Modern human dental enamel as a biomineral baseline for rare earth elements and yttrium in urban Nanjing, China.

Rare earth elements (REEs) and yttrium, collectively termed REY, occur in urban environments and biological matrices, yet their concentrations and interpretable pattern features in modern human enamel remain poorly constrained. Mature enamel is acellular and not physiologically renewed, allowing chemical information incorporated during formation to persist. Concentrations of La to Lu, excluding Pm, together with Y, were measured in 46 enamel samples from Nanjing, eastern China, by inductively coupled plasma mass spectrometry (ICP-MS). Concentrations, REE group proportions, CI-normalized patterns, λ coefficients and fitted Ce, Eu and Gd departures were evaluated in all 46 samples. Formation timing was assessed in 36 third molars. Total REE concentrations ranged from 6.1 to 24 ng/g and total REY concentrations from 7.6 to 32 ng/g. Light rare earth elements comprised a median of 73% of the REE inventory. Normalized patterns showed substantial local scatter, while λ coefficients summarized their broad shape. Eu showed a broadly positive departure from the fitted background, whereas Ce and Gd showed no stable directional departure across samples or model settings. In third molars, later estimated formation midpoints were associated with lower λ0 and λ1 values. Because formation midpoint was derived from extraction age and the models explained only limited variation, these associations represent differences among individuals rather than changes within enamel. The dataset provides a modern reference for enamel REY concentrations and supports cautious comparison of broad pattern features across populations, environments, and developmental periods.