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Adapted from the Rhode Island Committee on Occupational Safety &Health
Hazards of Mercury in the Workplace
(There are 3 forms of mercury: elemental mercury, inorganic mercury, and organic mercury. Organic or methyl mercury is the most hazardous.)
The mercury we usually encounter is elemental mercury also known as metallic mercury, liquid mercury, liquid silver, and quicksilver. It is an extremely heavy, odorless, silver-colored liquid. Because it has such a low viscosity it is hard to contain and spills and splashes easily and breaks up into smaller and smaller beads of liquid. Elemental mercury is found in mercury thermometers, fluorescent light bulbs, dental amalgam fillings, electrical equipment. Elemental mercury is also used as a folk medicine.
Inhalation of elemental mercury vapors is the main source of toxicity, as mercury is well-absorbed through the lungs. Problems from inhalation result either from a large one-time high exposure or a long-term exposure. Long-term exposure of inhaled vapors is generally more dangerous, with the nervous system being the primary target of mercury toxicity. Symptoms may occur within weeks but usually develop insidiously over a period of years. Neurologic symptoms include tremors, headaches, short-term memory loss, incoordination, weakness, loss of appetite, altered sense of taste and smell, numbness and tingling in the hands and feet, insomnia, and excessive sweating. Psychiatric effects are also seen after long-term exposure. The kidneys can also be effected. Intense exposure to high concentrations of mercury vapor can lead to severe respiratory damage.
Elemental Mercury is not well-absorbed through the skin, so skin contact is not likely to cause mercury poisoning, especially with a brief one-time exposure. However, mercury liquid and vapor can be absorbed through the skin in small amounts and this route of exposure can contribute to the overall exposure, especially if exposure to mercury is constant over time. Organic or methyl mercury is rapidly absorbed through the skin.
Mercury levels in urine are used as a general marker of how much mercury exposure has occurred. Urine mercury levels are reported in micrograms/gram of creatinine (a component of the urine). The relationship between airborne mercury levels and urine mercury levels is complicated. Some published benchmarks (based on healthy adult males) include the following: urinary mercury levels below 35 micrograms/gram of creatinine are considered to reflect relatively low mercury exposure; 50 to 100 micrograms/gram of creatinine reflects high exposure.
Mercury vapor in the air is measured by attaching a tube near the breathing zone. A mercury vapor lamp can be used in an emergency. Mercury vapor levels in the air believed to be unhealthy:
- NIOSH: at or above 0.05mg/m3 as a 10hour average.
- OSHA requires that mercury exposure be kept below 0.1mg/m3 at all times.
- If airborne levels of elemental mercury reach 10mg/M3 then a self-contained breathing apparatus [SCBA] must be worn. For organic or methyl mercury the standard is lower and set at 2mg/m3 and skin protection is mandatory.
At normal air temperatures elemental mercury evaporates slowly. Mercury vapors are heavier than air and tend to remain near the floor or source, but as the temperature rises and as the mercury is disturbed, more vapors can become airborne. Outdoors, mercury vapors tend to go away quickly, but indoors (particularly with windows closed), mercury vapors will accumulate in the air.
To protect against mercury hazards.Where a worker encounters elemental mercury by removing it from meters, gauges and other equipment this operation should be performed in a hooded enclosure where there is efficient local exhaust ventilation directly capturing vapor before it reaches the breathing zone.
A mercury spill kit should be available. (Spill kit should contain powdered zinc which is sprinkled on spilled mercury to keep vapors out of the air and an absorbent that turns the liquid mercury into a paste that is handled easier.)
Where a respirator is used then a full OSHA respiratory protection program must be in place. A few key OSHA requirements on respirators include: air measurements must be taken, workers fit tested and medically approved, respirators assigned based on levels of the hazard, trained in wearing and limitations of respirators. Protective clothing should also be used to minimize skin contact, and to prevent mercury liquid from attaching to regular work clothing. To evaluate the use of PPE materials, users should consult the best available garment performance data and manufacturers' recommendations.