ISOTOPIC ANALYSIS OF HAIR: ITS APPLICATION IN IDENTIFYING INDIVIDUALS AND CHANGES IN DIET (BEFORE AND DURING PANDEMIC)

Isotopic analysis has many purposes, including the interpretation of diet. Values of δ¹³C and δ¹⁵N in hair vary based on whether a person is a vegetarian, pescatarian, or carnivore. δ¹³C values can indicate whether one eats mostly C3 plants (fruits, vegetables, wheats) or C4 plants (grains, maize, sugar cane). δ¹⁵N values are reflective of trophic levels, which range from plants (primary producers) to herbivores (consumers) to carnivores (secondary consumers). Called the “trophic effect”, each step up the food chain increases δ¹⁵N values 3-4‰ (Mingawa 1984). A lower δ¹⁵N value generally indicates the consumption of more plants and less meat. For this study, it was hypothesized that 1) the isotopic profile of hair would indicate if a person’s diet changed as a result of the COVID-19 pandemic, and 2) that isotopic composition of hair could be used in individualizing hairs. Ten strands of hair were collected from seven subjects, measured, cut into 2cm sections, then washed in a (2:1) methanol: chloroform solution to remove any lipids or residue. The samples were then rinsed, dried at 60˚C, subsampled into tin capsules, and analyzed via EA/IRMS. A growth rate of 402 µm a day was assumed, and the average length of each 2cm section was used to calculate the distance of the sample from the root (Loussouarn et al, 2016). The age of the sample was then calculated by multiplying the distance from the root by the growth rate and subtracting from the day sample was taken. Statistical tests, including Welch’s t-test, one-way ANOVA, and Tukey’s range test were performed using PAST 3.0 (Hammer et al, 2012). As to the first hypothesis, changes in the diet due to the pandemic could only be seen in δ¹³C, where 57% of subjects had significant changes in values (p<0.04). As to the second, 67% of possible comparisons between individuals were significantly different in δ¹³C, and 52% were significantly different in δ¹⁵N. These results seem to indicate that 1) some individuals’ change in diet or circumstance due to the COVID-19 pandemic is visible in their δ¹³C hair profiles, and that 2) in some cases, more likely in δ¹³C than δ¹⁵N, it is possible to distinguish between individuals by stable isotopes in hair. Future studies could include larger and more geographically diverse subjects, as well as other stable isotopes of interest, namely δ²H, δ¹⁸O, and δ³⁴S.