystals. Mercury also combines with carbon
to make organic mercury compounds. The most common one, methyl mercury,
is produced mainly by microscopic organisms in the water and soil. More
mercury in the environment can increase the amounts of methyl mercury
that these small organisms make.
Metallic mercury is used to produce chlorine gas and caustic soda, and is
also used in thermometers, dental fillings, and batteries. Metallic mercury
enters the environment through seepage from broken thermometers and mercury
blood pressure cuffs. Mercury salts are sometimes used in skin lightening
creams and as antiseptic creams and ointments.
Inorganic mercury (metallic mercury and inorganic mercury compounds) enters
the air from mining ore deposits, burning coal and waste, and from manufacturing
plants. It enters the water or soil from natural deposits, disposal of
wastes, and volcanic activity. Methyl mercury may be formed in water and
soil by small organisms called bacteria. Methyl mercury builds up in the
tissues of fish. Larger and older fish tend to have the highest levels
of mercury.
Eating fish or shellfish contaminated with methyl mercury, breathing
vapours in air from spills, incinerators, and industries that burn mercury-containing
fuels and the release of mercury from dental work and medical treatments
can all affect your health. Breathing contaminated workplace air or skin
contact during use in the workplace (dental, health services, chemical,
and other industries that use mercury) also adversely affects your health.
Human Health Effects
The nervous system is very sensitive to all forms of mercury. Methyl
mercury and metallic mercury vapours are more harmful than other forms,
because more mercury in these forms reaches the brain. Exposure to high
levels of metallic, inorganic, or organic mercury can permanently damage
the brain, kidneys, and developing foetus. Effects on brain functioning
may result in irritability, shyness, tremors, changes in vision or hearing,
and memory problems.
Short-term exposure to high levels of metallic mercury vapours may cause effects
including lung damage, nausea, vomiting, diarrhoea, increases in blood
pressure or heart rate, skin rashes, and eye irritation. The Thor chemicals
plant in Cato Ridge, KwaZulu-Natal is responsible for adverse affects
to its workers as well as the death of some workers due to mercury exposure
and poisoning.
Exposure limits
- The US EPA has set a limit of 2 parts of mercury per billion parts
of drinking water (2 ppb).
- The US Food and Drug Administration (FDA) has set a maximum permissible
level of 1 part of methyl mercury in a million parts of seafood (1 ppm).
- The US Occupational Safety and Health Administration (OSHA) has set
limits of 0.1 milligram of organic mercury per cubic meter of workplace
air (0.1 mg/m3) and 0.05 mg/m3 of metallic mercury
vapour for 8-hour shifts and 40-hour work weeks.
- The US National Institute for Occupational Safety and Health (NIOSH)
recommends a 0.05 mg/m3 TWA (8 hour shift) of Mercury vapours.
Sources & Links:
www.atsdr.cdc.gov/tfacts46.html
www.epa.gov/oerrpage/superfund/programs/er/hazsubs/sources.htm
www.osha-slc.gov/SLTC/pel/
www.cdc.gov/niosh/critdoc2.html
Back to chemical profiles
| 