Reconstruction of human exposure to heavy metals using synchrotron radiation microbeams in prehistoric and modern humans

Objective  Teeth can serve as records of environmental exposure to heavy metals during their formation. We applied a new technology — synchrotron radiation microbeams (SRXRF) — for analysis of heavy metals in human permanent teeth in modern and historical samples. Methods  Each tooth was cut in half. A longitudinal section 200 μm in thickness was subjected to the determination of the heavy metal content by SRXRF or conventional analytical methods (ICP-MS analysis or reduction–aeration atomic absorption spectrometry). The relative concentrations of Pb, Hg, Cu and Zn measured by SRXRF were translated in concentrations (in g of heavy metal/g of enamel) using calibration curves by the two analytical methods. Results  Concentrations in teeth in the modern females (n = 5) were 1.2 ± 0.5 μg/g (n = 5) for Pb; 1.7 ± 0.2 ng/g for Hg; 0.9 ± 1.1 μg/g for Cu; 150 ± 24.6 μg/g for Zn. The levels of Pb were highest in the teeth samples obtained from the humans of the Edo era (1603–1868 ad) (0.5–4.0 μg/g, n = 4). No trend was observed in this study in the Hg content in teeth during 3,000 years. The concentrations of Cu were highest in teeth of two medieval craftsmen (57.0 and 220 μg/g). The levels of Zn were higher in modern subjects (P < 0.05) than those in the Jomon (~1000 bc) to Edo periods [113.2 ± 27.4 (μg/g, n = 11)]. Reconstruction of developmental exposure history to lead in a famous court painter of the Edo period (18th century) revealed high levels of Pb (7.1–22.0 μg/g) in his childhood. Conclusions  SRXRF is useful a method for reconstructing human exposures in very long trends.