Other Cohort Studies
A cohort of 199 workers at 3 plants who were exposed predominately to crocidolite (especially at the Ottawa plant) and chrysotile during the manufacture of gas masks for the Canadian army between 1939 and 1942 indicated that 9 of the deaths were probably due to mesothelioma. Two additional pleural mesothelioma cases in men who had worked for decades at one of the plants were found in a national survey, but they are not included in the study's tables because their names were not on the roster from the plant foreman who had been responsible for production of gas mask filters (McDonald and McDonald, 1978). An epidemiological study of mesothelioma was published of 181 railroad machinists involved with steam engines hired between 1920 and 1929 followed through 1986 whose exposure was "almost exclusively, if not solely" to chrysotile. Of 41 cancer deaths, 14 mesotheliomas were identified (Mancuso, 1988, 1989a, 1989b). It appears that amphibole exposures were likely involved in this cohort (Ohlson, 1989). In a cohort study (734 subjects) of cancer risk associated with asbestos exposure in railway carriage construction and repair in Italy, 7 mesotheliomas were observed. Starting in the 1950s, crocidolite-chrysotile mixtures were sprayed on the entire internal surface of the carriage by workers in the facility (Battista et al., 1999). In a study of locomotive engineers who undertook a 2-year training program where exposures to anthophyllite asbestos with chrysotile were documented, 8 of 8391 subjects were subsequently diagnosed as having mesothelioma (Nokso-Koivista and Pukkala, 1994).