Measuring PAH availability in contaminated soils with thermodesorption coupled to molecular analyses

International audienceWithin the framework of PAH contaminated soils, PAH availability is a key parameter to consider in risk assessment and remediation strategy as it determines the impact of the contaminant on the biota and the efficiency of remediation treatments.Several methods are actually proposed to estimate the bioavailable fraction of the PAH contamination (mild solvent extraction, Tenax, cyclodextrine, passive sampling, microbial incubation) but, when compared, they showed inconsistent results.In this study, a new method of thermodesorption coupled with gas chromatography-mass spectrometry/flame ionization detection was developed to estimate the PAH availability in contaminated soils. It is based on the link between the desorption temperature of a molecule and the bond strength between the molecule and the matrix.Thermodesorptions were carried out on several soils and their respective solvent(dichloromethane) extracts. All the extracts showed similar thermodesorption profiles whereas differences in desorption temperature were observed among the soils. These results indicates that the matrix has a major impact on the thermodesorption temperatures. The soil thermodesorption profiles were compared to the efficiency of microbial incubation and chemical oxidation (potassium permanganate) carried out on those same soils. Multivariate analyses (principal component analyses) were carried out in order to determine, for each PAH and each treatment, the desorption temperatures corresponding to the bioavailable fraction and the fraction available for potassium permanganate oxidation.These results highlight the potential of this method to estimate different availabilities in PAH contaminated soils. This method is currently being adapted to other types of contaminant (petroleum hydrocarbons, polar-PACs