Mapping bone microstructure trace element composition: Sr, Ba, Cu, and Pb in an early modern Danish skeleton

Abstract

Objectives A Geographical Information System (GIS) approach enhances the acquisition, management, and analysis of trace element data from cortical bone. A high‐resolution spatial dimension expands the research potential of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS) data from cortical bone cross‐sections. The chemical characterization of hundreds of osteons, notably sequences of superimposed osteons, permits more exacting studies of individual life histories than is possible with analyses of bulk bone samples. Methods A GIS procedure was used to estimate Sr, Ba, Pb, and Cu concentrations, originally generated through LA‐ICP‐MS, for bone microstructural features, notably fragmentary and intact osteons, in a human femoral cross‐section. The skeleton is from Ribe, Denmark, and dates to the early modern period. Results Postmortem chemical alteration was limited to the bone's outer and inner margins. Two dietary indicators, Sr and Ba, and two socioeconomic indicators, Pb and Cu, measured for individual osteons were correlated with one another. Osteon sequences indicate concentrations of all four elements increased late in life for this individual. Conclusions The application of GIS procedures expedites fine‐grained analyses of variation in the distribution of trace elements in bone microstructure identifiable in cortical bone cross‐sections. It provides an efficient means of extracting the most information possible from LA‐ICP‐MS data about the lives of people in the past. Combining the two procedures makes it easier to track exposure to elements such as Pb across the part of an individual's life represented by osteon sequences.

Variation in Bioavailable Lead, Copper, and Strontium Concentrations in Human Skeletons from Medieval to Early Modern Denmark

“…For elements such as Pb, the uneven distribution even extends to different parts of osteons (Pemmer et al, 2013;Simpson et al 2021b). That is precisely what has been found in centuries-old Danish archaeological bones (Milner et al, 2023;Rasmussen et al, 2019Rasmussen et al, , 2020b. For example, in the archaeological samples the distribution of Pb within osteons, when visualized through Laser Ablation Inductively Coupled Plasma Mass Spectrometry, is consistent with its concentration in cement lines, the highly mineralized outer margins of osteons, and the borders of central canals (Skedros et al, 2005;Wittig et al, 2019).…”

“…The critical issue, of course, is whether long-buried bones have been so thoroughly altered through exposure to soil and groundwater, and whatever contaminants they might contain, that their value for archaeological purposes is fatally compromised. Recent work focused on a cross-section of an archaeological femur from Denmark showed that concentrations of Pb, Cu, and Sr were both high and variable near the cortical bone's surface (Milner et al, 2023). In the interior, however, the concentrations of these three elements varied from one osteon (Haversian system) to the next, not according to an osteon's distance from the exposed surface of the bone.…”

“…The process started with sampling intact cortical bone in the facility where the skeletons were stored. Exterior and interior bone surfaces were not sampled to reduce the possibility of diagenetic alternation that affects element concentrations (Milner et al, 2023;Rasmussen et al, 2019). Trabecular bone was likewise avoided.…”

“…Before sampling the cortical bone, ca. 1 mm of the bone's exterior was removed, leaving a pristine sampling area though the elimination of bone likely to have been altered by diagenetic changes (Milner et al, 2023;Rasmussen et al, 2019). The uppermost sheet of Al foil was then replaced before the sample that would be subsequently analysed was drilled from the now-decontaminated bone (surface bone removed).…”

“…Glossing for the moment over details, for premodern Danes, Sr yields a dietary signature, and Pb and Cu reflect social status and settlement type, specifically life within urban settings in contrast to the surrounding countryside (Rasmussen et al, 2015(Rasmussen et al, ,2017(Rasmussen et al, , 2020a. Fortunately, trace element concentrations can be measured reliably in archaeological bones, and several elements, including Pb, Cu, and Sr, retain a biogenic signal free of significant postmortem alterations (diagenesis) when appropriate sampling procedures are employed (Milner et al, 2023;Rasmussen et al, 2019). Sitespecific information supporting inferences about varied chemical life histories in medieval to early modern Denmark is presented in Supplemental Information.…”