The Physician and Environmental Radiation Hazards

THE

PHYSI~IAN

AND

ENVffiONMENTAL RADIATION HAZARDS ERIC REISS, M.D. MALCOLM L. PETERSON, M.D.

Modern science and technology have brought about an extraordinary improvement in medical diagnosis and treatment. Progress, however, may not be an unmixed blessing; it frequently creates new problems requiring attention and eventual solution. The purpose of this presentation is to make an appraisal of exposures to various sources of radiation with emphasis on aspects that are of greatest interest to pediatricians. TI1c damaging effects of large doses of ionizing radiation were recognized soon after Roentgen had discovered x-rays (1895) and the Curies had purified radium ( 1898), but not until considerable human suffering had been inflicted. Radiation burns, cataracts, and the induction of leukemia in response to high doses of ionizing radiation were gradually recognized. As experience increased, more subtle long-range effects were appreciated. In 1928 the International Commission on Radiological Protection was formed and began to formulate standards of safety. This Commission and the National Committee on Radiation Protection and Measurements have served as the principal agencies for setting standards through the years. In 1959, concern about increased environmental contamination with radioactive matter from industrial uses of atomic energy and weapons-test fallout resulted in the establishment of the Federal Radiation Council, which is now required by law to develop standards for use by federal agencies. Thus the control of radiation has been the subject of continuous expert study for a long time. As new data have become available and From the Departments of Medicine (Metabolism and Gastroenterology Divisions) and Preventive Medicine (Irene \\falter Johnson Institute of Rehabilitation), Washington University School of Medicine, St. Louis.

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4)0

THE PHYSICIAN AND ENVIRONMENTAL RADIATION HAZARDS

potential hazards have been better defined, there has been a consistent tendency to decrease the allowable radiation exposure of populations. GENETIC EFFECTS

Genes are characterized by an inherent stability which ensures that each duplication produces identical copies. This stability, however, is not absolute, and changes in genes do occur on rare occasions. These changes are known as mutations. Mutation

The phenomenon of mutation has been rightly called the fountainhead of evolution. It has made possible the generation of many varieties of living forms, some of which have become established, owing to their suitability for survival in particular environments. \Vhy, it may then be asked, are mutations arising today potentially harmful? Mutations that appear today have probably occurred repeatedly during the long history of man's development. Those favoring survival have become a part of the normal genetic complement; deleterious genes have probably arisen and been eliminated on many occasions in the past. New mutations are likely to recreate earlier constituents of the genetic make-up which have been eliminated by natural selection. Efforts should therefore be directed towards keeping the mutation rate as low as possible. The statement that most mutations are harmful requires one modification. If an abnormal gene is associated with selective disadvantages, it will sooner or later be eliminated unless new mutations bring it into being again. Under certain circumstances, however, an abnormal gene can confer selective advantages to the heterozygote, even though it is decisively harmful in the homozygote state ("heterosis") .5 The best studied example in man is the apparent resistance to falciparum malaria of persons who are heterozygous for the sickle cell gene. This would confer considerable selective advantage to people living in malariainfested regions. The frequency of heterosis is unknown, but it is possible that many abnormal genes are maintained in populations by this mechanism rather than new mutations. MuTAGENIC AGENTS. Industrial and automobile exhaust fumes, food additives, tobacco, drugs, hormones and many other agents in common use must be considered possible sources of genetic damage to man. Although mutations can be induced in experimental animals by various chemical agents, the mutagenic capacity for these environmental factors has not been demonstrated in man. RADIATION-INDUCED MuTATION. The mutagenic potential of radiation

ERIC REISS AND MALCOLM L. PETERSON

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was first demonstrated in 1927 by the classic experiments of H. J. Muller. Exposure of fruit flies to radiation results in many different kinds of mutations. At any given dose rate the mutation rate is directly proportional to radiation dose at all dose levels studied so far. Glass and Ritterhoff8 in a remarkable experiment have recently shown that this linear relation between dose and mutation holds true for doses as low as 5 roentgens. Geneticists are generally agreed that there is probably no threshold dose of radiation below which no genetic effects occur, and no informed person doubts that this conclusion, which is based on experimentation with the fruit fly, holds true for man. Until recently it was assumed that the mutation rate is independent of the rate at which exposure to radiation takes place. Experiments by Russell, 22 however, have shown that in mice the same dose of radiation induced fewer mutations when given at a low dose-rate than at a high dose-rate. These observations are of great importance in considerations of background and fallout radiations, which are delivered at a low rate for a long time. MuTATION RATES. Estimation of spontaneous and induced mutation rates has proved exceedingly difficult, and only crude guesses are available. Some of the problems include the unavailability of reliable statistics for many defects, different mutation rates for different genes, uncertainty about the number of human genes, and difficulties in detecting some abnormalities. Most natural mutation rates in man have been calculated to lie between I0- 5 (one mutation per 100,000 sex cells per generation) and 10-4 • The average mutation rate per gene approximates 10-5 • Assuming that every human being carries only 20,000 genes, 20 per cent of all people carry one or more newly arisen mutant gene. 5 • 21 Since most mutant genes are recessive, only a few of them become manifest in the first generation as obvious defects. Perhaps the magnitude of the affected population can be appreciated from the United Nations estimate that about 6 per cent of all live-born infants have visible defects of genetic origin. 21 Of the 6 per cent, 2 types of genetic abnormality are of special importance to this discussion because they can be produced experimentally by radiation in species other than man. One per cent of live births show known gross chromosomal aberrations of the type discussed elsewhere in this symposium (mongolism, Turner's syndrome, Klinefelter's syndrome, and so on). Since most persons so affected are sterile or have low reproductive capacity, these defects are rarely transmitted to subsequent generations. The other genetic abnormality involves point mutations, i.e. single gene alterations that give rise to harmful effects with known inheritance patterns. One per cent of live births are so affected. Only a small fraction of naturally occurring mutations can be at-

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THE PHYSICIAN AND ENVIRONMENTAL RADIATION HAZARDS

tributed to background radiation (approximately O.l rad per year).* The dosage of radiation required to double the mutation rate in man has been estimated to be between 10 and 100 rads, with 15 to 30 rads as the most probable value for acute exposure and 100 rads for chronic exposure. 21 Physicians treating young patients have a special obligation to keep gonadal exposure to a minimum, since even small changes of the mutation rate have serious long-range biologic and social implications. The problem of radiation-induced mutations is so important that ill-advised statements concerning it should be strenuously avoided. Some speak of "negligible" radiation exposure. Since radiation dosage and mutation are related linearly, the term "negligible" has no scientific meaning. Radiation exposure that involves a statistically small risk for an individual may produce many thousands of genetic defects when the population of the world receives this exposure. If these distinctions were kept in mind, much acrimonious and meaningless public debate could be avoided. The Committee on Environmental Hazards of the American Academy of Pediatrics has recently issued a statement that assesses the genetic effects of fallout in part as follows: The very careful and exhaustive studies carried out by the Atomic Bomb Casualty Commission on the populations of Hiroshima and Nagasaki in Japan have thus far failed to detect any genetic effects that could be attributed to radiation exposure from the bomb explosions ... ts

This statement is erroneous and embodies a misleading limitation. A highly probable genetic effect has, in fact, been observed in exposed Japanese populations: namely, a change in the sex ratio of children of irradiated parents in the direction of fewer males. 21 The misleading aspect of the Academy's report ignores the recessive character of most radiation-induced mutations. These would not be readily detected in the first generation, but would become apparent in future generations when homozygotes are produced. Sources of Radiation

The principal sources of radiation exposure are listed in Table 5, and their relative contributions to hereditary effects are indicated. For purposes of comparison, natural background radiation is assigned an arbitrary unit of 1. This radiation is derived chiefly from cosmic rays and terrestrial sources and delivers whole body radiation. *For sake of uniformity, tissue doses are expressed in rad(s), which is the preferred unit and is defined as 100 ergs per gram. In the literature, doses arc often stated in rem (s), which is the dose in rad (s) multiplied by the RBE (relative biological effec· tiveness). Since the RBE of x-, beta and gamma radiation is one, rem and rad may be used interchangeably for these forms of radiation.

ERIC REISS AND l\fALCOLM L. PETERSON TABLE

453

5. Radiation from Various Sources HEREDITARY EFFECTS

Natural sources ........................ . 1.00 Medical radiation ........................ . 0.30 Fallout from tests up to December, 1961 .... . 0.11 From fallout if testing continues* ........ .

0.23

Adapted from U.N. Report, 1962. * Assuming yearly injection into atmosphere of 1 megacurie of strontium-90 and 102s atoms of carbon-14. 21

MEDICAL RADIATION. This is clearly of greatest significance to physicians. The estimate in Table 5 that medical exposure contributes approximately 30 per cent of the radiation from natural sources may well represent a minimum value. Wide variations can be expected, depending on the intensity of medical care in the community and the skill of the physicians performing the examinations. Certain types of examination, mainly those of the pelvic region, contribute 90 per cent of the genetically significant radiation dose. A rough appreciation of the order of magnitude of radiation doses associated with various diagnostic studies may be obtained by inspection of Table 6. The "average" radiologic examination of "abdomen and colon," including the fluoroscopy, contributes a gonadal dose of 2 rads, or approximately 20 times the yearly exposure from background sources. An impressive feature of the table is the large doses attributable to fluoroscopy. The medical profession has taken an increasing interest in measures designed to minimize gonadal exposure from diagnostic studies. Under the leadership of the American College of Radiologists, an intensive program of physician education has been conducted. Frequent inspection of radiographic equipment (especially fluoroscopes) by competent health physicists is now routine practice in good medical institutions. Gonadal shielding has been recommended for studies where this safety TABLE

6. Female Gonadal Dose from Radiologic Procedures (in Rad per Examination) RADIOGRAPHY

"Skeleton-pelvic region" ............. . "Urinary tract" .......................... . Stomach and upper gastrointestinal tract .... . Pelvimetry ........................... . "Abdomen and colon" .. . Chest ............................ . Mass surveys .... . Dental ................................... .

FLUOROSCOPY

1.0 1.0

0.3

0.75

2.5 0.5 0.0003 0.003 0.002

0.015

1.5

Adapted from U.N. Report, 1958. 20 Radiography dosage estimate based on examinations by radiologists as well as nonradiologists; fluoroscopy by radiologists only. Age of patients, 12 to 29 years.

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THE PHYSICIAN AND ENVIRONMENTAL RADIATION HAZARDS

practice is possible. There is a growing tendency to avoid unnecessary examinations. Despite these improvements, carelessness persists and constant vigilance is required. Every physician requesting radiographic examinations of his patients ought to know the standards of practice of the consulting radiologist. If he performs his own examinations, he has an obligation to consult a competent expert to check his procedures and to make sure that his equipment delivers the minimum dose needed to obtain a satisfactory study. Some medical societies have facilitated this important safety check by arranging for their members initial and follow-up consultations with radiation monitoring firms. Since dental use of x-ray is a factor in this exposure (Table 6), dentists and dental societies would be well advised to institute similar health physics practices. FALLOUT. Of the many radioactive materials in worldwide fail out from weapons testing, cesium-137 and carbon-14 contribute the largest genetically significant dose. Since the isotopes of strontium are concentrated in bone and iodine-131 is concentrated in the thyroid, these radioactive substances contribute little radioactivity to the gonads. Milk and meat are man's chief source of cesium-137. The food chain begins with incorporation of the fission product from fallout into plants, both by direct contamination of foliage and by uptake from the soil. When cows and other meat-yielding animals ingest these plants, the cesium-137 enters the metabolic pathways of potassium. In turn, man derives 60 per cent of his intake of cesium-137 from milk and 25 to 35 per cent from meats. Gastrointestinal absorption is virtually complete. Distribution in the body generally follows that of potassium, so that gonadal radiation from this isotope is significant. Various tissues have different cesium-potassium ratios. When a single dose of cesium-137 is injected, 10 to 15 per cent is excreted rapidly with a half-time of 1.0 to 1.5 days; the remainder is excreted more slowly with a half-time of 100 to 120 days. 21 This relatively rapid turnover serves as a protective factor; cesium-137 has a physical half-life of 30 years. Carbon-14 is the most important of the genetically significant corn: ponents of fallout. This isotope, in contrast to most of the fission products, has a very long half-life, 5600 years, so that, once created, it is recycled many times through the biosphere. Carbon-14 is normally produced in the atmosphere by cosmic-ray bombardment: neutrons knocked out of atoms by this bombardment are captured by nitrogen in the air, and the nitrogen is converted to carbon-14. Nuclear weapons testing increases the rate of formation of carbon-14 by the same mechanism, i.e. neutron bombardment of atmospheric nitrogen. By rnid-1959 a 27 per cent increase in the northern tropospheric content of carbon-14 had been rneasured. 7 Estimation of gonadal exposure from

ERIC REISS AND MALCOLM L. PETERSON

455

carbon-14 requires consideration not only cif its rate of formation, but also of the rate of mixing with various carbon pools that occur in nature. Mixing of newly formed carbon-14 with atmospheric carbon dioxide and with the carbon dioxide in ocean waters has a diluting effect. From the rates of mixing, the size of the various carbon pools, and the intensity of testing, carbon-14 content of the biosphere can be calculated for future times. A survey of radiation dose commitments attributable to fallout from the assumed weapons testing practice, 1954-1961, is given in Table 7. Carbon-14 will contribute a large fraction of the radiation dose to gonads as well as to other tissues. The effect of carbon-14 is protracted; only 10 per cent of the total dose attributable to it will be biologically effective by the year 2000. By contrast, all the cesium-137 from past testing is expected to have exerted its activity by that time. Since estimates of genetic damage resulting from carbon-14 released during weapons testing will depend on whether only the present generation or all future generations are considered, there is abundant opportunity for confusion. TABLE

7. Survey of Dose Commitments from Fallout

TISSUE OR ORGAN

SOURCE

Gonads .•................... External Internal Cs'•r

C" Cells lining bone surfaces ..... External Internal Sr90

Cs'•7

cu

Bone marrow ................ External Internal Sr90 Qg137

Q14

DOSE

FRACTION OF

COMMITMENT

DOSE COMMITMENT

(RAD)

REACHED BY

0.03

0.97

0.011 0.07 0.111 0.03

0.1 0.42 0.97

0.079 0.019 0.116 0.244

0.03 0.04 0.014 0.07 0.154

2000

1.0

0.91

1.0 0.1 0.54 0.97 0.91

1.0 0.1 0.56

Adapted from U.N. Report, 1962.21 SOMA TIC EFFECTS

By definition, somatic effects of radiation involve altered biologic behavior of any cell other than gonadal cells. The manifestation of this effect depends largely on the radiation dose and the area of the body that is irradiated. Acute whole body radiation in large doses causes the acute radiation syndrome. Accidental exposure to high levels of

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THE PHYSICIAN AND ENVIRONMENTAL RADIATION HAZARDS

radiation from weapons tests or reactor operations has provided information about this syndrome. It has been found that the LD-50 for man is 300 to 600 roentgens of whole body radiation. 25 Acute radiation sickness is a well described entity, but is not within the scope of this discussion.10 Some of the somatic effects which can be attributed to lower doses of radiation include the induction of leukemia and other malignant diseases, formation of cataracts, and shortening of the life span. Dose-Response Relation

The apparent linearity of the relation between dose and response was emphasized in the foregoing discussion of genetic effects of radiation. Our understanding of the dose-response relation for somatic effects is incomplete, and there appears to be little hope of resolving this problem soon. Thresholds, radiation levels below which no observable changes occur, have been noted for some somatic effects in experimental animals. If one could be certain that this is true for all somatic radiation effects and could experimentally identify the threshold level, the development of radiation standards would be a relatively simple matter. Unfortunately, information is sparse, and the complexities of a rigorous experimental evaluation are formidable. A few examples will suffice to illustrate the problem: (I ) The role of co-carcinogens (hormones, viruses, chemicals) is almost completely unknown in radiation carcinogenesis. Co-carcinogens are known to alter the dose-response curve in chemical carcinogenesis. ( 2) Experimental data on tumor and leukemia induction that appear to demonstrate a linear dose-effect relation have been obtained only in the higher dosage range (I 00 rads and above). An enormously large experiment would be required to demonstrate an effect at lower doses comparable to those from diagnostic x-ray and fallout. ( 3) It has been suggested that, for the initial changes in any structures of an organism at the molecular level, no threshold dose exists, whereas compensatory responses and regenerative processes permit a threshold at cellular, tissue and organ levels. 21 A voluminous literature attests to leukemogenesis in man at high doses. 4 The study of Heyssel and colleagues 11 on Hiroshima survivors conducted under the auspices of the Atomic Bomb Casualty Commission is of particular interest. An estimate of radiation dosage was made on the basis of such factors as the characteristics of the bomb, distance of exposed persons from the center of the detonation, and shielding. A perceptible increase of leukemia occurred about one and a half years after the bombing. The greatest number of cases of leukemia was reported after six to seven years. Heyssel's data suggest a linear relation between dose and the incidence of leukemia down to a dose of 77 rads. Yet both the estimates of radiation and the incidence of leukemia are

ERIC REISS AND MALCOLM L. PETERSON

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subject to error. Even if one could assume linearity down to a dose as low as 77 rads, the critical lower doses still remain unexplored. The unresolved dilemma about the dose-response question for somatic effects makes any estimate of risk dependent on the basic assumptions. This can be illustrated by a recent Federal Radiation Council Report 19 in which estimates are given for the number of cases of leukemia expected to occur in the United States during the next 70 years. On the basis of the present incidence, a total of 840,000 cases may be anticipated. Of these, anywhere from zero to 10 per cent may be caused by natural radiation. If a threshold exists, none of the cases of leukemia could be attributed to fallout because the radiation dose is of such a low magnitude. If there is no threshold and one can extrapolate from high doses, the Council estimates that as many as 2000 additional cases of leukemia may result from all tests conducted through 1961. By similar calculation, the risk to an individual of developing the disease is zero to 1/100,000, depending on whether a threshold or no-threshold assumption is made. Acceptance of a no-threshold hypothesis when a threshold in fact exists would cause overestimation of radiation damage. On the other hand, a threshold assumption when none exists would result in an underestimation. Since the scientific evidence is inconclusive, taking a chance on erring in the direction of overestimation (nothreshold) has been considered the wisest policy by most of the authorities responsible for the development of standards. Unfortunately, in this instance, public policy must be set in the absence of adequate scientific information. RADIATION-INDUCED l\1ALIGNANCIES, The carcinogenic potential of high doses of radiation based on the experience in radium dial painters, patients treated with x-rays for certain diseases, and survivors of the bombing in Japan is well established. Because of its relevance to the subsequent discussion, only carcinoma of the thyroid is briefly considered here. A significantly increased incidence of thyroid cancer has been reported in children who received radiation of the neck in the treatment of thymic enlargement. 24 This observation has been abundantly confirmed by others. 1 In these studies there is a latent period of 5 to 20 years between radiation and detection of cancer. Statistical evidence on carcinogenesis is available only in a high dosage range ( 100 to 200 rads and above). Because of the unsettled dose-response problem, no reliable estimate of thyroid carcinogenesis can be made for low doses. On the no-threshold hypothesis, and taking into account all available data, Beach and Dolphin 1 of the United Kingdom Atomic Energy Authority have recently calculated the incidence of thyroid cancer following radiation as 35 per million exposed per rad. If x-rays can be carcinogenic to the thyroid, other forms of radiation

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THE PHYSICIAN AND ENVIRONMENTAL RADIATION HAZARDS

no doubt have the same potential. Until evidence to the contrary is available, the beta radiation from iodine-131, in equivalent doses and dose-rates, must be considered to have the same biologic effect as x-rays. Comparison of the data on x-rays to the necks of children with observation in adults treated with iodine-131 strongly suggests that the thyroids of adults are more resistant to the carcinogenic effects of radiation than those of children. Convincing evidence that iodine-131 causes an increased incidence of thyroid cancer in adults is not available. X-ray experience with the children, however, has resulted in the standard practice of avoiding iodine-131 therapy for all patients under 40 years of age. Radiation therapy of thyrotoxicosis in young people is contraindicated except under most unusual circumstances. ENVIRONMENTAL RADIATION SOURCES Industrial and Research Applications of Nuclear Technology

Within 40 years, about half of electric-powered generating capacity in the United States will be derived from nuclear power reactors. 27 Tracer technology in basic and applied research has become standard technique. Propulsion of rockets, planes, and ships by nuclear power sources is operational or planned. All these applications are potential sources of environmental contamination through waste disposal or accidental release. Radioactive waste disposal is achieved by ( 1) storage to prevent exposure of man to the radionuclides before they decay into nonradioactive substances and ( 2) dispersal into reservoirs which permit enormous dilution. An example of the storage technique is the tanks which are held in some Atomic Energy Commission installations. These contain concentrates of radioactive wastes derived mostly from fuel reprocessing. Estimates of storage time required to achieve the necessary decay may exceed the known life of the container materials, so that at present there is no permanent answer to the problem of waste disposal of some substances. The dilution technique as practiced today includes discharge of gases of low radioactivity into the air and discharge of fluids of low activity into oceans or rivers. These are mostly effluents from reactors. Disposal of urine and feces from patients given radioisotopes follows the same principle, i.e. dilution before possible recycling to man from his environment. Some disposal techniques are combinations of the storage and dilutions principles. In Oak Ridge and Hanford many liquid wastes are poured into the soil, where they very slowly migrate to greater depth. A premise of this mode of disposal is that the radionuclides will decay before they have moved far in the soil; if some do reach the water tables, they will be greatly diluted before man is exposed to them.

ERIC REISS

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MALCOLM L. PETERSON

459

The purpose of these disposal techniques is to prevent exposure to man in concentrations which are measurably above background. Nevertheless, reconcentration of the radionuclides in our foodstuffs has been observed, and accidental exposure to the concentrated wastes has occurred. Reconcentration of the radionuclides from radioactive wastes has been impressively demonstrated in many areas. In Washington State the plankton of the Columbia River incorporates the radionuclides which are discharged in the cooling wastes from the Hanford installation of the Atomic Energy Commission. 16 The plankton are eaten by the fish, and the concentrations of radioactive substances in the fish are much higher than in the river water. Transportation of radioactive wastes has been carried out under strict regulations of the Atomic Energy Commission. Nevertheless accidents have occurred. Unexpected events have also occurred in disposal of wastes in the ocean. For example, a barrel containing radioactive sodium wastes failed to sink and for some time floated off the New England coast before it could be sunk. Although an impressive safety record has been established for reactor operations, some serious accidents have occurred. One of the most dramatic took place at vVindscale (England) in 1957.3 • 28 Despite safeguards, an accident in the operation of the reactor caused not only intense local radiation, but also some fallout throughout Europe. Fallout

Since the beginning of the nuclear age in 1945, and especially since 1954, much public discussion has been focused on worldwide fallout of radioactive debris produced by nuclear weapons testing. Patients and the parents of children often consult their physician for advice about the significance of fallout and the indications for various possible countermeasures. An exhaustive body of information concerning fallout now exists. The two United Nations Reports are invaluable sources of data and interpretations.20 • 21 "Radiological Health Data" is a monthly publication issued by the Public Health Service. Publications of the Atomic Energy Commission Health and Safety Laboratory and testimony submitted to the Joint Congressional Committee on Atomic Energy also are useful sources of information. In addition, private organizations now issue factual summaries. STRONTIUM-90. The general pattern of strontium-90 fallout and its passage through the food chain were reviewed by Forbes. 6 To avoid repetition, only a few pertinent points will be reviewed and extended. Since publicity is often given to the strontium-90 content of milk, some mothers have assumed that they should decrease the child's milk

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THE PHYSICIAN AND ENVIRONMENTAL RADIATION HAZARDS

intake and thereby limit ingestion of the isotope. Such a change of diet habits would not only fail to accomplish the desired objective, but would probably also produce a greater health hazard than that which the anxious mother seeks to avoid. Milk and milk products, which constitute the most important source of calcium, contain less strontium-90 per unit of calcium than most other calcium-containing foods. Thus, in a typical adult diet, approximately 60 per cent of the dietary calcium, but only 45 to 50 per cent of the ingested strontium-90, is derived from milk. Nutritionists agree on the dietary importance of milk as a source of protein as well as of calcium; hence a decrease of milk consumption by children would surely be undesirable. Most of the strontium-90 can be removed from milk by running it over ion-exchange resins. This process has not yet been adapted on a commercial scale, and the milk so processed has not been widely tested for safety with respect to factors other than radiation. Since fallout is often unevenly distributed throughout the country, the strontium-90 content of milk may be much lower in some sections than in others. To obtain processed milk from low fallout areas is impracticable. It has been suggested that increasing the calcium intake with tablets or wafers not containing strontium-90 would reduce the body burden of the isotope, and some experimental evidence points to the effectiveness of this approach. The safety, however, of very high calcium intakes is open to question. It appears, therefore, that no satisfactory countermeasures exist for strontium-90 once it has been introduced into the environment. Avoidance of unwise changes in dietary habits is the best that an individual pediatrician now has to offer to his patients. IomNE-131. This fallout isotope is discussed in detail since it illustrates many of the problems that the modern era has created for the physician, and especially the pediatrician. Iodine-131 was not at first suspected of requiring serious attention as a component of fallout. \Vith a half-life of only 8.1 days, most of the isotope was expected to have decayed by the time it reached the food chain. Monitoring for P 31 was so sporadic that there is virtually no reliable environmental information until 1957. In 1960 Knapp 12 focused attention on the uneven distribution of fallout with high environmental isotope concentrations in some geographic areas ("hot spots"). When more funds were made available to the Public Health Service for monitoring, the characteristic pattern of P 31 fallout became evident, and detailed data are available since the resumption of testing in the fall of 1961. The hot spot problem is illustrated in Table 8. In the 1957-1958 period, unusually high thyroidal radiation was received by children in Salt Lake City and St. Louis. Since background accounts for approxi-

ERIC REISS AND MALCOLM L. PETERSON TABLE

8. Estimated Thyroidal Irradiation (Rad) from Fallout APRIL, -MAY,

Cincinnati . . . . . . . . . . . . . New York ............. Sacramento. . . . . . . . . . . . . Salt Lake City. . . . . . . . . . St. Louis.. . . . . . . . . . . .

1957 * 1958**

0. 85 0.49 0 . 19 1 . 56 1. 61

MAY,

1958** 1959

-APRIL,

0.20 0.15 0.19 0.16 0.47

/131

461

in Children 1961 *** 1962

SEPTEMBER, -AUGUST,

0.21 0.18 0.08 0.63 0.32

*These doses are lower than those given by Knapp. 12 Our calculations are based on the assumptions of the Federal Radiation Council. (29,200 micromicrocuries ingested P 31 = 0.5 rad thyroid radiation for children; one quart of fresh milk consumed daily; 30 per cent uptake; 2 gm. thyroid; effective half-life 7.6 days.) The Radiation Protection Guide for thyroid is 0.5 rad per year (Table 9). **Environmental data from reference 9. ***Environmental data from reference 17.

mately 0.1 rad thyroid radiation, the values in these cities were 16 times greater than background radiation. More extreme instances of hot spots are now on record. In April, 1953, a rainstorm brought down radioactive debris over the Troy, New York, area a few days after the Simon test in Nevada. According to Lapp,l 3 the F 31 contamination in Troy was in the range of 2 to 4 curies per square mile. Cattle grazing in this area would have yielded milk containing 100,000 micromicrocuries per liter. Lapp has estimated that some 10,000 babies in the 6- to 18-month age group living in the Troy-AlbanySchenectady area may have been exposed to a thyroid radiation of about 10 rads. In 1953 no adequate monitoring network existed, and the available data were classified as secret. Hence no protective actions could be taken by public health authorities. In late July, 1962, however, the concentration of 1131 in milk exceeded 200 micromicrocuries per liter in Utah. The levels rose from "not detectable" on July 6 to 1660 micromicrocuries per liter on July 20, then decreased to 450 micromicrocuries and rose again to 2050 micromicrocuries per liter on July 25. This radioactivity was attributed to the Nevada tests of July 6 and July 12. Further study showed that the milk from some areas was much more heavily contaminated than that from others. Preventive actions initiated by state and city health officials resulted in limitation of the F 31 intake by the population.29 These examples illustrate the problem. Iodine-131 is discussed in some detail because it affords unique opportunities for radiation protection. With knowledge of the physical and biologic characteristics of the isotope, the pattern of fallout, and the food chain, protection is possible, and it is relatively simple. Because of rapid decay in the environment, any indicated countermeasures usually need be applied for only short periods (weeks) .

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THE PHYSICIAN AND ENVIRONMENTAL RADIATION HAZARDS

Iodine-131 is a component of tropospheric fallout and descends to earth with rainfall. Owing to the short physical half-life, much decay may occur before the isotope reaches the earth if there is a long delay between the explosion and rainfall. In any particular locale the fallout pattern is usually characterized by sharply rising levels followed by rapid decay (see Utah experience) . The geographic area in which p:n will be high is unpredictable, for this depends not only on the site of the test explosion, but also on the vagaries of wind patterns and local weather conditions. \Vhen P 31 is deposited on a pasture, it is ingested by cows, which then secrete a small fraction in the milk. Except for areas in the immediate vicinity of a test where P 31 may reach the body fluids by inhalation, milk constitutes the chief human source of P 31 • Although P 31 contaminates many foods, fresh milk is consumed soon after being shed, so that there is little time for radioactive decay. Gastrointestinal absorption is complete, and 99 per cent of the total body iodine is found in the thyroid. Possible approaches to radiation protection have been considered by the National Advisory Committee on Radiation. 15 ... One of the first countermeasures to consider against I-131 is the placing of all children of early age, lactating mothers and pregnant women on evaporated milk or powdered dry skim milk. This provides protection for the most susceptible individuals within the population. Since the average transit time for evaporated milk and powdered milk to reach the consumer is at least two months, close to 100 per cent reduction in I-131 intake is provided. The countenneasure produces no deleterious side-effects to health. The dairy industry has sufficient capacity to supply the additional quantities of processed milk which the women and children may need. Costs are reasonable and no legal problems are foreseen. The Surgeon General has authority to recommend the countermeasure when requested. Other control measures concerning the milk supply which have been considered include the use of (a) refrigerated storage of fluid milk, (b) frozen fluid milk, (c) frozen whole-milk concentrate and (d) canned, sterile whole-milk, each of which has been stored an appropiate time. Although such countermeasures are effective in reducing population exposures from I-131, the milk industry does not have, at the present time, the storage, refrigeration or processing capacities to make them applicable for the entire population. However, a combination of these measures may be helpful in reducing exposure to a portion of the population. A countermeasure comprising the pooling of fresh fluid milk from regions of high contamination with that produced in uncontaminated areas has been suggested. Such a countermeasure, however, is considered generally unsatisfactory. The logistics of pooling milk of high and low radionuclide content are difficult and costly. Furthermore, it would require a detailed knowledge of radionuclide levels that are not now generally available. The decontamination of I-131 from milk by the ion-exchange method is another countermeasure which has been studied intensively. However, at this time, the research needed to bring it to the point where it is fully satisfactory has not been completed. Furthermore, the ion-exchange process poses a number of legal questions due to changes in the composition of the decontaminated milk which are of concern to the Food and Drug Administration. These questions must be resolved before the method can be applied. The feeding of dairy cows with uncontaminated feeds, or with feeds which have been stored long enough for their radioactivity to decay, reduces substantially the con-

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tamination of the milk supply. This countermeasure, of course, requires the availability of a large feed storage capacity the year round unkss ways and means are found to produce feed under conditions where contamination cannot take place. The latter possibility seems unlikely in the near future although experimental methods of feed production to achieve this goal are currently under study. The addition of stable iodine to the diet and the medical administration of thyroid extract are two countermeasures which have received considerable study in recent years .... Evidence is at hand which indicates that relatively small amounts of stable iodine, 1.0 mg. in children and 5.0 mg. in adults when taken daily, will induce gradually over a few days a reduction of about 80 per cent in radioiodine accumulation by the thyroid gland; greater and more rapid reduction can be achieved by larger doses ....

Since this report was issued, Saxena, Chapman and Pryles23 have established that maximal suppression of Jl 31 uptake in children can be achieved with an iodide dosage of 1.5 to 2.0 mg. per square meter of body surface per day. Toxic effects of iodide from these small doses over short periods of time· are extremely unlikely. Iodism and temporary hypothyroidism with goiter have been reported, but, to our knowledge, only with much larger doses given over a long time. In rare instances an association between sensitivity to iodine and periarteritis nodosa has been suggested. 14 With the availability of other countermeasures, it is likely that the use of stable iodide will be limited to emergency conditions such as might prevail in the vicinity of a reactor accident. Physicians may wonder why they should be acquainted with these details when the Public Health Service, local health officials, and expert committees are constantly concerned with problems of radiation protection. Parents rightly tum to their physician or pediatrician for advice and guidance. If countermeasures are indicated, the individual physician can act with greater speed than the health officials, who cannot always be guided solely by scientific considerations: it is easier to formulate recommendations for individual patients than for the thousands and millions in the population at large. Yet if physicians are to give expert advice, they must have access to the relevant data. At present, communication between the monitoring authorities and the medical profession is most inadequate. In many instances high environmental levels are not made known to the profession for weeks or months. Iodine-131 values are usually published in Radiological Health Data two to three months after the measurements have been made. At that time the values are only of historical interest, since virtually complete decay has occurred. RADIATION STANDARDS

The principal agency responsible for the development of radiation standards is the Federal Radiation Council. In its first report (May, 1960), the Council defined the Radiation Protection Guide ( RPG) as "the radiation dose which should not be exceeded without careful con-

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sideration of the reasons for doing so; every effort should be made to encourage the maintainance of radiation doses as far below this guide as practicable." 25 This report contains background information about radiation standards in general. After tracing the history, the Council made the following important statement: Thus, over the past decade or two, there has been an increasing reluctance on the part of knowledgeable scientists to establish radiation protection standards on the basis of the existence of a threshold for radiation damage and on the premise that this threshold lies not too distant from the point at which impairment is detectable in an exposed individual. Although many scientists are prepared to express individual opinions as to the likelihood that a threshold does or does not exist, we believe that there is insufficient scientific evidence on which to base a definitive conclusion in this regard. Therefore, the establishment of radiation protection guides, particularly for the whole population, should take into account the possibility of damage, even though it may be small, down to the lowest levels of exposure.* This involves considerations other than the presence of readily detectable damage in an exposed individual. It also serves as a basis for such fundamental principles of radiation protection as: there should not be any man-made radiation exposure without the expectation of benefit resulting from such exposure;* activities resulting in man-made radiation exposure should be authorized for useful applications provided the recommendations set forth in this staff report are followed. On the assumption that there is no threshold, every use of radiation involves the possibility of some biological risk either to the individual or his descendents. On the other hand, the use of radiation results in numerous benefits to man in medicine, in· dustry, commerce, and research. If those beneficial uses were fully exploited without regard to radiation protection, the resulting biological risk might well be considered too great. Reducing the risk to zero would virtually eliminate any radiation use, and result in the loss of all possible benefits. It is therefore necessary to strike some balance between maximum use and zero risk. In establishing radiation protection standards, the balancing of risk and benefit is a decision involving medical, social, economic, political, and other factors.* Such a balance cannot be made on the basis of a precise mathematical formula but must be a matter of informed judgment.

This statement well defines the difficulties in setting radiation standards. Determination of risk alone is difficult enough in view of the uncertainties outlined in the preceding discussion. Determination of benefits clearly involves a nonscientific judgment. Although the detailed evidence on which the RPG's are based has not been made available for public scrutiny, numerical values of RPG for various tissues have been assigned. In addition, the Council has defined three ranges of intakes of various isotopes, each range calling for different actions. 26 Range I requires only surveillance. Intakes falling into range II would be expected to result in an average exposure of population groups not exceeding the RPG. Such intakes would call for "active surveillance and routine control." Range III is of particular interest to the practicing physician, and the Council's statements concerning it are therefore quoted at length. * Italics ours.

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Intakes within this range would be presumed to result in exposures exceeding the RPG if continued for a sufficient period of time. However, transient rates of intake within this range could occur without the population group exceeding the RPG if the circumstances were such that the annual average intake fell within Range II or lower. Therefore, any intake within this range must be evaluated from the point of view of the RPG and if necessary, appropriate positive control measures instituted. . . . The surveillance described for intakes in Range II should be adequate to define clearly with a minimum of delay the extent of the exposure (level of intake, size of population group) within Range III. Surveillance would need to provide adequate data to give prompt and reliable information concerning the effectiveness of control actions. . . . Control actions would be designed to reduce the levels to Range II or lower and to provide stability at lower levels. These actions can be directed toward further restriction of the entry of radioactive materials into the environment or the control of radioactive materials after entrv into the environment in order to limit intake by humans. Sharply rising trend in ·Range III would suggest strong and prompt action.

Table 9 lists the values for the RPG and the various ranges of intakes. The gonadal RPG is defined for the first 30 years of life, the period most relevant to reproduction. The value of 5 rads excludes natural background radiation and purposeful exposure of patients by practitioners of the healing arts. The Committee on the Genetic Effects of Atomic Radiation of the Natural Academy of Sciences suggests that the average gonadal dose accumulated during the first 30 years of life should not exceed 10 rads of man-made radiation. 2 All authorities agree that the gonadal exposure should be kept as low as possible or practicable. TABLE

9. Radiation Protection Guides Intake Ranges25, 2s RANGE (JLJLC/DAY)

RPG (RADS/YEAR)

Gonadal. .............. 5. 0/30 years Thyroid (1131 ) . . . . . • . • • . . . . • 0 . 5 Sr 90 . • . . • • • . . . . . . • • • . • . . . . Srs• ...................... . Bone marrow .............. 0. 17 Bone ..................... . 0.5

I

II

III

0-10 0-20 0-200

10-100 20-200 200-2000

100-1000 200-2000 2000-20,000

RPG refers to radiation dose of "average of a suitable sample of exposed population group."

The various ranges of intake are obviously higher for strontium-89 than for strontium-90, since the former has a half-life of 53 days, while the latter has one of 28 years. Since there arc several boneseeking isotopes, one cannot immediately equate the ranges with the RPG. For strontium-90, for example, a continuous intake of 200 micromicrocuries per day would yield only one third of the bone or bone marrow RPG. Since nearly all the man-made thyroidal radiation is derived from iodine-131, there is a close correspondence between RPG and ranges. For children, the RPG of 0.5 rad would be attained by the average daily

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THE PHYSICIAN AND ENVIRONMENTAL RADIATION HAZARDS

ingestion of 80 micromicrocuries per day. A total intake of 29,200 micromicrocuries (80 micromicrocurics per day x 365 days per year) per year would yield an RPG dose. The problem of radiation protection is complicated by the need for considering the characteristics of each isotope, and P 31 can again be used as an illustration. Although the Council specifically allows for "transient rates of intake" within range III, the height of excursions into this range and their frequency must be considered when control actions are contemplated. From the known characteristics of P 31 fallout, its rate of disappearance from the environment, and the Federal Radiation Council's assumptions (Table 8), we have calculated that when a transient excursion reaches 2,000 micromicrocuries per liter of milk, as occurred in Utah, the average thyroidal dose to children would be 0.4 rad unless control actions are instituted promptly. If protective actions are to be effective, they must be instituted at a time when environmental levels are high. Since one cannot predict the frequency of environmental rises, protection would be provided by use of one of the courses of action recommended by the Advisory Committee with each excursion into range III. To do this, a physician must have prompt access to the data for the area in which he practices. During the 12 months from September, 1961, to August, 1962, RPG doses were probably delivered to children in the following cities: Des Moines (0.56 rad), Minneapolis (0.55 rad), Kansas City (0.57 rad) and Salt Lake City ( 0.63 rad). Relatively high values were attained in Salt Lake City despite the protective action taken in July, 1962. That community also received high exposure during 1957-1958. Since the Federal Radiation Council's first report of May, 1960, physicians and public health officials have considered the protection guides and ranges as the relevant radiation standards. It was assumed by all, including officials of the Public Health Service, that, since these standards were defined for "normal peacetime use," they would apply to the present situation. In August, 1962, however, the Secretary of Health, Education, and Welfare, Mr. Anthony J. Celebrezze, who serves as chairman of the Federal Radiation Council, indicated that the Council's recommendations were applicable primarily to industrial uses. This unexpected interpretation has left some doubt about the pertinent standards at present. There is reason to believe that new standards will have been evolved by the time this issue goes to press. SUMMARY

Environmental radiation presents unique challenges to the practicing physician. There is general agreement that radiation can cause genetic

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damage even in the smallest doses. Whether a threshold exists for the somatic effects of radiation remains doubtful. Thoughtful and restrained radiologic practices by physicians in general can do much to avoid unnecessary radiation exposure while maintaining the extraordinary benefits of diagnostic and therapeutic radiation. Improved monitoring of instruments could contribute to progress in this field . Expanding industrial uses of atomic energy and continued fallout from weapons testing are major potential sources of radiation exposure. Fallout has already increased the radiation exposure of large populations. The genetic exposure so far has been only a fraction of the natural background radiation. In some areas heavy thyroidal radiation has been delivered to large segments of the population. Through the years the allowable exposure to radiation has been progressively decreased. The Federal Radiation Council, an agency responsible for the development of standards, has determined Radiation Protection Guides for various tissues. These Guides represent the Council's current estimate of the best balance between risk (scientific estimate) and benefit (social judgment). A re-evaluation of radiation standards is now in progress. REFERENCES

l. Beach, S. A., and Dolphin, G. W.: A Study of the Relationship between X-ray

2. 3. 4. 5. 6. 7. 8. 9. 10. ll. 12.

Dose Delivered to the Thyroids of Children and the Subsequent Development of Malignant Tumours. Physics Med. Bioi., 6:583, 1962. The Biological Effects of Atomic Radiation. Summary Reports. From a Study by the National Academy of Sciences. \Vashington, D.C .• National Academy of Sciences, National Research Council, 1960. Chamberlain, A. C., and Dunster, H. J.: Deposition of Radioactivity in Northwest England from the Accident at Windscale. Nature, 182:629, 1958. Cronkite, E. P., Moloney, \V., and Bond, V. P.: Radiation Leukemogenesis: An Analysis of the Problem. Am. J. Med., 28:673, 1960. Dobzhansky, T.: Mankind Evolving. The Evolution of the Human Species. New Haven, Yale University Press, 1962. Forbes, G. B.: Nutrition in Relation to Problems of Radioactivity. PEDIAT. CLIN. N. A:t\iER., 9:1009, 1962. Fowler, J. M. (Ed.): Fallout. A Study of Superbombs, Strontium 90 and Survival New York, Basic Books, Inc., 1960. Glass, H. B., and Rittcrhoff, R. K.: Mutagenic Effect of a 5-r Dose of X-rays in Drosophila Melanogaster. Science, l 33: 1366, 1961. Hearings before the Special Subcommittee on Radiation of the Joint Committee on Atomic Energy, May 5-8, 1959. Hempelmann, L. H., and others: The Acute Radiation Syndrome: A Study of Nine Cases and a Review of the Problem. Ann. Int. Med., 36:279, 19 52. Heyssel, R., and others: Leukemia in Hiroshima Atomic Bomb Survivors. Blood, 15:313, 1960. Knapp, H. A.: The Contribution of Short-Lived Isotopes and Hot Spots to Radiation Exposure in the U.S. from Nuclear Test Fallout. T.I.D. 8527. Fallout Branch, Division of Biology and Medicine. United States Atomic Energy Commission, June, 1960.

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THE PHYSICIAN AND ENVIRONMENTAL RADIATION HAZARDS

13. Lapp, R. E.: Nevada Test Fallout and Radioiodine in Milk. Science, 137:756, 1962. 14. Muller, C.: Periarteritis Nodosa-Asthma Bronchiale-Ioderma Tuberosum. Acta Med. Scandinav., 136:378, 1950. 15. National Advisory Committee on Radiation: Report to the Surgeon General, U.S. Public Health Service, on Radioactive Contamination of the Environment: Public Health Action. Testimony submitted before Joint Committee on Atomic Energy of the Congress, June, 1962. 16. Perkins, R. W., and Nielsen, J. M.: Zinc-65 in Foods and People. Science, 129:94, 1959. 17. Radiological Health Data. Division of Radiological Health, Public Health Service, U.S. Department of Health, Education, and Welfare, November, 1962, Vol III, no. II. 18. Report of the Committee on Environmental Hazards, American Academy of Pediatrics: Statement on the Hazards of Radioactive Fall-out. Pediatrics, 29: 845, 1962. 19. Report of the Federal Radiation Council: Health Implications of Fallout from Nuclear Weapons Testing through 1961. Report no. 3, May, 1962. Washington, D. C., United States Printing Office. 20. Report of the United Nations Scientific Committee on the Effects of Atomic Radiation. General Assembly. Official Records: Thirteenth Session. Supplement No. 17 (A/3838), 1958. 21. Idem: Official Records, Seventeenth Session, Supplement No. 16 (A/5216), 1962. 22. Russell, W. L., Russell, L. B., and Cupp, M. B.: Dependence of Mutation Frequency on Radiation Dose Rate in Female Mice. Proc. Nat. Acad. Sc., 45:18, 1959. 23. Saxena, K. M., Chapman, E. M., and Pryles, C. V.: Minimal Dosage of Iodide Required to Suppress Uptake of Iodine-131 by Normal Thyroid. Science, 138: 430, 1962. 24. Simpson, C. L., Hempelmann, L. H., and Fuller, L. M.: Neoplasia in Children Treated with X-rays in Infancy for Thymic Enlargement. Radiology, 64:840, 1955. 25. Staff Report of the Federal Radiation Council: Background Material for the Development of Radiation Protection Standards. Report no. 1, May 13, 1960. Washington, D. C., United States Printing Office. 26. Idem: Report no. 2, September, 1961. \Vashington, D.C., United States Printing Office. 27. "Steady Growth in Nuclear Power Seen." Chemical 6 Engineering News, 40 (50) :47, 1962. 28. Stewart, N. G., and Crooks, R.N.: Long-Range Travel of the Radioactive Cloud from the Accident at Windscale. Nature, 182:627, 1958. 29. Utah State Department of Health: Press Release, August 1, 1962. \V ashington U nivcrsity Medical School Euclid and Kingshighway St. Louis 10, Mo.

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