| Summary: | Vanadium (V) is a contaminant of emerging concern for the Alberta oil sands region that could present a risk for aquatic organisms. Petroleum coke (PC) has been experimentally used to treat oil sands process-affected water (OSPW) to reduce organic toxicants. However, PC contains up to 1,000 mg of V per kg of PC, and during OSPW treatment V leaches from coke reaching levels of up to 7 mg/L in “treated” OSPW, a concentration that is toxic to aquatic organisms. Little information is available on how common water quality variables affect the toxicity of V to aquatic organisms. Furthermore, there is no clear understanding of the mechanism(s) of toxicity of V in aquatic organisms. Vanadium is a transition metal with several oxidation states, and could potentially elicit its toxicity through either ion imbalance or oxidative stress. Therefore, the objectives of this research were to (i) investigate the influence of key water chemistry variables representative of the Alberta oil sands region on V toxicity to freshwater organisms, and (ii) determine if ion imbalance and oxidative stress are part of its mechanism of toxicity. To describe how water chemistry influences V toxicity to two representative freshwater organisms, Daphnia pulex and Oncorhynchus mykiss, descriptive relationships were developed between those parameters that differ the most between OSPW and the Athabasca River. Results indicate that an increase in pH increases V acute toxicity to both species, whereas increasing alkalinity and sulphate ameliorate V toxicity to both species. Sodium only causes amelioration of V toxicity to daphnids above 325 mg/L. The mechanistic studies with Daphnia magna and O. mykiss suggest that concentrations of V close to their respective median lethal concentration (LC50) cause sodium imbalance in both species, as well as calcium imbalance in rainbow trout, and oxidative stress in O. mykiss. In conclusion, the influence of pH, alkalinity and sulphate on V toxicity should be considered when creating new acute water quality ...
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