Microbes Endogenous to Oilsands-Eroding Tributaries Can Enhance Mobilization of Bitumen-Derived Naphthenic Acid Fraction Compounds into Water

The Athabasca Oil Sands region (AOSR) of Alberta, Canada has one of the largest proven unconventional petroleum deposits on earth. Petroleum extraction activities in the AOSR depend heavily on freshwater use, where toxic oil sands process-affected water (OSPW) rich in naphthenic acid fraction compounds (NAFCs) has now accumulated on the landscape since the ∼1960s. Previous work has shown that NAFCs are toxic and may have potential forensic value for source delineation. This work initially sought to use lab-modelled oilsands weathering processes to characterize a reliable forensic fingerprint for natural introduction of bitumen-derived NAFCs to water, with initial expectations that partitioning would be a largely physicochemical phenomenon. To assess this, ion-deplete (i.e., Milli-Q) and AOSR tributary waters were equilibrated with a batch of oilsand from 1999. Unexpectedly, we found that NAFC mobilization could not be adequately described solely as a physicochemical leaching process. These results informed an experimental re-design, where joint approaches of liquid-chromatography Orbitrap mass spectrometry and amplicon-based taxonomic sequencing were used to assess petroleum contaminant mobilization as a joint microbial-chemical phenomenon. This subsequent experiment used freshly sampled oil sands from the Steepbank and Ells Rivers, with the accompanying rivers’ waters equilibrated either as-is, or with autoclaving. Results indicated a specific and significant role of fluvial microbes driving NAFC occurrence, behaviour, and fate. Across the two experiments, the influence of (a) different sources and ages of bitumen, and (b) live microbial consortia (i.e., the influences of autoclaving) on NAFC molecular features were apparent. Temporal patterns of the equilibrations indicate that oilsands and water matrices became functionally coupled yet taxonomically distinct during incubation, reflecting microbial succession and ecological filtering under oilsands influence. These findings provide strong initial evidence of regional fluvial consortia adaptation to petroleum-derived ecosystem pressures, which has implications for future monitoring, risk assessment, and potential source delineation efforts.