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Introduction and Background
With proper controls and training, elemental mercury can be safely used in a laboratory setting. However, when spilled or misused it can present a significant hazard. See the following stories for some recent chilling (and expensive) examples:
- As difficult as it can be to believe, someone opened a day care center in a building that formerly housed a mercury thermometer factory. The building was eventually demolished and disposed of as hazardous waste (Franklinville, NJ, 2006-2010).
- How School's Huge Mercury Cleanup Unfolded - and the $800,000 cleanup it entailed, Avondale, AZ, February 2010.
- Kids playing with mercury contaminated several homes, Rosemount MN, September 2004.
- "Teen unaware of mercury risk", Las Vegas, January 2004.
- "Cleaning Up The Quicksilver Mess", Arkansas, January 1998.
- "Why Focus on Mercury in Schools?, details 1999 contamination incident in Green Bay, WI.
- "Mercury Spill Incidents..." discusses 78 incidents in New York state over 5 years.
- "Man dies from mercury poisoning after trying to extract gold", Oklahoma, March 2008.
- "Cleanup Controversy" (video), the aftermath of a residential mercury spill, Yakima WA, April 2007.
Therefore, minimize your use of mercury and mercury compounds whenever possible.
According to the MIT Department of Health and Safety's Safety Note dated October 6, 1989:
The element mercury is a liquid metal with a vapor pressure of 0.00185 mm at 25 degrees C. This corresponds to a saturation concentration in air of 20 milligrams of mercury per cubic meter of air or 2.4 ppm . The American Conference of Governmental Industrial Hygienists has established a threshold limit for mercury vapor of 0.05 milligrams of Hg per cubic meter of air for continuous 40 hour per week exposure. Long term chronic exposure to mercury vapor in excess of 0.05 mg Hg per cubic meter of air may result in cumulative poisoning. The use of mercury in laboratory amounts in well-ventilated areas is fairly safe; however, mercury can present a health hazard under the following circumstances:
[Such releases are also a violation of EPA regulations].
- When a mercury spill is not cleaned up promptly it may be ground into the floor, fracturing into extremely small particles with a large total surface area (6.4 ft for 1 ml as 10 micron spheres). From such large areas mercury may vaporize at a rate faster than the room's ventilation can safely dilute it.
- The rate of mercury volatilization is directly related to temperature. Whenever elevated temperatures are involved special care must be exercised to provide adequate ventilation. A common occurrence is the breaking of thermometers in ovens due to bumping or raising the oven above the thermometer's capacity.
- The impact of mercury at high velocities or its release into high air velocity systems will atomize mercury into extremely small particle sizes and large surface area. This generally results from inadequate connections in pressure systems.
- Mercury is often dumped into drains. These drains may eventually leak and a workman using a torch to free the joints may, as the result of another's carelessness, receive an overexposure.
Mercury compounds can be quite dangerous. A professor at Dartmouth University (an experienced researcher and expert on the toxicology of heavy metal poisoning) died in 1997 after spilling just a few drops of dimethylmercury on her latex gloves.
Working With Mercury in the Laboratory
Whenever you perform any action with mercury it will spill and splash. It inevitably forms tiny beads that cling to many surfaces and roll several feet away. Large drops quickly break up into thousands of small ones as described above.
Mercury can be handled safely by a professional chemist, although you should minimize or eliminate its use whenever possible. Here are some prudent practices when using mercury:
- Find an alternative to using mercury in the first place:
- Use alcohol thermometers instead of mercury ones.
- Use oil bubblers instead of mercury bubblers when possible.
- Consider using reducing agents other than mercury amalgams in your laboratory procedures.
- NEVER use a mercury thermometer in a laboratory oven. If it breaks in a hot oven, you have not only the obvious health concern, but also a HazMat response situation. Your lab will have to be shut down, probably for several days, for cleaning and testing. The oven will have to be disposed of as hazardous waste. A break in a cold oven is an equally serious situation.
The cost of cleaning up a thermometer break in a laboratory oven far exceeds that of a new laboratory oven with a built-in digital temperature display and fail-safe mechanism.
- Do not leave open containers of mercury in the laboratory. If used in a bubbler, the exhaust should go up a vertical tube to eliminate splashing and should be vented to a fume hood.
- Do not keep excess mercury around if you do not need it. We've seen dozens of research groups that have collected or accumulated tens or hundreds of pounds of mercury over the years - amounts that they could clearly never use. In the event of spill, accident, or fire, the release of this much mercury would be a major catastrophe.
- Clean up spills promptly. When handling mercury use a glass, plastic or steel tray to contain any spills that might occur. Caution: mercury amalgamates with many common metals such as aluminum, so choose your container carefully.
- Glass or plastic vessels should have a secondary steel or plastic container around them in case the vessel fails.
- Do not use mercury where it could contact a hot surface and vaporize.
- Avoid inhaling mercury vapor and use suitable gloves when working with it.
- Put mercury waste in a special waste container. Do not combine it with "regular" organic or inorganic wastes. NEVER dispose of it down the sink!
- Do not wear gold or silver jewelry when working with mercury; it will amalgamate and irreversibly damage your jewelry!
- Although not a safety issue, mercury is very expensive to dispose of as waste.
- Take appropriate measures in the event of a spill (see link #3 below). Sprinkling elemental sulfur on spilled mercury is virtually ineffective; the reaction between Hg and S is not appreciable at room temperature. Amalgamation with fresh zinc dust works fairly well for "soaking up" those noisome tiny beads of mercury once the bulk of the spill has been collected manually.
- Read the Material Safety Data Sheet (MSDS) for mercury before using it. As indicated on the MSDS, mercury is dangerously incompatible with aluminum, ammonia, chlorates, copper, copper alloys, ethylene oxide, halogens, iron, nitrates, sulfur, sulfuric acid, oxygen, acetylene, lithium, rubidium, sodium carbide, lead, nitromethane, peroxyformic acid, calcium, chlorine dioxide, metal oxides, azides, 3-bromopropyne, alkynes + silver perchlorate, methylsilane + oxygen, tetracarbonylnickel + oxygen and boron diiodophosphide.
- As with most other chemicals in your laboratory, access to mercury should be restricted to a locked cabinet or room. Do not leave mercury where a passerby or unauthorized person can swipe it (see the Quicksilver Mess article above).
Recycling Mercury in the Laboratory
Those who use mercury know that clean mercury has a wonderfully shiny surface. But over time, the mercury in your bubbler or diffusion pump tends to get dirty and contaminated, usually with a floating film of gray/black sludge. While you certainly need to clean your apparatus, you can easily recover most of the mercury for reuse rather than replacing it. This saves on disposal costs and reduces the amount of mercury you need to use.
The "best" cleanup method in a chemical sense would be distillation However, boiling mercury and then cleaning up the distillation apparatus afterward is not appealing for a number of obvious reasons. Luckily, there are two easier methods that work quite well for most needs. Before using either of these, set up a large steel or plastic spill tray in a fume hood! Do not try this on the bench because you will spill some mercury.
These cleanup methods work because the sludge is insoluble and less dense than mercury. If your mercury is contaminated with a metal that has amalgamated such as sodium, you may be able to remove the metal chemically, for example, by quenching the sodium metal using established procedures. If the metal is not easily or safely removable through such chemical means, then proper disposal (rather than dealing with distillation) is your best option.
- The syringe technique. Get a 10 mL syringe with needle. Stick the needle below the surface of the contaminated mercury and withdraw clean mercury. Hold onto the syringe with both hands when you withdraw it, keeping the syringe vertical and holding the plunger to prevent/reduce mercury from dribbling back out. Transfer the mercury to your recovery vessel (which should be only an inch or two away).
- The filter paper technique. Fold a filter paper into quarters and then rip a tiny hole in the bottom of the cone. Place the paper in a glass or plastic funnel with the stem of the funnel as close to the bottom of your collection vessel as possible (to minimize splashing). Slowly pour your contaminated mercury into the filter. Most of the sludge will remain behind on the filter paper. You may need to refilter one or more times.
Clean mercury has a mirror-like surface like the one on this 8 mm bead. The lens of the camera says "Carl Zeiss". Photo by Rob Toreki.
Small amounts of mercury residues left behind on contaminated glassware can be removed (dissolved) with a dilute nitric acid solution. Be sure not to pour the acid waste down the sink. Collect the used acid solution a waste container that is used only for mercury-contaminated nitric acid waste and dispose of it properly.
Risks and Environmental Impact
Remember, inhalation is the primary danger from mercury, especially if there is not good ventilation. In fact, some scientists believe that vapor inhalation from dental amalgams can cause Alzheimer's disease in certain genetically predisposed individuals, although the safety of dental amalgams is still a topic of hot debate. Brief, one-time exposures on the skin (from handling mercury) or even ingestion (it has been used as a laxative) are not likely to produce significant health effects in most cases, but don't test your luck. Chronic (long-term) exposure of any sort can lead to all sorts of nasty effects including permanent central nervous system damage, fatigue, weight loss, tremors, personality changes and death.
Because of the ease with which mercury is spilled, the difficulty of ensuring complete cleanup, the curiousity factor of a room temperature liquid metal, and the known health risks, we recommend that mercury use in high school and freshman-level college courses be discontinued entirely. This includes both mercury-containing compounds as well as equipment such as thermometers. In fact, the Centers for Disease Controls' MMWR reported on November 7, 2008 that the ATSDR found that mercury was the most common chemical released in school chemical incidents in the period 2002-2007.
Laboratory concerns aside, we'd like to see the use of mercury in dental amalgams discontinued regardless of whether there is a health risk to the patient. The exposure of the dental technicians, mercury waste discharge to the sewer during dental procedures, discharge of mercury during cremation etc. all present serious environmental and health hazards. See, for example, Characterization of Methyl Mercury in Dental Wastewater and Correlation with Sulfate-Reducing Bacterial DNA (2008).
We also strongly support the banning of mercury in consumer products such as thermometers, thermostats, batteries, lighting, and motion switches. There are equally good or better alternatives that do not present a risk of personal or environmental contamination. The use of mercury-containing fluorescent lighting, particularly compact fluorescent lighting (CFL's) meant for household use, has been the source of considerable debate. While CFL's provide significant energy savings, the potential hazard of mercury suggests that the government needs to do more to encourage consumer/household LED lighting adoption.
The United States has recently taken some very good steps towards limiting mercury environmental contamination. For example, the Mercury Export Ban Act of 2008 banned the export of metallic mercury effective 2013, a move that will prevent the wanton misuse of mercury in gold mining operations in developing nations. The act also requires the US Department of Energy to designate and manage an elemental mercury long-term disposal facility. Likewise, the European Parliament enacted an export ban effective in 2011 that also covers mercury compounds.
In other good mercury news, the Obama administration recently had Bush-era mercury emissions trading regulations overturned in favor of strict emissions caps that will rein in atmospheric emissions from coal-fired power plants at a much faster rate than the Bush rules. By an agreement reached in late October of 2009, the US EPA will regulate emissions of mercury (and other hazardous air pollutants emitted from coal and oil-fired power plants). The rule will formally be proposed in March 2011 and finalized in November of 2011.
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This page was last updated Tuesday, May 11, 2010 and is copyright 1996-2013 by Rob Toreki. All rights reserved.