Increasing exposure to ionizing radiation boosts the risk of multiple myeloma, a rare but often fatal cancer of blood-forming tissues, especially among people exposed later in life, according to a study of workers in four U.S. Department of Energy plants.
The study, conducted by University of North Carolina at Chapel Hill (UNC-CH) researchers, analyzed radiation exposures among plant employees and then compared them to health records.
Older workers with cumulative radiation doses of 5 rem or more were almost three-and-a-half times more likely to die from multiple myeloma than workers at the same plants whose cumulative exposure were less than 1 rem.
The current occupational limit for radiation workers is 5 rem per year. Average background radiation is between a tenth and a third of rem per year depending on what is being counted, such as radon.
A report on the findings appears in the April issue of Annals of Epidemiology.
"Workers exposed to ionizing radiation at older ages appeared to be more sensitive than younger workers," said Dr. Steve Wing.
"However, that does not mean that it is safe for young workers to be exposed to radiation. Exposures during the child-bearing ages might lead to genetic mutations that could affect children and future generations."
UNC-CH researchers identified 98 workers who died of multiple myeloma and 391 age-matched controls from a combined roster of 115,143 people hired before 1979 at the Hanford, Los Alamos National Laboratory, Oak Ridge National Laboratory and the Savannah River nuclear facilities.
The study included workers who died through 1990 or, among Hanford employees, through 1986.
The scientists found that male workers and those hired before 1948 died of multiple myeloma at about twice the rate of women and workers hired after 1948.
The National Institute of Occupational Safety and Health (NIOSH) requested and paid for the study because of previous reports suggesting a link between exposure to ionizing radiation and cases of the cancer at the Hanford site, Wing said.
"Our study, which was the largest ever done on this question in U.S. nuclear workers, was intended to include more cases of the disease, better evaluation of radiation does and measurement of other occupational exposures not available in the Hanford studies," said Wing.
Investigators also tried to determine whether workers exposed to solvents, metals, welding fumes, asbestos and other agents faced increased risks of multiple myeloma.
Records of such exposures, however, were inadequate to enable the scientists to calculate increased risks accurately.
Because exposures to ionizing radiation were almost entirely below what government regulations currently allow, the findings could affect federal occupational exposure standards, the scientists said.
"One important element of this work is that it comes at a time when the U.S. Department of Energy is expressing greater concern for workers' health and the history of radiation exposures in the nuclear weapons complex," said Wing.