I live in Northern California, where forest-biomass power plants are common. 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