Cobalt

Cobalt is a relatively rare element of the Earth's crust, essential to mammals in the form of cobalamin (vitamin B12). In humans, the dietary intake of cobalt varies between 5 and 50 μg/day, most of it in the inorganic form. Vitamin B12 represents only a small fraction of the oral Co intake. The oral bioavailability of inorganic cobalt compounds varies between 5% and 45% according to their respective water solubility. In occupational settings, workers can be exposed by inhalation to mainly inorganic cobalt compounds. The absorption rate of inhaled cobalt also varies with the species under consideration. Cobalt does not accumulate in the organism and is rapidly excreted, mainly in the urine. The concentration of cobalt in urine or in blood can be used as a biomarker of recent exposure to soluble cobalt species. Co 2+ ions are genotoxic, and several forms of cobalt are carcinogenic in experimental animals. Upon inhalation exposure, the respiratory system is the main target organ of cobalt in humans (asthma, fibrosing alveolitis). The risk of fibrosing alveolitis (hard metal disease) and lung cancer is specific of the hard metal industry, where workers are exposed to cobalt metal mixed with tungsten carbide particles. Other target organs include the erythropoietic system, the myocardium, the thyroid gland, and the nervous system. In patients with cobalt alloy implants, especially metal-on-metal hip prostheses, endogenous exposure to cobalt can result in local and/or systemic toxicity. The reproductive toxicity of cobalt compounds is not well documented.