Chemical and toxicological characterization of unresolved complex mixtures in the water-soluble fraction of an artificially weathered Norwegian Sea crude oil was determined by a combination of chemical analysis and toxicity testing in fish in vitro bioassays. The water-soluble fraction of the crude oil was separated into 14 increasingly polar fractions by preparative high-pressure liquid chromatography. The in vitro toxicity (7-ethoxyresorufin O-deethylase activity, estrogenicity, and metabolic inhibition) of these fractions was characterized in a primary culture of liver cells (hepatocytes) from rainbow trout (Oncorhynchus mykiss). The main contributor to toxicity was one of the most polar fractions, accounting gravimetrically for more than 70% of the organic material in the water-soluble fraction and dominated by an unresolved complex mixture. Chemical analysis by gas chromatography-mass spectrometry and comprehensive two-dimensional gas chromatography-time of flight-mass spectrometry identified a large number of cyclic and aromatic sulfoxide compounds and low amounts of benzothiophenes (<0.1% of total mass) in this fraction. Commonly monitored toxic components of crude oil (e.g., naphthalenes, polycyclic aromatic hydrocarbons, and alkylated phenols) eluted in less polar fractions, characterized by somewhat lower toxicity. Normalization of in vitro responses to the mass in each fraction demonstrated a more even distribution of toxicity, indicating that toxicity in the individual fractions was related to the amount of material present. Although polar and nonpolar compounds contribute additively to crude oil toxicity, the water-soluble fraction was dominated by polar compounds because of their high aqueous solubility and the high oil-water loading. Under these conditions, the polar unresolved complex mixture-rich fraction might account for a large portion of crude oil toxicity because of its high abundance in the water-soluble fraction.

The chemical composition and physical properties of a crude oil determine the behavior of the oil and the way its properties will change when the oil is spilled at sea. Reliable knowledge of the oil's behavior will enable the most effective countermeasure techniques to be used in a spill situation. A diverse range of crude oils is coming into production in the North Sea. The weathering behavior and chemical dispersibility of three very different crude oils—Troll (naphthenic), Balder (asphaltenic), and Nome (waxy)—have recently been thoroughly investigated through bench- and meso-scale experiments. The naphthenic crude oil was also exposed to full-scale studies in the North Sea. This study shows that emulsion formation, the viscosity of emulsion, and the potential for dispersing emulsions by dispersant treatment may vary greatly for the different crude oils. It would be impossible to predict these differences with existing oil-weathering models based on fresh oil properties alone. Especially for abnormal (e.g., highly asphaltenic, waxy) crude oils, the weathering and dispersibility behavior can be revealed only by experimental work. The findings have important implications for effective oil spill response planning, particularly for estimating the most appropriate “window of opportunity” and for optimizing a dispersant application strategy for crude oils.

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe laboratory methodology and main findings from a characterisation study of Water Accommodated Fraction (WAF) from crude oil / oil products are presented.The study emphasises a tight connection between chemical and toxicological characterisation of WAF. The WAF solutions were prepared in standardised, closed, low energy systems with oil/seawater. WAF is of special interest because it has a high bioavailability to marine organisms, and is relevant both in connection with accidental oil spills and release of produced water.The results have identified large variations in the composition and toxicity of WAF solutions, depending on the type of oil, oil loading rate and weathering degree of the oils.

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A critical need currently exists for standard laboratory procedures for evaluating demulsifiers over the range of applications encountered in oil spill response. The procedures should be flexible enough to generate emulsions that are representative of those encountered at various times during a spill situation, and the applications should cover emulsion inhibition, breaking emulsion slicks at sea, and breaking recovered emulsions. Two laboratory test procedures are proposed. The procedures have different mixing energy and treating conditions, but each has the desirable feature of utilizing the same apparatus to generate the emulsion and to test the demulsifier. One procedure, called the wrist-action shaker emulsion test (WRASET), utilizes a standard laboratory apparatus, and is applicable for emulsion inhibition and for simulating at-sea applications of demulsifiers. A second procedure, called the rotating flask emulsion test (ROFLET), can also be used for a range of applications and is applicable for treating emulsions during oil recovery operations. Data from each of the two laboratory emulsion tests are used to demonstrate their features and to provide guidance on their use. An important implication of this work is that laboratory tests currently used to evaluate the effectiveness of dispersants to break up emulsions at sea need to be modified to provide time for the emulsions to be first broken by the dispersant.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe laboratory methodology and main findings from a characterisation study of Water Accommodated Fraction (WAF) from crude oil / oil products are presented.The study emphasises a tight connection between chemical and toxicological characterisation of WAF. The WAF solutions were prepared in standardised, closed, low energy systems with oil/seawater. WAF is of special interest because it has a high bioavailability to marine organisms, and is relevant both in connection with accidental oil spills and release of produced water.The results have identified large variations in the composition and toxicity of WAF solutions, depending on the type of oil, oil loading rate and weathering degree of the oils.