Investigação da aplicabilidade da composição isotópica de oxigênio, hidrogênio e estrôncio na autenticação de águas naturais engarrafadas e/ou comercializadas no Estado do Pará – Brasil

Abstract

Bottled water obtained directly from natural sources or by extracting groundwater, in theory, is considered as good quality water, naturally pure, captured in environments free from pollution or contamination, therefore, considered a safe food. However, in addition to the vulnerability to which aquifers may be subject, the final product can be manipulated or even defrauded when considering the increasingly competitive and expanding market in bottled water. Therefore, it is recommended that the manufacturers of this segment look for strategies that highlight, differentiate, or add qualities of bottled water. The guarantee of the origin of its source, determined by analytical methods, can guarantee its quality and add important information to the consumer and their producers. Isotopic analyzes combined with chemical analyzes have been used in research on food products as a tool to identify and authenticate the geographical origin, certify and still control the quality, aiming at the safety of these foods. Also, isotopic analyzes can be used as excellent tracers assisting in forensic science. The isotopic compositions of hydrogen, oxygen, and strontium from bottled waters reflect, on average, the isotopic composition of the spring water, indicating that they preserve information about the water source from which they were bottled. In this context, this work proposed investigating the applicability of the isotopic composition of strontium, oxygen, and hydrogen as a tool to characterize, authenticate, and certify bottled waters. Between 2017 and 2019, several brand bottled waters were sampled in supermarkets of Belém, state of Pará. This sampling was conducted by observing the lithostratigraphic units of the water source, geographical locations, filling dates, and the bottle's validity. The work was carried out in two ways. In the first, seven samples were acquired periodically considering the filling date corresponding to the periods, drought and rainy, completing two seasons cycles. The second sought to assess any chemical and isotopic changes over the course of a year. In this case, samples of four different brands were acquired simultaneously and analyzed quarterly, from the filing date, including a water sample from Italy (sample IT). The waters bottled in Brazil used in this study, in general, have low mineralization (average of 87.2 mg L-1 STD). From a hydrogeochemical point of view, most waters were classified as chlorinated or bicarbonated. The minor and trace constituents contents were significantly lower than the limits recommended by the relevant legislation. The 87Sr/86Sr ratio and strontium concentration permitted to characterize three distinct groups of water. Group 1 is formed by bottled waters in the state of Pará with lower values of δ87Sr (water samples PV = 4.74 ‰, PSI = 10.5 ‰ and PB = 5.87 ‰), and lower concentrations of Sr2 + (2.76 μg L-1). These waters come from the Barreiras Aquifer, which consists of Miocene sedimentary rocks. It is a shallow aquifer with the direct influence of the rainwater. Group 2 is characterized by presenting intermediate values of δ87Sr and higher strontium ion concentrations (average of 110.3 μg L-1). It is formed by bottled waters in the states of Ceará (sample CH = 13.5 ‰), São Paulo (sample SPL = 11.9 ‰) and Paraná (sample PRCL = 18.8 ‰). The first one (CH) comes from the Barreiras aquifer, where the sedimentary rocks of the Barreiras Formation lie on the Paleoproterozoic crystalline basement. The aquifers of the other two water samples are in Proterozoic orthogneisses (SPL) and metasedimentary rocks (PRCL). The third group consists of bottled water in the state of Bahia (sample BA), whose aquifer is in the Lower Cretaceous São Sebastião Formation. This well is the deepest among the studied waters. It presents much higher values of δ87Sr (mean of 43.12 ‰) and intermediate values of Sr2+ concentration (mean of 12.75 μg L-1). The average values of δD and δ18O for these waters were as follows: PV (-15.4 ‰ and -3.26 ‰), PSI (16.6 ‰ and -3.42 ‰), PB (-15.4 ‰ and -3.23 ‰), CH (-13.6 ‰ and -2.95 ‰) BA (-2.07 ‰ and -1.79 ‰), SPL (-41.7‰ and -6.59 ‰) and PRCL (-32.4 ‰ and -5.66 ‰). The values of δD and δ18O were aligned along the global meteoric water line and were more enriched in the heavy isotopes in the north and northeast regions of the country. The range of variation of the isotopic data and the analytical parameters analyzed within the same sample was small, showing no dependence on seasonal influence. The geochemical data obtained were consistent with the information contained on the labels. The study regarding the shelf life of bottled waters (samples PB, SPL, SPCJ, and IT) indicated no significant variations in the chemical and isotopic composition of the elements analyzed over the twelve months period. Considering this information, the isotopic composition of bottled waters must preserve that of their sources. Thus, it was possible to characterize some of the sources individually using the obtained isotopic data. CH (δ87Sr = 13.5‰, δD = -13.6 ‰ and δ18O = -2.95 ‰); BA (δ87Sr = 43.1 ‰, δD = -2.07 ‰ and δ18O = -1.79 ‰); SPL (δ87Sr = 11.9 ‰, δD = -41.7 ‰ and δ18O = -6.59 ‰) and PRCL (δ87Sr = 18.8‰, δD = -32.4 ‰ and δ18O = -5.66 ‰). However, in waters from shallower aquifers located in areas with high rainfall and intense recharge (PV, PSI, and PB water sources), this characterization may become more difficult. Isotopic data guarantee digital printing and ensure its applicability as a tool to authenticate the origin of the product "bottled water" however; they are more suitable for aquifers where these waters have greater and more lasting interaction with the percolating rocks.