Thallium Toxicity

Excerpt

Thallium (Tl; atomic number 81) is a heavy metal know to cause a broad spectrum of adverse effects in humans. Thallium sulfate was once used as an ant and rat poison. The occupational limit for thallium skin exposure is 0.1 mg/m³ for 8 hours a day. [Occupational Safety and Health Administration, Thallium] Levels of 15 mg/m³ are considered immediately dangerous to one’s health. Thallium is readily absorbed dermally and inhalationally. As thallium is tasteless, odorless, and water-soluble, accidental and criminal intoxication has been reported.

Thallium salts were once used to treat dermatophytosis. The radioactive isotope thallous chloride Tl 201 was commonly used in stress tests before technetium Tc 99m became the standard for nuclear medicine studies; Tl 201 still used to evaluate coronary artery disease. Tl 201 is more than 4,000 times less potent than its toxic form. Scintigraphy with thallium assesses tissue blood supply by measuring thallium uptake. Normal coronary arteries dilate, altering blood distribution and potentially leading to reduced coronary circulation during exercise or the use of vasodilating drugs, a phenomenon known as coronary steal syndrome.

Natural History

Thallium is a gray posttransition metal not found free in nature. Though similar to tin when isolated, thallium discolors when exposed to air. Patterns of thallium spread include dermal absorption, inhalation, and ingestion.