Determination of polynuclear aromatic hydrocarbons in seawater following an experimental oil spill by stir bar sorptive extraction (SBSE) and thermal desorption GC-MS

Most analytical methods that identify and quantify semi-volatile contaminants from an oil spill on water are time-consuming and run the risk of contamination, particularly when dealing with trace levels. This study examined the feasibility of using stir bar sorptive extraction (SBSE) on-site, followed by analysis in the laboratory. The technique was applied in the context of 2 separate accidental oil spills in the North Sea in the fall of 2009. The 2 Grane crude oils were also tested with field gas chromatography/mass spectrometry (GC/MS). The first slick was immediately treated with dispersants, while the second was monitored for 2 days. Water samples containing dissolved oil fractions were taken at regular intervals at 1.5 and 8 m depths. Different chemical and biological techniques were applied for analyses. The oil exhibited a strong natural dispersion, and the slick could be monitored only during the first 26 hours following the spill. The objective of this analyses was to evaluate the behaviour of the dissolved fraction of hydrocarbons during a crude oil spill. The target molecules were polycyclic aromatic hydrocarbons (PAHs). The technique of SBSE coupled with GC/MS allowed quantification of dissolved apolar organic compounds at low levels, around 0.5 ng/L. The study showed a continuous decrease of concentrations over time, at 1.5 or at 8 m water depth. In addition, the concentrations measured at 8 m depth appeared to be more pronounced compared to samples collected at 1.5 m below the water surface. It was concluded that the SBSE technique represents an interesting solution for on-site measurement because of its simplicity and sensitivity. 5 refs., 4 figs.