Fallout Radiation: Effects on Marshallese People

Page 1

Fallout Radiation: Effects on Marshallese People An accidental exposure of 290 human beings to radioactive fallout occurred in the Marshall Islands in 1954. The results of this accident brought into sharp focus effects of fallout radiation on man, some of which had not been anticipated. The medical findings have had an important influence on the field of medicine and military and civil defense planning. Since this experience affords the only example of fallout exposure of human beings, this chapter will be devoted to a review of the results of medical examinations of these people over a 13 year period since exposure. For a more detailed description of the findings the reader is referred to the list of references at the end of the 12.2 Fallout from Nuclear Detonations; The 1954 Fallout Accident Radiation hazards from detonation of nuclear weapons can be divided into the immediate type and the residual or fallout type. a nuclear weapon there is an instantaneous release of gamma rays and neutrons which can produce penetrating With the detonation of tremendous numbers of radiation exposure to all personnel in the immediate vicinity. If the detonation has been at a high enough altitude, so that the fireball does not touch the ground, the fission product material will be ejected into the upper atmosphere where it will spread o.~t over large areas of the world, gradually filtering down to in diluted and less active form. This is known as worldwide fallout. The Medical Rcsearc!l Center

Page 2

bombs detonated over Hiroshima and Nagasaki, Japan were detonated high enough . above the ground to result in the immediate type of radiation exposure of the people in these cities with little or no fallout occurring. The effect of this type of exposure to penetrating radiation is covered in Chapters 8, 9 and 10. However, when the fireball does touch the surface of the earth large amounts of incinerated earth, water and d~bris are sucked up into the bomb cloud and adhere to the radioactive fission and induced products, This mixture of particles settles to earth, in accordance with Stoke’s law, for several hundred miles in a downwind direction. This is designated as the localized or “close-in” type of fallout and is characterized by radiation of much higher intensity than occurs with worldwide fallout. Such a fallout occurred in the Marshall Islands following the experimental detonation of a thermonuclear device at Bikini Island on March 1, 1954. Figure 1 shows a rough map of the The following table (Table 1) shows the island groups with degree of involvement. Summary of Fallout Exposure Estimated gamma Extent of Composition Fallout observed dose(rads) skin lesions 18 Marshallese Moderate(mistlike) 69 Less extensive 28 Americans Moderate (mistlike) 78 Slight 157 Marshallese None 14 No skin lesions and Kumatori; Koyama; Kumatori et al.).

Page 3

The island groups were evacuated two days after the accident and received extensive medical examinations over a three months period. The American servicemen, who had been exposed at Rongerik Island, were then returned to their duty stations and the people of Utirik Atoll were returned to their home island. Because Rongelap was too highly contaminated, the people were moved to a temporary home (Majuro Atoll) until 1957, by which time radioactive levels on Rongelap had become acceptable for habitation, a new village was constructed for them and they were returned home (Fig. 2). The low levels of body burdens of radionuclides acquired by the people subsequent to their return to Rongelap will be discussed in Chapter 11. 12.3 Characteristics of Fallout Material The chemical and physical makeup as well as the radiation characteristics of fallout will vary according to such conditions as the size of the weapon, height of burst and type of terrain or soil over which the detonation occurs. All fallout is particulate in nature, but the size, color and other characteristics of the particle will depend to some extent upon the chemical and physical properties of the soil. In the Marshall Island accident where the nuclear device was detonated near the ground, the fallout was a white powdery material largely composed of incinerated coral. The bulk of the radioactivity resided as insoluble oxides on particles of CaO of Ca(OH)2. A large amount of activity was also carried on NaCl particles. Aside from the radioactive component, the calciun oxiJti fn the mater:.. was in itself irritating to the skin due to its caustic nature. Fallout produced

Page 4

from other types of soil, not predominantly coral, might vary considerably in chemical and physical makeup, color and particle size. 12.4 Radioactive Hazards Associated with Fallout Radioactive fallout may result in 3 types of exposure: (1) whole body exposure from gamma radiation; (2) radiation of the skin from deposition of fallout material thereon; and (3) the internal absorption of radioactive materials . Figure 3 is a rough diagrammatic sketch showing the relatively uniform distribution of fallout on the ground, houses, trees and Marshallese personnel. The penetrating gamma radiation, which is represented by the wavy shaded areas, penetrates many yards in air before it is attenuated appreciably. There was, of course, no neutron radiation associated with the fallout. Beta radiation as represented by the stippling in the figure was completely attenuated in several feet of air. Estimates of the beta to gamma ratio vary widely up to 150/1 depending upon the exposure conditions. Alpha emitters were not present in the fallout to any great extent. Even if significant amounts had been, due to their weak penetrating ability, they would not likely add significantly to the skin damage, but might present a hazard from the point of view of internal absorption. Internal absorption of fallout occurs to some extent from inhalation but to a greater extent from ingestion of contaminated food and water. 12.5 Dose Estimations in the Marshallese 12.5.1 Whole body dose. The gamma radiation dose which resulted in a penetrating whole body exposure of the ?Iarshallese .:as calculated from field instrument readings taken shortly after the accident, spectrometric and

Page 5

radiochemical data taken at the time of the fallout, estimates of duration of fallout, exposure time, etc. (Sondhaus et al.). Spectrographic data of the fallout showed gamma energy peaks at roughly 100, 700 and 1500 kev. The varied energy distributions, the greater depth dose due to the near 41T geometry of exposure make the fallout dosimetry significantly different from that of ‘ radiation therapy or experimental radiobiology. Table 1 shows the calculated gamma doses (dose in air) for the different island groups. 12.5.2 Skin Dose. Skin exposure was largely from beta radiation. The dose to the first few millimeters of the body surface were considerably greater than the midline gamma dose. Measurement of beta doses from the skin from fallout was an exceedingly difficult problem due to the complicated spectrum of different energy beta emitters present, the non-uniform distribution on the skin, and the fact that practical dose meters were not between beta radiation and contaminating The penetration of beta particles into of the component isotopes. Each isotope available to adequately discriminate the skin depended on the beta energies has its own characteristic spectrum of beta energies. Figure 4 shows roughly the tissue depth necessary to produce 50% attenuation of the beta particles from several isotopes. In animal studies the dose required to produce recognizable skin lesions by a particular beta emitter has been demonstrated to be dependent on the energy of the beta particles. (Henshaw et al., Davis and Alpen, Snider and Raper, Lushbaugh and Hale, Moritz and Henriques). For example it was found that it takes 20,000 to 30,000 rep 35S(avg. energy 0.05 mev) to produce a reaction while it takes onl’y 1,000 to 2,000 rep of 90Sr or 90Y(avg. energy 0.3-o. ~ mev) to produce the same reaction.

Page 6

In the Maxshallcsc the dose to the skin could not be calculated with any degree of accuracy due to the aforementioned reasons. The majority of the beta radiation was of low energy(avg. 0.1 mev) and accounted for the fact that most of the lesions were superficial in nature. However there was sufficient penetration of more energetic components at the level of hair follicles to result in temporary epilation. Due to the rapid attenuation of beta particles in tissue, the skin surface dose may have been quite high. The contribution of beta radiation to the skin of the Marshallese from the ground has been estimated to have been about 2000 rep to the feet, 600 rep at hip level and 300 rep to the head. These doses were insufficient in themselves to produce detectable lesions though they probably contributed significantly to the sevsrity of the foot lesions that occurred. 12.5.3 Internal Dose. The fallout material was about 10% soluble in water and completely soluble in acid. Ingestion appeared to be a more important route for internal absorption than did inhalation. The activity in the air settles . out fairly rapidly, but contaminated food, water and utensils retain their activity for long periods of time ( Cohn et al.). The amount of fission products reaching the blood stream through the respiratory tract is a function of particle size, and the volubility of the airborne contaminants. The majority of particles with which the activity was associated wcs considerably larger than the optimum size for deposition in the alveolar tissue of the lung. Thus the probability of the retention of inhaled airborne contamination (except possibly for radioiodines) is not appreciable during the expo~ure period. Thi. was borne out by the fact that animals sacrificed at early intervals from Rongelap

Page 7

showed the major portion of activity in their gastrointestinal tract. Based on these studies it was estimated that the amount of radioactive material in the gastrointestinal tract of the more heavily exposed Rongelap group at 1 day post detonation was approximately 3mCi. The initial body burdens of internal emitters in the Rongelap people were estimated from data obtained by radiochemical analysis of the tissues of 2 pigs which had been simultaneously exposed, and subsequent comparison of human Znd animal urine analyses date (Cohn et al.). Information on the tissue distribution of fission products was obtained from the radiochemical analyses of the pigs living on Rongelap for 1 month. Of the internal activity 95% was localized in the skeleton of the pig. The pattern of deposition of the fission product mixture in the skeleton, as seen in an autoradiograph of a tibia of 1 of these pigs, resembles that seen after administration of alkaline earths, i.e. dense deposition in epiphyseal region (Figure 5). In the first few months following the acute exposure, 89Sr and 1311 (PIus the shorter lived iodine isotopes) contributed the greatest internal radiation dose to the Marshallese. Sr contributed the major portion of the beta dose to the skeleton at this time. The highest dose to an individual tissue (100 to 160 rep) was delivered to the thyroid by the iodine isotopes. Table 3 shows the estimates of the mean body burdens of the Marshallese at 1 and 92 days post exposure. Estimated Body Burden of Rongelap People (ye) Activity at Activity at Isotope Day L Day 82 Rare Earth Group 0-1.? 0.03

Page 8

In view of the the estimates of importance of the late development of thyroid abnormalities, dose to the thyroid gland are presented in some detail here. The dose from radioactive iodine is determined by its uptake by the gland, its half-life in the gland, the size of the gland, and the relative proportion of the several radioisotopes of iodine involved. The relative distributions of the radioiodines in fallout is reasonably well known. In addition to 1311, the isotopes I, and to a less extent I contributed significantly to the thyroid dose. The only direct data available on the Rongelap people are radiochemical analyses of pooled urine samples taken 15 days and longer 1311 was estimated to beafter the fallout. The 1 day thyroid content of 11.2 mCi (5.6 to 22.4 mCi). Assuming that 0~1%, (0.05 to 0.2%) of the maximum thyroid burden(not corrected for physical decay) was excreted in the urine on the 15th day(Ng), James has calculated a dose of 160 rad to the adult thyroid from oral intake and inhalation of the various iodine isotopes, considering their fission yield, the average energy deposited in the thyroid gland per disintegration, and the time of absorption. The dose to the thyroid glands of children less than 4 years of age was then calculated by means of these factors with consideration of pulmonary function and the thyroid size of a child of that age. The small size of the childhood thyroid then resulted in a substantially larger dose. The total estimated mean dose from the various iodine isotopes to the childs gland was about 1000 rad, with a range of 700 to 1400 rads. The glands received an additional 175 rads from external gamma radiation. Although the skin overlying the thyroid gland was frequently the site of “beta burns” as shown in Fi~ure 6, the deposit of radioactive materials in this area probably did not add significantly to the thyroid d~se, since most of the beta irradiations were too weak to have penetrated

Page 9

to the depth of the gland. The return of the Rong=lapese to their home island in 1957 resulted in exposure to low levels of radionuclides in their environment. This is discussed in Chapter 11 . Examinations were carried out over a 72 day period initially followed by re -examinations at 6 months and then on an annual basis. Findings have been compared with llarshallese people who were not exposed. Since i957 over 200 Rongelap people who were away from the island at the time of the accident have since returned to live with the exposed people. This group has formed an excellent comparison population. 12.6.1 Penetrating Gamma Radiation. During the first 48 hours typical radiationinduced gastrointestinal synptoms were associated with their gamma radiation exposure. About two-thirds of the Rongelap people experienced anorexia and nausea and a fcw vomited and had diarrhea. These symptoms were noted in the more heavily exposed group only. Following their evacuation from Rongelap the people appeared well until the development of skin lesions 2 weeks later. However, when first examined on the third day, it was apparent that significant radiation exposure had occurred in view of the lowered lymphocyte counts. Serial hematological determinations including total white count, differential, platelet count and hematocrit revealed that the hemopoietic depression was most marked in the 64 people on Rongelap who had received 175 rads, less marked in the “roups receiving less exposure. The averase leukocyte and platelet counts shown graphically in figures 7, 8 and 9. The first counts on the Rongelap

Page 10

were done on post exposure day 3, at which time a drop in total white count was evident. The count then fluctuated perhaps as a result of the beta lesions, with no severe depression over the first 4 weeks. A marked depression then occurred, reaching minimum levels at 6 weeks. The counts approached the levels of the unexposed populations by 2 years. The time course of neutrophil count changes followed closely that of the …