EXPOSURE AND MINERALOGICAL CORRELATES OF PULMONARY FIBROSIS IN CHRYSOTILE ASBESTOS WORKERS

Objectives-The relation between lifetime cumulative exposure to asbest os, pathological grade of pulmonary fibrosis, and lung burden of asbes tos at death, was explored in a necropsy population of former workers in a chrysotile asbestos textile plant in South Carolina. Methods-Esti mates of cumulative, mean, and peak exposures to asbestos were availab le for 54 workers. Necropsy records and lung tissue samples were obtai ned from hospital files. Matched control cases were selected from cons ecutive necropsies performed at the same hospitals. The extent and sev erity of pulmonary fibrosis was graded on tissue sections. Mineral fib res in lung tissue were characterised by transmission electron microsc opy combined with x ray spectroscopy. Results-A significant positive c orrelation (r = 0.67, P< 0.0001) was found between lifetime cumulative exposure to asbestos and total lung burden of asbestos fibres. This r elation was also found for the individual types of asbestos associated with the exposure: chrysotile and tremolite. Pulmonary fibrosis was c orrelated with both cumulative exposure to asbestos (r = 0.60, P< 0.01 ) and the concentration of asbestos fibres in the lung (r = 0.62, P< 0 .0001). The concentration of tremolite fibres in the lung provided a b etter estimate of lung fibrosis than did the concentration of chrysoti le. Asbestosis was usually present in asbestos textile workers with mo re than 20 fibre-years cumulative exposure. The lengths and aspect rat ios of chrysotile asbestos, but not amphibole asbestos, were greater i n the lungs of asbestos fibre workers than in the control population. Textile workers with lung cancer had significantly greater cumulative exposures and fibrosis scores than workers without lung cancer. Conclu sions-Both cumulative exposure to asbestos and lung fibre burden are s trongly correlated with severity of asbestosis. The data also support the hypothesis that the high prevalence of asbestosis and lung cancer in this population resulted from exposure to long fibres of chrysotile asbestos in the workplace.