The trace elements distribution embedded in tooth enamel offers a means to study exposure of toxic metals and allows the reconstruction of dietary behaviors. The quantification of most of the elements with a spatial high resolution (~50μm) is routinely achieved using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). However, the lack of a comprehensive framework of trace elements distribution in enamel jeopardizes any endorsed sampling strategy using LA-ICPMS. The present work is an effort to improve our knowledge on this issue. We studied a suite of 22 sectioned teeth with known dietary history, including 12 3rd molars from 12 living individuals and 10 primary teeth from 3 living individuals. Using LA-ICPMS, we measured Ca, Cu, Zn, Ni, Sr, Ba and Pb variations along 2 or 3 rasters from cervical to occlusal enamel. Calcium concentrations are lower in primary than in permanent teeth and do not vary spatially within a tooth suggesting that enamel matures homogeneously before eruption. The Pb/Ca ratio does not vary within tooth enamel and between primary and permanent tooth enamel. The Cu/Ca and Ni/Ca ratios do not vary within tooth enamel but discriminate primary from permanent tooth enamel. The Zn/Ca ratios are higher in permanent than in primary tooth enamel, and increase up to an order of magnitude in the last hundred of microns at the enamel surface. The Sr/Ca and Ba/Ca ratios are higher in permanent than in primary tooth enamel, and decrease from the enamel-dentine junction towards outer enamel in permanent but not in primary tooth enamel. Considering the Ca-normalized intra-tooth variations of Zn, Sr and Ba, we recommend to perform laser ablation rasters along the enamel-dentine junction because this area is likely to retain most of the original and complete chemical information related to individual's life.

Department of Anthropology and Human Genetics Faculty of Sciences Charles University Viničná 7 128 43 Prague Czech Republic

Laboratoire de Géologie de Lyon UMR 5276 CNRS Ecole Normale Supérieure de Lyon 46 Allée d'Italie 69364 Lyon Cedex 07 France

Laboratory of Archaeobotany and Palaeoecology Faculty of Science University of South Bohemia Na Zlaté stoce 3 370 05 České Budějovice Czech Republic

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