Asbestos: What are the risks?

Once considered safe enough to use in toothpaste, asbestos is now one of the most feared contaminants on Earth. Although health concerns arose two decades earlier, the asbestos panic began in 1986 when the Environmental Protection Agency (EPA) instituted the Asbestos Hazard Emergency Respose Act. It required inspection of all public and private schools for asbestos. This brought asbestos to public attention and raised parental fears that their child could contract asbestos-related cancer because of high levels of airborne fibers in schools. Since that time, billions of dollars have been spent on asbestos testing and removal.

What Is Asbestos?

Asbestos is not a single material. Rather asbestos is a general term for a group of silicate minerals that readily separate into thin, strong fibers (see Figure). Because these fibers are flexible, heat resistant and relatively chemically inert, they have many uses. Asbestos has been widely used to strengthen concrete, make fireproof fabrics, and insulate boilers and pipes that carry hot fluids. It was a component in floor tiles and the main ingredient in automobile brake linings. Wall coatings rich in asbestos fibers were used extensively during the U.S. building boom of the 1950s and early 1960s.

Most asbestos comes from three minerals. Chrysotile (white asbestos) is a fibrous form of the mineral serpentine. It is the only type of asbestos mined in North America and once made up 95 percent of world production. Crocidolite (blue asbestos) and amosite (brown asbestos) mined in South Africa and used to make about 5 percent of world production.

Exposure and Risk

There is no question that prolonged exposure to air laden with certain typees of asbestos dust in an unregulated work place can be dangerous. When the thin rodlike fibers are inhaled into the lurngs they are neither easily broken down nor easily expelled, but can remain for life.

Three lung diseases can result: (1) asbestosis, a scarring of tissue that decreases the lung's ability to absorb oxygen; (2) mesothelioma, a rare tumor that develops in the chest or gut; and (3) lung cancer.

Evidence that incriminates blue asbestos and brown asbestos comes from health studies at mines in South Africa and western Australia. Miners and mill-workers showed an extremely high incidence of mesothelioma, sometimes after less than a year of exposure.

However, the U.S. Geological Survey concludes that the risks from the most widely used form of asbestos (chrysotile or white asbestos) are minimal to nonexistent. They cite studies of miners

of white asbestos in Canada and in northern Italy, where mortality rates from mesothelioma and lung cancer differ very little from the general public.

Another study was conducted on miners' wives in the area of Thetford Mines, Quebec, once the largest chrysotile mine in the world. For many years there were no dust controls on mining and milling operations, so these women were exposed to extremely high levels of airborne asbestos. Nevertheless, they exhibited below-normallevels of the diseases thought to be associated with asbestos exposure.

The various types of asbestos fibers differ in their chemical composition, shape, and durability. The thin, rodlike blue asbestos and brown asbestos fibers, which can easily penetrate the

lining of the lungs, are certainly pathogenic. But chrysotile fibers are curly and can be expelled more easily than can the rodlike fibers. Further, if inhaled, chrysotile fibers break down within a year. This is not the case for the other forms of asbestos or for fiberglass, which is frequently used as a substitute for asbestos. These differences are thought to explain the fact that the mortality rates for chrysotile workers differ very little from the rates for the general population.

Although the EPA has lifted its ban on asbestos, very little of this once exalted mineral is presently used in the United States.

A Risk in U.S. Schools?

Does asbestos present a risk to the nation's students? Available data indicate that the levels of airborne asbestos in schools are approximately 0.01 of the permissible exposure levels for the U.S. workplace. In addition, the indoor concentrations of the most biologically active fibers are comparable to outdoor levels. With few exceptions, the type of asbestos found in schools is chrysotile, which in low concentrations has been shown to be relatively harmless.