Naphthenic acids (NAs) are persistent compounds that are components of most petroleum, including those found in the Athabasca oil sands. Their presence in freshly processed tailings is of significant environmental concern due to their toxicity to aquatic organisms. Gamma irradiation (GI) was used to reduce the toxicity and concentration of NAs in oil sands process water (OSPW) and fluid fine tailings (FFT). This investigation systematically studied the impact of GI on the biogeochemical development and progressive reduction of toxicity using laboratory incubations of fresh and aged tailings under anoxic and oxic conditions. GI reduced NA concentrations in OSPW by up to 97% in OSPW and in FFT by 85%. The GI-treated FFT exhibited increased rates of biogeochemical change, dependent on the age of the tailings source. Dissolved oxygen (DO) flux was enhanced in GI-treated FFT from fresh and aged source materials, whereas hydrogen sulfide (HS(-)) flux was stimulated only in the fresh FFT. Acute toxicity to Vibrio fischeri was immediately reduced following GI treatment of fresh OSPW. GI treatment followed by 4-week incubation reduced toxicity of aged OSPW to V. fischeri.

Jarosite minerals (AB₃(TO₄)₂(OH)₆) are iron hydroxysulfate minerals that can readily incorporate trace metals into their mineral structure. A range of metals can be incorporated into the jarosite structure, including oxyanions such as selenate (SeO₄²⁻). Selenium is a micronutrient, but is toxic in relatively low doses. Selenium is present in aqueous systems in its two oxyanion forms: selenate and selenite (SeO₃²⁻). The tetrahedral sulfate coordination site can be completely substituted for selenate in jarosite minerals (NaFe₃(SO₄)_x(SeO₄)_2-x(OH)₆). Bacteria have been observed to reduce Se oxyanions to both more reduced forms and insoluble elemental Se. This is a pathway for selenium immobilization at contaminated sites. This experiment investigates the reductive dissolution of two Se-jarosites (solid substitution containing high and low selenium concentrations) in the presence of Shewanella putrefaciens CN32. It was observed that both Fe(III) and selenate were metabolically reduced and released into solution through jarosite dissolution . Selenate was also found to be incorporated intracellularly and reduced to particulate Se which was released upon cell lysis. Compared to the abiotic samples, enhanced dissolution was found with both the live and dead bacteria treatments.