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Occupational exposure to chrysotile asbestos and cancer risk: a review of the amphibole hypothesis.

Authors
Stayner-LT; Dankovic-D; Lemen-RA
Source
Am J Publ Health 1996 Feb; 86(2):179-186
NIOSHTIC No.
00230920
Abstract
The evidence for the association between occupational chrysotile (12001295) exposure and cancer was reviewed to evaluate the amphibole hypothesis which proposed that the mesotheliomas observed among workers exposed to chrysotile may actually be caused by contamination by relatively low concentrations (below 1%) of tremolite (77536686) fibers. The review considered evidence obtained in studies investigating chrysotile lung burdens, epidemiologic and laboratory animal studies investigating asbestos carcinogenicity, and mechanistic studies. Low concentrations of chrysotile fibers have been found in the lungs of asbestos workers, even those who worked primarily in chrysotile producing industries. Unexpectedly high concentrations of amphibole asbestos (1332214) forms were found. These findings provided the primary basis for the amphibole hypothesis. Most case/control studies investigating associations between asbestos lung burdens and mesothelioma risk have found clear dose response relationships with amphibole lung burdens, but not chrysotile lung burdens. Some studies, however, have found associations between mesothelioma risk and chrysotile lung burdens. Both epidemiological and experimental studies have shown that chrysotile can cause lung cancer and mesothelioma and that its carcinogenic activity was not due to contamination with tremolite. Some of the epidemiologic evidence has indicated that chrysotile may be less potent than the amphiboles in causing mesothelioma. The experimental animal evidence showed than when expressed on a per weight basis, chrysotile fibers are as at least as potent as amphibole asbestos fibers in causing lung cancer. The authors conclude that the toxicologic and epidemiologic literature strongly support the view that occupational exposure to chrysotile increases the risk of lung cancer and mesothelioma. It is considered prudent that chrysotile be treated with the same level of concern as the amphibole forms of asbestos.
Keywords
NIOSH-Author; Asbestos-fibers; Risk-analysis; Malignant-neoplasms; Epidemiology; In-vivo-studies; Laboratory-animals; Lung-burden; Lung-cancer; Pulmonary-clearance; Occupational-exposure
CODEN
AJHEAA
CAS No.
12001-29-5; 77536-68-6; 1332-21-4
Publication Date
19960201
Document Type
Journal Article
Fiscal Year
1996
NTIS Accession No.
NTIS Price
Issue of Publication
2
ISSN
0090-0036
NIOSH Division
EID; OD
Source Name
American Journal of Public Health
State
OH; GA
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