The Intended Readership
Levels of Prior Knowledge :
This book has been written for everyone who has either a professional or a personal interest in the subject, and wants an independent analysis, as defined in Chapter 1.
The book does not require readers to have prior because there is so little quantitative human evidence knowledge in this particular field. However, because this is a scientifically rigorous piece of work, it demands some concentration from all its readers, regardless of their background.
Potential readers who lack comfort with numbers may be pleasantly surprised by the book, despite all its digits and tables. They will understand the most important parts of all the chapters, even if they decide in advance to pass over everything which they find intimidating.
Readers whose first language is not English, and readers who are not familiar with this field, can find the meaning of various terms and abbreviations by consulting the entries flagged by (*) in the Index.
Anyone who handles computations easily -- whether in chemistry, physics, engineering, accounting, computer science, marketing, or for any other purpose -- should have no trouble following all aspects of this book. I particularly hope, of course, that it will be useful in the fields of epidemiology, public health, environmental sciences, internal medicine, occupational medicine, nuclear medicine, radiology, dentistry, health physics, nuclear engineering, and radiobiology.
The Most Important Carcinogen?
The evidence in this book speaks directly to everyone who is interested in specific successful ways to prevent part of the human misery called cancer. The evidence in this book means that one effective way to prevent a large number of cancers would be to reduce human exposures to low-dose ionizing radiation.
To support this conclusion, we do not depend on expectations based on other species, cell-studies, or high-dose data. The evidence proving that LOW-dose ionizing radiation is a human carcinogen comes from epidemiological records -- from real, whole human beings.
Indeed, ionizing radiation may be the single most important carcinogen to which humans are actually exposed. It may account for a significant share of today's entire cancer problem (see Chapter 24, Part 10).
It is difficult, however, to compare the impact of ionizing radiation with the impact of other carcinogens on the other carcinogens (see Chapter 25, Part 5). By contrast, we know about ionizing radiation directly from human evidence.
-- Human evidence shows conclusively that no threshold exists with respect to induction of cancer by the lowest conceivable doses and dose-rates of low-LET ionizing radiation. There is no safe dose or dose-rate.
-- The new A-bomb evidence shows, when all ages are considered together, that the cancer-hazard per dose-unit is more severe at LOW doses than at intermediate and high doses; the dose-response curve is supra-linear. (See Figure 13-C).
-- The new A-bomb evidence confirms that the cancer-risk is much higher for younger people than for older people, when they receive the same dose.
Who Receives the Exposures?
Medical-Dental Diagnostic Doses :
A surprising number of Americans -- estimated at about 7 out of 10 every year -- receives some exposure to ionizing radiation from diagnostic X-rays in medicine and dentistry (Phs80). Such exams can have real benefits for patients.
But the same diagnostic benefits are often obtainable with much lower doses. Elsewhere, I have estimated that unnecessarily high X-ray doses cause about 1.5 million unnecessary cancers per generation in the United States alone (Go85, Chapter 17). The estimate excludes cancers induced by diagnostic nuclear medicine, and excludes all second cancers induced by therapeutic radiation.
Except for not smoking, probably the single most effective step which people could take, in order to reduce their chance of cancer, is to resist referrals to diagnostic X-ray facilities which cannot provide credible evidence that the doses which they give are well below (not well above) the national average. The carcinogenicity of X-rays is even greater than the carcinogenicity of A-bomb radiation (see Chapter 13).
Occupational Exposures :
According to a governmental estimate, about 1.5 million Americans receive occupational exposure to ionizing radiation. I wonder how many young workers in transport know what doses they receive from radioactive packages and cargo . . . how many young nurses know what doses they receive from the patients who contain gamma-emitting radionuclides after having some procedure in nuclear medicine . . . and how many young lab technicians who work on radioactive labeling experiments, with beta-emitters, are aware that beta-emitters produce X-rays especially when they interact with materials of high atomic number (the bremsstrahlung mechanism).
Of course, as long as a person's consent to occupational exposure is not based on deception, there is no fraud and therefore, in my view, outsiders have no right to do anything more than provide honest information to workers and employers alike. An independent analysis is an appropriate resource in such circumstances.
Environmental Exposures :
The environment is contaminated by two classes of radioactive isotopes: Those placed there by nature, and those placed there by human activities. The living cells which become irradiated by such contaminants cannot tell the difference, of course (see Chapter 19).
All people on earth receive environmental doses of low-LET ionizing radiation from nature-placed radioisotopes like potassium-40 and carbon-14, and man-placed radioisotopes like strontium-90 and cesium-137 (distributed globally by atomic bomb tests above ground, for instance).
There seems to be less recognition that we all receive some low-LET exposure also from various radionuclides in the decay-chains of uranium and thorium, two substances released into the biosphere by human activity as well as by nature. For instance, in the decay-chain of radon-220 (thoron gas), there is lead-212, which emits both gamma and beta radiations. Moreover, some of the alpha-emitters -- like radium-224 and radon-220 -- emit significant gamma rays of their own, in addition to alpha-particles.
The risk-estimates in this book apply to all low-LET environmental exposures, whether caused by man or by nature.
Effect of Wrong Information :
The effort which individuals, families, physicians, health physicists, engineers, and some public officials environmental exposures, whether caused by man or by make -- in order to reduce exposures to ionizing radiation -- is directly related to their perception of the health risk.
The link between perception and probable effort may be illustrated by statements from Robert E. Alexander, who is identified (Alex88a) as a scientist with the U.S. Nuclear Regulatory Commission and the 1988-89 president of the Health Physics Society -- the society whose official journal calls itself "the radiation protection journal."
Alexander's perception seems to be that low doses are probably safe doses with zero health effects. He calls this a "highly significant probability" (Alex88a, p.144). He reports, "Many health physicists are dismayed by the now-common practice of including extremely low doses in health effects estimations" (Alex88a, p.145). "Reasonable people will not knowingly want to support proposals for large expenditures to protect against risks that have an entirely theoretical basis, that may not exist, and that can never be demonstrated" (Alex88b, p.594).
Similar views are illustrated at length in Chapter 24, Parts 8, 9, and 10, because perceptions of this type have already culminated in two proposals which are now pending in the U.S.:
-- (1) The exclusion of very low-dose exposure when estimates are made of the health-consequences from various radiation-related activities.
-- (2) The de-regulation of a large fraction of radioactive waste, so that it can be "disposed of" in landfills and incinerators just like non-radioactive waste (see Chapter 24, Part 10).
Outcome of "the Controversy" :
If underestimates prevail concerning the health consequences from low-dose exposure, a realistic prediction is that doses received by the public will rise, and not only in the United States. I would hesitate to predict the limit.
So it seems self-evident that over time, the cancer-risk for everyone in the world (with the emphasis on children) is going to be affected by the outcome of the so-called "radiation controversy" -- by whether or not scientifically reasonable estimates of cancer-risk from low doses replace the widely used underestimates and threshold-claims.
This book results from an independent effort to find out what the scientifically reasonable estimates really are, in view of new data. The key findings were described in Chapter 1.