Exposure assessment in the hard metal manufacturing industry with special regard to tungsten and its compounds

Abstract

Objectives-To assess the exposure to tungsten, cobalt, and nickel in a plant producing hard metals. The main components of hard metals are tungsten carbide and cobalt metal. According to recent studies, these two components may be responsible for both fibrogenic and carcinogenic eVects. Methods-87 workers were investigated (86 male, one female) with a median age of 42 (range 22-58) and a mean duration of exposure of 13 years (range 1-27 years). Stationary and personal air sampling, and biological monitoring were carried out. Hard metals are widely used in diVerent industries, mainly because of their resistance to corrosion, temperature, and wear. The most important use is as a component of alloys (cemented carbides). These materials were developed decades ago with the sintering process. The main components are tungsten carbide (about 90%) and cobalt metal (about 10%). Also, small amounts of nickel may be added. Results-Ambient1 After occupational exposure to hard metal dust adverse eVects on the upper and lower respiratory tract and on the skin have been reported. Although hard metal asthma and eVects on the skin are considered to be immunologically mediated reactions, the pathogenic model for interstitial lung disease (hard metal dust fibrosis) is still unclear.2 Several studies in the hard metal producing and processing industry suggested that cobalt is the main aetiological agent for the development of interstitial fibrosis. As a consequence of these studies preventive measures were initiated to reduce exposure to cobalt.3-5 These measures were very successful, especially the use of a metal working fluid containing a complex binder which generated a cobalt complex that reduced the bioavailability of cobalt. According to the results of biological monitoring, this measure has led especially in hard metal grinders to a significant reduction in exposure to cobalt. 6Several in vitro and animal experiments carried out over the past few years suggest that tungsten carbide also plays an important part in the pathogenesis of hard metal dust fibrosis as a result of a synergistic eVect. In vitro experiments have shown that the toxicity of hard metal dusts is determined by the physicochemical interaction of cobalt and tungsten carbide. Animal experiments have shown that the incidence of fibrotic lung changes is higher when a mixture of cobalt and tungsten carbide is administered, whereas cobalt and tungsten carbide alone lead to only low fibrogenic activity. In the United States and in some European countries the ambient threshold limit values are in the range of 1 mg/m 3 for soluble tungsten compounds and 5 mg/m 3 for insoluble ones. The aim of these limits is to prevent eVects on the central nervous system occurring after exposure to soluble compounds and irritative eVects on the respiratory tract with insoluble compounds. In Germany a maximum concentration at the workplace (MAK) value of 1 mg/m 3 for soluble tungsten compounds and 5 mg/m 3 for insoluble compounds has been set. 9 To date there are no biological...

Biological monitoring of dermal and air exposure to cobalt at a Swedish hard metal production plant: does dermal exposure contribute to uptake?

“…Only 1% of our cobalt blood samples exceeded the BEI (17 nmol/l). As compared with other studies reporting cobalt air exposure concentrations of 0.001–6.4 mg/m 3 15 and 0.0009–0.12 mg/m 3 32, our cobalt levels (0.00003–0.056 mg/m 3 ) seem to be very low, which is most likely attritubale to the production techniques used. Our statistical analyses showed a significant correlation between cobalt in blood and cobalt air levels, which has also previously been shown 26, 27, 33.…”

Nanotoxicity: emerging concerns regarding nanomaterial safety and occupational hard metal (WC-Co) nanoparticle exposure

“…[47][48][49] Additionally, cobalt content can vary, depending on the application, and the dusts generated may not have uniform composition between multiple industrial sites. 50 More importantly, the combination of WC-Co is more toxic than Co, W, or WC particles alone (see section entitled Defining hard metal (WC-Co) toxicity: in vitro and in vivo studies). Therefore, understanding the toxic effects of hard metal WC-Co particles is crucial in order to develop occupational exposure guidelines.…”

Biological Monitoring of Exposure: Trends and Key Developments

“…ACGIH 3) set up two BEIs for cobalt: 15 µg/l for urine and 1 µg/l for blood samples collected at the end of the shift at the end of the workweek. The reference value for urinary cobalt is 1.5 µg/l 125) . The EKA value for nickel is 15 µg/l urine for 0.10 mg/m 3 nickel in air 34) .…”

“…The EKA value for nickel is 15 µg/l urine for 0.10 mg/m 3 nickel in air 34) . The reference value for urinary nickel is 2.2 µg/l 125) . Kraus et al 125) attempted to evaluate the excretion of tungsten in the urine of workers exposed to different tungsten compounds in a plant producing hard metals.…”