Geographic variation of Sr and S isotope ratios in bottled waters in Japan and sources of Sr and S

The geographic distribution of the stable isotope ratio of Sr (⁸⁷Sr/⁸⁶Sr) is useful for identifying the provenance of drinking water, organisms, and agricultural products. To explore how environmental factors influence this ratio, we determined the ⁸⁷Sr/⁸⁶Sr, sulfur isotope ratio (δ³⁴S), and elemental composition of 208 commercially available bottled waters in Japan, and compared them with the ⁸⁷Sr/⁸⁶Sr values of groundwater, rainwater, rocks, and vegetables from similar localities. We classified the bottled waters into seven categories based on the geology of their source aquifers. The ⁸⁷Sr/⁸⁶Sr and concentrations of several elements (Ca, K, Si, Rb, and Ba) of the bottled waters differed with the aquifer rock type and were well correlated with the ⁸⁷Sr/⁸⁶Sr of reported spring waters, indicating that bottled water, like other groundwater, reflects the lithology and chemistry of its aquifer. The ⁸⁷Sr/⁸⁶Sr of bottled water, taken as a proxy for groundwater, showed regional variations consistent with those of rocks and vegetables, demonstrating that an ⁸⁷Sr/⁸⁶Sr map of water and agricultural products has value for determining the production areas of these substances. However, the value and range of ⁸⁷Sr/⁸⁶Sr differed among these three materials, and the degree of the difference between groundwater and rock depended on the rock type. An analysis of geochemical data from rocks and rainwater suggests that groundwater contains Sr and additional S derived from atmospheric sources such as rainwater and sea salt aerosols. The atmospheric contribution of Sr to groundwater is greatest in areas of siliceous sedimentary rocks with low Sr concentrations and high resistance to weathering. A weak correlation of δ³⁴S of bottled waters with ⁸⁷Sr/⁸⁶Sr indicates the usefulness of maps of combined Sr and S isotope ratios for groundwater provenance. This study shows that for accurate provenance determinations of groundwater, organisms, and agricultural products, it is essential to better quantify the contributions of Sr and S from the atmosphere as well as from rocks and human activities.