Factories
A study of several factories of Cape Industries Ltd. was published in 1983. No mesothelioma cases were found among approximately 15,000 subjects of one large factory (Factory E) that started operations in 1902 and used chrysotile solely for producing textiles, insulation and friction materials (Browne and Smither, 1983). A cohort of 3641 men in a Connecticut packings plant is considered as exposed only to chrysotile asbestos. Chrysotile was the only type of asbestos used until 1957, when anthophyllite was added to some product lines, and approximately 400 pounds of crocidolite was used experimentally in the laboratory between 1964 and 1972. The cumulative exposure level for chrysotile was relatively high for this cohort at 46 f/ml-yr. No mesothelioma related to work at this plant was found on the death certificates collected for the study (McDonald et al., 1984; Hodgson and Darnton, 2000). Two mesothelioma cases were nevertheless identified for this cohort by reviewing the state's tumor registry and city directories. Both cases were women who were clerical workers but had confirmed peritoneal and possible pleural mesothelioma, respectively (Teta et al., 1986; McDonald, 1986; Berman and Crump, 2003, pp. 3-13,314). No cases of mesothelioma were reported in a retrospective mortality cohort study of 1172 chrysotile asbestos product workers (17,600 person-years) in Tianjin, China, from 1972 to 1987 (Cheng and Kong, 1992). Researchers followed a cohort of 2175 male workers at an asbestos factory in Lodz, Poland, producing packings, gaskets, needled cloth, yarn, cords, asbestos-rubber cardboards, and friction products, but no cases of mesothelioma were reported in the 1988 update, although one case was subsequently found in a man who had insignificant exposure at the plant. For the cohort of 1190 women who were employed at this Lodz plant, one peritoneal mesothelioma case is reported on a death certificate, but no details on her job history, estimated exposures, or latency period are provided (Szeszenia-Dabrowska et al., 1988a, 1988b; Wilcznska at al., 1996). Raw asbestos was imported by Poland after World War II mainly from the former Soviet Union (chrysotile) and Africa (crocidolite, amosite) (Foltyn, 2000). The maximum average asbestos dust level in Poland in 1990 was reported as 8 f/ml (Dobrovolsky, 1998). Differential diagnosis between this tumor and both serous papillary carcinoma of the peritoneum and ovary can be problematic, and the results of a panel of antibodies (which were unavailable for most of the Polish study's timeframe) should be interpreted to set the diagnosis, especially since peritoneal mesotheliomas have not been convincingly related to chrysotile exposure (National Academy of Sciences, 1984; Doll and Peto, 1985; Smith and Wright, 1996; Roggli et al., 1997; Sporn and Roggli, 2004; Markaki et al., 2005). A 20-year study in a shop in the Ural Mountains (USSR) where chrysotile dust predominated in the making of friction products observed no mesothelioma cases (Koganetal., 1993), yet regional workers' lung samples revealed amphiboles (Kashansky et al., 2001). A study of a partial cohort of workers of a plant in Cornwall, Ontario, that manufactured fiber conduit from 1929 until 1982 identified one mesothelioma. Exposures to chrysotile asbestos (and coal tar pitch) until 1974 are reported, but no air sampling or dust measurement was ever done at the plant (Finkelstein, 1989b).