Cobalt

Cobalt (chemical symbol Co) is an essential trace element. Its most important function in humans is as the active metal atomic center of vitamin B₁₂.

Chemistry

Basic chemistry

Cobalt is a shiny grey-silvery transition metal with an atomic number 27 and atomic weight 58.93. Its oxidation states are +1 and +2. 

Radiochemistry

A single stable isotope, cobalt-59 accounts for all the naturally-occurring cobalt on earth ⁷.

Dietary

Cobalt is found in fish, nuts, leafy vegetables, and cereal grains.

Toxicity

Chronic cobalt poisoning is rare and was formerly seen in chronic beer drinkers as cobalt chloride was added to beer to maintain a nice foamy head. Sequelae of toxicity include vomiting, sensorineural deafness, tinnitus and cardiomyopathy ^5,6. 

Biological function

• vitamin B₁₂ (cobalamin) is a complex structure and central to it is a cobalt ion within a corrin ring. Vitamin B₁₂ is vital for the normal functioning of every cell in the human body, being key to DNA synthesis. Since vitamin B₁₂ is a hematinic and cobalt is vital for its formation, it follows that cobalt is also one of the hematinics.

Radiological importance

• cobalt-57 is employed as a flood source to perform QA on gamma cameras in nuclear medicine departments
• cobalt-57 spot markers are used as orientation markers during nuclear medicine studies, e.g. thyroid scintigraphy
• cobalt-60 is used in radiotherapy (e.g. Gamma Knife^®)
• cobalt-60 is the sterilization method of choice in the medical device industry
• cobalt-60 was the isotope most commonly employed for the Schilling test which was used to evaluate vitamin B₁₂ deficiency

History and etymology

• Georg Brandt discovered cobalt in 1739 ⁴. It was a difficult metal to extract from its ore and miners put this down to goblins who had cast evil magic upon the rock. The German word for goblin, kobbold, was subsequently adopted for this new element. Interestingly cobalt was the first metal to be discovered that was not known to the ancients.
• Bertrand and Macheboeuf first discovered cobalt in animal cells in 1925, this was later corroborated by more sophisticated spectrographic techniques.