Polar compounds as found in oils are hydrocarbon compounds containing nitrogen, sulphur or oxygen. Measurement of the presence of these compounds in oils can be carried out using sophisticated analysis techniques, however quantification and separation of compounds is very difficult and will remain a problem for many years to come. Characterization of polar compounds in oils is at a state of infancy and little polar analysis for many oils has been carried out to date.

In order to measure the toxicity of a specific compound or class of compounds, separation is needed. Separation is very difficult and in many cases, beyond the scope of today's technology. An alternative has been to synthesize the compound of concern and then test its toxicity. This approach ignores the matrix in which the compound is usually present and the compound of interest may be not bioavailable when present in the actual oil, due to its solubility in oil. Highly polar compounds are likely not present in produced oils due to the polar compound's high water solubility. Compounds with moderate or less polarity are typically more soluble in oil than water. Similarly, highly polar compounds produced by biodegradation or photo oxidation would be diluted in water during a spill.

The aquatic toxicity of polar compounds compared to aromatic compounds has been tested by using evaporative weathering. Aromatic compounds, particularly that of the 2 to 5 ring polyaromatic hydrocarbons (PAHs), are fairly well-established as the primary toxic component of oils. Polar compounds are soluble in water and thus may pose another source of toxicity. Evaporative weathering tests where photo oxidation is not involved, in which some of the low molecular weight compounds and PAHs are lost from the oil, are thought to be one test of the comparison of polar compound toxicity compared to that of the PAHs. These tests show that polar compounds are generally less-aquatically-toxic than the 2 to 5-ring PAHs. Another test that has been performed is that of physical separation of oil components. In these type of tests, polar compounds have again been shown to have less aquatic toxicity that the PAHs in the same oil. Both tests have obvious limitations in that there are many compounds involved.

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