Investigation of Chelating Agents for the Removal of Thorium from Human Teeth upon Nuclear Contamination

Thorium-232 (²³²Th) is a radioactive heavy metal that is of increasing interest as a source of nuclear energy. However, upon nuclear incidents, the ingestion or inhalation of Th in major quantities can contribute to chemical and radiological health problems, including accumulation in the bone tissue and an increased risk of developing pancreatic, lung, and hematopoietic cancers. The major mineral component of the bone is hydroxyapatite (HAP)─also the major mineral component of the teeth. As such, the teeth are the first site of exposure upon oral ingestion of Th-contaminated materials, and Th can pose a potential risk to teeth development. In essence, in the case of human contamination, it is critical to identify effective chelating agents capable of removing Th. Using a batch study methodology, this present work investigates the uptake and the removal of Th from synthetic HAP and from teeth samples by diethylenetriamine pentaacetate (DTPA), ethylenediaminetetraacetic acid (EDTA), and other promising chelating agents. Th uptake over synthetic HAP exceeds 98% at physiological pH with <1 min of contact time and uptake exceeds 90% across the entire pH range. Regarding teeth, over 1 mg Th uptaken per gram of tooth is observed after 24 h. The overall effectiveness of chelating agents for the removal of Th from is as follows: DTPA > EDTA > NaF/mouthwash/3,4,3-LI(1,2-HOPO); this trend was observed both in synthetic HAP and Th-impregnated teeth samples.