Environmental persistence and inefficiency of natural attenuation in the removal of pyrolysis oils in Canadian marine waters under cold temperatures: Implications for hazardous and noxious substances spill preparedness.

Pyrolysis oils are emerging alternative fuels that are increasingly being transported in marine environments. Although produced from renewable resources, their physicochemical properties result in their classification as hazardous and noxious substances (HNS). Limited information is available regarding the effectiveness of traditional clean-up and remediation strategies for their removal across geographically distinct marine environments, under cold-water conditions. The objective of this study was to evaluate the effectiveness of natural attenuation in three Canadian marine environments under cold temperatures. The aim was to determine whether pyrolysis oils can be effectively removed using conventional cleanup approaches or whether these strategies require re-evaluation considering environmental variability. Mesocosm experiments were conducted at 4 °C for up to 21 days to investigate the microbial fate of pyrolysis oils (wood oil and bio oil) in waters (1:2000, v/v) collected from the Beaufort Sea, Atlantic Ocean, and Pacific Ocean. Changes in physicochemical properties, microbial community composition (16S rRNA gene amplicon sequencing), surface activity, and toxicity (Microtox assay) were evaluated. The results demonstrated that both oils sank under static conditions, indicating limited natural dispersibility in water. Furthermore, both oils underwent limited biodegradation, ranging from only 3% to 20% at 4 °C across the tested waters. These findings suggest that natural attenuation is unlikely to be an effective remediation strategy under the conditions evaluated. Both oils also exhibited high toxicity to Vibrio fischeri, as indicated by their low IC50 values. Considering the high toxicity and low biodegradation rates, the tested oils may contribute to prolonged environmental persistence and extended ecological impacts. Therefore, conventional spill response and cleanup strategies should be re-evaluated when addressing pyrolysis oil spills.