Evidence of Organic Contamination in Urban Soils of Cotonou Town (Benin)

In Cotonou (Benin), growth of the population leads to an excessive use of natural resources, inducing organic contaminations. Surface soils collected in the town, were extracted and fractionated by liquid chromatography in three families: aliphatic, aromatic hydrocarbons and polar fractions. Each fraction was characterized by gas chromatography-mass spectrometry. All the results show that an anthropogenic input exists (waste oils). Indeed, aliphatic hydrocarbons have specific markers emphasizing the presence of petrogenic products: UCM (unresolved complex mixture), specific distribution of pentacyclic triterpane. However, specific molecular biomarkers reveal also natural input. Nevertheless, samples from similar origins do not always have the same pattern. This fact underlines that organic sources are numerous in theses soils and imply a mixture of fingerprints. Moreover, modifications of the organic matter fingerprints with time (alteration, lixiviation…) complicate correlation between organic sources and contaminated soils.