Effects of tanning on the stable isotopic compositions of hair

We investigated the effect of tanning on the stable isotopic compositions (CNHOS) of hair keratin. Samples of hair from polar bear (Ursus maritimus) hides were collected before and after the tanning process from a commercial tannery. With the exception of sulphur isotopes, tanning did not alter the stable isotopic compositions of hair. δ³⁴S values were slightly more positive (1 per mil) in hair that had gone through the tanning process, likely as a result of the tanning agent, alum (Al₂(SO₄)₃) or exposure to sulphuric acid (H₂SO₄). This indicates that, with the exception of sulphur isotopes, hair keratin is resistant to subsequent isotopic alteration by the techniques used in tanning of animal hides and thus the original stable isotopic information is likely to be preserved in archived samples, such as taxidermic mounts and museum specimens. This is an important consideration when dealing with ecological and forensic applications to wildlife, such as evaluating provenance or migratory reconstructions, and so will assist in conservation efforts and investigations of trafficking and poaching.