Occurrence, Behaviour, and Fate of Naphthenic Acid Fraction Compounds in Athabasca Oil Sands Wetlands

The Athabasca Oil Sands Region (AOSR) of Alberta, Canada, has a massive underlying deposit of unconventional petroleum resources. The region’s oil sands are a sticky mixture of sand, water, clay, salts, and bitumen, a degraded heavy hydrocarbon mix. To extract bitumen from mined oil sands ore, 2-4 barrels of fresh water are required per barrel of oil produced, which has led 1.4 billion m3 associated tailings retained in tailings ponds as of 2024. Discharge of oil sands process-affected water (OSPW) has not yet been permitted, but water will eventually need to be released and associated residual toxicity on affected landscapes will need to be ameliorated. Much of the toxicity of OSPW is attributable to naphthenic acids (NAs) and other naphthenic acid fraction compounds (NAFCs). Prior to discharge of OSPW, NA and NAFC-attributable toxicity must be mitigated to minimize potential adverse impacts on wildlife and downstream communities. Previous studies have indicated that wetlands can influence molecular characteristics of NAFCs to ameliorate toxicity. Abundant wetlands are also already a defining characteristic of the region, and so reconstructing similar features ought to be prioritized in reclamation designs for AOSR mine sites. However, there is a lack of available data on the occurrence, distributions, and behaviours of NAFCs in AOSR wetlands. Addressing this knowledge gap should be important to government and industrial stakeholders, describing an environmental baseline with respect to NAFCs while also highlighting ecosystem services offered by natural and constructed wetlands for reclamation. My research characterizes the fate and behaviour of NAFCs in wetland ecosystems using high-resolution orbitrap mass spectrometry. The hypothesis to be evaluated is that wetland ecosystems in the environment of the AOSR deliver ecosystem services in both natural and engineered contexts, attenuating problematic NAFCs by allowing for, fostering, and promoting oxidative degradation. I explore this hypothesis isolating NAFCs from AOSR wetland samples for analysis by high-resolution Orbitrap mass spectrometry to address three sub-objectives, (i) gathering baseline data on the occurrence of NAFCs in AOSR wetlands taking advantage of previous field sampling campaigns, (ii) gathering evidence of ecosystem services with respect to occurrence and attenuation behaviours of NAFCs in these wetlands by comparing and contrasting intensively-sampled slightly-lentic and lotic endorheic reclamation affected wetlands, and (iii) further enumerate parallel trends in an engineered wetland OSPW treatment system as part of a larger multi-part collaborative study. Focusing on occurrence, behaviour, and fate in natural and engineered wetlands, NAFCs in these ecosystems can gradually decrease in concentration, decrease in molecular size, and increase in oxygenated formulae. These findings parallel previous greenhouse-scale pilot treatment outcomes across these different themes, where NAFCs tend to decrease in concentrations, decrease in size, and become more oxygen-rich with age and residence time in wetlands, consistent with oxidative degradation.