The government-financed study also found evidence that workers who received long-term radiation exposure at Rocketdyne's facility in Los Angeles and Ventura counties may be at increased risk of dying from lung and certain other cancers. The findings were released today by UCLA researchers in conjunction with the study's advisory panel and the California Department of Health Services.

"We found that these occupational radiation exposures were more strongly linked to cancer deaths than has been found in several earlier studies, including those that have examined survivors of radiation from atomic bombs," said Beate Ritz, a UCLA epidemiologist and one of the study's investigators.

"This is an important study suggesting that the magnitude of the health effects of long-term exposures to low doses of radiation may be appreciably greater than previously believed," said Hal Morgenstern, a UCLA epidemiologist who headed the project. "Since 80 percent of the study group was still alive at the end of the project, we need to follow these workers in the decades ahead."

The study of worker health at Rocketdyne was initiated in the early 1990s at the urging of several state legislators. People working at or living near Rocketdyne in Simi Valley have been concerned about potential health risks since 1980, when critics of the facility released a report detailing radiation-related accidents at the facility.

State health officials decided to focus on worker health because workers were most likely to have received the highest dose of radiation, and because their exposures were routinely monitored and recorded.

Researchers from the UCLA School of Public Health analyzed company records for about 4,600 Rocketdyne workers who were monitored for radiation between 1950 and 1993. The researchers tracked each worker to determine who had died, when the death occurred and what caused the death.

Rocketdyne measured worker exposure both through film badges that measure external forms of penetrating radiation such as X-rays and through urinalysis or other methods that measure forms of internal radiation such as uranium dust that can be hazardous only if inhaled, swallowed or absorbed through wounds. Virtually all the workers were monitored for external radiation, and about half the group also received internal radiation monitoring. Researchers separately examined the number and types of cancer deaths among the external radiation group and the internal radiation group.

Of the workers studied, researchers identified 875 who had died (about 20 percent of the study group); 258 of those deaths (about 30 percent of the deaths) were due to cancer as the underlying cause. The study did not identify workers who developed cancer but have not died.

Workers with the highest cumulative doses of radiation were those most likely to have died from one or more types of cancer, among both externally and internally monitored workers.

Being exposed to external forms of radiation was associated with dying from cancers of the blood and lymph system, such as leukemia, from lung cancer and from all cancers combined. The death rates of these cancers were particularly high for workers exposed to more than 200 millisieverts of radiation. (A typical chest X-ray delivers about 0.1 millisievert of radiation.) Workers exposed to these high levels of external radiation were three times more likely to die from cancers than were workers exposed to less than 10 millisieverts of radiation.

Internal radiation exposures were linked with deaths from cancers of the blood and lymph system and of the upper aerodigestive tract, (oral cavity, pharynx, esophagus and stomach).

The UCLA study is one of the first to show a link between ingestion of radiation and deaths from cancers of the lungs and other internal organs. The link found between radiation exposure and cancers of the blood and lymph system are consistent with previous studies of human radiation exposure.

In addition, the follow-up period for the Rocketdyne workers was one of the longest achieved to date for any investigation of nuclear workers. This refinement may have allowed UCLA researchers to detect elevated deaths rates from cancers that had not before been associated with radiation exposures.

"People who have worked at Rocketdyne may want to consult with their personal physicians to discuss the implications of this study on their health," Morgenstern said. "Unfortunately, because of the statistical nature of epidemiologic findings, we cannot specify whether any individual's cancer is one of those triggered by radiation, nor can we say for sure who will develop these cancers in the future."

The group of workers examined at Rocketdyne is relatively small compared to many other nuclear industry studies. The group also was exposed to relatively low doses of radiation and is not yet old enough to have died in large numbers. Given these limitations, it becomes more difficult to statistically link deaths from specific cancers with radiation exposure.

The findings may also be limited by inaccuracies in the measurement of internal radiation doses, as well as uncertainties about the workers' exposure to other risk factors for cancer, such as workplace chemicals and diet. Researchers examined issues such as smoking and workplace chemicals and found no evidence they had changed the radiation findings.

UCLA researchers also are examining whether Rocketdyne workers exposed to toxic chemicals at the plant may have suffered health problems as a result. Conclusions from that study will be released at a later date.