CHAPTER 2-52: COBALT

INTRODUCTION

Cobalt is an essential trace metal element in the human diet, being an integral component of Vitamin B₁₂ (cobalamin). It can be found in certain ores with other metals such as nickel, copper or arsenic. It has high melting and boiling points, approximately 1,500°C and 3,000°C, respectively. Cobalt has elemental, organic, and inorganic forms. When combined with tungsten carbide, the material is termed "hard metal" and is used for industrial cutting, drilling, and polishing. Cobalt is also found in jewelry alloys and has ferromagnetic properties making it a useful component in magnets.

Rubratope-57 (Cyanocobalamin Co 57 Capsules) is intended for the diagnosis of pernicious anemia and as a diagnostic adjunct in other defects of intestinal vitamin B12 absorption. Cobalt-60, a radionuclide of cobalt, is used as a source for radiation therapy, in industrial radiography, and in the sterilization of foods and spices, as well as in linear accelerators and leveling devices. Historically, inorganic cobalt salts were used for the treatment of anemia including during pregnancy and were also the cause of "beer drinkers cardiomyopathy" resulting from cobalt additives to beer to stabilize foam. More recently, an excess body burden of cobalt has been linked to failing cobalt alloy metal-on-metal hip joint replacements.

MECHANISM OF TOXICITY

1. Cobalt can exert toxic effects by interacting with a complex array of biological receptors and proteins to stimulate erythropoiesis, foster generation of reactive oxygen species, interfere with mitochondrial function, inhibit thyroidal iodine uptake, and alter calcium homeostasis.

2. Cobalt is considered a possible carcinogen (Class 2B by the International Agency for Research on Cancer).

3. Overdose during pregnancy. There are no reports of overdose in pregnancy. Cobalt had previously been used therapeutically to treat anemia in pregnancy. No fetal anomalies have been reported. A pregnant woman with bilateral metal on metal hips had blood cobalt concentrations of 138 and 143 mcg/L at 7 and 38 weeks gestation, and delivered a healthy male who showed normal development through age 14 weeks.

4. Pharmacokinetics. Cobalt is well absorbed via inhalation and variably absorbed by ingestion. It is distributed in serum, whole blood, liver, kidney, heart and spleen. The major route of elimination is renal, with half-lives on the order of several hours to a week. Lung retention of relatively insoluble cobalt compounds such as cobalt oxide may be prolonged, with pulmonary clearance half-lives of 1–2 years.

TOXIC DOSE

1. Ingestion

   1. Acute ingestion of 2.5 g of cobalt chloride by a 6-year-old child caused only abdominal pain. Hemoglobin and electrolytes remained normal.

   2. Chronic doses of 45–90 mg per day were used to induce erythropoiesis in pregnancy, with no reported side effects. Fatal cases of dilated cardiomyopathy were reported among alcoholics who drank an average of 17 glasses of beer per day containing 0.5 ppm of cobalt (range of 0.0–5 ppm).

2. Inhalation of cobalt-containing dust may cause respiratory irritation at air concentrations ...