Comparison of measures of exposure to asbestos in former crocidolite workers from Wittenoom Gorge,W. Australia

Determinations of exposure-response relationships between crocidolite and the major asbestos-related diseases in the Wittenoom cohort have previously depended on the validity of estimates of airborne exposure to asbestos. This work aims to validate the airborne exposure measurements by obtaining measurements of the concentrations of uncoated crocidolite fibers and asbestos bodies retained in the lungs of individual workers, and to estimate the half-life of crocidolite fibers in the lungs. Samples of lung tissue, excluding tumor, of all former Wittenoom workers known to have died in Western Australia (WA) were sought from teaching hospitals, pathology departments, and the Coroner's pathologist. The lung specimens were processed using Pooley's method with TEM for counts of fibers of all types and using Smith and Naylor's method with conventional light microscopy for asbestos bodies (AB). Multiple linear regression was utilized to examine the associations between crocidolite concentrations in the lung and duration of employment at Wittenoom, time since last employed at Wittenoom, nature of job, estimated average fiber concentration at the worksite, and estimated cumulative crocidolite exposure (CCE) in fiber-years/ml for each subject. Lung tissue from 90 cases was processed and there was good agreement between counts of crocidolite fibers, asbestos bodies, and CCE. Correlations were 0.77 for AB and fibers, 0.54 for AB and CCE, and 0.58 for CCE and fibers, after log transformation. The half-life of crocidolite fibers in the lung was estimated at 92 months (95% CI 55–277 months). Previous estimates of airborne exposure to Wittenoom crocidolite have been reasonably reliable. The relatively simple technique of light microscopy for counting ABs in lung tissue also provides a useful and reliable indication of the level of past occupational exposure to crocidolite in subjects whose exposure has been only to crocidolite. The half-life of crocidolite fibers in the lungs of former Wittenoom workers is about 7–8 years. © 1996 Wiley-Liss, Inc.     

Pleural mesothelioma and exposure to asbestos: evaluation from work histories and analysis of asbestos bodies in bronchoalveolar lavage fluid or lung tissue in 131 patients.

Exposure to asbestos was evaluated in 131 patients with pleural malignant mesothelioma in the Paris area between 1986 and 1992 using data from a detailed specific questionnaire and light microscopy analysis of the retention of asbestos bodies in bronchoalveolar lavage fluid or lung tissue. Probable or definite exposure to significant levels of asbestos dust was identified in only 48 (36.6%) subjects, and significant asbestos body counts (above 1 asbestos body/ml in bronchoalveolar lavage fluid or 1000 asbestos bodies/g of dry lung tissue) were found in only 45 (34.3%) subjects. Overall 50 subjects had experienced exposure to only low levels of asbestos or no exposure at all and showed no significant retention of asbestos bodies in the biological sample analysed. Previous studies have shown that light microscopy may be useful in the identification of subjects with previous exposure to asbestos. In this study, apart from cases with obvious exposure to asbestos, a large group of subjects seemed to have a history of exposure or lung retention of asbestos bodies suggestive of very low levels of cumulative exposure, similar to those described in the general population.     

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.     

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.     

A rapid and simple method of extracting asbestos bodies from lung tissue by cytocentrifugation

During analyses of alkali digested lung tissue for asbestos bodies, we observed that the number of asbestos bodies in the discarded waste frequently exceeded the number in the filtered residue, the number reported in the standard diagnostic method. This observation led to the exploration of alternative techniques that would optimize the recovery of asbestos bodies. We describe a new, simple, and rapid method for extracting asbestos bodies from digested lung tissue using a cytocentrifuge, in which the waste extraction and filtration steps are eliminated. Samples of digested lung tissue are ready for light microscopy after 10 minutes of cytocentrifugation directly onto a glass slide. The standard method was compared with the cytocentrifuge technique using lung tissue from four asbestos-exposed workers and four controls with no known history of exposure. The number of asbestos bodies extracted by the centrifuge method was, on average, seven times higher than the number found with the standard method. A detailed quantitative study was made of the case that had the most asbestos bodies (comparison of the number of asbestos bodies counted in both "residue" and "waste", applying the filtration and cytocentrifuge methods). The number of asbestos bodies found in the discarded waste significantly exceeded the number in the "reportable" filtered residue.     

Asbestos fibres in bronchoalveolar lavage fluid from asbestos workers: examination by electron microscopy

The uncoated and coated fibre load in bronchoalveolar lavage (BAL) fluid was assessed using light microscopy, scanning electron microscopy, and x ray microanalysis in 15 subjects with previous, unprotected exposure to asbestos, including three with clinical and radiological evidence of asbestosis, and in 13 urban dwelling control subjects with no known occupational exposure to asbestos. The mean ferruginous body count per ml BAL fluid in asbestos exposed subjects as determined by light microscopy was 52 (range 0-333). No ferruginous bodies were detected in control subjects. The mean fibre count per ml BAL fluid in asbestos exposed subjects as determined by electron microscopy was 793 (133-3700), significantly greater than 239 (44-544) in controls (p less than 0.05). Electron microscopic counts correlated with duration of previous exposure to asbestos (r = 0.47, p less than 0.05) and with percentage neutrophil counts (r = 0.53, p less than 0.025). There was no relation between electron microscopic fibre counts and light microscopic ferruginous body counts. In 11 asbestos exposed cases x ray microanalysis confirmed the presence of asbestos and in six the asbestos fibre type was clearly identified. Of five subjects showing no asbestos bodies by light microscopy, all showed fibres by electron microscopy, and in three cases the presence of asbestos was confirmed by microanalysis. Among control subjects, fibres were either large organic fibres or smaller particles which microanalysis showed were not asbestos. In only one control case were a few fibres identified which were confirmed as asbestos fibres on microanalysis. Electron microscopic examination of BAL fluid may confirm past exposure to asbestos and probably gives a crude quantitative estimate of asbestos load.     

Asbestos fibres in bronchoalveolar lavage fluid from asbestos workers: examination by electron microscopy.

The uncoated and coated fibre load in bronchoalveolar lavage (BAL) fluid was assessed using light microscopy, scanning electron microscopy, and x ray microanalysis in 15 subjects with previous, unprotected exposure to asbestos, including three with clinical and radiological evidence of asbestosis, and in 13 urban dwelling control subjects with no known occupational exposure to asbestos. The mean ferruginous body count per ml BAL fluid in asbestos exposed subjects as determined by light microscopy was 52 (range 0-333). No ferruginous bodies were detected in control subjects. The mean fibre count per ml BAL fluid in asbestos exposed subjects as determined by electron microscopy was 793 (133-3700), significantly greater than 239 (44-544) in controls (p less than 0.05). Electron microscopic counts correlated with duration of previous exposure to asbestos (r = 0.47, p less than 0.05) and with percentage neutrophil counts (r = 0.53, p less than 0.025). There was no relation between electron microscopic fibre counts and light microscopic ferruginous body counts. In 11 asbestos exposed cases x ray microanalysis confirmed the presence of asbestos and in six the asbestos fibre type was clearly identified. Of five subjects showing no asbestos bodies by light microscopy, all showed fibres by electron microscopy, and in three cases the presence of asbestos was confirmed by microanalysis. Among control subjects, fibres were either large organic fibres or smaller particles which microanalysis showed were not asbestos. In only one control case were a few fibres identified which were confirmed as asbestos fibres on microanalysis. Electron microscopic examination of BAL fluid may confirm past exposure to asbestos and probably gives a crude quantitative estimate of asbestos load.     

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.     

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.     

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.     

Asbestos fiber analysis in 27 malignant mesothelioma cases.

The asbestos body counts per 5 gm wet lung tissue in 27 (23 pleural and 4 peritoneal) malignant mesothelioma cases derived from 19 autopsy and 8 surgical cases were, according to our own criteria, low level exposure in 13 cases (48.2%), moderate level exposure in 2 cases (7.4%), and high level exposure in 12 cases (44.4%). In our previous study on 235 consecutive autopsy cases, the low level exposure was considered to be environmental, the moderate level was secondary or blue collar, and the high level was occupational. In the present study, about half of the cases examined (44.4%, high level exposure) are closely related to some occupational asbestos exposure and the other half (48.2%) to environmental exposure. The type and size of asbestos fibers from the 12 cases of high level exposure were analyzed and the characteristics were compared with those of cases of low level exposure without lung cancer or mesothelioma. Most fibers analyzed (98%) were longer than 5 microns and thicker than 0.10 micron by our counting rules. In the control group, predominant fibers were tremolite or actinolite. In all the 11 pleural mesothelioma cases, the content of amosite fibers was significantly higher than in the controls. In one case of peritoneal mesothelioma, incipient asbestosis was found and the predominant fibers were crocidolite. It is suggested that the presence of amosite and crocidolite is linked to mesothelioma. The mean lengths of amosite and crocidolite, as detected by our resolution capabilities, were 36.0 and 20.9 microns, and the mean diameters were 0.51 and 0.27 micron, respectively. Both amosite and crocidolite fibers had high aspect ratios (94.2 and 115.4).     

Malignant mesothelioma and duration of asbestos exposure: Correlation with tissue mineral fibre content

Among 441 cases of malignant mesothelioma in the author's files, there were 324 for whom reliable information was available regarding the duration of exposure to asbestos. Included were 298 pleural and 26 peritoneal mesotheliomas. The mean duration of exposure to asbestos was 23 ± 14 years for all cases, and was not different for the pleural and peritoneal groups. Lung tissue was available for analysis of mineral fibre content in 94 cases. Linear regression analysis showed a significant correlation between duration of exposure and asbestos bodies per gramme of wet lung as determined by light microscopy, and between duration of exposure and total uncoated fibres (5 μm or greater in length) as well as commercial amphibole fibres per gramme as determined by scanning electron microscopy (P < 0.05). Individuals with direct exposures had on average higher asbestos contents than patients with indirect exposures. Furthermore, for each duration of exposure, shipyard workers had on average higher asbestos contents than non-shipyard workers (P < 0.05). Mesotheliomas are associated with a wide range of durations of exposure to asbestos and pulmonary asbestos burdens, and there is a rough correlation between duration of exposure and pulmonary commercial amphibole content.     

Clinical study of asbestos-related lung cancer

We analyzed the characteristics of 120 patients of primary lung cancer supposed to be induced by exposure to asbestos. Most of 120 patients were male and the age ranged from 47 to 87 years with a median of 70 years. No particular tendency was observed in the histological types of the lung cancer in 120 patients. Forty of the 120 patients were heavy smokers. When the occupational history was analyzed, most of the patients had been exposed to asbestos in former Japanese naval shipyard, commercial shipyards, construction industry and ironworks. The term of asbestos exposure was 2 to 60 years with a median 27 years. Lung cancers appeared after 15 to 69 years with a median 43 years from the initial exposure to asbestos. Lung cancer was accompanied by asbestosis in 35 patients and by pleural plaques in 77. Twenty-two patients had both asbestosis and pleural plaques. The number of asbestos bodies per 5 g wet lung tissue for 72 patients whose lung tissues obtained from autopsy or surgery was more than 150 bodies which meant the number of occupational asbestos exposure. As for the kinds of asbestos fibers of 32 patients, 14 patients exposed to crocidolite, 10 patients to amosite and 8 patients to chrysotile.     

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. © 1996 Wiley-Liss, Inc.     

Asbestos content of lung tissue in asbestos associated diseases: a study of 110 cases

Diseases associated with asbestos exposure include asbestosis, malignant mesothelioma, carcinoma of the lung, and parietal pleural plaques. In this study the asbestos content of lung tissue was examined in groups of cases representing each of these diseases and in several cases with non-occupational idiopathic pulmonary fibrosis. Asbestos bodies (AB), which are the hallmark of asbestos exposure, were present in the lungs of virtually everyone in the general population and present at increased levels in individuals with asbestos associated diseases. The highest numbers of AB occurred in individuals with asbestosis, all of whom had levels greater than or equal to 2000 ABs/g wet lung tissue. Every case with a content of 100,000 ABs/g or higher had asbestosis. Intermediate levels occurred in individuals with malignant mesothelioma and the lowest levels in patients with parietal pleural plaques. There was no overlap between the asbestos content of lung tissue from patients with asbestosis and those with idiopathic pulmonary fibrosis. Lung cancer was present in half the patients with asbestosis, and the distribution of histological patterns did not differ from that in patients with lung cancer without asbestosis. The asbestos body content in patients with lung cancer was highly variable. Control cases had values within our previously established normal range (0-20 ABs/g). There was a significant correlation (p less than 0.001) between AB counted by light microscope and AB and uncoated fibres counted by scanning electron microscopy. The previous observation that the vast majority of asbestos bodies isolated from human tissues have an amphibole core was confirmed.     

Analysis of asbestos bodies in BAL from subjects with particular exposures

Four patients with asbestos-related diseases and with unusual exposures underwent bronchoalveolar lavage (BAL) for mineralogical analysis. Asbestos bodies (AB) were counted by light microscopy and analyzed by transmission electron microscopy and X-ray energy spectrometry. AB's were found in all cases, after a mean delay from the end of exposure of 27.7 years. Analysis of the core fibers indicated the type of alveolar asbestos burden and was compared with the previous exposures: —Pleural plaques due to household exposure to amosite and crocidolite. —Pleural plaques due to occult occupational exposure to crocidolite in a coal miner. —Asbestosis due to environmental exposure to tremolite in Turkey. —Asbestosis, pleural plaques, and peritoneal mesothelioma due to a short, intense exposure to crocidolite. AB counting in BAL and identification of the central fibers by analytical electron microscopy is a useful, non-invasive and reliable method to evaluate the alveolar retention of bio-persistent fibers and to relate them to specific exposures. Am. J. Ind. Med. 31:699–704, 1997. © 1997 Wiley-Liss, Inc.     

Asbestos content of lung tissue in asbestos associated diseases: a study of 110 cases.

Diseases associated with asbestos exposure include asbestosis, malignant mesothelioma, carcinoma of the lung, and parietal pleural plaques. In this study the asbestos content of lung tissue was examined in groups of cases representing each of these diseases and in several cases with non-occupational idiopathic pulmonary fibrosis. Asbestos bodies (AB), which are the hallmark of asbestos exposure, were present in the lungs of virtually everyone in the general population and present at increased levels in individuals with asbestos associated diseases. The highest numbers of AB occurred in individuals with asbestosis, all of whom had levels greater than or equal to 2000 ABs/g wet lung tissue. Every case with a content of 100,000 ABs/g or higher had asbestosis. Intermediate levels occurred in individuals with malignant mesothelioma and the lowest levels in patients with parietal pleural plaques. There was no overlap between the asbestos content of lung tissue from patients with asbestosis and those with idiopathic pulmonary fibrosis. Lung cancer was present in half the patients with asbestosis, and the distribution of histological patterns did not differ from that in patients with lung cancer without asbestosis. The asbestos body content in patients with lung cancer was highly variable. Control cases had values within our previously established normal range (0-20 ABs/g). There was a significant correlation (p less than 0.001) between AB counted by light microscope and AB and uncoated fibres counted by scanning electron microscopy. The previous observation that the vast majority of asbestos bodies isolated from human tissues have an amphibole core was confirmed.     

Mortality of workers manufacturing friction materials using asbestos

A mortality (1942-80) study was carried out on 13460 workers of a factory producing friction materials. The only type of asbestos used was chrysotile, except during two well-defined periods before 1945 when crocidolite was used, and over 99% of the population was traced. Compared with national death rates there were no detectable excesses of deaths due to lung cancer, gastrointestinal cancer, or other cancers; 11 deaths were due to pleural mesothelioma. A case-control study was carried out on deaths due to mesothelioma; this showed that eight workers had been exposed to crocidolite and another was possibly exposed intermittently to crocidolite. The other two had been employed for most of their working lives outside the factory, and their mesotheliomas could not be definitely attributed to exposure to chrysotile. Limiting the study to cases and controls who had exposure to 5 fibres/ml of chrysotile asbestos it was found that five of the six cases compared with two of the 10 controls had also been exposed to crocidolite. The probability (1:36) of this occurring were there no association with crocidolite is most unlikely. A case-control study was also carried out on deaths due to lung cancer and gastrointestinal cancer to investigate the dose-response relationships between these tumours and exposure to chrysotile. Measured and estimated fibre concentrations were available for the different jobs over the period of the study. No dose-response relationships were observed, but the exposures were low with only 5% of men accumulating 100 fibre-years/ml. The experience at this factory over a 40-year period showed that chrysotile asbestos was processed with no detectable excess mortality.     

Mortality of workers manufacturing friction materials using asbestos.

A mortality (1942-80) study was carried out on 13460 workers of a factory producing friction materials. The only type of asbestos used was chrysotile, except during two well-defined periods before 1945 when crocidolite was used, and over 99% of the population was traced. Compared with national death rates there were no detectable excesses of deaths due to lung cancer, gastrointestinal cancer, or other cancers; 11 deaths were due to pleural mesothelioma. A case-control study was carried out on deaths due to mesothelioma; this showed that eight workers had been exposed to crocidolite and another was possibly exposed intermittently to crocidolite. The other two had been employed for most of their working lives outside the factory, and their mesotheliomas could not be definitely attributed to exposure to chrysotile. Limiting the study to cases and controls who had exposure to 5 fibres/ml of chrysotile asbestos it was found that five of the six cases compared with two of the 10 controls had also been exposed to crocidolite. The probability (1:36) of this occurring were there no association with crocidolite is most unlikely. A case-control study was also carried out on deaths due to lung cancer and gastrointestinal cancer to investigate the dose-response relationships between these tumours and exposure to chrysotile. Measured and estimated fibre concentrations were available for the different jobs over the period of the study. No dose-response relationships were observed, but the exposures were low with only 5% of men accumulating 100 fibre-years/ml. The experience at this factory over a 40-year period showed that chrysotile asbestos was processed with no detectable excess mortality.     

Carcinoma of the colon in asbestos-exposed workers: analysis of asbestos content in colon tissue.

Epidemiological studies have indicated an increased incidence of carcinoma of the colon in asbestos workers. The present study evaluated the colon tissue asbestos burden, by light and electron microscopic analytic techniques, in patients with a history of occupational asbestos exposure and colon cancer. Asbestos fibers and/or asbestos bodies were present in colon tissue from 14 of 44 (31.8%) asbestos workers with colon carcinoma (range 142,199 to 15,231, 543 fibers/g/wet weight, mean 2,517,823). Chrysotile was identified in 9 patients and amosite in 3 patients. Both amosite and chrysotile were found in the colonic wall in one individual. Other forms of asbestos (e.g., crocidolite, tremolite, or anthophyllite) were not found. Asbestos fibers and asbestos bodies were not found in colon tissue from 20 control patients (colon carcinoma and no asbestos exposure). Asbestos fibers frequently enter and reside in the wall of the colon and are often intimately associated with tumor tissue at the site of colon carcinoma in workers with asbestos exposure and colon carcinoma.