The use of a finite mixture distribution model in bottled water characterisation and authentication with stable hydrogen, oxygen and carbon isotopes — Case study from Slovenia

Abstract

This study investigates the comparison of the stable isotopic composition of oxygen (δ 18O), hydrogen (δ 2H) and carbon in dissolved inorganic carbon (δ 13C DIC) in domestic and foreign bottled waters randomly collected from the Slovene market. Empirical distributions of δ 2H, δ 18O and δ 13C DIC were examined. Mathematical models of unimodal and polymodal probability density functions were applied for their description. A normal (Gaussian) finite mixture model as a representation of the polymodal empirical distribution of δ 13C DIC was used as a classification tool. Finally, based on the classification, descriptive statistics of δ 2H, δ 18O and δ 13C DIC for different groups are calculated. Components of the normal finite mixture model of δ 13C DIC represent four groups of bottled water; a group of artificial sparkling bottled water, two groups of still and flavoured bottled water and a group of bottled water originating from deeper aquifers. Corresponding values of δ 2H and δ 18O show that only the group of bottled water originating from deeper aquifers has a distinct stable isotopic composition, where the others have similar empirical distributions. The proposed model showed that δ 13C DIC for bottled water can be used as a strong discrimination parameter for the classification of bottled water and it can be applied as an authentication tool.