Respiratory impairment due to asbestos exposure in brake-lining workers

Risk of asbestosis, mesothelioma, other lung disease or death among motor vehicle mechanics: a 45-year Danish cohort study

INTRODUCTION

The risk of asbestosis, malignant mesothelioma and lung cancer among motor vehicle mechanics is of concern because of potential exposure to chrysotile asbestos during brake, clutch and gasket repair and maintenance. Asbestos has also been used in insulation and exhaust systems.

METHODS

We examined the long-term risk of incident mesothelioma, lung cancer, asbestosis and other lung diseases and mortality due to mesothelioma, lung cancer, asbestosis and other lung diseases in a nationwide cohort of all men registered as motor vehicle mechanics since 1970 in Denmark. This was compared with the corresponding risk in a cohort of male workers matched 10:1 by age and calendar year, with similar socioeconomic status (instrument makers, dairymen, upholsterers, glaziers, butchers, bakers, drivers, farmers and workers in the food industry, trade or public services).

RESULTS

Our study included 138 559 motor vehicle mechanics (median age 24 years; median follow-up 20 years (maximum 45 years)) and 1 385 590 comparison workers (median age 25 years; median follow-up 19 years (maximum 45 years)). Compared with other workers, vehicle mechanics had a lower risk of morbidity due to mesothelioma/pleural cancer (n=47 cases) (age-adjusted and calendar-year-adjusted HR=0.74 (95% CI 0.55 to 0.99)), a slightly increased risk of lung cancer (HR=1.09 (95% CI 1.03 to 1.14)), increased risk of asbestosis (HR=1.50 (95% CI 1.10 to 2.03)) and a chronic obstructive pulmonary disease risk close to unity (HR=1.02 (95% CI 0.99 to 1.05)). Corresponding HRs for mortality were 0.86 (95% CI 0.64 to 1.15) for mesothelioma/pleural cancer, 1.06 (95% CI 1.01 to 1.12) for lung cancer, 1.79 (95% CI 1.10 to 2.92) for asbestosis, 1.06 (95% CI 0.86 to 1.30) for other lung diseases caused by external agents and 1.00 (95% CI 0.98 to 1.01) for death due to all causes.

CONCLUSIONS

We found that the risk of asbestosis was increased among vehicle mechanics. The risk of malignant mesothelioma/pleural cancers was not increased among vehicle mechanics.

Theoretical approach to the hit probability of lung-cancer-sensitive epithelial cells by mineral fibers with various aspect ratios

BACKGROUND

  Inhalation of fibers may lead to the damage and, as a further consequence, to the malignant transformation of specific (most of all non-ciliated) cells of the bronchial and bronchiolar airway epithelium. In order to accurately estimate the cancer risk induced by inhaled fibers, hit probabilities of non-ciliated (secretory) cells by mineral fibers (asbestos and chrysotile) were computed.

METHODS

  Besides the use of a stochastic lung geometry and a particle transport/deposition model being based upon the random-walk algorithm, histological data of cell distributions in the human lungs were applied for the theoretical calculations. Diameters of computer-generated fibers ranged from 0.1 µm to 10 µm, whilst two values (3 and 100) were selected for the aspect ratios (ratios of fiber length to fiber diameter), thereby simulating the behavior of short and very long fibrous particles.

RESULTS

  According to the modeling results, the highest regional hit probabilities (up to 10%) are available for fibers with a diameter of 1.0 µm, whereby cells of the bronchiolar compartment represent a preferential target of these particles. For fibers with a diameter of 0.1 µm, bronchiolar hit probabilities reach 2-3%, whereas fibers with a diameter of 10 µm penetrate to the peripheral lung parts with only low amounts (<0.1%). A change of the inhalation conditions from sitting to light-work breathing enhances the extrathoracic and bronchial filtering of large particles (diameter ≥1 µm), whilst penetration of small particles towards distal lung airways is subject to a reinforcement. Further refinement of hit probabilities by considering single airway generations results in the circumstance that fibers with diameters ≤1.0 µm preferably collide with cancer-sensitive cells of airway generations 12-15. In contrast, fibers with a diameter of 10 µm mainly represent a hazard for cancer-sensitive cells being located in the uppermost airways. A change of breathing conditions both supports the effect of short fibers and enhances the filtering of long ones.

CONCLUSION

  Based upon the results of this contribution it can be concluded that highest cancer risk is generated by the inhalation of mineral fibers with diameters ≤1.0 µm, whereby fiber length has to be classified as a parameter with lower importance.

Personal exposure to asbestos and respiratory health of heavy vehicle brake mechanics

Asbestos brake linings and blocks are currently used in heavy vehicle brake repair shops (BRSs) in Bogotá, Colombia. Some brake products are sold detached from their supports and without holes, requiring manipulation before installation. The aim of this study was to assess asbestos exposures and conduct a preliminary evaluation of respiratory health in workers of heavy vehicles in BRSs. To estimate asbestos exposures, personal and area samples were collected in two heavy vehicle BRSs. Each shop was sampled during six consecutive days for the entire work shift. Personal samples were collected on 10 workers including riveters, brake mechanics, and administrative staff. Among workers sampled, riveters had the highest phase contrast microscopy equivalent (PCME) asbestos concentrations, with 8-h time-weighted average (TWA) personal exposures ranging between 0.003 and 0.157 f/cm(3). Respiratory health evaluations were performed on the 10 workers sampled. Three workers (30%) had circumscribed pleural thickening (pleural plaques), with calcifications in two of them. This finding is strongly suggestive of asbestos exposure. The results of this study provide preliminary evidence that workers in heavy vehicle BRSs could be at excessive risk of developing asbestos-related diseases.

Chrysotile asbestos exposure in the manufacturing of thermal insulating boards

Exposure to asbestos fibers has been extensively studied in milling, mining of asbestos fibers, and in industries manufacturing asbestos-cement sheets, pipes, etc. However, very few studies have been reported in asbestos textiles, brake lining workers, and insulation products. In the present investigation, chrysotile exposure monitoring was carried out in a small thermal insulating boards manufacturing facility. Twenty-eight samples were analyzed from various locations like feeding of raw materials, weighing, pressing, machine grinding, and hand finishing of final products. Twenty-five percent of the samples were found to be above ACGIH TLV of 0.1 fibers per milliliter. However, mean fiber concentrations were found to be lower than 0.1 fibers per milliliter, except for the process of feeding of raw materials where the mean fiber concentration was 0.1087+/-0.0631 fibers per milliliter.