Mercury release rates are low, new data show, but can build to toxic levels if broken bulbs aren't cleaned up right away.

By Janet Raloff

Web edition: July 7, 2011

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When this happens...

A CFL's swirly tubes are remarkably fragile. When broken, the mercury they'd held can offgas for months, a study finds.

Credit: iStockphoto

My night-owl daughter woke me in a panic at around 2 a.m., a couple of weeks back. While swatting at a fly, she’d just broken the compact fluorescent light illuminating her closet — one of those highly efficient CFLs I’d installed all over the house. She didn’t shatter the whole bulb, just a roughly 3-inch segment of the swirly glass, which (naturally) embedded in the fibers of her carpet. Having heard me warn endlessly of how we should be careful in handling these bulbs — since they contain mercury — she wanted to know what kind of damage control was called for.

I only wish I knew then what I do now. It wouldn’t have changed how we cleaned up the mess, but we would have slept a bit better that night.

New data from Yadong Li and Li Jin of Jackson State University in Mississippi help put concerns about mercury from broken bulbs in perspective. They measured the mercury present in both new and used CFLs and recorded the continuous emissions from ones that they intentionally broke.

Airborne release rates following a break were low, they reported online July 6 in Environmental Engineering Science.  A 13-watt lamp (which has a light output equivalent to a 60-watt incandescent bulb) released from 0.04 to perhaps 0.7 milligrams of mercury during the first 24 hours. This suggests that exposures should be negligible if the pieces are immediately picked up, nestled in paper and then discarded in a zip-it-up plastic bag or a sealed glass jar. To play it safe, the authors recommend also ventilating the room so that any residual gas shed by missed shards of glass won’t accumulate.

And that’s what we did with our broken CFL. Picked up every visible piece of glass, wrapped it carefully and stowed it on the porch until it could be taken down to the trash can the next day. We also vacuumed the carpet for about 10 minutes to pick up glass pieces too small to see — and immediately discarded the vacuum’s bag as well.

Keep in mind, Li notes, a CFL's elemental mercury is not in vapor form unless the lamp is on with a current running through it. Otherwise, the mercury resides along the inside of the glass. And it's from there that the mercury will slowly volatilize once exposed to air. So another lesson: Breaking a CFL while it's turned on can initially disperse a bigger puff of mercury vapor into the air than if its glass is damaged while the bulb is off, Li says.

A more disturbing finding was how long a broken CFL can continue to release toxic vapors: a minimum of 43 days (which is how long Li and Jin ran their tests with bulbs from three different manufacturers). The engineers computed how much of each bulb’s starting mercury had been lost during that time (which wasn’t easy, since starting values and release rates both varied broadly between bulbs). Their calculations indicate that each CFL still contained enough residual elemental mercury at the end of their testing to continue releasing the toxic substance into the air for at least 10 more days, and in one instance, for 85 more days.

If not cleaned up, the bulb with the largest initial store of mercury could have spewed 1 milligram of the toxic metal into a room's air within 25 days; another could have reached that level within about 40 days. Li and Jin cited data by others indicating that the release of 1 milligram of mercury vapor into a 500 cubic meter room can yield air concentrations 10 times the current recommended limit for a child. Breaking a CFL can thus cause potentially toxic levels of pollution to develop, Li and Jin conclude.

Other interesting factoids from their paper:

• — The mercury in a bulb undergoes chemical changes over time as it’s used, rendering it less toxic. Explains Li, the mercury oxidizes, turning it into a solid that will not volatilize. Therefore, an unused bulb poses a significantly bigger pollution risk than is one near the end of its life.
• — Bulbs produced by the major manufacturers since 2008 meet or far exceed the mercury-reduction goal set by the National Electric Manufacturers Association of 5 milligrams per CFL for lamps 25 watts or lower. In fact, most bulbs had less than 2.5 milligrams.
• — For the most popular, 13-watt CFLs, mercury concentrations varied dramatically between brands, from 0.17 to 3.6 milligrams.

The Environmental Protection Agency offers consumers guidance on how to deal with cleaning up a broken CFL. It also recommends something that we should have thought about: Don’t use these lights where they will be unprotected. Like the ceiling fixture in my daughter’s closet. What EPA failed to add: Consumers should ignore any pest that flies within swatting distance of a CFL.