Strontium and lead isotope ratios in human hair: investigating a potential tool for determining recent human geographical movements

Three cleaning techniques that remove external contamination of human hair are assessed to investigate the potential use of Sr and Pb isotope composition of hair for human provenancing. These techniques are; (i) a centrifugation technique using diiodomethane where hair and soil particles are separated by density difference; (ii) a leaching technique of the hair surface using 2 M HNO3 acid and (iii) cleaning the hair with chloroform, methanol and ultra pure water. These techniques are validated and are successfully applied to demonstrate the capability of modern and archaeological human scalp hair and modern human facial hair to record Sr and Pb isotope variations related to geographic location. In this study, Sr isotope ratios analysed in modern human scalp hair from a female vegetarian and non-smoker register marked isotopic change on a monthly timescale when an individual moves to locations with contrasting Sr isotope compositions. Pb isotope ratios do not show significant changes after moving locations, possibly due to comparable Pb isotope ratios in the two environments. In contrast, Pb isotopes ratios analysed in facial hair from a male omnivore and smoker record isotopic changes within a two week period when moving between locations with significant differences in environmental Pb isotope compositions. Further research is needed to determine the exact rate of change in isotopic composition in scalp and facial hair in humans with different diets and life styles that move from geographical locations with isotopic contrasting composition.