EH-91-0 Mortality Analysis at ORNL                                    

                         DEPARTMENT OF ENERGY (DOE)

                       OFFICE OF HEALTH -- BULLETIN

Issue No. 91-0
On January 28, 1991, Dr. Steve Wing, University of North Carolina (UNC),
presented the results of an epidemiologic study to Oak Ridge National
Laboratory (ORNL) workers.  The investigation updated a previous mortality
analysis performed by Dr. Harvey Checkoway of UNC.  Dr. Checkoway's 1985
study included 8,375 white male ORNL workers and reported less than expected
mortality from all causes combined and a statistically nonsignificant
increase in mortality from leukemia.  The earlier study found no cause of
death associated with increased radiation exposure.  Dr. Wing's study
included 17,517 ORNL workers, but focused specifically on a group of 8,318
white male workers who had worked at ORNL between 1943 and 1972.  The study
focused primarily on white males because their larger numbers provided the
best basis for statistically meaningful results.

Dr. Wing reported that mortality rates for most causes of death were lower
among white male workers than among the general United States' population;
a finding consistent with other studies of DOE workers and consistent with
Dr. Checkoway's study of 1985.  However, in a separate analysis comparing
workers exposed to external ionizing radiation with workers who had no
recorded exposure, there was an apparent association between very long-term
low-level radiation exposure and an increased risk of death from all types of
cancer combined.  The association was strongest for workers exposed 20 or
more years before their deaths.  For most workers, total career doses of
external radiation exposure were quire low (average 1.7 rem); approximately
8 percent of the 8,318 workers had received career exposures to 5 rem or
more.

An additional finding was a greater than expected number of deaths from all
types of leukemia combined (28 deaths observed versus 17.2 expected among
while males).  Although this observation was statistically significant, it
apparently was not related to radiation exposure.

The study could not determine whether the associations were causal or simply
statistical.  In an epidemiologic study, it is possible for two factors to be
closely related because of the way in which the study was designed or the
method by which participants were selected, rather than because the two
factors are biologically related as a cause and effect.  Thus, it is
important to emphasize that an association is not necessarily causal. 
Moreover, the broad category of "all cancers combined" should not be
interpreted to mean that an increased risk was detected for each individual
type of cancer.  Cancer is actually a group of diseases with diverse causes,
and a given category of cancer may contain tumors with very different
underlying causes.  The "combined" category does not permit detection of
different risks for specific types of cancer.  An additional concern is that
the investigators were unable to examine other potential risk factors for
cancer such as exposure to solvents or other environmental factors such as
smoking.

The results of the Wing study contrast with a number of other studies at DOE
facilities that have shown no association between low-levels of occupational
radiation exposure and increased cancer mortality risk.  The study will be
published in the March 20, 1991, issue of the Journal of the American
Medical Association.  The recently signed Memorandum of Understanding
between DOE and the Department of Health & Human Services (DHHS) provides
for the transfer of continued mortality followup of DOE workers and many
other types of epidemiologic research to DHHS.  Future research conducted
under DHHS auspices may provide opportunities for more indepth
investigations of the diverse causes of specific cancers such as leukemia,
and thereby, offer opportunities for further investigation of the findings
reported by Dr. Wing.

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