Estimation of PAH bioavailability to Lepidium sativum using sequential supercritical fluid extraction – a case study with industrial contaminated soils

For the determination of PAH availability to plants a plant accumulation test with Lepidium and sequential supercritical fluid extraction (SSFE) with carbon dioxide as extraction solvent was used, during which the extraction conditions were changed from mild to harsh in order to represent a broad range of potential pollutant-soil interactions. Both approaches were applied in laboratory experiments on industrial contaminated soils which, in addition, were also freshly spiked with PAHs in order to increase the bioavailability. Only Naphthalene, Phenanthrene and, in some cases, Pyrene accumulated from the industrial contaminated soils. Accumulation experiments with spiked industrial soils showed that other PAHs, for example Anthracene, Fluorene and even high weight PAHs like Benzo(a)pyrene, also could be taken up by plants. SSFE extraction data were compared to accumulated amounts of PAHs in the plants. Strong correlations were found for Phenanthrene between plant accumulation and extractability under very mild extraction conditions. For Naphthalene, accumulation did not correlate with its extractability in the industrial soils. The possibility exists that bioavailability in soil was eclipsed by an accumulation in the gas phase due to the high volatility of Naphthalene. Supercritical fluid extraction appears to be a promising tool to estimate Phenanthrene availability to plants, but further studies for the evaluation of other PAHs are recommended. This could be helpful for the determination of the feasibility of phytoremediation applications on industrially contaminated soils.