Fallout from Nuclear Weapons Tests and Cancer Risks

Home , Ailinginae Atoll, Ground Zero, Nevada Test Site, Nuclear weapons testing, Semipalatinsk Test Site

A reprint from American Scientist the magazine of Sigma Xi, The Scientific Research Society

This reprint is provided for personal and noncommercial use. For any other use, please send a request to Permissions, American Scientist, P.O. Box 13975, Research Triangle Park, NC, 27709, U.S.A., or by electronic mail to [email protected]. ©Sigma Xi, The Scientific Research Society and other rightsholders Fallout from Nuclear Weapons Tests and Cancer Risks

Exposures 50 years ago still have health implications today that will continue into the future

Steven L. Simon, André Bouville and Charles E. Land

rior to 1950, only limited consider- weapons in the atmosphere. By the ear- explosive power of 440 megatons of Pation was given to the health im- ly 1960s, there was no place on Earth TNT (see Figure 2). pacts of worldwide dispersion of ra- where the signature of atmospheric The earliest concern about health ef- dioactivity from nuclear testing. But in nuclear testing could not be found in fects from exposure to fallout focused on the following decade, humanity began soil, water and even polar ice. possible genetic alterations among off- to significantly change the global ra- Cancer investigators who specialize in spring of the exposed. However, herita- diation environment by testing nuclear radiation effects have, over the interven- ble effects of radiation exposure have not ing decades, looked for another signature been observed from decades of follow-up of nuclear testing—an increase in cancer studies of populations exposed either to Steven L. Simon received a Ph.D. in radiological health rates. And although it is difficult to de- medical x rays or to the direct gamma ra- sciences from Colorado State University in 1985. He tect such a signal amid the large num- diation received by survivors of the Hiro- has served on the faculties of the University of Utah and the University of North Carolina at Chapel Hill. ber of cancers arising from “natural” or shima and Nagasaki bombs. Rather, such He spent five years directing the Marshall Islands “unknown” causes, we and others have studies have demonstrated radiation-re- Nationwide Radiological Study and also participated found both direct and indirect evidence lated risks of leukemia and thyroid cancer in the radiological monitoring of the former nuclear that radioactive debris dispersed in the within a decade after exposure, followed test sites at Johnston Island, in Algeria, and in French atmosphere from testing has adversely by increased risks of other solid tumors Polynesia. Simon joined the National Cancer Institute affected public health. Frequently, how- in later years. Studies of populations ex- (NCI) in 2000 and now focuses on retrospective dose ever, there is misunderstanding about posed to radioactive fallout also point to estimation in support of epidemiologic studies of radio- the type and magnitude of those effects. increased cancer risk as the primary late active fallout and occupational exposure in medicine. Thus today, with heightened fears about health effect of exposure. As studies of André Bouville was born in France and obtained his the possibilities of nuclear terrorism, it biological samples (including bone, thy- Ph.D. in physics at the Université Paul-Sabatier in Toulouse in 1970. He served as a consultant to the is worthwhile to review what we know roid glands and other tissues) have been United Scientific Committee on the Effects of Atomic about exposure to fallout and its associ- undertaken, it has become increasingly Radiation for 30 years and the International Commis- ated cancer risks. clear that specific radionuclides in fallout sion on Radiological Protection (ICRP) for 17 years. are implicated in fallout-related cancers Bouville joined the National Cancer Institute in 1984 Historical Background and other late effects. and has since been heavily involved in the estimation The first test explosion of a nuclear of radiation doses resulting from radioactive fallout weapon, Trinity, was on a steel tower in Nuclear Explosions: The Basics from atmospheric nuclear weapons tests and from the south-central New Mexico on July 16, Nuclear explosions involve the sudden Chornobyl accident. Charles E. Land received a Ph.D. 1945. Following that test, nuclear bombs conversion of a small portion of atomic in statistics from the University of Chicago. He stud- were dropped on Hiroshima and Naga- nuclear mass into an enormous amount ied the risk of radiation-related cancer at the Atomic Bomb Casualty Commission and the Radiation Effects saki, Japan, in August of 1945. In 1949, of energy by the processes of nuclear Research Foundation in Hiroshima, Japan, before join- the Soviet Union conducted its first test fission or fusion. Fission releases energy ing the NCI in 1975. Land served on the ICRP for 20 at a site near Semipalatinsk, Kazakh- by splitting uranium or plutonium at- years and was instrumental in producing the 1985 stan. The U.S., the Soviet Union and oms, each fission creating on average National Institutes of Health radio-epidemiological ta- the United Kingdom continued testing two radioactive elements (products), one bles and the 2003 NCI-CDC interactive computer pro- nuclear weapons in the atmosphere un- relatively light and the other relatively gram developed to assist adjudication of compensation til 1963, when a limited test ban treaty heavy. Fusion, triggered by a fission ex- claims for cancers following occupational exposures to was signed. France and China, coun- plosion that forces tritium or deuterium radiation. His research interests include quantifying tries that were not signatories to the atoms to combine into larger atoms, pro- lifetime radiation-related cancer risk with emphasis 1963 treaty, undertook atmospheric test- duces more powerful explosive yields on implications of uncertainty for public policy. Ad- dress for Simon: Division of Cancer Epidemiology and ing from 1960 through 1974 and 1964 than fission. Both processes create three Genetics, National Cancer Institute, National Insti- through 1980, respectively. Altogether, types of radioactive debris: fission prod- tutes of Health, 6120 Executive Blvd., Bethesda, MD 504 devices were exploded at 13 prima- ucts, activation products (elements that 20892. Email: [email protected]. ry testing sites, yielding the equivalent become radioactive by absorbing an ad-

© 2006 Sigma Xi, The Scientific Research Society. Reproduction 48 American Scientist, Volume 94 with permission only. Contact [email protected]. ditional neutron) and leftover fissionable material used in bomb construction that does not fission during the explosion. A nuclear explosion creates a large fireball within which everything is vaporized. The fireball rises rapidly, incorporating soil or water, then ex- pands as it cools and loses buoyancy. The radioactive debris and soil that are initially swept upwards by the explosion are then dispersed in the directions of the prevailing winds. Fallout consists of microscopic particles that are deposited on the ground.

How People Are Exposed to Fallout The radioactive cloud usually takes the form of a mushroom, that familiar icon of the nuclear age. As the cloud reaches its stabilization height, it moves downwind, and dispersion causes vertical and lateral cloud movement. Because wind speeds and directions vary with altitude (Figure 3), radioactive materials spread over large areas. Large particles settle lo- cally, whereas small particles and gases may travel around the world. Rainfall can cause localized concentrations far from the test site. On the other hand, large atmospheric explosions injected radioactive material into the stratosphere, 10 kilometers or more above the ground, where it could remain for years and sub-

Figure 1. Between 1945 and 1980, the U.S., the U.S.S.R, the U.K., France and China carried out more than 500 atmospheric tests of nuclear weapons totaling the explosive equivalent of 440 megatons of TNT. These tests injected radioactive material into the atmosphere, much of which became widely dispersed before be- ing deposited as fallout. Cancer investigators have been studying the health effects of radioactive fallout for decades, making radiation one of the best-understood agents of environmental injury. The legacy of open-air nuclear weapons testing includes a small but significant increase in thyroid cancer, leukemia and certain solid tumors. Mushroom clouds, such as the one from the 74-kiloton test HOOD on July 5, 1957 (detonated from a balloon at 1,500 feet altitude), are a universally recognized icon of nuclear explosions. The characteristic cap forms when the fireball from the explosion cools sufficiently to lose buoyancy. HOOD was the largest atmospheric test conducted at the Nevada Test Site (and in the continental U.S.). Fortunately, the U.S., the Soviet Union and the U.K. stopped atmospheric testing in 1963, when the nations signed the Limited Test Ban Treaty. (France ceased atmospheric testing in 1974 and China in 1980.) President John F. Kennedy signed the treaty on October 5, 1963 (bottom). (Top photograph from the Nevada Test Site, U.S. Department of Energy. Bottom photograph from the National Archives.)

��

Figure 2. Primary atmospheric nuclear weapons test sites were widely distributed around the globe, with South America and Antarctica the only continents to be spared. No spot on Earth escaped the fallout, however, as larger tests injected radioactive material into the stratosphere, where it could remain for several years and disperse globally. The numbers shown at each test site indicate the number of tests and (following the comma) the total yield in the equivalent of megatons of TNT. (Data here and in Figures 3 and 7–10 from NCI 1997.)

sequently be deposited fairly homoge- fallout is directly deposited on exter- transferred to people in dairy foods neously (”global” fallout). Nuclear tests nal surfaces of plants and when it is (Figure 4). In general, only those chil- usually took place at remote locations at absorbed through the roots of plants. dren in the U.S. with lactose intol- least 100 kilometers from human pop- Also, people can be exposed when they erance or allergies to milk products ulations. In terms of distance from the eat meat and milk from animals graz- consumed no milk products, partic- detonation site, “local fallout” is within ing on contaminated vegetation. In the ularly in the 1950s and 1960s when 50 to 500 kilometers from ground zero, Marshall Islands, foodstuffs were also there were fewer choices of prepared “regional fallout” 500–3,000 kilometers contaminated by fallout directly depos- foods. Radioiodine ingested or inhaled and global fallout more than 3,000 ki- ited on food and cooking utensils. by breast-feeding mothers can also be lometers. Because the fallout cloud dis- The activity of fallout deposited on the transferred to nursing infants via the perses with time and distance from the ground or other surfaces is measured in mother’s breast milk. explosion, and radioactivity decays over becquerels (Bq), defined as the number The two nuclear weapons dropped time, the highest radiation exposures are of radioactive disintegrations per sec- on Hiroshima and Nagasaki were generally in areas of local fallout. ond. The activity of each radionuclide detonated at relatively high altitudes Following the deposition of fallout per square meter of ground is important above the ground and produced mini- on the ground, local human popula- for calculating both external and internal mal fallout. Most of the injuries to the tions are exposed to external and in- doses. Following a nuclear explosion, populations within 5 kilometers of the ternal irradiation. External irradiation the activity of short-lived radionuclides explosions were from heat and shock exposure is mainly from penetrating is much greater than that of long-lived waves; direct radiation was a major gamma rays emitted by particles on radionuclides. However, the short-lived factor only within 3 kilometers. Most the ground. Shielding by buildings radionuclides decay substantially dur- of what we know about late health ef- reduces exposure, and thus doses to ing the time it takes the fallout cloud to fects of radiation in general, including people are influenced by how much reach distant locations, where the long- increased cancer risk, is derived from time one spends outdoors. lived radionuclides are more important. continuing observations of survivors Internal irradiation exposures can Iodine-131, which for metabolic rea- exposed within 3 kilometers. arise from inhaling fallout and absorb- sons concentrates in the thyroid gland, ing it through intact or injured skin, has a half-life (the time to decay by Understanding Radiation Dose but the main exposure route is from half) of about eight days. This is long Radiation absorbed dose is the energy consumption of contaminated food. enough for considerable amounts to per unit mass imparted to a medium Vegetation can be contaminated when be deposited onto pasture and to be (such as tissue). Almost all radionu-

© 2006 Sigma Xi, The Scientific Research Society. Reproduction 50 American Scientist, Volume 94 with permission only. Contact [email protected]. clides in fallout emit beta (electron) and gamma (photon) radiation. A cas- cade of events follows once tissue is exposed to radiation: The initial radiation scatters, and atoms in the body are ionized by removal of weakly bound �� electrons. Radiation can damage DNA �� by direct interaction or by creating �� highly reactive chemical species that interact with DNA. �� The basic unit of the system used �� internationally to characterize radiation dose is the gray (Gy), defined as �� the absorption of 1 joule of energy per �� kilogram of tissue. (The international �� system of units is gradually supplant- �� ing the previous system based on dose �� units of rad, but conversion is easy: 1 �� Gy = 100 rad.) For perspective, it is helpful to remember that the external Figure 3. Wind shear (variations in wind speed and direction with altitude) causes fallout to dose received from natural sources of spread over large areas. The 43-kiloton test SIMON was detonated at 4:30 a.m. local time on radiation—from primordial radionu- April 25, 1953, at the Nevada Test Site. Trajectories of the fallout debris clouds across the U.S. are clides in the earth’s crust and from cos- shown for four altitudes. Each dot indicates six hours. The numbered dots are the date in April. mic radiation—is of the order of 1 milligray (mGy, one-thousandth of a gray) out deposition data. There have been 1954), was responsible for most—al- per year; the dose from a whole-body only a few studies involving detailed though not all—of the radiation ex- computer-assisted tomographic (CT) estimation of the doses received by lo- posure of local populations from all examination is about 15–20 mGy, and cal populations; the exceptions include of the tests. The fallout-related doses that due to cosmic rays received during some towns and cities in Nevada and received as a result of that one test at a transatlantic flight is about 0.02 mGy. adjacent states, a few villages near the Bikini Atoll are the highest in the his- Soviet Semipalatinsk Test Site (STS), and tory of worldwide nuclear testing. Examples of Fallout Exposures some atolls in the Marshall Islands. Wind shear (changes in direction Doses from fallout received in the 1950s Marshall Islands. One of the 65 tests and speed with altitude) and an unex- and 1960s have been estimated in re- conducted in the Marshall Islands, the pectedly high yield resulted in heavy cent years using mathematical exposure explosion of a U.S. thermonuclear de- fallout over populated atolls to the east assessment models and historical fall- vice code-named BRAVO (March 1, of Bikini rather than over open seas to

��

Figure 4. One major means by which fallout and nuclear debris are transferred through the atmosphere to people is via the production and consumption of dairy products. Fallout descends onto vegetation, which is eaten by dairy animals. The fallout passes into the animals’ milk, which is prepared for human consumption. This pathway is the single largest means by which people in the U.S. were exposed to iodine-131 from fallout generated by nuclear weapons testing. (Figure adapted from the National Cancer Institute).

© 2006 Sigma Xi, The Scientific Research Society. Reproduction www.americanscientist.org 2006 January–February 51 with permission only. Contact [email protected]. they were estimated to be several tens �� of Gy for an adult and more than 100 � �� Gy for a one-year old. Estimated thyroid doses at Ailinginae were about half �� those at Rongelap, and doses at Utrik �� were about 15 percent of those at Ron- gelap. The external whole-body doses � � �� estimated were about 2 Gy at Rongelap, �� 1.4 Gy at Ailinginae, 2.9 Gy at Rongerik �� and 0.2 Gy at Utrik. Much lower expo- �� sures have been estimated for most of �� the other Marshall Islands atolls. �� Twenty-three Japanese fishermen on the fishing vessel Lucky Dragon were � �� also exposed to heavy fallout. Their �� doses from external irradiation were estimated to range from 1.7 to 6 Gy. Figure 5. BRAVO, detonated on March 1, 1954, was a 15-megaton thermonuclear device that Those doses were received during the resulted in the highest radiation exposures to people of any nuclear test. Unanticipated wind 14 days it took to return to harbor; direction and an explosive yield higher than expected sent a fallout cloud from the Bikini test about half were received during the site towards the inhabited atolls of Rongelap, Ailinginae, Rongerik and Utrik in the Marshall first day after the onset of fallout. Islands. Doses from external exposure were about 1–2 Gy on Rongelap and Ailinginae. Semipalatinsk, Kazakhstan. The Semi- palatinsk Test Site, in northeastern Ka- 1 the north and west. About 3/2 hours detonation, it reached the 167 residents zakhstan near the geographical center after the detonation, the radioactive of Utrik Atoll. of the Eurasian continent, was the Soviet cloud began to deposit particulate, Doses received by the Rongelap equivalent of the U.S. Nevada Test Site; ash-like material on 18 Rongelap resi- group were assessed by ground and 88 atmospheric tests and 30 surface tests dents who were fishing and gather- aerial exposure rate measurements were conducted there from 1949 through ing copra on Ailinginae Atoll about and radioactivity analysis of a commu- 1962. The main contributions to local 135 kilometers east of the detonation nity-pooled urine sample. The doses and regional environmental radioactive site, followed 2 hours later by deposi- received before evacuation were essen- contamination are attributed to particu- tion on Rongelap Island 65 kilometers tially due to external irradiation from lar atmospheric nuclear tests conducted farther to the east, affecting 64 resi- short-lived radionuclides and internal in 1949, 1951 and 1953. 1 dents. The fallout arrived 2 /2 hours irradiation from ingestion of short-lived Doses from local fallout originating later at Rongerik Atoll another 40 kilo- radioiodines deposited on foodstuffs at the STS depended on the location meters to the east, exposing 28 Ameri- and cooking utensils. Thyroid doses, in of villages relative to the path of the can weathermen; about 22 hours after particular, were very high: At Rongelap fallout cloud, the weather conditions at the time of the tests, the lifestyles of residents, which differed by ethnicity (Kazakh or European), and whether they were evacuated before the fallout arrived at the village. Some unique circumstances included strong winds that resulted in short fallout transit times and little radioactive decay before deposition for at least one test. Also, the residents of the area were heavily dependent on meat and milk from grazing animals, including cattle, horses, goats, sheep and camels. Dose-assessment models predict a de- creasing gradient in the ratio of external radiation doses to internal doses from inhalation and ingestion with increasing time from detonation to fallout ar- rival. The relatively large particles that tend to fall out first are not efficiently transferred to the human body. At more Figure 6. Subsequent to the explosion of BRAVO at the Bikini test site, teams of medical doc- distant locations in the region of local tors and health physicists made annual trips to the Marshall Islands to check on the health of fallout, internal dose is relatively more islanders accidentally exposed to radioactive fallout. In this photograph, Dr. Robert Conard important because smaller particles that is examining a Marshall Islander for any thyroid abnormalities. (Photograph courtesy of predominate there are biologically more Brookhaven National Laboratory.) available. For example, in rural villages

© 2006 Sigma Xi, The Scientific Research Society. Reproduction 52 American Scientist, Volume 94 with permission only. Contact [email protected]. along the trajectory of the first test (Au- gust 1949) at the Semipalatinsk Test Site, �� average estimated radiation dose from fallout to the thyroid glands of juvenile �� residents decreased with increasing distance from the detonation, but the pro- �� portion of that total due to internal radiation sources increased with distance. At �� 110 kilometers from the detonation site, the average dose was 2.2 Gy, of which �� 73 percent was from internal sources, whereas at 230 kilometers, 86 percent �� of the average dose of 0.35 Gy was from internal sources Nevada Test Site (NTS). The NTS was �� used for surface and above-ground nuclear testing from early 1951 through Figure 7. Cesium-137 deposition density resulting from the cumulative effect of the Nevada mid-1962. Eighty-six tests were con- tests generally decreases with distance from the test site in the direction of the prevailing wind across North America, although isolated locations received significant deposition as a ducted at or above ground level, and result of rainfall. 14 other tests that were underground involved significant releases of radio- ported from less contaminated areas. In response to Public Law 97-414 (en- active material into the atmosphere. Bone-marrow doses less than 50 mGy acted in 1993), the U.S. National Cancer In 1979 the U.S. Department of En- were estimated for communities in a Institute (NCI) estimated the absorbed ergy described a methodology for esti- local fallout area within 300 kilometers dose to the thyroid from I-131 in NTS mating radiation doses to populations of the NTS, where ground-monitoring fallout for representative individuals in downwind of the NTS. Doses from in- data were available, and an order of every county of the contiguous United ternal irradiation within this local fall- magnitude less for other communities States. Calculations emphasized the out area were ascribed mainly to inha- in Arizona, New Mexico, Nevada, Utah pasture-cow-milk-man food chain, but lation of radionuclides in the air and to and portions of adjoining states. also included inhalation of fallout and ingestion of foodstuffs contaminated Investigators at the University of ingestion of other foods. Deposition of with radioactive materials. Doses from Utah estimated radiation doses to the I-131 across the United States was re- internal irradiation were, for most or- bone marrow for 6,507 leukemia cases constructed for every significant event gans and tissues, substantially smaller and matched controls who were res- at the NTS using historical measure- than those from external irradiation, idents of Utah. Average doses were ments of fallout from a nationwide net- with the notable exception of the thy- about 0.003 Gy with a maximum of work of monitoring stations operational roid, for which estimated internal doses about 0.03 Gy. Subsequently, thyroid between 1951 and 1958. Thyroid doses were substantially higher. Estimated doses were estimated to members of were estimated as a function of age at thyroid doses were ascribed mainly to a cohort exposed as school children in exposure, region of the country and di- consumption of foodstuffs contami- southwestern Utah and who are part etary habits. For example, for a female nated with iodine-131 (I-131) and, to of a long-term epidemiology study. born in St. George, Utah, in 1951 and a lesser extent, iodine-133 (I-133), and The mean thyroid dose was estimat- residing there until 1971, the thyroid to inhalation of air contaminated with ed to be 0.12 Gy, with a maximum of doses are estimated to have been about both I-131 and I-133. Thyroid doses var- 1.4 Gy. Among children who did not 0.3 Gy if she had consumed commercial ied according to local dairy practices drink milk, the mean thyroid dose was cow’s milk, 2 Gy if she had consumed and the extent to which milk was im- on the order of 0.01 Gy. goat’s milk, and 0.04 Gy if she had not

more than 100 ��

30-100 ��

10-30 ��

3-10 ��

1-3 ��

0-1 ��

Figure 8. Total external and internal dose to the red bone marrow of persons born on January 1, 1951, from all Nevada tests is shown at left. To- tal external and internal dose to the thyroid of adults in 1951 from all Nevada tests is shown at right. Note that the dose is roughly proportional to the deposition density shown in Figure 7.

© 2006 Sigma Xi, The Scientific Research Society. Reproduction www.americanscientist.org 2006 January–February 53 with permission only. Contact [email protected]. received from global fallout are shown in Figures 9 and 11. Figure 9 shows the pattern of deposition of Cs-137 from global fallout, as well as the total dose to red bone marrow, which is roughly �� proportional to the deposition. A com- �� parison of Figures 9 and 7 shows very �� different patterns of Cs-137 in global �� fallout (related to rainfall patterns) and NTS fallout, which depended mainly �� on the trajectories of the air masses �� originating from the NTS. Estimates of �� average thyroid and bone-marrow doses for the entire U.S. population from �� global fallout are presented in Figure Figure 9. Cesium-137 deposition density (right scale) and dose to red bone marrow (left scale) 11; the thyroid dose from I-131 is higher from global fallout for persons born on January 1, 1951, show a different pattern than that than the internal doses from any other �� from the Nevada tests, as they are strongly influenced by rainfall amounts. radionuclide, but it is no greater than the doses from external irradiation. �� consumed milk. For a female born in ples of results extracted from the report Los Angeles, California, at the same (a link is available in the bibliography) Fallout and Cancer Risk time, the corresponding values would are shown in Figures 7 through 9 and 11. Increased cancer risk is the main long- have been 0.003, 0.01, and 0.0004 Gy. Figure 7 shows the pattern of deposition term hazard associated with exposure (A link to these data is available in the of cesium-137 (Cs-137), a radionuclide to ionizing radiation. The relationship bibliography.) traditionally used for reference, resulting between radiation exposure and subse- Following the publication of the NCI from all NTS tests in the entire United quent cancer risk is perhaps the best un- findings in 1997, the U.S. Congress re- States. Fallout decreased with distance derstood, and certainly the most highly quested that the Department of Health from the NTS along the prevailing wind quantified, dose-response relationship and Human Services extend the study direction, which was from west to east. for any common environmental human to other radionuclides in fallout and to Very little fallout was observed along the carcinogen. Our understanding is based consider tests outside the U.S. that could Pacific coast, which was usually upwind on studies of populations exposed to ra- have resulted in substantial radiation ex- from the NTS. Estimated bone-marrow diation from medical, occupational and posures to the American people. Exam- and thyroid doses are illustrated in Fig- environmental sources (including the ure 8. The fact that both external and atomic bombings of Hiroshima and Na- internal doses were roughly proportion- gasaki, Japan), and from experimental �� al to the deposition density is reflected studies involving irradiation of animals �� in similarities between the two figures. and cells. Numerous comprehensive �� Estimates of average thyroid and of reports from expert committees sum- �� bone-marrow doses for the entire U.S. marize information on radiation-related �� population are presented in Figure 11; cancer risk using statistical models that �� the thyroid doses from I-131 are much express risk as a mathematical function higher than the internal doses from any of radiation dose, sex, exposure age, age other radionuclide and also much higher at observation and other factors. Using �� than the doses from external exposure. such models, lifetime radiation-related Global fallout within the U.S. Global risk can be calculated by summing es- fallout originated from weapons that timated age-specific risks over the re- � derived much of their yield from fusion maining lifetime following exposure, reactions. These tests were conducted adjusted for the statistical likelihood �� by the Soviet Union at northern lati- of dying from some unrelated cause tudes and by the U.S. in the mid-Pacific. before any radiation-related cancer is �� For global fallout, the mix of radionu- diagnosed. �� clides that might contribute to exposure Relatively little of the information � �� differs�� from that of NTS fallout, largely on radiation-related risk comes from �� because radioactive debris injected studies of populations exposed mostly into the stratosphere takes one or more or only to radioactive fallout, because Figure 10. Lifetime risk per gray of absorbed years to deposit, during which time the useful dose-response data are difficult radiation dose can be calculated as a func- shorter-lived radionuclides largely dis- to obtain. However, the type of radiation of age at exposure; here these risks are appear through radioactive decay. Of tion received from external sources in graphed on a logarithmic scale. The curves for leukemia refer to the absorbed doses to greater concern are two longer-lived fallout is similar to medical x rays or red bone marrow, whereas the curves for thy- radionuclides, strontium-90 and cesi- to gamma rays received directly by roid cancer refer to the absorbed doses to the um-137, which have 30-year half-lives the Hiroshima and Nagasaki A-bomb thyroid gland, and the curves for all cancers and did not decay appreciably before survivors, allowing information from refer to whole-body absorbed doses. final deposition. Examples of the doses individuals so exposed to be used to

��

Figure� 11. Average doses in milligray (mGy)� for adults (unless accompanied by a superscripted “a,” which denotes a child born January 1, 1951) living in the contiguous United States during the era of atmospheric testing are shown for the most important radionuclides. Note that the radionuclides are organized by half-life, from longest to shortest (in years, y, or days, d), descending, rather than by atomic weight.

estimate fallout-related risks from ex- The applicability of risk estimates of U.S. residents from I-131 in fallout ternal radiation sources. Estimates�� of based on studies�� of external radiation from tests in Nevada. In a related activ- �� radiation-related lifetime cancer� risk exposure to a population exposed main- ity, we evaluated the risks of thyroid per unit dose from external radiation ly to internal sources, and to I-131 in par- cancer from that exposure and esti- sources to the organs and tissues�� of ticular, has been debated for many years. mated that about 49,000 fallout-related interest are shown in Figure 10 for leu- This uncertainty relates to the uneven cases might occur in the United States, kemia, thyroid cancer and all cancers distribution of I-131 radiation dose with- almost all of them among persons who combined. Estimated risks, in percent, in the thyroid gland and its protraction were under age 20 at some time dur- are given separately by sex, as func- over time. Until recently, the scientific ing the period 1951–57, with 95-percent tions of age at exposure. consensus had been that I-131 is proba- uncertainty limits of 11,300 and 212,000. Thyroid cancer is a rare disease over- bly somewhat less effective than external The estimated risk may be compared all—with U.S. lifetime rates estimated radiation as a cause of thyroid cancer. with some 400,000 lifetime thyroid can- to be 0.97 percent in females and 0.36 However, observations of thyroid cancer cers expected in the same population percent in males—and it is extreme- risk among children exposed to fallout in the absence of any fallout exposure. ly rare at ages younger than 25. Fur- from the Chornobyl reactor accident in Accounting for thyroid exposure from thermore, the malignancy is usually 1986 have led to a reassessment. An In- global fallout, which was distributed indolent, may go long unobserved in stitute of Medicine report concluded that fairly uniformly over the entire United the absence of special screening efforts the Chornobyl observations support the States, might increase the estimated and has a fatality rate of less than 10 conclusion that I-131 has an equal effect, excess by 10 percent, from 49,000 to percent. These factors make it difficult or at least two-thirds the effect of internal 54,000. Fallout-related risks for thyroid to study fallout-related thyroid cancer radiation. More recent data on thyroid cancer are likely to exceed those for any risk in all but the most heavily exposed cancer risk among persons in Belarus other cancer simply because those risks populations. Thyroid cancer risks from and Russia exposed as young children to are predominantly ascribable to the thy- external radiation are related to gender Chornobyl fallout offer further support roid dose from internal radiation, which and to age at exposure, with by far the of this inference. is unmatched in other organs. highest risks occurring among women In 1997, NCI conducted a detailed External gamma radiation from fall- exposed as young children. evaluation of dose to the thyroid glands out, unlike beta radiation from I-131,

© 2006 Sigma Xi, The Scientific Research Society. Reproduction www.americanscientist.org 2006 January–February 55 with permission only. Contact [email protected]. Fallout and Radiological Terrorism Concern about the possible use of radio- Estimating Your Thyroid Cancer Risk active materials by terrorists has been heightened following the attacks on the A Web-based calculator World Trade Center and the Pentagon developed by the Na- on September 11, 2001, and other acts tional Cancer Institute elsewhere in the world. Conventional is available to anyone attacks, including use of a dirty bomb— wishing to estimate in- that is, a conventional explosive coupled dividual thyroid cancer with radioactive material—seem more risks associated with likely (because they are easier to carry exposure to I-131 radia- out) than a fission event, but it is still use- tion in fallout from the ful to ask ourselves “What lessons from Nevada Test Site, for our research on fallout are applicable to persons who lived in the events of radiological terrorism?” The U.S. during the 1950s. potential for health damage downwind The calculator can be of a terrorist event involving any degree accessed through the In- of fission will be dominated by exposure ternet at its stand-alone to early highly radioactive fallout. web page (http://ntsi131. Accurately projecting fallout patterns nci.nih.gov/) or through requires knowledge of the location and the main NCI website altitude at which the device is explod- (http://www.cancer.gov/i131), which provides more general information ed, and the local meteorology—particu- about the NTS, I-131 and radioactive fallout. Information required for the larly a three-dimensional characteriza- calculation includes gender, age at exposure, places of residence during the tion of the wind field in the vicinity of years 1951–71, and sources and approximate amounts of milk consumed. the explosion. Logistics would likely lead a terrorist organization to explode a small-scale, fission-type nuclear de- is penetrating and can be expected to in 1954, because the total dose to the vice at ground level. According to the affect all organs. Leukemia, which is be- thyroid gland (88 Gy on average) far National Council on Radiation Protec- lieved to originate in the bone marrow, exceeded those in any of the studies on tion and Measurements, an explosive is generally considered a “sentinel” ra- which the estimates are based. Other yield of only 0.01 kiloton would cause diation effect because some types tend islands in the archipelago, with about more physical damage than the explo- to appear relatively soon after exposure, 14,000 residents in 1954, had average sion that destroyed the Oklahoma City especially in children, and to be noticed estimated doses of 0.03 Gy to bone mar- Federal Building in 1995. Persons with- because of high rates relative to the un- row and 0.68 Gy to the thyroid gland. in 250 meters of a 0.01-kiloton nuclear exposed. Lifetime rates in the general Altogether, excess lifetime cancers are detonation would receive whole-body population, however, are comparable estimated to be three leukemias (com- doses of 4 Gy from the initial radiation, to those for thyroid cancer (on the order pared to 122 expected in the absence resulting in the mortality of almost half of one percent), whereas those for all of exposure, an excess of 2.5 percent), of those exposed. The same dose would cancers are about 46 percent in males 219 thyroid cancers (compared to 126 be received within one hour from expo- and 38 percent in females. expected in the absence of exposure, sure to fallout by those who remained A total of about 1,800 deaths from ra- an excess of 174 percent) and 162 other within 1.3 kilometers of the detonation. diation-related leukemia might eventu- cancers (compared to 5,400 expected, an Acute life-threatening effects would ally occur in the United States because of excess of 3 percent). dominate treatment efforts within the external (1,100 deaths) and internal (650 It is important to note that, even initial weeks of a terrorist event. Later, deaths) radiation from NTS and global though the fallout exposures discussed increase levels of chronic disease, includ- fallout. For perspective, this might be here occurred roughly 50 to 60 years ing cancer, would be expected to con- compared to about 1.5 million leukemia ago, only about half of the predicted tribute to radiation-related mortality and deaths expected eventually among the total numbers of cancers have been ex- morbidity among survivors, including 1952 population of the United States. pressed so far. The same can be said of those with lesser exposures. Among all About 22,000 radiation-related cancers, the survivors of the atomic bombings persons in the U.S. and most other de- half of them fatal, might eventually re- of Hiroshima and Nagasaki. Most of veloped countries, cancer causes about sult from external exposure from NTS the people under study who were ex- 1 in 4 deaths. The total additional cancer and global fallout, compared to the cur- posed to fallout or direct radiation—for risk from exposure to radioactive fallout rent lifetime cancer rate of 42 percent example, A-bomb survivors—at very is relatively small, although follow-up of (corresponding to about 60 million of the young ages during the 1940s, 1950s and the Japanese atomic bomb survivors has 1952 population). 1960s are still alive, and the cumulative shown that elevated cancer risks con- The risk estimates in Figure 10 do not experience obtained from all studies of tinue throughout the remainder of life. apply to the extremely high-dose fallout radiation-exposed populations is that exposures experienced by 82 residents radiation-related cancers can be expect- Fallout—What We’ve Learned of the Marshall Islands exposed to BRA- ed to occur at any time over the entire Over the more than five decades since VO fallout on Rongelap and Ailinginae lifetime following exposure. radioactive fallout was first recognized

© 2006 Sigma Xi, The Scientific Research Society. Reproduction 56 American Scientist, Volume 94 with permission only. Contact [email protected]. as a potential public-health risk, it has facture of luminescent (radium) watch Kerber, R. A., J. E. Till, S. L. Simon, J. L. Lyon, D. stimulated interdisciplinary research dials and in uranium mining, and to C. Thomas, S. Preston-Martin, M. L. Rallison, R. D. Lloyd and W. Stevens. 1993. A cohort in areas of science as diverse as nuclear direct radiation from the atomic bomb- study of thyroid disease in relation to fallout and radiation physics, chemistry, sta- ings of Hiroshima and Nagasaki. Since from nuclear weapons testing. Journal of the tistics, ecology, meteorology, genetics, then, organ-specific dose-response re- American Medical Association 270:2076–2082. cell biology, physiology, exposure and lationships for radiation-related risks Knapp, H. A. 1963. Iodine-131 in Fresh Milk and risk assessment, and epidemiology. of malignant and more recently benign Human Thyroids Following a Single Deposition of Nuclear Test Fallout. U.S. Atomic Energy Individual radionuclides in fallout disease (for example, cardiovascular Commission, Division of Biology and Med- were recognized early on as opportune disease and benign neoplasms of vari- icine, TID-19266. Washington, D.C.: Atomic tracers by which the kinetic behavior ous organs) have been increasingly well Energy Commission. Available from the of elements could be studied, both quantified with further follow up of DOE/NV Nuclear Testing Archive, P.O. among components of ecosystems and these and other populations, and it is Box 98521, Las Vegas, NV in their transport to people. The phe- increasingly clear that radiation-related National Cancer Institute. 1997. Estimated Expo- sure and Thyroid Doses Received by the American nomenon of fallout, while contributing risk may persist throughout life. Fallout People from Iodine-131 Fallout Following Nevada only modestly to our overall under- studies have substantially clarified the Atmospheric Nuclear Bomb Tests. Washington, standing of radiation risks, has taught consequences of exposure to specific or- D.C.: U.S. Department of Health and Hu- us much about pathways of exposure gans from internal contamination with man Services, National Institutes of Health, National Cancer Institute. http://rex.nci.nih. and about cancer risks to the public in radioactive materials—for example, gov/massmedia/Fallout/index.html settings outside the medical and oc- I-131 in the thyroid gland—and there National Cancer Institute. 2004. Estimation cupational arenas. And in particular, is every reason to believe that, on a of the Baseline Number of Cancers Among fallout studies helped increase our un- dose-specific basis, increased risks from Marshallese and the Number of Cancers At- derstanding of health risks from spe- fallout should be similar to those from tributable to Exposure to Fallout from Nuclear cific radionuclides, for example, I-131. other radiation sources. Our improved Weapons Testing Conducted in the Marshall Islands. http://dceg.cancer.gov/RMIdocs/ This has made possible the develop- understanding of individual radionu- 9-28Response_appendix.pdf ment of the National Cancer Institute’s clides, radiation dose and related health National Council on Radiation Protection and thyroid dose and risk calculator (see risk is due in part to decades of study of Measurements (NCRP). 2001. Management of “Estimating Your Thyroid Cancer Risk,” fallout from nuclear testing; that same Terrorist Events Involving Radioactive Material, facing page). understanding today makes us better NCRP Report No. 138, Bethesda, Md.: NCRP. In the U.S., it took a number of years prepared to respond to nuclear ter- National Research Council. 2005. Health Risks from Exposure to Low Levels of Ionizing Ra- for the differences in dose and cancer rorism, accidents or other events that diation: BEIR VII Phase 2. Washington, D.C.: risk from regional and global fallout to could disperse radioactive materials in National Academy Press. be understood. We have learned that the atmosphere. Simon, S. L., and A. Bouville A. 2002. Radia- the internal doses from global fallout tion doses to local populations near nuclear were considerably smaller for the thy- Bibliography weapons test sites worldwide. Health Phys- ics 82:706-725. roid, but greater for the red bone mar- Bouville, A., S. L. Simon, C. W. Miller, H. L. Simon, S. L., A. Bouville and H. L. Beck. 2004. row, than those from Nevada fallout, Beck, L. R. Anspaugh and B. G. Bennett. The geographic distribution of radionuclide 2002. Estimates of doses from global fallout. whereas the doses from external ir- deposition across the continental U.S. from Health Physics 82:690–705. radiation were similar for Nevada and atmospheric nuclear testing. Journal of Envi- Cardis, E., et al. 2005. Risk of thyroid cancer ronmental Radioactivity 74:91–105. for global fallout. 131 We estimate that in the U.S. the pri- after exposure to I in childhood. Journal of Stevens, W., D. C. Thomas, J. L. Lyon, J. E. Till, the National Cancer Institute 97:724–732. mary cancer risks from past exposure R. Kerber, S. L. Simon, R. D. Lloyd and S. Church, B. W., D. L. Wheeler, C. M. Camp- Preston-Martin. 1990. Leukemia in Utah to radioactive fallout are thyroid can- bell, R. V. Nutley and L. R. Anspaugh. 1990. and radioactive fallout from the Nevada cer and leukemia, whereas in a very Overview of the Department of Energy’s Test Site—a case-control study. Journal of the few cases—for example, the Marshall Off-Site Radiation Exposure Review Project American Medical Association 264:585–591. Islands—large internal doses as a re- (ORERP). Health Physics 59:503–510. VanMiddlesworth, L. 1956. Radioactivity in sult of ingestion of radionuclides have Department of Health and Human Services. thyroid glands following nuclear weapons led to significant risks of cancers in the 2005. A Feasibility Study of the Health Conse- tests. Science 123:982–983. stomach and colon. Our research has quences to the American Population from Nucle- Whicker, F. W., T. B. Kirchner, L. R. Anspaugh ar Weapons Tests Conducted by the United States and Y. C. Ng. 1996. Ingestion of Nevada quantified the likely number of cancer and Other Nations. See http://www.cdc.gov/ Test Site fallout: internal dose estimates. cases to be expected in the U.S. from nceh/radiation/fallout/default.htm Health Physics 71:477–486. Nevada exposures and has contrib- Gilbert, E. S., C. E. Land and S. L Simon. 2002. uted to the assessment of risk at other Health effects from fallout. Health Physics worldwide locations. 82: 727–735. Nuclear testing in the atmosphere Gilbert, E. S., R. Tarone, A. Bouville and E. Ron. 1998. Thyroid cancer rates and I-131 began 60 years ago. It ended in 1980, in For relevant Web links, consult this part because of public concerns about doses from Nevada atmospheric nuclear bomb tests. Journal of the National Cancer issue of American Scientist Online: involuntary exposure to fallout. By that Institute 90:1654–1660. time, increased cancer risk had been Glasstone, S., and P. J. Dolan. 1977. The Effects of established as the principal late health http://www.americanscientist.org/ Nuclear Weapons. 3rd ed. Washington, D.C.: IssueTOC/issue/801 effect of radiation exposure, based pri- U.S. Dept. of Defense and Energy Research marily on studies of populations ex- and Development Administration. posed to medical x rays, to radium and Health Physics. 2002. 50 years of fallout re- radon decay products from the manu- search. Health Physics 82(5):573–748.