RETENTION PATTERNS OF ASBESTOS FIBERS IN LUNG-TISSUE AMONG ASBESTOS-CEMENT WORKERS

Retention patterns in lung tissue (determined by transmission electron microscopy and energy dispersive spectrometry) of chrysotile, tremoli te, and crocidolite fibres were analysed in 69 dead asbestos cement wo rkers and 96 referents. There was an accumulation of tremolite with ti me of employment. Among workers who died within three years of the end of exposure, the 13 with high tremolite concentrations had a signific antly longer duration of exposure than seven in a low to intermediate category (medians 32 v 20 years; p = 0.018, one sided). Crocidolite sh owed similar patterns of accumulation. In workers who died more than t hree years after the end of exposure, there were no correlations betwe en concentrations of amphibole fibres and time between the end of expo sure and death. Chrysotile concentrations among workers who died short ly after the end of exposure were higher than among the referents (med ian difference in concentrations 13 million fibres (f)/g dry weight; p = 0.033, one sided). No quantitative differences in exposure (duratio n or intensity) could be shown between workers with high and low to in termediate concentrations. Interestingly, all seven workers who had ha d a high intensity at the end of exposure (>2.5 f/ml), had low to inte rmediate chrysotile concentrations at death, whereas those with low ex posure were evenly distributed (31 subjects in both concentration cate gories); hence, there was a dependence between last intensity of expos ure and chrysotile concentration (p = 0.014). Among 14 workers with a high average intensity of exposure, both those (n = 5) with high tissu e concentrations of chrysotile and those (n = 10) with high tissue con centrations of tremolite fibres had more pronounced fibrosis than thos e with low to intermediate concentrations (median fibrosis grades for chrysotile: 2 v 1, p = 0.021; for tremolite: 2 v 0.5, p = 0.012). Addi tionally, workers who died shortly after the end of exposure with high concentrations of chrysotile and crocidolite had smoked more than tho se with low to intermediate concentrations (medians for chrysotile 35 v 15 pack-years, p = 0.030; for crocidolite 37 v 15 pack-years, p = 0. 012). The present data indicate that chrysotile has a relatively rapid turnover in human lungs, whereas the amphiboles, tremolite and crocid olite, have a slower turnover. Further, chrysotile retention may be de pendent on dose rate. Chrysotile and crocidolite deposition and retent ion may be increased by tobacco smoking; chrysotile and tremolite by f ibrosis.