Mercury is a heavy silvery-white metal that is liquid at room temperatures. It is commonly used in thermometers, mano-meters, and barometers, thus it is present in nearly every chemistry and physics lab. Confined in such instruments mercury itself is not likely to cause health problems, but if there is a means for mercury vapor to enter the lab environment, these highly toxic vapors present a health hazard.

Experiments using mercury should be designed to confine the mercury as much as possible to prevent its vapors from escaping into the laboratory where workers might breathe them. For example, mercury diffusion vacuum pumps should have a liquid nitrogen cold trap to condense the vapors before they escape into the room. Even systems that might require short-term open exposure of mercury to the room environment should have cotton plugs in the mouths of mercury containers to reduce vapor escape to the room.

The most serious atmospheric contamination is that which results from accidental mercury spills. Mercury droplets are difficult enough to pick up when they are large enough to see; but the very tiny ones fall into cracks in floors, into pores of rough surfaces, where they remain, slowly vaporizing into the lab environment. If such a spill occurs, immediate clean-up is in order. An aspirator can be used to capture the large drops. All contaminated surfaces should then be scrubbed with a slurry of water and calcium polysulphide, or a water solution containing HgX. This is commer-cially available as a dry powder to be mixed in the proportion of 1.5 pounds to 5 gallons of water.

Most spills result from carelessness, from misjudging the care required when handling this unusually heavy and elusive liquid. The amount of splashing resulting from simply pouring mercury is surprising to the inexperienced worker. And again, what you don't see can be most dangerous, for the splashing can produce almost invisible droplets. When adjusting manometers one must move the mercury-containing glass tubing very slowly, and avoid sudden accelerations. The large mass of mercury makes it unresponsive to any change in its motion.

Finally, to emphasize how seriously one should take these precautions, we list some of the medical effects of mercury on the human system: Illness results primarily from inhalation of vapors, fumes, or dust, and is usually gradual and chronic. The mercury salt compounds can cause dermatitis, and mercury fulminate can cause skin irritation. Mercury poisoning can result from direct skin contact, or by ingestion. Prolonged exposure can cause kidney disease and chronic nervous disorders.

(Much of the above information was supplied by the Pennsylvania Department of Health, Division of Occupational Health.)

Edited 1997, 2004