Antimony in the human body

The background level of antimony in bodily fluids used to be almost undetectable but techniques have improved in recent years so that it is now measurable at parts per trillion. The level in urine is normally around 250 ppt (which is equivalent to a mere 0.000000025%). Some organs of the body have relatively high amounts, such as the brain with 0.1 ppm, the hair with 0.7 ppm, the liver with 0.2 ppm, and the kidneys with 0.2 ppm, yet none of this poses a threat to health. In all these organs there is usually more antimony present than arsenic for the simple reason that arsenic is rapidly excreted from the body whereas antimony tends to linger. Tests on patients who were given antimony-based drugs to treat parasitic infections were found to retain the element for longer than expected. A typical total dose, given by a succession of injections over several days, would amount to around 500 mg of antimony and even after six months the level in urine was relatively high at 1 ppm, and after a year it was still registering 0.25 ppm.

The average daily intake of antimony in our food and drink is around 0.5 mg and it comes mainly from the traces of antimony in vegetables. The total body burden of antimony in the average person is around 2 mg and it is associated with the sulphur atoms that are present in proteins. Provided these sulphur atoms are not those located at the active sites of an enzyme, the antimony will not seriously interfere with the body's metabolism.

A far more deadly form of antimony is the gas stibine (antimony hydride, SbH3) but this is rarely encountered outside certain industries, although in the 1990s it was thought to be responsible for cot death, as we shall see. Stibine can be formed when certain antimony alloys come in contact with strong acids. It is the most toxic form of antimony and causes headaches, nausea, and vomiting, and it can block the anticholinesterase enzymes which ensure the heart beats properly. Another source of industrial poisoning has been the solution of antimony trichloride in hydrochloric acid known as bronzing fluid, a name which describes it usefulness in imparting a bronzelike finish to other metals such as cast iron. The liquid is sometimes used in furniture polishes and patent leather treatment. Deaths from drinking bronzing fluid have been reported but this has never been a suitable agent for perpetrating a murder because the liquid is corrosive and it would be impossible to administer without the intended victim being aware of it.

When antimony enters the bloodstream it first accumulates in the liver, from where it transfers to other parts of the body. It is slowly excreted by the kidneys but this is not helped by the drop in urine production, which is a symptom of antimony poisoning. If a victim of antimony poisoning survives for 48 hours then the prognosis is complete recovery, given moderate care and treatment. Post-mortem findings may reveal no sign of antimony poisoning beyond inflammation of the gastrointestinal tract.

The best test for antimony in Victorian times was the Marsh test which gave a metallic mirror, just as it did with arsenic. The antimony mirror was blacker and was deposited on the tube walls nearer the flame used to decompose the stibine gas that was evolved from the solution being analysed. Moreover, when the antimony deposit was heated in a stream of air, it was not converted to a volatile oxide as happens with arsenic, and this extension of the Marsh test served to distinguish between the two metals. Confirmation that it was antimony was obtained by passing hydrogen sulphide gas over the heated mirror which converted it to an orange-red deposit of antimony sulphide; the same treatment of an arsenic mirror gives a canary yellow deposit of arsenic sulphide. In the twentieth century, analytical tests became much more sensitive as described in the Glossary.

Once antimony poisoning has been diagnosed treatment can begin, and today there is little likelihood of a victim dying because there are chelating drugs - see Glossary - that will scavenge the antimony from the blood and organs and transport it from the body. Before the introduction of these drugs, the standard treatment had been to pump out the contents of the stomach, wash several times with water, and then encourage the patient to drink lots of fluids. This treatment, too, would often save a patient's life, and there are cases on record in which patients with blood antimony levels of 0.1 ppm - which is more than 60 times the normal level and a sign of severe poisoning - being successfully treated without resorting to chelating drugs.

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