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Introduction
Mercury is unique among the toxic metals since more information is available concerning the toxic effects of mercury on humans than is available from animal studies. The ancients realized mercury was toxic and assigned the task of mining quicksilver to slaves and prisoners. The average life span of miners was 3 years. In 1665 the workday was reduced to 6 hours in the Adriatic quicksilver mines. By the 1800s mercuric nitrate was widely used to soften fur for hats. The resulting exposure of workers lead to a classic syndrome and the phrase "mad as a hatter." In Danbury, Connecticut, a center of hatmaking, the effects of exposure were characterized as "Danbury Shakes." It was not until 1941 that the use of mercury nitrate in hatmaking was banned in most states. Mercury is used today in barometers, mercury switches, and fungicide resistant paint, the manufacturing of mirrors, batteries, mercury vapor lamps, and fluorescent light bulbs, in analytical chemistry, and in some pharmaceuticals.
Elemental mercury is a silver colored highly mobile liquid at room temperature. It is toxic by ingestion, inhalation and skin absorption (see: MSDS for Mercury). Inhalation is the primary route of occupational exposure. About 80% of inhaled mercury vapor passes into the blood stream. Soluble mercury salts such as mercuric chloride and mercuric oxides are highly toxic with oral LD50 in the range of 1.0 to 18 mg kg-1. (see for example: MSDS for Mercuric Chloride, Mercuric Nitrate, Mercuric Oxide).
Use in Schools
Service products containing mercury include mercury switches, mercury vapor lamps, mercury containing paint and fluorescent light bulbs. Mercury is regulated as a hazardous waste and each of these products must be disposed of in a ccordance with state environmental regulations. In most states both fluorescent light bulbs and mercury vapor lamps can be stored on site (provided certain procedures are followed) and recycled. Broken lamps and bulbs can result in exposure; therefore they should be stored in a secure location.
Mercury can be found in the science area as mercury thermometers, barometers, Charles' law tubes, J tubes, diffusion demonstration apparatus, density demonstrations, elemental mercury, sphygmomanometers, mercury compounds such as mercurous nitrate, mercuric nitrate, mercuric oxide and solutions containing mercury such as Million's solution and Hayem diluting fluid. Mercury containing solutions may also be found in kits such as LaMotte water quality test kits. We strongly recommend the removal of all mercury and mercury containing compounds from schools. This recommendation is based on the growing number of incidents involving mercury (see: Accidents and Incidents), the cost of disposal and the probability that many teachers and students are exposed to mercury unknowingly. For all current applications safe alternatives are available. For most applications alcohol thermometers are adequate. Temperature probes are available (see: Vernier) which give nearly the same precision and accuracy as precision mercury thermometers. Vernier also provides a barometric pressure probe, which provides reasonable accuracy for most applications. If you elect to retain your mercury barometer move it into a locked chemical storage area and locate it in an area where it will not be broken. A typical barometer contains 1 pound of mercury and poses a significant spill risk. For example, vandalism of a barometer cost one school district $7000 to clean up. Use of mercury solutions should be avoided, as mercury is highly toxic to the environment and very expensive to dispose of properly.
Mercury Spills
All schools should develop a spill control policy as part of their chemical hygiene plan. During a spill is not the time to formulate a plan. A complete inventory of all elemental mercury, mercury compounds and solutions should be generated. Spills of nonvolatile mercury compounds pose an exposure risk through skin absorption and inhalation of particles generated during the spill and the cleanup process. Be certain the gloves wore are appropriate to the chemical being cleaned up (see: Personal Protective Equipment). The spill control policy requires thorough analysis. You do not want to store chemicals that require a haz-mat team to abate.
Spills of elemental mercury:
Small spills: This procedure assumes that you have a current mercury spill kit (we suggest the mercury spill control station from Laboratory Safety Supply, item #9A-20753) and that the spill involves a thermometer containing approximately 4-10 grams of mercury (2ml). The process should take an hour and the cost approximately $100.
1. Wear latex gloves and working form the perimeter of the spill push the mercury to the center using the plastic scoop.
2. Spread the mercury suppression powder over the area as you clean it.
3. Collect the mercury using the suction apparatus.
4. After one hour collect the suppression powder and wash the surface with a detergent.
5. Store the contaminated gloves, collected mercury and the debris in a labeled plastic bottle for later removal as hazardous waste.
6. Use a mercury indicator to detect any residual mercury.
Medium spills: This procedure assumes that the room temperature is 25ºC or less and that the spill is cleaned up within one day of the incident and that the surface is smooth. This spill procedure uses a mercury spill kit from Laboratory Safety Supply (item #9A-20754 ). This procedure is appropriate for spills in the range of 10ml to 35ml.
1. Wear a tyvek suit with booties and a double pair of latex gloves.
2. Starting from the perimeter push the mercury towards the center using the plastic scoop.
3. Use the vacuum pump to collect any mercury trapped in the cracks of the floor tile.
4. Spread the mercury suppression powder over the area you clean.
5. Collect the pooled mercury using the pump.
6. After one hour collect the mercury suppression powder and wash the surface with a detergent.
7. Place all the contaminated material in a labeled container for later removal as hazardous waste.
8. Use a detection tube or mercury indicator badge to determine if mercury vapors are present.
Large spills: Mercury spills involving more than a pound of mercury require thorough evaluation before abatement. Since evaporation is a function of surface area, the size of the mercury particles is critical in determining the hazard. The surface type is also critical in spill evaluation. For example, a mercury barometer broken by vandalism in a room having carpet would probably require a haz-mat response. To avoid the problems associated with mercury spills, locate your barometer in the chemical storage area in an area free of traffic. Do not store elemental mercury and avoid the use of mercury thermometers, solutions and compounds. For large spills we recommend a professional evaluate the situation.
Spills involving mercury compounds: Each mercury compound must be evaluated individually as to the proper method of abatement. For example, if a 1 pound container of mercuric chloride falls off a 10 foot high shelf sufficient dust may be generated that a haz-mat team may be required, whereas a small spill in the fumehood could easily be abated with latex gloves and damp paper towels. The debris from any mercury-containing spill must be disposed as hazardous waste. We recommend avoiding the problem of mercury spills be avoiding the use of mercury and mercury compounds. But if you do choose to use these compounds develop a written standard operation procedure for abating spills and anticipate the cost of disposal. For qualitative analysis mercurous salts are preferred over mercuric salts due to their lower toxicity.
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