Clearance of anthophyllite fibers from the rat lung and the formation of asbestos bodies

High frequency and severity of pleural changes in former workers exposed to anthophyllite associated with other contaminating amphibole asbestos in Brazil

OBJECTIVE

To evaluate the frequency and severity of pleuropulmonary alterations in anthophyllite-exposed former workers in Itapira, São Paulo, Brazil. The amphibole anthophyllite, a magnesium-iron silicate, had its mining, marketing, and use forbidden in Brazil in 1995.

METHODS

Former workers were followed from 1999 to 2011. All completed chest X-ray interpreted using the International Labour Office (ILO) classification. High-resolution computed tomography was used at the final evaluation. Spirometry assessed forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), and FEV1/FVC throughout the follow-up period. Samples from the mined ore were analyzed by X-ray diffraction (XRD) and scanning electron microscopy coupled to energy dispersive spectroscopy (SEM-EDS).

RESULTS

XRD and SEM-EDS confirmed the presence in ore of anthophyllite at a concentration of 75%, in addition to tremolite and other amphiboles in lower concentrations. Twenty-eight subjects were evaluated. Median time of exposure was 3 years (minimum = 1; maximum  = 18; interquartile interval = 1-4). Twenty cases of pleural abnormalities were diagnosed in 26 evaluated (77%). The average latency time was 25.6 ± 7.4 years. Two individuals (7.7%) showed progressive worsening of diffuse pleural thickening (DPT) and exhibited an annual FVC decrease of 85 mL and 150 mL, respectively.

CONCLUSION

This small sample showed a very high index of nonmalignant pleural abnormalities in anthophyllite-exposed workers compared with workers exposed to other kinds of fibers. Rapidly progressive DPT, defined by the severity of pleural compromise, was possibly secondary to the presence of other amphibole types in the inhaled dust. No significant loss of FVC was found in the studied group as a whole. No cases of asbestosis, lung carcinoma, and mesothelioma were diagnosed in this cohort.

Investigation on the biodurability of chemically different stone wool fibres

The biodurability is one of the essential factors for a carcinogenic potential of mineral fibres. The in vivo solubility of commercial fibre products can be influenced by modifications of the chemical composition. Two types of experimental stone wool samples with new chemical composition were compared to a commercial stone wool sample. Sized fractions of these samples with median lengths of 7.1, 9.3 and 6.7 microns, respectively, and median diameters of 0.76, 1.02 and 0.63 microns, respectively, were intratracheally instilled into female Wistar rats with a single dose of 2 mg in 0.3 ml. 5 animals per group were sacrificed after 2 days, 1, 3, 6, 12 and 18 months. After low-temperature ashing of the lungs about 1,000 fibres per group and sacrifice date were analysed in SEM for length and diameter. The number of fibres in the total lung was calculated. An analysis of fibre number of different length and diameter fractions was used to estimate whether dissolution, breakage or mechanical clearance is responsible for the elimination of fibres from the lung. Results indicate that the breakage of fibres with length above 20 microns and the dissolution of fibres was faster in the experimental stone wool samples compared to the commercial sample.

Investigation on the durability of man-made vitreous fibers in rat lungs

Two types of sized stonewool with median lengths of 6.7 and 10.1 microns and median diameters of 0.63 and 0.85 microns, and crocidolite with fibers of median length of 4.8 microns and median diameter of 0.18 microns were instilled intratracheally into female Wistar rats. A single dose of 2 mg in 0.3 ml saline was used for the stonewool samples and 0.1 mg in 0.3 ml saline for crocidolite. The evenness of distribution of fibers in the lung was checked by scanning electron microscopy (SEM). Five animals per group were sacrificed after 2 days, 1, 3, 6, and 12 months. After low-temperature ashing of the lungs about 200 fibers per animal were analyzed by SEM for length and diameter. The number and mass of fibers in the total lung were calculated. For the stonewool samples the decrease in the number of fibers in the lung ash followed approximately first order kinetics resulting in half-times of 90 and 120 days. The analysis of fiber number and diameter of different length fractions was used to estimate the contribution of three processes of fiber elimination: transport by macrophages for short fibers, breakage of fibers, and dissolution of fibers. (The process of transport by macrophages was found fastest for fibers with length < 2.5 microns). For the elimination of critical fibers with length > 5 microns, the breakage and dissolution were the most important processes. The breakage of fibers was predominant for one of the stonewool samples. The preferential type of the mechanism of fiber elimination is dependent on chemical composition and size distribution.

Role of asbestos and other fibres in the development of diffuse malignant mesothelioma

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Pathophysiologic correlations in asbestos-induced airway disease in the guinea pig

To determine whether asbestos-induced changes in the structure of the walls of small airways might be associated with abnormalities of pulmonary function, guinea pigs were given 10 mg of amosite asbestos (test group) or saline (control group) by intratracheal instillation. Pulmonary function tests performed 6 months later revealed significant increases in FRC, RV, and TLC in the test group. Measurement of airway wall thickness showed that both membranous and respiratory bronchioles were significantly thickened in the test group; this group also had airways of smaller internal diameter than the controls. Analysis for lung collagen content as hydroxyproline showed a 50% increase in the asbestos exposed animals. There was, however, only minimal and very focal interstitial fibrosis (asbestosis) in the lung parenchyma. Analysis of fiber size indicated that the fibers obtained by digestion of the tissue or from the lavage fluid were significantly longer and wider than those in the original asbestos sample; however, the tissue contained considerably larger fibers than the lavage fluid. We conclude that: Asbestos can produce airway fibrosis and narrowing causing air trapping on pulmonary function examination; this process occurs in the absence of significant interstitial fibrosis of the parenchyma (asbestosis), implying that abnormalities of pulmonary function which are consistent with airflow obstruction in asbestos exposed animals can be caused by pathologic changes in the small airways alone; long asbestos fibers are preferentially retained in the lung, and the longest fibers appear to be in a compartment inaccessible to lavage, presumably, in this model, in airway walls. Enhanced penetration of long fibers into tissue may be one reason why long fibers are more pathogenic than short ones.

Changes in numbers and dimensions of chrysotile asbestos fibers in lungs of rats following short-term exposure

Previous studies from this laboratory have demonstrated that in rats exposed briefly to aerosolized chrysotile asbestos, fibers initially deposited in the distal lung impact primarily at bifurcations of alveolar ducts. Subsequently, there is a progressive decrease in the numbers of fibers seen by scanning electron microscopy at the bifurcations with increasing time from initial exposure. The purpose of the present study was to assess the number and dimensions of fibers deposited in the lungs of these rats and to determine how these parameters changed at various intervals after the termination of exposure. This was accomplished using a sodium hypochlorite digestion-concentration technique to recover the fibers on a membrane filter. The numbers and dimensions of the fibers were then assessed using scanning electron microscopy. Utilizing these data, the mass of asbestos retained in the lung was calculated with a newly developed formula. Twenty-three percent of the respirable fraction was deposited in the lungs, and 19% of this amount was still present 31 days after exposure. Over the 31 days, there was a progressive increase (p less than 0.05) in mean fiber length and a significant decrease (p less than 0.05) in the diameter of the population of fibers retained in the lung. Such data should prove useful in attempting to understand the progressive pathogenesis of asbestos-induced interstitial lung disease, which seems to be related, at least in part, to the dimensions of the inhaled fibers.

Asbestos bodies in a bile duct cancer after occupational exposure

A case of asbestosis after 5 years of occupational asbestos exposure is presented. At the postmortem examination, cholelithiasis and a cancer developing from the cystic duct were found and identified histologically as a squamous cell carcinoma. After digesting the tumor tissue, short asbestos bodies and fragments could be identified having a similar shape as those observed in the lung. The possible role of asbestos in the carcinogenesis of the observed bile duct cancer is proposed. The digestive examination of all malignant tumors of any origin after an asbestos exposure is suggested for the identification of the possible presence of ingested asbestos fibers, and to obtain further comprehensive human pathological data.

Concentrations and characteristics of amphibole fibres in the lungs of workers exposed to crocidolite in the British gas-mask factories, and elsewhere, during the second world war

Concentrations and length distributions of uncoated and coated amphibole fibres in the lungs of 27 workers at the Leyland, Nottingham, and Blackburn gas-mask factories were measured after death with the light microscope using the membrane filter technique. Measurements were also made on a worker exposed to crocidolite at the Chemical Defence Experimental Establishment, Porton, and on three miners from the Wittenoom mine in Western Australia where the crocidolite used in the manufacture of military respirators is reputed to have originated. In selected cases, fibre concentrations and dimensions were also measured with the electron microscope. All but two subjects died with a mesothelial tumour. Fibre concentrations ranged from 7 x 10(4) to almost 10(9) fibres/g dry weight. There appeared to be no relation between latent period and fibre concentration. The significance of the wide range of fibre concentrations which was associated with the development of mesothelial tumours is discussed and also the relation between the relative frequency and dimensions of uncoated and coated fibres.