Letters from the September 23, 2006, issue of Science News

Moo juiced?

I live in Northern California, where forest-biomass power plants are common (“Radiation Redux: Forest fires remobilize fallout from bomb tests,” SN: 7/15/06, p. 38). One power plant takes the ashes that result and places them where cows forage. I’m wondering to what level of concentration this process will accumulate the cesium in organic dairy products.

Jesse Noell
Eureka, Calif.

The amount of radioactive cesium-137 taken up by trees is small, and the amount taken up by grass fertilized with ash from those trees would be even smaller, says geochemist Mark Fuhrmann of the Brookhaven National Laboratory in Upton, N.Y.—S. Perkins

Hidden meaning

Scientists seek environments that are weightless, near-perfect vacuums in which to conduct experiments. If genuine cloaking were achieved (“Out of Sight: Physicists get serious about invisibility shields,” SN: 7/15/06, p. 42), I would expect there would be a host of experiments that might be conducted in “perfect darkness”—environments free of various energy wavelengths.

Bernard Rice
Hinsdale, Ill.

Cause, effect, or neither?

I was surprised to see in Science News, conclusions about causation made on the basis of correlational research (“Keep on Going: Busy seniors live longer, more proof that it pays to stay active,” SN: 7/15/06, p. 37). The variance in activity levels may have been a consequence of differing levels of energy among the participants at the outset of the study, perhaps due to differences in general health. We should be careful about this victim-blaming habit.

Joan Sophie
Chicago, Ill.

Perhaps the more sedentary people in the study had underlying medical problems that caused them to lack energy and to die earlier than the active people. In an effort to address that issue, the study authors accounted for many factors, such as body fat, race, heart disease, diabetes, cancer, and smoking status, in the study participants.—N. Seppa