Mercury emissions
CFLs, like all fluorescent lamps, contain small amounts of mercury as vapor inside the glass tubing. Most CFLs contain 3–5 mg per bulb, with the eco-friendly bulbs containing as little as 1 mg. Because mercury is poisonous, even these small amounts are a concern for landfills and waste incinerators where the mercury from lamps may be released and contribute to air and water pollution. In the U.S., lighting manufacturer members of the National Electrical Manufacturers Association (NEMA) have voluntarily capped the amount of mercury used in CFLs. In the EU the same cap is required by the RoHS law.
In areas with coal-fired power stations, the use of CFLs saves on mercury emissions when compared to the use of incandescent bulbs. This is due to the reduced electrical power demand, reducing in turn the amount of mercury released by coal as it is burned. In July 2008 the US EPA published a data sheet stating that the net system emission of mercury for CFL lighting was lower than for incandescent lighting of comparable lumen output. This was based on the average rate of mercury emission for US electricity production and average estimated escape of mercury from a CFL put into a landfill. Coal-fired plants also emit other heavy metals, sulfur, and carbon dioxide.
 Broken and discarded lamps
Health and environmental concerns about mercury have prompted many jurisdictions to require spent lamps to be properly disposed or recycled rather than being included in the general waste stream sent to landfills. It is unlawful to dispose of fluorescent bulbs as universal waste in the states of California, Minnesota, Ohio, Illinois, Indiana, Michigan, and Wisconsin. In the European Union, CFLs are one of many products subject to the WEEE recycling scheme. The retail price includes an amount to pay for recycling, and manufacturers and importers have an obligation to collect and recycle CFLs. Safe disposal requires storing the bulbs unbroken until they can be processed. In the US, The Home Depot is the first retailer to make CFL recycling options widely available.
Special handling instructions for breakage are currently not printed on the packaging of household CFL bulbs in many countries. The amount of mercury released by one bulb can temporarily exceed U.S. federal guidelines for chronic exposure. Chronic however, implies that the exposure continues constantly over a long period of time and the Maine DEP study noted that it remains unclear what the health risks are from short-term exposure to low levels of elemental mercury. The Maine DEP study also confirmed that, despite following EPA best-practice cleanup guidelines on broken CFLs, researchers were unable to remove mercury from carpet, and agitation of the carpet—such as by young children playing—created spikes as high as 25,000 ng/m3 in air close to the carpet, even weeks after the initial breakage. Conventional tubular fluorescent lamps have been in commercial and domestic use since the 1930s with little public concern about their handling; these and other domestic products such as thermometers contain far more mercury than modern CFLs.
The U.S. Environmental Protection Agency (EPA) recommends that, in the absence of local guidelines, fluorescent bulbs be double-bagged in plastic before disposal. The Maine DEP study of 2008 compared clean-up methods, and warned that the EPA recommendation of plastic bags was the worst choice, as vapors well above safe levels continued to leach from the bags. The Maine DEP now recommends a sealed glass jar as the best repository for a broken bulb.
According to the Northwest Compact Fluorescent Lamp Recycling Project, because household users in the U.S. Northwest have the option of disposing of these products in the same way they dispose of other solid waste, in Oregon "a large majority of household CFLs are going to municipal solid waste". They also note the EPA's estimates for the percentage of fluorescent lamps' total mercury released when they are disposed of in the following ways: municipal waste landfill 3.2%, recycling 3%, municipal waste incineration 17.55% and hazardous waste disposal 0.2%.
 Mercury poisoning of Chinese factory workers
In the past decade, hundreds of Chinese factory workers who manufacture CFLs for export to first world countries were being poisoned and hospitalized because of mercury exposure. Examples include workers at the Nanhai Feiyang lighting factory in Foshan where 68 out of 72 were so badly poisoned that they required hospitalization. At another CFL factory in Jinzhou, 121 out of 123 employees were found to have excessive mercury levels with one employee's mercury level 150 times the accepted standard.
The first step of processing CFLs involves crushing the bulbs in a machine that uses negative pressure ventilation and a mercury-absorbing filter or cold trap to contain mercury vapor. Many municipalities are purchasing such machines. The crushed glass and metal is stored in drums, ready for shipping to recycling factories.
 Greenhouse gases
In some parts of the world (e.g. Quebec and British Columbia) central heating for homes is provided by the burning of natural gas, whereas electricity is primarily provided by hydroelectric or nuclear power. In such areas, heat generated by conventional electric light bulbs significantly reduces the release of greenhouse gases from the natural gas . Ivanco, Karney, and Waher estimate that "If all homes in Quebec were required to switch from (incandescent) bulbs to CFLs, there would be an increase of almost 220,000 tonnes in CO2 emissions in the province, equivalent to the annual emissions from more than 40,000 automobiles."