title: Potency factors for risk assessment at Libby, Montana.
abstract: We reanalyzed the Libby vermiculite miners' cohort assembled by Sullivan to estimate potency factors for lung cancer, mesothelioma, nonmalignant respiratory disease (NMRD), and all-cause mortality associated with exposure to Libby fibers. Our principal statistical tool for analyses of lung cancer, NMRD, and total mortality in the cohort was the time-dependent proportional hazards model. For mesothelioma, we used an extension of the Peto formula. For a cumulative exposure to Libby fiber of 100 f/mL-yr, our estimates of relative risk (RR) are as follows: lung cancer, RR = 1.12, 95% confidence interval (CI) =[1.06, 1.17]; NMRD, RR = 1.14, 95% CI =[1.09, 1.18]; total mortality, RR = 1.06, 95% CI =[1.04, 1.08]. These estimates were virtually identical when analyses were restricted to the subcohort of workers who were employed for at least one year. For mesothelioma, our estimate of potency is K(M) = 0.5 x 10(-8), 95% CI =[0.3 x 10(-8), 0.8 x 10(-8)]. Finally, we estimated the mortality ratios standardized against the U.S. population for lung cancer, NMRD, and total mortality and obtained estimates that were in good agreement with those reported by Sullivan. The estimated potency factors form the basis for a quantitative risk assessment at Libby.
authors.affiliation: Exponent, Inc., Bellevue, WA, USA. smoolgavkar@exponent.com
authors.forename: Suresh H
authors.initials: SH
authors.lastname: Moolgavkar
authors.forename: Jay
authors.initials: J
authors.lastname: Turim
authors.forename: Dominik D
authors.initials: DD
authors.lastname: Alexander
authors.forename: Edmund C
authors.initials: EC
authors.lastname: Lau
authors.forename: Colleen A
authors.initials: CA
authors.lastname: Cushing
mesh_terms: D000328:Adult; D000368:Aged; D000538:Aluminum Silicates / Q000009:adverse effects*; D015331:Cohort Studies; D004781:Environmental Exposure; D006801:Humans; D008175:Lung Neoplasms / Q000401:mortality; D008297:Male; D008654:Mesothelioma / Q000401:mortality; D008875:Middle Aged; D008906:Mining; D009009:Montana / Q000453:epidemiology; D009784:Occupational Diseases / Q000401:mortality; D016273:Occupational Exposure; D016016:Proportional Hazards Models; D012140:Respiratory Tract Diseases / Q000401:mortality; D018570:Risk Assessment / Q000706:statistics & numerical data
chemical_list: D000538:Aluminum Silicates; C003760:vermiculite