Oil sands surface mining in Alberta has generated over a billion cubic metres of waste, known as tailings, consisting of sands, silts, clays, and process-affected water that contains toxic organic compounds and chemical constituents. All of these tailings will eventually be reclaimed and integrated into one of two types of mine closure landforms: end pit lakes (EPLs) or terrestrial landforms with a wetland feature. In EPLs, tailings deposits are capped with several metres of water while in terrestrial landforms, tailings are capped with solid materials, such as sand or overburden. Because tailings landforms are relatively new, past research has heavily focused on the geotechnical and biogeochemical characteristics of tailings in temporary storage ponds, referred to as tailings ponds. As such, the geochemical stability of tailings landforms remains largely unknown. This review discusses five mechanisms of geochemical change expected in tailings landforms: consolidation, chemical mass loading via pore water fluxes, biogeochemical cycling, polymer degradation, and surface water and groundwater interactions. Key considerations and knowledge gaps with regard to the long-term geochemical stability of tailings landforms are identified, including salt fluxes and subsequent water quality, bioremediation and biogenic greenhouse gas emissions, and the biogeochemical implications of various tailings treatment methods meant to improve geotechnical properties of tailings, such as flocculant (polyacrylamide) and coagulant (gypsum) addition.

This review compares the occurrence of pharmaceuticals in Canadian sewage treatment plant (STP) effluents and surface waters (SWs) to those from different countries. The occurrence in Canadian aquatic environments was found to be similar to other countries. The most concentrated drugs in STP effluents were: analgesic drugs, salicylic acid (59.6 μg/L) and naproxen (33.9 μg/L); antibiotics, trimethoprim (3.528 μg/L) and sulphamethoxazole (3.278 μg/L); antidepressants, venlafaxine (0.808 μg/L) and fluoxetine (0.799 μg/L); the antiepileptic and mood-stabilizing drug carbamazepine (3.287 μg/L); a lipid regulator gemfibrozil (2.09 μg/L); and atenolol (a β-blocker) reported at a concentration of 1.68 μg/L. The occurrence of pharmaceuticals in Canadian STPs is likely related to drug consumption and water treatment inefficiencies at the STPs investigated. A similar trend was observed for SWs, but the most concentrated drugs were found at lower concentrations such as salicylic acid (17 μg/L), sulphamethoxazole (0.286 μg/L), gemfibrozil (0.58 μg/L), desmethylvenlafaxine (1.472 μg/L), fluoxetine (0.141 μg/L), and carbamazepine (0.7 μg/L). A risk quotient using maximum concentrations of pharmaceuticals, representing a worst-case scenario, was calculated for Canadian STP effluents and SWs, which included analgesics (i.e. ibuprofen, naproxen, and salicylic acid), antibiotics (i.e. sulphamethoxazole, ofloxacin, and ciprofloxacin), antidepressants (i.e. fluoxetine), and lipid regulators (i.e. clofibric acid and gemfibrozil). This risk characterization showed that pharmaceuticals in Canadian STP effluents are suspected to pose a high ecological risk to aquatic organisms, while in SWs, even at the worst-case scenario, a low to medium risk is suspected for all drugs, except sulphamethoxazole.