LETHAL RADIOACTIVITY

But what about a nuclear disaster with a large city devastated and the corpses piled up in the streets?

There ain't no such accident. A nuclear explosion is physically impossible in a power plant, and large scale loss of life could be caused only by the release of large amounts of radioactivity (in an extremely improbable sequence of independent events, the last two of which are a temperature inversion and the wind blowing in the direction of a large, densely populated, nearby city). There would be no immediate fatalities from this radiactivity, and comparatively few cases of radiation sickness, which would claim its victims within a few weeks. The major threat would come from an increased incidence of cancer, which would claim its victims from 15 to 45 years later.

How many would die of cancer for a given exposure? The number is known with unusual precision, for though cancer itself remains a mysterious disease, the effect of radioactivity on its incidence is known from numerous observations, and not just from experiments with animals (one of which involved microscopic examination of each of 50,000 mice); for there has been a high toll of radiation-induced cancers among humans, especially in the first half of this century.

The reader is reminded that last month, when we discussed the normally received doses, they were given in millirems; but lethal doses will be given in rems, which are units 1,000 times bigger. In fact, the doses where detectable fatalities begin to appear are some million times bigger than routine doses from nuclear (or coal-fired) plants. Moreover, the doses discussed last month were in millirems per year, whereas in an accident, the rems (or hundreds of rems) would be received in a matter of hours.

It is often thought that the only "human" data come from the bomb explosions in Japan, but that is not so. More than 100,000 people died there, the vast majority due to the immediate effects of heat and blast; only some 24,000 people were exposed to radioactivity (average dose 140 rems), and among these, more than 100 additional cancer deaths were detected in the subsequent decades (additional meaning beyond the people who would have died of cancer anyway, an amount that can be detected only by sophisticated statistical methods).

There were, however, many other cases of massive exposure to lethal doses of radioactivity, most of them coming from the time before the effects of radioactivity were fully understood: physicians exposed to X-rays, watch dial painters licking their brushes, l5,000 people treated for arthritis of the spine by heavy X-ray doses (400 rems) in Britain and Germany, 4,000 US miners who inhaled radon gas, and other cases where detailed analysis of large samples was possible.

Cancer induction by radioactivity is probabilistic: Of a large number of people exposed to the same strong dose under identical conditions, only a fraction will actually contract cancer. The pertinent effect of radioactivity, therefore, is to increase the chances of dying of cancer beyond what they were already, i.e., before exposure. The data mentioned above have been analyzed by many national and international institutions, and their conclusions agree in all significant points. The important figure for risk assessment is this: The increase in probability of dying of cancer is close to 0.018% per rem of radiation to which an individual was exposed.

For example, if a person in a major nuclear accident were so unfortunately situated as to receive a dose of 200 rems (a dose so large that radiation sickness would actually be the bigger risk), then his chances of dying of cancer would increase by 3.6%, assuming that no cure of cancer were found in the subsequent 15 to 45 years, the time span for which actual death would be delayed.