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.

     

Mesothelioma in an Individual Following Exposure to Crocidolite-containing Gaskets as a Teenager

Abstract

Mesothelioma is considered a signal tumor for asbestos exposure and typically occurs decades after first exposure to asbestos. Tissue analysis often indicates past exposure to mixed types of asbestos. This report describes the case of a 58-year-old man who developed mesothelioma after reported exposure to crocidolite from asbestos-containing gaskets beginning at age 16 during three summers during high school and for approximately four hours per day during the last semester of his senior year. He had no further known exposure to asbestos. Analytical transmission electron microscopy analysis of digested tissue samples revealed elevated levels of crocidolite asbestos fibers and the presence of crocidolite cored ferruginous bodies. This case is unique in that it establishes that relatively short and/or intense exposures to crocidolite asbestos traumatically released from a previously classified Category 1 nonfriable asbestos-containing material (NESHAP) was confirmed via tissue burden analysis years following the historically defined exposures.     

Mortality in a cohort of vermiculite miners exposed to fibrous amphibole in Libby, Montana

Background: Fibrous tremolite is a widespread amphibole asbestiform mineral, airborne fibres of which constitute an environmental hazard in Libby, Montana, northern California, and elsewhere.

Aims: To determine excess risk from lung cancer, mesothelioma, and all-cause mortality in a cohort of men exposed to tremolite, but no other form of asbestos.

Methods: Mortality by certified cause and various measures of exposure to tremolite and related amphibole fibres was assessed in a cohort of 406 vermiculite mineworkers in Libby, Montana, employed before 1963 and followed until 1999.

Results: Total deaths were: lung cancer 44 (SMR 2.40), non-malignant respiratory disease (NMRD) 51 (SMR 3.09), all causes 285 (SMR 1.27); included among the total were 12 deaths ascribed to mesothelioma (4.21% of all deaths). Adjusted linear increments in relative risks (per 100 f/ml.y), estimated by Poisson regression, were: lung cancer (0.36, 95% CI 0.03 to 1.20), NMRD (0.38, 95% CI 0.12 to 0.96), and all deaths (0.14, 95% CI 0.05 to 0.26).

Conclusions: The all-cause linear model would imply a 14% increase in mortality for mine workers exposed occupationally to 100 f/ml.y or about 3.2% for a general population exposed for 50 years to an ambient concentration of 0.1 f/ml. Amphibole fibres, tremolite in particular, are likely to be disproportionately responsible for cancer mortality in persons exposed to commercial chrysotile, but to what extent cannot be readily assessed.

     

Malignant pleural and peritoneal mesotheliomas in former miners and millers of crocidolite at Wittenoom, Western Australia

Methods: A group of 6493 men and 415 women who had worked at the former Wittenoom crocidolite mine and mill at some time between 1943 and 1966 have been followed up throughout Australia and Italy to the end of 2000.

Results: The cumulative number of mesotheliomas up to 2000 was 235 in men (202 pleural, 33 peritoneal) and seven (all pleural) in women. There had been 231 deaths with mesothelioma (9% of known deaths).

Conclusions: The number of deaths in men with mesothelioma between 1987 and 2000 was at the low end of the predictions made earlier based on the number of cases to 1986. If this trend continues, it is predicted that about another 110 deaths with mesothelioma will occur in men by 2020.

     

Radiological survey of men exposed to asbestos in naval dockyards

Harries, P. G., Mackenzie, F. A. F., Sheers, G., Kemp, J. H., Oliver, T. P., and Wright, D. S. (1972).Brit. J. industr. Med.,29, 274-279. Radiological survey of men exposed to asbestos in naval dockyards. Asbestos related abnormalities were found in 3% of a 10% sample population in radiological surveys of the naval dockyards at Portsmouth, Chatham, and Rosyth. The prevalence of these abnormalities was related to the type of occupation and duration of exposure to asbestos. The results confirm the findings of an earlier survey at Devonport dockyard.

No association between smoking, or the amount smoked, and the incidence of parenchymal or pleural disease due to asbestos was detected.

Pleural abnormalities were found 10 times more frequently than parenchymal disease, and concern is felt over the uncertainty of the prognosis in men with pleural abnormalities, especially as 37 men have developed pleural mesothelioma at Devonport since 1965.

More work is required to establish the true significance of pleural abnormalities caused by asbestos and to explore possible methods of treatment.

     

Malignant mesothelioma in Australia, 1945-2000

BACKGROUND: Australia has maintained a total national malignant mesothelioma case register since 1980. There has been a marked increase in the incidence of mesothelioma in the last 20 years. Currently 450-600 cases are notified annually in a population of 20 million. While the history of the Wittenoom (Western Australia) crocidolite mine and its aftermath is well known, these cases comprise only 5% of the total. This study describes the incidence of mesothelioma in Australia from 1945 to 2000. METHODS: Using register data, time trends in mesothelioma incidence were calculated. Analyses of incidence are reported by age, sex, anatomical site, and state of notification. Associations with occupational and environmental asbestos exposure histories are described. Lung fiber content measurements were made on a subset of cases. RESULTS: Australia has had 6,329 cases of mesothelioma from 1 January 1945 to 31 December 2000. (A further 620 cases were notified in the period from 1 January 2001 to 31 October 2001.) Annual incidence rates for Australia per million population > or = 20 years (1997) were: male, 59.8; female, 10.9; total, 35.4. Incidence rates have been continually increasing and are the highest reported national rates in the world. While Western Australia has the highest rate (1997 total rate, 52.8), most cases arise from the two most populous eastern states, New South Wales and Victoria. In 88% (male 90%, female 61%) of cases, a history of asbestos exposure was obtained. Exposures occurred in a wide variety of occupational and environmental circumstances. In 80% of cases with no history of exposure, TEM lung asbestos fiber counts > 200,000 fibers > 2 microm length per gm dry lung were obtained, suggesting unrecognized exposure. CONCLUSIONS: Australia's high incidence of mesothelioma is related to high past asbestos use, of all fiber types, in a wide variety of occupational and environmental settings. The number of cases in total is expected to be about 18,000 by 2020, with about 11,000 yet to appear.     

Mesothelioma in a community in the north of England.

OBJECTIVES: To find the numbers of mesotheliomas in Calderdale over the period 1966-94 and determine their relation to asbestos exposure, pathology, and mineral fibre burden within the lungs of affected subjects. METHODS: Cases were entered into the study if the subject has been diagnosed with mesothelioma after postmortem and histopathological examinations. Occupational data were obtained mainly from the case records of the Cape Asbestos medical officer, hospital, and medical practitioner and from death certificates. Analyses of the mineral fibres were performed with transmission electron microscopy and energy dispersive x ray spectrometry. RESULTS: 73 mesotheliomas were diagnosed from 1966 to 1994. Forty four were associated with exposure at the Acre Mill factory, which manufactured asbestos products. Concentrations of amphibole asbestos fibres were found to be raised above controls in 31 out of 32 cases associated with Acre Mill exposure, in 10 out of 12 other cases exposed to asbestos and eight out of 17 cases not exposed to asbestos. CONCLUSIONS: There was a high number of mesotheliomas in Calderdale. More than half of the cases were associated with occupation at the Acre Mill factory and were associated with exposure to amphibole asbestos, predominantly crocidolite. No cases associated with neighbourhood exposure to asbestos were identified.     

Mesothelioma in an individual following exposure to crocidolite-containing gaskets as a teenager

Mesothelioma is considered a signal tumor for asbestos exposure and typically occurs decades after first exposure to asbestos. Tissue analysis often indicates past exposure to mixed types of asbestos. This report describes the case of a 58-year-old man who developed mesothelioma after reported exposure to crocidolite from asbestos-containing gaskets beginning at age 16 during three summers during high school and for approximately four hours per day during the last semester of his senior year. He had no further known exposure to asbestos. Analytical transmission electron microscopy analysis of digested tissue samples revealed elevated levels of crocidolite asbestos fibers and the presence of crocidolite cored ferruginous bodies. This case is unique in that it establishes that relatively short and/or intense exposures to crocidolite asbestos traumatically released from a previously classified Category 1 nonfriable asbestos-containing material (NESHAP) was confirmed via tissue burden analysis years following the historically defined exposures.     

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.     

An updated review on asbestos and related diseases in China

Abstract

Background: Asbestos is an industrial mineral that can cause diseases such as asbestosis, lung cancer, and mesothelioma. Asbestos consumption in China has increased steadily since the 1960s and is currently at half a million tonnes per year. Work conditions in the asbestos-related industries are poor and exposure levels frequently exceed the occupational exposure limit.

Objective: To provide an updated overview on asbestos production and consumption in China and discuss what is known about the resulting burden of asbestos-related diseases.

Findings: China is the world's top chrysotile consumer and second largest producer. Over a million people may be occupationally exposed, yet reliable disease statistics are unavailable and the national burden of asbestos-related disease (ARD) is not well known. Nevertheless, ARD prevalence, incidence, and mortality are expected to be high and will increase for many decades due to the volume of asbestos consumed historically, and a long latency period.

Conclusions: Government policies to prevent ARD have been implemented but more actions are necessary to ensure compliance and ultimately, the complete elimination of asbestos to prevent a heavy future disease burden.     

Asbestos-related mesothelioma: factors discriminating between pleural and peritoneal sites.

Up to the end of 1980, 144 confirmed cases of mesothelioma were identified among employees of an organisation using asbestos in manufacturing and insulation. The primary site was peritoneal in 74 cases, pleural in 66, and undetermined in four. All employees had been exposed to amphibole asbestos, and evidence from different factories confirmed the predominant role of crocidolite in the production of mesothelioma. The ratio of pleural to peritoneal sites showed a continuous change when related to the year of first exposure, varying from 5:1 pleural to peritoneal before 1921 to 1:3 after 1950. The strong temporal relationship appeared to reflect progressive dust suppression, including the non-fibrous dusts present in insulation materials and perhaps also the degree to which the fibres had been opened. Other predisposing factors were related to the degree of individual exposure, the peritoneal site being associated preferentially with longer and heavier exposures.     

Asbestos-related mesothelioma: factors discriminating between pleural and peritoneal sites

Up to the end of 1980, 144 confirmed cases of mesothelioma were identified among employees of an organisation using asbestos in manufacturing and insulation. The primary site was peritoneal in 74 cases, pleural in 66, and undetermined in four. All employees had been exposed to amphibole asbestos, and evidence from different factories confirmed the predominant role of crocidolite in the production of mesothelioma. The ratio of pleural to peritoneal sites showed a continuous change when related to the year of first exposure, varying from 5:1 pleural to peritoneal before 1921 to 1:3 after 1950. The strong temporal relationship appeared to reflect progressive dust suppression, including the non-fibrous dusts present in insulation materials and perhaps also the degree to which the fibres had been opened. Other predisposing factors were related to the degree of individual exposure, the peritoneal site being associated preferentially with longer and heavier exposures.     

Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry

Aims: To update the analysis of the cohort mortality and cancer incidence study of employees in the Australian petroleum industry.

Methods: Employees from 1981 to 1996 were traced through the Australian National Death Index and the National Cancer Statistics Clearing House. Cause specific mortality and cancer incidence were compared with those of the Australian population by means of standardised mortality ratios (SMRs) and standardised incidence ratios (SIRs). Associations between increased incidence of specific cancers and employment in the petroleum industry were tested by trends according to period of first employment, duration of employment, latency, and hydrocarbon exposure, adjusting for personal smoking history where appropriate. Total follow up time was 176 598 person-years for males and 10 253 person-years for females.

Results: A total of 692 of the 15 957 male subjects, and 16 of the 1206 female subjects had died by the cut off date, 31 December 1996. In males, the all-cause SMR and the SMRs for all major disease categories were significantly below unity. There was a non-significant increase of the all-cancer SIR (1.04, 95% CI 0.97 to 1.11). There was a significant increase of the incidence of melanoma (SIR 1.54, 95% CI 1.30 to 1.81), bladder cancer (SIR 1.37, 95% CI 1.00 to 1.83), and prostate cancer (SIR 1.19, 95% CI 1.00 to 1.40), and a marginally significant excess of pleural mesothelioma (SIR 1.80, 95% CI 0.90 to 3.22), leukaemia (SIR 1.39, 95%CI 0.91 to 2.02), and multiple myeloma (SIR 1.72, 95% CI 0.96 to 2.84).

Conclusions: Most cases of mesothelioma are probably related to past exposure to asbestos in refineries. The melanoma excess may be the result of early diagnosis. The excess bladder cancer has not been observed previously in this industry and is not readily explained. The divergence between cancer incidence and cancer mortality suggests that the "healthy worker effect" may be related to early reporting of curable cancers, leading to increased likelihood of cure and prolonged mean survival time.

     

Role of occupational asbestos exposure in Hungarian lung cancer patients

Objective: What is the frequency of occupational asbestos exposure among patients suffering from malignant respiratory tumours and how many of these tumours are associated with asbestos in Hungary? Methods: An internationally established questionnaire with 29 questions, covering the most characteristic activities of asbestos exposure at the workplace was completed for 300 patients with respiratory malignancies, i.e. 297 patients with lung cancer and three with mesothelioma of the pleura. From the questionnaire, the smoking habits were estimated and cumulative asbestos exposure was assessed in fibre-years. Additionally, lung X-rays were classified and the national data on the incidence of malignant pleura mesothelioma were analysed. Results: A cumulative asbestos exposure of 25?fibre-years or more was detected in 11 patients with lung cancer (4%) and in each of the three patients with pleural mesothelioma (100%). In a further 72 patients (24%), cumulative occupational asbestos exposure was assessed as below 25?fibre-years (between 0.01 and 23.9?fibre-years). In this group, car and truck mechanics, and installation and construction workers using asbestos-cement were registered. Among patients with an asbestos exposure of 25?fibre-years or more, six asbestos-cement production workers were observed, among them the three mesothelioma cases. A weak but significant association between positive X-ray findings and exposure estimates could be demonstrated. Additionally, results of the lung tissue fibre counts by scanning transmission electron microscopy were available for 25 of the lung cancer patients. A good correlation was observed between the asbestos fibre counts and the assessment of cumulative asbestos exposure. In Hungary, 84 cases of pleural mesothelioma were registered in 1997 and 73 in 1998. These numbers correspond to an annual incidence of about one new case per 100,000 inhabitants older than 15?years. Conclusions: The annual incidence of lung cancer in Hungary is about 6,000. Since in our series of lung cancer patients about 4% were observed, which could be accepted as representing occupational disease because of a cumulative exposure to 25?fibre-years or more, the annual asbestos related lung tumour incidences may be estimated to be approximately 150 or more. The proportion of nearly two estimated cases of lung cancer per case of pleural mesothelioma corresponds to international experience. Up to now, lung cancer cases only exceptionally have been registered as occupational diseases, i.e. they were seriously under-diagnosed in Hungary. For improving this situation, diagnostic assistance by a self-interview with a questionnaire covering the working history for all newly diagnosed lung cancer patients would be helpful.     

Asbestos fibreyears and lung cancer: a two phase case-control study with expert exposure assessment

Aims: To assess the cumulative effect of asbestos on lung cancer risk where the exposure is assessed by an expert rating.

Methods: 1678 male cases and controls were enrolled in a population based matched case–control study, focused on occupational risk factors, carried out in West Germany. The exposure to asbestos was computed as lifelong working hours. For a validation subsample of 164 matched pairs from this study the intensity of asbestos exposure was further assessed by a panel of experts in order to obtain an estimate of the cumulative exposure on a time by intensity scale (fibreyears). The information on duration of asbestos exposure in the original study was combined with the fibreyears following the two phase case control study paradigm.

Results: The number of exposed subjects in the validation subsample was 75 cases and 71 controls. The percentage of subjects with a cumulative exposure ≤1, 1 to ≤10, and >10 fibreyears was 16%, 15%, and 15% for the cases and 18%, 16%, and 9% respectively for the controls. The smoking adjusted odds ratios for the fibreyears based on an unconditional logistic regression were 0.81, 1.02, and 1.60 respectively with increasing exposure categories (not significant). The coefficient (beta) for a log transformed trend was 1.156. Applying the two phase paradigm, these odds ratios became 0.86, 1.33, and 1.94; the latter reached significance and the beta coefficient was 1.178.

Conclusions: The two phase paradigm allowed us to obtain a more precise estimate of the effect of asbestos on lung cancer. Results are consistent with a doubling of the lung cancer risk with 25 fibreyears asbestos exposure.

     

Mortality from all cancers of asbestos factory workers in east London 1933-80

OBJECTIVE—To give the observed and expected deaths due to cancer at all separate sites in asbestos workers in east London, and to analyse these for overall effect and exposure-response trend.
METHODS—The mortality experience of a cohort of over 5000 men and women followed up for over 30 years since first exposure to asbestos has been extracted.
RESULTS—There was a large excess of deaths due to cancer (537 observed, 222 expected). Most of these were due to cancer of the lung (232 observed, 77 expected) and pleural (52) and peritoneal (48) mesothelioma. The exposure-response trend for all these three causes was highly significant. There was also an excess of cancer of the colon (27 observed, 15 expected) which was significantly related to exposure. There were significant excesses of cancer of the ovary, of the liver, and of the oesophagus but with no consistent relation to exposure.
CONCLUSIONS—The excess risk of cancer after exposure to asbestos was mainly due to cancer of the lung and mesothelioma. An exposure related excess of cancer of the colon was also detected but the possibility that some of these deaths may have been peritoneal mesotheliomas could not be excluded. There was no consistent evidence of exposure related excesses at any other site.


Keywords: asbestos; cancer; exposure-response     

Tumor incidence was not related to the thickness of visceral pleural in female Syrian hamsters intratracheally administered amphibole asbestos or manmade fibers.

Histological observations were performed on female Syrian hamsters 2 years after the intratracheal administration of amphibole asbestos, amosite, and crocidolite to evaluate the tumorigenicity of six types of fine manmade fibers (reported previously). A mesothelioma and a lung tumor were induced in 20 animals administered amosite, but no tumors were found in the crocidolite group. Because this incidence is not higher than that of manmade fibers, such as basic magnesium sulfate fiber [9 tumor-bearing hamsters in 20 hamsters (9/20)], metaphosphate fiber (5/20), calcium sulfate fiber (3/20), and fiberglass (2/20), it is suggested that some types of manmade fibers have a greater ability than asbestos to induce tumors. Moreover, as a specific observation in manmade fiber groups, tumors were induced at intracelial organs rather than at the pleural cavity. On the other hand, the average thickness of visceral pleura was higher in all asbestos and manmade fiber groups than in the control (2.9 microns), for instance, 36.95 microns in potassium titanate fiber group, 15.90 microns crocidolite group, 13.00 microns basic magnesium sulfate fiber group, and 10.45 microns in the rockwool group. Although both pleural thickening and mesothelioma are known as peculiar lesions in asbestos-exposed people, it might also be suggested that these lesions could be induced by different mechanisms from the result that there was no relation between the pleural thickening and mesothelioma incidence in hamsters.     

The quantitative risks of mesothelioma and lung cancer in relation to asbestos exposure

Mortality reports on asbestos exposed cohorts which gave information on exposure levels from which (as a minimum) a cohort average cumulative exposure could be estimated were reviewed. At exposure levels seen in occupational cohorts it is concluded that the exposure specific risk of mesothelioma from the three principal commercial asbestos types is broadly in the ratio 1:100:500 for chrysotile, amosite and crocidolite respectively. For lung cancer the conclusions are less clear cut. Cohorts exposed only to crocidolite or amosite record similar exposure specific risk levels (around 5% excess lung cancer per f/ml.yr); but chrysotile exposed cohorts show a less consistent picture, with a clear discrepancy between the mortality experience of a cohort of xhrysotile textile workers in Carolina and the Quebec miners cohort. Taking account of the excess risk recorded by cohorts with mixed fibre exposures (generally<1%), the Carolina experience looks uptypically high. It is suggested that a best estimate lung cancer risk for chrysotile alone would be 0.1%, with a highest reasonable estimate of 0.5%. The risk differential between chrysotile and the two amphibole fibres for lunc cancer is thus between 1:10 and 1:50.Examination of the inter-study dose response relationship for the amphibole fibres suggests a non-linear relationship for all three cancer endpoints (pleural and peritoneal mesotheliomas, and lung cancer). The peritoneal mesothelioma risk is proportional to the square of cumulative exposure, lung cancer risk lies between a linear and square relationship and pleural mesothelioma seems to rise less than linearly with cumulative dose. Although these non-linear relationships provide a best fit ot the data, statistical and other uncertainties mean that a linear relationship remains arguable for pleural and lung tumours (but not or peritoneal tumours).Based on these considerations, and a discussion fo the associated uncertainties, a series of quantified risk summary statements for different elvels of cumulative exposure are presented.     

Mineral fibres, fibrosis, and asbestos bodies in lung tissue from deceased asbestos cement workers

Lung tissue from 76 deceased asbestos cement workers (seven with mesothelioma) exposed to chrysotile asbestos and small amounts of amphiboles, has been studied by transmission electron microscopy, together with lung tissue from 96 controls. The exposed workers with mesothelioma had a significantly higher total content of asbestos fibre in the lungs than those without mesothelioma, who in turn, had higher concentrations than the controls (medians 189, 50, and 29 x 10(6) fibres/g (f/g]. Chrysotile was the major type of fibre. The differences were most pronounced for the amphibole fibres (62, 4.7, and 0.15 f/g), especially crocidolite (54, 1.8 and less than 0.001 f/g), but were evident also for tremolite (2.9, less than 0.001, and less than 0.001 f/g) and anthophyllite (1.7, less than 0.001, and less than 0.001 f/g). For amosite, there was no statistically significant difference between lungs from workers with and without mesothelioma; the lungs of workers had, however, higher concentrations than the controls. Strong correlations were found between duration of exposure and content of amphibole fibres in the lungs. Asbestos bodies, counted by light microscopy, were significantly correlated with the amphibole but not with the chrysotile contents. Fibrosis was correlated with the tremolite but not the chrysotile content in lungs from both exposed workers and controls. Overall, similar results were obtained using fibre counts and estimates of mass.