Karin Lemkau, Marine Chemistry & Geochemistry
The San Francisco Oil Spill: Exploring Stability of Asphaltenes in the Environment
Background and Scientific Problem
On November 7, 2007 the cargo ship M/V Cosco Busan struck the San Francisco – Oakland Bay Bridge in San Francisco Bay. Two port tanks were ruptured in the collision resulting in the release of approximately 50,000 gallons of heavy fuel oil into the Bay impacting over 100 miles of coastline. Once in the environment, oil is weathered by four primary processes: evaporation, water-washing, biodegradation and photodegradation. Understanding the fate of these oils in the environment entails disentangling the different processes altering the composition of the oil and the timeframes of these processes. Such understanding has implications for damage assessment and environmental restoration as required by the Oil Pollution Act of 1990 (33 USC 2701-2761).
Heavy fuel oils are composed of the residue from crude oil distillation supplemented with a less viscous distillate fuel in order to meet regulatory specifications and enable transport and use. During the refining processes large polar compounds known as asphaltenes are concentrated in the distillation residue used to make heavy fuel oils; as a result heavy fuel oils typically have high asphaltene concentrations.
Asphaltenes are operationally defined and are generally assumed to be recalcitrant in the environment; their presence as black stains on previously oil-coated rocks has been noted in the environment decades after a spill. However, several laboratory studies have suggested that these compounds may not be as inert as traditionally thought. If this is the case, asphaltenes or their transformation products may have detrimental effects on the environment long after an oil-impacted area has been deemed clean.
Traditionally oil spill studies use gas chromatography (GC) to examine changes in an oil after a spill. However, GC-amenable compounds are only a fraction of the total components present in a heavy fuel oil. Many large and bulky compounds, including asphaltenes, cannot be detected with these GC-based techniques, and these compounds have never been examined in an environmental system. The development of Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) enables examination of the molecular-level changes within these previously unexplored compounds and could provide a first look at their behavior and transformations in the environment. Are asphaltenes changing once released into the environment? On what timescale are they changing? And how? These are the questions I am seeking to answer in the proposed research.