Sunlight-Induced Molecular Progression of Oil into Oxidized Oil Soluble Species, Interfacial Material, and Dissolved Organic Matter

Spilled oil is highly susceptible to sunlight-induced transformations, both as films on the surface of water and material dissolved or dispersed in the water column. We utilized ultrahigh-resolution mass spectrometry and optical spectroscopy to understand shifts in oil photoproduct distributions as a function of photo-oxygenation. Oxygenation of oil produces compounds that have increased polarity, resulting in greater partitioning to the oil–water interface and eventually greater partitioning into the aqueous phase. Such partitioning was shown to be dependent on the carbon number and oxygen content of the photoproducts, providing an empirical basis for predicting the partitioning of oil photodegradation products between the oil phase, the interfacial region, and into the aqueous phase to form petroleum-derived dissolved organic matter. While such photochemical transformations have been predicted for many years, there has not been direct evidence previously for the photodissolution process. Furthermore, the relationship of carbon number and oxygen content with progression from the oil phase to the interfacial phase to the aqueous phase has not been demonstrated. This paper details this progression and observable properties that can be used to understand oil behavior after a spill during sunlight exposure, thus providing greater predictability of oil fate, transport, impact, and effective remediation strategies.