Respiratory hazards in hard metal workers: a cross sectional study.

Abstract

A cross sectional study was conducted on 513 employees at three hard metal plants: 425 exposed workers (351 men, 74 women) and 88 controls (69 men, 19 women). Cough and sputum were more frequent in workers engaged in "soft powder" and presintering workshops compared with controls (12-5% and 16X5% v 3 5%). Spirometric abnormalities were more frequent among women in sintering and finishing workshops compared with control women (56-8% v 23-8%) and abnormalities of carbon monoxide test were more frequent in exposed groups than in controls; this difference was more pronounced in women (31[4% v 5-6%) than in men (18-5% v 13%). No significant correlation was observed between duration ofexposure and age adjusted lung function tests. Slight abnormalities of chest radiographs (0/1, 1/1 according to ILO classification) were more frequent in exposed men than controls (12-8% v 1-9%) and mostly in soft powder workers. In subjects with abnormal chest radiographs FVC, FEV1 and carbon monoxide indices (fractional uptake of CO or CO transfer index or both) were lower compared with those with normal chest radiographs. Although relatively mild, the clinical, radiological, and functional abnormalities uncovered call for a regular supervision of workers exposed to hard metal dust.The industrial use of hard metal tools began in Germany in 1922. Owing to their hardness and resistance to wear and high temperatures they are used to make cutting tools, drill tips, and armament components. Their qualities are due mainly to tungsten carbide which, with cobalt (Co), constitutes the essential part of this alloy. They are produced according to the powder metallurgy technique in specialised factories in relatively large quantities (in France 300 tons a year at present).About 20 years later, hard metals were suspected of being responsible for bronchopulmonary disorders, first in Germany, then in the other industrialised countries. Despite a certain heterogeneity of the symptoms and signs, the condition progresses towards a diffuse pulmonary fibrosis and leads to severe respiratory insufficiency. Except for sporadic case reports, the frequency and intensity of clinical and functional respiratory disorders which can be observed among a group of workers exposed to hard metal dust are not well known. Thus a cross sectional survey was conducted among a group of 425 workers exposed to hard metal dusts and of 88 controls who worked in three factories.

Characteristics of Dusts Encountered during the Production of Cemented Tungsten Carbides

“…If Co particles in the presence of WC particles cause HMD via generation of ROS [4][5][6] , then our characterization of airborne particles may help to explain the inconsistent findings of epidemiological studies, e.g., between Meyer-Bisch et al 1) and Sprince et al 2) ; only Sprince et al 2) showed a higher risk in the later stages of the CTC manufacturing process. We observed that airborne particles potentially available for inhalation in spray drying and all subsequent work areas were a mixture of elemental tungsten and elemental Co particles and/or multi-constituent W/Co particles (ostensibly WC/Co particles, but the relative carbon contribution of the collection substrate and metal carbides is unknown).…”

“…Occupational asthma has been reported among employees who handle feedstock powders and among sinterers and grinders 1,3) . If exposure to Co, either alone or in the presence of WC, is sufficient to cause OA 3,8) , then our identification of Co in aerosols generated in the powder mixing and all downstream work areas may help to understand these epidemiological observations.…”

Characterization of exposures among cemented tungsten carbide workers. Part I: Size-fractionated exposures to airborne cobalt and tungsten particles

“…If occupational asthma is caused by exposure to particles with aerodynamic sizes capable of depositing in the tracheobronchial, bronchial, and alveolar regions of the lung and with chemical composition that contains cobalt (alone or in the presence of tungsten carbide), then our air-monitoring results in conjunction with in vitro dissolution test results may help to explain why cases of occupational asthma are observed among workers who handle pre-sintered hard metal powders and grind and manipulate sintered CTC parts (Davison et al, 1983;Sprince et al 1988;Meyer-Bisch et al, 1989;Shirakawa et al, 1989;Kusaka et al, 1996) and among diamond polishers whose only exposure is to cobalt (Gheysens et al, 1985). Consistent with these studies, we observed exposures to cobalt in all work areas spanning powder production to handling finished product parts.…”

“…If HMD and lung cancer are caused by alveolar deposition of respirable-size particles that contain cobalt associated with tungsten, then our air monitoring exposure data may help to understand lung cancer and explain why HMD is observed among workers exposed to pre-sintered material alone (Meyer-Bisch et al, 1989), post-sintered CTC material alone (Sprince et al, 1988), and both pre-and post-sintered materials (Bech et al, 1962;Coates and Watson, 1971;Sjo¨gren et al, 1980;Davison et al, 1983;Sprince et al, 1984;Cugell et al, 1990;Figueroa et al, 1992;Fischbein et al, 1992). Consistent with these studies, we observed that workers were co-exposed to respirable cobalt-and tungstencontaining particles in all work areas (see Tables 4 and 5) spanning powder production (pre-sintered materials) through handling final product parts (post-sintered materials).…”

“…Workplace studies have identified cases of occupational asthma among CTC workers exposed to both cobalt and tungsten (Davison et al, 1983;Sprince et al 1988;Meyer-Bisch et al, 1989;Shirakawa et al, 1989;Kusaka et al, 1996) and diamond polishers exposed to cobalt alone (Gheysens et al, 1985). Cases of HMD have been reported among workers in all phases of CTC production (Bech et al, 1962;Coates and Watson, 1971;Sjo¨gren et al, 1980;Davison et al, 1983;Sprince et al, 1984Sprince et al, , 1988Meyer-Bisch et al, 1989;Cugell et al, 1990;Figueroa et al, 1992;Fischbein et al, 1992), which may be due to exposures to tungsten carbide particles in association with cobalt particles (Lasfargues et al, 1992(Lasfargues et al, , 1995Lison and Lauwerys, 1990, 1994, 1995Lison et al, , 1996. In humans, excess lung cancer has been observed among hard metal workers exposed to CTC dusts (Lasfargues et al, 1994;Moulin et al, 1998;Wild et al, 2000;Lison et al, 2001), but not among cobalt production workers exposed to cobalt alone (Moulin et al, 1993).…”