The asbestos fibre burden in human lungs: new insights into the chrysotile debate

Abstract

The traceability of asbestos fibres in human lungs is a matter of discussion especially for chrysotile. This issue is of high significance for differential diagnosis, risk assessment and occupational compensation. At present no intra-individual longitudinal information is available. This study addresses the question whether the asbestos fibre burden in human lungs decreases with time after exposure cessation.The database of the German Mesothelioma Register was screened for patients with asbestos body counts of at least 500 fibres per gram of wet lung, which had been analysed twice from different tissue excisions at minimum intervals of 4 years.Twelve datasets with individual longitudinal information were discovered with a median interval of about 8 years (range 4-21 years). Both examinations were performed after exposure cessation (median: surgery, 9.5 years; autopsy, 22 years). Pulmonary asbestos fibre burden was stable between both examinations (median 1623/4269 asbestos bodies per gram wet lung). Electron microscopy demonstrated a preponderance of chrysotile (median 80%).This study is the first to present longitudinal intra-individual data about the asbestos fibre burden in living human lungs. The high biopersistence of amphiboles, but also of chrysotile, offers mechanistic explanations for fibre toxicity, especially the long latency period of asbestos-related diseases.

FIGURE 1

Scheme of patient selection. Flow process chart showing how the register's database has been filtered. AB: asbestos bodies.

FIGURE 2

Time course of events. Illustration of birth, duration of exposure and time interval between tissue excisions/bronchoalveolar lavage (first fibre analysis from surgery, second fibre analysis from autopsy) in comparison to asbestos consumption in Germany. t: tons. Data source of asbestos consumption: [32].

FIGURE 3

Results of fibre analyses at surgery (first tissue excision) and autopsy (second tissue excision) in relation to time from 10 patients. From these 10 patients the asbestos fibre burden of the lung has been determined from tissue both times. Two patients with fibre analysis from a bronchoalveolar lavage are not considered here. Illustrated are the results of the highest asbestos body count in relation to time (a) and all asbestos body counts from one patient's lungs separately (b). The corresponding time interval is already illustrated in figure 2 and listed in table 1. It is easily seen in (b) that the counts from surgery are within the range of the counts from autopsy. For two patients the lower count from surgery tissue could be explained histologically (supplementary material). Patient 2 had tuberculosis in the first tissue and patient 6 had fibrosis with a multi-etiological clinical picture with an asbestos-dependent and an asbestos-independent component (see supplementary material for details).

FIGURE 4

Amphibole-fibre with the corresponding spectra obtained by energy-dispersive X-ray (EDX) analysis. a) Field emission scanning electron microscopic image from an edged fibre extracted from lung tissue of an asbestos exposed patient. The fibre is greater than 5 µm and thinner than 3 µm. 10 000-fold magnification. b) The EDX spectra of the fibre with magnesium (Mg), silicon (Si) and iron (Fe). The elemental composition and morphology of the fibre is typical for amphibole. The gold (Au) signal originates from the filter and should be ignored. c) Transmission electron microscopy image of an amphibole fibre with residual macrophage body and the corresponding EDX spectra (d). The copper (Cu) signal originates from the grid and should be ignored.

FIGURE 5

Chrysotile fibre with the corresponding spectra obtained by energy-dispersive X-ray analysis (EDX). a) Field emission scanning electron microscopic image from a markedly thin fibre extracted from lung tissue of an asbestos exposed patient. The fibre is more than 10 µm in length with a shell of ferruginous bodies. 6000-fold magnification. b) The EDX spectra of the denudated part of the asbestos body with magnesium (Mg), silicon (Si) and iron (Fe). The elemental composition and morphology of the fibre is typical for chrysotile. The gold (Au) signal originates from the filter and should be ignored. c) Transmission electron microscopy image of a chrysotile fibre and the corresponding EDX spectra (d).