Metal uptake in wetland plants from oil sands process-affected waters: a case study

Treatment wetlands have emerged as a potential remediation option for oil-sands process affected waters (OSPW) which contains a suite of organic and inorganic constituents of potential concern. The aim of this study was to evaluate the fate of metals in a treatment wetland exposed to OSPW. Data was collected over three operational seasons testing freshwater and OSPW inputs at the Kearl Treatment Wetland in northern Alberta. Overall, results show that OSPW from the Kearl oil sands mine has relatively low concentrations of metals and trace elements compared to other industrial OSPW. Of the inorganic constituents introduced into the wetland from OSPW, six analytes (As, Ba, Cu, Mo, Ni, and U) were found to depurate by wetland treatment, were distributed among wetland media (water, sediment, plants), and translocated into water sedge and cattail tissue. Depuration of these analytes from the OSPW occurred mainly through sorption to sediment, while Mo and Cu had higher uptake and storage within plant tissue compared to the other analytes. No significant differences in metal uptake were observed between cattails and water sedge; root concentrations were higher than leaf concentrations. Root and leaf concentration factors were similar across years indicating that mechanisms of plant uptake were not impacted by exposure to OSPW and that bioconcentration was mainly a function of exposure. These findings support continued investigation into the application of treatment wetlands for OSPW remediation and underscore the need for further studies to optimize these systems for diverse OSPW types.