Selenium enhances Conyza canadensis phytoremediation of polycyclic aromatic hydrocarbons in soil

Purpose To determine whether supplemental selenium (Se) enhances the tolerance of Conyza canadensis (C. canadensis) to polycyclic aromatic hydrocarbons (PAHs) and thereby accelerates PAH dissipation in soils. Materials and methods We examined the dissipation of different concentrations of two PAHs, phenanthrene (PHE) and pyrene (PYR), from contaminated soils after 60days of growth of C. canadensis supplemented with or without a low level of Se (0.5 mg kg(-1)) in a pot culture experiment. PAH concentrations were 0, 50, 200, and 800 mg kg(-1). Response variables included plant biomass, PAH accumulation in plants, soil microbial biomass carbon (MBC), root morphogenesis, antioxidant enzyme activity, and PHE/PYR dissipation. Results and discussion Plant biomass and root morphogenesis decreased with increasing PAH concentration, whereas malondialdehyde concentration, an indicator of oxidative stress, increased. Catalase activity, total superoxide dismutase activity, MBC, and the PAH dissipation ratio all increased with increasing PAH concentration until 800 mg kg(-1). Se supplementation of soil increased the tolerance of C. canadensis to PAHs and significantly increased PAH phytoremediation after 60 days of plant growth. The PHE dissipation ratios with and without Se supplementation were 57 +/- 3% and 28 +/- 8%, respectively, and PYR dissipation ratios were 30 +/- 7% and 24 +/- 8%. The increase in the PAH dissipation ratio with Se supplementation was largest in PHE-contaminated soils at 800 mg kg(-1). Conclusions A low concentration of supplemental Se in soil enhances the dissipation of PHE and PYR by C. canadensis. This enhancement is due to an increased plant tolerance toward PAHs, which results in increased C. canadensis biomass, soil MBC, and decreased plant uptake of PAHs. This study suggests that Se supplementation can contribute to ongoing efforts to develop effective phytoremediation systems for soils contaminated with PAHs.