Enhanced Phytoremediation of Crude Oil-Polluted Soil by Four Plant Species: Effect of Inorganic and Organic Bioaugumentation

A field experiment investigating the removal and/or uptake of Polycyclic Aromatic Hydrocarbons (PAHs) and specific metals (As, Cd, Cr) from a crude oil polluted agricultural soil was performed during the 2013 wet season using four plant species: Fimbristylis littoralis, Hevea brasilensis (Rubber plants), Cymbopogom citratus (Lemon grass), and Vigna subterranea (Bambara nuts). Soil functional diversity and soil-enzyme interactions were also investigated. The diagnostic ratios and the correlation analysis identified mixed petrogenic and pyrogenic sources as the main contributors of PAHs at the study site. A total of 16 PAHs were identified, 6 of which were carcinogenic. Up to 42.4mg kg(-1) total PAHs was recorded prior to the experiments. At 90 d, up to 92% total PAH reduction and 96% As removal were achieved using F. littoralis, the best performing species. The organic soil amendment (poultry dung) rendered most of the studied contaminants unavailable for uptake. However, the organic amendment accounted for over 70% of the increased dehydrogenase, phosphatase, and proteolytic enzymes activities in the study. Overall, the combined use of soil amendments and phytoremediation significantly improved the microbial community activity, thus promoting the restoration of the ecosystem.