asbestos--crocidolite and Silicosis

Topics: Asbestos; Asbestos, Amosite; Asbestos, Crocidolite; History, 19th Century; History, 20th Century; Mesothelioma; Mining; Occupational Medicine; Pathology; Physicians; Public Health; Research; Research Personnel; Respiratory Tract Diseases; Silicosis; South Africa; Workplace

The different pulmonary macrophage (airway macrophages, alveolar macrophages, interstitial macrophages, intravascular macrophages, pleural macrophages) are an important part of the lungs' defences against non-fibrous and fibrous particles deposited by inhalation. The first line of defence is airway macrophages and alveolar macrophages (AM) which initially interact with deposited chrysotile fibres and subsequently release a number of mediators including growth regulatory and chemotactic proteins, arachidonic acid metabolites, proteases, NO and active oxygen species, all of which can affect--also adversely--specific target cells in the lung. Mechanical clearance via the mucociliary escalator and dissolution of phagocytized fibres in the acidic milieu of the phagolysosome in pulmonary macrophages are further important functions of AM. Chrysotile appears to be more toxic or at least has the same toxicity to AM as amphibole fibres when doses of a similar mass are administered. However, on a fibre number basis chrysotile appears to be less toxic to AM. The importance of the appropriate dose parameter--i.e. fibre mass, number or surface area--needs to be considered in in vitro as well as in in vivo studies. Short chrysotile fibres are cleared from rat lungs very rapidly whereas longer ones are cleared at a much slower rate. This is due to efficient phagocytosis of short fibres by AM accompanied by dissolution in the acidic milieu of the phagolysosome. Prediction of chrysotile clearance in primate lung based on results from rat studies result in an overall retention half-time of approximately 105 days, based on which no long-term accumulation of chrysotile in the primate lung is to be expected. Long-term inhalation studies in baboons exposed to chrysotile confirm the very fast build up of a low steady-state lung burden, consistent with a pulmonary retention half-time for chrysotile of approximately 90 days. Despite the fast clearance and low pulmonary accumulation of chrysotile, the resulting effects, such as asbestosis, were found to be of the same severity in rats as those induced by amphibole exposure. In the amphibole-exposed rats, the fibre lung burden continued to increase with exposure time. The potential contamination of chrysotile with tremolite cannot explain these results since there was no increased pulmonary accumulation of fibres in the chrysotile-exposed rats. Effects due to lung particle overload are not to be expected in long-term chrysotile inha

Topics: Animals; Asbestos, Amosite; Asbestos, Crocidolite; Asbestos, Serpentine; Asbestosis; Coal Mining; Cytokines; Dogs; Dust; Humans; Lung; Lymph; Macrophages, Alveolar; Papio; Pneumoconiosis; Quartz; Rats; Silicosis; Time Factors

Six cases of silicosis in workers involved in the processing of semiprecious gem stones have been seen in our clinic since 1976. They had been employed as stone sculptors in lapidaries where they processed tiger's-eye, rose quartz, amethyst, quartz crystal, and a variety of other locally occurring semiprecious stones. In five of the cases, exposure was in small and poorly regulated lapidaries without specific dust control measures. The sixth was detected during the course of a health and hygiene survey (including dust sampling) that was conducted in one of two lapidaries still operating in our area. Progressive massive fibrosis (PMF) or accelerated silicosis was noted in four of the six cases, three of whom had progression of their disease after cessation of exposure. With the development of PMF, the initial restrictive pulmonary function abnormalities were followed by steadily worsening airflow obstruction. Lung biopsies confirmed silicosis in three cases. Tuberculosis was confirmed in two cases and suspected and treated in a third. Workmen's Compensation was awarded in five cases. The survey confirmed that in semiprecious gem stone processing, the risk of silicosis appears to be confined to stone sculptors. Tried and proven techniques of general and local exhaust ventilation combined with water or oil to control dust at source were capable of effectively reducing dust emission to acceptable levels.

Topics: Adult; Asbestos; Asbestos, Crocidolite; Humans; Male; Middle Aged; Occupational Exposure; Occupations; Respiratory Function Tests; Risk Factors; Silicon Dioxide; Silicosis; South Africa