ABSTRACT

This chapter provides a detailed discussion on the occurrence and production, uses, chemical and physical properties, exposure and exposure limits, toxicokinetics, and effects of thorium in humans. Thorium is a by-product of uranium recovery from uraininite and is recovered chiefly from monazite, the principal ore of rare earth elements. Thorianite is another important ore source of thorium and uranium. In the United States, thorium is produced as a by-product of mining beach sands including monazite in Florida for titanium and rare earths. Exposures to significant amounts of thorium are chiefly through occupational exposure during the production and use of thorium compounds and alloys, during the casting and machining of alloy parts, and during welding with thorium electrodes. The effects of thorium in humans include information on acute toxicity, chronic toxicity, biochemistry, specific organs and systems, teratogenicity, mutagenicity, and carcinogenicity.