What are the Connections between Mercury and CFLs?

Using CFLs (and other fluorescent bulbs) instead of incandescent bulbs reduces the amount of mercury released into the environment

Mercury is found in many rocks, including coal. When coal is burned at a utility power plant to produce electricity, mercury is released into the environment.
In the U.S., burning coal at power plants results in a little more than 40% of all mercury emissions from man-made sources (source: Section 2.7 of the 2014 National Emissions Inventory, version 1 (December 2016) of the Technical Support Document (PDF)).
Using energy-saving CFLs instead of incandescent bulbs reduces demand for electricity, which in turn reduces the amount of coal burned by power plants, which reduces emissions of mercury when the coal is burned.
LED bulbs are more efficient and versatile than either CFLs or incandescents, and last longer. Learn more about LED bulbs, and the differences between LEDs, incandescents and CFLs.

Small amounts of mercury can be released into the environment when CFLs break, or if they are improperly disposed of at the end of their useful lives.
Mercury, an essential part of CFLs, allows a bulb to be an efficient light source.
On average, CFLs contain about four milligrams of mercury sealed within the glass tubing. By comparison, older thermometers contain about 500 milligrams of mercury – an amount equal to the mercury in over 100 CFLs.
Manufacturers of fluorescent lighting products are working to reduce the amount of mercury content in CFLs.
No mercury is released when the bulbs are intact (i.e., not broken) or in use, but mercury vapor and very small beads of mercury can be released when a CFL is broken.