GRAND ROUNDS - GUYS-HOSPITAL - THALLIUM POISONING

Thallium is a heavy metal whose salts are used in some rodent poisons and in the manufacture of optical lenses, semiconductors, scintillatio n counters, low temperature thermometers and switching devices, green coloured fireworks, and imitation jewellery, and as chemical catalysts . In clinical practice thallium isotopes are used in cardiac scanning, 1 2 but the use of thallium salts to treat scalp ringworm was abandone d earlier this century because of their toxicity. The sale of thallium in Britain is strictly licensed because of its toxicity and potential for use in murder, which is helped by the fact that thallous salts ar e colourless, tasteless, and odourless. The more water soluble salts ( such as thallium sulphate, acetate, or carbonate) have higher toxicity , and although the toxic dose is variable most deaths occur after the ingestion of 10-15 mg/kg of soluble salt. Most cases of thallium toxic ity occur after oral ingestion but severe toxicity has been reported a fter inhalation of contaminated dust from pyrite burners, in zinc and lead smelting, and in the manufacture of cadmium, after dermal absorpt ion through protective rubber gloves,3 and after snorting what was tho ught to be cocaine.4 The elimination half time of thallium is between 1.7 and 30 days2 5 depending on the time since, and chronicity of, ing estion. The elimination time phases are apparent and because of the lo ng terminal elimination half time thallium may act as a cumulative poi son. We present two cases of thallium poisoning with intent to kill.