Academic journal article Environmental Health Perspectives

The Effects of Internal Radiation Exposure on Cancer Mortality in Nuclear Workers at Rocketdyne/Atomics International

Academic journal article Environmental Health Perspectives

The Effects of Internal Radiation Exposure on Cancer Mortality in Nuclear Workers at Rocketdyne/Atomics International

Article excerpt

We examined the effects of chronic exposure to radionuclides, primarily uranium and mixed-fission products, on cancer mortality in a retrospective cohort study of workers enrolled in the radiation-monitoring program of a nuclear research and development facility. Between 1950 and 1994, 2,297 workers were monitored for internal radiation exposures, and 441 workers died, 134 (30.4%) of them from cancer as the underlying cause. We calculated internal lung-dose estimates based on urinalysis and whole-body and lung counts reported for individual workers. We examined cancer mortality of workers exposed at different cumulative lung-dose levels using complete risk-set analysis for cohort data, adjusting for age, pay type, time since first radiation monitored, and external radiation. In addition, we examined the potential for confounding due to chemical exposures and smoking, explored whether external radiation exposure modifies the effects of internal exposure, and estimated effects after excluding exposures likely to have been unrelated to disease onset. Dose-response relations were observed for death from hemato- and lymphopoietic cancers and from upper aerodigestive tract cancers, adjusting for age, time since first monitored, pay type, and external (gamma) radiation dose. No association was found for other cancers, including cancers of the lung. Despite the small number of exposed deaths from specific cancer types and possible bias due to measurement error and confounding, the positive findings and strong dose-response gradients observed suggest carcinogenic effects of internal radiation to the upper aerodigestive tract and the blood and lymph system in this occupational cohort. However, causal inferences require replication of our results in other populations or confirmation with an extended follow-up of this cohort. Key words: cancer mortality, hematopoietic cancers, internal (alpha) radiation, lymphopoietic cancers, occupational cohort study, upperaerodigestive tract cancers. Environ Health Perspect 108:743--751 (2000). [Online 28 June 2000] http ://ehpnet1.niehs.nih.gov/docs/2000/108p743-751ritz/abstract.html

Compared to a wealth of information about effects of low-dose external radiation exposures (gamma and X rays), considerably fewer data are available for quantifying human health risks associated with chronic internal exposure to radionuclides. In animal experiments, high internal doses from alpha- and beta/gamma-emitting radionuclides have resulted in immunosuppressive and carcinogenic effects in organs where these radionuclides concentrate (1). The carcinogenic potential of such radionuclides has been confirmed in a few human populations exposed to high doses, including uranium miners and millers, radium dial painters, and patients treated with Thorotrast and [sup.224]Ra (2,3). The sites of cancer have coincided with distribution patterns for the radionuclides within the body, with increases in the incidence of lung, liver, and head--sinus carcinomas, as well as leukemias and bone sarcomas.

Studies published to date examining health effects in workers in the nuclear industry who were exposed internally to radionuclides have yielded inconsistent findings at dose levels less than 1 Sv (100 rem) (Table 1). The lack of consistency may be partly a function of differences in the types of alpha radiation-emitting particles to which workers have been exposed at different nuclear facilities; for example, some workers were primarily exposed to [sup.239]Pu and [sup.238]Pu, others to uranium dusts, a mixture of tritium, plutonium, and other radionuclides, and others to [sup.222]Rn or [sup.210]Po (Table 1). After ingestion or inhalation, radioactive particles, depending on their size, solubility, and chemical structure, differ in their distribution through the body, their organ residence time, and the transfer, dissolution, and absorption of the radioactivity associated with the particles (3), and hence might be expected to vary in their effects across organ systems. …

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