Thallium (Tl) is a silver-colored, soft, metallic element found in trace quantities with several other metals, and is usually recovered as a byproduct from smelting lead, copper and zinc. The minute amount of the chemical which occurs naturally in water is relatively harmless, but thallium is highly toxic in larger quantities, 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 water-soluble; qualities which made it the weapon of choice in several homicides in Australia in the 1950’s.
Thallium was discovered in 1861 by Sir William Crookes, an English chemist. At that time, little was known about the danger of thallium poisoning to humans, and it was used in a number of over-the-counter health applications. The toxic qualities of the element made it a favorite ingredient in insecticides and rodent poisons. Over time, research and usage made it apparent that this was an element which posed grave potential danger to the general public if not handled properly. In 1973, the World Health Organization recommended that the use of thallium sulfate in insect and rodent poisons be banned, and most countries have followed that recommendation.
Symptoms of thallium poisoning include extreme pain, vomiting, diarrhea, weakness and rapid hair loss. The poison is systemic, which means it can affect multiple organs including the heart, lungs, kidneys, and liver. A person may not know that he has been poisoned immediately because it can take several days to manifest symptoms. A person may 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 through blood analysis. The best way to accurately diagnose thallium poisoning is by examining the hair follicles. Prussian blue, a dark blue pigment used in paints, is recommended as an antidote if administered in time. The dye binds with the metal in the intestines, blocking absorption.
The ban on thallium usage 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 becomes involved. In 1988, five members of a family 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 recall was initiated because it was an isolated incident. Some time later a neighbor was convicted of the crime.
In spite of the toxicity of this element, there are some commercial and medical uses for thallium compounds. It is used to make specialized eyeglasses, imitation diamonds, photo-electric sensors, and infrared detection and transmission devices. The medical field also uses thallium as a part of a cardiac stress test called myocardial perfusion imaging test. A minute dose of thallium, much too small to cause thallium poisoning, is administered to a patient during a treadmill or stationary bike stress test. The patient then lies down on a table where a gamma ray camera tracks the path of the thallium through the arteries to detect any obstructions.
New research is being conducted to expand the positive uses of thallium, including semiconductor and medical applications. The United States continues to use the product in manufacturing and medicine, yet it ceased all production in the 1980’s. Some of the countries involved in thallium recovery include Belgium, China, Germany, Kazakhstan, Mexico, the Netherlands, Poland and Russia.