Rapid Chemical Remediation of Freshwater Enclosures Treated with Conventional Heavy Crude Oil Spills Followed by Enhanced Monitored Natural Recovery

Canada is a top producer and exporter of crude oil but also has many in-land freshwater ecosystems that need protection using non-invasive remediation methods that are effective in sensitive environments. To assess the efficacy of enhanced monitored natural recovery (eMNR) as a secondary remediation strategy for freshwater oil spills, we conducted controlled spills of conventional heavy crude oil (CHV) in a freshwater lake at the IISD-Experimental Lakes Area in northwestern Ontario, Canada, in 2021. Three shoreline enclosures (5 × 10 m) were deployed on a wetland shoreline and treated with ~1.5 kg of weathered CHV. Four days later primary recovery of oil was conducted using shoreline washing followed by secondary remediation of residual oil using eMNR. Three unoiled, reference enclosures were also treated with shoreline washing but not secondary remediation. Polycyclic aromatic compounds (PAC) in water and sediment, and general water quality were monitored in the enclosures for 412 days after oiling. Total PACs in the water, mostly of 2- and 3-ring alkylated compounds, peaked three days after oiling (1188 ± 251 ng/L), declined to half of initial concentrations 8.26–11.75 days later and to near background levels by day 73. Total PACs were elevated in sediment of the oiled enclosures until day 70 likely due to sorption or settling oil but were heterogenous and influenced by pyrogenic compounds. Results from this study suggest that eMNR may be an effective remediation method following primary recovery efforts at sensitive aquatic sites where mechanical recovery is contraindicated.