Naphthenic acids are toxic and corrosive substances in oil sands leachates comprising a group of saturated aliphatic and alicyclic carboxylic acids in hydrocarbon deposits (petroleum, oil sands bitumen, and crude oils). In the current study, photolysis was applied to naphthenic acid mixtures and individual compounds to determine the efficacy of a variety of UV/vis radiation sources for reducing both concentration and aryl hydrocarbon (Ah) receptor binding as a measure of toxicity. The results show that the concentrations of neither the compounds nor the mixtures were significantly reduced in Athabasca River water, although compositional changes occurred within the mixtures and Ah receptor binding potential was affected by photolysis. Photolysis at UV254 was the most effective radiation source applied in all instances.