Oak Ridge Mortality Study

SUMMARY ( From ORAU Fact Sheet FY97-28 , July 8, 1997)

Investigators (see previous page for affiliations):

E L Frome, D L Cragle, J P Watkins, S B Wing, C M Shy,W G Tankersley, C M West

Funding Source:

Funding was provided by the U.S. Department of Energy (DOE) with management and scientific oversight from the National Institute for Occupational Safety and Health (NIOSH).


This report is the second phase of a study of the mortality of workers employed between 1943 and 1985 at the federal nuclear plants in Oak Ridge, Tenn. The first phase was limited to white males who were employed only during the World War II era when radiation monitoring programs were being developed. Workers omitted from earlier studies are included in this report. The mortality rates of workers at the Oak Ridge plants are compared with each other and with U. S. rates. Dose-response analysis for those individuals who were potentially exposed to external radiation are presented.

This study was initiated out of the need to develop statistical methods for combining mortality data from multiple nuclear facilities. Historically, there were major differences between facilities in terms of when they opened, the kind and frequency of monitoring for radiation exposures, etc. The data from the different facilities were combined to fully utilize all available information concerning the potential adverse health effects related to working at these facilities.

Study Population:

An analysis of mortality rates was conducted among 106,020 persons (27,982 deaths) employed for at least 30 days at the federal nuclear plants in Oak Ridge, Tenn., between 1943 and 1985. They are the X-10, K-25, Y-12, and TEC facilities; the TEC facility is the Y-12 plant before 1948.

Major Findings:

I.  Overall Results

  1. Overall death rate was in close agreement with national death rates.
  2. The cancer death rate ( for all cancer causes as a group) was in close agreement with national death rates.
  3. The death rates for diseases of the digestive system (both malignant and nonmalignant) and diseases of the circulatory system were substantially lower than the national rates.
  4. Among white males, substantial elevations in lung cancer deaths (18% increase), nonmalignant respiratory disease deaths (12% increase) and deaths caused by external sources such as automobile accidents, homicide, drowning, etc. (5% increase) were observed.
  5. Among white males, substantial decreases in deaths were observed in 13 other disease-specific categories for this group.
  6. Among non-white males, a substantial elevation in deaths due to cancer of the large intestine (73% increase, based on 23 deaths) was observed.
  7. Among white and non-white females, no elevations were observed and many decreases were noted.

    II.  Differences Between Facilities

    1. For white males, substantial differences in death rates were observed for the different facilities in the study (X-10, TEC, Y-12, and K-25 ).
    2. Higher death rates were observed among those who worked only at TEC or K-25 and among those who worked at more than one facility. These death rates were higher than death rates among workers who worked only at X-10 or Y-12. This overall difference was primarily due to noncancer causes of death.
    3. Analysis of selected cancer causes for white males showed large differences among the facilities for:
      • lung cancer (increase for all facilities except X-10).
      • leukemia (increase for X-10, and multiple facility workers; decrease for Y-12).
      • other lymphatic cancer (increase for Y-12; decrease for X-10).

      III.  Dose-Response Analysis

      A smaller group of 28,347 white males employed at X-10 or Y-12 who were at risk for exposure to external penetrating radiation was examined to determine if there was a relationship between rates of death from selected causes and level of radiation dose. Observations were:

      1. A 20% fewer deaths overall, compared with national death rates.
      2. A 13% fewer deaths from cancer compared with national death rates.
      3. An association between external radiation dose and death from cancer (all cancers taken together).
      4. Among the specific cancer categories analyzed:
        • - There was a positive association between lung cancer and external radiation dose that was dependent on two deaths in a high dose group. Information on cigarette smoking for this cohort is not available for analysis and residual confounding by cigarette smoking patterns cannot be ruled out. Such confounding could bias dose response estimates in either direction. There was no evidence for an association between diseases of the circulatory system or nonmalignant respiratory disease and external radiation.
        • -There was no evidence for an association between leukemia deaths and external radiation. Leukemia death rates for X-10 workers were higher than U. S. rates and other similar Oak Ridge workers.
        • -Prostate cancer rates were about two times higher for workers with external radiation doses greater than zero when compared to workers with zero dose. There was , however, no evidence for a smoothly increasing dose-response for prostate cancer.

      IV.  Conclusions:

      1. All cause mortality rates were similar to national rates, which is unusual in a study of an occupational group. Death rates in occupational groups are usually lower because national rates include people who cannot work because of health problems. One possible explanation is the large proportion of male workers who were hired at young ages during the war years and who worked only for a short amount of time. These workers may have been transient workers not eligible for the draft because of poor health, or they may have been subjected to more hazardous working conditions because of the war effort.
      2. Monthly paid workers had substantially lower mortality than weekly or hourly workers.
      3. Mortality rates were higher for workers employed for less than one year.
      4. Mortality differences between workforces at these facilities may be due to differences in exposure to internal and/or external radiation; other non-radiation exposures; or residual confounding due to other socioeconomic factors.
      5. Dose-response results for all cancers derived from this study are compatible with those found in other studies.

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