Sr isotopic signatures of Portuguese bottled mineral waters, their relationships with the geological setting and potential use for product authentication

Abstract

The Sr isotopic ratios of nine bottled natural mineral waters from Portugal were measured in the Laboratory of Isotope Geology of the University of Aveiro (LGIUA). The results obtained show that the Sr isotopic variability of these waters is strongly correlated with the age and mineralogical composition of the aquifer source rocks. The lowest 87Sr/86Sr ratios are found in water samples from the Monchique aquifer (87Sr/86Sr = 0,70447), located in Late Cretaceous alkaline magmatic rocks of mantle origin. The Vimeiro waters are hosted in carbonate and evaporite formations of Jurassic age and have 87Sr/86Sr values of 0,70808, whereas the waters sourced in Cenozoic siliciclastic sediments tend to exhibit higher 87Sr/86Sr ratios, close to the rainwater value (São Silvestre; 87Sr/86Sr = 0,71078). Finally, the waters coming from granitic and/or metamorphic terrains of the Iberian Variscan basement (Vitalis, Luso, Carvalhelhos, Fastio, Serra da Estrela) display the most radiogenic Sr isotopic signatures (87Sr/86Sr > 0,7136). In the modern commercial context, the differences encountered provide a powerful tool for fingerprinting the mineral water origin and may be used for purposes of mineral water authentication. The use of 87Sr/86Sr ratios may also be extended to studies on the provenance of some foods and beverages, taking into account the influence of the geological / pedological factor on the Sr isotopic composition recorded by the plants.