Wednesday, Oct. 08, 2008

Study looks at leukemia deaths

By Annette Cary, Herald staff writer

A new study of Hanford and other nuclear defense site workers found exposure to low levels of radiation slightly increased the risk that workers would die of leukemia.

The study was conducted by the National Institute for Occupational Safety and Health, a federal research agency, and looked at doses that a worker at a nuclear site might receive over a lifetime of work. Previous studies that look at a correlation between exposure and leukemia typically have looked at higher levels of exposure, according to NIOSH.

In the United States, 71 of 10,000 men can expect to die from leukemia. The study indicated that for workers who were exposed to three rem of radiation in the workplace the risk of dying from leukemia increased to 77 men out of 10,000.

"We emphasize that if workers are exposed to three rem the risk is very low," said Mary Schubauer-Berigan, a NIOSH epidemiologist.

The study looked at workers exposed to more than one rem of radiation and compared their rate of dying from leukemia to those exposed to less than one rem.

The average exposure for those who had more than one rem of radiation was 6 rem. But overall, 3 rem was an average exposure for workers in the study.

The Department of Energy limits radiation exposure to 5 rem per year, but in practice the radiation exposure is controlled to less than 0.5 rem a year, said DOE spokesman Geoff Tyree.

The average person is exposed to about 0.15 rem a year from natural sources of ionizing radiation, excluding radon which has not been linked to leukemia, said Schubauer-Berigan.

Studies more commonly have looked at high doses of radiation in groups such as Japanese atomic bomb survivors, medical patients who receive radiation and nuclear workers in the former Soviet Union.

But the results of the new NIOSH study are consistent with those studies in finding that the risk of death from leukemia increases uniformly as the amount of exposure increases, Schubauer-Berigan said.

The study looked at records for five federal sites: Hanford, Los Alamos National Laboratory in New Mexico, Oak Ridge National Laboratory in Tennessee, Portsmouth Naval Shipyard and Savannah River Site in South Carolina.

Between the 1940s and '90s, a total of 94,517 workers were monitored at the sites for radiation exposure. A search of death certificates found 257 workers at five nuclear weapons sites, including Hanford, died of radiation, but the study included only the 249 for whom the type of leukemia was clear.

Each worker was matched with four other workers who were the same age and were employed at sites in the study but who did not die from leukemia.

Radiation exposure was estimated for all workers, and smoking and exposure to benzene and carbon tetrachloride were taken into account, Schubauer-Berigan said.

The study found the death rate for chronic myeloid, acute lymphocytic and acute myeloid leukemia was slightly higher for workers exposed to more than one rem of radiation than workers who received less exposure. When all types of less common types of leukemia were lumped together, a slight increase in the death rate for workers receiving more than one rem also was seen.

The exception was chronic lymphocytic leukemia, for which no increased death rate could be tied to exposure of more than one rem.

The study also found that workers hired after 1952 seemed to have a higher chance of dying of leukemia than workers hired earlier. Although the study could not explain that, it could be because later monitoring for radiation exposure was more accurate, Schubauer-Berigan said.

DOE believes the results of the study are consistent with the results of previous studies of atomic bomb survivors and nuclear facility workers, said DOE's Tyree.

DOE does not believe the study indicates a need to change radiation exposure limits, he said.

w On the Net: www.cdc.gov/niosh/oerp/msl

w Annette Cary: 582-1533; acary@tricityherald.com