Influence of inorganic anions on metals release from oil sands coke and on toxicity of nickel and vanadium to Ceriodaphnia dubia

► Sulfate influences release of Ni, Fe, Mn and Zn from oil sands coke. ► Bicarbonate influences release of Al, As, Mo and V from oil sands coke. ► Bicarbonate enhances chronic Ni toxicity. ► Sulfate protects against chronic V toxicity. ► Ni and V act additively at their sub-lethal doses. In a previous study it was shown that pH significantly influences the release of metals from oil sands coke, particularly Ni and V which were identified as the cause of coke leachate toxicity. Coke comes in contact with oil sands process water (OSPW) during its transport to and long term storage in reclamation landscapes. However, the influence of dominant inorganic anions present in OSPW (i.e. HCO 3 - , Cl − and SO 4 2 - ) on metals release from coke and on speciation and toxicity of Ni and V, has not been characterized before. Coke was subjected to a 15-d batch leaching process at four levels of HCO 3 - , Cl − and SO 4 2 - to determine the influence on metals release and speciation. Further, the effects of each of the three anions on Ni and V toxicity, as well as the mixture toxicity of Ni and V, were assessed using the three-brood Ceriodaphnia dubia test. Inorganic anions had a significant influence on the type and amount of metals released from coke. Specifically, sulfate increased the mobilization of cationic metals (e.g. Ni, Fe, Mn and Zn), whereas bicarbonate enhanced the release of oxyanion forming metals (e.g. Al, As, Mo and V) from coke. Chloride had no particular effect on the type and amount of metals released. With respect to toxicity, elevated bicarbonate levels decreased the 7-d Ni IC50 from 6.3 to 2.3 μg L −1, whereas sulfate showed an ameliorative effect against V toxicity to C. dubia. In combination, Ni and V acted additively at their highest sub-lethal concentrations. Aqueous chemistry and toxicity of Ni and V are discussed with the goal of informing reclamation efforts at the Athabasca oil sands.