Characteristics of Naturally Occurring and Pollutant Hydrocarbons in Marine Sediments

Abstract

ABSTRACT Hydrocarbons spilled on the sea may, naturally or by sinking agent, settle on the sea bed and pollute marine muds which are the substratum of the benthic fauna and flora. They may be absorbed by these organisms which are the basis of the nutrition for a large part of the aquatic fauna. This hydrocarbon pollutants will enter by this way in the marine food chain and raise the problem of long term toxicity. Therefore it is important to measure the quantity of hydrocarbons in the marine sediments in order to know the level of pollution. We must, however, be able to make the difference between indigenous hydrocarbons and crude-oil derived hydrocarbons. Both contain, n and iso-alkanes, cyclo-alkanes and aromatics, but their quantity, the percentage of each type of compounds and the distribution of some specific molecules are often very particular. A detailed analysis of the chloroform extract of the sediment by chromatography, mass spectrometry and U. V. fluorescence can discriminate between unpolluted and polluted sediments even in the case of low level pollution. The samples which have been analysed, were collected on the French coast of the English channel in Normandie and in the Seine Bay. It has been noted in the unpolluted samples a higher percentage of heavy products (resins and asphaltènes), a more important odd carbon dominance in the n-alkanes distribution than in the polluted ones. The aromatic fraction of the indigenous hydrocarbons is mainly composed of polycyclic aromatic hydrocarbons without alkyl chains whereas polluted samples show many types of alkylaromatics.