Radiation and Public Perception - ACS Publications - American


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13 A Health Assessment of the Chernobyl Nuclear Power Plant Accident Fred A. Mettler, Jr., and Jonathan E. Briggs Department of Radiology, School of Medicine, University of New Mexico, Albuquerque, NM 87131-5336 In 1989 the then Soviet government requested that the Inter­ national Atomic Energy Agency(IAEA)assess the steps it took to protect the health of villagers in areas surrounding the site of the 1986 Chernobyl nuclear power plant accident. The In­ ternationalChernobyl Project(ICP)performed the assessment. "Task 4" of theICPstudied sample populations from three So­ vietrepublics. Teams of physicians from several nations visited seven "control" (uncontaminated) and six "contaminated" vil­ lages to obtain in-depth medical histories on and to perform extensive physical examinations of over 1300 persons. No ad­ verse health effects directly attributable to radiation were found by Task 4. Many of the villagers demonstrated increased stress and anxiety related to the accident, but no significant differ­ ences were seen between residents of the contaminated and the control villages. However, a high incidence of hypertension, poor dental health, and obesity in the population samples from all the villages did exist. Although it was too early to see increases in leukemia and solid tumors in the populations examined, the authors expect that there will be increases in the incidence of both these types of cancers over the next several decades.

The Accident The release of radioactive and other materials from the Chernobyl nuclear power plant began at approximately 1:23 a.m. on Saturday, April 0065-2393/95/0243-0161$08.00/0 © 1995 American Chemical Society

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26, 1986, just after the roof was blown off of the Unit 4 building. Smoke, fumes, vaporized elements, and debris continued to rise out of the reactor fire for the next several days. The plume that rose from the fire reached a maximum height of 1800 m, decreasing during the first 6 days but increasing from the seventh to the tenth day. Surface winds were light but variable during the release, and there were heavy rains on some days. Radioactive iodine and cesium were carried to the greatest heights and detected outside Russia. Heavier elements, such as cerium, zirconium, neptunium, plutonium, and strontium, were deposited in significant amounts only within Russia. Estimates of the amount of radioactivity freed from the reactor core are about 50 million curies (1.9 X 10 Bq), including nearly 10 million curies (37.0 X 10 Bq) of iodine and 2 million curies (74 X 10 Bq) of cesium. Because of the magnitude of the accident, the duration of the release, the fire and resulting plume, and the weather, hundreds of thousands of people were exposed to a variety of radioactive materials through many and varied pathways. Several exposed population groups can be identified. First, workers at the plant at the time of the accident received high doses from lengthy exposure to the open reactor, contaminated water, and fallout. About 200-300 workers suffered from beta burns and acute radiation syndrome, and about 30 of these died. After the fire was extinguished, about 650,000 workers assisted in the cleanup of the plant and construction of the sarcophagus. These socalled "liquidators" were exposed to dose rates that were high but were limited by time. Finally, villagers in thousands of settlements and towns surrounding the plant received low but continuous exposure from fallout and contaminated food. Little information is available as to how much exposure most of the people in the first two groups received. Consequently, what health effects were and will be attributable to the accident will remain difficult to assess for these people. However, we may assess to a limited degree the medical status of some of the villagers living in settlements around the plant. This information is useful not only in determining the current health of these people, but also as a baseline for future assessments. 18

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Medical Assessment by Task 4 of the International Chernobyl Project The actual and potential medical effects of the Chernobyl accident greatly concern those people directly involved, former Soviet and present Confederation of Independent States (CIS) authorities, and

Young and Yalow; Radiation and Public Perception Advances in Chemistry; American Chemical Society: Washington, DC, 1995.

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people all over the world. Soon after the accident stories of increased illness of all types were reported in the press, although it was very difficult to verify these confusing and often conflicting reports. The complexity and scope of the accident made it difficult for the authorities and politicians to determine if what they did and were still doing to protect the people living in areas contaminated from fallout was appropriate and effective. In late 1989 representatives of the former Soviet government requested the International Atomic Energy Agency (IAEA) to assess the steps it took to protect settlement residents (1). The IAEA proposed that experts and consultants from a large number of countries should perform a radiological evaluation, and the International Chernobyl Project (ICP) was born. Participating agencies included The Commission of the European Communities, The Food and Agriculture Organization of the United Nations, The International Labour Office, the United Nations Scientific Committee on the Effects of Atomic Radiation, the World Health Organization, the World Meteorological Organization, and representatives from more than a dozen nations. One of the five parts or "tasks" of the project was to evaluate the health effects from radiation exposure and health in general. "Task 4", as the health evaluation of the general population was called, conducted its assessment in three affected areas: the Ukraine, Byleorus, and the Russian Soviet Federated Socialist Republic.

The Scope of Task 4.

The health evaluation focused on four

basic questions. 1. What was the current health status of the general population? 2. What health problems were related to the Chernobyl accident? 3. What health effects were directly caused by radiation exposure? 4. What health effects may be expected in the future? Task 4 leaders used a two-point attack to answer these questions. First, there was a review of Soviet data that was gathered since the accident. These data were analyzed using standard epidemiological criteria. Second, medical examinations were performed of persons from the three republics. To obtain the existing Soviet data, project physicians met with over 70 scientists in Moscow, Kiev, and Minsk. These data and meetings established the goals of the field studies. A review of Soviet data

Young and Yalow; Radiation and Public Perception Advances in Chemistry; American Chemical Society: Washington, DC, 1995.

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on nutrition in the area studied was also performed. This review was followed by an independent, though limited, evaluation of the participating settlements' nutritional statuses. The selection of settlements to be studied was made by the Task 4 leaders with the intent to include communities that were representative of the study areas, especially in terms of socioeconomic factors. Thirteen settlements ranging in population from 3000 to 15,000 were chosen. Of these, seven were "control" settlements and six were "contaminated" settlements. Control settlements were defined as having ground level contamination of less than 1 Ci/km (37 kBq/m ), and contaminated settlements were defined as having more than 15 C i / km (555 kBq/m ) of cesium. Because time and resources limited the number of persons who could be examined, a representative sample from each settlement was selected. To create such a sample the individuals who underwent examination in the small settlements were selected by the year of their birth, and those in the larger settlements, by the month and year of their birth. Samples from five age groups (2, 5, 10, 40, and 60 years old) numbering about 20 people each were used. This typically resulted in 10-80% of a settlement's population being represented, depending on the settlement's size. Approximately 250 persons from each settlement were examined, totaling 1356 for the overall study. The examinations were conducted in 1990, and thus the 2-year-old children examined had not been born at the time of the accident and the 5-year-old children were under a year old when the accident occurred. This methodology has some limitations: only those people still residing in the areas selected were examined (it was not possible to identify, locate, and examine those who had left); only small- and medium-sized settlements were visited, and thus urban areas with relatively minor contamination were not represented; and, finally, official data on health prior to the accident were very limited. 2

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Physical Examinations and Data Gathering, Thefieldteams included specialists from the following disciplines: radiation effects, pediatrics, hematology, thyroid disease, ultrasonography, and internal medicine. A World Health Organization representative also was present on each trip, and on one trip a specialist in psychological disorders was also included. The examinations focused on the following areas: the person's past medical history, general psychological state, general health, cardiovascular status, growth parameters, nutrition, thyroid structure and function, and hematological status, as well as the presence of cataracts or neoplasms. An assessment of biological dosimetry was also made from the blood samples taken.

Young and Yalow; Radiation and Public Perception Advances in Chemistry; American Chemical Society: Washington, DC, 1995.

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The medical examinations were performed during three 2-week field trips. In all nearly 3000 people were examined. Of these more than half were self-referred. If, after examination, a disorder was felt to be present, the person was referred to their local health care providers for treatment. Only the findings from the examinations of those selected by age sampling as described previously were included in the project results. The examinations were quite thorough. First, specially trained interpreters assisted the settlement residents who had been selected in filling out an extensive questionnaire consisting of more than 100 inquiries. Data, such as height, weight, blood pressure, and pulse, were measured, and information about the persons diet was recorded. Then a Task 4 physician performed a physical examination, including a review of the person's medical history, again assisted by an interpreter. Thyroid ultrasonography was done, and thermal images were made of all examinations. Blood samples were taken. These samples underwent a variety of analyses to establish levels of thyroid hormones, hemoglobin, leukocytes, lymphocytes, and levels of potentially toxic materials, such as lead, cadmium, mercury, and boron. (Food samples were also examined for these contaminants.)

Results Review of nutritional and medical data from Soviet institutions and individual investigators is, in most cases, inconclusive at best. When specific areas of interest were looked at, such as hematology, often a conclusive determination could not be made from the Soviet data as to whether abnormalities had occurred before or since the accident. For example, although levels of hemoglobin were reported to be low in some children from contaminated settlements, there were no data from these children nor were there data for children from comparable but uncontaminated villages. Methodologies for evaluating conditions varied greatly, and terminology was not standardized. In cases where comparisons could be made, the Soviet data studies rarely used controls or standards so that the significance was limited. The Soviet data did not show a significant increase in the incidence of leukemia or cancers. However, because the Soviet system of typing tumors used categories larger than those of the international system, it was not possible to determine if there were increases in the number of some rare types of tumors nor was it possible to rule out an unseen increase. As for the future it is unlikely that hereditary effects or increases of cancers above the natural incidence can be ascertained using dose estimates and current radiation risk estimates, even if long-term studies are carefully performed.

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General Health.

No disorders affecting the general health of

any of the individuals examined or of any of the population samples taken as a whole could be directly attributed to the Chernobyl accident. It was determined, however, that 10-15% of the adults examined needed to see a doctor for existing conditions, such as hypertension, obesity, or dental problems. Children were generally found to be healthy and growing in accordance with both Russian and current U.S. standards, despite differences in nutrition and health care. The only generalized finding that could be interpreted as a result of the accident was the high levels of stress and anxiety seen in the settlement residents. This anxiety was most often produced by individual concerns about the future, the prospect of having to relocate, or both. These conditions were much more prevalent than the biological threat of the contamination would warrant. Many of the people examined believed or suspected they had physical problems from the contamination. Relocation also induced anxiety in many of these people, as evidenced by the fact that, although most had lived in the same place since birth, 72% of the adults in the contaminated settlements wanted to relocate. In contrast only 8% in the control settlements wanted to leave. Toxicology. Blood levels of several toxic materials other than radionuclides were measured. In addition there was particular concern about the possibility of lead poisoning from food and water contaminated by lead that was dumped into the reactor and vaporized by the fire. Levels of cadmium, mercury, and lead were low when compared to those found in the general populations of Italy, Sudan, and the United States. Hematology. Hematocrit, hemoglobin, erythrocyte number, and erythrocyte mean corpuscular volume were obtained for persons living in control and contaminated settlements. No significant differences were found between control and contaminated settlements. Low hemoglobin levels and low red cell counts were seen in some children. However, no statistically significant difference in values for any age group in either contaminated or control settlements was found. There also was no difference in leukocytes and platelets between the control and contaminated populations nor was there any apparent significant effect on the immune systems of these populations, as determined by the levels of lymphocytes and the prevalence of other diseases.

Thyroid Gland.

The thyroid is particularly susceptible to ra-

dioiodine and so was of particular interest to the Task 4 investigators. Blood levels of both thyroid stimulating hormone (TSH) and thyroid

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hormone (free T4) were normal in the children examined. A compar­ ison of these levels from children in the control settlements with those from children in contaminated settlements showed no significant dif­ ference. A comparison of thyroid sizes and size distributions of these two groups also showed no differences. The incidence of thyroid nod­ ules in both children and adults was similar to those reported in other countries. Neoplasms. The incidence of cancer began rising in Russia be­ fore the accident. Task 4 did determine that reporting had been in­ complete but could not determine if this was due to methodological differences, improvements in detection, or some other cause. A l ­ though the data did not show a striking increase in leukemia or thy­ roid tumors since the accident, this possibly was the result of several factors, including the classification method used. Thus, an increase in such tumors must be considered a possibility.

Potential Health Effects in the Future.

Overall, there are

two future health concerns for the villagers affected by Chernobyl, one more immediate than the other. The first and current effect is the stress produced by the accident itself combined with that induced by the prospect or actμality of relocation. The majority of these people have lived in remote, rural areas for generations, and relocation, even to areas similar in geography and with similar lifestyles, is not easy for them. The second potential effect is more long-term: the possibility of radiation-induced problems, particularly cancer. How long it will take for this effect to be observed and to what degree it will be seen de­ pend on many factors, such as the duration of exposure, the age at exposure, degree of exposure, means of exposure, and so on. The po­ tential carcinogenic risk is greater for children than it is for adults. Because exposure for the villagers is low and at a low rate, their risk is less for cancer induction than the risk for those people who received high doses in short periods of time (e.g., at the plant). It is nearly impossible to calculate the risk for individuals, because their doses varied so greatly. There will, however, certainly be an increase in the number of cases of leukemia and solid tumors in the next several years. A typical estimate for a village of 10,000 persons is that the number of such deaths is estimated to possibly increase from 1700 to 1750 during the next 10-50 years.

Conclusions Technological disasters like the accident at the Chernobyl nuclear power plant present unique and enormously complex problems in terms of

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assessing their effects on health. Unlike natural disasters high-tech accidents often include hazards that are invisible and arcane, and therefore the people affected have different attitudes about the event than they do about more familiar natural disasters. In addition there is a tremendous sense of loss of control. Much of the anxiety seen in the villagers examined by Task 4 physicians, for instance, was the result of no information or conflicting information. The tremendous increase in adverse health effects reported by much of the media after Chernobyl was not confirmed by the Task 4 investigation. There are two fundamental reasons for this. The first reason is that not enough time has elapsed since the accident for those effects that will become manifest to be seen. The second reason is that the original dose estimates for the people in contaminated villages were much too high. A major factor in the revision of these dose estimates was the ability of the Soviet authorities to bring uncontaminated food to the villages. The new Confederation of Independent States is undergoing enormous political, social, and economic change. What can and will be done in the future by the government is uncertain. The International Chernobyl Project, in general, and Task 4, in particular, made recommendations concerning the need for more and better equipment, improved methodology, increased education, and continued health care efforts.

Reference 1. Report by an International Advisory Committee. The International Cher­ nobyl Project: Technical Report: An Assessment of Radiological Conse­ quences and Evaluation of Protective Measures; International Atomic En­ ergy Association: Vienna, Austria, 1991. RECEIVED

for review August 7, 1992.

ACCEPTED

revised manuscript April 1,

1993.

Young and Yalow; Radiation and Public Perception Advances in Chemistry; American Chemical Society: Washington, DC, 1995.