Unusually High Incidence of Malignant Pleural Mesothelioma in a Town of Eastern Sicily: An Epidemiological and Environmental Study

In a recent epidemiological study, researchers investigated mortality from malignant pleural neoplasms in Italy, and they detected some geographic clusters of cases of this disease. We found a town located in a volcanic area of eastern Sicily to be of special interest. The residents, some of whom were diagnosed with pleural mesothelioma, had never had any relevant exposure to asbestos during their professional lives. The results of an environmental survey suggested that a possible cause of asbestos exposure was the stone quarries near the town. The products of the quarries contain fibrous amphiboles, which are used widely in the local building industry. These fibrous amphiboles were identified as intermediate phases between tremolite and actinolite. Samples were collected from buildings in the town, and concentrations of amphibole fibers were evaluated. Fibrous phases were detected in 71 % of the samples, and fiber concentrations ranged from a few thousand to more than 4 × 10⁴ fibers/mg of material. In addition, we conducted a study on the mineral fiber lung burden in a pleural mesothelioma case. Many mineral fibers that were classified as the same tremolite-actinolite fibrous amphibole found in the quarries and in the building materials were detected in the lung tissue. The results suggest that the inhabitants of the town we studied had been exposed for several decades to asbestos fibers that were present in the material extracted from the local stone quarries. The material was subsequently used in the building industry, and this has caused an increased risk of pleural mesothelioma in the area.     

Pleural mesothelioma cases in Biancavilla are related to a new fluoro-edenite fibrous amphibole

A cluster of deaths from pleural mesothelioma was previously reported for Biancavilla, Italy, a city in eastern Sicily. An environmental survey suggested that the stone quarries located southeast of the city might be a source of asbestos exposure. The materials extracted from the quarries, used widely in the local building industry, contain large quantities of a fibrous amphibole that was initially referred to as an anomalous intermediate phase of sodium- and fluorine-rich tremolite-actinolite. A subsequent crystal chemistry investigation identified the mineral as fluoro-edenite, a new end-member of the edenite --> fluoro-edenite series. The material is very similar in morphology and composition to the minerals of the tremolite-actinolite series. To the authors' knowledge, fluoro-edenite becomes the 3rd mineral fiber (along with erionite and winchite), not yet classified as asbestos, with a demonstrable mesotheliomatogenous action in humans.     

Electron microscopy analysis of mineral fibers in human lung tissue.

In the present study, lung samples from 126 autopsied cases were examined to determine the content of mineral fibers using analytical transmission electron microscopy (ATEM). The cases were divided into four groups (22 lungs of persons exposed to ambient environmental pollution, 32 cases of mesothelioma, 38 cases of primary lung cancer, and 34 asbestosis cases, 13 of these with additional pleural plaques). Fibers were counted, measured, and mineralogically identified using a combination of X-ray microanalysis and electron diffraction of the non-oriented fiber. Concentration of fibrous particles (defined as particles above 1 micron in length with roughly parallel long sides and an aspect ratio of 5:1 and greater) was calculated as fibers 10(6)/g dry lung weight. The concentration of chrysotile was found to be similar throughout the groups except for two cases in the asbestosis group with comparably high numbers of chrysotile. However, a remarkable difference for amphiboles could be observed between the groups. Asbestos bodies were mostly found in the asbestosis group. There was a rather good correlation between numbers of amphibole fibers and asbestos bodies, with an average ratio of 10:1. For comparison purposes between occupationally exposed/non-exposed individuals, a transition was found in the concentration range of 3-10(7) asbestos fibers/g dried lung weight.     

Asbestos tissue burden study on human malignant mesothelioma

Asbestos fibers in the lung and mesothelial tissues (mesotheliomatous tissue and hyaline plaque) taken from 151 human malignant mesothelioma cases were identified and characterized by high resolution analytical electron microscopy. Asbestos fibers were present in almost all of the lung tissue as well as in the mesothelial tissue. The most common asbestos types seen in the lung were an admixture of chrysotile with amphiboles followed by amphiboles alone and chrysotile alone. The majority of asbestos types seen in the mesothelial tissues were chrysotile alone, followed by chrysotile plus amphibole and amphibole alone. A disproportion of asbestos types between the lung and mesothelial tissues was frequently observed. The most common pattern of the disproportion was chrysotile plus amphibole(s) in the lung and chrysotile only in the mesothelial tissues, followed by amphibole(s) in the lung and chrysotile only in the mesothelial tissues. Such a disproportion was considered to have been caused by chrysotile fiber's strong capacity to translocate from the lung to mesothelial tissues. The number of asbestos fibers in the lung was 456.4 x 10(6) fibers/dry gram in maximum, 0.08 x 106 fibers/dry gram in minimum and 105 x 10(6) fibers/dry gram on average; in the mesothelial tissues it was 240.0 x 106 fibers/dry gram in maximum, 0.03 x 106 fibers/dry gram in minimum and 49.84 x 106 fibers/dry gram on average. These numbers were greater than those seen in the general population. The majority of asbestos fibers detected in the lung and mesothelial tissues were shorter than 5 microm in length. Asbestos fibers fit to Stanton's hypothetical dimensions (> or =8.0 microm in length and < or =0.25 microm in diameter) were only 4.0%, since the majority of these fibers were shorter (<8 microm) and thinner (<0.25 microm) fibers. We concluded that such short, thin asbestos fibers should not be excluded from those contributing to the induction of human malignant mesothelioma. The present study supports that chrysotile asbestos can induce human malignant mesothelioma, since, in some of the mesothelioma cases, asbestos fibers detected in both the lung and mesothelial tissues, or lung tissue alone or mesothelial tissues alone were exclusively chrysotile fibers.     

The in vitro release of hydroxyl radicals from dust containing fluoro-edenite fibers identified in the volcanic rocks of Biancavilla (eastern Sicily)

BACKGROUND: Epidemiological studies revealed an unusually high incidence of malignant pleural mesothelioma in Biancavilla, a town in eastern Sicily located in a volcanic area. In the absence of occupational risk factors connected with asbestos inhalation, a nearby stone quarry, which has long been providing most of the local building materials (e.g. plaster), was suspected to be the source of mineral fibres. These fibres had never been studied before and were identified as fluoro-edenite. OBJECTIVE: To investigate the ability of the fluoro-edenite fibres present in mineral dusts and house plaster to release hydroxyl radicals in vitro. METHODS: After fibre characterisation and the determination of particulate specific surface, the ability of quarry rock dust and house plaster dust to generate hydroxyl radicals was measured in vitro using the deoxyribose degradation assay. Treatment with 1,3-dimethyl-2-thiourea (DMTU), a hydroxyl radical scavenger, or deferoxamine (DFX), an iron chelator, was performed to confirm hydroxyl radical production and study the role of iron. Crocidolite (UICC) was used as positive control. RESULTS: The rocks were found to contain fibrous amphiboles, identified as fluoro-edenite, which are chemically similar to tremolite. All samples generated hydroxyl radicals, with rocks yielding consistently higher values than plaster. Treatment of the dusts with DMTU or DFX significantly reduced hydroxyl radical production by both samples. The type of biological reactivity observed with these fluoro-edenite fibres resembled that of asbestos fibres. CONCLUSIONS: The hydroxyl radicals generated by asbestos fibres have long been known to mediate inflammatory fibrosis of the lung and DNA damage that may ultimately result in lung carcinoma and mesothelioma.     

Asbestos content of lung tissue and carcinoma of the lung: a clinicopathologic correlation and mineral fiber analysis of 234 cases

The aim of this study was to investigate the asbestos content of lung tissue in a series of patients with lung cancer and some history of asbestos exposure. This information was then correlated with demographic information, occupational and smoking history, presence or absence of pathologic asbestosis or pleural plaques, and pathologic features of the cancer. The pulmonary concentration of asbestos fibers in 234 cases of primary carcinoma of the lung was determined by means of a tissue digestion technique. Asbestos body counts were performed in 229 cases and fiber analysis by scanning electron microscopy in 221 cases. Asbestos content was recorded as total asbestos fibers, commercial amphibole fibers, noncommercial amphibole fibers, and chrysotile fibers 5 microm or greater in length per gram of wet lung tissue. The study group included 70 patients with asbestosis (Group I), 44 patients with parietal pleural plaques but without asbestosis (Group II), and 120 patients with neither (Group III). The median asbestos body content of Group I was more than 35 times greater than Group II and more than 300 times greater than Group III. The total asbestos fiber count for Group I was nearly 20 times greater than Group II and more than 50 times greater than Group III. The difference was due almost entirely to commercial amphiboles.In a series of primary lung cancer cases with some history of asbestos exposure, a markedly elevated asbestos content was identified among those with pathologic asbestosis as compared with patients with pleural plaques alone or with neither plaques nor asbestosis.     

Asbestos-related disease associated with exposure to asbestiform tremolite

Tremolite is nearly ubiquitous and represents the most common amphibole fiber in the lungs of urbanites. Tremolite asbestos is not mined or used commercially but is a frequent contaminant of chrysotile asbestos, vermiculite, and talc. Therefore, individuals exposed to these materials or to end-products containing these materials may be exposed to tremolite. We have had the opportunity to do asbestos body counts and mineral fiber analysis on pulmonary tissue from five mesothelioma cases and two asbestosis cases with pulmonary tremolite burdens greater than background levels. There were no uncoated amosite or crocidolite fibers detected in any of these cases. Three patients were occupationally exposed to chrysotile asbestos; two patients had environmental exposures (one to vermiculite and one to chrysotile and talc) and one was a household contact of a shipyard worker. The tremolite burdens for the asbestosis cases were one to two orders of magnitude greater than those for the mesothelioma cases. Our study confirms the relationship between tremolite exposure and the development of asbestos-associated diseases. Furthermore, the finding of relatively modest elevations of tremolite content in some of our mesothelioma cases suggests that, at least for some susceptible individuals, moderate exposures to tremolite-contaminated dust can produce malignant pleural mesothelioma.     

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 μm, 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 ? 5 μm were in the following decreasing order: tremolite > crocidolite > chrysotile > other fibers > talc-anthophyllite > amosite. For total fibers < 5 μm, 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 μm 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.     

Mineral phases and some reexamined characteristics of the international union against cancer standard asbestos samples

Standard asbestos samples to be used for biomedical research were first prepared by the International Union Against Cancer (UICC) in 1966 in the United Kingdom and South Africa. Using modern techniques, X-ray diffractometry, analytical transmission electron microscopy, and thermal analysis, we have now analyzed these UICC samples to determine the mineral compositions (mineral phases) and their respective quantities. UICC chrysotile A (from Zimbabwe) contains 2% fibrous anthophyllite as impurity; chrysotile B (from Canada) does not contain any fibrous impurities, only non-fibrous minerals. UICC amosite and crocidolite are almost pure. UICC anthophyllite has 20–30% talc as impurity. The chemical compositions and fiber size distributions of the UICC asbestos samples have also been determined. The mean widths of the fibers of chrysotile A and B are smaller than those of the amphibole fibers. This agrees well with the earlier results which showed the two chrysotile samples to have a larger respirable fraction than the amphiboles. © 1996 Wiley-Liss, Inc.     

Exposure to brake dust and malignant mesothelioma: a study of 10 cases with mineral fiber analyses

OBJECTIVES: A large number of workers in the USA are exposed to chrysotile asbestos through brake repair, yet only a few cases of malignant mesothelioma (MM) have been described in this population. Epidemiologic and industrial hygiene studies have failed to demonstrate an increased risk of MM in brake workers. We present our experience of MM in individuals whose only known asbestos exposure was to brake dust and correlate these findings with lung asbestos fiber burdens. METHODS: Consultation files of one of the authors were reviewed for cases of MM in which brake dust was the only known asbestos exposure. Lung fiber analyses were performed using scanning electron microscopy (SEM) in all cases for which formalin-fixed or paraffin-embedded lung tissue was available. RESULTS: Ten cases of MM in brake dust-exposed individuals were males aged 51-73 yr. Nine cases arose in the pleura and one in the peritoneum. Although the median lung asbestos body count (19 AB/g) is at our upper limit of normal (range 0-20 AB/g), half of the cases had levels within our normal range. In every case with elevated asbestos fiber levels by SEM, excess commercial amphibole fibers were also detected. Elevated levels of chrysotile and non-commercial amphibole fibers were detected only in cases that also had increased commercial amphibole fibers. CONCLUSIONS: Brake dust contains exceedingly low levels of respirable chrysotile, much of which consists of short fibers subject to rapid pulmonary clearance. Elevated lung levels of commercial amphiboles in some brake workers suggest that unrecognized exposure to these fibers plays a critical role in the development of MM.     

Occupational exposure to chrysotile asbestos and cancer risk: a review of the amphibole hypothesis.

OBJECTIVES. This article examines the credibility and policy implications of the "amphibole hypothesis," which postulates that (1) the mesotheliomas observed among workers exposed to chrysotile asbestos may be explained by confounding exposures to amphiboles, and (2) chrysotile may have lower carcinogenic potency than amphiboles. METHODS. A critical review was conducted of the lung burden, epidemiologic, toxicologic, and mechanistic studies that provide the basis for the amphibole hypothesis. RESULTS. Mechanistic and lung burden studies do not provide convincing evidence for the amphibole hypothesis. Toxicologic and epidemiologic studies provide strong evidence that chrysotile is associated with an increased risk of lung cancer and mesothelioma. Chrysotile may be less potent than some amphiboles for inducing mesotheliomas, but there is little evidence to indicate lower lung cancer risk. CONCLUSIONS. Given the evidence of a significant lung cancer risk, the lack of conclusive evidence for the amphibole hypothesis, and the fact that workers are generally exposed to a mixture of fibers, we conclude that it is prudent to treat chrysotile with virtually the same level of concern as the amphibole forms of asbestos.     

Cancer mortality among workers exposed to amphibole-free chrysotile asbestos.

The issue of whether exposure to chrysotile asbestos alone, without contamination from amphibole asbestos, causes lung cancer and mesothelioma was investigated in a 25-year longitudinal study (1972-1996) in Chongqin, China. The study cohort comprised 515 male asbestos plant workers exposed to chrysotile only; the control cohort included 650 non-dust-exposed workers. The results of analysis in which the proportional hazards model was used indicated that mortality due to all causes, all cancers, and lung cancer was related to asbestos exposure; the relative risks, adjusted for age and smoking, were 2.9, 4.3, and 6.6, respectively. Fiber concentrations in the raw material section and the textile section of the plant were 7.6 and 4.5 fibers/ml, respectively. Because of differences between the study and control plants, the authors also compared various sections of the asbestos plant that had different levels of dust exposure. The adjusted relative risk of lung cancer was 8.1 for workers exposed to high versus low levels of asbestos. Two cases of malignant mesothelioma, one pleural and the other peritoneal, were found in the asbestos cohort. These results suggest that heavy exposure to pure chrysotile asbestos alone, with negligible amphibole contamination, can cause lung cancer and malignant mesothelioma in exposed workers.     

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.     

Lung asbestos burden in shipyard and construction workers with mesothelioma: comparison with burdens in subjects with asbestosis or lung cancer

Although mesothelioma is generally considered to be caused by asbestos, epidemiologic studies indicate that some cases have another cause. In order to determine whether pulmonary asbestos burden can be used to define asbestos-related mesotheliomas, asbestos burden was quantified in 27 shipyard or construction workers with diffuse malignant mesothelioma of the pleura or peritoneum and a history of asbestos exposure. Their burden was significantly greater than the burden found in 19 unexposed men (P less than 0.001). The burdens were also compared to those of previously reported subjects with asbestosis or lung cancer. The median concentration for total amphibole fibers (2.7 million/g dry lung) in subjects with mesothelioma did not differ significantly from our previously reported median values for 14 subjects with asbestosis (1.3 million/g dry lung) or for 60 asbestos workers with lung cancer (1.3 million/g dry lung). Fiber size distribution for amosite, the most prevalent fiber type, was similar in all three subject groups. Fifteen of 25 (60%) subjects with mesothelioma had mild asbestosis. Asbestos body (AB) concentrations were greater than or equal to 1900/g dry lung, and total amphibole fiber concentrations were greater than or equal to 390,000/g dry lung. Counts of ABs greater than or equal to 0.5/cm2 in histologic sections always signified both of these concentrations in extracts. Thus, histologic sections showing greater than or equal to 0.5 ABs/cm2 or extracts containing asbestos body or amphibole fiber concentrations of at least 1900 or 390,000/g dry lung, respectively, will confirm an asbestos-related mesothelioma.     

Chrysotile asbestos is the main cause of pleural mesothelioma

In contrast to amphibole forms of asbestos, chrysotile asbestos is often claimed to be only a minor cause of malignant pleural mesothelioma, a highly fatal cancer of the lining of the thoracic cavity. In this article we examine the evidence from animal and human studies that relates to this issue. Reported data do not support widely quoted views regarding the relative inertness of chrysotile fibers in mesothelioma causation. In fact, examination of all pertinent studies makes it clear that chrysotile asbestos is similar in potency to amphibole asbestos. Since asbestos is the major cause of mesothelioma, and chrysotile constitutes 95% of all asbestos use world wide, it can be concluded that chrysotile asbestos is the main cause of pleural mesothelioma in humans. © 1996 Wiley-Liss, Inc.     

Malignant mesothelioma from neighborhood exposure to anthophyllite asbestos

BACKGROUND: Anthophyllite asbestos has been reported to cause asbestosis, lung cancer, mesothelioma, and pleural plaques in occupationally exposed workers. Anthophyllite has also been associated with pleural plaques in Finland and Japan among those who live near mines and mills and have neighborhood or environmental exposure. METHODS: We evaluated a 38-year-old patient with pleural mesothelioma who lived, attended school, and delivered newspapers near a manufacturing facility that used exclusively anthophyllite asbestos fiber from ages 8-17 years. He had no work exposure to asbestos. RESULTS: The pleural mesothelioma was an epithelial type with tubulopapillary structures and was treated with an extrapleural pneumonectomy followed by radiation therapy. The malignant cells were positive by immunohistochemistry for cytokeratin but negative for carcinoembryonic antigen, S100, B72.3, and leu M1 antigen. Anthophyllite fibers were > 5 microm in length in lung tissue compared to 3 microm from a general population study. CONCLUSIONS: Anthophyllite asbestos has been associated with neighborhood environmental exposure and pleural plaques; we now report a neighborhood exposure and pleural mesothelioma.     

Short, thin asbestos fibers contribute to the development of human malignant mesothelioma: pathological evidence

Based on animal studies, long and thin asbestos fibers (> or =8 microm in length and < or = 0.25 microm in width) have been postulated to be strongly carcinogenic inducing pleural malignant mesothelioma, while shorter, thicker fibers have been postulated to pose a lesser risk (Stanton hypothesis). The objective of this study is to test the validity of the Stanton hypothesis through direct pathologic analysis of human mesothelioma tissue. Digested bulk tissue samples, or ashed 25 microm thick sections, or both, were prepared from lung and mesothelial tissues taken from 168 cases of human malignant mesothelioma. In these tissues, 10,575 asbestos fibers (4820 in the lung and 5755 in mesothelial tissues (1259 in fibrotic serosa and 4496 in mesotheliomatous tissue)) were identified by high-resolution analytical electron microscopy. Dimensions of these asbestos fibers were measured in printed electron micrographs. Results were as follows: (1) long, thin asbestos fibers consistent with the Stanton hypothesis comprised only 2.3% of total fibers (247 / 10,575) in these tissues; (2) the majority (89.4%) of the fibers in the tissues examined were shorter than or equal to 5 microm in length (9454 of 10,575), and generally (92.7%) smaller than or equal to 0.25 microm in width (9808 of 10,575). (3) Among asbestos types detected in the lung and mesothelial tissues, chrysotile was the most common asbestos type to be categorized as short, thin asbestos fibers. (4) Compared with digestion technique of the bulk tissue, ashing technique of the tissue section was more effective to detect short, thin fibers. We conclude that contrary to the Stanton hypothesis, short, thin, asbestos fibers appear to contribute to the causation of human malignant mesothelioma. Such fibers were the predominant fiber type detected in lung and mesothelial tissues from human mesothelioma patients. These findings suggest that it is not prudent to take the position that short asbestos fibers convey little risk of disease.     

Exposure to man-made mineral fibers: a summary of current animal data

The inhalation of asbestos fibers (crocidolite, chrysotile and amosite) has been implicated in the development of a number of lung disorders including lung cancer, asbestosis, and mesothelioma. The mechanism responsible for these effects is not well characterized but is generally thought to be related to the fibrous nature of these materials. Therefore, concerns have also been raised as to the potential health impact of other fibrous materials including man-made mineral fibers. Man-made mineral fibers are being used as substitutes for asbestos in a wide range of products. However, relatively little data are available on the potential health impact of these fibrous materials. Epidemiology and clinical studies have served as an important source of information on the effect of various environmental pollutants, but have not been sufficient to date to fully address the potential health impact of man-made mineral fibers. This is due in part to the relatively recent introduction of a number of these materials, the long latency period before the onset of clinical symptoms, and in general, the lower exposure levels associated with these materials. Therefore, a number of animal studies have been performed to predict or confirm the toxicity of various man-made mineral fibers in humans. Both fibrosis and mesothelioma have been induced in experimental animals exposed to man-made mineral fibers although no disease has been consistently observed in occupationally exposed workers.2+ While little is known about the mechanism of this response, information from animal and cell culture experiments indicate that dose, fiber dimension, and fiber durability are the most important factors in determining the biological activity of these materials.(ABSTRACT TRUNCATED AT 250 WORDS)     

Asbestos bodies or fibers and the diagnosis of asbestosis

A committee of the College of American Pathologists has proposed that the diagnosis of asbestosis requires fibrosis in respiratory bronchiolar walls and the presence of asbestos bodies (ABs) in tissue sections. To determine whether histologic ABs reliably reflect asbestos fiber concentrations in asbestosis, we compared the concentration of ABs in histologic sections to concentrations of ABs and fibers in tissue extracts of 14 asbestos workers with nonspecific interstitial fibrosis. ABs in histologic sections and extracts correlated well, r = 0.95. Counted and classified by electron microscopy, electron diffraction, and X-ray spectroscopy, commercial amphibole fibers (r = 0.94) also correlated well with ABs, but noncommercial amphiboles (r = -0.02) or chrysotile (r = 0.29) did not. In five subjects with a high percentage of noncommerical amphibole fibers, fewer than 0.5 histologic ABs/cm2 were present despite a total amphibole concentration that was similar to that in subjects with more histologic ABs. We conclude that ABs will be scarce or absent in histologic sections from some subjects with asbestosis, and that for such subjects, extracts of asbestos fibers should yield over 500,000 total amphibole fibers/g dry lung to signify that interstitial fibrosis may be caused by asbestos.     

Man-made mineral fibers (MMMF): human exposures and health risk assessment

MMMF are made by spraying or extruding molten glass, furnace slag, or mineral rock. Health concerns are based on the morphological and toxicological similarities between MMMF and asbestos, and the well-documented evidence that asbestos fibers can cause lung fibrosis (asbestosis), bronchial cancer, and mesothelioma in humans. Epidemiological evidence for human disease from inhalation exposures to fibrous glass is largely negative. Some positive associations have been reported for slag and rockwools. Most of the toxicological evidence for MMMF toxicity in laboratory animals is based on non-physiological exposures such as intratracheal instillation or intraperitoneal injection of fiber suspensions. The risks for lung fibrosis, lung cancer, and mesothelioma for industrial exposures to most fibrous glass products are either low or negligible for a variety of reasons. First, most commercial fibrous glass products have mean fiber diameters of approximately 7.5 microns, which results in mean aerodynamic diameters greater than 22 microns. Thus, most glass fibers, even if dispersed into the air, do not penetrate into the lung to any great extent. Second, the small fraction of smaller diameter fibers which do penetrate into the lungs are not persistent within the lungs for most fibrous glass products, due to mechanical breakage into shorter lengths and dissolution. Dissolution is most rapid for the smaller diameters (less than 0.1 micron) capable of producing mesothelioma. The greater hazards for slag and rockwools, in comparison to conventional fibrous glass, appear to be related to their smaller diameters and greater durability within the lungs.