RADIATION EFFECTS IN MAYAK WORKERS
Bobby R. Scott, Ph.D.Contents
This information relates to radiation effects among irradiated persons in the southern Ural Mountains area of Russia. There, large populations were exposed over years to relatively large radiation doses. The radiation exposures resulted from the operation of a nuclear complex (Mayak PA) that in produced plutonium for nuclear weapons. Information summarized here is based on peer-reviewed and other publications. [1-8].
The Ural Mountains form the western edge of Siberia and divide Europe from Asia. In the southern part of this region, just east of the Ural Mountains are the cities of Yekaterinaburg (population approximately 1.4 million) and, 125 miles south, Chelyabinsk (population approximately 1.1 million). The southern Ural region is about 1,000 miles east of Moscow and is called the Chelyabinsk region.
1.2 Mayak Plutonium Facility
Shortly after the end of World War II, the former Soviet Union began construction of a nuclear weapons production complex (Mayak PA) in the Chelyabinsk region and established nearby a secret, closed city to house the workers [2]. Because of the secrecy, the city was originally known only by its postal destination, Chelyabinsk-40 (later Chelyabinsk-65) [2]. Although the city is no longer secret, it is still closed to outsiders and is called Ozyorsk (sometimes spelled Ozersk). Entry into Ozyorsk is through guarded, double gates. Presently, the city has approximately 90,000 occupants [2].
The major purpose of the Mayak facility was plutonium production for nuclear weapons [1]. The complex included nuclear reactors, radiochemical and plutonium plants, and associated nuclear waste storage areas. The reactors were used to breed plutonium. The resulting material was chemically processed at the radiochemical facilities. The plutonium was then obtained at the plutonium-extraction facilities.
A letter from then NRC Commissioner Gail de Planque to the U. S. Department of State [2] in 1992 alerted the U.S. government to the opportunity to study large irradiated populations in the Chelyabinsk region.
As a result of Commissioner de Planque's initiative, the U. S. and Russian Federation governments agreed to jointly carry out research on radiation health effects [2]. Scientists and physicians around the world are now studying radiation health effects in different populations in the Chelyabinsk region of Russia as well as populations outside Russia.
Information provided here relates mainly to workers from the Mayak plutonium production facility exposed to single and mixed radiations.
1.3 Radiological Contamination
In its earliest years of operation, 1948-1952, the Mayak PA released massive quantities of radioactive materials, essentially with little or no controls, to the atmosphere and to the nearby Techa River. This, in turn, resulted in massive contamination of the environment [1].
From 1949-1956, the Mayak PA discharged about 3 million curies of liquid wastes into the Techa River. As a result, approximately 124,000 persons were exposed to radiation and radioactive materials [2]. About 7,500 were relocated in the years between 1953 and 1961 [2].
Additional environmental contamination resulted from a 1957 chemical explosion in a radioactive waste storage tank [1,2]. Twenty million curies of radioactive material were thrown from the tank, and 2 million curies were dispersed downwind as a plume. This plume contaminated about 23,000 square kilometers and became known as the "Eastern Ural Radioactive Trace." About 270,000 persons were exposed, and approximately 8,000 were relocated after the explosion.
Starting in October 1951, Mayak PA liquid waste, previously discharged to the Techa River, was diverted to nearby Lake Karachai [1]. This resulted in the accumulation of approximately 120 million curies of radioactive material in this open storage body of water.
In 1967, after a drought caused the water level in Lake Karachai to drop and exposed the contaminated shoreline, windstorms dispersed approximately 600 curies into the surrounding environs contaminating approximately 2,700 square kilometers [1].
As a result of poorly controlled operations of the Mayak plant and accidents there, plant workers and the surrounding populations in the Chelyabinsk region were exposed to high levels of radiation and radioactive materials over prolonged periods.
Additional radioactive materials in the vicinity of Mayak include buried waste, wastes that were discharged into other bodies of water or wastes in storage. The total amount of radioactive waste could be as much as a billion curies [2].
Information on environmental contamination is summarized in (Table 1).
1.4 Established Registries
Russian scientists and physicians have established registries of persons in exposed populations including registries of Mayak workers [1]. The Mayak PA worker registries include personal and medical data.
From the beginning, Mayak workers were provided with personal monitoring devices [8]. These included ionization-type devices for recording daily exposures and film badges (later replaced by the TLD). Early film devices lacked filters to differentiate the type and energy of the radiation, but Russian scientists are reconstructing the early dosimetry systems and exposure environs to help clarify the early exposure records.
Only limited bioassay and other data are available for the early years of the Mayak PA for persons who inhaled mainly plutonium-239 (but also some americium-241) [6]. This makes it difficult to accurately estimate radiation doses for many persons that inhaled plutonium-239. References to plutonium-239 below should be interpreted to mean "mainly plutonium-239 but also some americium-241." Both isotopes emit alpha particles.
1.5 Types of Radiation Exposure
Mayak PA workers employed at nuclear reactor facilities (used for plutonium breeding) were exposed mainly to gamma rays but in some cases also to neutrons, including exposures during some criticality accidents [5]. Presently, it is difficult to get information about who was involved in these accidents.
Mayak PA workers employed at radiochemical facilities and plutonium extraction facilities were exposed to external gamma rays in combination with alpha radiation from inhaled plutonium-239 [5].
The periods of greatest exposure of Mayak workers occurred in the first decade of operation, 1948-1958. Some workers received external gamma-ray doses as high as 10 Gy (1000 cGy) accumulated over many years [5].
The Mayak worker registry for this period covers 8,800 workers [2]. A unique feature of the Mayak worker population is that female workers comprised a significant fraction (about one-third) of the 1948-1958 worker registry.
The Mayak PA workers are summarized by work category in (Table 2).
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1.6 Health Effects Seen In 1959, when radiation exposures decreased to presently permissible levels, 1828 cases of occupational diseases associated with radiation exposure were diagnosed
[5]. Of these cases, 92% were registered between 1949 and 1953. Most of the occupational illness (84% of the cases) was due to chronic radiation disease, a disease not so far observed outside of Russia. Chronic gamma-ray doses observed to cause chronic radiation disease total 1 – 10 Gy (100 – 1000 cGy). Chronic radiation disease and other radiation-related injuries are discussed below. During the period when of the Mayak facility was formed, 41 men suffered from the acute radiation syndrome due to total external gamma or gamma plus neutron doses of various degrees of criticality [5]. Four of the 41 acute radiation syndrome cases did not survive.
3. Local Radiation Injuries Cases
A total of 188 persons had signs of local radiation injury, mainly burns of the extremities [5]. These injuries arose from local external gamma or beta-gamma-neutron irradiation. The burns were mainly 1st and 2nd degree, but rarely 3rd and 4th degree. Late effects of the most serious local injuries included trophic changes with recurring ulcers (surgically treated), contracture, organ dysfunction, and in one person, a skin cancer.
4. Radiation Cataracts Cases
Only one radiation cataract was reported to occur in the late period of observation of acute radiation sickness patients [5]. That person was exposed to both neutrons and gamma rays. The dose was reported to exceed 3 Gy (300 cGy). The maximum period of observation was 35 years. Ongoing studies will determine whether additional radiation cataracts were induced in Mayak PA workers.
5. Plutonium-Caused Pneumosclerosis Cases
Some Mayak workers inhaled significant amounts of plutonium. In a registry of 2,283 workers, 120 cases of plutonium pneumosclerosis were reported [5,6]. Pneumosclerosis is a clinical finding that has been described by Dr. N. D. Okladnikova (Table 3) who is presently in charge of the clinic at Branch No. 1 of the Institute of Biophysics in Ozyorsk. This is the clinic where Mayak PA workers are currently treated for radiation-related problems. In the west, pneumosclerosis has been seen only in experimental animals exposed by inhalation to radionuclides. However, a similar effect, radiation pneumonitis, has been recognized in humans and experimental animals as a result of a high-level exposure of the lung from external sources of radiation.
6. Chronic Radiation Disease Cases
Chronic radiation disease (or chronic radiation sickness) was originally reported by the Russian physicians A. K. Guskova and G. D. Baysogolov. They described chronic radiation disease as being characterized by varying degrees of cardiovascular (CV), gastrointestinal (GI), and neural system (NS) disorders
(Table 4). Chronic radiation disease occurred mainly in workers with accumulated gamma-ray doses in excess of 1 Gy (100 cGy). Some workers with the disease had gamma-ray doses less than 1 Gy (100 cGy) but may have also been chronically exposed to neutrons
(Table 5).
6.1 Early Changes
Chronic radiation disease was diagnosed based on changes in radiosensitive systems (hematopoietic and nervous) [5]. Early changes were observed in leukocytes, platelets, and erythrocytes. At the beginning of the development of chronic radiation disease, leukocyte and neutrophil counts progressively fell to 60-65 % of starting values over about 2.5 years. When significant exposure to radiation stopped, the leukocyte count improved, reaching 80-85% of the initial level after 5 years and 90-95% after 20-25 years [5]. At the beginning of the development of chronic radiation disease, thrombocyte counts progressively fell to 50-60 % of starting values over about 2.5 years. Recovery was observed. Significant recovery occurred by 5 years after removal of workers from excessive radiation environments. However, full recovery required more than 20 years [5]. At the beginning of the development of chronic radiation disease, erythrocyte counts decreased to the minimum of normal values. Thereafter, counts fluctuated over years for both men and women [5]. Bone marrow status was studied by Dr. N. D. Okladnikova and colleagues in 374 Mayak PA workers using myelograms. The myelograms revealed normal bone marrow cellularity in 50% of the cases examined. The remainder had compensatory reactions associated with formation of new erythrocytes and granulocytes. The frequency of bone marrow hypoplasia increased with both dose and dose rate [5]. Significant central nervous system changes occurred during chronic radiation disease. Several syndromes were identified by Dr. N. D. Okladnikova and colleagues [5]: the first syndrome involved a disturbance of neurovascular regulation; the second was the asthenic (weakness) syndrome; and the third was a syndrome involving organic changes related to the loss of myelin by nerves. Based on 30 years of observation by physicians in Ozyorsk, Russia, the frequency of atherosclerosis was found to increase progressively after the first 10 years of observation for persons who developed chronic radiation disease. The induction of atherosclerosis was found by the Russian physicians to be associated with cumulative gamma-ray doses greater than 2 Gy (200 cGy) and annual gamma-ray doses greater than 1 Gy (100 cGy) [5].
6.7 Main Causes of Death
Cause of death falls into two main categories: (1) malignant neoplasm and (2) other. 6.7.1 Malignant Neoplasms Malignant neoplasms considered to cause deaths include lung, stomach, colon, rectum, pancreas, uterus, and breast cancer. Also included are acute and chronic myeloid leukemia and acute lymphatic leukemia [5]. 6.7.2 Other Other causes of death include aplastic anemia, ischemic heart disease, intracerebral hemorrhage, and thrombosis [5].
7. Likely Life-Saving Measures Taken When Russian physicians observed signs of significant radiation injuries, the worker was temporarily removed from the radiation environment and provided medical assistance in a specialized hospital [5]. Stay at a sanatorium during the worker’s recovery period was also allowed. This form of worker protection likely saved many lives as some gamma radiation doses (over years) were as large as 10 Gy (1000 cGy) but were not lethal in at least some cases. Work conducted at the specialized hospital became the basis for scientific research later conducted at the Institute of Biophysics, then headed by G. D. Baysogolov, who was considered the leading specialist in the country in the field of radiation medicine.
References Radioactive Contamination in the Chelyabinsk Region Arising from Mayak PA Activities [2]
Site or Source
Radioactivity
(million curies)
Techa River
2.7
120
0.0006 [1]*
Buried
2
20
2
Other waste
(in storage, other discharges
to environment)
unknown
Mean Gamma-Ray Doses for Mayak PA Workers from 1948 to 1958 [2]
| Work Area | Registry |
Mean Dose (cGy or rad) |
||
|
|
|||
Reactors |
2,400 |
|
||
Radiochemical Processing |
4,500 |
|
||
Plutonium Extraction |
1,900 |
|
||
Total |
8,800 |
Plutonium Pneumosclerosis as Defined by Dr. N. D. Okladnikova [2,5,6]
Chronic Radiation Disease as Defined by A. K. Guskova and G. D. Baysogolov [2,3]*
| 1st Degree: | Neuroregulatory disorders (CV in particular)
Leukopenia (unstable, moderate) Thrombocytopenia (rare) |
| 2nd Degree: |
|
| 3rd Degree: | Hematopoietic disruption GI mucosal atrophy Myocardial dystrophy Disseminated encephalomyelitis (mild course) Weakened general immunity (infections, sepsis) |
Mayak PA Workers with Chronic Radiation Disease by Gamma Ray Dose Level [2]
|
Gamma Dose (cGy)* |
Number of Cases** |
|---|---|
| <100 100-249 250-499 >500 |
222 594 789 208 |
Support for preparing this manuscript was provided by U.S. Department of Energy Environmental Management Science Program.
Editorial assistance was provided by Ms. Paula Bradley. The HTML version was prepared by Ms. Alice Fencl.
Please send comments related to the manuscript to bscott@lrri.org