AUTHOR=Simpson Emily M. B. , Crowley Brooke E. , Sturmer Daniel M. 

TITLE=Is the damage worth it? Testing handheld XRF as a non-destructive analytical tool for determining biogenic bone and tooth chemistry prior to destructive analyses

JOURNAL=Frontiers in Environmental Archaeology

VOLUME=1

YEAR=2023

URL=https://www.frontiersin.org/journals/environmental-archaeology/articles/10.3389/fearc.2022.1098403

DOI=10.3389/fearc.2022.1098403

ISSN=2813-432X

ABSTRACT=<p>Isotopic analysis is destructive and requires that a specimen retains its original (biogenic) chemical composition. A specimen's relative abundance of calcium and phosphorous (Ca/P) or carbonate and phosphate (CO<sub>3</sub>/PO<sub>4</sub>) is often used to assess preservation. If a specimen's Ca/P or CO<sub>3</sub>/PO<sub>4</sub> is similar to modern specimens, a specimen's isotopic composition may be biogenic. However, most methods for measuring these proxies are destructive. Moreover the relationships between Ca/P, CO<sub>3</sub>/PO<sub>4</sub> and isotopic preservation are poorly established. In this study, we assessed the ability of handheld X-ray fluorescence (hXRF) to non-destructively evaluate a specimen's preservation by characterizing the calcium to phosphorous ratio (Ca/P). We first established that surface Ca/P (Ca/P<sub>surface</sub>) for modern specimens was consistent with expectations for unaltered bone (1.3–2.3). Several specimens had slightly larger ratios, suggesting the currently accepted range may need to be expanded. Second, we tested the ability of Ca/P<sub>surface</sub> to detect alteration using twenty Quaternary mammal teeth from Big Bone Lick, Kentucky. Ten specimens had Ca/P<sub>surface</sub> between 1.3 and 2.3 and ten had larger ratios, suggesting alteration. Because most methods measure Ca/P in powder (Ca/P<sub>powder</sub>), we compared Ca/P<sub>surface</sub>, Ca/P<sub>powder</sub>, and the enamel subsurface (Ca/P<sub>subsurface</sub>). With two exceptions, Ca/P<sub>subsurface</sub> and Ca/P<sub>powder</sub> were below 2.3, regardless of Ca/P<sub>surface</sub>, suggesting that Ca/P<sub>powder</sub> and Ca/P<sub>subsurface</sub> underestimate alteration. We next compared Ca/P<sub>surface</sub>, CO<sub>3</sub>/PO<sub>4</sub>, and carbon (δ<sup>13</sup>C) and oxygen (δ<sup>18</sup>O) isotope values for the fossil teeth. Fourteen specimens were identified as altered or unaltered by both proxies, but six specimens only had one altered proxy. Specimens with both proxies altered had lower, less variable δ<sup>13</sup>C values than specimens with both proxies unaltered. Median δ<sup>18</sup>O values were similar between these groups. Individuals with altered Ca/P<sub>surface</sub> but unaltered CO<sub>3</sub>/PO<sub>4</sub> isotopically resembled specimens with both proxies altered. Conversely, specimens with unaltered Ca/P<sub>surface</sub> and altered CO<sub>3</sub>/PO<sub>4</sub> were similar to specimens with both proxies unaltered. Notably, all individuals with both proxies altered had relatively low δ<sup>13</sup>C values, including a horse and mammoth, which are normally considered grazers (and therefore should have higher δ<sup>13</sup>C values). These and other altered specimens may be isotopically compromised. Overall, our results suggest that Ca/P<sub>surface</sub> is effective at detecting alteration non-destructively, quickly, and affordably, making it an attractive approach for analyzing unique specimens.</p>