Cancer mortality in relation to measures of occupational exposure to crocidolite at Wittenoom Gorge in Western Australia

The separate and combined effects of duration and intensity of exposure to crocidolite on mortality from lung cancer, malignant mesothelioma, and stomach cancer were examined in 6506 male former crocidolite miners and millers at Wittenoom Gorge, Western Australia. Each subject who had died from lung cancer (92), mesothelioma (31), or stomach cancer (17) was matched with up to 20 control subjects of the same age who were not known to have died before the index subject. Relations of dose and time of exposure to crocidolite to risk of death were modelled by conditional logistic regression. For lung cancer, the best fitting multiplicative model was one which estimated a relative risk (RR) of 1.12 (95% CI 1.04-1.20) per year of exposure and 1.01 (95% CI 1.00-1.01) per fibre/ml. This was statistically indistinguishable from an additive model showing an increase in RR of 0.01045 (95% CI 0.008-0.020) per f/ml year. For mesothelioma the best fitting model appeared to be one estimating a RR of 24.9 (95% CI 3.51-1.77) per log year since first exposed and a RR of 10.5 (95% CI 3.12-35.1) if exposed for longer than six months. This was not distinguishable statistically from a model that showed mortality increasing as the fourth power of time since first exposed less the fourth power of time since last exposed. The effect of intensity of exposure on the RR for mesothelioma was only slight. There was no consistent effect of any measure of exposure to crocidolite on death from stomach cancer.     

Mesothelioma and lung cancer among motor vehicle mechanics: a meta-analysis

We conducted a systematic review and analysis of the epidemiological literature that examines the risk of lung cancer and mesothelioma among motor vehicle mechanics who may have been engaged in brake repair and, thus, were potentially exposed to asbestos. All relevant studies were classified into three tiers according to their quality. Tier III (lowest quality) studies were cited for completeness, but were not included in the meta-analysis. Meta relative risks (meta-RRs) were calculated for mesothelioma and lung cancer using both fixed and random effects models for Tiers I and II, separately, followed by stratified analyses based on study design or exposure characterization (garage workers versus brake workers) and, for lung cancer studies, based on adequate adjustment for smoking. The meta-analysis for Tier I (higher quality) and Tier II (lower quality) studies of mesothelioma yielded RR estimates of 0.92 (95% CI 0.55-1.56) and 0.81 (95% CI 0.52-1.28), respectively. Further stratification according to exposure characterization did not affect the results. The meta-analysis for lung cancer produced RR estimates of 1.07 (95% CI 0.88-1.31) for Tier I and 1.17 (95% CI 1.01-1.36) for Tier II. When the lung cancer analysis was limited to studies that used adequate control for smoking, the resulting RR estimate was 1.09 (95% CI 0.92-1.28). Based on these findings, we conclude that employment as a motor vehicle mechanic does not increase the risk of developing mesothelioma. Although some studies showed a small increase in risk of lung cancer among motor vehicle mechanics, the data on balance do not support a conclusion that lung cancer risk in this occupational group is related to asbestos exposure.     

青石棉污染区恶性肿瘤9年回顾队列研究

为了证实非职业性环境接触青石棉与恶性肿瘤，特别是肺癌和间皮瘤危险的关系，采用回顾性队列调查方法对大姚县青石棉污染区进行９年的死亡率调查。选择同省无石棉污染的禄丰县作为对照。结果表明：恶性肿瘤的死亡率为１８２．６０／１０万，其中肺癌死亡率为５３．２６／１０万，相对危险度高于对照，ＲＲ分别为１．４７，２．１４（Ｐ＜０．０１）；观察组中７例死于间皮瘤。提示：间皮瘤的死亡率在青石棉污染区是很高的，在３０岁以上人中，年死亡率为１７．７５／１０万人年，而对照组中未观察到间皮瘤。     

Asbestos related diseases from environmental exposure to crocidolite in Da-yao,China. I. Review of exposure and epidemiological data

Background: Scattered patches of crocidolite, one form of asbestos, were found in the surface soil in the rural county of Da-yao in southwestern China. In 1983, researchers from the West China University of Medical Sciences (WCUMS) discovered that residents of two villages in Da-yao had hyperendemic pleural plaques and excessive numbers of pleural mesotheliomas.

Aims: To review and summarise epidemiological studies, along with other relevant data, and to discuss the potential contribution to environmental risk assessment.

Methods: This report is based on a review of several clinical/epidemiological studies conducted by WCUMS researchers since 1984, which included one cross sectional medical examination survey, one clinical/pathological analysis of 46 cases of mesothelioma, and three retrospective cohort mortality studies. Additional information acquired from reviewing original data first hand during a personal visit along with an interview of medical specialists from Da-yao County Hospital was also incorporated.

Results: The prevalence of pleural plaque was 20% among peasants in Da-yao over 40 years of age in the cross sectional survey. The average number of mesothelioma cases was 6.6 per year in the 1984–95 period and 22 per year in the 1996–99 period, in a population of 68 000. For those mesothelioma cases that were histology confirmed, there were 3.8 cases/year in the first period and 9 cases/year in the second. Of the 2175 peasants in this survey, 16 had asbestosis. Lung cancer deaths were significantly increased in all three cohort studies. The annual mortality rate for mesothelioma was 85 per million, 178 per million, and 365 per million for the three cohort studies, respectively. The higher exposed peasants had a fivefold increased mesothelioma mortality compared to their lower exposed counterparts. There were no cases of mesothelioma in the comparison groups where no crocidolite was known to exist in the environment. In the third cohort study, almost one of five cancer deaths (22%) was from mesothelioma. The ratio of lung cancer to mesothelioma deaths was low for all three studies (1.3, 3.0, and 1.2, respectively).

Conclusions: The observation of numerous mesothelioma cases at Da-yao was a unique finding, due mainly to their lifetime exposure to crocidolite asbestos. The finding of cases dying at a younger age and the relatively high ratio of mesothelioma cases to lung cancer could also be another unique result of lifetime environmental exposure to crocidolite asbestos. Although the commercial use of crocidolite has been officially banned since 1984, the incidence of mesothelioma has continued to show a steady increase, particularly among peasants. Since the latency of mesothelioma is approximately 30–40 years, the ban had little effect in the 1990s. The increased awareness and changes in diagnosis over time may also contribute to the increase. Furthermore, exposure to asbestos stoves and walls continued. The government implemented reduction of these exposures. However, from a public health standpoint, the most important issue is the complete avoidance of further exposure to asbestos.

     

青石棉污染区农民恶性肿瘤死亡率的回顾队列调查

目的：了解在生活环境中接触低浓度青石棉、农民患恶性肿瘤,特别是间皮瘤和肺癌之间的关系。方法：采用回顾队列调查方法对青石棉污染区的农民进行恶性肿瘤死亡率的调查,以该县无石棉污染的农民为对照,结果：观察组有5人死于间皮瘤死亡率为36．46／10万人年,而对照组无1例发生;肺癌死亡率为43．75／10万人年,与对照组比较,差别有非常显著性意义（P＜0．001）,结论：间皮瘤死亡率在青石棉污染区很高,青石棉与间皮瘤,肺癌之间存在很强的病因学联系。     

Different measures of asbestos exposure in estimating risk of lung cancer and mesothelioma among construction workers

To analyze occupation, expert-evaluated cumulative exposure, and radiographic abnormalities as indicators of asbestos-related cancer risk we followed 16,696 male construction workers for cancer in 1990-2000. We calculated standardized incidence ratios (SIR) in comparison to the Finnish population and relative risks (RR) in a multivariate analysis in comparison to the internal low-exposure category of each indicator. Overall, the risk was increased for mesothelioma (SIR 2.0, 95% CI = 1.0-3.3), but not for lung cancer (SIR 1.1, 95% CI = 0.9-1.2). Radiographic lung fibrosis indicated a 2-fold and a high value of the exposure index a 3-fold RR of lung cancer, while there was no risk among those with pleural plaques. The risk of lung cancer was the highest in insulators (RR 3.7, 95% CI = 1.4-9.9). Occupation, expert-evaluated cumulative exposure, and lung fibrosis are useful indicators of lung cancer risk among construction workers.     

Excess mortality from stomach cancer, lung cancer, and asbestosis and/or mesothelioma in crocidolite mining districts in South Africa

To determine whether exposure to crocidolite is associated with excess mortality, the authors calculated standardized mortality ratios based on deaths in South African crocidolite mining districts from 1968 to 1980 for selected causes of death. Contiguous districts were used as controls. To take account of background geographic variability, they divided the control districts into groups of population size similar to those of the crocidolite mining districts. Standardized mortality ratios in crocidolite mining districts were elevated for asbestosis and/or mesothelioma, and cancer of the lung and stomach. These findings could not be explained by background geographic variability in mortality and are likely to be due to exposure to South African crocidolite during mining and milling or to environmental contamination. The increased standardized mortality ratios for stomach cancer are of particular interest, since excess deaths have not previously been shown in individuals exposed to crocidolite alone.     

Cancer incidence among workers in the asbestos-cement producing industry in Norway

OBJECTIVES: The incidence of cancer among employees of a Norwegian asbestos-cement factory was studied in relation to duration of exposure and time since first exposure. The factory was active in 1942-1968. Most of the asbestos in use was chrysotile, but for technical reasons 8% amphiboles was added. METHODS: For the identification of cancer cases, a cohort of 541 male workers was linked to the Cancer Registry of Norway. The analysis was based on the comparison between the observed and expected number of cancer cases. Standardized incidence ratios (SIR) and 95% confidence intervals (95% CI) were estimated. Period of first employment, duration of employment, and time since first employment were used as indicators of exposure. Poisson regression analysis was used for the internal comparisons. RESULTS: The standardized incidence ratio was 52.5 (95% CI 31.1-83.0) for pleural mesothelioma, on the basis of 18 cases. The highest standardized incidence ratio was found for workers first employed in the earliest production period (SIR 99.0, 95% CI 51.3-173). No peritoneal mesothelioma was found. The standardized incidence ratio for lung cancer was 3.1 (95% CI 2.14.3), but no dose-response effect was observed. The ratio of mesothelioma to lung cancer cases was 1:2. CONCLUSIONS: This study showed a high incidence of mesothelioma and a high ratio of mesothelioma to lung cancer among asbestos-cement workers. The high incidence of mesothelioma was probably due to the fact that a relatively high proportion of amphiboles was used in the production process.     

Incidence of cancer among anthophyllite asbestos miners in Finland.

A cohort of 736 male and 167 female workers of two anthophyllite mines in Finland was followed up through the Finnish Cancer Registry for cancer in 1953-91. Compared with the total cancer incidence of the east Finnish population, the men had a raised risk of total cancer (standardised incidence ratio (SIR) 1.7; 95% confidence interval (95% CI) 1.4-1.9), mainly attributable to an excess in lung cancer (SIR 2.8; 95% CI 2.2-3.6). The risk of lung cancer was somewhat higher among workers classified as heavily exposed (SIR 3.2; 95% CI 2.4-4.1) than among those moderately exposed (SIR 2.3; 95% CI 1.5-3.6) and the risk increased with increasing smoking and with increasing time of work with exposure. There were four cases of mesothelioma v 0.1 expected, all in men who smoked and had had a long and heavy asbestos exposure. Among women, a non-significant excess in total cancer (SIR 1.5; 95% CI 0.9-2.4) was found in the subgroup with heavy exposure to asbestos. Anthophyllite asbestos seems to have high potency in the carcinogenesis of lung cancer and low potency in carcinogenesis of mesothelioma in comparison with the other types of asbestos.     

Temporal variation in the association between benzene and leukemia mortality

BACKGROUND: Benzene is a human carcinogen. Exposure to benzene occurs in occupational and environmental settings. OBJECTIVE: I evaluated variation in benzene-related leukemia with age at exposure and time since exposure. METHODS: I evaluated data from a cohort of 1,845 rubber hydrochloride workers. Benzene exposure-leukemia mortality trends were estimated by applying proportional hazards regression methods. Temporal variation in the impact of benzene on leukemia rates was assessed via exposure time windows and fitting of a multistage cancer model. RESULTS: The association between leukemia mortality and benzene exposures was of greatest magnitude in the 10 years immediately after exposure [relative rate (RR) at 10 ppm-years = 1.19; 95% confidence interval (CI), 1.10-1.29]; the association was of smaller magnitude in the period 10 to < 20 years after exposure (RR at 10 ppm-years = 1.05; 95% CI, 0.97-1.13); and there was no evidence of association > or = 20 years after exposure. Leukemia was more strongly associated with benzene exposures accrued at > or = 45 years of age (RR at 10 ppm-years = 1.11; 95% CI, 1.04-1.17) than with exposures accrued at younger ages (RR at 10 ppm-years = 1.01; 95% CI, 0.92-1.09). Jointly, these temporal effects can be efficiently modeled as a multistage process in which benzene exposure affects the penultimate stage in disease induction. CONCLUSIONS: Further attention should be given to evaluating the susceptibility of older workers to benzene-induced leukemia.     

Occupational risk factors for mortality from stomach and lung cancer among rubber workers: an analysis using internal controls and refined exposure assessment

OBJECTIVES: To determine occupational risk factors for stomach and lung cancer among workers in the German rubber industry. METHODS: A cohort of all male German rubber workers (n = 11,633) who had been employed for at least one year in one of five study plants and who were alive and actively employed or retired on 1 January 1981 was followed for mortality from 1 January 1981 through December 1991. A subcohort of n = 8,933 workers who were hired after 1 January 1950 was defined to focus on working conditions in the more recent rubber industry. Work histories were reconstructed using routinely documented 'cost centre codes' and classified into six work areas as well as subgroups of some work areas. The work areas are: 1. preparation of materials, 2. production of technical rubber goods, 3. production of tyres, 4. storage and dispatch, 5. maintenance, 6. others. Standardized mortality ratios (SMR) and Cox proportional hazards models were calculated for each of the work areas (>1 year of employment in the respective work area). Hazard rate ratios were adjusted for age (time marker) and stratified for year of hire (1950-1959, > or =1960) and years of employment in the respective work area (1-9 years, > or =10 years); years of employment were lagged 10 years to account for latency. RESULTS: Compared to the national reference population mortality from cancer of stomach (observed 44, SMR = 117; 95% CI: 85-157) and lung (observed 154, SMR = 123; 95% CI: 104-144) was slightly increased. Using internal controls we observed excess deaths from stomach cancer in work area 1 (relative risk [RR] = 2.3; 95% CI: 1.2-4.2) and from lung cancer in work areas 1 (RR = 1.7; 95% CI: 1.2-2.3), 2 (RR = 1.5; 95% CI: 1.1-2.1), and 3 (RR = 1.3; 95% CI: 0.9-1.8). On the basis of cumulative years of employment an exposure response relationship was observed for mortality from both cancer sites among a subcategory of work area 1: weighing and mixing. Increased risks were also seen for lung cancer among workers employed in production of technical rubber goods. CONCLUSION: Our results support an association between an excess mortality from stomach and lung cancer and employment in early production stages of rubber manufacturing, especially weighing and mixing. This may point to an aetiologic role of asbestos or carbon black. For stomach cancer additional risk factors, e.g. exposure to dust and talc, deserve further investigation. The results of the present study do not support a causal role of nitrosamines for stomach or lung cancer.     

Epidemiological investigation on the health status of employees in two factories manufacturing and repairing railway rolling stock: a historical perspective study of mortality

BACKGROUND: Epidemiological studies of cancer risk due to occupational exposure to asbestos in production and repair of railway rolling stock has so far given consistent results for mesothelioma, but conflicting evidence for lung cancer. OBJECTIVES: The main purpose of this study was to investigate risk for mesothelioma and lung cancer in relation to estimated patterns of exposure in the occupational environment of railway rolling stock manufacture and repair. METHODS: A historical prospective study approach was adopted. The mortality experience of the study population was compared to that of the population of the Veneto Region. Two historical cohorts of workers employed in two plants manufacturing and repairing railway coaches were followed up for mortality. A total of 1,621 workers were enrolled in the study from the first factory, and 1,190 from the second. RESULTS: An elevation of both pleural mesothelioma and lung cancer was reported in the two factories with SMRs of 21.52 (CI 95%=1.64-32.29) and 6.46 (CI 95%=1.33-18.88), and 1.26 (CI 95%=1.01-1.54) and 1.18 (CI 95%=0.81-1.66) respectively. The two excesses however showed different patterns in relation to historical exposure estimates, which appear to correlate with mesotheliomas but not with lung cancer. An elevation of mortality for non-neoplastic respiratory diseases was associated with employment during periods when it was estimated that exposure was at higher levels in one of the two firms. CONCLUSIONS: The results confirm the high carcinogenic risk deriving from asbestos exposure, although inconsistencies were found between target organs in relation to exposure estimates, and the existence of time periods in production in which cancer risk was different.     

Cohort mortality study among French asphalt workers

BACKGROUND: In conjunction with the European cohort study among asphalt workers coordinated by the International Agency for Research on Cancer (IARC), we studied the mortality of 15,011 French men who were followed for 17 years for a total of 175,062 persons-years. This group contained 2,506 subjects who had ever been employed as asphalt workers: they contributed 30,692 person-years of risk. A reference group was composed of 6,675 subjects (i.e., 61,856 persons-years) who had been employed only in building or ground construction. METHODS: Mortality ratios standardized for age and period were computed with their 95% confidence intervals (CI) from the age and period mortality rates of all French men for the years covered by the study (1979-1996). We also compared the mortality of exposed workers and the reference group with Poisson regression models after adjustment for age, calendar period, and either duration of employment or length of follow-up. RESULTS: Mortality from lung cancer was equivalent to the expected rate [SMR = 1.01 95% CI (0.6-1.6)], but was 40% greater than among the non-exposed reference group [RR = 1.4 95% CI (0.7-2.8)]. We also found an excess of gastrointestinal cancers, especially of the esophagus [SMR = 1.94, 95% CI (0.9-3.6)] and stomach [SMR = 2.2, 95% CI (0.8-4.7)]. Comparison with the internal reference group confirmed these findings, especially for stomach cancer [RR = 2.8, 95% CI (0.7-11.4)]. CONCLUSIONS: Although our results are not statistically significant, they suggest that road-paving workers may have a slightly higher rate of lung cancer and a moderately higher rate of stomach cancer than their non-exposed counterparts. The excess of lung cancer may be due to potential confounding factors, including the occupational risk factor of coal tar exposure and the lifestyle risk factor of smoking. A nested case-control study is under way that will make it possible to control for smoking and other potential carcinogenic exposures; this is necessary before any definitive conclusions can be drawn.     

Diesel exhaust exposure and lung cancer: adjustment for the effect of smoking in a retrospective cohort study

BACKGROUND: The extent that cigarette smoking may confound the relationship between diesel exhaust exposure and lung cancer was assessed in a retrospective cohort study of 55,395 U.S. railroad workers followed from 1959 to 1976. METHODS: The relative risk (RR) of lung cancer due to diesel exhaust was indirectly adjusted using job-specific smoking data from a case-control study of railroad workers who died between 1981-1982 and from a survey of 514 living workers from an active railroad in 1982. Adjustment factors were developed based on the distribution of job-specific smoking rates. RESULTS: The unadjusted RR for lung cancer was 1.58 (95% CI = 1.14-2. 20) for workers aged 40-44 in 1959, who experienced the longest possible duration of exposure, and the smoking adjusted RR was 1.44 (1.01-2.05). CONCLUSIONS: After considering differences in smoking rates between workers exposed and unexposed to diesel exhaust in a relatively large blue-collar cohort, there were still elevated risks of lung cancer in workers in jobs with diesel exhaust exposure.     

Exposure to nickel compounds and smoking in relation to incidence of lung and nasal cancer among nickel refinery workers.

OBJECTIVES: To investigate the relation between occupational hazards among nickel refinery workers and their exposure to different forms of nickel over time and the interaction between smoking and total exposure to nickel. METHODS: The cohort consisted of 379 workers with first employment 1916-40 and at least three years of employment and 4385 workers with at least one year of employment 1946-83. Data on smoking (ever or never) were available for almost 95% of the cohort. Two analyses were used, indirect standardisation from observed and expected numbers and Poisson regression. RESULTS: During the follow up 1953-93, 203 new cases of lung cancer were observed v 68 expected (standardised incidence ratio (SIR) 3.0, 95% confidence interval (95% CI) 2.6-3.4) and 32 cases of nasal cancer were observed v 1.8 expected (SIR 18.0, 95% CI 12-25). The Poisson regression analysis showed an excess risk of lung cancer in association with exposure to soluble forms of nickel, with a threefold increase in relative risk (RR) (P < 0.001) and a multiplicative effect of smoking and exposure to nickel. The RRs were 1.1 (95% CI 0.2-5.1) for exposed workers who had never smoked and 5.1 (95% CI 1.3-20.5) for exposed workers who smoked. CONCLUSION: It is not possible to state with certainty which specific nickel compounds are carcinogenic, but a significant excess risk was found for workers exposed to soluble nickel alone or in combination with other forms of nickel. The present study suggests a multiplicative effect of smoking and nickel exposure.     

Cancer mortality in a surveillance cohort of German males formerly exposed to asbestos

The objective of this analysis was the estimation of the cancer risks of asbestos and asbestosis in a surveillance cohort of high-exposed German workers. A group of 576 asbestos workers was selected for high-resolution computer tomography of the chest in 1993-1997. A mortality follow-up was conducted through 2007. Standardised mortality ratios (SMRs) were calculated and Poisson regression was performed to assess mesothelioma risks. A high risk was observed for pleural mesothelioma (SMR 28.10, 95% CI 15.73-46.36) that decreased after cessation of exposure (RR 0.1; 95% CI 0.0–0.6 for ≥30 vs. <30 years after last exposure). Asbestosis was a significant risk factor for mesothelioma (RR 6.0, 95% CI 2.4-14.7). Mesothelioma mortality was still in excess in former asbestos workers although decreasing after cessation of exposure. Fibrosis was associated with subsequent malignancy.     

青石棉污染区恶性肿瘤死亡率10年回顾队列研究

为了探讨环境低浓度石棉接触对居民恶性肿瘤尤其是肺癌和间皮瘤发生绎大姚县部门青石棉污染区３０岁以上的农村居民进行了１０年回顾性队列调查。队列人数为３３６３人,其中男１５０３人,女１８６０人。对照选用石青石棉污染的该县龙街乡农民和远离该县２３０多公里的禄丰县金山镇农民居民共７６３９人,观察期９年。     

Mortality in miners and millers of crocidolite in Western Australia.

It is known that 6505 men and 411 women were employed in the mining and milling of crocidolite at Wittenoom in the Pilbara region of Western Australia between 1943 and 1966. Employment was usually brief (median duration four months) and exposure intense (median estimated cumulative exposure 6 fibres/cc years). The vital status of 73% of the men and 58% of the women employed in the industry was known at 31 December 1980, providing 95 264 person-years of follow up with 820 deaths in men and 4914 person-years with 23 deaths in women. The standardised mortality ratio (SMR) for all causes in men was 1.53 (95% confidence interval 1.43 to 1.64). Statistically significant excess death rates were observed in men for neoplasms, particularly malignant mesothelioma (32 deaths), neoplasms of the trachea, bronchus, and lung (SMR 2.64), and neoplasms of the stomach (SMR 1.90); respiratory diseases, particularly pneumoconiosis (SMR 25.5); infections, particularly tuberculosis (SMR 4.09); mental disorders particularly alcoholism (SMR 4.87); digestive diseases, particularly peptic ulceration (SMR 2.46) and cirrhosis of the liver (SMR 3.94); and injuries and poisonings, particularly non-transport accidents (SMR 2.36). The excess mortality from pneumoconiosis, malignant mesothelioma, and respiratory cancers, but not stomach neoplasms, was dependent on time since first exposure and cumulative exposure. There was no increase in mortality from laryngeal cancer (SMR 1.09) or neoplasms other than those listed. The SMR for all causes in women was 1.47 (95% confidence interval 0.98-2.21) and for neoplasms 1.99; there was one death from malignant pleural mesothelioma.     

Airborne fibre concentrations and lung burden compared to the tumour response in rats and humans exposed to asbestos

The excess risk of tumours exposed to asbestos were previously compared with the results of rat inhalation experiments. It could be demonstrated that humans at the workplace suffer from a tumour risk at fibre concentrations which are 300 times lower than those needed in the rat inhalation model to produce the same risk. However, the estimation of human risk was based on the study of workers at a chrysotile textile factory, whereas animal experimental results were related to exposure to amphiboles. Since for this comparison the risk of cancer due to exposure to amosite or crocidolite fibres at the workplace is of interest, quantitative exposure-response relationships for lung cancer and mesothelioma for the white workforce of South African amosite and crocidolite mines were discussed. On comparing the risk of lung cancer in this study with the risk of lung cancer for chrysotile textile workers, it can be concluded, that the risk of lung cancer and mesothelioma from crocidolite and amosite was higher than in the chrysotile textile factory.It could be also demonstrated, on the basis of a study of the lung burden of mesothelioma cases and of controls, that a significantly increased odds ratio of about 5 was established at amphibole concentrations of between 0.1 and 0.2 f μg⁻¹ dry lung (WHO fibres longer than 5 μm from TEM analysis). On the other hand, carcinogenic response was observed at a fibre concentration 6000 times higher in animal inhalation experiments with crocidolite asbestos (SEM analysis of WHO fibres). As a result of these findings, it has been concluded that inhalation studies in rats are not sufficiently sensitive for the detection of hazards and risks to humans exposed to man-made fibres.     

Mortality in miners and millers of crocidolite in Western Australia

It is known that 6505 men and 411 women were employed in the mining and milling of crocidolite at Wittenoom in the Pilbara region of Western Australia between 1943 and 1966. Employment was usually brief (median duration four months) and exposure intense (median estimated cumulative exposure 6 fibres/cc years). The vital status of 73% of the men and 58% of the women employed in the industry was known at 31 December 1980, providing 95 264 person-years of follow up with 820 deaths in men and 4914 person-years with 23 deaths in women. The standardised mortality ratio (SMR) for all causes in men was 1.53 (95% confidence interval 1.43 to 1.64). Statistically significant excess death rates were observed in men for neoplasms, particularly malignant mesothelioma (32 deaths), neoplasms of the trachea, bronchus, and lung (SMR 2.64), and neoplasms of the stomach (SMR 1.90); respiratory diseases, particularly pneumoconiosis (SMR 25.5); infections, particularly tuberculosis (SMR 4.09); mental disorders particularly alcoholism (SMR 4.87); digestive diseases, particularly peptic ulceration (SMR 2.46) and cirrhosis of the liver (SMR 3.94); and injuries and poisonings, particularly non-transport accidents (SMR 2.36). The excess mortality from pneumoconiosis, malignant mesothelioma, and respiratory cancers, but not stomach neoplasms, was dependent on time since first exposure and cumulative exposure. There was no increase in mortality from laryngeal cancer (SMR 1.09) or neoplasms other than those listed. The SMR for all causes in women was 1.47 (95% confidence interval 0.98-2.21) and for neoplasms 1.99; there was one death from malignant pleural mesothelioma.