The distribution of amosite asbestos in the periphery of the normal human lung

Although theoretical models and experiments on animals exist that predict the distribution of asbestos fibres in the lung, there are few studies in man that relate to this question and they have generated contradictory results. To examine this distribution analytical electron microscopy was employed to determine the amosite fibre concentration, size, surface area, and mass in 29 circumferential sites around the periphery of a mid-sagittal slice from nine morphologically normal left lungs of heavily exposed shipyard workers and insulators. Fibre concentrations were heaviest in the apical segment of the upper lobe, and low concentrations were seen in the posterior basal portion of the lower lobe. Overall, the upper lung zones had significantly greater concentrations than the lower lung zones. Fibre length was shortest in the anterior portion of the upper lobe, greater in the lingula, and greatest in the posterior basal portion of the lower lobe; fibre length overall was significantly greater in the lower compared with the upper zones. Aspect ratio followed a similar pattern. Distinct geographic runs of high or low concentrations and long or short lengths and aspect ratios were present. No consistent distribution patterns for fibre width, surface area, or mass were found. It is concluded that: (1) in the periphery of the normal lung, concentration of amosite fibres is greatest in the apex and least in the peripheral lower lobe. This distribution is the opposite of what would be expected from the known distribution of asbestosis (peripheral lower zone); nor does it correlate with bronchial pathlength or branch number, contrary to predictions from studies on animals and theoretical models; (2) fibre length and related parameters show a distribution opposite to that of fibre concentration and again do not correlate with theoretical predictions.