Oregon Health & Science University
All crude oil, including that released in the Gulf of Mexico, contains toxic and/or carcinogenic polycyclic aromatic hydrocarbons (PAHs). Many PAHs freely dissolve and can persist in the environment, increasing their potential to bioaccumulate in exposed organisms. Ever-increasing exploitation of oil resources and subsequent accidents (such as the Deepwater Horizon spill, the largest marine oil spill in United States history) demand a greater understanding of their environmental impacts to improve response and recovery. Due to the presence of PAHs (the fluorescent component of crude oil), spectral fluorescence techniques are used to help characterize crude oil. During the 2010 Gulf of Mexico spill, highly sensitive fluorometers were used for in situ tracking of the underwater hydrocarbon plumes that resulted from crude oil released on the sea floor. However, existing fluorometers are not designed to specifically target PAHs. While fluorometric data provide valuable information, it is unclear how changing fluorescence signals relate to the dynamic environmental fate of crude oil. Concerns over sensitivity, relative performance of different sensor products, interferences, and simply how fluorescence signals should be interpreted highlight the need to better understand fluorescence behavior of oil during spills. An investigation of the fluorescence properties of the water-accommodated fraction (WAF) of a variety of crude oils in seawater was undertaken to further refine in situ instrument sensitivity for targeting PAHs. A subset of these samples was subjected to photodegradation to determine changes associated with this weathering process. In addition, we used two-dimensional gas chromatography analysis with time of flight mass spectrometry detection was employed to verify WAF composition and PAH concentration. Key excitation and emission wavelength ranges (240-270 nm and 305-360 nm, respectively) were ubiquitous throughout the crude oils tested. After exposure to a full-spectrum solar simulator (2500 Î¼E/m2/sec) over seven hours, degradation rate constants of key excitation/emission (ex/em) peak pairs showed persistent fluorescence signals at 270/310 and 270/325 nm ex/em for Merey crude oil WAF, 270/305 nm for Hoops crude oil WAF, and 270/305 nm for South Louisiana crude oil WAF. GCxGC-TOFMS analysis of the WAF of two distinctive crude oils revealed compositional similarities of PAH constituents. The known PAH compounds found in WAF solution of the crude oils tested make a compelling case for refined in situ tracking of dispersed toxic crude oil components. In situ fluorometers could be adapted for improved tracking of a variety of crude oils, targeting the persistent peaks found in the range of 240-270 nm ex and 305-360 nm em.
Div. of Environmental and Biomolecular Systems
School of Medicine
Slasor, Leslie, "Slick spectra : a spectral fluorescence study of the water-accommodated fraction of crude oil" (2012). Scholar Archive. 924.