Plutonium is definitely poisonous, as are all heavy metals when they are in a biologically assimilable form. Mercury in the liquid form is so little assimilable that we handled it freely when I was in high school, and I'll bet some people swallowed some. On the other hand, the Minimata disaster killed a few tens of Japanese when methylated mercury got into Minimata Bay. Cohen's offer to eat a gram of plutonium oxide was based on the oxide being not biologically assimilable. In the 1950s experiments were made with dogs, and the level of poisonousness of plutonium was well calibrated. Whether the contamination of the Rocky Flats area is significantly harmful to human health is questionable if it depends on the "linear hypothesis" that the harm from radiation at low levels can be determined by linear extrapolation from high doses. The evidence is against it, but the regulators persist in using it. Cohen mentioned Denver because its 5,000 foot altitude means that people there are exposed to more cosmic radiation than people closer to sea level. If the linear hypothesis were correct Denver would have a high rate of cancer, and it doesn't. How does the amount of radiation in the vicinity of Rocky Flats compare with the radiation in the same area from cosmic rays?