Twenty-five years of fiber analysis: what have we learned?

Asbestos exposure has resulted in a variety of diseases, including asbestosis, carcinoma of the lung (LC), pleural plaques, and malignant mesothelioma (MM). We hypothesized that there have been significant changes in the mineral fiber content of lung tissue from individuals with these diseases over the past 25 years. Asbestos content was measured in lung tissue samples from 819 individuals using light microscopy (to measure asbestos body concentrations) and scanning electron microscopy (to measure types and concentrations of mineral fibers). Cases were divided chronologically according to those occurring in the first half (group 1) versus those occurring in the second half (group 2). The study included 419 cases of MM, 206 cases of asbestosis, and 340 cases of LC. The median asbestos body count (in asbestos bodies per gram) decreased from group 1 to group 2 for each disease: MM, 480 to 350; asbestosis, 24700 to 19200; and LC, 1600 to 174 (reference range, 0-20). A similar trend was observed for fiber counts by scanning electron microscopy. Amosite was the most frequently detected asbestos fiber type and decreased in frequency of detection and median concentration from group 1 to group 2. Crocidolite showed an increased detection frequency from group 1 to group 2 across all 3 disease categories. The decrease in asbestos body and amosite concentrations over time is consistent with the banning of asbestos from insulation products in 1972. The source for the increased detection of crocidolite was not identified and needs further investigation.