Abstract
The optical behaviour of seawater exposed to a residual amount of oil pollution is presented and a comparison of the fluorescence spectra of oil dissolved in both n-hexane and seawater is discussed based on excitation-emission spectra. Crude oil extracted from the southern part of the Baltic Sea was used to characterise petroleum properties after contact with seawater. The wavelength-independent fluorescence maximum for natural seawater and seawater artificially polluted with oil were determined. Moreover, the specific excitation-emission peaks for natural seawater and polluted water were analysed to identify the natural organic matter composition. It was found that fluorescence spectra identification is a promising method to detect even an extremely low concentration of petroleum residues directly in the seawater. In addition, alien substances disturbing the fluorescence signatures of natural organic substances in a marine environment is also discussed.
Highlights
Optical methods, including those based on various kinds of electromagnetic radiation, have preferential position in oil pollution detection in natural waters, because only light can penetrate the water comparatively deeply
This paper reports on studies of the differences between excitation-emission spectra (EEMs) for oil dissolved in nhexane and oil dissolved in seawater after seawater exposure to crude oil as well as on the mutual shadowing of Received August 09, 2015; revised ms. received September 21, 2015; published October 28, 2015
For the “PORT” seawater sample, intense fluorescence is observed at an excitation wavelength from 200 nm to 260 nm corresponding to an emission wavelength from 300 nm to 400 nm and a second slight intense fluorescence is observed at an excitation wavelength from 255 nm to 280 nm corresponding to an emission wavelength from 320 nm to 350 nm while for ORLOWO seawater sample, an intense fluorescence is observed only at an excitation wavelength from 200 nm to 280 nm corresponding to an emission wavelength from 300 nm to 460 nm
Summary
Optical methods, including those based on various kinds of electromagnetic radiation, have preferential position in oil pollution detection in natural waters, because only light can penetrate the water comparatively deeply. If an in-water or above-water optical detector of petroleum substances (oil) is employed, integrated information on the spectroscopic features of an oil and the natural constituents of the water should be known. Chromatographic methods are preferred for studying the complex structure of petroleum products, fluorescence spectroscopy seems to be the most efficient tool for low oil concentrations. Fluorescence spectroscopy allows measurements based on various methods, such as fluorescence spectroscopy for single excitation wavelength (SWEx), single emission wavelength (SWEm), excitation-emission spectroscopy (EEMs) or synchronous fluorescence spectroscopy (SFS) [8]– [13] and has been used to study petroleum products [14], inter alia, in marine environments [15]
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