The most important breakdown in the public's understanding of nuclear power is in its concept of the dangers of radiation. What is radiation, and how dangerous is it?
Radiation consists of several types of subatomic particles, principally those called gamma rays, neutrons, electrons, and alpha particles, that shoot through space at very high speeds, something like 100,000 miles per second. They can easily penetrate deep inside the human body, damaging some of the biological cells of which the body is composed. This damage can cause a fatal cancer to develop, or if it occurs in reproductive cells, it can cause genetic defects in later generations of offspring. When explained in this way, the dangers of radiation seem to be very grave, and for a person to be struck by a particle of radiation appears to be an extremely serious event. So it would also seem from the following description in what has perhaps been the most influential book from the opponents of nuclear energy1:
When one of these particles or rays goes crashing through some material, it collides violently with atoms or molecules along the way. . . . In the delicately balanced economy of the cell, this sudden disruption can be disastrous. The individual cell may die; it may recover. But if it does recover, after the passage of weeks, months or years, it may begin to proliferate wildly in the uncontrolled growth we call cancer.
But before we shed too many tears for the poor fellow who was struck by one of these particles of radiation, it should be pointed out that every person in the world is struck by about 15,000 of these particles of radiation every second of his or her life,2 and this is true for every person who has ever lived and for every person who ever will live. These particles, totalling 500 billion per year, or 40 trillion in a lifetime, are from natural sources. In addition, our technology has introduced new sources of radiation like medical X-rays a typical X-ray bombards us with over a trillion particles of radiation.
With all of this radiation exposure, how come we're not all dying of cancer? The answer to that question is not that it takes a very large number of these particles to cause a cancer. As far as we know, every single one of them has that potential; as we are frequently told, "no level of radiation is perfectly safe." What saves us, rather, is that the probability for one of these particles to cause cancer is very low, about 1 chance in 30 quadrillion (30 million billion, or 30,000,000,000,000,000)! Every time a particle of radiation strikes us, we engage in a fatal game of chance at those odds. However, this is not unique to radiation; we are engaged in innumerable similar games of chance involving chemical, physical, and biological processes that may lead to any form of human malady, and the one involving radiation has odds much more favorable to us than most. Only about 1% of fatal human cancers are caused by the 30 trillion particles of radiation that hit us over a lifetime (this estimate does not include the effects of radon, to be discussed below), while the other 99% are from losing in one of these other games of chance.
Of course every extra particle that strikes us increases our cancer risk, so many people feel that they should go to great lengths to avoid extra radiation. If that is your attitude, there are many things you can do. You can reduce it 10% by living in a wood house rather than a brick or stone house,3 because brick and stone contain more radioactive materials like uranium, thorium, and potassium. You could reduce it 20% by building a thick lead shield around your bed to reduce the number of hits while you sleep, or you could cut it in half by wearing clothing lined with lead like the cover dentists drape over you when they take X-rays.
But most people don't bother with these things. Rather, they recognize that life is full of risks. Every time you take a bite of food, it may have a chemical that will initiate a cancer, but still people go on eating, more than necessary in most cases. Every ride or walk we take could end in a fatal accident, but that doesn't keep us from riding or walking. Similarly, the sensible attitude most of us take is not to worry about a little extra radiation; after all, 1 chance in 30 quadrillion is pretty good odds!
The moral of the this story is that hazards of radiation must be treated quantitatively. If we stick to qualitative reasoning alone, we can easily conclude that nuclear power is bad it leads to radiation exposure which can cause cancer. The trouble with this is that, by a similar type of qualitative reasoning, just about anything else we do can be shown to be harmful: coal or oil burning causes air pollution which kills people, so coal or oil burning is bad; using natural gas leads to explosions which kill people, so burning gas is bad; and so on. Any discussion of dangers from radiation must include numbers; otherwise, it can be as completely deceptive as the quote above about the tragedy of being struck by a single particle of radiation. But how often do stories we hear about radiation include numbers?
MEET THE MILLIREM
In order to discuss radiation exposure quantitatively, we must introduce the unit in which it is measured, called the millirem, abbreviated mrem. One millirem of exposure corresponds to being struck by approximately 7 billion particles of radiation, but it takes into account variations in health risks with particle type and size of person. For example, a large adult and a small child standing side by side in a field of radiation would suffer roughly the same cancer risk and hence would receive the same dose in millirems, although the adult would be struck by many more particles of radiation being a larger target. In nearly all of our discussions about radiation, we will be considering doses below about 10,000 mrem, which is commonly referred to as low-level radiation.
We frequently hear stories about incidents in which the public is exposed to radiation; radioactive material falling off a truck; contaminated water leaking out of a tank or seeping out of a waste burial ground; a radioactive source used for materials inspection being temporarily misplaced; malfunctions in nuclear plants leading to releases of radioactivity; and so on. Perhaps a hundred of these stories over the past 45 years have received national television coverage. The thing I always look for in these stories is the radiation exposure in millirems, but it is hardly ever given. Eventually it appears in a technical journal, or I trace it down by calls to health officials. On a very few occasions it has been as high as 5-10 mrem, but in the great majority of cases it has been less than 1 mrem. In the Three Mile Island accident, average exposures in the surrounding area4 were 1.2 mrem this drew the one-word banner headline "RADIATION" in a Boston newspaper. In the supposed leaks of radioactivity from a low-level waste burial ground near Moorhead, Kentucky, there were no exposures5 as high as 0.1 mrem; yet this was the subject of a three-part series in a Philadelphia newspaper6 bearing headlines "It's Spilling All Over the U.S.," "Nuclear Grave is Haunting KY," and "There's No Place to Hide." In the highly publicized leak from a nuclear power plant near Rochester, New York, in 1982, no member of the public was exposed to as much as 0.3 mrem.7 Yet this was the top news story on TV network evening news for two days.
For purposes of discussion, let us say that a typical exposure in these highly publicized incidents was 1 mrem. Did these incidents really merit all this publicity? How dangerous is 1 mrem of radiation?
Perhaps the best way to understand this is to compare it with natural radiation3 the 15,000 particles from natural sources that strike us each second throughout life. We are constantly bombarded from above by cosmic rays showering down on us from outer space, hitting us with 30 mrem per year; from below by radioactive materials like uranium, potassium, and thorium in the ground 20 mrem/year; from all sides by radiation from the walls of our buildings (brick, stone, and plaster are derived from the ground) l0 mrem/year; and from within, due to the radioactivity in our bodies (mostly potassium) 25 mrem/year. All of these combined give us a total average dose of about 85 mrem per year from natural sources, or 1 mrem every 4 days. Thus, radiation exposures in the above mentioned highly publicized incidents are no more than what the average person receives every few days from these natural sources.
But, you might say, the extra radiation is what we should worry about because there is nothing we can do about natural radiation. Not true. The numbers given above are national averages, but there are wide variations. In Colorado and other Rocky Mountain states (Wyoming, New Mexico, Utah), where the uranium content in soil is abnormally high, and where the high altitude reduces the amount of air above that shields people from cosmic rays, natural radiation is nearly twice the national average; but in Florida, where the altitude is minimal and the soil is deficient in radioactive materials, natural radiation is 15% below the national average. Thus, the radiation exposures in the highly publicized incidents are about equal to the extra radiation you get from spending five days in Colorado. Of course, millions of people spend their whole lives in Colorado, and as it turns out, the cancer rate8 in that state is 35% below the national average. Leukemia, probably the most radiation-specific type of cancer, occurs at only 86% of the national average rate in Colorado, and at 61% of that rate in the other high-radiation Rocky Mountain states. This is a clear demonstration that radiation is not one of the important causes of cancer. (Recall our estimate that, excluding radon, it is responsible for about 1% of all fatal cancers.)
Diagnostic X-rays are our second largest source of whole body exposure. A dental X-ray gives us about 1 mrem, and a chest X-ray gives us about 6 mrem, but nearly all other X-rays give far higher exposures9: pelvis, 90 mrem; abdomen, 150 mrem; spine, 400 mrem; barium enema, 800 mrem. Often a series of X-rays is taken, giving total exposures of several thousand millirems. The average American gets about 80 mrem per year3 from this source, 80 times the exposure in the highly publicized radiation incidents. Again this diagnostic X-ray exposure is not unavoidable much could be done to reduce it substantially without compromising medical effectiveness, and large numbers of X-rays are taken only to protect doctors and hospitals against liability suits.
There are several trivial sources of whole body radiation that give us10 about 1 mrem: an average year of TV viewing, from the X-rays emitted by television picture tubes; a year of wearing a luminous dial watch, since the luminosity comes from radioactive materials; and a coast-to-coast airline flight, because the high altitude increases exposure to cosmic rays. Each of these activities involves about the same radiation exposure as the highly publicized incidents.
All of the above-listed sources bombard all organs of our body, but the most important source of our exposure to radiation is radon gas in our homes, which only irradiates our lungs, causing lung cancer. It gives us a cancer risk equal to that of exposing all of our body organs to 200 mrem per year. In some states, like Colorado and Iowa, the average level is 3 times this average, about 600 mrem per year. Several other areas, like an extensive one covering Altoona, Harrisburg, Lancaster, York, Allentown, Bethlehem, and Easton, Pennsylvania, and the regions around Columbus Ohio, Nashville Tennessee, and Spokane, Washington, have equally high radon levels. Radiation exposures in the highly publicized incidents are thus considerably lower than those received by people in these areas every day. Note that the Pennsylvania area includes the region around the Three Mile Island plant; people living near that plant get more radiation exposure from radon in their homes every day than they got from the 1979 accident. Within any area, there is a wide variation in radon levels from house to house. About 5% of us, 12 million Americans, get more than 1,000 mrem per year, and perhaps 2 million Americans get over 2,000 mrem per year from radon. In a few houses, exposures have been found to be as high as 500,000 mrem per year.
How dangerous is 1 mrem of radiation? The answer can be given in quantitative terms, with some qualifications to be discussed later, but in most situations, for each millirem of radiation we receive, our risk of dying from cancer is increased by about 1 chance in 4 million. This is the result arrived at independently by the U.S. National Academy of Sciences Committee on Biological Effects of Ionizing Radiation11 and the United Nations Scientific Committee on Effects of Atomic Radiation.12 The International Commission on Radiological Protection has always accepted estimates by these prestigious groups, as has the U.S. National Council on Radiation Protection and Measurements, the British National Radiological Protection Board, and similar groups charged with radiation protection in all technologically advanced nations.
This risk corresponds to a reduction in our life expectancy by 2 minutes. A similar reduction in our life expectancy is caused by13
These examples should put the risk of 1 mrem of radiation into proper perspective. Many more examples will be given in Chapter 8.
There has been intermittent publicity over the years about the fact that nuclear power plants, as a result of minor malfunctions or even in routine operation, occasionally release small amounts of radioactivity into the environment. As a result, people living very close to a plant receive about 1 mrem per year of extra radiation exposure. From the above example we see that, if moving away increases their commuting automobile travel by more than 5 miles per year (25 yards per day), or requires that they cross a street more than one extra time every 8 weeks, it is safer to live next to the nuclear plant, at least from the standpoint of routine radiation exposure.
SCIENTIFIC BASIS FOR RISK ESTIMATES
How do we arrive at the estimated cancer risk of low-level radiation, 1 chance in 4 million per millirem? We know a great deal about the cancer risk of high-level radiation, above 100,000 mrem, from various situations in which people were exposed to it and abnormally high cancer rates resulted.11 The best-known example is the carefully followed group of 90,000 JapaneseA-bomb survivors, among whom 8,500 people were exposed to doses in the range 100,000-600,000 mrem and suffered about 300 excess (i.e. more than would be normally expected) cancer deaths. In the period 1935-1954, it was fashionable in British medical circles to treat an arthritis of the spine called "ankylosing spondylitis" with heavy doses of X-rays, averaging about 300,000 mrem, which produced over 100 excess cancers among 14,000 patients so treated. In Germany, that disease and spinal tuberculosis were treated with radium injections which administered 900,000 mrem to the bone; in a study of 900 patients treated before 1952, there were 54 excess bone cancers.
The International Radiation Study of Cervical Cancer Patients has been following 182,000 women treated for cervical cancer with radiation in Canada, Denmark, Finland, Norway, Sweden, United States, United Kingdom, and Yugoslavia; exposures were typically 2-7 million mrem to the pelvis, 0.1-1 million mrem to the kidneys, stomach, pancreas, and liver; and lower doses to other body organs. There have been up to 250 excess cancers among them.
In Germany, Denmark, and Portugal, thorium (a naturally radioactive element) was injected into patients to aid in certain types of X-ray diagnosis between 1928 and 1955, giving several million millirem to the liver; among 3,000 patients there have been over 300 excess liver cancers. Between 1915 and 1935, numerals on luminous watch dials were handpainted in a New Jersey plant using a radium paint, and the tip of the brush was formed into a point with the tongue, thereby getting radium into the body; among 775 American women so employed, the average bone dose was 1.7 million rem, and there were 48 excess bone cancers among them. (Over 3,000 other radium watch dial painters have been studied in less detail, with similar findings.)
There have been studies of about 10,000 radiologists from early in this century; there were numerous excess cancers from the very high doses they received, but unfortunately, it has been difficult to quantify those doses. There are data on about 10,000 patients treated with radiation for Hodgkins disease, among whom there was a large excess of leukemia and some excess of other types of cancer; however, chemotherapy, which also causes cancer, is an important complication here. There is information on patients treated with radiation for cancer of the ovaries, breast, and other organs who survived to develop other cancers from that radiation. There are data on patients given large doses of radiation for immune suppression in organ transplants (mainly for kidneys and bone marrow). Other studies include British women given X-ray treatments for a gynecologic malady, women in a Nova Scotia tuberculosis sanatorium who were repeatedly subjected to X-ray fluoroscopic examination, American women given localized X-ray treatment for inflammation of the breasts, American infants treated with X-rays for enlargement of the thymus gland and other problems, Israeli infants treated with X-rays for ringworm of the scalp, and natives of the Marshall Islands exposed to fallout from a nuclear bomb test.
Numerous studies have examined radon's effects on miners, since it tends to reach high concentrations in mines. Extensive studies have been carried out on uranium miners in the Colorado plateau, among whom there were 256 cases of lung cancer versus 59 expected cases; for uranium miners in Czechoslovakia, where there were 212 cases versus 40 expected; for iron miners in Sweden, who suffered 51 cases versus 15 expected, for uranium miners in Ontario, Canada, who experienced 87 cases versus 57 expected; and for several other smaller groups.
The most recent analyses of the data other than for radon are those reported in 1990 by the National Academy of Sciences Committee on Biological Effects of Ionizing Radiation (BEIR)11 and in 1988 by the United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR).12Both of them depended primarily on the Japanese A-bomb survivors and, to a lesser extent, the British ankylosing spondylitis patients. UNSCEAR also used the cervical cancer patients, and the BEIR analysis utilized data on the fluoroscopy patients and those treated with X-rays for inflammation of the breasts, thymus gland enlargement, and ringworm of the scalp. The analyses for effects of radon were carried out separately by another BEIR committee,14 by the U.S. National Council on Radiation Protection and Measurements (NCRP),15 and by the International Commission on Radiological Protection (ICRP).16
In the earlier BEIR analysis17 of 1980, there was good general agreement among results obtained from the most important data sets. But during the 1980s, very extensive new evaluations were carried out on the radiation doses received by the Japanese A-bomb survivors, including new estimates of the radiation emitted from the bombs and more careful consideration of how each individual was shielded from this radiation by building materials and the outer parts of their bodies. As a result, the risk estimates from the A-bomb survivor data increased substantially and are now about 1.5 times and 3 times higher, respectively, than those from the ankylosing spondylitis and cervical cancer patients. They are also 5 times higher than the risks obtained from radon exposure to miners. Since both the BEIR and UNSCEAR analyses give very heavy weight to the A-bomb survivor data, the risk estimates they obtain are substantially higher than those given previously.
Another problem in deriving estimates arises from the fact that the younger members of the exposed groups are nearly all still alive, and one must make estimates of how many of them will eventually die of cancer from the exposure. This is done by use of mathematical models, and the results obtained can vary considerably with the model chosen.18 The UNSCEAR Report gives results for two different models, but the 1990 BEIR Report uses only the model that yields the higher risk. This risk comes out to be 0.78 chances in a million (1 chance in 1.3 million) of a fatal cancer per millirem of exposure to the whole body.
Note that this risk is based on the high doses, 100,000-600,000 mrem, received by the most exposed A-bomb survivors during a few seconds following the bomb explosions. There is a large body of evidence indicating that the risk per millirem is much less at low doses, especially if the dose is received over an extended time period; i.e. at low dose rates. In essentially all situations we will be discussing, dose and dose rates are in this low range, in which there are no direct experimental data for deriving risk estimates.
If we were to use the above stated BEIR risk estimate at low doses, we would be assuming that there is a straight line relationship, independent of dose rate, between cancer risk and radiation dose. That is, for example, given that there is a 0.78 (78%) risk of cancer from exposure to 1,000,000 mrem, we would be assuming that there is a risk of 0.78/1,000,000 from exposure to 1 mrem. Let us review the evidence demonstrating that the actual risk at low dose and low dose rate is much less than predicted by this straight line relationship.12
The theories of how radiation induces cancer predict this reduced risk effect, and experiments on both human and mouse cells exposed to radiation and grown in culture exhibit it. Experiments on laboratory animals injected with radioactive materials clearly show the reduced risk at low dose, as do experiments on animals exposed to external radiation sources. The data on radium dial painters indicate this behavior with high statistical significance, even though it involves alpha particles, a type of radiation where the low dose reduction is expected to be least important. One-third as many thyroid cancers as would be expected from the straight line theory were later found in 35,000 patients treated for hypothyroidism with radioactive iodine. In all of these cases, the straight line theory predicts far more cancers at low doses than are actually observed. There is a lot of evidence that cancers arising from lower radiation levels take longer to develop, which implies that cancers from low radiation doses would often be delayed until after death from other causes and therefore never materialize.
In view of all this evidence, both UNSCEAR12 and NCRP19 estimate that risks at low dose and low dose rate are lower than those obtained from the straight line relationship by a factor of 2 to 10. For example, if 1 million mrem gives a cancer risk of 0.78, the risk from 1 mrem is not 0.78 chances in a million as stated previously, but only 1/2 to 1/10 of that (0.39 to 0.078 chances in a million). The 1980 BEIR Committee accepted the concept of reduced risk at low dose and used it in its estimates. The 1990 BEIR Committee acknowledges the effect but states that there is not enough information available to quantify it and, therefore, presents results ignoring it but with a footnote stating that these results should be reduced. As an intermediate between the factor of 2 and 10, in this chapter I use the 1990 BEIR results reduced by a factor of 3 for situations where dose and dose rates are low. The risk is then 0.26 chances in a million (1 chance in 4 million) for a fatal cancer per millirem of exposure to the whole body.
In Chapter 6, and to a small extent in Chapters 11 and 12 of this book, however, I quote results from a variety of sources, and it would be a difficult task to go back through each of them and make corrections for the different risk factors they use. I have, therefore, not made such corrections. For many situations discussed there, cancer risks should be approximately doubled.In no case would this make a qualitative change in the conclusions.
THE MEDIA AND RADIATION
We now turn to the question of why the public became so irrationally fearful of radiation. Probably the most important reason is the gross overcoverage of radiation stories by television, magazines, and newspapers. Constantly hearing stories about radiation as a hazard gave people the subconscious impression that it was something to worry about. In attempting to document this overcoverage, I obtained the number of entries in the New York Times Information Bank on various types of accidents and compared them with the number of fatalities per year caused by these accidents in the United States. I did this for the years 1974-1978 so as not to include the Three Mile Island accident, which generated more stories than usual. On an average, there were 120 entries per year on motor vehicle accidents, which kill 50,000 Americans each year; 50 entries per year on industrial accidents, which kill 12,000; and 20 entries per year on asphyxiation accidents, which kill 4,500; note that for these the number of entries, which represents roughly the amount of newspaper coverage, is approximately proportional to the death toll they cause. But for accidents involving radiation, there were something like 200 entries per year, in spite of there not having been a single fatality from a radiation accident for over a decade.
From all of the hundred or so highly publicized incidents discussed earlier in this chapter (with the exception of the Three Mile Island accident), the total radiation received by all people involved was not more than 10,000 mrem.20 Since we expect only one cancer death from every 4 million mrem,
there is much less than a 1% chance that there will ever be even a single fatality from all of those incidents taken together. On an average, each of these highly publicized incidents involved less than 1 chance in 10,000 of a single fatality, but for some reason they got more attention than other accidents that were killing an average of 300 Americans every day and seriously injuring 10 times that number. Surely, then, the amount of coverage of radiation incidents was grossly out of proportion to the true hazard.
Another problem, especially in TV coverage, was use of inflammatory language. We often heard about "deadly radiation" or "lethal radioactivity," referring to a hazard that hadn't claimed a single victim for over a decade, and had caused less than five deaths in American history.21 But we never heard about "lethal electricity," although 1,200 Americans were dying each year from electrocution; or about "lethal natural gas," which was killing 500 annually with asphyxiation accidents.
A more important problem with TV stories about radiation was that they never quantified the risk. I can understand their not giving doses in millirem that may have been too technical for their audience but they could have easily compared exposures with natural radiation or medical X-rays. In the 1982 accident at the Rochester power plant, which was the top story on the network evening news for two days, wouldn't it have been useful to tell the public that no one received as much exposure from that accident as he or she was receiving every day from natural sources? This is not a new suggestion; similar comparisons had consistently been made by scientists for 35 years in information booklets, magazine articles, and interviews, but the TV people never used them.
Another reason for public misunderstanding of radiation was that the television reports portrayed it as something very new and highly mysterious. There is, of course, nothing new about radiation because natural radioactivity has always been present on Earth, showering humans with hundreds of times more radiation than they can ever expect to get from the nuclear power industry. The "mystery" label was equally unwarranted. As mentioned earlier, radiation effects are much better understood by scientists than those of air pollution, food additives, chemical pollutants in water, or just about any other agent of environmental concern. There are several reasons for this. Radiation is basically a much simpler phenomenon, with simple and well-understood mechanisms for interacting with matter, whereas air pollution and the others may have dozens or even hundreds of important components interacting in complex and poorly understood ways. Radiation is easy to measure and quantify, with relatively cheap and reliable instruments providing highly sensitive and accurate data, whereas instruments for measuring other environmental agents are generally rather expensive, often erratic in behavior, and relatively insensitive. And finally our knowledge of radiation health effects benefits from a $2 billion research effort extending over 50 years. More important than the total amount of money is the fact that research funding for radiation health effects has been fairly stable, thereby attracting good scientists to the field, allowing several successive generations of graduate students to be trained and excellent laboratory facilities to be developed.
Television gave wide publicity to any scientist or any scientific work indicating that radiation might be more dangerous than the usual estimates. A study by Mancuso and collaborators22 was the best-known example of such work. In spite of the fact that it was universally rejected by the scientific community,23 and completely ignored by BEIR, UNSCEAR, ICRP, and other such groups, it was frequently referred to in the media. I remember the meeting of the Health Physics Society in Minneapolis in 1978, where Mancuso and some of his critics were scheduled to speak. The TV cameras were set up well ahead of time, and they operated continuously as Mancuso presented his arguments. But when he finished and his critics began to speak, the TV equipment was disassembled and carried away.
Innumerable stories of this sort could be recited. As a result, it came to pass that the public's estimate of the cancer risk of 1 mrem of radiation (a strictly scientific question if there ever was one), was not that of the National Academy of Sciences Committee, not that of the United Nations Scientific Committee, and not that of the International Commission on Radiological Protection (all three of which agreed), but rather that of TV producers with no scientific education or experience, and possibly influenced by political prejudices.
It was my impression that TV people considered the official committees of scientific experts to be tools of the nuclear industry rather than objective experts. The facts don't support that attitude. The National Academy of Sciences is a nonprofit organization chartered by the U.S. Congress in 1863 to further knowledge and advise the government. It is composed of about a thousand of our nation's most distinguished researchers from all branches of science. It appointed the BEIR Committee and reviewed its work. The BEIR Committee itself was composed of about 21 American scientists well recognized in the scientific community as experts in radiation biology; 13 of them were university professors, with lifelong job security guaranteed by academic tenure. The United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR) was made up of scientists from 20 nations from both sides of the iron curtain and the Third World. The countries with representation on the International Commission on Radiological Protection (ICRP) were similarly distributed, and the chairman was from Sweden.
To believe that such highly reputable scientists conspired to practice deceit seems absurd, if for no other reason than that it would be easy to prove that they had done so and the consequences to their scientific careers would be devastating. All of them had such reputations that they could easily obtain a variety of excellent and well-paying academic positions independent of government or industry financing, so they were not vulnerable to economic pressures.
But above all, they are human beings who have chosen careers in a field dedicated to protection of the health of their fellow human beings; in fact, many of them are M.D.'s who have foregone financially lucrative careers in medical practice to become research scientists. To believe that nearly all of these scientists were somehow involved in a sinister plot to deceive the public indeed challenges the imagination.
The Media Institute, a Washington-based organization, published an extensive study24 of TV network evening news coverage of nuclear power issues during the 1970s. By far the most often quoted source of information was the group opposed to nuclear power, Union of Concerned Scientists, whose membership includes only about 0.1 percent of all scientists. The most widely quoted "nuclear expert" was Ralph Nader. During the month following the Three Mile Island accident, the only scientist among the 10 most frequently quoted sources was Ernest Sternglass, almost universally regarded in the scientific community as one of the least reliable of all scientists (see next section). During that time there were no pronuclear "outside experts" among the top 10 quoted sources. The only pronuclear sources in the top 10 were from the nuclear industry, who clearly had low public credibility, especially during that period.
For those who can't understand why television excessively covered and distorted information about the hazards of radiation, I believe it was because their primary concern is entertainment rather than education. One point in the ratings for the network evening news is worth $11 million per year in advertising revenue. In that atmosphere, what would happen to a TV producer who decided to concentrate on properly educating the public rather than entertaining it? As an illustration of the low priority the networks place on their educational function, I doubt if there are more than one or two Ph.D. level scientists in the full-time employ of any television network, in spite of the fact that they are the primary source of science education for the public. Even a strictly liberal arts college with no interest in training scientists typically has one Ph.D.-level scientist for every 200 students, whereas the networks have practically none for their 200 million students.
If TV producers took their role of educating the public seriously, they would have considered it their function to transmit scientific information from the scientific community to the public. But this they didn't do. They wanted to decide what to transmit, which means that they made judgments on scientific issues. When I brought this to their attention, they always said that the scientific community was split on the issue of dangers from radiation. By "split" they seemed to mean that there was at least one scientist disagreeing with the others. They didn't seem to recognize that a unanimous conclusion of a National Academy of Sciences Committee should be given more weight than the opinion of one individual scientist who is far outside the mainstream. Their position was that, since the scientific community was split, they had no way to find out what the scientific consensus was. To this I always proposed a simple solution: pick a few major universities of their choice, call and ask the operator for the department chairman or a professor in the field, and ask the question; after five such calls the consensus would be clear on almost any question, usually 5 to 0. The TV people never were willing to do this. My strong impression was that they weren't really interested in what scientists had concluded. They were only after a story that would arouse viewer interest. Clearly, a scare story about the dangers of radiation serves this purpose best.
A Poll of Radiation Health Scientists
Here and elsewhere in communicating with the public, I try to represent the position of the great majority of radiation health scientists. My understanding of this position is derived from innumerable conversations, remarks, and innuendos, but the number of people encompassed by these is rather limited. In 1982, I became concerned that I had no real proof that I was properly representing the scientific community. I, therefore, decided to conduct a poll by mail.
The selection of the sample to be polled was done by generally approved random sampling techniques using membership lists from Health Physics Society and Radiation Research Society, the principal professional societies for radiation health scientists. Selections were restricted to those employed by universities, since they would be less likely to be influenced by questions of employment security and more likely to be in contact with research. Procedures were such that anonymity was guaranteed.
Questionnaires were sent to 310 people, and 211 were returned, a reasonable response for a survey of this type. The questions and responses are given in Figure 1.
1. In comparing the general public's fear of radiation with actual dangers of radiation, I would say that the public's fear is (check one):
|2||grossly less than realistic (i.e., not enough fear).|
|9||substantially less than realistic.|
|18||slight greater than realistic.|
|104||substantially greater than realistic.|
|70||grossly greater than realistic (i.e., too much fear).|
2. The impressions created by television coverage of the dangers of radiation (check one)
|59||grossly exaggerate the danger.|
|110||substantially exaggerate the danger.|
|26||slightly exaggerate the danger.|
|5||are approximately correct.|
|3||slightly underplay the danger.|
|2||substantially underplay the danger.|
|1||grossly underplay the danger.|
3. From the standpoint of our national welfare and in comparison with other health threats from which the public needs protection, the amount of money now being spent on radiation protection in the United States is (check one)
4. How would you rate the scientific credibility in the field of radiation health of the following scientists or groups of scientists. Write a number between 0 and 100 indicating in which percentile of credibility of radiation health scientists their credibility falls; for example, "60" would mean that person's work is more credible than that of 60% of all scientists in the field, and less credible than that of 40%.
|E-82(175)||BEIR Committee (National Academy of Sciences)|
|E-81(116)||UNSCEAR Committee (United Nations Scientific Commission)|
|A-25(157)||The Ralph Nader research organizations|
|E-85(157)||International Commission on Radiological Protection (ICRP)|
|A-41(122)||Union of Concerned Scientists|
|E-85(157)||National Council on Radiation Protection (NCRP)|
|E-72(60)||Reactor Safety Study Panel on Health Effects|
|E-78(102)||Establishment Scientist A|
|E-71(113)||Establishment Scientist B|
|E-75(52)||Establishment Scientist C|
|E-80(114)||Establishment Scientist D|
|E-71(80)||Establishment Scientist E|
In the questionnaire that was sent out, the spaces above the lines were blank, to be used by the respondent to check or insert a number. In questions 1, 2, and 3 of Figure 1, the numbers on the lines are the numbers of respondents that checked that choice. In question 4, the entries on the lines start with an E or an A to designate whether the person or organization is generally considered to be part of "the Establishment," or mainstream (E), or "anti-Establishment," or out of the mainstream (A). Following the E or A is the average of all responses (which were individually numbers from 0 to 100), and in parentheses is the number of respondents who replied to that item rather than leaving it blank. In the questionnaire as sent out, the Establishment Scientists were named; there was no indication of whether the person or group was "Establishment" or "anti-Establishment".
The results listed in Figure 1 strongly confirmed my feeling that the involved scientists considered the public's fear of radiation to be greatly exaggerated and that television coverage greatly exaggerated the dangers of radiation. Question 4 confirmed my strong impression that they supported the Establishment, whose conclusions I always use, and rejected the anti-Establishment scientists and groups. Note that this was a secret poll with guaranteed anonymity for respondents.
The responses to Question 3 were really shocking to me because respondents were voting against their own best interests. In all normal circumstances, scientists will claim that their field should get more money. But in this poll, under the protection of anonymity, they said that they were already getting too much considering how trivial a danger they were protecting against. This represents a truly admirable degree of honesty.
GENETIC EFFECTS OF RADIATION11,12,25
Other than inducing cancer, the most significant health impact of low-level radiation is causing inherited disabilities in later generations. These disabilities, often called genetic defects, range from minor problems like color blindness to very serious maladies like mongolism. There is further discussion of their nature in the Chapter 5 Appendix.
Some people believe that radiation can produce two-headed children, or various types of subhuman or superhuman monsters. In order to understand why this cannot be so, one need only recognize that when a reproductive cell is struck by a particle of radiation, it has no way to "know" whether that radiation came from something produced in a nuclear reactor or from a natural source. The effects must, therefore, be the same. Since humans have always been exposed to natural radiation at intensities hundreds of times higher than what they will ever receive from the nuclear industry, no new types of genetic disease can be expected from the latter. In fact, if by some odd circumstance a new type of genetic disease were to develop, there would be no way to determine its cause, but it would be hundreds of times more likely to have been caused by natural radiation (or by medical X-rays) than by radiation from the nuclear industry. It would most likely be due to a spontaneous mutation.
Some people have the impression that radiation-induced genetic effects can destroy the human race, but that is also false. To understand this, consider the fact that new mutations are occurring all the time, in most cases spontaneously. How come the incidence of genetic disease is not continuously increasing? The reason lies in Darwin's famous law of natural selection: bad mutations reduce chances for success in reproduction and survival, and are therefore lost in the breeding process. As a very obvious example, children born with Down's syndrome almost never grow to adulthood and have offspring. Conversely, in the extremely rare situation where a mutation causes a favorable trait, it leads to increased success in reproduction and survival. Thus the law of natural selection causes good traits to be bred in and bad traits to be bred out of the human race, so any bad traits induced by radiation will eventually disappear. In the very long term, small additional radiation exposures can therefore only improve the human race. That is how evolution works. However, that effect is negligibly small. The important genetic effects are the short-term human misery created by genetic disease.
Since the radiation we can expect to receive from the nuclear industry is less than 1% of what we receive from natural sources, the genetic effects of the nuclear industry increase man's radiation exposure by less than 1% over that from natural radiation. As natural radiation is responsible for only about 3% of all normally encountered genetic defects,11 the impact of a large-scale nuclear industry would increase the frequency of genetic defects by less than 1% of 3%, or less than 1 part in 3,000.
Another way to understand the genetic effects of nuclear power is to make a comparison with other human activities that induce genetic defects. One good example is older adults having children, which increases the likelihood of several types of genetic disease. Increased maternal age is known26 to enhance the risk of Down's syndrome, Turner's syndrome, and several other chromosomal disorders, while increased paternal age rapidly raises the risk of achondroplasia (short-limbed dwarfism) and presumably a thousand other autosomal dominant diseases.27 The genetic effects of a large nuclear industry would be equal to those of delaying the conception of children by an average of 2.6 days.25 Between 1960 and 1973, the average age of parenthood increased by about 50 days, causing 20 times as much genetic disease as would be induced by a large nuclear industry.
To be quantitative about genetic effects of radiation, we can expect 1 genetic defect in all future generations combined for every 11 million mrem of individual radiation exposure to the general population. For example, natural radiation exposes the gonads to 85 mrem per year, or a total of (85 x 240 million = ) 21 billion mrem per year to the whole U.S. population. It can therefore be expected to cause (21 billion / 11 million = ) 2,000 cases per year of genetic disease, about 2% of all the cases normally occurring. (Since our present population includes an abnormally large number of younger people, this result is increased to 3%.) This is the estimate of the National Academy of Sciences BEIR Committee,11 and those of UNSCEAR12 and ICRP28 are similar. It is interesting to point out that these estimates are derived from studies on mice, because there is no actual evidence for radiation causing genetic disease in humans. The best possibility for finding such evidence is among the survivors of the A-bomb attacks on Japan, but several careful studies have found no evidence for an excess of genetic defects among the first generation of children born to them. If humans were appreciably more susceptible to genetic disease than mice, a clear excess would have been found. We can therefore be confident that in utilizing data on mice to estimate effects on humans, we are not understating the risk.
Often an individual worries about his or her own personal risk of having a genetically defective child; it is about 1 chance in 40 million for each millirem of exposure received prior to conception somewhat more for men and somewhat less for women. This is equal to the risk of delaying conception by 1.2 hours.25
It may be relevant here to mention that air pollution and a number of chemicals can also cause genetic defects. There is at least some mutagenic information29 on over 3,500 chemicals including bisulfites, which are formed when sulfur dioxide is dissolved in water (these have caused genetic changes in viruses, bacteria, and plants), and nitrosamines and nitrous acid, which can be formed from nitrogen oxides. Sulfur dioxide and nitrogen oxides are the two most important components of air pollution from coal burning. Other residues of coal burning known to cause genetic transformations are benzo-a-pyrene (evidence in viruses, fruit flies, and mice), ozone, and large families of compounds similar to these two. The genetic effects of chemicals on humans are not well understood, and there is practically no quantitative information on them, but there is no reason to believe that the genetic impacts of air pollution from coal burning are less harmful than those of nuclear power.
Caffeine and alcohol are known to cause genetic defects. One study30 concludes that drinking one ounce of alcohol is genetically equivalent to 140 mrem of radiation exposure, and a cup of coffee is equivalent to 2.4 mrem.
Perhaps the most important human activity that causes genetic defects is the custom of men wearing pants.31 This warms the sex cells and thereby increases the probability for spontaneous mutations, the principal source of genetic disease. Present very crude estimates are that the genetic effects of 1 mrem of radiation are equivalent to those of 5 hours of wearing pants.
TV coverage of genetic effects of radiation has been sparse, but there was one TV special which featured two beautiful twin babies (dressed in very cute dresses) afflicted with Hurler's syndrome, a devastating genetic disease. All sorts of details were offered on its horrors they will go blind and deaf by the time they are 5 years old, and then suffer from problems with their hearts, lungs, livers, and kidneys, before they die at about the age of 10. Their father, who had worked with radiation for a short time, told the audience that he was sure that his radiation exposure had caused the genetic disease of his children. There was no mention of the fact that the father's total occupational radiation exposure was only 1,300 mrem, less than half of his exposure to natural radiation up to the time his children were conceived. With that much exposure, the risk of a child deriving a genetic defect is one chance in 25,000; their normal risk is 3%, due to spontaneous mutations, so there is only once chance in a thousand that their genetic problems were due to their father's job-related radiation exposure.
If one is especially concerned with genetic effects, there is much that can be done to reduce them. By using technology now available, like amniocentesis, sonography, and alpha fetoprotein quantification, we could avert 6,000 cases per year of genetic defects in the United States, at a total cost of $160 million in medical services.32 By comparison, a large nuclear power industry in the United States would eventually cause 37 cases per year, while producing a product worth $50 billion and paying about $8 billion in taxes. Thus, if 2% of this tax revenue $l60 million were used to avert genetic disease, it could be said that the nuclear industry is averting (6,000 / 37 = ) 160 cases for every case it causes. If the money were spent on genetic research, it would be even more effective.
One bothersome aspect of the genetic impacts of nuclear power is the conscience-burdening idea that we will be enjoying the benefits of the energy produced while future generations will be bearing the costs. However, we must recognize that there are many other, and much more important, situations in which our generation and its technology are adversely affecting the future. Perhaps the most important is our consumption of oil, gas, coal, and other mineral resources mentioned in Chapter 3; we are also overpopulating the world, exhausting agricultural land, developing destructive weapons systems, and cutting down forests. By comparison with any one of these activities, the genetic effects of radiation from the nuclear industry are exceedingly trivial. Moreover, this is not a new situation: forests in many parts of Europe were cut down at a time when wood seemed to be the most important resource for both energy and structural materials, and local exhaustion of agricultural land, game, and fish stocks has been going on for millennia.
Nevertheless, at least in recent times, each succeeding generation has lived longer, healthier, and more rewarding lives. The reason, of course, is that each new generation receives from its predecessors not only a legacy of detriments, but also a legacy of benefits. We leave to our progeny a tremendous fund of knowledge and understanding, material assets including roads, bridges, buildings, transport systems, and industrial facilities, well-organized and generally well-functioning political, economic, social, and educational institutions, and so on, all far surpassing what we received from our forbears. The important thing from an ethical standpoint is not that we leave our progeny no detrimental legacies that would be completely unrealistic and counterproductive to all concerned but rather that we leave them more beneficial than detrimental legacies.
In the case of the nuclear industry and the genetic effects it imposes on later generations, any meaningful evaluation must balance the value to future generations of an everlasting source of cheap and abundant energy developed at a cost of tens of billions of dollars and tens of thousands of man-years of effort, against a few cases of genetic disease which we also leave them the tools to combat cheaply and efficiently.
Other Health Impacts of Radiation
When a particle of radiation penetrates a cell, the damage it does may cause the cell to die. If enough cells in a body organ die, the organ may cease to function, and this can lead to a person's death by what is termed radiation sickness. A dose of 500,000 mrem received over a short time period gives about a 50% risk of death, and with 1,000,000 mrem this risk is 100% unless there is heroic medical intervention, as by bone marrow transplants. After such an intense exposure, loss of hair, swelling, and vomiting are typical symptoms. If death does not occur within 30 days, the victim normally recovers fully.
There were a few deaths from radiation sickness in government operations, with the last one occurring in 1963, and there was at least one death from an error in a hospital. But this disease is relevant to nuclear power only in the most disastrous type of reactor accident. It will be discussed in the next chapter.
We might wonder whether diseases other than radiation sickness, cancer, and genetic defects can result from radiation. Careful studies33 among the survivors of the atomic bomb attacks on Japan revealed no such evidence. Moreover, our understanding of how various diseases develop leads us not to expect other diseases from radiation.
One other effect of radiation is developmental abnormalities among children exposed to radiation in utero.11,34 This is well known from animal studies, and there is also extensive human evidence from medical exposures and from studies of the Japanese A-bomb survivors. Among the latter, children exposed prior to birth to more than 25,000 mrem were, at age 17, an average of 0.9 inches shorter, 7 lb. lighter, and nearly a half inch smaller in head diameter than average. Among the 22 children who received more than 150,000 mrem from the bomb before the 18th week of gestation, 13 had small head size and 8 suffered from mental retardation. There were only two cases of mental retardation among those exposed after the 18th week. There was no evidence for mental retardation for exposures less than 50,000 mrem. From animal studies, it is expected that there may be slight developmental abnormalities for doses as low as a few thousand millirem at critical times during fetal development. (A woman living very close to a nuclear power plant would typically receive less than 1 mrem during pregnancy.)
Researchers have also investigated the possibility that in utero exposure may give a large risk of childhood cancer.34 It was initially reported that children whose mothers received pelvic X-rays during pregnancy had tenfold elevated risks for this disease. However, many factors other than X-rays have been found to be similarly correlated with childhood cancer, including use by the mother of aspirin and of cold tablets, and the child's blood type, viral infections, allergies, and appetite for fish and chips (this was a British study). It was shown that the original correlations would have predicted 18 excess childhood cancers among those exposed in utero to the A-bomb attacks on Japan, whereas none occurred. The initial observations could be explained as effects of the medical problems that required the mothers' X-rays. A study of children whose mothers were given X-rays for nonmedical reasons showed no evidence for increased cancer. Nevertheless, the official committees still consider this excess cancer risk to be a possibility; it is therefore taken into account in setting radiation protection regulations for occupational exposure of pregnant (or potentially pregnant) women. From the public health viewpoint, in utero exposure is not of great importance since only 1% of the population is in utero at any given time.
These in utero effects are often exaggerated in the public mind. There were widely circulated pictures of grossly deformed farm animals with claims that they were caused by in utero exposure to radiation from the Three Mile Island accident. There were no such claims to be found in the scientific literature. Recall that average exposures from that accident were 1.2 mrem, which is equal to the radiation received from natural sources every 5 days, so even if the deformities were due to radiation, they would much more likely be due to natural radiation. There have been large numbers of careful experiments on the effects of radiation to various animals I have visited farms operated for that purpose in Tennessee and in Idaho and no such effects were observed in those experiments from exposures less than several thousand millirem. It is therefore extremely hard to believe that such effects can occur at 1.2 mrem. Naturally, a small fraction of all animals (or humans) born anywhere and under any circumstances are deformed, so there would be no great difficulty in collecting pictures of deformed animals. Before one can claim evidence that these effects are due to radiation from the Three Mile Island accident, however, it would have to be shown that the number of deformed animals in that area at that time was larger than the number in that area at previous times, or in other areas at that time, by a statistically significant amount. That has certainly never been shown for any health effects among humans or animals.
IRRATIONAL FEAR OF RADIATION
Because of the factors we have been discussing and perhaps some others, the public has become irrational over fear of radiation. Its understanding of radiation dangers has virtually lost all contact with the actual dangers as understood by scientists. Perhaps the best example of this was the howl of public protest when plans were announced more than a year after the accident at Three Mile Island to release the radioactive gas that had been sealed inside the containment structure of the damaged reactor. This was important so that some of the safety systems could be serviced, and it was obviously necessary before recovery work could begin. Releasing this gas would expose no one to as much as 1 mrem, and the exposure to most of the protesters would be a hundred times less. Simply traveling to a protest meeting exposed the attenders to far more danger than release of the gas; moreover, an appreciable number fled the area, traveling a hundred miles or more, at the time of the release. Recall that 1 mrem of radiation has the same risk as driving 5 miles or crossing a street five times on foot. Needless to say, the statements of fear by the protesters were transmitted to the national TV audience with no accompanying evidence that their fears were irrational.
One disheartening aspect of that episode was the effort by the Nuclear Regulatory Commission (NRC) to handle it. An early survey of the local citizenry revealed that there was substantial fear of the release of the gas. The NRC therefore undertook a large program of public education, explaining how trivial the health risks were. When this public education campaign was completed, another poll of the local citizenry was taken. It showed that the public's fear was greater than it was before the campaign. The public's reaction on matters of radiation defied all rational explanation.
One tragic consequence of this public irrationality was the impact it had on medical uses of radiation. Radioactive materials and accelerator radiation sources are widely used for medical diagnosis and therapy, saving tens of thousands of lives each year. Even those opposed to nuclear energy claim that there may be an average of only a few hundred lives lost per year from all aspects of nuclear power (see Chapter 6), whereas most estimates are more than 10 times lower. Thus manmade radiation is saving hundreds or thousands of times as many lives as it is destroying. But as a result of the public's irrationality, patients were refusing radiation procedures with growing frequency, and physicians were becoming more hesitant to use them. In less than an hour of discussion during intermissions at a local meeting on nuclear medicine in New York City, I learned of the following situations:
I don't know of any elaborate quantitative estimates of the percentage by which fear is reducing medical use of radiation, but even if it is only 10%, the public's irrational fear of radiation is killing at least many hundred, and probably several thousand, Americans each year.
We have shown that any discussion of radiation hazards must be quantitative, giving doses in millirem. If we know the radiation dose in millirem, we can estimate the risk. We can then understand this risk by comparing it with other risks with which we are familiar. Unfortunately, the public does not go through this rational process. Largely because of poor television coverage, the public has reacted irrationally and emotionally to even the most trivial radiation hazards. A lot of education is needed here, and hopefully this chapter will contribute to that process. But in any case, the risk estimates described here will be used extensively in the rest of this book.
CHAPTER 5 APPENDIX
We have referred to "genetic defects" and "genetic disease" several times in this chapter. For those interested we here present a deeper discussion of these.11,25
The male sperm and the female egg that unite in the reproductive process each carry 23 threadlike chromosomes, each of which is composed of many thousands of genes, and it is these genes that determine the traits of the newborn individual. At conception, the corresponding chromosomes from the two parents find one another and join, bringing the corresponding genes together. In the process, a fateful lottery takes place in which the traits of the new individual are determined by chance from a variety of possibilities passed down from previous generations. While the selections in each lottery are strictly a matter of chance, the overall process of genetics is not, because an individual with traits less favorable for survival is less likely to reproduce. This is Darwin's celebrated law of natural selection: favorable traits are bred into the race, while unfavorable traits are bred out.
But not quite all of the entries in the lottery are inherited from previous generations, because there can be changes in them, called mutations. The information contained in genes is encoded in the structure of the complex molecules of which they are composed, so if some change occurs in this structure, the information can be changed, leading to an alteration of the traits the genes determine. The great majority of these altered traits are harmful and are therefore referred to as genetic defects. Thousands of different diseases are medically recognized as arising from genetic defects. In fact, an appreciable fraction of ill health, with the notable exception of infectious diseases, is due to them. These genetically related diseases range from problems that are so mild as to be hardly noticeable to some so severe as to make life impossible. In the latter category, genetic defects are responsible for something like 20% of all spontaneous abortions.
It should not be inferred that every mutation causes a genetic defect. When the chromosomes from the sperm and egg join up at conception, there is a competition between each pair of matching genes to determine which determines the trait. Some genes are dominant and others are recessive, and in the competition, the former win out over the latter.
In a small fraction of mutations, the changed gene is dominant, causing its effects to be expressed in the child with high probability. For example, achondroplasia (short-limbed dwarfism), congenital cataracts and other eye diseases, and some types of muscular dystrophy and anemia are due to this type of mutation, and it sometimes causes children to be born with an extra finger or toe (which is easily removed by cosmetic surgery shortly after birth). About a thousand different medically recognized conditions are due to dominant mutations, and roughly 1% of the population suffers from them.
But in the great majority of cases, mutations are recessive, which means that they cause characteristic diseases only in the highly unusual situation where the same mutation occurs in the corresponding genes from both parents. Sickle cell anemia, cystic fibrosis, and Tay-Sachs disease are relatively well-known recessive diseases, but most of the 500-1,000 known recessive diseases are extremely rare, and only about one person in 1,000 suffers from them.
Another type of genetic damage involves the chromosomes rather than the genes of which they are composed. Chromosomes can be broken recall that they are like threads often followed by rejoining in other than their original configuration; for example, a broken-off piece of one chromosome can join to another chromosome. In some situations, there can be an entire extra chromosome or missing chromosome. About 1 person in 160 suffers from a disease caused by some type of chromosome aberration. Down's syndrome (mongolism) is perhaps the best-known example.
There is one type of genetic defect that is rather different from the ones we have been discussing. About 9% of all live-born children are seriously handicapped at some time during their lives by one of a variety of diseases that tend to "run in families," like diabetes, various forms of mental retardation, and epilepsy, in which genetic factors play a role but other factors are also important. It is estimated that the genetic component of these irregularly inherited diseases is something like 16%, with the other 84% due to environmental factors, food, smoking habits, and the like. Effectively, then, 16% of 9%, or 1.4%, of the population suffers from these diseases due to genetic factors. Adding them to the victims of dominant, recessive, and chromosomal disorders, we find that about 3% of the population is afflicted with some type of genetic disease.
Genetic Effects of Radiation
New mutations are constantly occurring in the sex cells of people destined to bear children, but this does not cause the 3% to increase, because mutations from earlier generations are being bred out by natural selection at an equal rate. That is, there is an equilibrium between introduction of new mutations and breeding out of old mutations. The great majority of new mutations occur spontaneously as a random process, due to the random motions that characterize all matter on an atomic scale. Occasionally these motions cause a complex molecule to break apart or change its structure, and that can result in a mutation. Similar damage can be done by foreign chemicals, or viruses, or radiation which happen to penetrate into the cell nucleus where the chromosomes are housed, but here we are concerned with the last of these, the genetic effects of radiation.
It should not be inferred that a particle of radiation striking the sex cells always leads to tragedy. On an average, the nucleus of every cell in our bodies is penetrated by a particle of radiation once every 3 years due just to the natural radiation to which we are all exposed, but this is responsible for only one-thirtieth as much genetic disease as is caused by spontaneous mutations (that is, 1/30 of 3%, or 0.1%, of the population suffers from genetic disease caused by natural radiation).
In the introduction to Chapter 5, we discussed the number of gamma rays that strike an average person per second. To understand how these numbers are derived requires use of some definitions. One millirem (1 mrem) is defined for gamma rays as absorption by the body of 10-5 joules of energy per kilogram of weight. One MeV of energy is defined as 1.6 x 10-13 joules (J), and an average gamma ray from natural radiation has an energy of about 0.6 MeV, which is therefore (0.6 x 1.6 x 10-13= ) 1 x 10-13 J; 10-5 J then corresponds to 108 gamma rays. An average person weighs 70 kg (154 lb.), hence 1 mrem of radiation exposure corresponds to being struck by (70 x 108 = ) 7 x 109 gamma rays. Natural radiation exposes us to about 80 mrem/year,3 which corresponds to (80 x 7 x 109 = ) 5 x 1011 gamma rays. There are 3.2 x 107 seconds in a year, so we are struck by (5 x 1011 / 3.2 x 107 = ) 15,000 gamma rays every second. In a lifetime we are struck by about (72 x 5 x 1011 = ) 4 x 1013 = 40 trillion gamma rays.
A medical X-ray may expose us to 50 mrem, which would be (50 x 7 x 109 = ) 3.5 x 1011 gamma rays. But the energy of X-rays is typically 10 times lower than the 0.6 MeV we have assumed for gamma rays, so ten times as many particles would be required to deposit the same energy; this is (3.5 x 1011 x 10 = ) 3.5 trillion X-ray particles striking us when we get an X-ray.
Since 1 mrem of gamma ray exposure corresponds to being struck by 7 x 109 particles, and the cancer risk from 1 mrem is 0.26 x 10-6, the risk from being struck by one gamma ray is 1 chance in (7 x 109 / .26 x 10-6 = ) 2.7 x 1016, or 1 chance in 27 quadrillion.
Since natural radiation exposes us to 4 x 1013 gamma rays over a lifetime, the probability that it will cause a fatal cancer is (4 x 1013 / 2.7 x 1016 = ) 1.5 x 10-3, 1 chance in 700. Our total probability of dying from cancer is now 1 chance in 5, whence (1/700 / 1/5 = ) 1/140 of all cancers are presumably caused by radiation.