Each CFL contains a very small amount of mercury, a potentially dangerous toxin at a high level of exposure, within its glass tubing. Mercury is an essential part of CFLs because it allows the bulb to be an efficient light source. In recent years, most light manufacturers have reduced the amount of mercury in their fluorescent lighting products.

The average mercury content in a CFL is 4 milligrams – roughly enough to cover the tip of a ball-point pen. By comparison, a watch battery contains 25 milligrams of mercury while an old thermometer contains up to 500 milligrams – the equivalent of more than 125 CFLs! Electricity is the main source of mercury emissions in the United States. CFLs use less electricity than incandescent lights. Therefore, CFLs actually reduce the amount of mercury entering the environment.  See Environmental Protection Agency's (EPA) Web site: Basic Information About Mercury 

No mercury is released when CFL bulbs are intact (not broken) or in use. However, when fluorescent lights are no longer usable, they should be disposed of properly or recycled if possible. There are several options available:

• Home Depot now offers a CFL bulb recycling program at all of its home improvement stores. According to Home Depot, consumers can simply bring in any expired, unbroken bulbs and give them to the store associate behind the returns desk. The bulbs will be packaged, transported and recycled safely by an environmental management company.
• San Antonio residents can dispose of CFLs and incandescent bulbs at the City of San Antonio's Household Hazardous Waste (HHW) Drop-off Center located at 7030 Culebra Road. Disposal is free to San Antonio residents who are asked to bring a copy of a recent CPS Energy bill as proof of residency (the Environmental Fee included on a CPS Energy bill indicates that you are a San Antonio solid waste ratepayer). The HHW Center is open Fridays from 7:00 a.m. to 4:00 p.m. and Saturdays from 8:00 a.m. to 3:00 p.m. Call 311 or see the City's website for other household hazardous waste disposal options available through the center.
• If you're looking for other recycling options, consult the EPA's Web site.

If a CFL or fluorescent light should break, precautions should be taken. The EPA offers specific clean-up and disposal instructions to reduce mercury exposure and ensure consumer safety.