Effects of rapeseed oil on the rhizodegradation of polyaromatic hydrocarbons in contaminated soil.

Plants have the ability to promote degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soil by supporting PAH degrading microorganisms in the rhizosphere (rhizodegradation). The aim of this study was to evaluate if rapeseed oil increases rhizodegradation because various studies have shown that vegetable oils are able to act as extractants for PAHs in contaminated soils and therefore might increase bioavailability of PAHs for microbial degradation. In this study different leguminous and grass species were tested. The results suggested a significant impact of vegetable oil (1 and 3% w/w) on plant growth (decrease of plant height and biomass). The results of the pot experiment showed a decrease in the PAH content of the soil without amendment of rapeseed oil after six months. In soil amended with 1% and 3% of oil, there was no decrease in PAH content within this period. Although no enhancement of PAH degradation by plants could be measured in the bulk soil of the pot experiments, a rhizobox experiment showed a significant reduction of PAH content in the rhizosphere of alfalfa (Medicago sativa cv. Europe). Our investigations also showed significant differences in the degradation behaviour of the 16 individually analysed PAHs.