New analytical strategies to evaluate the bioavailable fraction of polycyclic aromatic hydrocarbons (PAHs) in dissimilar soils

Abstract : Diffuse pollution of surface soils with polycyclic aromatic hydrocarbons (PAHs) is problematic in terms of health effects. Total PAH concentration in two different soils was assessed following an exhaustive extraction technique by MAE (microwave assisted extraction) using organic solvent mixtures. But it was demonstrated that the measure of contaminant exposure by this way is not appropriate to assess ecological risks. Moreover, it is well known that the effectiveness of in situ soil remediation processes (by degrading microorganisms) are constrained by low PAH bioavailability, due to their limited aqueous solubility and the magnitude of sorption on soils organic matter or clayey fine particles. The aim of this study was to evaluate different less exhaustive extraction methods in order to access the labile PAHs and to correlate them with bacterial degradation. Thus, aqueous-based extraction techniques using various original additives were performed. They were compared with butanol or-hydroxypropyl -cyclodextrin extractions, methods which were already described but that did not fit with our degradation tests or were too expensive. The new additives tested were original amphiphilic ionic liquids and a derivatized -cyclodextrin with micellization properties. Their critical micellar concentrations (cmc) were determined by a non-conventional method using capillary electrophoresis. These additives were introduced at 10 or 50 times their cmc in the extraction aqueous medium and time contact with soils was 24h. Desorbed PAHs, which were at trace levels, were quantified by HPLC (coupled to a fluorimetric detector) after a concentration step by SPE (solid phase extraction). Found labile PAHs were compared to PAH biodegradability (during three months) in the two studied soils in order to ensure that one of the new tested method could effectively predict the bioavailability of PAHs.