Enhancement of phenanthrene and pyrene degradation in rhizosphere of tall fescue (Festuca arundinacea)

A greenhouse experiment was conducted with varying concentrations of phenanthrene (11-344 mg kg−1) and pyrene (15-335 mg kg−1) spiked in the soil to evaluate the phytoremediation of PAHs contaminated soil using tall fescue (Festuca arundinacea). After 65-day of tall fescue growth, plant biomass, microbial viable counts, dehydrogenase activity, water-soluble phenolic compounds, phenanthrene and pyrene residual concentrations and removal percentages were determined. The results showed that target PAHs (phenanthrene and pyrene) did not affect plant biomass at lower concentrations but a reduced biomass (only 53.5% of shoot and 29.7% of root compared to control) was observed at higher concentrations. Higher biological activities (microbial viable counts, water-soluble phenolic compounds, dehydrogenase activity) and PAHs degradation rates were detected in planted soils than unplanted controls. After harvest, 91.7-97.8% of phenanthrene and 70.8-90.0% of pyrene had been degraded in the planted soils, which were 1.88-3.19% and 8.85-20.69% larger than those in corresponding unplanted soils. This enhanced dissipation of target PAHs in planted soils might be derived from increased biological activity in the rhizosphere. The results of the present study suggest that the presence of tall fescue roots were effective in promoting the phytoremediation of PAHs contaminated soil.