Mechanisms of the removal and remediation of phenanthrene and pyrene in soil by dwarf lilyturf

Pot experiments were carried out to investigate the mechanisms of the removal and accumulation of phenanthrene and pyrene by dwarf lilyturf(Ophiopogon japanicus Ker Gawl).The results showed that plantation of dwarf lilyturf significantly removed phenanthrene and pyrene from soils at their initial concentrations of 0 to 322 mg·kg-1.After 60 days plantation of dwarf lilyturf,the extractable phenanthrene and pyrene were lower in planted soils than in non-planted soils.About 77.58%-96.3% of phenanthrene and 65.25%-83.25% of pyrene was removed from the soils,respectively.Dwarf lilyturf removed averagely 82.27% of phenanthrene and 72.73% of pyrene from the soils as compared to CK1(with addition of 0.1% NaN3),and 43.26% of phenanthrene and 46.27% of pyrene as compared to CK2(without NaN3).Dwarf lilyturf did show ability to accumulate phenanthrene and pyrene from the soils,the contents of polycyclic aromatic hydrocarbons(PAHs) in its root and shoot increased with the increase of PAHs concentrations in the soils.The bioconcentration factors(BCFs) for phenanthrene and pyrene tended to decrease with increasing concentrations of these contaminants in soil,the BCFs for pyrene were higher than those for phenanthrene,and the BCFs for phenanthrene(1.1-6.36) and pyrene(4.3-9.43) in shoots were much lower than those in roots(1.41-9.35 and 8.13-17.88) at same treatment.Despite the plantation of dwarf lilyturf evidently enhanced the remediation of phenanthrene and pyrene in soils,contributions of biotic and abiotic factors to phytoremediation process displayed distinct diversity.Abiotic loss,plant accumulation and phytodegredation accounted for 6.61%,0.157% and 6.54% of the total removal of phenanthrene,and 3.18%,1.21% and 5.72% of pyrene from soils,respectively.In contrast,39.01% of the total removal of phenanthrene and 26.47% of pyrene were attributed to the contributions of microbial degradation,and 36.57% of phenanthrene and 39.34% of pyrene to plant-microbial interactions.Thus plant-microbial interactions and microbial degradation are the main mechanisms for the remediation of soil PAHs pollution.