What if you drop a CFL and it breaks? How much trouble are you in?

Despite some alarming news reports, you don’t have much to worry about. If a CFL breaks, some of the mercury that’s contained in the bulb will evaporate into the air. How much? It’s hard to be certain, but one study [PDF] looking at long tubular fluorescent bulbs found that over a two week period, only 17 to 40 percent of the mercury in the bulb evaporated. The rest remained stuck in the bulb. Roughly one-third of the mercury that evaporated did so in the first eight hours after the breakage; the rest seeped out slowly over the remainder of the study period.

The amount of mercury in a CFL is very small, only 4-5 milligrams. This is almost one thousand times less than what was in mercury thermometers! So, let’s assume that what happens with CFLs is comparable to what happens with tubular fluorescents. If a bulb breaks, only 0.67 milligrams of mercury (one-third of 40 percent of 5 milligrams) might become airborne in the room during the first eight hours, and only a fraction of that would be breathed in. In short, the exposure from breaking a compact fluorescent bulb is in about the same range as the exposure from eating a can or two of tuna fish. (See our list of "Best and Worst Seafood Choices" for more on mercury in fish.)

The tiny amount of mercury you’re exposed to when breaking a CFL is extremely unlikely to cause any ill effects, noticeable or otherwise. But how do you minimize even this tiny amount of risk?

Remove children and pets from the room, and then clean up the broken bulb as quickly as possible....

Haley and colleagues carried out an experimental study in rats because mercury vapour (Hg0) is continuously released from "silver" amalgam tooth fillings and is absorbed into brain. The rats were exposed to Hg0 4h/day for 0, 2, 7, 14 and 28 days at 250 or 300 micrograms Hg/m3 air, concentrations present in mouth air of some humans with many amalgam fillings.6 Average rat brain Hg concentrations increased significantly (11 -47 fold) with duration of Hg0 exposure. By day 14 Hg0 exposure, photo affinity labelling on the beta-subunit of the tubulin dimer in brain homogenates was decreased 41-74%. The identical neurochemical lesion of similar or greater magnitude is evident in Alzheimer brain homogenates from approximately 80% of patients, when compared to human age-matched neurological controls. The authors concluded that chronic inhalation of low-level Hg0 can inhibit polymerization of brain tubulin essential for formation of microtubules.