Article: Jonas Gros et al. First Day of an Oil Spill on the Open Sea: Early Mass Transfers of Hydrocarbons to Air and Water. Environ. Sci. Technol. 2014, 48, 9400−9411. DOI: 10.1021/es502437e
Twelve large oil spills have occurred since 1990. With each occurrence thousands of tons of crude oil were dumped into the ocean causing significant damage to the environment. Birds and marine mammals suffer from oil penetrating into their plumages and furs, respectively, which causes reduced insulating ability and loss of buoyancy in the water.
Crude oil is mostly composed of n-alkanes and polycyclic aromatic hydrocarbon (PAHs) which are toxic to organisms. After an oil spill it is crucial to investigate the fractionation of compounds partitioning into the air and water to aid in predicting their threat to downwind population and the marine community. The distribution and fractionation of crude oil also provide the information necessary for taking actions for cleaning-ups.
Experiments and Results
An oil release experiment was conducted by Jonas. in 2009 in the North Sea, Netherlands. Within 26 hours after the release of 4.3 m3 of Norwegian Grane crude oil over the sea surface, oil slick and sheen samples (from the sea surface) and water column samples (from deeper ocean) were collected. These samples were then taken to laboratories and analyzed by Comprehensive Two-dimensional Gas Chromatography (GC×GC) coupled to a flame ionization detector. The GC×GC system is able to analyze compounds ranging from C9 to C45, which corresponds to 68.9% of the Grane crude oil mass.
Analysis of collected samples revealed that volatile and/or soluble hydrocarbons were removed rapidly from the floating oil during the first day. Approximately 55% of undecane (n-C11) and 41% of naphthalene were lost 0.58h after the end of oil release; >50% of n-alkane up to n-C17 and partial to total of two- to three- ring PAHs were lost after 25.23h.
Figure 2 is a mass loss table (MLTs) derived from GC×GC data. It shows the mass loss of individual cells in a weathered sample compared to neat oil. Each cell symbolizes a group of compounds falling into a certain range of y-axis and x-axis values. Y-axis stands for solubility which indicates the dissolution process of compounds. X-axis represents vapor pressure with a higher value indicating larger tendency to evaporate. The whole plot reveals an oil removal process from the upper left side to the lower right side, meaning higher volatilization/solubility compounds disappeared faster in the system.
This is the first study to report on the evaporation/dissolution during the initial day of an open ocean oil spill. Vaporized compound levels are important to understand inhalation exposure levels to downwind population and personnel involved in emergency response. Dissolved compounds levels exhibit the exposure level of aquatic organisms and these concentrations can be most elevated during the initial hours.
A model was developed in addition to the experiment to describe the transfer of crude oil into the air and water column. Temperature, wind, and wave conditions were used to parameterize the model. The model correctly predicted the observed fractionation of petroleum hydrocarbons. This is crucial in that this model can be extended to infer oil spills under other conditions and may be in use for future emergency response. For example, cold weather are expected to produce more mass apportionment to water than to air; higher wind speed enhances both water and air fractionation; a thinner slick would cause more rapid fractionation arising from evaporation and dissolution.
Caoxin is a graduate student in the Graduate School of Oceanography at the University of Rhode Island. Her research interest lies in persistent organic pollutants in the environment. When she is not doing research she likes to create new cuisines.