This is from Canada
How much plutonium does it take
to overdose a person?
Excerpt
We feel compelled to point out that, although the probability of a severe accident that would release plutonium to the atmosphere is admittedly small, the potential health and environmental consequences of such an accident can be serious due to the extraordinary toxicity of plutonium when inhaled.
It is for this reason alone that the United States of America has made it illegal to transport plutonium by air in US territory. Such a prohibition does not exist for any other radioactive material.
Atomic Energy of Canada Limited has admitted, in documents submitted to Transport Canada, that in four out of eight categories of serious road transportation accidents, the MOX containers would be completely destroyed and a plume of plutonium dust would be spread downwind to a distance of about 80 kilometers.
Snip
Industry and government spokespersons have insisted that 120 grams of plutonium is too small an amount to raise legitimate health and environmental concerns. They have made the irrelevant observation that 120 grams of plutonium is about the size of two A-A batteries.
Such remarks are manipulative in nature; they do not help people to weigh the risk. The important quantity is not the VOLUME or MASS of plutonium, but its TOXICITY. Based on data supplied by AECB (see letter above) we can address the toxicity question as follows:
Continues
http://www.ccnr.org/max_plute_aecb.html
One-tenth of a microgram of plutonium, a microscopic amount, attached to a dust particle, is lethal. Tons of mixed plutonium-uranium oxide fuel rods were stored at Fukushima Reactor 3, all exposed to the environment when the containment building exploded.