Strontium isotope ratios of human hair record intra-city variations in tap water source

Abstract

The oxygen ( ¹⁸O/ ¹⁶O) isotope analysis of hair is commonly applied to reconstruct an individual’s residence history. However, region-of-origin as determined from oxygen isotope values ( δ ¹⁸O) alone is often spatially indistinct. Adding additional geochemical recorders can refine region-of-origin estimates. In this capacity, strontium ( ⁸⁷Sr/ ⁸⁶Sr) isotope analysis has attracted increased interest. While ⁸⁷Sr/ ⁸⁶Sr reflects the influences of local geology, ⁸⁷Sr/ ⁸⁶Sr of hair includes both external environmental signals as well as the internal dietary indicators. To better understand the impact of these contributions to the spatial signal encoded within ⁸⁷Sr/ ⁸⁶Sr of hair, human hair was collected from three locations within Salt Lake City, Utah along with the donor’s sex. The ⁸⁷Sr/ ⁸⁶Sr and δ ¹⁸O of hair and local tap water were measured. There were no significant relationships between sex and either δ ¹⁸O or ⁸⁷Sr/ ⁸⁶Sr of hair, nor between collection location and the δ ¹⁸O of hair. However, we found significant associations between collection location and ⁸⁷Sr/ ⁸⁶Sr of hair. These findings suggest that interactions with local water may be an important source of Sr to human hair and that the ⁸⁷Sr/ ⁸⁶Sr of hair may have the capacity to record differences in ⁸⁷Sr/ ⁸⁶Sr of tap waters on small spatial scales.