Spectrum of light absorption as the indicator of lubricate oil dispsersed in the natural water

Oil pollutants in the natural water masses – especially in the seawater column – can be found in two forms, namely as dissolved oil or as dispersed one. With a broad set of methods, for studying the complex structure of petroleum products, due to the ability of petroleum products to absorb UV-light, absorbance spectra could be a relevant indicator to oil identification in aquatic environment and could support methods provided by the fluorescence technique. The intention of the study described in this article is to characterise the absorption properties of lubricate oil possible to found in the marine environment. Two types of oil as the representative of lubricate oils using in the ship engines are considered. One form of oil possible to found in the marine environment – oil-in-water emulsion was taken into account for analysis. Dispersed in water lubricate oil samples were prepared for several oil concentration for each type of oil. Spectrofluorometer Aqualog Horiba was used to register the absorbance spectra of oils. Based on the Lambert-Beer law the absorbance spectra were derived and specific parameter – absorption coefficient – for each wavelength of excitation, in the range 240-600 nm, was determined. Obtained results indicate decreasing of the oil absorbance value when excitation wavelength increases. Moreover, basing on the absorbance spectra it could be concluded that the main maximum for this kind of oils is located below 240 nm. However, in the considered range of excitation wavelength small flat peak, centred about 265 nm for both types of oils, was detected. Therefore one could conclude that absorbance of oils could be used as the indicator to detect of oil pollution in the natural environment omitting the labour intensive chemical methodology.