In early September 1994 , the NCI Working Group presented a status report to the NRC Commissioners. Their research will focus on the risk of thyroid cancer from exposures to radioactive Iodine-131, especially among the one million children who were exposed in Belarus -- which received some 70% of the Chernobyl fallout -- and in Ukraine. A second study will focus on the incidence of leukemia among clean-up workers. Agreements for protocols and funding, initiated with the USSR in 1990, have now been approved for Belarus and Ukraine.
Estimates of the total radiation release from Chernobyl still vary, from official Soviet government estimates of 50 million curies to release of the entire core inventory (upward of one billion curies); the figures in the range of 100 million to 250 million curies may be most nearly accurate. Other release estimates from Belarussian experts suggest about 15 million curies of Cesium-137 escaped. It has a half-life of 30 years, hazardous life of three hundred to six hundred years, and is identified as a major component of the residual radioactivity that blankets the agricultural lands of most of Belarus and much of Ukraine, extending beyond their borders into Russia and areas of Eastern and Northern Europe. Radioactive Cesium-137 in soils and water is taken up by plants, entering the food chain; when ingested, it is absorbed in tissues throughout the body and will continue to irradiate the recipient as it slowly decays.
In the eight years since the Chernobyl disaster, there has been at least a forty to fifty-fold increase in thyroid cancer of children in Belarus. The occurrence of this disease, considered rare in children, has risen rapidly from zero reported cases in the years 1979, 1980, 1983 and 1984 before the accident. For Belarussian adults, the thyroid cancer incidence has also risen, but more slowly, from about 100 cases in 1979 to 150 cases by 1986, and to more than 500 cases reported in 1993, with a marked increase in the years after 1986.
Ukrainian data are only slightly less dramatic: for persons who were of childhood age in 1986, the cases rose from seven in that year to 47 in 1992. Incidence per 100,000 for Ukrainian children (of that age group in 1986) increased from 0.07 cases per 100,000 in 1986 to 0.43/100,000 in 1992. In Belarus, comparable figures show an increase from 0.1/100,000 childhood thyroid cancer cases in 1986 to 3.4/100,000 in 1993.
The National Cancer Institute Working Group will undertake both case- control and cohort studies of cancers, thyroid nodules, and hypothyroidism. Iodine 131 doses were measured for only about 10% of the exposed children. Of these, thyroid dose estimates indicate that about 80% of the children tested in Belarus and Ukraine had received doses up to 100 rads to the thyroid (0.0 - 1.0 Gy), although only about 2000 children were reported to have received more than 500 rads (5 Gy). [The "Gray" (Gy) is a new international unit of dose measurement; one Gray equals 100 rads ("radiation absorbed dose"). U.S. public dose standards limit the calculated annual individual total effective dose equivalent to approximately 0.1 rad (0.001 Gy) whole body exposure; weighting factors are applied to specific organ doses, which must be kept as low as reasonably achievable.]
The detailed case-control studies will include some 119 Belarussian children who already have thyroid cancer, and a number still undetermined in Ukraine. The cohort studies will examine 15,000 Belarussian children and 70,000 children in Ukraine, with dose reconstructions based on 1986 measurements, fallout maps, and exposure histories, plus follow-up annual or biennial medical exams.
The National Cancer Institute Working Group expressed interest in obtaining risk estimates for leukemia from "low" doses and low dose rate exposures. At the present time, they told the NRC, these risks are not known, despite extensive research on previously exposed populations. These include Japanese who received acute doses from the Hiroshima and Nagasaki bombings, and U.S. and other nuclear industry workers whose doses were deemed "low".
The upcoming Chernobyl leukemia studies will be designed to provide risk coefficients for low-to-moderate doses, compared with Japanese data. They will also assess the time-response function and influence of dose rate; investigate pathogenesis of radiogenic leukemia; provide for future molecular biologic studies, and finally, estimate future excess leukemias and solid tumors among clean-up workers. A long-term epidemiological follow-up study is included. Its ten year budget for Ukraine is projected to be only $3 million, however, suggesting a relatively limited U.S. research effort.
The biologic impact of chronic low-dose irradiation is now believed to take the form of damage to the immunological system, especially in rapidly growing young children. Immune dysfunctions are associated with higher susceptibility to infections of many kinds and to the normal diseases of childhood, but with a greater degree of severity, longevity, and recurrence. Russian, Belarussian and Ukrainian radiation biologists and physicians who treat the sick children, have suggested that children in this segment of the population appear to experience a higher incidence also of allergies, asthma, childhood diabetes, A Progress Report on U.S. Investigations of Chernobyl-Radiation- Linked Illnesses:
What Is, and Is Not, Being Studied respiratory, gastrointestinal, and endocrine disorders, plus chronic fatigue, lack of stamina, and overall failure to thrive. These societally significant illnesses are not included in the joint American-Belarussian - Ukrainian studies, nor in U.S. radiation exposure standards.
It will be important to maintain a close watch on post-Chernobyl health studies. The radiation impacts of this power reactor accident are a forerunner of what we may expect, worldwide, from an increasing "environmental loading" of ionizing radiation in the biosystem.
Dr. Johnsrud received her PhD in Geography in 1977; her thesis was titled: "A Political Geography of the Nuclear Power Controversy: The Peaceful Atom in Pennsylvania." She is the director of the Environmental Coalition on Nuclear Power, working out of State College, Pennsylvania. She is also a member of the Board of Directors of ECOLOGIA.