Oxygen and Hydrogen Isotopes in Human Hair and Tap Water: Modeling Relationships in a Modern Mexican Population

Abstract

This study investigates the relationship between O and H isotopes in samples of Mexican hairand drinking water. The purpose of this study was twofold. First, we wanted to quantify the relationship between isotopes in Mexican hair and tap water to understand the impact of water stress and differing socioeconomic status on accurate predictions of drinking water. Second, we wanted to determine whether currently existing semi mechanistic models could accurately represent the relationship between hair and tap water. For this study, we used a subset of paired (N = 62) human hair and (N = 76) tap water samples. Isotope values in tap water spanned a range from -11.4 ‰ to -4.3 ‰ and -79.1 ‰ to -22.5 ‰ for δ 18 O and δ 2 H, respectively. Isotope values in hair ranged from +9.5 ‰ to +16.1 ‰ and -90.8 ‰ to -53.7 ‰ for δ 18 O and δ 2 H, respectively.The most depleted δ 18 O and δ 2 H hair values came from individuals in the state of Morelos. For our modern Mexican population, positive correlations between isotopes in hair and water were not significant, with correlation coefficients of r = 0.61 (p = 0.05) and r = 0.60 (p = 0.06) for 18 O and 2 H respectively. Error-in-variables regression yielded linear fits that were somewhat better for 2 H relative to 18 O: δ 18 Oh = 0.183 [± 0.132] δ 18 Otw + 15.7 [± 0.9] ‰ (r 2 = 0.23); δ 2 Hh = 0.181 [± 0.076] δ 2 Htw -64.0 [± 3.0] ‰ (r 2 = 0.34). In short, data from this Mexican population do not exhibit the strong relationships between isotope values of 18 O and 2 H in tap water and hair that have been characteristic of other populations studied to date. Given the economic stratification of this region and the poor correlation between hair and water samples, we chose to consider the possibility that lthe fraction of the diet derived from local sources -and fsthe fraction of nonexchangeable H in keratin that was fixed in vivo-are local, rather than global, parameters for this population. We estimated a different value of l and fs for each location. Given the anticipated importance of the non-local dietary contribution, we treated the isotopic content of non-local

Examination of amino acid hydrogen isotope measurements of scalp hair for region‐of‐origin studies

“…Overall, our data suggest that the consumption of local/regional versus continentally sourced foods could playing a larger role in human tissue δ 2 H composition than previously assumed; however, further research needs to be conducted on this topic. Essential amino acid δ 2 H analysis could be useful for geolocation studies in contexts where tap water is not locally sourced 34,63,64 because these compounds may more faithfully represent regional or local sources of food than hydrogen in bulk tissues.…”

The use of stable isotopes in postconflict forensic identification

“…This has led investigators to use Sr in combination with C and/or O to predict the likely origin of recovered UBC remains (e.g., Bartelink et al, 2018, 2020; Bartelink & Chesson, 2019; Kramer et al, 2020). Mapping products (isoscapes) needed for these geolocation efforts are being rapidly created—that is, for Mexico (Ammer, Kootker, et al, 2020; Juarez et al, 2018; see Figure 2), and the circum‐Caribbean region (Bataille et al, 2012; Laffoon et al, 2017; see Figure 3) as well as other parts of the world (Adams et al, 2019; Bataille et al, 2018, 2020; Daux et al, 2021; Gautam et al, 2020; Shin et al, 2020; Wang & Tang, 2020; Zieliński et al, 2021). These products, in conjunction with more regular use of isotope testing, should help foster more widespread application of the technique in the coming years.…”