Isotopic Comparison of Hair, Nail and Bone: Modern Analyses

This paper presents a comprison of the isotopic values of eight pairings of hair keratin and bone collagen and 12 pairings of hair keratin and nail keratin taken from living humans resident in the U.K., with the aim of examining whether modern human isotopic data can be directly compared to archaeological isotopic data. Results showed that bone collagen was enriched relative to hair keratin from the same individual by +1·4‰ in δ13C and +0·86‰ in δ15N, with some small degree of variability. Isotopic comparison of hair keratin and nail keratin from the same individual showed that there is no significant difference between hair and nail keratin in δ13C, but that nail keratin is on average +0·65‰ more enriched in δ15N than hair. Differences in amino acid composition between hair keratin and bone collagen may account for the carbon isotopic differences between the two proteins, and there is no significant overall carbon isotopic difference between hair and nail. However there are significant isotopic differences for nitrogen in the two pairings, that differences in amino acid composition and turnover times cannot explain. We suggest that these results indicate that constancy of isotopic values between tissues, even for similar proteins, cannot be taken for granted.