Oil Irradiation Experiments Document Changes in Oil Properties, Molecular Composition, and Dispersant Effectiveness Associated with Oil Photo-Oxidation

Abstract

While chemical dispersants are a powerful tool for treating spilled oil, their effectiveness can be limited by oil weathering processes such as evaporation and emulsification. It has been suggested that oil photo-oxidation could exacerbate these challenges. To address the role of oil photo-oxidation in dispersant effectiveness, outdoor mesocosm experiments with crude oil on seawater were performed. Changes in bulk oil properties and molecular composition were quantified to characterize oil photo-oxidation over 11 days. To test relative dispersant effectiveness, oil residues were evaluated using the Baffled Flask Test. The results show that oil irradiation led to oxygen incorporation, formation of oxygenated hydrocarbons, and higher oil viscosities. Oil irradiation was associated with decreased dispersant efficacy, with effectiveness falling from 80 to <50% in the Baffled Flask Test after more than 3 days of irradiation. Increasing photo-oxidation-induced viscosity seems to drive the decreasing dispersant effectiveness. Comparing the Baffled Flask Test results with field data from the Deepwater Horizon oil spill showed that laboratory dispersant tests underestimate the dispersion of photo-oxidized oil in the field. Overall, the results suggest that prompt dispersant application (within 2–4 days), as recommended by current oil spill response guidelines, is necessary for effective dispersion of spilled oil.

Exploring the Role of Nanobubbles in the Fate and Transport of Spilled Oil on Shorelines

“…Bubbles produced by breaking waves are also found in offshore areas . More importantly, the shoreline is not only a sink for pollutants but also plays host to further transport and transformation of pollutants. − As a traditional pollutant in the ocean, oil spills seriously harm local ecosystems once stranded in the shoreline environment. , There have been many studies investigating the fate and transport of oil stranded on shorelines, but almost all have paid attention to only light irradiation, temperature, salinity, shoreline substrate, microbial degradation, and other conventional factors. − NBs affect not only the physical transport of pollutants but also their chemical weathering, biodegradation, and adsorption with other environmental pollutants. Meanwhile, no studies have thus far focused on the potential effects of NBs on spilled oil in the shoreline environment.…”

Hot and Cold: Photochemical Weathering Mediates Oil Properties and Fate Differently Depending on Seawater Temperature

“…It is well recognized that some weathering processes increase oil viscosity and that these increases have consequences for spill response. Changes caused by evaporative weathering are considered significant enough that the ExxonMobil Oil Spill Response Field Manual states that evaporation “generally increases the viscosity of the remaining spilled oil,” which “affect[s] the selection of response options.” To date, multiple studies have observed increases in oil viscosity due to sunlight exposure, in some cases resulting in viscosities orders of magnitude greater compared to the viscosity of evaporatively weathered oil. ,,, In addition, multiple studies have also found that the more viscous, photochemically weathered oil is less susceptible to chemical dispersion at both lab bench and mesocosm scales. ,, Therefore, insofar as oil viscosity continues to be understood as a key variable controlling the effectiveness of oil spill response operations, ,, photochemical weathering should be considered when responding to future spills in sunlit waters.…”

“…2,9,35,56 In addition, multiple studies have also found that the more viscous, photochemically weathered oil is less susceptible to chemical dispersion at both lab bench and mesocosm scales. 2,9,35 Therefore, insofar as oil viscosity continues to be understood as a key variable controlling the effectiveness of oil spill response operations, 52,53,57 photochemical weathering should be considered when responding to future spills in sunlit waters.…”

Effects of oil characteristics on the performance of shoreline response operations: A review

“…Typically, 85% of hydrocarbons are removed under optimal conditions within a month or two (Haritash and Kaushik, 2009). Rather less is known about the biodegradation of resins and asphaltenes, whether initially in the oil or generated by photooxidation, although some of them have proved to be biodegradable (Aeppli et al, 2022). Head et al (2006) collected data from studies and showed that saturated hydrocarbons are degraded quickly, whereas other hydrocarbons like aromatic ones take longer (Figure 2B), which indicates that the mechanisms involved in saturated hydrocarbon and PAH degradation are different.…”