A new study by federal scientists indicates that exposure to a gas widely used by health care workers to sterilize medical supplies and equipment may pose more risk than previously believed.

As many as 100,000 health care technicians may be exposed to the gas, according to estimates by the National Institute for Occupational Safety and Health Administration.

The study, conducted by scientists at Oak Ridge National Laboratory, found that ethylene oxide caused genetic damage in mice when the animals were exposed to high concentrations for short periods of time.

The findings are likely to refuel a regulatory debate among federal agencies about setting stricter exposure limits for workers. They are also likely to be used in a lawsuit against the federal government asserting that current regulations on the sterilizing gas are too lenient.

The first court hearing of the lawsuit, filed by Public Citizen Litigation Group against the Occupational Safety and Health Administration (OSHA), is scheduled to be held today in the U.S. Court of Appeals for the District of Columbia.

Ethylene oxide is a colorless gas that previous studies have shown to be a mutagen -- a compound that causes random genetic alterations. It is also a carcinogen -- a compound that causes cancer.

The human studies available, which are limited and scientifically controversial, suggest that ethylene oxide is associated with leukemia, miscarriages and chromosomal damage.

Just over a year ago, OSHA set an exposure limit on ethylene oxide, but critics say the agency should have set a tougher standard. It regulated exposure over an eight-hour day, not over a brief period.

Health care technicians are typically exposed to quick, concentrated bursts of the gas when the door of a sterilizing machine is opened and when gas is released from the protective wrappings of freshly sterilized material.

OSHA originally proposed a short-term exposure limit in 1984 and had the backing of two federal health research agencies, the National Institute for Environmental Health Sciences and the National Occupational Safety and Health Administration.

The proposal was to restrict exposure to 10 parts per million over a 15-minute period. But then OSHA withdrew the plan, a day after the Office of Management and Budget in June 1984 charged that the agency's analysis was flawed. In the meantime, Johnson & Johnson, a company that uses large amounts of ethylene dioxide to sterilize products such as bandages, set a short-term exposure limit, the same as the OSHA proposal, for its employes based on the existing studies.

More than a year later, OSHA said that before it could set a short-term limit, it would need evidence that the same total dose of ethylene oxide causes more harm when delivered in a spurt than over a long period. The new study helps to fill that hole in the scientific data, federal scientists said.

The experiment was headed by Walderico Generoso at Oak Ridge and was sponsored by the National Institute for Environmental Health Sciences and the Department of Energy. The results are about to be published in the journal Environmental Mutagenesis.

According to the experimental results, laboratory mice suffered more genetic damage when they inhaled bursts of ethylene oxide than when they were exposed to low concentrations over a longer period. The total dose was the same.

Male mice were exposed to a total of 1,800 parts per million over four days, delivered at 300 ppm in six hours, 600 in three hours, or 1,200 in 1 1/2 hours. Then, using a standard test procedure, Generoso and colleagues checked for genetic damage.

The exposed males were mated with unexposed females. If chromosome breakage occurred in the male sperm, the animals' offspring would die. The results were dramatic. Embryos bred from the males exposed briefly to the higher concentrations died more often than the embryos from the lowest exposure group. Three times as many embryos died from the 600 ppm group compared with the 300 ppm. Six times as many embryos died from the 1,200 ppm group compared to the 300 ppm group.

The study cautions that the exposure levels in the experiment were at much higher concentrations than workers normally encounter on the job.

The current OSHA exposure limit is 1 ppm over eight hours, which means a person could be exposed to 480 ppm for one minute.

" [W]e cannot assume" that the extent of the effects seen in the experiment is also true for humans, the study said.

Even with these new findings, Generoso said in an interview, OSHA will have a tough time deciding whether to regulate the gas because of the lack of reliable human studies. Nonetheless, he said, the implications of his study and others are worrisome for health care technicians because their results indicate that ethylene oxide is a powerful mutagen.

An earlier Oak Ridge study showed that when mice were exposed to even low concentrations of ethylene oxide for a short peroid of time, the chemical caused changes in sperm called alkylations. Alkylations are known to trigger a series of genetic changes, including chromosome exchanges, that are "always harmful," Generoso said.

Ethylene oxide "is a very reactive compound," he said. "In the absence of human data, you have to consider the possibility that the effects in animals might occur in humans. We should take the most conservative approach" to protect workers. Other government scientists say that the results are important.

"There is no question that [Generoso's study] shows a dose-rate effect," said Michael Shelby, a senior scientist at the National Institute of Environmental Health Sciences. Shelby said it would be reasonable to assume that a similar effect might occur in people.

Donald Millar, head of the National Institute for Occupational Safety and Health, wrote to OSHA in September that Generoso's findings "strengthen our previous conviction" that a short-term limit should be established.

Ethylene oxide, however, has not been high on OSHA's list of regulatory priorities, according to Patrick Tyson, the acting head of OSHA. The agency recently proposed to restrict further worker exposure to formaldehyde and benzene and announced it would require better medical surveillance of workers exposed to cotton dust.

But some critics say that these actions do not signal that OSHA will rush to regulate ethylene oxide more stringently.

David Vladeck, a senior attorney for Public Citizen Litigation Group who is handling the ethylene oxide lawsuit, said that OSHA was under court order to produce the formaldehyde and benzene proposals. Regarding cotton dust, both industry and labor groups agreed on the need to beef up monitoring.

"So that was easy for OSHA to agree to," Vladeck said. "All of this activity [by OSHA] is nothing to get excited about."