Gunnar Nordberg
Occurrence and Uses
In nature, bismuth (Bi) occurs both as the free metal and in ores such as bismutite (carbonate) and bismuthinite (double bismuth and tellurium sulphide), where it is accompanied by other elements, mainly lead and antimony.
Bismuth is used in metallurgy for the manufacture of numerous alloys, especially alloys with a low melting point. Some of these alloys are used for welding. Bismuth also finds use in safety devices in fire detection and extinguishing systems, and in the production of malleable irons. It acts as a catalyst for making acrylic fibres.
Bismuth telluride is used as a semiconductor. Bismuth oxide, hydroxide, oxychloride, trichloride and nitrate are employed in the cosmetics industry. Other salts (e.g., succinate, orthoxyquinoleate, subnitrate, carbonate, phosphate and so on) are used in medicine.
Hazards
There have been no reports of occupational exposure during the production of metallic bismuth and the manufacture of pharmaceuticals, cosmetics and industrial chemicals. Because bismuth and its compounds do not appear to have been responsible for poisoning associated with work, they are regarded as the least toxic of the heavy metals currently used in industry.
Bismuth compounds are absorbed through the respiratory and gastrointestinal tracts. The main systemic effects in humans and animals are exerted in the kidney and liver. The organic derivatives cause alterations of the convoluted tubules and may result in serious, and sometimes fatal, nephrosis.
Gum discolouration has been reported with exposure to bismuth dusts. The insoluble mineral salts, taken orally over prolonged periods in doses generally exceeding 1 per day, may provoke brain disease characterized by mental disorders (confused state), muscular disorders (myoclonia), motor coordination disorders (loss of balance, unsteadiness) and dysarthria. These disorders stem from an accumulation of bismuth in the nerve centres which manifests itself when bismuthaemia exceeds a certain level, estimated at around 50 mg/l. In most cases, bismuth-linked encephalopathy gradually disappears without medication within a period of from 10 days to 2 months, during which time the bismuth is eliminated in the urine. Fatal cases of encephalopathy have, however, been recorded.
Such effects have been observed in France and Australia since 1973. They are caused by a factor not yet fully investigated which encourages the absorption of bismuth through the intestinal mucous membrane and leads to an increase in bismuthaemia to a level as high as several hundred mg/l. The danger of encephalopathy caused by inhaling metallic dust or oxide smoke in the workplace is very remote. The poor solubility of bismuth and bismuth oxide in blood plasma and its fairly rapid elimination in the urine (its half-life is about 6 days) argue against the likelihood of a sufficiently acute impregnation of the nerve centres to reach pathological levels.
In animals, inhalation of insoluble compounds such as bismuth telluride provokes the usual lung response of an inert dust. However, long-term exposure to bismuth telluride “doped” with selenium sulphide can produce in various species a mild reversible granulomatous reaction of the lung.
Some bismuth compounds decompose into dangerous chemicals. Bismuth pentafluoride decomposes on heating and emits highly toxic fumes.