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Thallium is a highly toxic metallic element that can be fatal in small amounts. It was once used in over-the-counter healthcare products and insecticides, but its use has been banned in most countries. Symptoms of thallium poisoning include pain, vomiting, weakness, and rapid hair loss. Thallium is now primarily used in commercial and medical applications, including special glasses, imitation diamonds, and cardiac stress tests. Research is underway to expand its positive uses.
Thallium (Tl) is a soft, silver-colored metallic element that occurs in trace amounts with many other metals and is usually recovered as a by-product from lead, copper, and zinc smelting. The smallest amount of the chemical found naturally in water is relatively harmless, but thallium is highly toxic in larger amounts and as little as 0.3 ounces (1 gram) can be fatal in humans. It can be absorbed through the skin, by inhalation or ingested orally. The element is odorless, tasteless, and soluble in water; qualities that made it the weapon of choice in several murders in Australia in the 1950s.
Thallium was discovered in 1861 by Sir William Crookes, an English chemist. At the time, little was known about the danger of thallium poisoning to humans, and it was used in a number of over-the-counter healthcare applications. The element’s toxic qualities have made it a favorite ingredient in insecticides and rodent poisons. Over time, research and use made it apparent that this was an item that posed a serious potential danger to the general public if not handled properly. In 1973, the World Health Organization recommended banning the use of thallium sulfate in insect and rodent poisons, and most countries followed that recommendation.
Symptoms of thallium poisoning include extreme pain, vomiting, diarrhea, weakness, and rapid hair loss. The venom is systemic, meaning it can affect multiple organs including the heart, lungs, kidneys, and liver. A person may not know they have been poisoned right away because it can take several days for symptoms to appear. A person can live up to two weeks or more even after ingesting a fatal dose
Thallium dissolves quickly in liquids, so its presence may not always be detected in blood tests. The best way to accurately diagnose thallium poisoning is to examine the hair follicles. Prussian blue, a dark blue pigment used in paints, is recommended as an antidote if given in time. The dye binds to the metal in the intestine, blocking its absorption.
The ban on the use of thallium in household products has significantly reduced the likelihood of accidental ingestion, so when thallium poisoning is indicated, criminal intent is generally assumed and law enforcement agencies are involved. In 1988, five family members in the United States were hospitalized with thallium poisoning, one of whom died. The chemical was found in soft drinks in the home, but no product recalls were initiated because it was an isolated incident. Some time later a neighbor was convicted of the crime.
Despite the toxicity of this element, there are some commercial and medical uses for thallium compounds. It is used to make special glasses, imitation diamonds, photoelectric sensors and infrared sensing and transmission devices. The medical field also uses thallium as part of a cardiac stress test called a myocardial perfusion imaging test. A minimal dose of thallium, too small to cause thallium poisoning, is given to a patient during an exercise test on a treadmill or stationary bike. The patient then lies down on a table where a gamma-ray camera follows the path of thallium through the arteries to detect any blockages.
New research is underway to expand the positive uses of thallium, including semiconductor and medical applications. The United States continues to use the product in manufacturing and medicine, but ceased all production in the 1980s. Some of the countries involved in thallium recovery include Belgium, China, Germany, Kazakhstan, Mexico, the Netherlands, Poland and Russia.
