Cobalt is absorbed though the lungs, gastrointestinal tract, and skin. Since it is a component of the vitamin B12 (cyanocobalamin), it is distributed to most tissues of the body. It is transported in the blood, often bound to albumin, with the highest levels being found in the liver and kidney. Cobalt is excreted mainly in the urine and faeces. (L29)
IDENTIFICATION: Cobalt sulfate is a red powder. It is used in storage batteries; in cobalt-electroplating baths; as drier for lithographic inks, and varnishes; in ceramics, enamels, and glazes to prevent discoloring; in cobalt pigments for decorating porcelain. HUMAN EXPOSURE AND TOXICITY: Cardiomyopathy has been observed in individuals who consume large quantities of beer where cobalt sulfate was added as a foam stabilizer. Repeated or prolonged contact may cause skin sensitization. Repeated or prolonged inhalation exposure may cause asthma. The substance may have effects on the heart, thyroid and bone marrow, resulting in cardiomyopathy, goiter and polycythemia. ANIMAL STUDIES: Rats and mice exposed short term to cobalt sulfate by inhalation exhibited necrosis and inflammation of the respiratory tract epithelium. Rats developed thymus necrosis and testicular atrophy. Rats exposed for 2-3 months to cobalt sulfate in the diet for 24 weeks had significant reductions in heart enzyme activity levels. Rats and mice were exposed to cobalt sulfate heptahydrate by inhalation 6 hr/day, 5 days/week for 13 weeks developed adverse effects throughout the respiratory system. At higher concentrations both rats and mice developed squamous metaplasia of the larynx. At high doses, rats developed chronic inflammation of the larynx along with more severe effects in the nose, larynx and lung. Mice exhibited acute inflammation of the nose, larynx and lungs. Mice also exhibited hyperplasia of the mediastinal lymph nodes and testicular atrophy and increased esterous cycle in females. Both rats and mice exhibited histiocytic infiltrates of the lung at similar exposure levels. Sperm motility was decreased in mice and mice that received high dosages developed increased abnormal sperm and decreased testis and epididymal weights. Rats exposed for 2-3 months of copper sulfate in the diet exhibited increased heart weight and degenerative heart lesions. Rats exposed to cobalt sulfate in their diet for 24 weeks experienced significant reductions in cardiac enzyme activity levels, such as manganese superoxide dismutase, cytochrome c oxidase, NADH, cytochrome reductase and a reduction in mitochondrial ATP production. Groups of 50 male and 50 female rats exposed to copper sulfate heptahydrate by inhalation for 6 hr/day, 5 days/week for 105 weeks. Mean body weights and survival were unaffected by treatment. Rats exhibited a concentration increase in the incidence of benign and malignant alveolar/bronchiolar neoplasms in male and female rats and benign and malignant pheochromocytomas in female rats. The carcinogenicity of cobalt sulfate heptahydrate by inhalation was studied in mice. Also evaluated was the K-ras mutation frequency and spectra in lung tumors. A higher G-T transversions was detected in codon 12 of K-ras compared to chamber controls.
Cobalt is believed to exhibit its toxicity through a oxidant-based and free radical-based processes. It produces oxygen radicals and may be oxidized to ionic cobalt, causing increased lipid peroxidation, DNA damage, and inducing certain enzymes that lead to cell apoptosis. Cobalt has also been shown to block inorganic calcium channels, possibly impairing neurotransmission. Cobalt can also chelate lipoic acids, impairing oxidation of pyruvate or fatty acids. In addition, cobalt may inhibit DNA repair by interacting with zinc finger DNA repair proteins, and has also been shown to inhibit heme synthesis and glucose metabolism. Cobalt may activate specific helper T-lymphocyte cells and interact directly with immunologic proteins, such as antibodies (IgA and IgE) or Fc receptors, resulting in immunosensitization. (L29)
This listing of the class of cobalt and cobalt compounds that release cobalt ions in vivo supersedes the previous listing of cobalt sulfate in the Report on Carcinogens. The compound cobalt sulfate was first listed in the Eleventh Report on Carcinogens in 2004 as reasonably anticipated to be a human carcinogen based on sufficient evidence of carcinogenicity in experimental animals.
There is inadequate evidence for the carcinogenicity of cobalt and cobalt compounds in humans. There is sufficient evidence for the carcinogenicity of cobalt metal powder in experimental animals. There is limited evidence for the carcinogenicity of metal alloys containing cobalt, chromium and molybdenum in experimental animals. ... Overall Evaluation: Cobalt and cobalt compounds are possibly carcinogenic to humans (Group 2B). /Cobalt and cobalt compounds/
The effects of cobalt sulfate administered to pregnant C57BI mice, OFA-SD rats, and New Zealand rabbits was studied on fetal and postnatal offspring. Cobalt concentration in the maternal blood was increased in proportion to the administered doses. Cobalt crossed the placenta and appeared in the fetal blood and amniotic fluid. Regardless of the administered dose of cobalt sulfate, cobalt concentration in the blood peaked 2 hr after administration.
Sheep given a single dose of hydrated cobalt sulfate were killed. ...The livers contained 400-1200 ppm of cobalt. In cattle dying after a massive overdose of hydrated cobalt sulfate livers contained 5-300 ppm, kidneys 30-200 ppm. /Hydrated cobalt sulfate/
Following longer-term exposure (8 weeks) to cobalt sulfate in the diet, exposed rats showed a 30-fold increase in the cobalt concentration in the myocardium, a 26-fold increase in the concentration in the soleus muscle, and a 100-fold increase in the concentration in serum compared with nonexposed controls. Long-term oral exposure of rats to cobalt chloride resulted in significantly increased levels of cobalt in the liver, kidney, muscle, brain, and testes of treated rats.
Cobalt metabolism and toxicology are summarized. The biological functions of cobalt are updated in the light of recent understanding of cobalt interference with the sensing in almost all animal cells of oxygen deficiency (hypoxia). Cobalt (Co(2+)) stabilizes the transcriptional activator hypoxia-inducible factor (HIF) and thus mimics hypoxia and stimulates erythropoietin (Epo) production, but probably also by the same mechanism induces a coordinated up-regulation of a number of adaptive responses to hypoxia, many with potential carcinogenic effects. This means on the other hand that cobalt (Co(2+)) also may have beneficial effects under conditions of tissue hypoxia, and possibly can represent an alternative to hypoxic preconditioning. Cobalt is acutely toxic in larger doses, and in mammalian in vitro test systems cobalt ions and cobalt metal are cytotoxic and induce apoptosis and at higher concentrations necrosis with inflammatory response. Cobalt metal and salts are also genotoxic, mainly caused by oxidative DNA damage by reactive oxygen species, perhaps combined with inhibition of DNA repair. Of note, the evidence for carcinogenicity of cobalt metal and cobalt sulfate is considered sufficient in experimental animals, but is as yet considered inadequate in humans. Interestingly, some of the toxic effects of cobalt (Co(2+)) have recently been proposed to be due to putative inhibition of Ca(2+) entry and Ca(2+)-signaling and competition with Ca(2+) for intracellular Ca(2+)-binding proteins. The tissue partitioning of cobalt (Co(2+)) and its time-dependence after administration of a single dose have been studied in man, but mainly in laboratory animals. Cobalt is accumulated primarily in liver, kidney, pancreas, and heart, with the relative content in skeleton and skeletal muscle increasing with time after cobalt administration. In man the renal excretion is initially rapid but decreasing over the first days, followed by a second, slow phase lasting several weeks, and with a significant long-term retention in tissues for several years. In serum cobalt (Co(2+)) binds to albumin, and the concentration of free, ionized Co(2+) is estimated at 5-12% of the total cobalt concentration. In human red cells the membrane transport pathway for cobalt (Co(2+)) uptake appears to be shared with calcium (Ca(2+)), but with the uptake being essentially irreversible as cobalt is effectively bound in the cytosol and is not itself extruded by the Ca-pump. It is tempting to speculate that this could perhaps also be the case in other animal cells. If this were actually the case, the tissue partitioning and biokinetics of cobalt in cells and tissues would be closely related to the uptake of calcium, with cobalt partitioning primarily into tissues with a high calcium turn-over, and with cobalt accumulation and retention in tissues with a slow turn-over of the cells. The occupational cobalt exposure, e.g. in cobalt processing plants and hard-metal industry is well known and has probably been somewhat reduced in more recent years due to improved work place hygiene. Of note, however, adverse reactions to heart and lung have recently been demonstrated following cobalt exposure near or slightly under the current occupational exposure limit. Over the last decades the use of cobalt-chromium hard-metal alloys in orthopedic joint replacements, in particular in metal-on-metal bearings in hip joint arthroplasty, has created an entirely new source of internal cobalt exposure. Corrosion and wear produce soluble metal ions and metal debris in the form of huge numbers of wear particles in nanometric size, with systemic dissemination through lymph and systemic vascular system. This may cause adverse local reactions in peri-prosthetic soft-tissues, and in addition systemic toxicity. Of note, the metal nanoparticles have been demonstrated to be clearly more toxic than larger, micrometer-sized particles, and this has made the concept of nanotoxicology a crucial, new discipline. As another new potential source of cobalt exposure, suspicion has been raised that cobalt salts may be misused by athletes as an attractive alternative to Epo doping for enhancing aerobic performance. The cobalt toxicity in vitro seems to reside mainly with ionized cobalt. It is tempting to speculate that ionized cobalt is also the primary toxic form for systemic toxicity in vivo. Under this assumption, the relevant parameter for risk assessment would be the time-averaged value for systemic cobalt ion exposure that from a theoretical point of view might be obtained by measuring the cobalt content in red cells, since their cobalt uptake reflects uptake only of free ionized cobalt (Co(2+)), and since the uptake during their 120 days life span is practically irreversible. This clearly calls for future clinical studies in exposed individuals with a systematic comparison of concurrent measurements of cobalt concentration in red cells and in serum.