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

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