Abstract
Widespread exposure to cobalt metal dust occurs occupationally through the production of alloys, in the manufacture of cobalt salts, and in nuclear technology. It is an effective catalyst for many organic reactions, particularly in hydrotreating catalysts, which have molybdenum and cobalt sulfides as active components. Concerns have been raised about the occurrence of occupational disease, i.e. hard metal disease, associated with exposure to cobalt and its compounds, including cobalt metal-tungsten carbide. Cobalt metal is also widely dispersed in low concentrations in the environment and the general population may be exposed by breathing air, drinking water, or skin contact with soil, water, cobalt alloys, or other substances that contain cobalt. In addition, cobalt metal is an essential trace element as a component of cyanocobalamin (vitamin B12). Cobalt metal dust was nominated for toxicology and carcinogenesis studies by the United Auto Workers and the Cobalt Development Institute based on the widespread occupational exposure and limited availability of data on chronic toxicity and carcinogenic potential of inhaled insoluble cobalt compounds, particularly cobalt metal dust. Inhalation was selected as the route of exposure because this is the most common route of exposure to cobalt metal dust in occupational settings in humans. Male and female F344/N or F344/NTac rats and B6C3F1/N mice were exposed to cobalt metal by inhalation for 2 weeks, 3 months, or 2 years (F344/NTac rats). In addition, genetic toxicology studies were conducted in Salmonella typhimurium, Escherichia coli, and mouse peripheral blood erythrocytes. (Abstract Abridged).