Urinary thorium (Th) provides an indication of recent or ongoing exposure to the radioactive metal, and endogenous detoxification to a lesser extent. This test measures Th232 which is the most abundant, naturally occurring radioactive isotope of Th.
Th is found almost everywhere in the earth’s crust, so exposure to small amounts of Th from air, food and water is unavoidable. Th is a naturally occurring radioactive metal that is found at low levels in soil, rocks, water, plants, and animals. Th is almost as abundant in the earth’s crust as lead, and three times more abundant than uranium (U238).
Gastrointestinal absorption of Th from food and water is very low (0.1 to 1%). Most assimilation of Th occurs via inhalation of contaminated dust and microparticles in air.
Individuals who work in or near the mining, milling or Th industries may experience greater than normal Th exposure. Th is used to make ceramics, gas lantern mantles, welding rods, and camera and telescope lenses. It is also used as an alloying element with magnesium to coat tungsten wire that is used in electronic equipment, and metals used in the aerospace industry.
The amounts of Th in the environment may be increased in association with accidental release from a processing facility. Large amounts of Th may be found near hazardous waste sites where Th has not been disposed of properly. People that live near these hazardous waste sites may be exposed to more Th than usual via inhalation of dust and consumption of locally grown food.
The radiation from Th232 and its decay products is in the form of alpha and beta particles and gamma radiation. While Th exposure for most people is well below levels associated with toxic effects, occupational exposure to Th dust increases risks for lung disease, lung cancer and pancreatic cancer. Th may have adverse health effects on bone and bone metabolism in association with long-term retention of Th-based radioactivity in the skeletal system.
Hair elemental analysis may be used to assess exposure to Th over the past 2-4 months.
Chelation may acutely increase urinary Th excretion.
Thorium
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