As a result of catastrophic nuclear accidents such as Fukushima and Chernobyl, the proliferation of actinides in the environment has become a major concern. Actinides, such as isotopes of uranium and thorium, can spread through the environment both naturally and because of anthropogenic activities, such as mining and smelting. Distributed actinides can be taken in by humans via ingestion from sources such as contaminated drinking water, or by inhalation, whether oral or nasal. Once ingested, actinides either exhibit chemical and/or radiological toxicity, e.g., 238U and 232Th mainly exhibit chemical toxicity. Potential non-radiological adverse effects include long-term accumulation in the skeleton and arrests in bone growth. A major area of concern is the teeth, since they are one of the first points of contact of actinides entering the body, and consequences of contact include delays in tooth eruption and development. The major mineral component of both bone and teeth is hydroxyapatite (HAP,) and this present work studies and models the influence of pH, contact time, initial metal concentration, and buffer solution on the uptake and removal of a long-lived actinide (238U) onto synthetic HAP. pH had negligible effects on the uptake of U, and the kinetics of uptake were extremely fast, as 98% of U was uptaken in one second of exposure. The uptake followed pseudo-second order kinetics and a Freundlich isotherm model. A 0.2 M sodium carbonate solution removed all the U from HAP after one hour. Another series of in vitro tests were performed with real teeth as targets. We found that for a 50 mg/L U in PBS solution adjusted to physiological pH, ~35% of the uranyl was uptaken by the tooth after one hour, following pseudo-first order kinetics. Among several washing solutions tested, a commercially available carbonate as well as a commercially available fluoride solution, enabled removal of all the uranyl taken up by the teeth. Finally, characterization of the interaction between U and the tooth surface was performed using FT-IR spectroscopy. Similar studies were also conducted using 232Th, and will be reported later.

The adsorption and removal of actinides from human teeth

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.