Particle size matters: The effect of particle size on carbon and oxygen isotope composition of bone hydroxyapatite

Abstract

Objectives Stable isotope studies often focus on hydroxyapatite (bioapatite) to answer questions of paleodiet, paleomobility, and paeloenvironment. This study seeks to determine the effect that sample particle size (in particular SA:V, or surface area to volume ratios) has on measured carbon and oxygen stable isotope values (δ13C and δ18O) in bone hydroxyapatite. Materials and methods Previously ground Homo sapiens sapiens cortical bone samples were subdivided using geological screens to obtain three separate sub‐samples, differing only in their particle size. These aliquots (n = 60) were then treated using established protocols to remove any exogenous organic material (2.5% NaOH) and adsorbed carbonates (0.1 M CH3COOH), and analyzed for δ13C and δ18O using a Kiel‐IV Carbonate Device coupled to a Thermo‐Finnigan DeltaPlus IRMS. Results Data obtained indicate that decreased particle size leads to increases in both δ13C and δ18O, with oxygen isotope values being more dramatically affected. Specifically, it is possible to produce isotopic shifts of as much as 1.0‰ and 4.0‰ for δ13C and δ18O, respectively, solely by analyzing different sized particles from the same individual, bone, and sample. Discussion Based upon the variability seen between different size fractions from the same sample, it is clear that particle size has a meaningful impact on carbon and oxygen isotope composition. We attribute these shifts to the differential adsorption or precipitation of environmental carbon and oxygen during pretreatment. We recommend that particle size be added to the list of potential variables affecting isotope composition, alongside other factors including diagenesis, reagent concentration, and treatment time. We would also note that while most individuals exhibit consistent changes, some do not, and thus further investigation into these phenomena is warranted.

Temporal, spatial and gender-based dietary differences in middle period San Pedro de Atacama, Chile: A model-based approach

“…As all samples considered herein were extracted and analyzed using the same protocols and instruments, the issue of inter-laboratory differences in resulting stable isotope signatures [74][75][76] are not of concern.…”

Paired stable carbon and oxygen isotope analyses of human enamel for forensic human geolocation: An exploratory study

“…Both sets of enamel samples were formed no earlier than An important consideration that cannot be ignored when comparing data with published studies is the possibility of interlaboratory differences in measured isotope values. Isotopic variability of measured values for bioapatite across various laboratories could arise due to differences in sample particle size and/or analytical techniques [62,63]. As such, maximum isotopic variations between δ 13 C values acquired from different laboratories were reported to be approximately 0.6‰ for differences stemming solely from analytical techniques with the same sample preparation methods [64] and an increase of up to 1‰ for differences in surface area to volume ratios for sampled materials [63].…”

“…Isotopic variability of measured values for bioapatite across various laboratories could arise due to differences in sample particle size and/or analytical techniques [62,63]. As such, maximum isotopic variations between δ 13 C values acquired from different laboratories were reported to be approximately 0.6‰ for differences stemming solely from analytical techniques with the same sample preparation methods [64] and an increase of up to 1‰ for differences in surface area to volume ratios for sampled materials [63]. Sample preparation methods, including the amount of acid and the methodology for organic carbonate removal, were shown not to significantly influence δ 13 C values of bone bioapatite [62].…”

The use of stable isotopes in postconflict forensic identification

“…In short, the temperature used for acidification will impact the δ 18 O values measured for a carbonate sample and should be corrected for (Kusaka & Nakano, 2014; Passey et al, 2007). Additionally, research has found that the particle size of bioapatite can impact measured δ 13 C and δ 18 O values, potentially due to reaction differences during sample preparation (Moloughney et al, 2020). An alternative approach to measuring the δ 18 O values of bioapatite involves analysis of the O atoms in phosphate (PO 4 ), using a high temperature conversion (HTC) elemental analyzer attached to an isotope ratio mass spectrometer.…”