COMMENTARY

An Epidemiological Overview of Chernobyl-Related Research

WILLIAM J. SCHULL

University of Texas Health Sciences Center, Medical Genetics Center, Houston, Texas, USA

On April 26,1986, a series of misguided decisions at the Chemobyl nuclear power plant in the Ukraine led to the world’s worst nuclear accident. Large amounts of radioactive nuclides, primarily those of iodine and cesium, were released to the surrounding area and dispersed over vast regions of the then-Soviet Union and the northem hemisphere. Continued release of radionuclides over a period of 10 days or so and their spread into the environment posed major health problems for the authorities of the areas most concerned, primarily Belarus, the Russian Federations, and the Ukraine. Efforts were made as quickly as was practical to assess the extent of the radioactive contamination, to mitigate the effects on the environment and on humans, and to determine the probable radiation doses of individuals residing in the vicinity of the plant and elsewhere. It was soon apparent that the medical, scientific, and social ramifications of the disaster posed serious public health challenges to the affected republics, but evaluation of the magnitude of these challenges required careful research.

The six papers in this section detail some of the ensuing research activities, largely as they reflect studies in Belarus. Although this republic is the smallest of the three, geographically and by population, two of its oblasts, Gomel and Mogdev, were severely contaminated. N. Krissenko’s presentation summarizes briefly the status of research in Belarus in 1993 and sets forth some of the administrative issues the Ministry of Health had to con- front. He reminds us that as catastrophic as the Chemobyl accident was, assessment of its effects must be seen in a larger context of public health, especially when there are other no less important demands on a system of health care that must strive to address the needs of all of the republic’s citizens with limited resources.

Reliable assessment of the health issues hinges on sound study designs and the appropriate analysis of their findings. L.E. Peterson and colleagues set forth some of the basic principles of epidemiology, and, more specifically, the design of studies to estimate the excess cancer risk among children exposed externally or internally to Chernobyl radionuclides. Their manuscript is more a statement of “how to do it” than “what has been done” and is directed largely toward the medical investigator inexperienced in epidemiology rather than the experienced epidemiologist. Nonetheless, it is a useful primer that identi- fies clearly some of the problems that have to be surmounted if the findings of a study are to be credible, such as the selection of the most appropriate design, the estimation of the requisite sample size needed to establish a significant result, issues of quality control, and the like.

J . van Hoff and associates summarize the findings on childhood cancer in Belarus over the years 1978-1994, based on cancer registry data and then describe the new Belarusian Childhood Cancer Registry established in 1996. They examine critically the history of registry activities in Belarus which began in 1965, and point to research that is under way to address two important problems that impinge on the utility of the registry data, namely, the assessment of the completeness of mandatory registration of cancer in the republic and the accuracy of the information that exists. This paper, like the one of Peterson et al., should be required reading for anyone contemplating epidemiological studies associated with the Chernobyl accident.

Radiation Injury and the Chernobyl Catastrophe. STEM CELLS 1997;15(suppl2):205-206 0 1997 AlphaMed Press. All rights reserved.

206 Commentary: Epidemiology and Chernobyl

As early as 1990, evidence began to emerge that there were an increasing number of children diag- nosed with thyroid cancer residing in regions adjacent to the Chernobyl nuclear accident site [I , 21. This finding has stimulated further studies aimed at establishing the relationship of this apparent increase to exposure to iodine-131 released in the accident. J. Bleuer and coworkers review the data from Belarus and examine the validity of concerns of skeptics who have questioned the reality of the findings. They conclude, based on the geographic location of the affected children and the temporal sequence of the increase in thyroid cancer, that the most likely cause of the excess risk was the ingestion of iodine-131, although they cautiously note the need for further scrutiny of the findings.

Since the inception in 1947 of the studies of survivors of the atomic bombing of Hiroshima and Nagasaki and their children, a variety of different strategies have been used to estimate the extent of the mutational damage arising from parental exposure to atomic radiation. Although as yet there has been no discernible increase in genetic damage among the children [3], the issue of whether a signif- icant increase does or does not occur remains a pressing one. None of the strategies used thus far to assess the risk of mutations among the children of the atomic bomb survivors has addressed the full gamut of possible genetic damage. The validity of extrapolating effects seen with acute exposure, as in the instance of the atomic bomb survivors, to chronic low-level exposure such as that received as a result of the Chernobyl accident is also uncertain. G.Z. Laduk and coworkers of the Belarusian Institute for Hereditary Diseases describe their findings on congenital malformations among abortuses as well as neonates. They state that there appears to be no significant increase in congenital defects among abortuses or evidence of an increase in trisomy 21, but congenital malformations seem more common among neonates from areas of high contamination. This increase cannot be unambiguously assigned to exposure to ionizing radiation, however, since doses are not yet available on the parents of the neonates and the association is basically ecologic.

The last paper, that of D.F. Gluzman, returns to the issue of radiation-related cancer, specifically malignant diseases of the hematopoietic and lymphoid tissues in the Ukraine. The World Health Organization’s Hematology Pilot Project, a component of the International Program on the Health Effects of the Chernobyl Accident, has concluded that no increase in leukemias has occurred among those exposed to Chernobyl radiation [4]. However, Gluzmnn argues that this conclusion may be pre- mature. He details the need for a reference laboratory suitably equipped and funded not only to charac- terize leukemias according to the current French-American-British classification, but also to explore the role of a variety of oncogenes that have been implicated in leukemogenesis.

REFERENCES 1 Kazakov VS, Demidchik EP, Astakova LN.

Thyroid cancer after Chernobyl. Nature 1992;359:21.

2 Baverstock K, Egloff B, Pincheira A et al. Thyroid cancer after Chernobyl. Nature 1992;359;21-22.

3 Nee1 JV, Schull WJ. The Children of Atomic Bomb

Survivors: A Genetic Study. Washington, DC: National Academy Press, 1991.

4 World Health Organization. Health consequences of the Chemobyl accident. Results of the IPHECA pilot projects and related national programmes. Summary Report. Geneva: World Health Organization, 1995.