Strontium isotope ratios of human hair from the United States: Patterns and aberrations

Abstract

Rationale Strontium isotope ratios (87Sr/86Sr) of hair may be a valuable tool to estimate human provenance. However, the systematics and mechanisms controlling spatial variation in 87Sr/86Sr of modern human hair remain unclear. Here, we measure 87Sr/86Sr of hair specimens from across the USA to assess the presence of geospatial relationships. Methods Ninety‐eight human hair specimens were collected from salon/barbershop floors in 48 municipalities throughout the conterminous USA. [Sr] and 87Sr/86Sr ratios were measured from hair using quadrupole and multi‐collector inductively coupled plasma mass spectrometers, respectively. The [Sr] and 87Sr/86Sr ratios of hair were compared with the measured [Sr] and 87Sr/86Sr ratios of tap waters from the collection locations. In addition, the 87Sr/86Sr ratio of hair was compared with the modeled ratios of bedrock and surface waters. Results Hair color was independent of the 87Sr/86Sr ratio, but related to [Sr]. The 87Sr/86Sr ratios of hair and leachate were not statistically different and were positively correlated; however, in several hair‐leachate pairs, the ratios were conspicuously different. The 87Sr/86Sr ratios of both hair and leachate were linearly correlated with tap water. The 87Sr/86Sr ratio of hair was also significantly correlated with the modeled ratio of bedrock and surface waters, although the 87Sr/86Sr ratio of hair was most strongly correlated with the measured ratio of tap water. Conclusions The 87Sr/86Sr ratio of hair is related to the ratio of tap water, which varied geographically. The ratio of hair provided geographic information about an individual's recent residence. Differences in the 87Sr/86Sr ratios of hair and hair leachate may be concomitant with travel and could potentially be used as a screening tool to identify recent movements.

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

“…However, because of the complexity of the modern supermarket diet, it is almost impossible to compile the 87 Sr/ 86 Sr ranges of local foods from all traveled locations. As previous studies have shown that the hair samples usually have the same 87 Sr/ 86 Sr as the local tap water (Tipple et al, 2019;Ammer et al, 2020), we chose the 87 Sr/ 86 Sr ratios of the tap water samples in the FAD (Chartrand and St-Jean, 2015) and the river or tap water samples in the literature (Voerkelius et al, 2010;Chesson et al, 2012;Bataille et al, 2020b) to estimate the range of hair 87 Sr/ 86 Sr for the studied individual.…”

“…Previous studies demonstrated that the 87 Sr/ 86 Sr ratios in hair are strongly related to the 87 Sr/ 86 Sr ratio of local tap water (Tipple et al, 2018(Tipple et al, , 2019Ammer et al, 2020). If the hair of the volunteer recorded the 87 Sr/ 86 Sr ratios of tap water at traveled locations by drinking the tap water and incorporating its 87 Sr/ 86 Sr ratio into hair through the bloodstream like the light stable isotope systems, we would expect large 87 Sr/ 86 Sr variations throughout the predicted profile shown in Figure 5.…”

“…As shown in previous studies, exogenous Sr can be rapidly incorporated into hair keratin after the eruption from the scalp (Chittleborough, 1980;Kempson and Lombi, 2011), and the 87 Sr/ 86 Sr ratios in human keratinous tissues can rapidly inherit the 87 Sr/ 86 Sr of bathing or showering water (Mancuso and Ehleringer, 2018;Tipple et al, 2018;Hu et al, 2020). Therefore, we would expect the 87 Sr/ 86 Sr ratios in the hair of the volunteer to incorporate exogenous Sr from the last location where the volunteer resided and/or from the location where the volunteer resided the longest (Hu et al, 2018(Hu et al, , 2020Tipple et al, 2018Tipple et al, , 2019. Indeed, the 87 Sr/ 86 Sr ratios in the hair of the volunteer (0.7110-0.7119) fall close to the 87 Sr/ 86 Sr ratios of tap water in Ottawa, the last city where the volunteer resided (0.7126-0.7128) (Table 1).…”

Comparison of strontium isotope ratios in Mexican human hair and tap water as provenance indicators

“…Three main sources are considered to contribute to the 87 Sr/ 86 Sr ratios in human hair: exogenous, drinking water, and diet. Despite the fact that several studies have reported potential exogenous signatures embedded in human hair, most likely influenced by bathing in local tap water and from local dust [33][34][35][36], it is argued in this study, that the "contamination" would be of local origin and therefore not significantly offset the results in terms of potential provenance information. As previously mentioned, Mexico is known to be one of the highest bottled water consumers in the world.…”

“…Researchers have argued that the 87 Sr/ 86 Sr ratios in human hair may be skewed due to exogenous signatures embedded in human hair, such as bathing water and dust [33][34][35][36]. Any "contamination" is in fact local and therefore will not significantly influence the goal of characterizing the bioavailable Sr of a region.…”