Cobalt

Chemical Properties#

Transition metal (Group 9); primarily exists as cobalt(II) (Co2+) and cobalt(III) in biological systems. Density 8.9 g/cm3; ferromagnetic. Essential component of cobalamin (vitamin B12), where cobalt(III) is coordinated in a corrin ring.

U-shaped dose-response: both deficiency (as B12 deficiency) and excess cause harm.^{[1]Heavy Metal Pollution in the Environment and Their Toxicological Effects on HumansJessica Briffa, Emmanuel Sinagra, Renald Blundell · 2020Open reference 1 ↓}

Dietary#

As vitamin B12: meat, fish, dairy, eggs (exclusively animal sources for preformed B12). Inorganic cobalt: leafy greens, nuts, cereals; low bioavailability.

Occupational and Environmental#

Hard metal (tungsten carbide-cobalt) manufacturing, diamond polishing, battery production (lithium-cobalt oxide). Cobalt-chromium orthopedic implants release cobalt (Co) ions into surrounding tissue and systemic circulation. Classified by IARC as Group 2B (possibly carcinogenic to humans) for cobalt metal and cobalt compounds.

Vitamin B12 (Cobalamin)#

Cobalt's sole essential function in mammals is as the central metal ion in vitamin B12.

Methylcobalamin: Cofactor for methionine synthase (converts homocysteine to methionine; critical for methylation reactions and DNA synthesis). Adenosylcobalamin: Cofactor for methylmalonyl-CoA mutase (propionate metabolism; odd-chain fatty acid and branched-chain amino acid catabolism). B12 deficiency causes megaloblastic anemia and neurological damage (subacute combined degeneration of the spinal cord).

Microbial Cobalt Biology#

Cobalt is more broadly used in prokaryotic enzymes. NiCoT-type transporters: The NixA transporter family in pathogens transports both nickel and cobalt, reflecting shared coordination chemistry.^{[2]Role of Nickel in Microbial PathogenesisRobert J. Maier, Stéphane L. Benoit · 2019Open reference 2 ↓}

CznABC efflux pump in Helicobacter pylori: Exports cadmium, zinc, and nickel—cobalt is also a substrate, reflecting the need to manage multiple divalent cation concentrations.^{[2]Role of Nickel in Microbial PathogenesisRobert J. Maier, Stéphane L. Benoit · 2019Open reference 2 ↓}

Staphylopine (Staphylococcus aureus): A nicotianamine-like metallophore originally characterized for zinc but also binds nickel and cobalt, facilitating metal acquisition during infection.^{[2]Role of Nickel in Microbial PathogenesisRobert J. Maier, Stéphane L. Benoit · 2019Open reference 2 ↓}

Cobalt is relevant to the Nutritional Immunity (Metal Sequestration) framework: hosts may sequester cobalt (Co) alongside other transition metals to limit pathogen access.

Nickel-Cobalt Cross-Reactivity and Allergy#

Concomitant nickel-cobalt contact allergy is well established. cobalt and nickel share similar ionic radii (cobalt(II) (Co2+) = 0.74 A; nickel(II) (Ni2+) = 0.72 A) and coordination chemistry, leading to cross-sensitization. Patients with Nickel Allergy and Allergic Contact Dermatitis frequently test positive for cobalt on patch testing.

Relevant to the interpretation of Low-Nickel Diet studies, as dietary cobalt sources overlap with nickel sources (legumes, whole grains, nuts, chocolate).

Toxicity at High Levels#

Cardiomyopathy: Historic "beer drinker's cardiomyopathy" from cobalt-stabilized beer foam (1960s Quebec, Belgium); cobalt damages mitochondria in cardiomyocytes. Hard metal lung disease: Interstitial lung disease (giant cell pneumonitis) from tungsten carbide-cobalt dust inhalation.

Implant-related toxicity: Cobalt-chromium hip prostheses release cobalt/chromium (Cr) ions; elevated blood cobalt associated with neurological symptoms, thyroid dysfunction, and cardiomyopathy (arthroprosthetic cobaltism). Cobalt generates ROS through Fenton-like chemistry (cobalt(II) (Co2+)/cobalt(III) cycling), though less efficiently than iron or copper.^{[1]Heavy Metal Pollution in the Environment and Their Toxicological Effects on HumansJessica Briffa, Emmanuel Sinagra, Renald Blundell · 2020Open reference 1 ↓}