An updated evaluation of reported no-observed adverse effect levels for chrysotile, amosite, and crocidolite asbestos for lung cancer and mesothelioma

This analysis updates two previous analyses that evaluated the exposure-response relationships for lung cancer and mesothelioma in chrysotile-exposed cohorts. We reviewed recently published studies, as well as updated information from previous studies. Based on the 16 studies considered for chrysotile (<10% amphibole), we identified the "no-observed adverse effect level" (NOAEL) for lung cancer and/or mesothelioma; it should be noted that smoking or previous or concurrent occupational exposure to amphiboles (if it existed) was not controlled for. NOAEL values ranged from 2.3-<11.5 f/cc-years to 1600-3200 f/cc-years for lung cancer and from 100-<400 f/cc-years to 800-1599 f/cc-years for mesothelioma. The range of best-estimate NOAELs was estimated to be 97-175 f/cc-years for lung cancer and 250-379 f/cc-years for mesothelioma. None of the six cohorts of cement or friction product manufacturing workers exhibited an increased risk at any exposure level, while all but one of the six studies of textile workers reported an increased risk at one or more exposure levels. This is likely because friction and cement workers were exposed to much shorter chrysotile fibers. Only eight cases of peritoneal mesothelioma were reported in all studies on predominantly chrysotile-exposed cohorts combined. This analysis also proposed best-estimate amosite and crocidolite NOAELs for mesothelioma derived by the application of relative potency estimates to the best-estimate chrysotile NOAELs for mesothelioma and validated by epidemiology studies with exposure-response information. The best-estimate amosite and crocidolite NOAELs for mesothelioma were 2-5 f/cc-years and 0.6-1 f/cc-years, respectively. The rate of peritoneal mesothelioma in amosite- and crocidolite-exposed cohorts was between approximately 70- to 100-fold and several-hundred-fold higher than in chrysotile-exposed cohorts, respectively. These findings will help characterize potential worker and consumer health risks associated with historical and current chrysotile, amosite, and crocidolite exposures.

[Monitoring and analysis of asbestos concentration in working environment of different asbestos-producing technologies in a certain area]

OBJECTIVE

To analyze asbestos exposure level between 1984 and 2010 in a district of malignant mesothelioma with clustering incidence in Zhejiang Province, in order to improve the recognizing and early diagnosis of malignant mesothelioma, protect the health of workers.

METHODS

Monitoring data of total asbestos dust concentration in the air of workplace from 1984 to 2010 in asbestos textile enterprises, family hand spinning operation, brake production, and asbestos board production in Zhejiang Province were collected in the local CDC. A total of 766 TWA copies of mass concentration were collected, and 1233 copies of MAC data. Asbestos mass concentration and fibre counting concentration of 29 points of family hand spinning operation were parallel determinated in the same time and the same sampling point. Raw asesbtos materials and dust composition of local asbestos processing corporations were collected and analyzed using X-ray diffraction method.

RESULTS

Raw materials of asbestos used between 1984 and 2010 in this area were chrysotile from Sichuan, Qinghai, Xinjiang, Russia, Zimbabwe, and some were mixed with SiO2, CaCO3 and other impurities. Raw materials used in asbestos board production were blue asbestos. Dust concentration between 1960s and 1980s in asbestos processing plants far exceeded the national standard. After then the dust concentration decreased significantly, but still higher than the national standard. 95.2% of air dust concentrations in the workplaces of asbestos factories exceeded the standard, and dust concentrations of workplaces of raw material, spinning, weaving, carding and labor insurance were above 90% in which carding work had the highest median concentration. 37.9% of dust mass concentrations in hand spinning work exceeded the standard where textile machinery side had the highest value. Beating job in asbestos board manufacturing and grinding job in brake production had higher concentrations.

CONCLUSIONS

Most of production technologies in asbestos processing industry exceed the standard level, indicating that the workers were at risk for malignant mesothelioma and other asbestos related diseases, which should draw high attention.

[A case-control study on the relationship of crocidolite pollution in drinking water with the risk of gastrointestinal cancer in Dayao County]

OBJECTIVE

To explore the relationship of crocidolite pollution in drinking water with the risk of gastrointestinal cancer's death in Dayao County.

METHODS

A 1:2 matched case-control study involving 54 death cases of gastrointestinal cancer from a population-based cohort of twenty-seven years and 108 controls matched by age, gender, death time, etc was conducted to analyze the effect of local water condition on the risk of gastrointestinal cancer in Dayao County.

RESULTS

Results from logistic regression analysis suggested the longer of asbestos furnace use over time, the higher the mortality risk of gastrointestinal cancer (6 - 10 years: OR = 2.920, 95% CI 1.501 - 5.604. 11 - 15 years: OR = 3.966, 95% CI 2.156 -7.950. Over 15 years: OR = 4.122, 95% CI 1.211 - 7. 584). Drinking unboiled water leaded to an increased risk of gastrointestinal cancer (OR = 1.43, 95% CI 1.07 - 1.88). Type of drinking water was associated with gastrointestinal cancer. When compared with drinking tap water, OR for drinking well water was 1.770 (95% CI 1.001 - 2.444), 2.442 for drinking river water (95% CI 0.956 - 3.950), 2.554 for drinking house and field ditch water (95% CI 1.961 - 6.584), and 3.121 for drinking pond water (95% CI 1.872 - 6.566).

CONCLUSION

Related factors of drinking water in crocidolite-contaminated area in Dayao County were significantly associated with the mortality of gastrointestinal cancer.

Concentrations of asbestos fibers and metals in drinking water caused by natural crocidolite asbestos in the soil from a rural area

Asbestos fibers and metals in drinking water are of significant importance to the field of asbestos toxicology. However, little is known about asbestos fibers and metals in drinking water caused by naturally occurring asbestos. Therefore, concentrations of asbestos fibers and metals in well and surface waters from asbestos and control areas were measured by scanning electron microscopy (SEM), inductively coupled plasma (ICP) optical emission spectrometer, and ICP-mass spectrometry in this study. The results indicated that the mean concentration of asbestos fibers was 42.34 millions of fibers per liter by SEM, which was much higher than the permission exposure level. The main compositions of both asbestos fibers in crocidolite mineral and in drinking water were Na, Mg, Fe, and Si based on energy dispersive X-ray analysis. This revealed that the drinking water has been contaminated by asbestos fibers from crocidolite mineral in soil and rock. Except for Cr, Pb, Zn, and Mn, the mean concentrations of Ni, Na, Mg, K, Fe, Ca, and SiO2 were much higher in both surface water and well waters from the asbestos area than in well water from the control area. The results of principal component and cluster analyses indicated that the metals in surface and well waters from the asbestos area were significantly influenced by crocidolite mineral in soil and rock. In the asbestos area, the mean concentrations of asbestos fibers and Ni, Na, Mg, K, Fe, Ca, and SiO2 were higher in surface and well waters, indicating that asbestos fibers and the metals were significantly influenced by crocidolite in soil and rock.

All-cause mortality and cancer incidence among adults exposed to blue asbestos during childhood

BACKGROUND

There are few data on the long-term health outcomes of exposure to asbestos in childhood. This study investigated cancer and mortality of adults exposed to blue asbestos as children.

METHODS

Data linkage to relevant health registries was used to identify cancers and mortality in a cohort of adults (n = 2,460) that had lived in an asbestos mining town during their childhood (<15 years).

RESULTS

There were 217 (93 female) incident cancers and 218 (70 female) deaths among the cohort. Compared with the Western Australian population females had elevated mesothelioma, ovarian and brain cancers, and increased "all cause" and "all cancer" mortality. Males had elevated mesothelioma, leukemia, prostate, brain, and colorectal cancers, and excess mortality from "all causes," "all cancers," circulatory disease, diseases of the nervous system, and accidents.

CONCLUSION

Exposure to blue asbestos in childhood is associated with an increased risk of cancer and mortality in adults.

[Application of infrared spectrometry (FT-IR) for mineral identification of asbestos in bulk samples]

BACKGROUND

The aim of this study was to apply infrared spectrometry (FTIR) in mineral identification of asbestos in bulk materials.

MATERIAL AND METHODS

The identification of asbestos was based on infrared spectra of UICC and NIST: SRM 1866a and SRM 1867 standard asbestos, and infrared spectra of heat treatment chrysotile, crocidolite and amosite asbestos. The samples of bulk materials were grinded and fibers were isolated from samples. The KBr disc standard technique was used in the preparation of samples for infrared measurements. The infrared spectra were recorded in transmittance function, at resolution of 4 cm1 and for 32 averaged scans.

RESULTS

The analysis of the infrared spectra revealed that chrysotile, crocidolite, amosite and anthophyllite asbestos can be identified in industrial products and distinguished in mixtures. Spectra of fibrous materials do not interfere with spectra of asbestos. When analyzing the whole sample mass, interferences from the components of construction materials can be eliminated or reduced by using computer transforming spectra, preliminary purification of samples or separation of sample components. The method used permit to identify from 2 to 4 microg of the three basic forms of asbestos. Spectra of chrysotile and amosite heated to 500 degrees C and crocidolite heated to 300 degrees C are the same as non-heated forms. Heating in higher temperature induces characteristic changes in spectra and the transformation of asbestos into other minerals.

CONCLUSIONS

Infrared spectrometry can be used for routine identification of asbestos in samples of bulk materials also treated with high temperature, and to assess the effectiveness of asbestos waste detoxification.

[Asbestos fibre lung burden and exposure indices in asbestos-cement workers]

BACKGROUND

In many previous studies, the asbestos fibres retained in the lung were regarded as a good index of cumulative occupational asbestos exposure. Twelve workers suffering from asbestos-related diseases and had been employed in an asbestos-cement factory operating from 1961 to 1994 underwent post mortem investigations in the course of a criminal law suit.

OBJECTIVES

Samples of lung tissues were collected for electron microscopy analysis to measure the asbestos fibre burden of the lungs in workers with high exposure, and assess the possible correlation between asbestos fibre lung burden and the estimated levels of cumulative exposure.

METHODS

Samples of lung parenchyma obtained from a consecutive series of 12 post-mortem examinations that were performed between 1994 and 2007and included 5 cases of malignant pleural mesothelioma, 4 lung cancers, 1 case of asbestosis and2 ofpleuralplagues, were collected, stored and analysed by SEM electron microscopy, according to the methods suggested by the current scientific literature. For each worker, all males, a detailed occupational history was reconstructed by means ofpersonal interviews; both the measurements of airborne asbestos fibresperformed by the factory in the 1970's and the duration of each single job in the plant were taken into account to estimate an individual cumulative exposure index.

RESULTS

A wide variation of total asbestos fibre concentrations in the lung (1,320-118 million) was observed; in all 12 workers, the lung amphibole fibre burden exceeded 1,000,000 fibres per g/dry tissue, The highest values were detected in the mesothelioma cases, in which the mean fibre concentrations differed statistically (t=2.29, p=0.045) from the mean calculated for the other asbestos-related diseases; in 9 subjects only amphibole fibres were detected. There was a good correlation between total asbestos fibre concentration and cumulative exposure index (r=0.91, p<0.0001).

CONCLUSION

This study, which was numerically the biggest ever performed in Italy for this category of workers, confirms a wide range of total asbestos fibre burden in heavily occupationally exposed workers and showed that of the asbestos-related diseases, the highest lung concentrations of asbestos fibres were reached in cases of mesothelioma. It was also observed that almost the entire lung burden consists of only amphibole fibres, all exceeding 1 million per gramme of dry tissue. This study tested a synthetic cumulative occupational exposure index, which appears to be well correlated to the level of exposure established by biological analysis.

Pleural mesothelioma in a woman whose documented past exposure to asbestos was from smoking asbestos-containing filtered cigarettes: the comparative value of analytical transmission electron microscopic analysis of lung and lymph-node tissue

Asbestos has had many commercial applications, including its use as a major component in various types of filters. Between 1952 and 1956, crocidolite asbestos was used as a component of filters for cigarettes, reportedly greatly reducing tars and nicotine from mainstream smoke. This case report quantifies asbestos burden in lung and lymph node tissue in a 67-yr-old woman who succumbed to mesothelioma. Her only historically documented exposure to asbestos was from smoking crocidolite asbestos-containing filtered cigarettes between 1952 and 1956. Tissue digestion analysis by analytical transmission electron microscopy (ATEM) identified crocidolite fibers in lungs and thoracic lymph nodes. Combined ATEM data of lung and lymph node tissue clarified the patient's exposure to asbestos and particularly to crocidolite asbestos and thus to the presence of an entity recognized as the causal agent for mesothelioma.

Quantitative detection of asbestos fiber in gravelly sand using elastic body-exposure method

Chrysotile or crocidolite colloidal solution containing donor plasmid DNA and Escherichia coli cells was subjected to elastic body friction. These acicular clay minerals mediated E. coli antibiotic resistance plasmid transformation. Other clay minerals had no effect on E. coli transformation. The number of E. coli transformants was counted after elastic body exposure with various crocidolite concentrations. There was a correlation between the number of E. coli transformants and crocidolite concentration (between 40 and 1,000 ng/ml). A mixture consisting of sea sand and crocidolite was utilized as a model for quantitative detection of asbestos in gravelly sand. With sea sand containing 0.15-15 mg of crocidolite, a correlation between crocidolite concentration and the number of colonies derived from E. coli transformants was observed. This indicates that measurement of asbestos is possible even when the asbestos sample includes gravelly sand. Fluorescence microscopic observation of crocidolite colloidal solution indicated that crocidolite was present as spherical aggregates having diameters of 6-9 microm. Thus, the number of transformants correlated with that of 6-9 microm crocidolite aggregates.

[Assessment of asbestos exposure, mortality study, and health intervention in workers formerly exposed to asbestos in a small factory making drying machines for textile finishing and the paper mill industry in Pistoia, Italy]

BACKGROUND AND OBJECTIVES

Three malignant pleural mesotheliomas occurred among workers of a small factory that manufactured drying machines for the textile and paper mill industries using asbestos cement (crocidolite, amosite and chrysotile) as insulating panels. The Occupational Medicine Unit of the Local Health Unit of Pistoia, Italy, carried out an intervention programme in the plant in order to 1) assess past asbestos exposure via analysis of the fibre content of samples from drying machines, and of dust samples collected in the factory. Information on the characteristics of occupational exposure was also collected; 2) investigate cancer mortality by means of a mortality study of the employees and, 3) carry out a health intervention programme in workers formally exposed to asbestos in the past.

METHODS

Samples from the drying machines and dust samples collected in the factory were analysed using X-ray diffractometric methods. Information on the characteristics of occupational exposure were collected by interviewing plant workers. Two-hundred and fifty employees who had worked in the factory between 1962 and 2000 were included in the mortality study. Follow-up was performed from 1962 to 2002. Health intervention in workers exposed to asbestos in the past involved general practitioners and occupational physicians (first level medical examinations); pneumologists and radiologists (second level medical examinations) of the local health unit.

RESULTS

Asbestos fibres were found both in samples from drying machines and in dust samples collected in the factory. Interviews with workers showed that asbestos exposure varied considerably. The SMR for mesothelioma and lung cancer in 234 male workers were 37.0 (95%CI: 4.47-130.0), and 1.29 (95%CI: 0.26-3.78), respectively, based on mortality rates for Tuscany region. Sixty-two workers underwent first level medical examinations; 57 second level examinations. Chronic obstructive lung disease was found in 3 workers; restrictive lung disease was found in 3 employees, one of whom had pleural plaques.

CONCLUSIONS

Further investigation is needed in order to identify unknown asbestos exposures in small metal engineering factories.

Quantitative analysis of asbestos burden in women with mesothelioma

BACKGROUND

Lung tissue from 15 women who died from mesothelioma was evaluated for tissue burden of ferruginous bodies and uncoated asbestos fibers. The group contained individuals who had occupational exposure to asbestos and others had family members whose work history included vocations where contact with asbestos containing materials occurred.

METHODS

Tissue samples from tumor free lung were digested and filtered and then investigated for ferruginous bodies by light microscopy and asbestos and non-asbestos fibers by analytical transmission electron microscopy (ATEM). Size and type of fibers were also analyzed.

RESULTS

Asbestos bodies were found in 13 of the 15 samples and asbestos fibers were found in all cases. The most commonly found uncoated asbestos fiber in these individuals was amosite whereas tremolite was the second most commonly found form. The asbestos fiber burden in these females was often of mixed types.

CONCLUSIONS

The asbestos body and fiber burden in these cases show variation in tissue burden. Some cases in this study had appreciable burden, which was attributed to secondhand exposure from occupationally exposed family members. Mesothelioma can occur also in individuals with comparatively low tissue burdens of asbestos.

Lung mineral fibers of former miners and millers from Thetford-Mines and asbestos regions: a comparative study of fiber concentration and dimension

Fiber dimension and concentration may vary substantially between two necropsy populations of former chrysotile miners and millers of Thetford-Mines and Asbestos regions. This possibility could explain, at least in part, the higher incidence of respiratory diseases among workers from Thetford-Mines than among workers from the Asbestos region. The authors used a transmission electron microscope, equipped with an x-ray energy-dispersive spectrometer, to analyze lung mineral fibers of 86 subjects from the two mining regions and to classify fiber sizes into three categories. The most consistent difference was the higher concentration of tremolite in lung tissues of workers from Thetford-Mines, compared with workers from the Asbestos region. Amosite and crocidolite were also detected in lung tissues of several workers from the Asbestos region. No consistent and biologically important difference was found for fiber dimension; therefore, fiber dimension does not seem to be a factor that accounts for the difference in incidence of respiratory diseases between the two groups. The greater incidence of respiratory diseases among workers of Thetford-Mines can be explained by the fact that they had greater exposure to fibers than did workers at the Asbestos region. Among the mineral fibers studied, retention of tremolite fibers was most apparent.

Using in vitro iron deposition on asbestos to model asbestos bodies formed in human lung

Recent studies have shown that iron is an important factor in the chemical activity of asbestos and may play a key role in its biological effects. The most carcinogenic forms of asbestos, crocidolite and amosite, contain up to 27% iron by weight as part of their crystal structure. These minerals can acquire more iron after being inhaled, thereby forming asbestos bodies. Reported here is a method for depositing iron on asbestos fibers in vitro which produced iron deposits of the same form as observed on asbestos bodies removed from human lungs. Crocidolite and amosite were incubated in either FeCl(2) or FeCl(3) solutions for 2 h. To assess the effect of longer-term binding, crocidolite was incubated in FeCl(2) or FeCl(3) and amosite in FeCl(3) for 14 days. The amount of iron bound by the fibers was determined by measuring the amount remaining in the incubation solution using an iron assay with the chelator ferrozine. After iron loading had been carried out, the fibers were also examined for the presence of an increased amount of surface iron using X-ray photoelectron spectroscopy (XPS). XPS analysis showed an increased amount of surface iron on both Fe(II)- and Fe(III)-loaded crocidolite and only on Fe(III)-loaded amosite. In addition, atomic force microscopy revealed that the topography of amosite, incubated in 1 mM FeCl(3) solutions for 2 h, was very rough compared with that of the untreated fibers, further evidence of Fe(III) accumulation on the fiber surfaces. Analysis of long-term Fe(III)-loaded crocidolite and amosite using X-ray diffraction (XRD) suggested that ferrihydrite, a poorly crystallized hydrous ferric iron oxide, had formed. XRD also showed that ferrihydrite was present in amosite-core asbestos bodies taken from human lung. Auger electron spectroscopy (AES) confirmed that Fe and O were the only constituent elements present on the surface of the asbestos bodies, although H cannot be detected by AES and is presumably also present. Taken together for all samples, the data reported here suggest that Fe(II) binding may result from ion exchange, possibly with Na, on the fiber surfaces, whereas Fe(III) binding forms ferrihydrite on the fibers under the conditions used in this study. Therefore, fibers carefully loaded with Fe(III) in vitro may be a particularly appropriate and useful model for the study of chemical characteristics associated with asbestos bodies and their potential for interactions in a biosystem.

Pulmonary mineral fibers after occupational and environmental exposure to asbestos in the Russian chrysotile industry

BACKGROUND

As an indicator of occupational, domestic, and environmental exposure, the level and type of asbestos fibers were determined from lung tissue samples of workers and residents who resided in the area of the world's largest asbestos mine at Asbest, Russia.

METHODS

Electron microscopy was used to analyze and measure the concentration of asbestos fibers in a series of 47 autopsies at the Asbest Town Hospital. Work histories were obtained from pathology reports and employment records.

RESULTS

In 24 chrysotile miners, millers, and product manufacturers, the pulmonary concentrations of retained fibers (over 1 microm in length) were 0. 8-50.6 million f/g for chrysotile, and < 0.1-1.9 million f/g for amphiboles (tremolite and anthophyllite). The concentrations were lower in 23 persons without any known occupational contact with asbestos; 0.1-14.6 million f/g for chrysotile, and < 0.1-0.7 million f/g for amphiboles. On average, 90% of all inorganic fibers were chrysotile, and 5% tremolite/anthophyllite. No amosite or crocidolite fibers were detected in any of the samples.

CONCLUSIONS

The mean and range of pulmonary chrysotile concentrations were about the same as reported previously from the Canadian mining and milling industry. In the Russian samples, the mean concentration of tremolite fibers were less by at least one order of magnitude. Occupational contact was the most important source of asbestos exposure.

Pulmonary and intraperitoneal inflammation induced by cellulose fibres

The inflammatory effects of respirable cellulose fibres were studied in two short-term animal models: intraperitoneal injection in mice, and inhalation in rats. The mouse peritoneal cavity is particularly sensitive to fibrous compared to non-fibrous particles. Both cellulose fibres and the positive control fibre, crocidolite asbestos, were administered in doses ranging from 10(4) to 10(8) fibres and caused marked, dose-dependent recruitment of inflammatory cells to the mouse peritoneal cavity, which was highest 1 day following injection. Crocidolite was much more active than cellulose, despite the mass dose of cellulose being 66 times greater for an equivalent number of fibres. Crocidolite at the higher doses caused inflammation to persist through 7 days. For the inhalation study, rats were exposed daily, 5 days per week, to aerosols of cellulose dust for ca. 3 weeks at a concentration of 1000 fibres ml(-1). Inhalation exposure induced an early inflammatory response in rat lungs, as determined by bronchoalveolar lavage, which peaked at 1 day following the start of inhalation and thereafter declined, despite a further 13 days of exposure over a period of 18 calendar days. In vitro production of the pro-inflammatory cytokine tumour necrosis factor alpha (TNF-alpha) by lavaged alveolar macrophages was markedly depressed by the end of the exposure period in cellulose-exposed animals, compared to sham-exposed controls, and this effect was still present in rats that had been allowed to recover for 28 days beyond the end of exposure. We conclude that the cellulose material studied is less inflammogenic than crocidolite and that the extent of the inflammatory response within the lung appears to reduce with continued exposure over a 14-day period.

Risk assessment of lung cancer and mesothelioma in people living near asbestos-related factories in Taiwan

Estimates from environmental risk assessments are criticized by professionals who indicate that inaccuracies occur in exposure assessment, model selection, and determination of the population at risk. In the current study, we tackled the aforementioned issues and estimated the risks of lung cancer and mesothelioma caused by airborne asbestos among individuals who lived near asbestos factories in Taiwan. We conducted 8-h full-period samplings upwind and downwind from each factory, and we used transmission-electronic microscopy (10,000x) and phase-contrast microscopy to determine asbestos concentrations in and around each factory. We estimated the numbers of residents who lived in concentric circles of 200-m, 400-m, and 600-m diameters around each factory. A dose-response model for asbestos-induced lung cancer was adopted from a summary of seven epidemiological studies. The asbestos-mesothelioma models were patterned after the first-exposure-effect models developed by Peto and Finkelstein. The data obtained from phase-contrast microscopy significantly overestimated the risk, compared with transmission-electronic microscopy. The estimates we calculated from adopting the arithmetic mean were approximately 2-fold higher than those we calculated with the geometric mean. There were relatively low concentrations of asbestos in the study areas, thus causing an absence of a significant difference in risk estimates between different models for mesothelioma. Among the more than 20,000 residents who lived near 41 asbestos factories in Taiwan, we found that the numbers of expected excess deaths from lung cancer and mesothelioma were 5 and less than 1, respectively. We concluded that in future risk assessments for ambient asbestos exposure, investigators should adopt transmission-electronic microscopy and the geometric mean estimate. Moreover, Taiwan should enhance asbestos-control programs to assure the safety of residents who live near asbestos factories.

[Sedimentation method for measuring dispersion of fibers from asbestos cement roofs]

In order to define the need for removal versus conservative interventions regarding asbestos-cement roofs and the possible priorities, visual judgement of the state of deterioration or assessments based on the weight of the superficial friable material that can be removed with adhesives are not sufficient. Since in similar deterioration conditions the dispersion of fibres may vary considerably from case to case, only counting of the dispersed fibres will ensure a correct assessment of the pollution potential of an asbestos-cement weathered surface. The paper describes a simple method for measuring the atmospheric dispersion of fibres based on the well demonstrated fact that primary dispersion from the covering, as from many other sources of asbestos pollution, consists of course bundles that are subject to rapid sedimentation. By means of aluminium boxes containing object-holder slides installed under the edge of the covering for about one month, it is possible, using optical phase-contrast microscopy, to count the fibres that have sedimented and calculate the number of fibres/m2/day. If the method is used with the standardized criteria described, it gives reproducible results, involves low costs and has the advantage of balancing the possible variations in primary dispersion intensity due to changes in the local weather conditions over the relatively long sedimentation sampling period.

A risk assessment for exposure to grunerite asbestos (amosite) in an iron ore mine

The potential for health risks to humans exposed to the asbestos minerals continues to be a public health concern. Although the production and use of the commercial amphibole asbestos minerals-grunerite (amosite) and riebeckite (crocidolite)-have been almost completely eliminated from world commerce, special opportunities for potentially significant exposures remain. Commercially viable deposits of grunerite asbestos are very rare, but it can occur as a gangue mineral in a limited part of a mine otherwise thought asbestos-free. This report describes such a situation, in which a very localized seam of grunerite asbestos was identified in an iron ore mine. The geological occurrence of the seam in the ore body is described, as well as the mineralogical character of the grunerite asbestos. The most relevant epidemiological studies of workers exposed to grunerite asbestos are used to gauge the hazards associated with the inhalation of this fibrous mineral. Both analytical transmission electron microscopy and phase-contrast optical microscopy were used to quantify the fibers present in the air during mining in the area with outcroppings of grunerite asbestos. Analytical transmission electron microscopy and continuous-scan x-ray diffraction were used to determine the type of asbestos fiber present. Knowing the level of the miner's exposures, we carried out a risk assessment by using a model developed for the Environmental Protection Agency.

[First intercalibration test of diffractometric measurements of asbestos in National Italian laboratories]

The Ministry of Health established by law (D.M. 14/5/96) minimum requirements for laboratories intending to perform asbestos analyses, and identified the central facilities that are to coordinate the future quality control programme (based on the kind of techniques used), to which the laboratories must refer in order to continue to operate in the "asbestos" field. Before initiating the quality control programme for the gravimetric technique based on X-ray diffraction measurement, the central facilities decided to carry out a pilot test in a group of sample laboratories in order to assess the current situation in Italy and identify the main problems involved in implementing the programme. In fact, up to the present, no standardized method for the diffractometric measurement of asbestos exists in Italy, so that the various laboratories use different procedures and reference standards. In the pilot test, a group of 15 national laboratories with proven experience performed diffractometric measurements on 3 samples each containing one of the 3 commercial forms of asbestos (chrysotile, crocidolite and amosite). Besides the final result consisting of the percentage by weight compared to the whole sample, information was requested on the measurement procedure and on the reference standards used. The results, although they do not permit definite conclusions to be drawn due to their small number, do provide information that will be of relevance to the organisation of the future quality control programme. Analysis of the data appear to show that neither the measurement procedure used nor the type of asbestos influence the accuracy of the results. The main source of variability and of deviation from the true values seemed instead to depend on the type of standards used and on compatibility, in terms of particle size and comminution technique, between these standards and the samples analyzed.

Induction of manganese superoxide dismutase gene expression in bronchoepithelial cells after rockwool exposure

Superoxide dismutases play an important protective role in the lung defense against the pro-oxidative effect of fibrous dusts (e.g. crocidolite fibers). Particularly crocidolite, but also other asbestos fibers, are known to induce cellular antioxidant defense. Although rockwool, a man-made fiber made from rock, is used widely for insulation purposes, its effects on the superoxide dismutases in bronchoepithelial cells have not been investigated. Thus, the purpose of this study was to determine whether human bronchoepithelial cells (BEAS 2B) respond to rockwool fibers (115-4 experimental rockwool fiber) by induction of MnSOD mRNA and an increase of MnSOD activity levels. The results were compared with BEAS 2B cells exposed to silica (alpha-quartz: DQ12; SiO2) and UICC (Union Internationale Contre le Cancer) crocidolite (concentrations of all dusts: 0, 2, 5, 10, 25, 50 micrograms/cm2 = 0, 2.4, 6, 12, 30, 60 micrograms/ml; 24-h exposure) as control fibers. Scanning electron microscopy confirmed close dust cell contact under all experimental settings. Very low MnSOD mRNA baseline levels rose significantly (p < 0.001) in BEAS 2B cells exposed to all three dusts at 2 micrograms/cm2. However, at > 25 micrograms/cm2 MnSOD mRNA levels in silica- and crocidolite- but not in rockwool-exposed cells decreased. Slight (no significance) increases of MnSOD activity were observed which decreased at higher dust (> 5 micrograms/cm2) concentrations. These results suggest that: (1) like crocidolite and silica, rockwool accelerates MnSOD gene expression in bronchoepithelial cells; (2) an increase of MnSOD mRNA levels is not accompanied by MnSOD activity elevation; (3) in contrast to rockwool, high concentrations (> or = 25 micrograms/cm2) of crocidolite and silica reduced MnSOD activity and MnSOD mRNA levels. Because oxidants (H2O2) and crocidolite fibers were shown to reduce SOD activity, lack of active MnSOD protein may be caused by inactivation on a post-translational level. Furthermore, the decline of MnSOD mRNA and MnSOD activity levels coincides with increasing cytotoxicity. In conclusion, rockwool was demonstrated to induce MnSOD gene expression, perhaps because of its pro-oxidative effect in bronchoepithelial cells. In contrast to crocidolite and silica, rockwool fibers are not cytotoxic in this experimental setting.

Asbestos in the lungs of persons exposed in the USA

Tissues obtained at autopsy or biopsy from 81 workers and 2 household persons, were chemically digested. The asbestos fibres recovered were characterized by analytical transmission electron microscopy. Among the 83 causes of death were 33 mesotheliomas, 35 lung cancers, 12 asbestosis and 3 from other cancers. Of the three major commercial asbestos fibre types, amosite was found to be the most prevalent fibre, occurring in approximately 76% of the cases, followed by chrysotile in approximately 60% and crocidolite in approximately 24%. Amosite and chrysotile were observed as the single commercial fibre in approximately 22 and approximately 17% of the cases respectively, whereas crocidolite and tremolite were found as the single fibre type in only approximately 2.5% of the cases. Among the fifteen cases where chrysotile and tremolite occurred together, the amount of chrysotile fibre always exceeded tremolite. However, tremolite was also found in ten additional cases where chrysotile was not detected. Amosite was present in four, amosite plus crocidolite in three, and crocidolite alone in one. Amosite was present in all of the insulation workers' lungs studied and was found in the highest concentration in this exposure category. The highest chrysotile concentration was found among workers in general trades. Although most prevalent in shipyard workers lungs, crocidolite concentration is not statistically different among the exposure groups studied. Although crocidolite was found in twenty cases, amosite accompanied it in eighteen of these. Eleven of the 20 cases were from shipyard workers. Of the 8 mesothelioma cases, 7 also contained amosite. Crocidolite alone only occurred in 1 of the 33 mesothelioma cases analysed. We concluded the following: crocidolite exposure occurred among USA insulators and a large percentage of other workers as well; insulation workers are primarily exposed to amosite; mixed fibre exposures are associated with more mesotheliomas than single fibre exposures; chrysotile only exposure is associated with approximately 12% of the mesothelioma cases studied; and if tremolite exposure is associated with chrysotile exposure, the chrysotile amount exceeds that for the associated tremolite.

A comparison of historic asbestos measurements using a thermal precipitator with the membrane filter-phase contrast microscopy method

The published results and analytical methods used in a 1938 survey of the spinning area in a UK crocidolite asbestos factory have been described and re-interpreted, by comparing the method used with the current membrane filter-phase contrast microscopy (MF-PCM) method for asbestos. By good fortune, most of the original microscope, and thermal precipitator sampling heads similar to those used for sampling were available, as well as guidance from the factory inspector who collected and analysed the original samples. A textile grade crocidolite asbestos was used to generate a fibrous dust cloud whose size distribution was characterised by scanning and transmission electron microscopy and found to give a close approximation to the fibre size distributions monitored in 1938. Samples taken over the same sampling time, but at lower concentrations than originally sampled, showed that the thermal precipitator-oil immersion microscopy (TP-OI) method used at x 2000 magnification, gave higher > 5 microns long fibre counts by a factor of between 3 and 4, than the current MF-PCM method. The differences in performance could be explained by the superior resolving power of the TP-OI method for fine crocidolite fibres. Exposures of airborne asbestos fibres in the spinning area were found to be equivalent to about 20 f ml-1 for personal samples and 10 f ml-1 for area samples, but due to the high levels of ventilation on the day the samples were collected, the average levels throughout the year may have been somewhat higher.

Demonstration of nitric oxide on asbestos and silicon carbide fibers with a new ultraviolet spectrophotometric assay

Nitric oxide (NO) has a number of important functions in biological systems and may play a role in the toxicity of mineral fibers. We investigated whether NO might be present on the surface of mineral fibers and if crocidolite could adsorb NO from NO gas or cigarette smoke. NO was determined with a new gas chromatography-ultraviolet spectrophotometric technique after thermal desorption from the fiber surface and injection in a gas flow cell. NO was found in different amounts on chrysotile B, crocidolite, amosite, and silicon carbide whiskers. There was a strong correlation between the amount of NO and the specific surface area of these fibers (r = 0.98). NO could not be demonstrated on rockwool fibers [man-made vitreous fiber(s) (MMVF)21 and MMVF22] or silicon nitride whiskers. NO on crocidolite, amosite, and silicon carbide whiskers was readily desorbed from the fibers at increased temperature, while NO on chrysotile B seemed to be more firmly adsorbed to the fiber and required a longer period of time to be desorbed. The amount of NO bound to crocidolite increased from 34 micrograms/g fiber to 85 and 474 micrograms/g after exposing the fibers to cigarette smoke and NO gas, respectively. These findings indicate that a) NO adsorbs to fiber surfaces, b) some fibers adsorb more NO than others, c) some fibers adsorb NO more strongly than others, and d) the amounts of NO on fibers may be increased after exposure of the fiber to cigarette smoke or other sources of NO. The biological significance of NO on mineral fibers remains to be investigated.

Talc and amosite/crocidolite preferentially deposited in the lungs of nonoccupational female lung cancer cases in urban areas of Japan

To analyze the correlation between asbestos lung burden and lung cancer, lungs of 211 female cases with and without lung cancer were examined. Phase-contrast microscopic (PCM) counting of ferruginous (FBs) and uncoated fibers (UFs), which had length longer than 5 microns and aspect ratios greater than 3:1, revealed a significantly higher level of FBs plus UFs in urban lung cancer cases than urban non-lung cancer cases (1380.5 vs. 550.3; p < 0.001). No difference was noted between rural lung cancer and non-lung cancer cases. Analytical electron microscopic studies identified various kinds of mineral fibers with an aspect ratio greater than 3:1 in the lung tissue including chrysotile, actinolite/tremolite, amosite/crocidolite, fibrous talc, mica, silica, iron, wollastonite, chlorite, kaoline, and others. The most frequently detected fibers were thin, short chrysotile fibers, most of which could not be found by PCM, followed by relatively thick, long actinolite/tremolite fibers, fibrous talc, and in a smaller number, amosite/crocidolite of intermediate length and width. Amosite/crocidolite and fibrous talc counts in urban lung cancer cases were greater than those of urban non-lung cancer cases, rural lung cancer, and rural non-lung cancer cases; these findings were consistent with PCM analysis. Therefore, it is suggested that fibers detected in PCM observation may be mainly amosite/crocidolite with some parts fibrous talc and that fibrous talc in urban environments may be another candidate for carcinogenic or cocarcinogenic factors of female lung cancer.

The epidemiology of mesothelioma in historical context

Primary malignant mesothelial tumours were recognized by pathologists before asbestiform minerals (chrysotile, crocidolite and amosite) were mined commercially. The discovery, 40 yrs ago, of a causal link with crocidolite and the wide-ranging epidemiological studies which followed are the subject of this review. Early case-control and descriptive surveys, supplemented by cohort studies in insulation workers and chrysotile miners, quickly demonstrated major occupational and geographical differences, with high risk in naval dockyard areas and in the heating trades. In the 1980s, reliable cohort surveys showed that in mining and in the manufacture of asbestos products the mesothelioma risk was much higher when exposure included crocidolite or amosite than chrysotile alone. However, qualitative and quantitative information on exposure was too often inadequate for this evidence to be conclusive. Well-controlled lung fibre analyses have reduced these deficiencies and demonstrated the probable implications of the greater biopersistence of amphibole fibres. Chrysotile for industrial use often contains low concentrations of fibrous tremolite, which may well explain the few cases of mesothelioma associated with this type of asbestos. Progress in this field has been much retarded by controversy, for which the 20 year gap between the availability of reliable estimates of risk for the mining of chrysotile and that for crocidolite or amosite may have been largely responsible.

Short-term crocidolite inhalation studies in mice: validation of an inhalation chamber

A nose-only inhalation chamber is described: this chamber being computer automated has been particularly designed for mice on which it was validated using a crocidolite aerosol at a nominal concentration of 13.6 mg/m3, 6 h/day during 5 days. A month later the mice showed typical inflammatory bronchoalveolar liquids with many polynucleated or activated macrophages and asbestos bodies. The burden of crocidolite fibers ranged from 345,000 to 1,300,000 fibers per mg of dried lung. This study demonstrates that during the month that followed a short-term mice exposure to crocidolite fibers, the inflammatory response was still persistent. These toxicological endpoints validate the nose-only inhalation chamber to be useful for common or transgenic mice.

Asbestos exposure and ovarian fiber burden

Epidemiologic studies suggest increased risk of epithelial ovarian cancer in female asbestos workers and increased risk of malignancy in general in household contacts of asbestos workers. Ovaries were studied from 13 women with household contact with men with documented asbestos exposure and from 17 women undergoing incidental oophorectomy. Ovarian tissue was examined by analytic electron microscopy. Significant asbestos fiber burdens were detected in 9 out of 13 women with household asbestos exposure (69.2%), and in 6 out of 17 women who gave no exposure history (35%). Three exposed women had asbestos counts over 1 million fibers per gram wet weight (23%), but only 1/17 women without an exposure history had a count that high (6%). Although asbestos has been documented as a contaminant of some older cosmetic talc preparations, the chrysotile and crocidolite types of asbestos we detected are more indicative of background and/or occupational exposure. This study demonstrates that asbestos can reach the ovary. Although the number of subjects is small, asbestos appears to be present in ovarian tissue more frequently and in higher amounts in women with a documentable exposure history.

Comparative proliferative and histopathologic changes in rat lungs after inhalation of chrysotile or crocidolite asbestos

Patterns of cell proliferation in lung and pleura and development of histopathologic lesions were studied in lungs from Fischer 344 rats after inhalation exposure to chrysotile or crocidolite asbestos at average airborne concentrations of approximately 8 mg/m3 air for 5 and 20 days and after 20 days of exposure followed by an additional 20 days in room air (20 + 20 days). To assess cell proliferation rats were injected with 5-bromo-2'-deoxyuridine (BrdU) at various time points after initiation of exposure to asbestos. Image analysis was used to quantitate the effects of chrysotile and crocidolite on BrdU labeling indices in the following lung compartments: (1) interstitium, (2) alveolar duct region, (3) bronchial epithelium, and (4) visceral mesothelium. With the exception of mesothelium, which exhibited significant increases in BrdU incorporation in rats exposed to crocidolite at 20 + 20 days, asbestos-induced elevations in BrdU uptake in other compartments were transient with labeling comparable to sham controls at later time points. Histopathology of rat lungs revealed fibrotic lesions of a greater extent and severity at 20 days in rats exposed to crocidolite, but fibrosis occurred in both asbestos-exposed groups after an additional 20 days in clean air (20 + 20). Quantification of fiber burden in rat lung after inhalation of comparable airborne concentrations of either fiber type demonstrated that inhalation of crocidolite asbestos led to a higher fiber retention when compared to chrysotile asbestos. Our results indicate that chrysotile and crocidolite asbestos induce different patterns of cell proliferation in lung and pleural cells. The protracted increases in BrdU labeling of mesothelial cells by crocidolite may reflect increased retention of fibers and/or inherent differences between types of asbestos.

Asbestos bodies in lung tissue following exposure to crocidolite

A series of 206 necropsies in Western Australia (WA) have had routine counts made of asbestos bodies in samples of lung tissue using conventional light microscopy. Thirty-two cases had worked in the asbestos industry at Wittenoom, WA and (log) counts of asbestos bodies in their lung tissue correlated well with estimates of their (log) cumulative airborne exposure to crocidolite fibers (r = 0.60). There was no association between the number of asbestos bodies and time since exposure to asbestos ceased. In subjects without known exposure to asbestos, there was a weak but nonsignificant increase in number of asbestos bodies with increasing age, with 26% of cases having no asbestos bodies present. It is concluded that the relatively simple technique of light microscopy for counting of asbestos bodies in lung tissue provides a reliable indication of the level of past occupational exposure to crocidolite in subjects whose exposure has been only to crocidolite. This could be extremely useful in follow-up studies of cohorts that lack reliable measures of airborne exposure to crocidolite asbestos.

Crocidolite asbestos fibers in smoke from original Kent cigarettes

The original version of the Kent Micronite cigarette filter used crocidolite, a form of asbestos, from 1952 until at least mid-1956. Cigarettes from intact, unopened packs of the brand from this period were examined. One filter contained approximately 10 mg of crocidolite. Crocidolite structures were found in the mainstream smoke from the first two puffs of each cigarette smoked. At the observed rates of asbestos release, a person smoking a pack of these cigarettes each day would take in more than 131 million crocidolite structures longer than 5 microns in 1 year. These observations suggest that people who smoked the original version of this cigarette should be warned of their possible substantial exposure to crocidolite during the 1950s.

Fibers in lung tissues of mesothelioma cases among miners and millers of the township of Asbestos, Quebec

Twenty cases of mesothelioma among miners of the township of Asbestos, Quebec, Canada, have been reported. To further explore the mineral characteristics of various fibrous material, we studied the fibrous inorganic content of postmortem lung tissues of 12 of 20 available cases. In each case, we measured concentrations of chrysotile, amosite, crocidolite, tremolite, talc-anthophyllite, and other fibrous minerals. The average diameter, length, and length-to-diameter ratio of each type of fiber were also calculated. For total fibers > 5 microns, we found > 1,000 asbestos fibers per mg tissue (f/mg) in all cases; tremolite was above 1,000 f/mg in 8 cases, chrysotile in 6 cases, crocidolite in 4 cases, and talc anthophyllite in 5 cases. Among cases with asbestos fibers, the tremolite count was highest in 7 cases, chrysotile in 3 cases, and crocidolite in 2 cases. The geometric mean concentrations of fibers > or = 5 microns were in the following decreasing order: tremolite > crocidolite > chrysotile > other fibers > talc-anthophyllite > amosite. For total fibers < 5 microns, we found > 1,000 fibers per mg tissue (f/mg) in all cases; tremolite was above 1,000 f/mg in 12 cases, chrysotile in 8 cases, crocidolite in 7 cases, and talc-anthophyllite in 6 cases. Tremolite was highest in 8 cases, chrysotile in 2 cases, and crocidolite and amosite in 2 cases. The geometric mean concentrations of fibers < 5 microns were in the following decreasing order: tremolite > other fibers > chrysotile > crocidolite > talc-anthophyllite > amosite. We conclude, on the basis of the lung burden analyses of 12 mesothelioma cases from the Asbestos township of Quebec, that the imported amphibole (crocidolite and amosite) were the dominant fibers retained in the lung tissue in 2/12 cases. In 10/12 cases, fibers from the mine site (chrysotile and tremolite) were found at highest counts; tremolite was clearly the highest in 6, chrysotile in 2, and 2 cases had about the same counts for tremolite and chrysotile. If a relation of fiber burden-causality of mesothelioma is accepted, mesothelioma would be likely caused by amphibole contamination of the plant in 2/12 cases and by the mineral fibers (tremolite and chrysotile) from the mine site in the 10 other cases.

[A case of asbestosis with long survival by artificial ventilation]

We treated a 63-year-old man in whom asbestosis developed after he had sprayed asbestos for 24 years. He was admitted with the chief complaint of dyspnea and was managed for 4 years with artificial ventilation. We believe that he survived for this long because he was free of severe pneumonia and because the lower lung, which is primarily affected by asbestos, was relatively intact so his pulmonary function did not deteriorate rapidly. Pathological findings included plate-like atelectasis in both upper lung fields and marked thickening of the pleura. Lung fibrosis was centrilobular but showed no honeycombing. The lung tissue contained 265 X 10(6) asbestos particles and 910 X 10(6) asbestos fibers per gram (dry weight), and the pleura also had 805 asbestos particles and 3,035 asbestos fibers. Most of these asbestos fibers were 20 microns or longer and were crocidolite.

Relation between lung asbestos fibre burden and exposure indices based on job history

Lung asbestos burden was compared with exposure indices derived from job history interviews in 42 male subjects originating from the Montréal Case-Control Study project, 12 of whom had documented asbestos exposed job histories. Job interview data consisting of a chronological timetable of job histories were translated into detailed exposure indices by an expert group of hygienists and chemists. Total and individual asbestos fibre type concentrations were quantified by transmission electron microscopy with fibre identification by energy dispersive chi ray spectrometry after deparaffinisation of tissue blocks and low temperature plasma ashing. Geometric mean or median asbestos content was higher in subjects with an asbestos exposed job history than those without for retained dose of amosite, total commercial amphiboles, and total asbestos fibre. Except for crocidolite fibre diameter, which was significantly less in the lungs of exposed workers, no consistent differences were found in measurements of fibre dimension for any fibre type. Subgroups of subjects exposed to silica, metals, or smokers and non-smokers without significant occupational exposure showed varying patterns of lung asbestos fibre type deficit compared with the asbestos exposed subgroup. There was an overall trend for higher lung asbestos content proportional to higher exposure indices for asbestos representing concentration, frequency, and reliability. These exposure indices as well as duration of exposure (in years) were independent predictors of total asbestos content in regression analyses when combined in a model with age. Stepwise regression indicated that exposure concentration was the most important variable, explaining 32% of the total variation in total asbestos content. Smoking, whether expressed in ever or never smoked dichotomy or in smoked-years, had no relation to lung asbestos content in this model.

Asbestos and nonasbestos fiber content in lung tissue of Japanese patients with malignant mesothelioma

BACKGROUND

Pulmonary fiber content of both asbestos and nonasbestos types were evaluated in Japanese patients with malignant pleural mesotheliomas.

METHODS

Pulmonary fiber content was analyzed in 16 patients and 16 case-matched control subjects by transmission electron microscopy with energy-dispersive X-ray analysis using a low-temperature ashing procedure.

RESULTS

The geometric mean content of total asbestos was significantly higher in the patients (22.0 x 10(6) fibers/g dry lung) than in the control subjects (2.24 x 10(6) fibers/g dry lung) (P < 0.01). When the asbestos content was analyzed by fiber type, the geometric means were also consistently and significantly higher among the patients compared with the control subjects (P < 0.01). Results were as follows: (1) amosite: patients 3.94 times 10(6) versus control subjects 0.23 x 10(6); (2) crocidolite: patients 3.56 times 10(6) versus control subjects 0.35 times 10(6); (3) total amphiboles: patients 16.0 times 10(6) versus control subjects 0.77 times 10(6); and (4) chrysotile: patients 3.76 times 10(6) versus control subjects 1.01 times 10(6). However, when individual total asbestos content was considered, 7 of the 16 patients (44%) had levels lower than the highest value noted among the control subjects. Pulmonary fiber content of patients and control subjects also revealed the presence of nonasbestos fibers. The geometric mean of nonasbestos fibers was significantly higher in the patients (87.3 x 10(6)) than in control subjects (33.8 x 10(6)) (P < 0.01). The major type of nonasbestos fibers in both groups was aluminum silicates. The mean of ratios of nonasbestos fiber contents to total asbestos contents in the patients and control subjects was 7.0 and 17.3, respectively.

CONCLUSIONS

The results were mainly in agreement with the findings of earlier investigations, but fiber content of both chrysotile and nonasbestos fiber as well as those of amphibole asbestos were significantly higher in the patients than in the control subjects.

Air samples from a building with asbestos-containing material: asbestos content and in vitro toxicity on rat pleural mesothelial cells

Buildings equipped with asbestos-containing material may release asbestos fibers, the toxicity of which remains uncertain because of the generally low dose level. In 22 air samples collected in a building the asbestos level ranged between 0 and 0.027 f/ml. Both chrysotile and amphiboles were found. There was no association between in vitro cytotoxicity on rat pleural mesothelial cells and asbestos content, but there was a significant correlation with the total amount of particulate material. Four samples exhibited an enhancement of DNA synthesis in cells arrested in G1 with 5 mM hydroxyurea. This is more likely related to the particulate matter associated with asbestos fibers.