Hydrocarbon pollution in particle-rich waters (Gulf of Fos-sur-mer): comparative study of extraction procedures

The direct liquid-liquid extraction of hydrocarbons, without filtration of water samples, cannot be used for particle-rich waters because of low yields and the selectivity towards particulate lipid classes. The ratios of hydrocarbons/total extractable matter and n-alkanes/total hydrocarbons - as pollution indices - are altered in unfiltered water samples. The separation of dissolved and particulate phases and their specific extraction are indispensable for complete recovery of the total hydrocarbons and alkanes in the water. Likewise, the n-alkane distribution and related Carbon Preference Index are influenced by incomplete extraction of high molecular weight compounds in unfiltered samples. Conversely, the n-C 17/pristane (Pr), n-C 18/phytane (Phy) and Pr/Phy ratios are not significantly affected by direct extraction. However, these indices sometimes are strongly influenced by biological contributions. The Pr/Phy ratio generally seems to be convenient for characterization of the anthropogenic origin of hydrocarbons.