Publisher Summary This chapter discusses the chemical, physicochemical, and biological properties of mineral fibers. Among the most important occupational air pollutants are particles of coal, quartz, and fibers of asbestos, which are inhaled by miners and exposed industrial workers. Mineralogically, asbestos is divided into two classes: serpentine and amphibole. The former is a sheet silicate, whereas the latter is built up of double chains of tetrahedra. Chrysotile is the principal asbestos member of the serpentine family, whereas all other asbestos minerals belong to the amphibole group. Chrysotile asbestos is usually worked relatively near the surface by open-cast pit methods. Once the overburden has been cleared, explosives are used to release large tonnages of rock and fiber, the latter accounting for only a few percent of the parent rock. Crude asbestos, together with associated mother rock is conveyed to sorting stations, where waste rock is rejected and the ore undergoes a series of crushing and grinding operations. Fiber bundles of widely different lengths are inevitably mixed together. Subsequent screening results in a rough separation into grades but such screening is too imperfect to remove all the shorter fibers from the longer grades and even the lower grades contain a few long fibers.

Mineral Fibers: Chemical, Physicochemical, and Biological Properties

Analyses of asbestos bodies from the general population have confirmed that these structures, like asbestos bodies from the lungs of asbestos workers, contain an asbestos core. In members of the general population this core is almost always an amphibole, whereas asbestos workers may have bodies formed on either amphibole or chrysotile. Most adults have a few bodies, and increasing numbers are seen in blue collar workers and others who handle small amounts of the fiber, with the highest levels being seen in asbestos workers. In men with minimal or extensive occupational exposure, asbestos bodies are formed on the commercial fibers, amosite and crocidolite, whereas women also form a significant number of bodies on the noncommercial fibers, anthophyllite and tremolite. These findings suggest that women may be exposed to specific asbestos-containing products, eg, cosmetic talc. The commercial fibers found in women and white collar men probably reflect atmospheric pollution with asbestos. At the highest levels of exposure, numbers of asbestos bodies correlate in a general way with the presence of asbestosis, although no precise value has been determined above which asbestosis is always found. In persons with much lower or environmental exposure, there does not appear to be any correlation between numbers of bodies and disease, in particular between numbers of bodies and carcinoma of the lung or gastrointestinal tract. The situation for mesothelioma is uncertain.

Asbestos and other ferruginous bodies: their formation and clinical significance.

The relation between quantified emphysema and measured lung content of coal and silica was investigated in the lungs of 264 deceased underground coalworkers who had been exposed to mixed coal and silica dust. Lung specimens obtained at postmortem and inflated and fixed under standard conditions were used to quantify the extent of emphysema and then to measure the amount of coal and silica present in the lungs at the time of death. These data were combined with clinical and other pathological information from the subjects. Multiple regression analysis showed that the extent of emphysema (E score) had a strong positive quantitative relation with coal content of the lungs (p < 0.0003), age (p < 0.0001), and smoking (p < 0.0001). There was a significant negative interaction of uncertain biological importance between coal content of the lungs and smoking (p < 0.004; E score = -1.79 + 0.62 coal + 0.06 age + 0.21 smoking -0.17 coal x smoking; adjusted R2 = 0.25). In lifelong non-smokers emphysema was particularly strongly related to coal content and age (coal: p < 0.001; age: p < 0.002; E score = -1.56 + 0.78 coal + 0.06 age; adjusted R2 = 0.66). The relation was basically unchanged by adding a lung silica content term. Emphysema score was highly negatively correlated with forced expiratory volume in one second (FEV1; % predicted, obtained within five years of death) (r = -0.44, p < 0.0001). Degree of lung fibrosis was highly positively associated with lung silica content (chi 2(1) = 12.9, p < 0.0003). These results provide strong evidence that emphysema in coalworkers is actually related to lung coal content. The role silica in development of emphysema, however remains unclear.

https://oem.bmj.com/content/oemed/51/6/400.full.pdf

Quantitative relation between emphysema and lung mineral content in coalworkers.

Post-mortem study of emphysema in coalworkers and non-coalworkers.

Mineral analysis of tissue specimens has provided very useful information in pathological conditions associated with occupational exposures to mineral particles, particularly when combined with epidemiological information. Most of the data have been related to exposures to fibrous particles such as asbestos. More investigations of this nature are required in diseases associated with exposure to non-fibrous particles. In the future it is likely that these types of investigation will be extended into the effects of pollutants.

https://thorax.bmj.com/content/thoraxjnl/51/3/327.full.pdf

Analysis and interpretation of inorganic mineral particles in lung tissues

Emphysema and pneumoconiosis. A comparative quantitation of dust content of pneumoconiotic rodent lungs with and without emphysema.

Reproducible methods are described for quantitating inhaled fibrous dust particles and ferruginous bodies found in lungs. The size of the fibers, their volume, and weight are estimated by first photographing an aliquot of the fibers and then tabulating their dimensions as obtained from scaled enlargements. These dimensions serve as the basis for estimating the volume and weights of all the fibrous dust isolated from a given pair of lungs. The lungs of seven city dwellers, two long-time employees of a fiber glass factory and one of an asbestos products factory were studied. These lungs were found to contain 15,000 to 66,000 fibrous particles and 300 to 3,900 ferruginous bodies per gram of dry lung. The mean dimensions of the fibers in all lungs were within a surprisingly narrow range.

Fibrous dust particles and ferruginous bodies. Methods for quantitating them and some results from the lungs of city dwellers.

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Emphysema and pneumoconiosis. A comparative quantitation of dust content of pneumoconiotic rodent lungs with and without emphysema.

Fibrous dust particles and ferruginous bodies. Methods for quantitating them and some results from the lungs of city dwellers.