The conventional wisdom among technical types who don't work for the Environmental Protection Agency is that most people have nothing to fear from the vapor released from a broken fluorescent bulb or CFL. The reason: The small amount of mercury inside the bulb gradually gets absorbed into the glass and so little of it would be airborne in the event of a break.

But that idea was recently tested by researchers from the Dept. of Civil and Environmental Engineering at Jackson State University in Mississippi. Writing in the journal Environmental Engineering Science, researchers say they tested CFLs of eight different brands and four different wattages. They also tested bulbs that had been in use for three years. were tested.

Researchers ran tests designed to see how much Hg came off the bulbs from rain water and how much might leach off if the bulbs went into a landfill. They also checked for mercury vapor coming off broken CFLs.

One interesting result was that Hg contents in CFLs turned out to vary significantly with brand. The total amount of Hg contained in each CFL ranged from 0.1 to 3.6 mg. Researchers also found that and less than 4% of the Hg leached off under landfill conditions. And even new CFLs leached off less than 0.2 mg/L and thus aren't considered hazardous waste. Ditto for Hg leaching off from rainwater.

Results from Hg vapor emission tests weren't so benign, however. They revealed that the CFLs continuously release Hg vapor once they are broken and the release can last over 10 weeks. Total amount of Hg vapor released from a broken CFL can exceed 1.0 mg, which can cause Hg level in a regular room to exceed the safe human exposure limit under poor ventilation conditions.

The researchers also point out breakage of unused CFLs during transportation, handling, sales, and installation causes more release of Hg into the air than that of the used ones. Other researchers have found that the release of 1 mg of Hg vapor into a 500-m3 room can yield an Hg level 10 times that of a child’s exposure limit (0.2 lg/m3) recommended by the Agency for Toxic Substances and Disease Registry. Thus, in most cases, one broken CFL could cause the Hg vapor concentration in such a room to exceed the safe level for children if the room is not vented.

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