A Nested Case-Control Study of Leukemia and Ionizing Radiation at the Portsmouth Naval Shipyard
DHHS (NIOSH) Publication Number 2005-104
This study analyzed the relationship between external ionizing radiation and leukemia mortality among civilian employees of the PNS to help determine whether occupational exposures to radiation were associated with a risk for leukemia. Exposure assessments for benzene and carbon tetrachloride were also completed since these chemicals might also cause leukemia.
The study population included 115 PNS employees who had died from leukemia. They were compared with a total of 460 other PNS workers who served as controls. All workers in this study were selected from the 37,853 civilians employed at the Shipyard for at least one day between January 1, 1952 and December 31, 1992. Thirty-four of the leukemia cases and 167 controls were monitored for ionizing radiation exposures while employed at PNS.
The case-control study results suggest that leukemia mortality risk increased with increasing cumulative occupational ionizing radiation dose among PNS workers. The magnitude of increase in leukemia risk is consistent with other radiation epidemiology study results. Workers potentially exposed to benzene or carbon tetrachloride for longer periods of time also appear to have greater risk of death from leukemia. Uncertainty in the risk estimates, i.e., the rather wide confidence intervals, is attributed to the relatively small number of leukemia deaths (34) among radiation-monitored workers and reliance on job titles and shops to estimate benzene and carbon tetrachloride exposures instead of individual monitoring results for these chemicals.