Pure thallium is a soft, bluishwhite metal that is widely distributed in trace amounts in the earth's crust. In its pure form, it is odorless and tasteless. It can be found in pure form or mixed with other metals in the form of alloys. It can also be found combined with other substances such as bromine, chlorine, fluorine, and iodine to form salts. These combinations may appear colorless to white or yellow. Thallium remains in the environment since it is a metal and cannot be broken down to simpler substances.
Thallium exists in two chemical states (thallous and thallic). The thallous state is the more common and stable form. Thallous compounds are the most likely form to which you would be exposed in the environment. Thallium is present in air, water, and soil. We do not know how much time it takes for thallium to move from one medium to another.
Thallium is used mostly in the manufacture of electronic devices, switches, and closures. It also has limited use in the manufacture of special glasses and for medical procedures that evaluate heart disease. Up until 1972 thallium was used as a rat poison, but was then banned because of its potential harm to man. Thallium is no longer produced in the United States. All the thallium used in the United States since 1984 has been obtained from imports and thallium reserves.
Exposure to thallium
You can be exposed to thallium in air, water, and food. However, the levels of thallium in air and water are very low. The greatest exposure occurs when you eat food, mostly homegrown fruits and green vegetables contaminated by thallium. Small amounts of thallium are released into the air from coalburning power plants, cement factories, and smelting operations. This thallium falls out of the air onto nearby fruit and vegetable gardens. Thallium enters food because it is easily taken up by plants through the roots. Very little is known on how much thallium is in specific foods grown or eaten. Cigarette smoking is also a source of thallium. People who smoke have twice as much thallium in their bodies as do nonsmokers. Although fish take up thallium from water, we do not know whether eating fish can increase thallium levels in your body. It has been estimated that the average person eats, on a daily basis, 2 parts thallium per billion parts (ppb) of food. Even though rat poison containing thallium was banned in 1972, accidental poisonings from old rat poison still occur, especially in children.
Thallium is produced or used in power plants, cement factories, and smelters. People who work in these places can breathe in the chemical or it may come in contact with their skin. Information on the amount of thallium in workplace air in the United States could not be found. Hazardous waste sites are also possible sources of exposure to thallium. An average of 23 ppb of thallium in surface water and 11 ppb in groundwater have been found at hazardous waste sites. Since thallium compounds mix easily in water, you can be exposed if you live near a chemical waste site where thallium emissions have contaminated the water. An average of 1.7 parts of thallium per million parts (ppm) of soil was found at hazardous waste sites. Since thallium sticks to soil, you can be exposed at hazardous waste sites if you swallow or touch contaminated soil. Thallium contaminated dust in the air can also be swallowed after it is cleared from the lungs. Thallium is naturally found in soil at levels from 0.3 to 0.7 ppm.
Pathways for thallium in the body
Thallium can enter your body when you eat food or drink water contaminated with thallium, breathe thallium in the air, and when your skin comes in contact with it. When thallium is swallowed most of it is absorbed and rapidly goes to various parts of your body, especially the kidney and liver. Thallium leaves your body slowly. Most of the thallium leaves your body in urine and to a lesser extent in feces. It can be found in urine within 1 hour after exposure. After 24 hours, increasing amounts are found in feces. It can be found in urine as long as 2 months after exposure. About half the thallium that enters various parts of your body leaves them within 3 days.
The significant, likely routes of exposure near hazardous waste sites are through swallowing thallium contaminated soil or dust, drinking contaminated water, and skin contact with contaminated soil.
Health effects of thallium
Thallium can affect your nervous system, lung, heart, liver, and kidney if large amounts are eaten or drunk for short periods of time. Temporary hair loss, vomiting, and diarrhea can also occur and death may result after exposure to large amounts of thallium for short periods. Thallium can be fatal from a dose as low as 1 gram. No information was found on health effects in humans after exposure to smaller amounts of thallium for longer periods. Birth defects observed in children of mothers exposed to small amounts of thallium did not occur more often than would be expected in the general population. The length of time and the amount of thallium eaten by the mothers are not known exactly. As in humans, animal studies indicate that exposure to large amounts of thallium for brief periods of time can damage the nervous system and heart and can cause death. Animal reproductive organs, especially the testes, are damaged after drinking small amounts of thallium contaminated water for 2 months. These effects have not been seen in humans. No information was found on effects in animals after exposure to small amounts of thallium for longer periods of time. No studies were found on whether thallium can cause cancer in humans or animals.
Medical tests for thallium
Reliable and accurate ways to measure thallium in the body are available. The presence of thallium in the urine and hair can indicate exposure to thallium. Tests of your urine can detect thallium up to 2 months. The normal amount of thallium in human urine amounts to less than 1 ppm and 5–10 ppb in human hair. Although thallium can be measured in blood, this tissue is not a good indicator of exposure since thallium stays there too short a time. We do not know yet whether thallium levels measured in the body can be used to predict possible health effects.
Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Agency for Toxic Substances and Disease Registry. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Agency for Toxic Substances and Disease Registry should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.