Asbestos fiber size and how it relates to carcinogenic potency/toxicity

Asbestos fiber size and relation to carcinogenic toxicity

The main concern with respect to asbestos exposure is the inhalation of asbestos fibers. Ingestion of asbestos poses little or no risk of non-cancer effects. However, some evidence shows that acute oral exposure might induce precursor lesions of colon cancer, and that chronic oral exposure might lead to an increased risk of gastrointestinal tumors.

In general, inhaled asbestos fibers wider than 3 µm lodge in upper airways, and narrower ones can reach deeper into the lung and alveolar region. Exposure to long, thin, needle-like fibers is of the most concern because these fibers can reach the lower airways and become embedded in the lung tissue, where they may remain for the remainder of the person’s life. Repeat exposure to asbestos in air has been shown to cause lung disease, including asbestosis, lung cancer, and mesothelioma.

Some reports have suggested that amphibole asbestos is more toxic than chrysotile asbestos, mainly because of physical characteristics of the fibers that allow chrysotile to be broken down and cleared from the lung, whereas amphibole is not removed and builds up to high levels in lung tissue.

Some researchers believe that the resulting increased duration of exposure to amphibole asbestos significantly increases the risk of mesothelioma and, to a lesser extent, asbestosis and lung cancer.

However, EPA’s current risk models consider asbestos toxicity to be independent of size and mineralogy, and the Occupational Safety and Health Administration (OSHA) continues to regulate chrysotile and amphibole asbestos as one substance, as both types increase the risk of disease.

The lack of exposure information distinguishing the different fiber types limits evidence suggesting that the different types of asbestos fibers vary in carcinogenic potency. Other data indicate that differences in fiber-size distribution and other process differences can impact toxicity as much as, or more than, fiber type.

Courtesy of the Washington Department of Health