Asbestos-Related Diseases - Amphiboles, Chrysotile
7.1.2.3 Other relevant studies
(a) Mining and milling
Kogan (1982) reported on the morbidity and mortality of chrysotile miners and millers in the former USSR. Dust exposure levels were reported to be extremely high in the 1950s (over 100 mg/m3) and were substantially reduced to 3 to 6 mg/m3 in the 1960s and 1970s. The occurrence of asbestosis was substantially reduced by 1979; SMRs of lung cancer in male miners based on reference rates from a neighbouring city were 3.9 during 1948 to 1967 and 2.9 during 1968-1979. In male millers the corresponding values were 4.3 and 5.8. Corresponding figures for women were: miners, 3.9 and 9.4; millers, 2.9 and 9.7 (observed deaths not reported).
Zou et al. (1990) conducted a retrospective cohort mortality study of 1227 men employed at a chrysotile mine in Laiyuen, Hebei province of China, prior to 1972. Mortality in this cohort was compared with that from 2754 local residents of Laiyuen who had never been exposed to asbestos. Based on follow-up of this cohort from 1972 to 1981, 67 deaths were identified (of which 6 were from lung cancer and 3 from mesothelioma) in the asbestos cohort and 247 deaths in the referent population. The lung cancer rate in the exposed cohort was reported to be significantly greater (p<0.001) than the rate in the referent group. The interpretation of this study is limited by the poor description of the methodology used for standardization and statistical testing.
Cullen & Baloyi (1991) reviewed the X-rays, demographic data, and medical and occupational histories for 51 workers with asbestos-related diseases that had been submitted for compensation to a medical board in Zimbabwe since its independence in 1980. One pathologically confirmed case of mesothelioma and one case that radiologically resembled mesothelioma were identified. These cases were associated with occupational exposures to chrysotile asbestos in the Zimbabwe mines and/or mills.
(b) Asbestos-cement production
In other studies of asbestos-cement workers, there has been greater exposure to commercial amphiboles. A study by Neuberger & Kundi (1990, 1993) showed an increased lung cancer risk (SMR = 1.72), which became a small, non-significant one (SMR = 1.04) after adjustment for individual smoking histories. Two studies, (Finkelstein., 1984; Magnani et al., 1987) showed high lung cancer risks (SMRs = 4.8 and 2.68, respectively), suggesting very heavy exposures. All other asbestos-cement worker studies (Clemmensen & Hjalgrim-Jenson, 1981; Alies-Patin & Valleron., 1985; Raffn et al., 1989; Albin et al., 1990) showed positive results, with SMRs up to 1.8; however, smoking was not controlled for in these studies.
(c) Mixed products manufacture
In several reported studies, workers have been exposed to unspecified forms of asbestos in production of either unspecified or mixed products (see, for example, Berry et al., 1985; Enterline et al., 1987).
Epidemiological data for asbestos-exposed workers in Germany who died between 1977 and 1988 were reported in a proportional mortality study by Rösler et al. (1993), although diagnostic criteria were not clearly specified nor was it possible to clearly separate exposure to chrysotile alone from that to mixed fibre types. Among those exposed mainly to chrysotile (464 deaths), the lung cancer proportional mortality ratio (PMR) was 1.54 (95% CI = 1.16-2.01); 24 deaths (5.2%) were due to pleural mesothelioma and 5 (1.1%) to peritoneal mesothelioma. Mortality for those exposed to both chrysotile and crocidolite (115 deaths) was similar, and there was a higher proportion of deaths (3.5%) due to peritoneal mesothelioma. The PMR for pleural mesothelioma was highest in textile manufacture, followed by insulation, paper, cement and polymers, and was lowest in friction product manufacture. Peritoneal mesotheliomas were reported in textile, insulation and cement manufacture.
A series of 843 mesothelioma cases identified during 1960 to 1990 in the state of Saxony-Anholt, which was formerly part of the German Democratic Republic, was reported by Sturm et al. (1994). According to the authors, asbestos products were primarily made from chrysotile asbestos from the Ural mountains of Russia. Only small amounts of chrysotile from Canada and even smaller quantities of amphiboles from Mozambique or Italy were used in manufacturing. The authors indicated that, out of 812 cases with complete data, 67 were exposed only to chrysotile, 331 were exposed to chrysotile and possibly amphiboles, 279 were exposed to both chrysotile and amphiboles, and 135 were exposed only to amphiboles.
(d) Application and use of products
Cohort studies of populations of workers using only or predominantly chrysotile-containing products in applications such as construction have not been identified. Some relevant information is available, however, from population-based analyses of primarily mesothelioma in application workers exposed generally to mixed fibre types.