Levels of Radon Low in Homes in California : Health: A statewide sampling indicates that 1% of houses may harbor dangerous amounts of the radioactive gas.

Confirming earlier studies, the first statewide survey of radon in California has found that the radioactive gas--believed to be the second-most frequent cause of lung cancer in the United States--is present only in low levels in most California homes.

Based on a yearlong sampling of 385 dwellings statewide, an estimated 88,000 single-family houses in California--about 1% of them--may contain radon beyond the recommended maximum.

The study also found, however, that radon levels in between 10% and 15% of dwellings in the Ventura County region may surpass the guideline. That finding was based on results of tests in 15 homes in that area, where geological factors are believed to contribute to surface radon levels.

The U.S. Environmental Protection Agency recommends that homeowners take steps to reduce radon if it exceeds 4 picocuries per liter of air. The average level in California is 0.85 picocuries per liter of air.

Exposure to radon at a level of 4 picocuries for one year represents a lung cancer risk comparable to taking between 200 and 300 chest X-rays, or to smoking a half a pack of cigarettes daily for a year, according to the EPA.

The EPA has calculated that 13 to 50 of every 1,000 individuals exposed to radon at those levels over a 70-year period could die of lung cancer. Radon, which is present in soil everywhere, is produced by the natural decaying of uranium.

Although they have not yet been made public, results of the California survey--conducted by the state Department of Health Services at the request of the state Air Resources Board--were confirmed by experts familiar with them.

The results back up those from a survey by The Times, completed in October, 1988, in which about 1.2% of homes tested in five Southern California counties exceeded radon guidelines. In that survey, 436 residences in Los Angeles and Orange counties and in parts of Riverside, San Bernardino and Ventura counties were monitored for 12 months.

The Times study, assisted by the state Department of Health Services, also concluded that radon levels were higher in an area including southwestern Ventura County, Simi Valley, Thousand Oaks and Moorpark than in the rest of Southern California, but still far lower than in radon “hot spots” in the East.

The latest findings bolster California’s contention that the EPA overreacted when it and the U.S. surgeon general in 1988 issued an unprecedented nationwide health advisory urging that virtually every dwelling in the country be tested for radon.

Radon testing experts noted, however, that while the statewide average radon level may be lower than the EPA standard, that does not mean the amount of the gas in an individual home may not exceed it.

“I’m not going to ignore taking my blood pressure just because the average blood pressure of 40-year-olds in California is considered to be healthy,” said one radon authority familiar with the study.

The EPA has estimated that radon causes 5,000 to 20,000 lung cancer deaths a year. Many of those who die are smokers also exposed to the gas.

In conducting their survey, state health authorities placed radon detectors in 385 single-family houses throughout California, including the 15 in the Ventura County region. The detectors were in place for 12 months.

Using standard statistical techniques, researchers using small samples are able to draw conclusions applicable to much larger numbers.

A more extensive state survey of 1,000 homes in the Ventura region is scheduled to be completed in June.

In 300 of those 1,000 homes, a second detector was placed during the months of June, July and August to determine if radon levels are lower during warm months. Although none of the measurements of last summer exceeded 4 picocuries per liter, scientists said that increased ventilation in summer could allow some radon to escape.

Radon levels may be higher in the Ventura County area for several reasons, according to Terrence Gilday, manager of technical services with the Ventura County Environmental Health Department.

Gilday said that layers of marine sediment in parts of Ventura County are not as deep as those found elsewhere in Southern California.

“This alluvial mat is relatively thin over a large area (in the Ventura region), not like the Los Angeles Basin or Oxnard, where it is hundreds or thousands of feet thick,” he said. “Here it is just a few hundred feet thick at most, and on the hillsides there are direct outcroppings.”

Thinner sediment layers may make it easier for radon to reach the surface and seep into homes.

Because of slight differences between air pressure inside houses and outdoors, radon can be drawn into a dwelling much as fireplace smoke is drawn up a chimney. The gas can enter through cracks in concrete slab foundations, openings around plumbing and elsewhere.

The principal threat to health occurs as the radon gas decays and throws off atoms of heavy metals, called alpha particles or radon daughters. The radon daughters stick to particles of smoke and dust, are inhaled and lodge in the lungs, where they emit cell-damaging radiation.

Anthony V. Nero Jr., a physicist at Lawrence Berkeley Laboratory and a leading authority on radon, said that researchers have long believed that radon levels are fairly low in California, except in so-called hot spots.

The state study, for example, found such hot spots in the Sierra foothills counties of Fresno, Mono, Tulare and Inyo, where levels were slightly higher than the statewide average. Specific numbers were not available, however. The average in those areas was 1.3 picocuries per liter.

“In general, what I would say is most people shouldn’t be concerned about radon in California,” Nero said, “but they should start to do something when any particular area has higher-than-average concentrations.”