DOCTOR'S VIEW ARCHIVE
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
The March 2007 poisoning of an American woman and her daughter in Russia with the element thallium sparked widespread media attention. After the women became ill in Moscow, they returned to the U.S. for treatment, where the diagnosis of thallium poisoning was confirmed.
Thallium is a soft, malleable gray metal that was previously widely used in rat poisons and insecticides. Thallium itself and compounds containing the element are highly toxic. It is particularly dangerous because compounds containing thallium are colorless, odorless, and tasteless. Because of this high toxicity, the World Health Organization (WHO) recommends against the use of thallium in rodent and insect poisons. However, poisons containing thallium are still in use in some parts of the world.
Small amounts of thallium are normally found in the earth's crust and atmosphere. It is also present in small amounts in cigarette smoke. Thallium has multiple industrial uses, and certain isotopes of thallium are used in medical imaging studies. Thallium can be absorbed from the skin as well as be ingested or inhaled. If a significant amount (significant poisoning is usually defined as ingesting over 1 gram of thallium, or over 8 milligrams per kilogram of body weight) of thallium enters the body, symptoms of thallium poisoning develop.
In the first 48 hours after serious thallium exposure, the affected individual will usually experience nausea, vomiting, and diarrhea. Within a few days, symptoms of nervous system damage become apparent. These symptoms can include pain, loss of reflexes, convulsions, muscle wasting, headaches, numbness, dementia, psychosis, and even coma. After two to three weeks, characteristic changes are seen in the bases of hair shafts, and there is hair loss (alopecia). Finally, after around three weeks post-exposure, heart rhythm disturbances may occur.
Thallium poisoning can be treated. Effective treatment to prevent absorption of thallium is available if therapy is begun within six hours following ingestion. The antidote against thallium (known as potassium ferrihexacyanoferrate, or Prussian blue or Berlin blue) works by sequestering thallium molecules and preventing their absorption by the intestine. Other treatments that may be successful for victims of thallium poisoning include dialysis and medications to increase the kidneys' excretion of thallium.