Thorium and thorium dioxide

Discovered in 1829, thorium, CASRN 7440-29-1, is a naturally occurring radioactive metal with no stable isotopes. It is about as abundant as lead. Soil commonly contains an average of about six parts of thorium per million parts of soil. Ingestion of liquid, inhalation of dust or gas, and percutaneous absorption are the routes of exposure. Acute exposure results in dermatitis. Thorium is a carcinogen and developmental toxin. The removal of thorium from the body has been achieved by the use of chelating agents. Studies of thorium workers have shown that breathing thorium dust may cause an increased chance of developing lung disease and cancer of the lung or pancreas many years after being exposed.