Monitoring of classical, oxidized, and heteroatomic naphthenic acids species in oil sands process water and groundwater from the active oil sands operation area

Highlights: • Analysis of classical, oxidized, and heteroatomic NA species in 30 water samples • Semiquantitative and qualitative analysis of NAs using UHPLC-TOF-MS and FTICR-MS • PCA analysis for source differentiation and marker compounds screening • Observation of distinct compositions of NA species with different water types The classical, oxidized, and heteroatomic naphthenic acids (NAs) species were monitored in the oil sands process water (OSPW) and groundwater from the active oil sands operation area, using solid phase extraction sample preparation and high resolution mass spectrometry analysis. Groundwater samples include Pleistocene channel aquifer groundwater (PLCA) and oil sands basal aquifer groundwater (OSBA) from different depth of underground. The concentrations of O_x–NAs decreased from OSPW to PLCA, and then increased from PLCA to OSBA, which is deeper than PLCA. The NAs in PLCA mainly comprised of O_x–NAs and N–NAs and the percentage of S–NAs was negligible. Results revealed relative abundances of individual NA species in total NAs varies among different water layers and the potential environmental impacts are expected to be variable. Principal component analysis results of O₂–NAs or O₄–NAs could be used for differentiation of water types. O₂–NAs with n = 12–16 and |Z| = 4–6, and O₄–NAs with n = 14–20 and |Z| = 6–8, were identified as marker compounds that could serve as surrogates of the larger complex NA mixture for source differentiation. This work utilized a combination of sample preparation, instrumental analysis, and statistical analysis methods to obtain knowledge of the occurrence, composition, and transfer of NAs in the groundwater of the Alberta oil sands operation area.