Copyright © 1995 by Steven J. Milloy. All rights reserved. First edition. Published by the Cato Institute, 1000 Massachusetts Avenue, N.W., Washington, D.C. 20002. Library of Congress Catalog Number: 95-72177. International Standard Book Number: 0-9647463-2-8.
Chapter 7
Instant Risk
Haven't got time to do your own soup-to-nuts risk assessment? Then "instant" risk is for you. No fuss, no muss and guaranteed results. The classic example of this is risk assessment for ionizing radiation.
Everyone is exposed to ionizing radiation every day. It's unavoidable and natural. The two main sources of ionizing radiation are the earth and space. Soils and rock contain naturally occurring radioactive elements that either give off radiation or emit radioactive particles. Space is continually bombarding us with cosmic rays. You would not consider either of these to be dangerous because they occur naturally. Even if you lived the idyllic lifestyle in the Garden of Eden, you would still be exposed to ionizing radiation from these sources.
Some human populations have had very, very, very high exposures to ionizing radiation. Survivors of atomic bomb explosions. Uranium miners. Women who, in the 1920s, painted watch dials and instrument panels with radium paint and licked their brushes to get better points. Studies have shown a generally accepted association between these very, very, very high radiation exposures and cancer.
Notwithstanding what we know about high levels of ionizing radiation, there is not a generally accepted association between lower levels of ionizing radiation from manmade sources (like medical X-rays) or environmental levels of ionizing radiation from naturally occurring sources (like radon in the home).
Now ordinarily, you might conduct a case-control epidemiologic study to try to identify such an association and many folks have. But you don't need to. Just base your study on those of the atomic bomb survivors, underground uranium miners and radium watch dial painters, and you've got instant risk. How? Why?
Years ago, some genius came up with the theory that if something (say radiation) can be harmful at very high exposure levels, in the absence of knowledge to the contrary, it should be assumed it is harmful at any exposure level. This theory is known in risk assessment circles as the linear nonthreshold model.
Using a graph similar to that above, all you need to do is measure or estimate the exposures to your population, find that exposure level on the graph and follow it over to a risk level. What could be easier? Just make believe that getting a medical X-ray is like surviving an atomic bomb explosion. Or that playing ping-pong in your basement rec room is like working in an underground uranium mine! Sounds silly, you say? Don't worry; this is one of the most commonly accepted tenets in the public health community.
You'll need to be prepared for real scientists who might say the linear nonthreshold model flies in the face of everything we know about risks from low levels of exposures. For example, studies of the atomic bomb survivors report an increased incidence of cancer only at the very highest exposures. Among those survivors with less than the highest levels of exposures, a decreased incidence of cancer (as compared to the general population) was observed.
Epidemiologic studies of workers show what is called the "healthy worker effect." That means despite being exposed to comparatively more "risks" on the job, workers are typically healthier than nonworkers. Finally, vaccines (like those for polio, measles, mumps, diphtheria and the like) intentionally expose humans to low levels of toxins but keep individuals healthy, not sick.
But, as I said earlier, the linear nonthreshold model is a public health mantra. It's not open to criticism.
A final word about the "instant risk" technique. It can save you lots of headaches. Consider the following story.
Not long ago, the National Cancer Institute conducted a very large and well-designed study to look at risk factors for lung cancer, including radon in the home. NCI's study failed to find an association between radon in the home and lung cancer. But at the same time, the Environmental Protection Agency was spending $20 million a year on its own radon program. When NCI published its results, EPA got upset.
Study results threatening the existence of the $20 million dollar radon program won't win friends or influence people in the program. They immediately screamed, "Fix this or else!" To atone for its sin, NCI repudiated its own epidemiologic study and published a new study applying the linear nonthreshold model to the underground uranium miner data. That produced an instantly acceptable risk assessment. And NCI and the EPA radon program were on speaking terms again.
The moral of the story? If you go nonlinear, you will be straightened out by your friends — or else!
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Copyright © 1996 Steven J. Milloy. All rights reserved. Site developed and hosted by WestLake Consulting.