New analytical strategies to evaluate bioavailability of polycyclic aromatic hydrocarbons (PAH) in dissimilar soils

National audiencePolycyclic Aromatic Hydrocarbons (PAHs) are carcinogenic molecules mainly produced by the incomplete combustion of organic matter and they are found in all parts of environment. Concerning the remediation of contaminated soils and sediments, only few methods exist to assess the bioavailability of PAHs for bacterial degradation and they are not well correlated to biodegradation in real soils; however, this assessment is necessary for an effective treatment of pollution.The aim of this study is to develop a simple and rapid method for evaluating PAHs bioavailability in polluted soils by the use of non-exhaustive extraction methods that would permit to extract only labile PAHs and not the sequestrated part of PAHs (strongly sorbed on organic matter or clays), part which is not bioavailable for degradation by microorganisms. Thus, several tests were performed on two spiked soils (meadow soil, Yvetot, France and Seine river soil, Petiville, France), using aqueous phase extractions containing original additives. We tested the hydroxypropyl-β-cyclodextrin (HPCD) (Gomez-Eyles et al., 2001; Swindell and Reid, 2006), or the butan-1-ol extraction (BuOH) (Liste & Alexander, 2001) which are the two reference methods for the evaluation of bioavailability of PAHs in soils. Other assays were performed with additives such as an ionic liquid 1-hexadecyl-3-methylimidazolium bromide (HDMIm Br), the turquey red oil (TRO) or the sodium lauryl sulfate (SDS), in order to have a panel of different additives with different molecular properties, especially micellisation properties. Results of these assays did not seem to be reliable to the bioavailability of PAHs in soils. Perspectives are to study degradation kinetics of PAHs in these soils on three months and to correlate the biodegradation efficiency to PAHs bioavailability, using other additives such as new cyclodextrins or ionic liquids which form micelles in aqueous media. Other studies are also in progress to find bacterial communities responsible for the PAH degradation (by using DNA-SIP and Bioscreen technics)