Dear MARMAM community, My co-authors and I are pleased to share our new open-access paper investigating different treatment methods for the preparation of killer whale teeth for stable isotope analysis:
M. Terrapon, Hammond, P.S., McGill, R.A.R., Newton, J., Dougans, J., Matthews, C.J.D., and Hooker, S.K. “ Stable Isotope Analysis (δ13C, δ15N and δ18O) of Killer Whale Dentine: Evaluating Treatment Methods and Establishing Best Practices,” *Rapid Communications in Mass Spectrometry* 40, no. 23 (2026): e70176, https://doi.org/10.1002/rcm.70176. Abstract: Stable isotope measurements in odontocete teeth can be used to reconstruct lifetime ecology, but some pre-treatments may introduce bias. Isolating dentine collagen with HCl decalcification, removing the organic matrix or drying dentine prior to the analysis of structural carbonates can introduce unintended variability, limiting comparability among studies and populations. This study tested pre-treatment methods to quantify their effects. Killer whale teeth were sectioned, annual growth layers microdrilled, and powder allocated to treatments. For collagen δ13C and δ15N, 75 samples were analysed via EA-IRMS as untreated bulk dentine and after 0.25 N HCl decalcification. For structural carbonate δ13C and δ18O, treatment with 30% H2O2 was compared with plasma-ashing and with no treatment (*n* = 16); and we examined the removal of residual water by comparing samples oven-dried at 80°C or 100°C with untreated samples (*n* = 10). All samples for carbonate analysis were injected with 104% orthophosphoric acid to generate CO2, which was analysed using continuous-flow IRMS. HCl decalcification caused mass loss (96.6% ± 2.0%) but yielded collagen of an acceptable quality (C:*N* = 3.3 ± 0.2). Compared with untreated dentine, collagen δ13C decreased (Δmedian = −0.34‰) while δ15N did not differ significantly. Organic-matrix removal treatments altered both isotopes: plasma-ashed samples showed large negative shifts compared with untreated samples in δ13C (Δmedian = −9.04‰) and δ18O (Δmean = −13.48‰) and reduced measurable carbon. H2O2 treatments lowered δ13C relative to untreated samples (Δmean = −0.93‰) but showed no consistent δ18O effect. Drying at 80°C minimised δ13C and δ18O variability. HCl decalcification is recommended before δ13C and δ15N collagen analysis of killer whale dentine, or a δ13C correction factor (here −0.34‰) should be applied. Treatments were unsuitable when undertaking structural carbonate analyses of hydroxyapatite: we suggest that untreated powder oven-dried overnight at 80°C should be used, and we emphasise the importance of pre-treatment tests prior to any new study. It is available open-access here: https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/rcm.70176 Many thanks, Maeva Terrapon, PhD Sea Mammal Research Unit University of St Andrews St Andrews, Fife, KY16 8LB [email protected]
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