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

Abstract

Studying the isotope variability in fast-growing human tissues (e.g., hair, nails) is a powerful tool to investigate human nutrition. However, interpreting the controls of this isotopic variability at the population scale is often challenging as multiple factors can superimpose on the isotopic signals of a current population. Here, we analyse carbon, nitrogen, and sulphur isotopes in hair from 590 Canadian resident volunteers along with demographics, dietary and geographic information about each participant. We use a series of machine-learning regressions to demonstrate that the isotopic values in Canadian residents' hair are not only influenced by dietary choices but by geographic controls. First, we show that isotopic values in Canadian residents' hair have a limited range of variability consistent with the homogenization of Canadian dietary habits (as in other industrialized countries). As expected, some of the isotopic variability within the population correlates with recorded individual dietary choices. More interestingly, some regional spatial patterns emerge from carbon and sulphur isotope variations. The high carbon isotope composition of the hair of eastern Canadians relative to that of western Canadians correlates with the dominance of corn in the eastern Canadian food-industry. The gradient of sulphur isotope composition in Canadian hair from coast to inland regions correlates with the increasing soil pH and decreasing deposition of marine-derived sulphate aerosols in local food systems. We conclude that part of the isotopic variability found in the hair of Canadian residents reflects the isotopic signature associated with specific environmental conditions and agricultural practices of regional food systems transmitted to humans through the high consumption rate of intra-provincial food in Canada. Our study also underscores the strong potential of sulphur isotopes as tracers of human and food provenance.

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

“…The majority of the measured δ 15 N values in the hair profile of the individual falls within a tight range of 9.5-10.25 (Figure 4). These values are in the upper range of other Canadians in the FAD (Chartrand and St-Jean, 2015;Bataille et al, 2020a), suggesting, as δ 13 C values do, that our volunteer had a specific diet, possibly high intake of animal or marine-based protein (O'Connell and Hedges, 1999;Petzke et al, 2005bPetzke et al, , 2010. Most of the values are within the predicted range except for a few outliers.…”

“…Sr concentration analysis was performed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) (Agilent 8800 triple quadrupole mass spectrometer) at the Department of Earth The estimates of isotope ranges for each location are discussed in section "Estimate isotope ranges from the Forensic Attribution Database and the literature." Data sources: a Ranges of stable isotope values of local residents' hair samples from CBRNE project (Chartrand and St-Jean, 2015;Bataille et al, 2020a). b Ranges of strontium isotope ratios of tap water samples from CBRNE project (Chartrand and St-Jean, 2015 and Environmental Sciences, University of Ottawa.…”

“…We compiled the ranges of δ 2 H values, δ 13 C values, δ 15 N values, and 87 Sr/ 86 Sr ratios of each location from our database, the Forensic Attribution Database (FAD; Chartrand and St-Jean, 2015;Bataille et al, 2020a), completed by literature data (Table 1). The FAD gathers isotope data in hair from 600 Canadian hair donors and tap water samples collected across Canada (Chartrand and St-Jean, 2015;Bataille et al, 2020a). In this study, we compiled those isotopic ranges from hair samples of the locations (or the nearest locations) visited by our volunteer from May 1, 2009 to Nov 20, 2010.…”

Calibration chain transformation improves the comparability of organic hydrogen and oxygen stable isotope data

“…We used the method to transform two sets of modern human hair δ 2 H data originally calibrated to the OldUT_H_1 (Ehleringer et al., 2008; Thompson et al., 2010) and CAN_H_1 (Bataille et al., 2020; C.P. Bataille, pers.…”

“…We validated the quality of the calibration chain transformations using several datasets in which data for the same or related samples were originally reported on different reference scales. These include modern human hair δ 2 H data reported on the OldUT_H_1 (Ehleringer et al., 2008; Thompson et al., 2010) and CAN_H_1 scales (Bataille et al., 2020; C.P. Bataille, pers.…”