Analysis of Water-Soluble Acidic Compounds Derived from Spilled Oil in a Controlled Marine Enclosure

The fate of Arabian light oil (1 litre), spilled in a controlled sea-water enclosure (320 litres), was studied. In addition to the usual monitoring of aliphatic and aromatic hydrocarbons contained in the crude oil, the formation of acidic compounds through the natural photochemical oxidation has been investigated while the biodegradation was shown to be insignificant. A liquid-liquid extraction procedure was developed in order to obtain acidic and basic-neutral compounds. Water-soluble acidic fraction was analysed after methylation by gas-chromatography on capillary columns coated with either SE-52 or PEG-20 M. On the other hand, the level of hydrosoluble acidic compounds in six samples (initial, 19h 30min, 8, 20, 45 and 70 days) was evaluated by fluorimetry and by reversed-phase HPLC combined with fluorimetric detection. Preliminary results indicated the formation of numerous oxygenated products derived from the spilled oil. The photo-oxidative process led to the formation of fatty acids and oxygenated two-ring aromatic compounds. The results showed that the concentration of the fluorescent acidic products attained after 70 days of experience a level significantly higher (6mg/l) than that of parent PAH (0.4mg/l). This result suggests that the photochemical oxidation could be accountable for the degradation of ca 0.3% of the initial crude oil. The analytical approach can be considered as a first step towards the development of routine assay procedures for analyzing such acidic compounds. These “new” molecules may contribute to the global toxicity of oil towards marine biota.