A simplified sample pretreatment method for industrially PAH-contaminated soils applying automated Soxhlet (Soxtherm) with ethyl acetate as extraction solvent is presented. Laborious pretreatment steps such as drying of samples, cleanup of crude extracts, and solvent exchange were allowed to be bypassed without notable performance impact. Moisture of the soil samples did not significantly influence recoveries of PAHs at a wide range of water content for the newly developed method. However, the opposite was true for the standard procedure using the more apolar 1:1 (v/v) n-hexane/acetone solvent mixture including postextraction treatments recommended by the U.S. EPA. Moreover, ethyl acetate crude extracts did not appreciably effect the chromatographic performance (HPLC-(3D)FLD), which was confirmed by a comparison of the purity of PAH spectra from both pretreatment methods. Up to 20% (v/v) in acetonitrile, ethyl acetate proved to be fully compatible with the mobile phase of the HPLC whereas the same concentration of n-hexane/acetone in acetonitrile resulted in significant retention time shifts. The newly developed pretreatment method was applied to three historically contaminated soils from different sources with extraction efficiencies not being significantly different compared to the standard procedure. Finally, the certified reference soil CRM 524 was subjected to the simplified procedure resulting in quantitative recoveries (>92%) for all PAHs analyzed.

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Sequential supercritical fluid (CO2) extraction (SSFE) was applied to eight historically contaminated soils from diverse sources with the aim to elucidate the sorption-desorption behavior of high molecular weight polycyclic aromatic hydrocarbons (PAHs). The method involved five extraction phases applying successively harsher conditions by increasing fluid temperature and density mobilizing target compounds from different soil particle sites. Two groups of soils were identified based on readily desorbing (available) PAH fractions obtained under mildest extraction conditions (e.g., readily desorbing fractions of fluoranthene and pyrene significantly varied between the soils ranging from <10 to >90%). Moreover, extraction behavior strongly correlated with molecular weight revealing decreasing available PAH fractions with increasing weight. Physicochemical soil parameters such as particle size distribution and organic dry mass were found to have no distinct effect on the sorption-desorption behavior of PAHs in the different soils. However, PAH profiles significantly correlated with readily available pollutant fractions; soils with relatively less mobile PAHs had higher proportions of five- and six-ring PAHs and vice versa. Eventually, biodegradability corresponded well with PAH recoveries under the two mildest extraction phases. However, a quantitative relationship was only established for soils with biodegradable PAHs. Out of eight soils, five showed no biodegradation including the four soils with the lowest fraction of readily desorbing PAHs. Only one soil (which was found to be highly toxic to Vibrio fischeri) did not match the overall pattern showing no PAH biodegradability but large fractions of highly mobile PAHs, concluding that mass transfer limitations may only be one of many factors governing biodegradability of PAHs.

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