Use of A-bomb survivor studies as a basis for nuclear worker compensation. (Correspondence).

In the Spheres of Influence article in the July issue of EHP, Parascandola (2002) presented our concerns about the validity of extrapolating cancer risks from studies of A-bomb survivors to nuclear workers as a matter of differences in dose rate between the two populations. Our primary critiques of using A-bomb data, however, concern biases that arise from selective survival and dose misclassification (Wing et al. 1999), issues that are not mentioned. Stewart (1985, 1997, 2000) presented evidence of dose- and age-related selective survival in the Japanese cohort assembled for cancer studies 5 years after the nuclear bombing of Hiroshima and Nagasaki. This evidence is in concordance with basic biological principles of heterogeneity in susceptibility and may help explain the inability of A-bomb survivor studies to detect the impacts of in utero radiation exposures on childhood cancers, effects that have been demonstrated repeatedly in low dose studies (Doll and Wakeford 1997; McMahon 1962; Stewart et al. 1956). Age-related selective survival also helps to explain the reported decrease in radiation-cancer dose response among A-bomb survivors exposed at older ages, an observation that deviates from expectations based on the increased sensitivity of older adults to other physical, chemical, and biological agents, evidence of age-related decline in DNA repair capacity, and evidence from some studies of nuclear workers (Richardson et al. 2001; Wing 2000).

Epidemiologic studies depend on accurate exposure classification for valid dose-response estimation. In addition to selective survival in a population subjected to nuclear attack and subsequent devastation of public health infrastructure, radiation-cancer dose-response estimates from A-bomb studies are further affected by a lack of individual dose measurements and the use of dose reconstruction based on interviews conducted in an occupied nation by a scientific team funded and directed by the U.S. government (Wing et al. 1999). The ability to elicit accurate information on location, position, and shielding was affected not only by traumatization of the survivors and their domestic stigmatization but by their distrust of medical teams working under occupation forces (Lindee 1994).

As Parascandola (2002) noted, we believe that findings from carefully conducted epidemiologic studies of badge-monitored nuclear workers exposed to chronic, low-level ionizing radiation should be considered in implementation of the Energy Employees Occupational Illness Compensation Program Act. Medical practices regarding exposures of pregnant women to diagnostic X rays were changed decades ago on the basis of low-dose studies, even though their findings were not predicted from studies of A-bomb survivors. The question today is, will A-bomb studies continue to dictate estimates of cancer risks in adulthood, despite evidence of bias and the availability of alternative epidemiologic data? The large number of highly exposed survivors in the study, cited as a major strength, may actually be a weakness if it encourages scientists and policy makers to confuse statistical precision with valid dose--response estimates that depend on an absence of selective survival and correct exposure classification.

Steve Wing
David Richardson
Department of Epidemiology
School of Public Health
University of North Carolina
E-mail: [e-mail]

REFERENCES

Doll R, Wakeford R. 1997. Risk of childhood cancer from fetal irradiation. Br J Radiol 70:130-139.

Lindee MS. 1994. Suffering Made Real: American Science and the Survivors at Hiroshima. Chicago:University of Chicago Press.

McMahon B. 1962. Prenatal X-ray exposure and childhood cancer. J Natl Cancer Inst 28:1173.

Parascandola M 2002. Compensating for cold war cancers. Environ Health Perspect 110:A405-A407.

Richardson DB, Wing S, Hoffmann W. 2001. Cancer risk from low level ionizing radiation: the role of age at exposure. Occup Med 16:191-218.

Stewart A. 1985. Detection of late effects of ionizing radiation: why deaths of A-bomb survivors are so misleading. Int J Epidemiol 14:52-56.

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Stewart AM, Webb J, Giles D, Hewitt D. 1958. Malignant diseases in childhood and diagnostic irradiation in utero. Lancet 2:447.

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Wing S, Richardson DB, Stewart A. 1999. The relevance of occupational epidemiology to radiation protection standards. New Solutions 9:133-151.