ALL AROUND US

For 200 rems to kill (within .a few weeks), they must be absorbed within a short time - a day or so. During a day, the average US citizen absorbs about half a millirem, so if milks were in this respect as safe radioactivity, then a man who usually drinks a pint of milk a day would not be killed until he drank 50,000 gallons of it in a day. In the ratio of lethal to normal intake, then, radioactivity is far safer than milk.

To get a feel for millirems, consider the doses absorbed by the human body in everyday life. Cosmic radiation (at sea level) delivers about 29 mrem/year; external terrestrial sources, such as the ground, rocks, and building materials materials made from them, deliver an average of 26 mrem/year; and the radionuclides in the body (particularly potassiunl 40 in the blood deliver about 24 mrem/year. The total that the average US citizen receives from all natural sources is about 80 mrem/year.

To this must be added the doses received trom man-made sources. By far the biggest contributor is medical equipment, in particular, X-ray equipment (X-rays are much like gamma rays, only with a longer wavelength). They give the average citizen a dose of 50 to 100 mrem/year; in fact, a single chest Xray will give the patient some 50 mrem just in the few seconds during which it is taken. Next on the list are building materials, particularly granite and other rocks rich in radionuclides; houses can give as much as 100 mrem/year. Then there is fall-out from nuclear test explosions from 1951 through 1978 (China, formerly Red, but now known to the best people as People's Republic of, is still testing bombs in the atmosphere, remember?). The fallout from these tests amounts to some 7 mrems/year.

Only then come nuclear plants? Not yet; luminous watches give their users a few mrem/year if the digits are painted with radium; if they are made of a tritium compound, they deliver 0.5 mrem/year.

Airplane travel exposes passengers to increased radiation due to high-altitude flying of jets, where there is a less dense atmosphere to screen off the cosmic radiation coming in from outer space: thev receive about 0.3 mrem/hour (not per year!) so that in the roughly 10 hours of a trip from New York to Los Angeles and back, the passengers receive 3 mrem.

The sum total of all consumer products (including smoke detectors and color television sets) give the US citizen an average dose of 1 mrem/year.

And what happened to nuclear plants? They are not even on the list, because their routine emissions are quite negligible in comparison: The US citizen gets an average of 0.01 mrem/year from them, though 5 mrem/year is allowed (but rarely reached) on the property line of such a plant. Beyond 50 miles from it its effect is for all practical purposes non-existent in the far stronger natural background. In a single flight from New York to Denver (3.5 hours), a passenger gets as big a dose as the average citizen gets from a nuclear plant in more than 100 years!

Most people are also unaware of the fact that coal-fired power plants release more radioactivity to the environment than nuclear ones, for coal contains a number of radionuclides, some of them soluble in water and chemically active; that, however, is not the prime reason why coal-fired power is associated with far higher health hazards

[Source of dose data: National Council on Radiation Protection, 1975; United Nations Scientific Committee on Effects of Atomic Radiation, 1977. For recent data on coal-fired plant radiation, see J.P. McBride and others, "Radiological impact of airborne effluents of coal and nuclear plants," Science, 12/8/78.]