Fluorescent lamps use less electricity than conventional incandescent lights, which is beneficial to the environment. All fluorescent lamps, however, contain mercury. Most compact fluorescent lamps (CFLs) contain 3 to 5 milligrams of mercury, with some of the newest models having as little as 1 to 3 milligrams.
Mercury is a toxic metal associated with contamination of water, fish, and food supplies, and that can lead to adverse health affects. A compact fluorescent lamp generally contains less than 4 mg of mercury, while power plants will typically emit about 10 mg of mercury into the atmosphere in order to generate the electricity needed for an incandescent lightbulb. The net benefit of using the more energy efficient lamp is positive, and this is especially true if the mercury in the fluorescent lamp is kept out of the waste stream when the lamp expires.
Products containing mercury, such as fluorescent lamps, should be disposed of in accord with local laws and regulations and not disposed of with regular trash likely to end up in landfills. Take expired compact fluorescents to a local recycling center, to your community's hazardous waste collection event, or to a local retailer that will accept spent CFLs for recycling.