Rare earth element profiles and fractionation patterns in modern human dental enamel from Beijing, China.

PURPOSE: Rare earth element (REE) occurrence and fractionation in modern human dental enamel remain poorly characterized, limiting the use of enamel as a biomineral archive and for archaeological comparisons. This study characterized REE abundance, lanthanide fractionation, anomaly behavior and Y/Ho variability in modern enamel. METHODS: REEs from La to Lu together with Y were measured by inductively coupled plasma mass spectrometry in modern human enamel samples from Beijing, China. Data were evaluated using total REE abundance, patterns normalized to Post-Archean Australian Shale (PAAS), Ce, Eu and Gd anomalies, and molar Y/Ho ratios. RESULTS: REEs were quantifiable at ng/g levels, with total REE abundance (ΣREE) ranging from 4.47 to 159 ng/g. Variation was primarily interindividual. Age at extraction and sex were treated descriptively and were not interpreted as independent controls. Light REEs dominated the total REE budget, neighboring lanthanides were generally correlated, and normalized patterns documented fractionation across the series. Ce remained broadly coupled with adjacent light REEs. Eu anomalies were predominantly positive, whereas positive Gd anomalies occurred in a smaller subset of samples. These departures require cautious interpretation in view of the low concentrations, analytical constraints and possible components retained on enamel surfaces. Molar Y/Ho ratios varied among samples, supporting Y and Ho fractionation rather than a simple provenance interpretation. CONCLUSION: Modern human enamel contains a low but internally structured REE inventory. These results provide a modern reference for REE concentrations, fractionation, anomaly behavior and Y/Ho variability, supporting comparisons with other biomineral tissues and diagenetically modified ancient enamel.