Department of Health and Human Services Identifies Tungsten Carbide-cobalt as Carcinogen
The complete list and report is available at ntp.niehs.nih.gov/go/roc12 including the 180 page background document and the 6 page substance profile on the reasoning behind classification of WC-Co. In its study of cobalt-tungsten carbide in both powder and sintered form, the Report covers both limited epidemiological evidence of carcogenicity from studies in humans, and also some supporting evidence from studies on mechanisms of carcinogenesis for WC-Co. It was stated in the report that whilst the reasons for cobalt–tungsten carbide causing cancer have not been fully elucidated, it has been shown that (1) cobalt–tungsten carbide releases cobalt ions, (2) cobalt ions affect biochemical pathways related to carcinogenicity, (3) cobalt compounds are carcinogenic in experimental animals, (4) cobalt–tungsten carbide increases the production of reactive oxygen species (ROS) and causes greater cytotoxic, toxic, and genotoxic effects than does cobalt alone, (5) cobalt–tungsten carbide causes key events related to carcinogenesis, including genotoxicity, cytotoxicity, inflammation, and apoptosis (programmed cell death), and (6) the oxidative stress response resulting from in-creased ROS production may play a role in these key events and may also interfere with cells’ ability to repair damage caused by cobalt–tungsten carbide. The combination of the effects from cobalt ions and the oxidative stress response from ROS production were said to provide plausible modes of action for the carcinogenicity of cobalt–tungsten carbide. These findings are reportedly disputed by the various trade bodies representing the companies involved in WC-Co production. The report also gives details on the major sources of exposure to WC-Co powders and sintered WC-Co materials – which are said to be mainly occupational in the manufacture of products from powder. Information on exposure from end-use of sintered hardmetal tools is said to be limited, and exposure therefore appears to be minimal (07/2011).