Revealing details of stays abroad by sequential stable isotope analyses along human hair strands

Abstract

Multi-element stable isotope analyses of δC, δN, δS and δH values were performed along scalp hair strands to detect isotopic changes resulting from different stays abroad. One hair strand with a hair length of more than 50 cm originated from a German woman, who frequently made long-distance travels of 1 to 4 weeks. The second hair strand with a length of 15 cm was taken from a Japanese woman who went to Germany for a period of some months. Stable isotopic influences due to the stays abroad were clearly reflected in the 5-mm segments along the proximal part of the hair strand; whereas in the more distal parts, the isotopic influences were blurred. This can be regarded as the result of the highly variable intra-individual hair growth rate of single hairs of at least ± 30% compared to the mean growth rate. Consequently, the initial isotope signal obtained by short stays abroad became rapidly attenuated in the more distal parts of the hair strand. Furthermore, decreasing sulphur content associated with higher sulphur isotope values was observed with increasing hair length. The isotope shifts along the scalp hair strand, provoked by dietary changes at new locations, appeared at such points of hair length, which correspond well with the maximum growth rate of single hairs. Consequently, the exact date for any changes coming along with isotopic shifts may be calculated by best approach considering a hair growth value of 1.4 cm per 30 days, instead of the commonly used mean monthly hair growth rate of 1.1 cm. This may be important in forensics, if detailed information about a person's recent lifetime should be figured out by segmental scalp hair analyses.

Assessing the Reliability of Mobility Interpretation From a Multi-Isotope Hair Profile on a Traveling Individual

“…However, the growth rate chosen in this study may not be suitable for other studies. We also added 0.8 cm to the distance of the hair segment to the hair root (Tables 2, 3) to make up the ∼0.5 cm of hair remaining at the scalp during cutting (LeBeau et al, 2011;Lehn et al, 2019) and ∼0.3 cm of hair residue left in the hair follicle (Jimenez et al, 2011). The "distance from hair root" is then used *"Distance from hair root" equals the "distance from cutting end" plus 0.8 cm, which accounts for the distance between the cutting end and the root (discussion in the section "Determining the age model of the observed isotopic profiles").…”

“…Interestingly, Lehn et al (2019) have found that the change of isotope signal on bundled hair profile is usually provoked by the fastest-growing hairs in the hair bundle because those fast-growing single hairs tend to be thicker and heavier thus their isotopic signals outweigh the others. Considering a commonly used mean hair growth rate of 1.1 cm/month and a proposed ± 30% intra-individual variability in single hair growth rate, they found that the growth rate of 1.4 cm per 30 days may be the best approach to calculate the exact dates of the isotopic shifts along the hair profile.…”

“…Therefore, although our chosen value of 1.5 cm per 30 days is the best estimate for the hair growth rate that was used to interpret the isotope profiles, it is likely to represent the fastest growth rate, instead of the average hair growth rate, of the studied individual. Lehn et al (2019) included the uncertainty of intra-individual hair growth rate in their calculation for the expected δ 13 C values along the hair strands. In this study, we calculate the predicted isotope values using a fixed growth rate and discuss the impact of the uncertainty of growth rate on our results in the following section.…”

“…However, such decrease is longer and does not match well with the timing of travel as shown in the predicted profile (Figure 2). This signal in distal part of hair has a high uncertainty in terms of timing (Lehn et al, 2019) and thus is probably highly attenuated by the isotopic signal from Ottawa.…”

Assessing geographic controls of hair isotopic variability in human populations: A case-study in Canada

“…In recent years, several studies have used the C, N and S isotope composition in human tissues (δ 13 C, δ 15 N, and δ 34 S) to investigate differences in human nutrition and dietary choices at the population scale [Reviewed in 3]. Keratinized tissues, hairs and nails, are an ideal substrate for analyzing δ 13 C, δ 15 N and δ 34 S values in dietary studies, as these elements are abundant in keratin and record dietary isotopic values chronologically as they grow [4][5][6][7]. Isotope data from hair can thus provide snapshots of the diet from an individual or population at a monthly temporal resolution [8][9][10][11][12].…”