few days is about a dozen milligrams (thousandths of a gram). All these estimates, particularly those related to shortening of life from lung cancer, are uncertain, partly because the responses of different individuals to the same doses of plutonium are likely to vary considerably. For purposes of this discussion, particularly for comparisons with other toxic substances, we assume that fifty micrograms of plutonium–239 represent a "lethal" dose, i.e., the amount that would be very likely to cause eventual death if it were internally absorbed.

In terms of the total weight of material that represents a lethal dose, plutonium–239 is at least 20,000 times more toxic than cobra venom or potassium cyanide, and 1,000 times more toxic than heroin or modern nerve gases. It is probably less toxic, in these same terms, than the toxins of some especially virulent biological organisms, such as anthrax germs.

The amounts of plutonium that could pose a threat to society are accordingly very small. One hundred grams (three and one half ounces) of this material could be a deadly risk to everyone working in a large office building or factory, if it were effectively dispersed. In open air, the effects would be more diluted by wind and weather, but they would still be serious and long-lasting.

The quantities of plutonium that might produce severe hazards in large areas are summarized in the very crude estimates presented in Table 2–2. To estimate the areas within which people might be exposed to lethal doses inside a building, we assume that dispersed plutonium is primarily plutonium–239 in the form of an aerosol of finely divided particles distributed uniformly in air throughout the building, We also assume that exposure of people to the contaminated air is for one hour, that ten percent of the inhaled particles are retained in their lungs, and that, as stated earlier, the lethal retained dose of plutonium is fifty micrograms. These conditions might be achieved by carefully introducing the plutonium aerosol into the intake of a building's air conditioning system. This might be quite difficult to do in many cases.

An area of 500 square meters (about 5,000 square feet) corresponds to the area of one floor of many typical office buildings. An area of 50,000 square meters (about 500,000 square feet) is comparable to the entire floor area of a large skyscraper. Even a few grams of dispersed plutonium could pose a serious danger to the occupants of a rather large office building or enclosed industrial facility.