Workplace exposure to tungsten carbide-cobalt (WC-Co) is the main route of contact for workers in the carbide industry. Workers are exposed to the dusts when handling the powders or grinding workpieces and may inhale particles or absorb them through the skin. Workplace exposure to tungsten carbide-cobalt is the main route of contact for workers in the carbide industry. Workers are exposed to the dusts when handling the powders or grinding workpieces and may inhale particles or absorb them through the skin. Coarser tungsten carbide-cobalt particles have been used in the carbide industry for many years, but the production and application of nanoparticles is relatively new. Extensive studies of microscale particles have been carried out in the past; only a few studies are available on nanoscale tungsten carbide-cobalt. Since workpieces made from nanoparticles are even stronger compared to those made from coarser particles, nanoparticles are increasingly being used.
From epidemiologic studies on hard metal workers the so called “hard-metal-disease” is known, which is characterised by lung fibrosis, asthma and lung cancer . However, this disease pattern only occurs, when workers are exposed to tungsten carbide-cobalt, not to tungsten carbide or cobalt alone. If exposed to only one of the compounds, no lung diseases were observed. The “hard-metal-lung” is an approved occupational disease in Germany, which very rarely occurs due to extensive work protection measures.
Besides the occurrence of lung diseases, a possible link of tungsten carbide-cobalt exposure with an increased rate of childhood leukaemia in Fallon (Nevada, USA) has been discussed, since the temporal occurrence of the diseases coincided well with an increase in airborne tungsten and cobalt levels . However, this potential link has been controversially discussed and viruses as alterniative cause for the enhanced leukaemia rate have been suggested.
To minimise exposure, suitable protective clothes like gloves and masks should be worn. For the users of tools made of tungsten carbide-cobalt an exposure to the particles is unlikely, since the sintered tools are extraordinary hard and wear-resistant. Hence, new release of particles during usage of drillers or others tolls is not relevant.
A mixture of tungsten carbide and cobalt, tungsten carbide-cobalt particles, exhibit a higher toxicity than cobalt alone. Cobalt is a compound of known human toxicity and a daily dose of 20 mg and above may induce severe health problems. Hence, the International Agency for Research on Cancer (IARC) classified cobalt alone as "possibly carcinogenic" to humans and the combination of tungsten carbide and cobalt, tungsten carbide-cobalt, as "probably carcinogenic" to humans. An mechanism called "contact-corrosion" between cobalt and tungsten carbide is assumed as a reason for this enhanced toxicity, inducing the formation of free radicals in the presence of oxygen, which in turn may damage cells of the body (mostly lung cells) . Alternative or additionally, particles may act as a "trojan horse" and increase the availability of cobalt in the cells.
In the small town of Fallon (Nevada, USA) human exposure by airborne tungsten carbide and Co particles has been reported. A hard metal facility located in the town or a close by military base (tungsten carbide-cobalt is also used for ammunition) have been discussed as potential sources for tungsten carbide-cobalt release . Modern hard metal facilities are equipped with filter systems which prevent particle release.
Studies Outside of Organisms
Many of the results described here on tungsten carbide-cobalt nanoparticles were obtained by the project INOS, a research project funded by the German Ministry of Education and Research (BMBF).
In in vitro assays, the enhanced toxicity of tungsten carbide-cobalt is marked by a decrease in metabolic activity of cells, damage of the cell membrane and in some studies also with DNA damage . In a study on various human cell lines originating from lung, liver, intestine and skin, nano-sized tungsten carbide-cobalt showed similar results, but cells differed in their sensitivity.
Which genes are influenced by tungsten carbide-cobalt particles was investigated on human skin cells. Such genes are able to unravel which functions of an organism may be influenced by particle uptake. The majority of influenced genes can be associated to cobalt exposure, and the observed effects were all known cobalt-effects; no new mechanisms of cobalt were found .
- Agency for toxic substances and disease registry (ASTDR). ToxFAQsTM for Tungsten.
- Agency for toxic substances and disease registry (ASTDR). ToxFAQsTM for Cobalt.
- International Agency for Research on Cancer (IARC) (2006). Cobalt in Hard Metals and Cobalt Sulfate, Gallium Arsenide, Indium Phosphide and Vanadium Pentoxide. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Lyon / France, Volume 86. ISBN 9789283212867