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

The oxygen (18 O/16 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 (δ18 O) alone is often spatially indistinct. Adding additional geochemical recorders can refine region-of-origin estimates. In this capacity, strontium (87 Sr/86 Sr) isotope analysis has attracted increased interest. While 87 Sr/86 Sr reflects the influences of local geology, 87 Sr/86 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 87 Sr/86 Sr of hair, human hair was collected from three locations within Salt Lake City, Utah along with the donor's sex. The 87 Sr/86 Sr and δ18 O of hair and local tap water were measured. There were no significant relationships between sex and either δ18 O or 87 Sr/86 Sr of hair, nor between collection location and the δ18 O of hair. However, we found significant associations between collection location and 87 Sr/86 Sr of hair. These findings suggest that interactions with local water may be an important source of Sr to human hair and that the 87 Sr/86 Sr of hair may have the capacity to record differences in 87 Sr/86 Sr of tap waters on small spatial scales.