Oil Sands Facilities Are an Emission Source of Naphthenic Acid Fractional Compounds to the Atmosphere

The oil sands (OS) region in Canada hosts one of the world’s largest unconventional crude oil deposits in the form of bitumen, which, when extracted, generates substantial tailings/wastewater that are stored in on-site ponds. Naphthenic acid fractional compounds (NAFCs), a complex mixture of alkyl-substituted acyclic and cycloaliphatic organic acids, are natural bitumen components known for their ecological toxicity and are concentrated during the extraction process into tailings ponds, where they are assumed to remain confined to the aqueous phase. Here, we quantify the emissions of up to 275 NAFCs to the atmosphere from a tailings pond and from facility-wide operations at major OS facilities. The results indicate that, despite the absence of NAFC air emissions in inventories, large quantities are emitted to the atmosphere, likely originating from surface photochemical and/or biodegradation processes. Emission rates across entire operations ranged from 3509 to 7286 kg h–1, translating to annual emissions of 1163–2660 tonnes from both primary and secondary sources. The findings imply that NAFC air emissions may serve as a key pathway for these chemicals to enter the environment, potentially impacting downwind ecosystems.