A new study of nuclear workers in California found that low levels of radiation will increase the risk of certain cancers, leaving some questioning the adequacy of federal exposure limits aimed at protecting workers.
The Rocketdyne worker health study, funded by the U.S. Department of Energy, is the latest contribution to a heated debate over low-level radiation's effect on the human body.
"Rocketdyne appeared to be effective in keeping exposures within occupational limits. Yet, we're still seeing the effects of cancer," Hal Morgenstern, the principal investigator for the study, said Tuesday from his office at University of California Los Angeles. "This suggests we might want to re-examine those limits."
The current federal exposure limit for radiation workers is 5,000 millirem per year. In comparison, people in the United States receive an average of 300 millirem annually from the sun, certain foods and other sources of natural radiation.
In one of the most serious contamination cases in years, a Savannah River Site crane operator who accidentally inhaled plutonium dust last fall will get an estimated, cumulative dose of 17,000 millirem over the next 50 years. Plant officials have stressed that the dose - which falls well below the annual limit - won't cause the man health problems.
UCLA researchers examined a group of 4,607 employees who were monitored for external and internal radiation exposure at the Santa Susana Field Laboratory of Rocketdyne/Atomics International, an Energy Department contractor. All worked at the facility northwest of Los Angeles between 1950 and 1993.
Comparing doses with death certificates, the researchers found that workers whose total external exposure was more than 20,000 millirem during their tenure at Rocketdyne had the highest risk of dying from cancer of the blood or lymph system. External radiation comes from a source outside the body.
Workers who accidentally inhaled or ingested specks of plutonium and uranium and received a cumulative dose of more than 3,000 millirem were also found to be at higher risk.
Based on those results, the overall risk of low-dose radiation was at least six to eight times greater than previously assumed, concluded a national oversight panel that examined the study.
"I think this study is significant because it's the third in a row showing cancer deaths at radiation exposures well below levels allowed by federal agencies," said Dan Hirsch, who co-chaired the oversight panel. "We now know that those levels still kill people."
The Energy Department said it will forward the results of the study to the Centers for Disease Control and Prevention in Atlanta for an independent peer review.
But some say the Rocketdyne findings should be taken with a grain of salt.
"I've been in this business in 50 years and it seems that every year we have some study showing that radiation causes cancer," said Bill Reinig of Citizens for Nuclear Technology Awareness, a South Carolina-based community group supporting SRS operations. "But when they continue to study that population, that relationship usually disappears. There have also been many studies that show nothing of the sort."
What sets the Rocketdyne study apart from many previous worker health studies is the fact that it tracked people over a long period of time, said Beate Ritz, a UCLA epidemiologist who coordinated the study.
Cancers generally take years to develop, which is why studies that cover just a decade or two fail to detect many cases, she said.