Analytical characterization of contaminated soils from former manufacturedgas plants

Detailed analytical characterization of the organic matter (OM) of aged pol luted soils from five former manufactured gas plants (MGP) and of two coal tars was completed. It was aimed at obtaining information relevant to the p hysicochemical state of the polycyclic aromatic hydrocarbon (PAH) pollutant s and to their in-situ evolution in time. Overall characterization of total OM (essentially polluting OM) was carried out directly on soil samples wit h or without prior extraction with solvent. It involved a technique of pyro lysis/oxidation coupled to flame ionization/thermal conductivity detection (Rock Eval). Extracts in solvent were fractionated by liquid chromatography into saturated hydrocarbons, PAH, and resins, the first two fractions bein g further characterized by gas chromatography and mass spectrometry. The co mpositions of OM of soils were found to be very similar. A total of 28% of organic carbon, including all PAH, was extractable by solvent. The composit ions of coal tars were qualitatively similar to those of OM of MGP soils bu t with a higher proportion (48%) of total extractable OM and of PAH, in par ticular lower PAH. Contamination of MGP soils appeared essentially as coal tar having undergone natural attenuation. The constant association of PAH w ith heavy OM in MGP soils is important with respect to the mobility and bio accessibility of these pollutants.