Collaborative Research: Experimental determination of trace element diffusion rates in tooth enamel

This project will investigate the rate of uptake of trace elements like barium, strontium, lead and the rare-earth elements (selected elements from lanthanum to lutetium) into tooth enamel. This project requires a key analytical technique 'Secondary Ion Mass Spectrometry (SIMS)' because the spatial scale of measurement is so small. This research is important for understanding how trace elements are taken up in the human body and their fidelity in distinguishing individuals on timescales ranging from years to millions of years. The work will have implications for paleontology, archeology, toxicology and forensics, including the litigation of fossil theft. This funding will support the research and training of a PhD student. This research will be used to leverage educational opportunities for non-scientists in the Boise region and connect researchers unaware of how all areas of microchemical research can benefit from SIMS, a tool that is most commonly applied to semiconductors.

The central focus of this project is to critically evaluate rates of diffusion of numerous trace elements in natural dental enamel. The research has been formulated to answer three main questions: How do diffusivities (D's) of trace elements in enamel depend on 1) charge vs. ionic radius and partitioning? 2) enamel orientation and enamel type? 3) fossilization state? To address these questions, uptake experiments will be conducted over a range of temperatures (4°, 20° and 37 °C) for a range of ions and ionic radii. D's will be measured in different directions for the two main enamel types in mammals - radial and decussate. Measurements in fossil enamel will be compared with similar measurements we make in modern enamel. The data will be inverted using standard diffusion equations, and natural datasets will be evaluated for their consistency (or not) with diffusion-limited uptake. The results will broadly constrain REE, uranium and alkaline element partition coefficients, which will improve models of diffusion rate and uptake of these geochemically- and toxicologically important elements. All data will be published rapidly in accessible international journals and/or archived in on-line geochemical databases. A PhD student will participate in a SIMS workshop, helping develop a community of SIMS users and present her work on fossils and fossilization to elementary school children and the public through established outreach programs.