title: Occupational exposure to chrysotile asbestos and cancer risk: a review of the amphibole hypothesis.
abstract: OBJECTIVE
  This article examines the credibility and policy implications of the "amphibole hypothesis," which postulates that (1) the mesotheliomas observed among workers exposed to chrysotile asbestos may be explained by confounding exposures to amphiboles, and (2) chrysotile may have lower carcinogenic potency than amphiboles.
  
  
  METHODS
  A critical review was conducted of the lung burden, epidemiologic, toxicologic, and mechanistic studies that provide the basis for the amphibole hypothesis.
  
  
  RESULTS
  Mechanistic and lung burden studies do not provide convincing evidence for the amphibole hypothesis. Toxicologic and epidemiologic studies provide strong evidence that chrysotile is associated with an increased risk of lung cancer and mesothelioma. Chrysotile may be less potent than some amphiboles for inducing mesotheliomas, but there is little evidence to indicate lower lung cancer risk.
  
  
  CONCLUSIONS
  Given the evidence of a significant lung cancer risk, the lack of conclusive evidence for the amphibole hypothesis, and the fact that workers are generally exposed to a mixture of fibers, we conclude that it is prudent to treat chrysotile with virtually the same level of concern as the amphibole forms of asbestos.
authors.affiliation: Risk Assessment Program, National Institute for Occupational Safety and Health, Cincinnati, OH 45226, USA.
authors.forename: L T
authors.initials: LT
authors.lastname: Stayner
authors.forename: D A
authors.initials: DA
authors.lastname: Dankovic
authors.forename: R A
authors.initials: RA
authors.lastname: Lemen
mesh_terms: D000818:Animals; D017636:Asbestos, Amphibole / Q000009:adverse effects* / Q000633:toxicity; D017632:Asbestos, Serpentine / Q000009:adverse effects* / Q000633:toxicity; D002273:Carcinogens; D004812:Epidemiologic Methods; D006801:Humans; D008175:Lung Neoplasms / Q000209:etiology; D008654:Mesothelioma / Q000209:etiology; D016273:Occupational Exposure; D051381:Rats; D012306:Risk
chemical_list: D017636:Asbestos, Amphibole; D017632:Asbestos, Serpentine; D002273:Carcinogens