Examining Biogenic and Diagenetic Lead Exposure with Synchrotron Radiation X-ray Fluorescence Imaging of Experimentally Altered Bone

Abstract

Trace elements, including the toxic trace metal of lead (Pb), have both the potential to provide valuable insights into past human lifeways, as well as a strong affinity for bone and dental tissues, making the analysis of them potentially useful to bioarchaeology. However, trace element analysis of archaeological skeletal remains is constantly hindered by diagenesis, the post-mortem chemical, physical, and biological transformations of skeletal remains, as these processes can interfere with the biogenic (lifetime) chemical composition of bone and teeth. New approaches may aid in overcoming some of these limitations. Synchrotron radiation X-ray fluorescence imaging (SR-XFI) can generate maps of trace metals, including Pb, in bone on a microstructural scale, and it has been proposed that this could be used to distinguish biogenic from diagenetic Pb exposure and provide insights into the individual life histories of Pb exposure. Recent technological improvements in SR-XFI, particularly the use of confocal optics, has permitted higher spatial resolution in element maps and optical, rather than physical, sectioning of fragile archaeological bone samples. The aim of this thesis was to experimentally test whether there are spatial differences in the distribution of Pb for diagenetic and biogenic modes of uptake in bone, and evaluate individual life histories of biogenic Pb exposure in a cadaveric population sampled from Saskatoon, Saskatchewan. To address these aims, this study used inductively coupled plasma-mass spectrometry (ICP-MS) and SR-XFI on bone samples from eighteenth to nineteenth century archaeological sites from Antigua and Lithuania representing biogenic and diagenetic Pb exposure, respectively, and experimentally altered modern bone samples donated to the Body Bequeathal Program (University of Saskatchewan, Saskatoon, SK). Pb concentrations in the cadaveric bone ranged from 1.2 to 7.1 µg/g. By contrast, the bulk Pb concentration of the Antigua sample was 253.94 µg/g and the bulk Pb concentration of the Lithuania individual was 125 µg/g. SR-XFI results demonstrated that there are marked differences in the spatial distribution of Pb corresponding to biogenic versus diagenetic uptake for both archaeological and experimentally altered modern samples. The modern Saskatchewan sample demonstrated a pattern of relatively low Pb exposure with higher levels of Pb exposure occurring in mature bone structures that formed earlier in life, likely during the era of leaded gasoline (pre-1980s).