Most asbestos poses little human risk.

Most asbestos poses little human risk

Since 1972, EPA has taken a number of steps to limit nonoccupational exposures to asbestos, a family of carcinogenic minerals. These regulations treat all members of the family equally. However, asbestos toxicologist Brooke T. Mossman asserts, human studies published by several researchers in the past two years suggest chrysotile asbestos poses no hazard at levels encountered outside the workplace--and perhaps not even in the workplace these days. Chrysotile has been the type most commonly used in the United States.

Mossman, of the University of Vermont in Burlington, and her colleagues measured mean levels of asbestos in U.S. schools and other buildings. In the Jan. 19 SCIENCE, they report that these exposures are quite low--on a par with outdoor levels -- even where asbestos-containing materials appear severely damaged. The researchers recommend that policymakers reevaluate the wisdom of equating chrysotile risks with those of other asbestos fibers and reassess the need to remove it from buildings. Indeed, Mossman says, "our data suggest that if chrysotile is handled properly in the workplace, it does not present a risk to human health."

Chrysotile's curly shape distinguishes it from other asbestos fibers, called amphiboles, which sport a needle-like structure. The serpentine shape may make chrysotile less likely to penetrate lung tissue and more likely to be cleared from tissue. In the past, researchers have cited this as a possible explanation for epidemiologic observations that workers in the chrysotile industry, compared with other asbestos workers, have a lower incidence of life-threatening lung ailments--in particular lung cancer and mesothelioma, a fatal cancer that strikes only those who have inhaled asbestos or another, similar fiber. But more recent studies suggest chrysotile exposure may have induced few if any such cancers, Mossman says. They reveal that the workers who developed these cancers were also exposed to other carcinogens, most notably cigarette smoke and several of the amphiboles.

Chrysotile fibers are more toxic to cells than are amphiboles, Mossman's work indicates. However, she syas, the extra toxicity may actually benefit exposed animals by killing damaged cells before they can multiply to spawn a malignancy.

EPA has "yet to reach a definitive decision about one type of asbestos being less harmful," says Tom Tillman of EPA's Office of Toxic Substances. He adds that the agency has officially begun a technical analysis of the new SCIENCE Report.