EH-91-3 A Study of Mortality in Shipyard Workers Involved in Work 
  on Naval Nuclear-Powered Ships
  
           OFFICE OF EPIDEMIOLOGY AND HEALTH SURVEILLANCE
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                            HEALTH BULLETIN
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U.S. DEPARTMENT OF ENERGY                             WASHINGTON, D.C.
Issue 91-3                                              September 1991
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                  A Study of Mortality In Shipyard Workers
              Involved in Work on Naval Nuclear-Powered Ships


Dr. Genevieve Matanoski, an epidemiologist at the Johns Hopkins
University School of Hygiene and Public Health, recently completed
a mortality study of workers employed at six Navy and two private
shipyards.  This study, a milestone among studies of groups of
workers exposed to radiation, is the largest of its kind.  These
workers were involved in the overhaul of nuclear-powered vessels
and have been occupationally exposed to low-level ionizing
radiation.  The purpose of the study was to determine if any excess
risk of leukemia or other cancers was associated with exposure to
low- level  gamma radiation.  Cobalt-60 (found within the piping
system) is the primary source of gamma radiation associated with
work on naval nuclear-powered ships.  The study was funded by a
Department of Energy grant.
  
The study population represents a sample of all civilian males who
worked at least 1 year at the shipyards, beginning with the
overhaul of nuclear-powered ships in 1957.  More than 70,000 men
were included in the study.  The population consisted of two
groups: 38,220 workers classified as radiation-exposed and 32,510
workers with no radiation exposure.  The radiation-exposed workers
were selected from two groups, men who received a cumulative
radiation dose of less than 0.5 rem, and men with a cumulative dose
of 0.5 rem or more.

The data were analyzed to determine if the risk of death from all
causes, leukemia and other blood-related cancers, lung cancer,
mesothelioma (a cancer linked with exposure to asbestos), and other
site-specific cancers in the shipyard worker population differed
from the death rates for white males in the U.S. general
population.

The results of this study indicate that the risk of death from all
causes for radiationexposed workers was much lower than that for
U.S. males.  These results are consistent with other studies
showing that worker populations tend to have lower mortality rates
than the general population because workers must be healthy to be
hired, and must remain healthy to continue their employment. 

While total mortality was lower than expected when compared to  the
general population, it was highest for the shipyard workers not
exposed to radiation.  The death rates from leukemia and other
blood-related cancers for both the radiationexposed and non-exposed
workers were similar to those for U.S. men.

The death rate for cancer among the radiation exposed workers was
slightly lower than that for the U.S. population, but this decrease
was not statistically significant.  The corresponding death rate
among workers not exposed to radiation was slightly higher (12
percent) due to a small increase of lung cancer. 

An increased rate of mesothelioma, a type of cancer linked to
asbestos exposure was found in both the radiation exposed and
unexposed shipyard workers.  Mesothelioma was about 5 times higher
than expected in the radiation-exposed workers and 2.5 times higher
than expected in the unexposed.  Even though elevated, the actual
number of mesothelioma cases is small (36 cases per 70,730
workers), reflecting the rarity of this disease in the general
population.  The researchers suspect that exposure to asbestos in
the early years, when the hazards associated with asbestos were not
well understood, might account for this excess risk of cancer. 
However, the study did not specifically look at asbestos or other
possible hazards such as cigarette smoking.  Additional studies are
planned to investigate this observation and update the study with
data beyond 1981.

The Johns Hopkins study found no evidence to conclude that the
health of men involved in work on nuclear-powered ships has been
adversely affected by exposure to low levels of radiation
incidental to work on these ships. 


      This Health Bulletin is one in a series of routine publications
      issued by the Office of Health to share data from health studies
      throughout the DOE complex. The authors conclusions do not
      necessarily reflect those of the Department.  For more information
      contact:  Dr. Terry L. Thomas, Director, Health Coordination and
      Communication Division, Office of Epidemiology and Health
      Surveillance, U.S. Department of Energy, Washington, D.C.  20585;
      Telephone FTS 233-5328, Commercial (301) 353-5328.

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