Effectiveness and microbial impact of N-acetyl-L-isoleucine-N’-n-Octylamide organogelator used to solidify oil spilled in fresh water

Abstract Phase-selective organogelators are spill-treating agents that self-assemble within oil slicks on water to render the oil a semi-solid, which can facilitate its containment and recovery from the environment. Gelators are often built from natural products and oleophilic moieties to impart phase-selectivity, while making them applicable as spill-treating agents offering net environmental benefits. We synthesize and investigate the effectiveness of N-acetyl-L-isoleucine-N’-n-octylamide (Ac-Ile-C8) as an organogelator applied to diluted bitumen (DB) and conventional crude (CC) oils spilled onto river water. An improved synthesis of Ac-Ile-C8 from natural isoleucine is achieved in two steps at 92% yield. When applied in powder form, it gelates CC and DB at gelator-to-oil ratios of 4.9 and 6.5 wt%, respectively, due to its self-assembly into nanofibers, as observed in scanning electron micrographs. In a biphasic oil–water system, the addition of Ac-Ile-C8 not only gelates these oils but also substantially decreases the amount of oil that disperses into the water after mixing by end-over-end rotary agitation for 9 h. Moreover, adding Ac-Ile-C8 slows the evaporation of volatile oil components. The changes to non-Newtonian behavior of gelated oils are explored in a range of shear rates. The activity and response of microbiota in North Saskatchewan River water to Ac-Ile-C8 is investigated using 16S ribosomal RNA gene-sequencing technique and biological oxygen demand (BOD). Analysis of the sequencing results revealed a considerable shift in microbial community composition following exposure to the gelator; however, statistical analysis did not support significant changes in either community composition or diversity. The BOD results show increased microbial activity with exposure to gelator, suggesting its biodegradation by the water’s native microbial communities. Overall, the findings indicate that Ac-Ile-C8 effectively contains spills of CC and DB. Further studies are underway to evaluate this gelator’s effectiveness in terms of providing a net environmental benefit during oil spill response, which is needed to gain regulatory approval of solidifier applications as an alternative response measure.