Named, in 1828, by its discoverer Jons Jacob Berzelius for the Scandinavian god of war Thorium, this metallic element led to one of the most unfortunate medical sagas of the 20th century when it was incorporated into the radiographic product called Thorotrast®.  Thorotrast®, was a 25% colloidal suspension of 232 ThO2 (occasionally enriched with Th230).  It was considered to be the "ideal radiographic-contrast material" for many diagnostic procedures including myelography, angiography, etc.  It was first injected, for diagnostic purposes, in legions of patients throughout the world starting in 1929 (United States in 1932).  Thorotrast® "fell into disuse" in about 1960.  It was only many years later that the medical community, through epidemiological studies first began to realize that Thorotrast® was dangerously radioactive emitting alpha particles, and the other decay products, which incorporated themselves into body tissues such as the arachnoid membrane as well as the reticuloendothelial system causing subsequent arachnoiditis, malignant tumors of the neuraxis, leukemia, hemangioendothelial sarcomas as well as liver cancer and other malignancies.  Thorotrast® has a half-life of 1.4 x 10(10) years.  Biological retention of Thorotrast® in the body has been estimated to have a half-life of 400 years.  As a highly radioactive substance (Th232 is primarily a alpha emitter) it was not surprising to find that when standardized mortality ratios from around the world were studied those persons exposed to Thorotrast® had significantly higher death ratesand significantly higher incidences of cancer, particularly those malignancies having a hematological etiology.  

Thorotrast® stands as only one of many examples of the medical community's chronic naiveté regarding toxic substances, particularly those of a radioactive nature.  One of the many proofs of this was a study by the National Institute of Standards and Technology which found that the radium-tipped applicators routinely used to shrink tonsils and adenoids in children during the 1950-1960s (patient numbers estimated at 500,000 to 2.5 million) subjected the individuals to unexpectedly large doses of beta radiation.  The influence of this on standardized morbidity ratios for subsequent head and neck malignancies in this patient population is still unknown.