Compact Bulbs Made Safer

Brown University researchers have engineered a nanoselenium material to absorb the mercury released from compact fluorescent light bulbs (CFLs). The bulbs have been hailed as energy-efficient successors of incandescent bulbs, but the fluorescent coating inside a CFL contains 3–5 mg of mercury.

As long as a CFL remains intact, no mercury is released. But if broken, the bulb releases small amounts of mercury vapor into the air. Growing concerns of the dangers of mercury in the environment mean that the presence of mercury in the bulbs could hinder sales of the otherwise popular CFLs.

Robert Hurt, a professor of engineering at Brown, and his team created the nanoselenium material from sodium selenite and glutathione through a colloidal synthesis. This synthesis resulted in an amorphous nanopowder of elemental selenium that could absorb mercury vapor. Selenium binds to mercury with high affinity and transforms the metal into biologically inactive mercury selenide (HgSe).

The nanoselenium compound absorbed more than 99% of the mercury vapor released from a single bulb over a 24-hour period, the researchers found. In addition, Hurt's group found that cloth impregnated with the nanoselenium powder is also effective at absorbing mercury. Proof-of-concept testing by Hurt's group showed that absorbing the mercury vapor from a single broken bulb requires less than 10 mg of the nanoselenium powder. Equivalent effects from similar micro- and nanoscale materials tested by Hurt, such as sulfur, zinc, and activated carbon, required several grams to several kilograms of material.

Currently, the group is engineering sorbent-containing disposal bags or recycle boxes to allow safe handling of the bulbs (Environ. Sci. Technol., DOI: 10.1021/es8004392). Although biologically significant exposure to mercury is unlikely to occur from breakage of a single CFL, exposures of workers in recycling plants and landfills could reach toxic levels over time. Hurt hopes to develop disposable selenium-impregnated packaging materials to deal with this risk.