White Light Black Light

Aug. 21, 2008 -- If you break a fluorescent light bulb, you've got a mess on your hands. The bulbs contain mercury, a potent neurotoxin that turns cleanup into a toxic waste management project.

Now, research led by Robert Hurt of Brown University has created a product that absorbs mercury 70 times better than the best available technology. The new sorbent -- made of nanoparticles of the element selenium -- could help clean up after breakages in the home, or during shipping or recycling.

Such a technology is likely to become more critical as people are encouraged to switch from incandescent bulbs to energy-saving fluorescent lighting.

To make the sorbent, the team layered the nano-selenium between a tissue and an impermeable backing layer.

By covering the breakage with the paper for several days, "you can stop almost all of the release," Hurt said. "We think it forms mercury selenide, which is a very stable compound.

Without the paper, the mercury slowly evaporates from the broken bulb over several days. Because the mercury vaporizes, Hurt says, "You are not supposed to vacuum it up. You can distribute the mercury around the house." (EPA's recommendations allow for vacuuming, with some precautions.)

The team proposes that the paper could be included with the packaging for the bulbs, so it could soak up spills that might occur during transit. They presented their results this week at a meeting of the American Chemical Society.

Although the potential for mercury release at home may seem scary, "It's not a really high risk, honestly," Hurt said. "It's very hard to imaging poisoning an adult with a CFL [compact fluorescent light bulb]."

The amount of mercury in the bulbs is relatively small, and although the greatest release happens immediately, it takes several days for it all to escape the bulb, where it is associated with a solid powder.

It's if breakage happens in a child's room or if several bulbs were to break at once -- perhaps at a recycling location -- that the risk would be greater. Large fluorescent tubes also contain more mercury than compact fluorescent light bulbs, Hurt said.

The green credibility of a CFL -- promoted for its significantly decreased energy use relative to an incandescent light bulb -- might seem to be compromised by the fact that the bulb relies on mercury. But, in fact, CFLs use less mercury than incandescent bulbs running on electricity from coal, which releases mercury when burned.

An incandescent bulb will release 13.6 milligrams of mercury from its energy demands, compared to 3.3 milligrams for a CFL. The CFL also contains an average of 5 milligrams of mercury, which can be recycled, according to the U.S. Environmental Protection Agency.

"Prof. Hurt's work is a nice application of nanotechnology to develop a very effective material -- a nanostructured sorbent -- for capturing the mercury, said Joseph Helble of Dartmouth College in Hanover, N.H. "The sorbent itself appears to be much more effective at capturing mercury than other approaches. It's a nice piece of work, both as a research study and as a demonstration of a simple technology that can be directly incorporated into a product for the consumer."

Hurt is talking with companies about commercializing the material.

// posted by Alice @ Sunday, August 24, 2008