Hard Metal Disease

Abstract

In Great Britain there have been no published reports of respiratory disease occurring amongst workers in the hard metal (tungsten carbide) industry. In this paper the clinical and radiological findings in six cases and the pathological findings in one are described. In two cases physiological studies indicated mild alveolar diffusion defects. Histological examination in a fatal case revealed diffuse pulmonary interstitial fibrosis with marked peribronchial and perivascular fibrosis and bronchial epithelial hyperplasia and metaplasia. Radiological surveys revealed the sporadic occurrence and low incidence of the disease. The alterations in respiratory mechanics which occurred in two workers following a day's exposure to dust are described. Airborne dust concentrations are given.The industrial process is outlined and the literature is reviewed. The toxicity of the metals is discussed, and our findings are compared with those reported from Europe and the United States.We are of the opinion that the changes which we would describe as hard metal disease are caused by the inhalation of dust at work and that the component responsible may be cobalt.Hard metal is manufactured by a process of powder metallurgy from tungsten and carbon with cobalt as a binder. The industry, starting in Germany after the first world war, has greatly increased in size. The extremely hard product (90 to 95 % the hardness of diamond) is used for the cutting edges of tools, rock drills, broaches, and dies. It is also used for radiotherapy screens and armaments.The process of manufacture involves the production of tungsten metal powder and cobalt powder from their respective oxides or salts. The tungsten metal powder is mixed with carbon and heated in an atmosphere of hydrogen to form tungsten carbide. Titanium carbide is added in some grades and is similarly formed. Small amounts of tantalum carbide and vanadium carbide may be incorporated in particular grades.The percentage by weight of tungsten carbide varies from 80 to 90, of titanium carbide 8 to 18 and of cobalt 5 to 25. More than three-quarters of production is of grades containing between 6 % and 9 % of cobalt.Carbides and cobalt are mixed wet in a ball-mill and dried. The dried powder is pressed to the required shape combined with wax using a solvent such as trichlorethylene, which is then driven off by heat in an oven in an atmosphere of hydrogen (presintering). After shaping, the product is heated again in an atmosphere of hydrogen (sintering). It is then ground, wet or dry, with diamond and carborundum wheels to its final shape.

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

“…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).…”

“…Historically, exposure assessments and epidemiological studies of hard-metal-induced adverse health effects have focused on measurements of total airborne cobalt aerosol mass concentration using 37-mm cassette samplers or other sampling heads without regard to particle size (Fairhall et al, 1947;Bech et al, 1962;Sprince et al, 1984Sprince et al, , 1988MeyerBisch et al, 1989;Sesana et al, 1994;Teschke et al, 1995;Kumagai et al, 1996). A few historical studies have investigated combined airborne exposures to cobalt and tungsten among CTC workers (Lichtenstein et al, 1975;Koponen et al, 1981Koponen et al, , 1982Kraus et al, 2001); however, these studies also used total mass concentration exposure estimates.…”

Role of cobalt, iron, lead, manganese, mercury, platinum, selenium, and titanium in carcinogenesis.

“…Although heavy occupational exposure has occurred to cobalt containing dusts, there have been very few reports of cancer developing in these workers. A single case of carcinoma of the bronchus in a worker with hard metal disease was reported as the first recorded case (12). In epidemiological surveys in nickel extraction plants in the USSR, an increased mortality from lung cancer was found in the cobalt recovery shops as well as in the nickel processing departments.…”

Role of metals in carcinogenesis. Problems of epidemiological evidence

“…Pulmonary fibrosis has been reported in workers from the hard metal industry (70,71). Despite these excessive exposures, there have been few reports of cancer mortality occurring in these workers.…”