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

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