TIMS analysis of neodymium isotopes in human tooth enamel using 1013 Ω amplifiers

Abstract

Human provenance studies employing isotope analysis are essential in archaeological and forensic sciences but current applications provide limited spatial resolution. This study reports on the potential of neodymium isotope composition (143Nd/144Nd) to improve human provenancing capabilities. Human tissues contain very low (<0.1 ppm) neodymium concentrations, such that previous composition analysis was not possible. Additionally, Nd composition analysis in human enamel is hindered by Ca in the sample matrix. A modified Nd chromatographic separation technique is reported here, which removes large Ca quantities and accommodates large sample sizes (300-1000 mg). Verification of the modified chromatographic procedure was achieved using an internal synthetic tooth standard. These advancements allow for high precision Nd isotope composition analysis on ~500 mg of tooth enamel, or >100 pg of Nd, by thermal ionization mass spectrometry (TIMS) using 1013 Ω resistors. Neodymium concentrations in enamel from third molars of modern Dutch residents range between 0.1-21.0 ppb (n = 23). The 143Nd/144Nd values for Amsterdam (0.51204-0.51259, n = 12) and Rotterdam (0.51187-0.51239, n = 8) are significantly different (P value = 0.02), demonstrating the potential of neodymium isotope composition to provide improved spatial resolution. Further assessment of Nd composition in enamel of residents from other geological contexts is required to better understand the human provenance capabilities of neodymium.

Evaluation of neodymium isotope analysis of human dental enamel as a provenance indicator using 1013 Ω amplifiers (TIMS)

“…Generally, older geological depositions have lower 143 Nd/ 144 Nd ratios compared to recently formed deposits, with 143 Nd/ 144 Nd ratios typically ranging between 0.510 and 0.514 [40]. Neodymium isotope ratios are transferred from rocks to the vegetation and bodies of water, entering the human body through diet, inhalation and potentially dermal contact [19,41,42]. It is expected that Nd isotopes are not isotopically fractionated during their uptake by the human body, thus reflecting the environmental ratios of the food, water and dust consumed [37,39].…”

“…It is expected that Nd isotopes are not isotopically fractionated during their uptake by the human body, thus reflecting the environmental ratios of the food, water and dust consumed [37,39]. Due to the low concentrations of Nd present in human tissues (<0.7 ppm) there have been few studies addressing neodymium in biological systems (see Plomp et al [19] for a summary). Low Nd concentrations (0.1 to 58.0 ppb [19,43]) in dental enamel limit its analysis and application to human provenancing.…”

“…Due to the low concentrations of Nd present in human tissues (<0.7 ppm) there have been few studies addressing neodymium in biological systems (see Plomp et al [19] for a summary). Low Nd concentrations (0.1 to 58.0 ppb [19,43]) in dental enamel limit its analysis and application to human provenancing. The low Nd concentrations in human tissues can be explained by (1) the low levels of bioavailable Nd in the food chain (ppb range), as vegetation and bodies of water take up limited Nd from the underlying geology [[44], [45], [46]], (2) the moderately toxic nature of Nd [47,48] and lack of physiological or biological function of Nd in the human body [47] and (3) the trivalent ion (Nd 3+ ), which is incompatible with calcium (Ca 2+ ) substitution in the hydroxyapatite crystal lattice of human bone and teeth [19,47].…”

“…Analysis was performed on the mineralised outer surface of the teeth, the enamel. Third molars were donated by inhabitants of the Netherlands ( n = 56, including data from Plomp et al [19]) (Fig. 1), the Caribbean ( n = 3), Columbia ( n = 1) and Iceland (n = 1) (Fig.…”

“…The 10 13 Ω amplifiers are essential for the measurement of small Nd samples, allowing reliable analysis of samples as small as 100 pg. These small Nd samples cannot be successfully analysed with the default 10 11 Ω amplifiers that require >1 ng Nd for analysis [19,20]. The findings of this study were examined and compared to previously published results on Nd and composition from Dutch individuals [19] to evaluate the application of Nd isotopes for human provenancing.…”