Web edition: December 19, 2005
Print edition: December 24, 2005; Vol.168 #29 (p. 419)

Bends, the truth

I very much enjoyed "Cool Birds" (SN: 10/22/05, p. 266). What struck me, however, was a passage that mentioned the "bird's resistance to the bends" and the researchers' alleged inability to explain that. As a scuba diver, I know that the bends, or decompression sickness, is caused by breathing compressed air underwater. More nitrogen is absorbed in body tissue per breath taken, which can cause expanding bubbles when surfacing too quickly. The bends does not occur when free diving: holding your breath and not breathing compressed air underwater. I do not believe penguins breathe underwater and am therefore confused why they'd be expected to suffer from the bends in the first place.

Bert Wissig
Kailua, Hawaii

Decompression sickness occurs in people who free dive repeatedly to great depths, researcher Paul Ponganis points out. Even-deeper penguin depths (200 meters, routinely) force nitrogen to dissolve into the body. Rapid surfacing might be expected to trigger nitrogen to form the dangerous bubbles that cause the bends.—S. Milius

Think ahead, 1

"Slim and Sturdy Solar Cells: Nanocrystals offer path to electricity" (SN: 10/22/05, p. 262) describes an inorganic solar cell prototype utilizing two types of cadmium nanocrystals. Do we really need to aim toward mass-producing more items that contain cadmium? This heavy metal is a toxin and carcinogen that is known for fast uptake in plants and buildup in animals' fat. Risks associated with such a solar cell's manufacture and disposal seldom seem to be discussed. Why not look for alternatives now rather than wait for problems later?

Valerie J. DelMedico
Columbus, Ohio

Think ahead, 2

In "Ghost Town Busters" (SN: 10/29/05, p. 282), cleanup of radioactive particles that have seeped into porous building materials such as brick and marble appears to be difficult and expensive, even given the described breakthroughs. Perhaps a more proactive measure would be to require these materials to be impregnated with a stable polymer or similar compound that precludes the "soaking up" of undesirable materials and makes cleanup of a dirty bomb or everyday pollutants as simple as wiping or spraying down the surface.

Sandra L. Hubscher
Atlantic Mine, Mich.