Documents amosite 8 results

"ObjectivesShort fibres of amosite asbestos (SFA), obtained by ball milling of long fibres (LFA), have been shown to be less pathogenic than long fibres. Accumulating evidence suggests an important role for differences in surface chemistry between fibres. Iron has been implicated in the pathogenesis of asbestos fibres. In this study infrared (IR) spectroscopy was used to compare LFA and SFA in terms of the coordination and oxidation state of iron at the three cation sites (M1, M3, M1). MethodsInfrared was used to examine LFA ad SFA, when dry and when hydrated in the presence and absence of the chelators desferroxamine and ferrozine. With appropriate software the proportions of iron and its oxidation states in the overlapping peaks were resolved and assigned, and the three coordination sites were identified. Data were obtained from 10 samples of both lengths of fibre for each of the four treatments. Iron release was also monitored. ResultsIron was significantly more oxidised in LFA than SFA. Further oxidation of the dry fibres with water, ferrozine, or desferroxamine tended to abolish these differences. There were also significant differences between the proportions of iron held in the different coordination sites of the fibres. For LFA, a higher proportion of its iron was held in the cation sites coordinating less with iron and more with Mg. Interestingly, the sites coordinating single irons were significantly more oxidised than multiple sites. The single iron sites were more oxidised in LFA than SFA and were more readily oxidised by the treatments. Conclusions—Important chemical differences between LFA and SFA were found. There seemed to be some mobility of iron near the surface. Based on these data it is speculated that the 1 iron surface site may be important in pathogenesis."

Background South Africa has, uniquely, mined, transported, and used crocidolite, amosite, and chrysotile. A multicenter case-control study was done in South Africa to examine the details of asbestos exposure in cases and controls, and to calculate relative risks for level of certainty of asbestos exposure, nature of exposure (e.g., environmental, occupational) and fiber type. Methods Cases and controls (one cancer and one medical per case) were collected by six study centers from referral hospitals, and exposure information was collected by interviewing cases and controls in life. Results One hundred and twenty-three cases were accepted into the study. None had purely chrysotile exposure. Twenty-three cases had mined Cape crocidolite; three had mined amosite; and three Transvaal crocidolite plus amosite. A minimum of 22 of the cases had exclusively environmental exposure, 20 were from the NW Cape crocidolite mining area. The relative risks associated with environmental exposure in the NW Cape (crocidolite) were larger than for environmental exposure in the NE Transvaal (amosite and crocidolite): 21.9 vs. 7.1 and 50.9 vs. 12.0 for the cancer control and medical control datasets, respectively. Conclusions The results confirm the importance of environmental exposure in the Cape crocidolite mining area, the relative paucity of cases linked to amosite, the rarity of chrysotile cases and are consistent with a fiber gradient in mesotheliomagenic potential for South African asbestos with crocidolite > amosite > chrysotile.

The production and export figures for South African asbestos (1332214) from 1959 through 1993 were evaluated, based on published information. By 1993, exports of crocidolite (12001284) dropped to 5% of their peak in the late 1970s. Amosite (12172735) exports peaked in 1968 and ceased in 1993. The chrysotile (12001295) trade remained steady. Through 1963, most asbestos exports went to western Europe and the United States, with smaller amounts to Australia, New Zealand, India, Pakistan, latin America, and Japan. This was followed by a shift of trade toward the Far East; by 1991, Japan imported 64%, South Korea imported 28%, and Thailand imported 5% of South African exports. Crocidolite was no longer imported by 12 countries by 1992. The future effects to be experienced in poor and developing countries to which asbestos has been exported remains to be seen. Along with the reduction of asbestos use in developed countries, the increasing use in developing countries, even though it is at lower overall tonnages, inevitably means that disease of long latency will continue to occur well into the twenty first century. The authors note that it is not likely that developing countries will be able to apply either adequate and appropriate protection or use the safety precautions which have been advocated as means of protecting the public and the workers. In spite of the earlier and numerous reports of the hazardous effects of crocidolite, the authors note that 59 countries continued to import it from South Africa in 1980 and 21 in 1992, so that the total ban that has been recommended is not likely to be achieved.

The mineral phases and chemical and physical characteristics of the chrysotile-A (12001295), chrysotile-B, crocidolite (12001284), amosite (12172735), and anthophyllite (17068789) samples prepared by the International Union Against Cancer (UICC) in 1966 were examined in this study. Mineral phases were determined through the use of X-ray diffraction (XRD). Anthophyllite, talc (14807966), and nonfibrous minerals were detected in samples of chrysotile-A. The quantity of anthophyllite in chrysotile-A was estimated at 2%. The proportions of chrysotile in chrysotile-A and chrysotile-B were 94% and 92%, respectively. Amosite and crocidolite samples each contained about 1% quartz (14808607). The anthophyllite sample contained about 5% each of chlorite and mica, and about 20 to 30% talc. Overall, the chemical compositions of the samples indicated high purity. Chrysotile-B contained higher concentrations of some constituents than chrysotile-A, while anthophyllite contained high concentrations of oxides, indicating an impurity. Thermal analysis of the chrysotiles and anthophyllite indicated dehydroxidation and recrystallization. No mineral impurities were detected in the amosite and crocidolite samples by thermal analysis. Analytical transmission electron microscopy revealed that the chrysotiles consisted of thin, curly fibrils, fiber bundles, and platy materials, while amosite, crocidolite, and anthophyllite consisted of wider, rectangular fibers. The mean lengths of the chrysotile and crocidolite fibers were shorter and exhibited less variability than those of the amosite and anthophyllite samples. The mean fiber widths of the chrysotiles were less than those of amosite, crocidolite, and anthophyllite. The authors conclude that further study is necessary, since the characteristics of the UICC asbestos samples measured with modern equipment and techniques differ from those that were established years ago.

"The term asbestos is a generic designation referring usually to six types of naturally occurring mineral fibers that are or have been commercially exploited. These fibers belong to two mineral groups: serpentines and amphiboles. The serpentine group contains a single asbestiform variety: chrysotile; five asbestiform varieties of amphiboles are known: anthophyllite asbestos, grunerite asbestos (amosite), riebeckite asbestos (crocidolite), tremolite asbestos, and actinolite asbestos. These fibrous minerals share several properties which qualify them as asbestiform fibers: they are found in bundles of fibers which can be easily separated from the host matrix or cleaved into thinner fibers; the fibers exhibit high tensile strengths, they show high length: diameter (aspect) ratios, from a minimum of 20 up to greater than 1000; they are sufficiently flexible to be spun; and macroscopically, they resemble organic fibers such as cellulose. Since asbestos fibers are all silicates, they exhibit several other common properties, such as incombustibility, thermal stability, resistance to biodegradation, chemical inertia toward most chemicals, and low electrical conductivity.
The term asbestos has traditionally been attributed only to those varieties that are commercially exploited. The industrial applications of asbestos fibers have now shifted almost exclusively to chrysotile. Two types of amphiboles, commonly designated as amosite and crocidolite are no longer mined. The other three amphibole varieties, anthophyllite asbestos, actinolite asbestos, and tremolite asbestos, have no significant industrial applications presently."