Pb and Sr concentrations and isotopic compositions in prehistoric North American teeth: A methodological study

- We measured Pb and Sr concentrations and isotopic compositions on dentin and enamel samples as small as 1 mg.
- There is real compositional variability at small (< 10 mg) sample sizes.
- Pb and Sr isotopic compositions discriminate between locations better than Sr alone.
- Pb is more susceptible to post-mortem exchange than Sr; dentin is more susceptible to exchange than enamel.
- We cannot unequivocally distinguish in-vivo from diagenetic compositions.

We present Pb and Sr isotopic compositions and elemental concentrations for dentin and enamel from 28 human teeth from 10 locations in the southwestern United States. These teeth represent Native American communities that were functioning between 300 BCE and 1200 CE. We wished to assess whether Pb isotopic data can extend the interpretations made from Sr isotopic data alone, and to determine the analytical requirements for doing Sr and Pb analyses from single samples. Pb concentrations in our samples are between 0.06 and 48 ppm, with Sr concentrations between 10 and 3300 ppm. 87Sr/86Sr compositions lie between 0.708 and 0.712. Pb isotopic compositions are more variable, with 206Pb/204Pb ranging between 17.9 and 21.7. Isotopic compositions and elemental concentrations for both Sr and Pb can be determined on samples smaller than 1 mg, but there is real heterogeneity between samples of this size. Neither concentrations nor isotopic compositions are reproducible to within analytical uncertainty in replicate aliquots from individual teeth. We cannot determine whether this variability is an in-vivo or a diagenetic effect. Combined Pb and Sr isotopic data discriminate most locations, and the inclusion of Pb data provides a stronger basis for archeological interpretations. Our data suggest that Pb is more susceptible to post-mortem exchange than Sr. Background isotopic data are needed to characterize Pb and Sr sources in the study areas. Pb concentration data for enamel samples indicate a blood Pb load of 0.1-0.2 μg Pb/dL for preindustrial Native Americans.