Although it’s a necessary chemical in some industrial processes and products—including fluorescent lights—mercury is best avoided. You won’t likely ever get a dose to make you “mad as a hatter” (hat makers once used mercury to make felt), but mercury pollution and poisoning are serious concerns.
Elemental mercury (Hg) enters the environment primarily from the burning of fossil fuels, especially burning coal or petroleum to make electricity. When released into the environment, bacteria in soil and water convert elemental mercury to methylmercury (CH3Hg), which is far more toxic than the toxic-enough elemental mercury. Methylmercury concentrates as it moves up the food chain, which is why health authorities recommend limiting consumption of some foods like certain fish. Fetuses and children are especially vulnerable to methylmercury.
Fluorescent lights, including compact fluorescent lights (CFLs), contain small amounts of elemental mercury vapor. As electrons are driven through the tube, ultraviolet (invisible) light is generated that excites the phosphor (fluorescent) coating on the tube to emit visible light. The amount of mercury in fluorescent lights has declined due to better manufacturing practices. Fluorescent tubes with green end-caps contain 3.5 to 4 milligrams of mercury rather than the typical 8 to 14 mg. Older CFLs contained about 4 mg of mercury, while new ones can have as little as 1 mg. (For perspective, older types of oral thermometers contained about 500 mg of Hg.)
New Federal Trade Commission labeling requirements for all lightbulbs require CFLs to reveal that they contain mercury and points consumers to the government’s CFL gateway web page: epa.gov/cfl. When their useful life is over, fluorescent lightbulbs need to be properly recycled. In fact, many jurisdictions require recycling instead of discarding them.
Energy Star says that “even though CFLs contain a small amount of mercury that could ultimately end up in the environment, that amount is significantly less than the amount of mercury avoided as a result of energy savings.” But what about the risk of mercury exposure in the home due to a broken fluorescent lightbulb or tube? While the risk of breakage is very low, accidents happen. To minimize breakage risk, make sure the bulb is cool before you remove it and twist from the base, not the bulb. Also, don’t overtighten when installing.
In 2007, the Maine Department of Environmental Protection measured mercury contamination from broken CFLs under various ventilation and cleanup strategies. Their worst-case scenario—designed to put the most mercury vapor in the air—resulted in an initial increase that exceeded the Occupational Safety and Health Administration permissible exposure level of 0.1 mg per cubic meter, spiking at 1 foot above the floor level. At 5 feet above the floor, it was only 18% of that amount (about where a standing adult breathes). After one hour, the concentration at the 1-foot level was about one-fifth of the spike.
However, most of the mercury in a broken CFL is not released in vapor form, but remains attached to the broken components and phosphor powder. If the bulb is broken, the vapor released into the surrounding air is between 0.001% and 0.007% of the total amount of mercury in the bulb. If you break a CFL in your home, don’t panic, but do take precautions (see sidebar).
Of course, you can eschew mercury in your lighting altogether by switching to LEDs, which contain no mercury, last far longer, and are coming down in price and going up in quality. Also mercury-free is the Vu1, with its electron-stimulated luminescence technology. Either option is more expensive initially than a CFL or an incandescent (which are increasingly not an option), but will result in a good energy savings payback.