An oil spil at sea – origin and fate
Abstract
The amount 100—1000 tons of mineral oil was spilt at sea between January 2 and 3 1977 in the neighbourhood of west istrian coast.
Methods employed for the identification of spill origin and for monitoring of the spreading out of spilt oil are discussed.
The combination of IR spectrophotometric, spectrofluorometric, and gas chromatographic technique makes possible a very complex monitoring of oil spilt at sea: its identification, determination, and its fate in the marine environment. Numerous physico-chemical (evaporation, dissolution, chemical degradation) and biological processes modify and change the original characteristics of oil. However, for a long period after the spill, oil remains essentially unchanged and demonstrates its high persistence in the environment. In this work a lot of data, important for the better understanding of weathering process, are obtained. A possibility to trace the environmental fate of oil by applied analytical methods is discussed.
Using standard IR spectrophotometric method it is possible to monitor oil dissolved and/or dispersed in sea-water only immediately after an oil spill because of its relatively low sensitivity. In Fig. 2 IR spectra of seawater extracts are given. Only the sea-water extracts taken immediately after an oil spill (under visible oil slick) produce spectra similar to that of oil (»a« and »b«). In these exstracts the spilled oil is the dominant constituent of the extract. After a few days, when dispersion process has been advanced, the dominant lipoid matter in the extract is no more oil. Spectra »c« and »d« show great differencies in comparison with spectra of spilled oil (»a« and »b«).
In Fig. 4 different spectra of stranded water-in-oil emulsions are given. Referent sample is signated with »a«. Spectra »b« and »d« show significant differencies in comparison with referent sample supporting the gas chromatographic data wich suggest that these samples do not originate from the same spill. Spectrum »c« is very similar to that of the referent sample and show the advance of chemical changes after an oil spill especially by magnification of CO band absorption.
The employed spectrofluorometric method for the determination of oil in sea-water is more sensitive and more specific than IR spectrophotometric method. This technique makes possible the identification of oil in water even after a long period the spill occured because of its high sensitivity on the most soluble and the most persistent fraction of oil. The changes of oil, especially of the aromatic fraction, caused by dissolution and evaporation, are well documented by this method.
In Fig. 3 fluorescent emission spectra are given. Curve »b« presents the spectrum of the sea-water extract. Maximum is produced at the emission wavelenght of 360 nm and show the predominance of di- and trinuclear aromatic hydrocarbons in the extract as the conseqence of their higher solubillity in sea-water. Stranded water-in-oil emulsions give spectra with the emission maximum at 440 nm indicating the high polynuclear aromatic hydrocarbons content. Curve »a« is produced by standard crude oil which consists of both dinuclear and polynuclear aromatic hydrocarbons and its maximum is between the first two (380—390 nm).
Gas chromatographic technique is very suitable for the examination of biochemical degradation and it illustrates well the effect of evaporation.
Chromatograms presented in Fig. 5 illustrate the suitability of the GC for fingerprint analysis. Chromatogram »a« represents the referent sample. Loss of the peaks in the first range of chromatogram indicate the effect of evaporation. Missing of n-alkanes peaks (chromatogram »c«) show the effect of biodegradation of oil.
The importance of quick action of all responsible institutions including the governmental institutions and research institutes, in the case of an oil spill, is pointed out in the conclusion section. Sampling must be performed as soon as possible and the samples must be distributed to the research institutions for the identification purposes.
