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ASBESTOS
CAS No: 1332-21-4
I. PHYSICAL AND CHEMICAL PROPERTIES (From HSDB (1998) except as noted)
Molecular weight
not applicable
Boiling point
decomposes
Melting point decomposes at 600ºC (NIOSH, 1994)
Vapor pressure
not applicable
Air concentration conversion not applicable
II.
HEALTH ASSESSMENT VALUES
Unit Risk Factor: 6.3 E-2 (µg/m 3 ) -1 [1.9 E-4 (100 PCM fibers/m 3 ) -1 ; see Appendix D]
Slope Factor: 2.2 E+2 (mg/kg-day) -1
[Human occupational asbestos lung tumor and mesothelioma incidence data, excess relative risk
model (CDHS, 1986).]
III.
CARCINOGENIC EFFECTS
Human Studies
Asbestos has been consistently demonstrated to be carcinogenic in humans and is recognized as a
human carcinogen by the International Agency for Research on Cancer (IARC, 1977; NRC, 1984;
Ontario Royal Commission, 1984). In occupational cohort mortality studies, exposure to the three
principal commercial forms of asbestos – chrysotile, amosite, and crocidolite – has been repeatedly
linked with increased risks for lung cancer, mesothelioma and, to a lesser extent, other neoplasm,
particularly gastrointestinal and laryngeal cancer (IARC, 1977; NRC, 1984). Occupational exposure to
anthophyllite has been associated with an increased risk for lung cancer. Cigarette smoking acts
synergistically with occupational exposure to asbestos in increasing the risk of lung cancer, but not
mesothelioma (Hammond et al., 1979; NRC, 1974).
Tremolite and actinolite are often contaminants of other ores and have not been extensively studied with
respect to their biological effects in humans.
The epidemiologic studies on asbestos are extensive. These have been reviewed by the Consumer
Product Safety Commission (1983), the National Academy of Sciences (NRC, 1984), Nicholson
(1985), and the Ontario Royal Commission (1984). The relevant studies used in deriving the cancer
risk for asbestos are summarized in the tables below.
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