Preliminary measurement-based estimates of PAH emissions from oil sands tailings ponds

Tailings ponds in the oil sands region (OSR) of western Canada are suspected sources of polycyclic aromatic hydrocarbons (PAHs) to the atmosphere. In the absence of detailed characterization or direct flux measurements, we present preliminary measurement-based estimates of the emissions of thirteen priority PAHs from the ponds. Using air concentrations measured under the Joint Canada-Alberta Oil Sands Monitoring Plan and water concentrations from a small sampling campaign in 2013, the total flux of 13 US EPA priority PAHs (fluorene to benzo[ghi]perylene) was estimated to be upward from water to air and to total 1069 kg y−1 for the region as a whole. By comparison, the most recent air emissions reported to Canadaʹs National Pollutant Release Inventory (NPRI) from oil sands facilities totalled 231 kg y−1. Exchange fluxes for the three remaining priority PAHs (naphthalene, acenaphthylene and acenaphthene) could not be quantified but evidence suggests that they are also upward from water to air. These results indicate that tailings ponds may be an important PAH source to the atmosphere that is missing from current inventories in the OSR. Uncertainty and sensitivity analyses lend confidence to the estimated direction of air–water exchange being upward from water to air. However, more detailed characterization of ponds at other facilities and direct flux measurements are needed to confirm the quantitative results presented herein.