Can the toxicity of naphthenic acids in oil sands process-affected water be mitigated by a green photocatalytic method?

• Main Authors: Barry N. Madison, Jessie Reynolds, Lauren Halliwell, Tim Leshuk, Frank Gu, Kerry M. Peru, John V. Headley, Diane M. Orihel
• Format: Article
• Language: English
• Published: Canadian Science Publishing 2020-06-01
• Series: FACETS
• Subjects: oil sands; naphthenic acids; green engineering; ecotoxicology; fish
• Online Access: https://www.facetsjournal.com/doi/full/10.1139/facets-2019-0053

Our study evaluates the efficacy of a “green” (i.e., sustainable, recyclable, and reusable) technology to treat waste waters produced by Canada’s oil sands industry. We examined the ability of a novel advanced oxidative method—ultra-violet photocatalysis over titanium dioxide (TiO2)-coated microparticles—to reduce the toxicity of naphthenic acid fraction components (NAFC) to early life stages of the fathead minnow (Pimephales promelas). Lengthening the duration of photocatalysis resulted in greater removal of NAFC from bioassay exposure waters; low- and high-intensity treatments reduced NAFC concentrations to about 20 and 3 mg/L (by Fourier-transformed infrared spectroscopy, FTIR), respectively. Treatments reduced the acute lethality of NAFC to fathead minnows by over half after low-intensity treatment and three-fold after high-intensity treatment. However, incomplete degradation in low-intensity treatments increased the incidence of chronic toxicity relative to untreated NAFC solutions and cardiovascular abnormalities were common even with >80% of NAFC degraded. Our findings demonstrate that photocatalysis over TiO2 microparticles is a promising method for mitigating the toxicity of oil sands process-affected water-derived NAFC to fish native to the oil sands region, but the intensity of the photocatalytic treatment needs to be considered carefully to ensure adequate mineralization of toxic constituents.