Application of an isoleucine-derived organogelator for diluted bitumen spill treatment and its effects on seawater microbial community dynamics

• Gelator applied to seawater remained afloat over a 42-day weathering period. • Gelator biodegradation was not observed over this period at 5°C. • Microbial community responded differently to gelator than to gelated or non-gelated oil. • The number of observed species decreased with gelator exposure. • Shannon diversity index decreased with diluted bitumen exposure. Effective response measures are crucial to minimizing the negative impacts of crude oil spilled into aquatic ecosystems. The phase-selective organogelator N-acetyl-L-isoleucine-N’- n -octylamide can effectively solidify light and heavy crude oils into a cohesive mass, aiding in their containment and cleanup. However, its biodegradation and ecological impacts remain largely unexplored. The objective of this study was to investigate the fate and biodegradability of the organogelator and gelated diluted bitumen (DB) in seawater, as well as to assess the microbial community response during a 42-day aerobic weathering experiment at 5°C. Seawater was treated either with (i) DB and gelator, (ii) gelator only, or (iii) DB only, with (iv) untreated seawater as a control. Results showed that the gelator, DB, and the combination thereof remained afloat on seawater throughout the 42-day weathering experiment at 5°C. Significant biodegradation of non-gelated DB was detected, indicated by a decrease in the pristane-to-phytane ratio from 1.29 ± 0.03 to 1.10 ± 0.10 after 42 days of weathering at 5°C., but biomarker and spectroscopic analyses did not detect significant biodegradation for the gelator and gelated DB. 16S rRNA gene sequencing revealed that while overall microbial abundances remained stable, community compositions diverged across treatments. The gelator alone elicited a distinct microbial response compared to both gelated and non-gelated DB. While observed species declined after exposure to gelator, the microbial diversity was more affected by non-gelated DB or gelated DB treatments. The prolonged persistence of gelated DB and the gelator underscores the need for their timely removal post-application to minimize ecological risks. This study is among the first to provide insights into the environmental impacts of N-acetyl-L-isoleucine-N’- n -octylamide organogelator as an oil spill-treating agent, emphasizing the need for further research on its sustainability as a spill response tool.