Polycyclic aromatic hydrocarbons (PAHs), a class of toxic xeno- biotic fused-ring aromatic compounds, are widely distributed in soil that has been contaminated with crude oil, creosote, coal tar and so on. PAHs in soil are contaminants of great concerns due to their recalcitrance to different types of degradation and mutagenic or carcinogenic properties and also their toxicity to living organ- isms [1,2]. While low-molecular-weight (LMW) PAHs composed of two or three benzene rings are easily degraded through biological processes, high-molecular-weight (HMW) PAHs with more than four rings are resistant to microbial degradation and are highly hydrophobic. This property results in their partitioning into clay and organic matter and concomitant low bioavailability [3].
Previous research has shown that phytoremediation is a cost-effective and environmentally friendly technology for the treatment of subsurface contamination using vegetation and has been successfully applied at sites containing a variety of organic compounds [4,5]. The mechanisms of phytoremediation systems comprise at least four pathways to reduce soil contaminants,