Leaching of chrysotile asbestos in human lungs: Correlation with in vitro studies using rabbit alveolar macrophages

The chemical microanalysis of chrysotile fibers obtained from human lungs and from chrysotile phagocytosed in vitro by rabbit alveolar macrophages (AM) was carried out with the use of an energy dispersive spectrometer mounted on a scanning electron microscope (SEM). This microanalysis was compared to natural fibers in order to investigate the chemical stability of chrysotile in biologic residence. The Mg versus Si content was estimated by the ratio of the peaks intensity Si:Mg. Lung samples were obtained from workmen with definite asbestos exposure, and chrysotile asbestos was extracted by chemical digestion. Phagocytosed chrysotile fibers were obtained after incubating standard chrysotile (A UICC) with rabbit alveolar macrophages for 24 hours or 5 days. Both chrysotile fibers from human lungs and from in vitro incubation with AM have shown an increase of the Si:Mg ratio in respect to standard fibers. Moreover, the results have shown that the magnesium leakage was not constant along the fiber axis and was different from one fiber to another.     

Simulation tests to assess occupational exposure to airborne asbestos from artificially weathered asphalt-based roofing products

Historically, asbestos-containing roof cements and coatings were widely used for patching and repairing leaks. Although fiber releases from these materials when newly applied have been studied, there are virtually no useful data on airborne asbestos fiber concentrations associated with the repair or removal of weathered roof coatings and cements, as most studies involve complete tear-out of old roofs, rather than only limited removal of the roof coating or cement during a repair job. This study was undertaken to estimate potential chrysotile asbestos fiber exposures specific to these types of roofing products following artificially enhanced weathering. Roof panels coated with plastic roof cement and fibered roof coating were subjected to intense solar radiation and daily simulated precipitation events for 1 year and then scraped to remove the weathered materials to assess chrysotile fiber release and potential worker exposures. Analysis of measured fiber concentrations for hand scraping of the weathered products showed 8-h time-weighted average concentrations that were well below the current Occupational Safety and Health Administration permissible exposure limit for asbestos. There was, however, visibly more dust and a few more fibers collected during the hand scraping of weathered products compared to the cured products previously tested. There was a notable difference between fibers released from weathered and cured roofing products. In weathered samples, a large fraction of chrysotile fibers contained low concentrations of or essentially no magnesium and did not meet the spectral, mineralogical, or morphological definitions of chrysotile asbestos. The extent of magnesium leaching from chrysotile fibers is of interest because several researchers have reported that magnesium-depleted chrysotile fibers are less toxic and produce fewer mesothelial tumors in animal studies than normal chrysotile fibers.     

In vitro cytological and cytogenetic effects of an Indian variety of chrysotile asbestos

The cytotoxic and cytogenetic effects of chrysotile asbestos (Indian Variety, AP-I) in vitro on Chinese hamster ovary cells were investigated. Chrysotile asbestos (AP-I) produces high vacuolization of cytoplasm, flattening of cells with increased size, and chromosomal aberrations. Both cytological and cytogenetic studies were dependent upon the dose and the period of exposure to chrysotile asbestos.     

The metabolism of benzo(a)pyrene in rat liver microsomes: The effect of asbestos-associated metal ions and pH

Experimental evidence is presented to support the hypothesis that trace metals and other factors associated with asbestos mined in different areas play a more critical role in the development of “asbestos tumours” than the actual fibre itself.In vitro experiments were performed to investigate the effect of these associated factors on the metabolism of benzo(a)pyrene, a carcinogen introduced into the lung as a result of smoking and atmospheric pollution. The amount of benzo(a)pyrene metabolized by the enzyme in rat liver microsomes was measured in the presence of increasing amounts of trace metal ions. Copper, zinc, lead, nickel, chromium, ferrous, ferric, and magnesium ions were found to inhibit enzyme activity to an increasing extent as their concentration increased; manganese was an exception in that it activated the enzyme at lower concentrations and inhibited it at higher concentrations.Enzyme activity was also considerably affected by changes in pH, with a great loss of activity at the high pH values measured for aqueous suspensions of crocidolite and chrysotile.The effect of manganese ions differed at various pH values, the enzyme-activating effect of these ions being restricted to a much smaller concentration range at a high pH.     

Investigation of micronucleus frequencies in lymphocytes of inhabitants environmentally exposed to chrysotile asbestos

Exposure to asbestos minerals has been associated with a wide variety of adverse health effects including lung cancer, pleural mesothelioma, and cancer of other organs. Many of the regions of Turkey have asbestos deposits. People in Do?anl? village – one of these regions – have been environmentally exposed to chrysotile asbestos since they were born. In this study the effects of asbestos on micronucleus (MN) frequencies of inhabitants exposed to chrysotile asbestos have been examined. Thirty subjects who had been environmentally exposed to chrysotile asbestos and living in Do?anl? village, and 25 controls were studied to assess the MN frequency. The control group was selected from healthy individuals with no exposure to asbestos and living in similar geographic conditions to Do?anl? village. Peripheral blood samples were collected from each subject and cultured for MN assay. Cytochalasin-B was added to lymphocyte cultures for evaluation of MN in binucleated (BN) cells. The differences between those exposed to chrysotile asbestos and controls were not statistically significant in terms of BN cells with MN (p > 0.05). There was not a significant relationship between MN frequencies and age, sex, smoking, both in chrysotile asbestos-exposed subjects and in controls (p > 0.05). Although the detection of calcified pleural plaques found in the inhabitants has indicated environmental exposure to chrysotile asbestos, our results show that chrysotile asbestos was not an inducer of MN in subjects exposed to chrysotile asbestos.     

Characteristics of peritoneal macrophages induced by asbestos injection

The effect of single intraperitoneal injections of UICC crocidolite, UICC chrysotile, and a latex control particulate on the induced murine peritoneal macrophage population was measured. Spreading, Fc receptor avidity, and phagocytosis were measured 3, 18, and 70 days after injection. When activation of the induced macrophage populations was found at all three times with asbestos, but not with latex, experiments were undertaken to determine whether the asbestos-activated macrophages had attained the full tumoricidally activated state. An in vitro assay measuring macrophage cytotoxicity to tumor cells revealed that the tumoricidal potential of asbestos-activated macrophages was low at 3 and 5 days and negligible by 35 days after injection. An in vivo assay measuring the effect of asbestos on tumor growth generally supported the contention that asbestos-activated macrophages were not tumoricidal, although one dose of UICC chrysotile did produce a small, significant reduction in growth of a concomitant tumor. It was concluded that a single intraperitoneal asbestos injection in mice induces activated macrophages which do not become fully tumoricidal.     

Asbestos in water sources of the Bazhenovskoye chrysotile asbestos deposit

The paper provides measurements of asbestos fiber levels in water sources from the area of the Bazhenovskoye chrysotile asbestos deposit. All study water samples contained asbestos fibers at concentrations one to three orders below the values standardized in the USA (7 x 10(6) fibers/liter). All the identified fibers belonged to chrysotile asbestos and no amphibole asbestos, such as tremolite asbestos, has been identified. The anthropogenic load of asbestos fibers in Asbest City's environment is increasing in the volume of 5.770 x 10(14) fibers/liter or 10.2 kg of chrysotile asbestos. The authors consider it advisable to continue studies to measure asbestos levels in the water sources in the areas located in the vicinity of other Russian asbestos deposits.     

Identification of carcinogens by measurement of cell-mediated immunity: III. Immunity to asbestos-induced rat peritoneal mesothelioma

Antitumor cell-mediated immune (CMI) responses were detected in rats with asbestos (Canadian chrysotile B)-induced peritoneal mesotheliomas. The CMI was determined by in vitro lymphoid-cell cytotoxicity expressed by committed peripheral blood lymphoid cells (PBLC) obtained from the tumor-bearing animals toward cultured target cells of the tumors. Two apparently different target cell cultures which were developed from tumors of the same rat, one with epitheliod and the other with fibroblastic morphology, were lysed to the same degree by the sensitized PBLC. Specificity was observed for the PBLC reactivity as no cytotoxicity was expressed toward target cells derived from tumors of either ectodermal or entodermal origin. Nor were PBLC obtained from rats bearing tumors of these two tissue types capable of expressing injury to the mesothelioma target cells. These findings indicate that immune responsiveness developed to mesothelioma and suggest that such measurements might be useful for detecting environmental exposures to asbestos fibers.     

The Case for a Global Ban on Asbestos

Background

All forms of asbestos are now banned in 52 countries. Safer products have replaced many materials that once were made with it. Nonetheless, many countries still use, import, and export asbestos and asbestos-containing products, and in those that have banned other forms of asbestos, the so-called “controlled use” of chrysotile asbestos is often exempted from the ban. In fact, chrysotile has accounted for > 95% of all the asbestos used globally.

Objective

We examined and evaluated the literature used to support the exemption of chrysotile asbestos from the ban and how its exemption reflects the political and economic influence of the asbestos mining and manufacturing industry.

Discussion

All forms of asbestos, including chrysotile, are proven human carcinogens. All forms cause malignant mesothelioma and lung and laryngeal cancers, and may cause ovarian, gastrointestinal, and other cancers. No exposure to asbestos is without risk. Illnesses and deaths from asbestos exposure are entirely preventable.

Conclusions

All countries of the world have an obligation to their citizens to join in the international endeavor to ban the mining, manufacture, and use of all forms of asbestos. An international ban is urgently needed. There is no medical or scientific basis to exempt chrysotile from the worldwide ban of asbestos.     

Detection of chrysotile asbestos in workers' urine

Urinary asbestos concentrations were evaluated as an indicator of occupational exposure to chrysotile asbestos via inhalation and ingestion. Detection of asbestos in the urine represents the first step in developing a biological indicator of exposure. Such an indicator could be used to supplement exposure data from workplace air sampling. A biological indicator would be particularly valuable in evaluating workers with intermittent airborne asbestos exposures and in determining if airborne exposure results in penetration of asbestos through the lung or gastro-intestinal tract. Transmission electron microscopy was selected as the most sensitive technique for identification of all sizes of asbestos fibers which might appear in the urine. First morning void urine samples were obtained from six workers (occupationally exposed to chrysotile asbestos in a factory producing roof coatings) and from a control group (six individuals with no occupational exposure). The levels of chrysotile asbestos detected in the urine of five workers were significantly greater than the asbestos concentrations in matched field blanks (both on a number and mass basis). Field blanks were designed to detect asbestos in the urine samples due to contamination which might occur during urine collection. Also, the workers' urinary asbestos levels were significantly greater than the concentrations found in the control group (both on a number and mass basis). Finally, the levels of chrysotile asbestos detected in the urine of two of six controls were significantly greater than those in matched field blanks (both on a number and mass basis). Although the project was not specifically designed to correlate urinary and airborne asbestos concentrations, preliminary data indicated that a correlation did not exist between these factors.     

Type of Asbestos and Respiratory Cancer in the Asbestos Industry

Differences in the physical properties and chemical composition of the various types of asbestos indicate that there should be differences in their carcinogenic potentials. This study of the mortality experience of 1,348 retirees from the asbestos industry shows that, after adjustment for cumulative dust exposure, men exposed only to chrysotile asbestos had a respiratory cancer mortality rate 2.4 times the expected, whereas men exposed to a combination of chrysotile and crocidolite asbestos had a mortality rate 5.3 times the expected. Since crocidolite was used largely in the asbestos cement industry, this was studied separately. Men who manufactured asbestos cement shingles and sheets containing only chrysotile asbestos had a respiratory cancer risk 1.4 times the expected, whereas men who manufactured asbestos cement pipe containing both chrysotile and crocidolite asbestos had a respiratory cancer risk 6.1 times the expected.     

Exposing the "myth" of ABC, "anything but chrysotile": a critique of the Canadian asbestos mining industry and McGill University chrysotile studies

BACKGROUND: Beginning in the 1930s, the Canadian asbestos industry created and advanced the idea that chrysotile asbestos is safer than asbestos of other fiber types. METHODS: We critically evaluate published and unpublished studies funded by the Quebec Asbestos Mining Association (QAMA) and performed by researchers at McGill University. RESULTS: QAMA-funded researchers put forth several myths purporting that Quebec-mined chrysotile was harmless, and contended that the contamination of chrysotile with oils, tremolite, or crocidolite was the source of occupational health risk. In addition, QAMA-funded researchers manipulated data and used unsound sampling and analysis techniques to back up their contention that chrysotile was "essentially innocuous." CONCLUSIONS: These studies were used to promote the marketing and sales of asbestos, and have had a substantial effect on policy and occupational health litigation. Asbestos manufacturing companies and the Canadian government continue to use them to promote the use of asbestos in Europe and in developing countries. Am. J. Ind. Med. 44:540-557, 2003.     

Asbestos bodies and the diagnosis of asbestosis in chrysotile workers

It has been suggested that because chrysotile asbestos forms asbestos bodies poorly, use of the traditional histologic requirements (diffuse interstitial fibrosis plus asbestos bodies) for the diagnosis of asbestosis, may lead to an underdiagnosis of this condition in workers exposed only to chrysotile. We examined lungs from 25 chrysotile miners with diffuse interstitial fibrosis. Asbestos bodies were found easily in histologic section using hematoxylin and eosin stains in all cases. Mineralogic analysis of four cases showed that 46 of 72 (64%) bodies isolated and examined contained chrysotile cores, and 21 of 72 (29%) bodies contained cores of the amphiboles tremolite and actinolite. By contrast, tremolite and actinolite constituted the majority of uncoated fibers in these cases. The mean length for bodies formed on chrysotile was 35 micron, and for bodies formed on tremolite or actinolite, 36 micron. We conclude that (1) the usual histologic criteria for the diagnosis of asbestos are applicable to chrysotile-exposed workers; (2) in workers with occupational chrysotile exposure, bodies form readily on this mineral; and (3) asbestos bodies in these lungs reflect the presence of long asbestos fibers.     

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.     

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.     

Epidemiology of occupational asbestos-related diseases in China

In 1950s and 60s, asbestosis had been a major health hazard for asbestos exposed workers. In the late 1970s, lung cancers with or without asbestosis were found among asbestos workers. All cohort studies on asbestos workers and on chrysotile miners in China showed excess deaths from lung cancer. In a large scale of cohort study on asbestos workers, a synergistic effect was found between cigarette smoking and asbestos exposure in the production of lung cancer. There have been not so many cases of malignant mesotheliomas reported, so far. In the cohort of chrysotile miners, 4 cases of pleural mesothelioma were observed. In the large scale of cohort study on asbestos workers in 9 factories using only chrysotile only one case of pleural mesothelioma was detected for 10 years' observation. In another 2 cohort studies, 2 cases of peritoneal mesotheliomas were found, one in Shanghai asbestos factory where a small amount of crocidolite had been used in 1960s, and one in Anqing asbestos factory that was located near tremolite mine. Further study is needed especially for the relationship between exposure to Chinese chrysotile and malignant mesotheliomas.     

How conflicted authors undermine the World Health Organization (WHO) campaign to stop all use of asbestos: spotlight on studies showing that chrysotile is carcinogenic and facilitates other non-cancer asbestos-related diseases

Abstract

The silicate mineral asbestos is categorized into two main groups based on fiber structure: serpentine asbestos (chrysotile) and amphibole asbestos (crocidolite, amosite, anthophyllite, tremolite, and actinolite). Chrysotile is used in more than 2 000 applications and is especially prevalent in the construction industry. Although its use is banned or restricted in more than 52 countries, an estimated 107 000 workers die from asbestos exposure each year, and approximately 125 million workers continue to be exposed. Furthermore, ambient exposures persist to which the public is exposed, globally. Today, the primary controversies regarding the use of asbestos are the potencies of different types of asbestos, as opposed whether or not asbestos causes morbidity and mortality. The asbestos industry has promoted and funded research based on selected literature, ignoring both clinical and scientific knowledge. In this piece, we highlight a prominent example of a conflicted publication that sought to undermine the World Health Organization (WHO) campaign to stop the use of all forms of asbestos, including chrysotile asbestos. Independent and rigorous scientific data provide sufficient evidence that chrysotile asbestos, like other forms of asbestos, is a cause of asbestos-related morbidity and premature mortality     

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.     

Chrysotile asbestos as a cause of mesothelioma: application of the Hill causation model

Chrysotile comprises over 95% of the asbestos used today. Some have contended that the majority of asbestos-related diseases have resulted from exposures to the amphiboles. In fact, chrysotile is being touted as the form of asbestos which can be used safely. Causation is a controversial issue for the epidemiologist. How much proof is needed before causation can be established? This paper examines one proposed model for establishing causation as presented by Sir Austin Bradford Hill in 1965. Many policymakers have relied upon this model in forming public health policy as well as deciding litigation issues. Chrysotile asbestos meets Hill's nine proposed criteria, establishing chrysotile asbestos as a cause of mesothelioma.     

Cell toxicity, hemolytic action and clastogenic activity of asbestos and its substitutes.

The cell toxicity, hemolytic and clastogenic activity were examined in various kinds of asbestos and some asbestos substitutes with reference to the their mineralogical and physicochemical characteristics. There were thirty-five fibrous and non-fibrous samples including UICC chrysotile, size-selected samples of UICC chrysotile, chrysotile altered by heating and grinding, Yamabe (Japan) chrysotile with long and short fibers, Coalinga (U.S. A.) chrysotile with short fibers, UICC crocidolite, amosite, and 19 non-asbestos samples such as, glass fibers, calcium silicates, sepiolites and some clay minerals. The cell toxicity and the hemolytic and clastogenic activity of asbestos were the strongest for chrysotile among all of the asbestos samples tested, and their strengths varied with fiber length and with the conditions of grinding and heating. These cellular effects of Yamabe chrysotile with long fibers and size-selected UICC chrysotile with long fibers were stronger than those of chrysotile of the same origin but with short fibers. These effects were weaker in chrysotile altered by heating and grinding. Among the asbestos substitutes, the cell toxicity, hemolytic and clastogenic activities of thin glass fibers were more marked than those of thick glass fibers. The four types of sepiolite were strongly hemolytic, but their cell toxicity and clastogenicity varied according to their grade of crystallinity and/or fiber size. These effects of calcium silicates and some clay minerals were generally low but varied with mineral species. In general, the cell toxicity, hemolytic and clastogenic activities of the asbestos substitutes tested here were mild compared with those of asbestos.