| Polycyclic aromatic hydrocarbons (PAHs), one of the widely existed persistent organic polluants (POPs) in the environment, are formed during the incomplete combustion of fossil fuel, wood, and other organic substances, which is a class organic compounds of two or more benzene in it. PAHs are threatende the health of human being and ecological safety of the environment because of their toxic, mutagenic, and carcinogenic properties. The remediation of PAHs is one of the hot spots in the environment fields.Phytoremediation is a promising approach to soil remediation due to its low investment and low cost compared to other approaches. In this dissertation, based on the review of phytoremediation of PAHs, pot experiments were applied to investigate the accumulation and remediation behavior and the interspecific difference of naphthalene (Nap) and benzo(a)pyrene pyrene (Pyr), two typical kinds of PAHs, in the system of soils and plants. The accumulation effect of plants to PAHs in the soils was cleared. These degradation effects of biological and non-biological factors were compared and analysed in order to reveal the remediaton mechanisms. On this basis, the removal and remediation of PAHs in soils by single-species and mixed species planting patterns were also compared. These results provided a theoretical basis for the formulation of ecomomic and effective remediation of PAHs. The main original conclusions are shown as follows.1. Screening of six plant species for phytoremediation of naphthalene or benzo(a)pyrene pyrene in soilsFive plant species, Cynodon dactylon L., Lolium multiflorum Lam, Festuca rubra, Zoysia japonica Steud, Axonopus affinis, were screened for their ability for the cleanup of PAH-spiked soil at their initial concentrations of ranging from 0 to 300 mg-kg-1 by pots experiments in a greenhouse. It is showed that the removal of Nap and Pyr were promoted by the five plant species, but the interspecific difference varied deeply. At the end of the experiment (55d), it is showed that the removal of Nap and Pyr by Axonopus affinis and Festuca rubra were better than others plants. The removal rates of Nap and Pyr in the vegetated soils were 57.62～82.27% and 48.17～77.41% by Festuca rubra, respectively. Phytoremediation efficiencies of Nap and Pyr in soils have little to do with the plant biomass. It is showed that these plants have absorbation and accumlation effect to PAHs in soil through the remedation. These results suggested that with the increase of their initial concentrations, the accumulations concentrations of Nap or Pyr in plant tissues monotonically increased, but BCFs (bio-concentration factors) of these compounds gradually decreased. Under the same contamination level, PAHs concentrations in shoot and SCFs (shoot concentration factors) were always significantly lower than those concentrations in root and RCFs (root concentration factors). The concentrations of Nap in plants are always lower than those of Pyr. Plants uptake and accumulations of these compounds were evident, RCFs of these compounds significantly positively correlated to root lipid contents, but similar correlations to root water contents could not be found. Results from this study also suggested a feasibility of the establishment of phytoremediation for soil PAHs contamination.2. Removal and remediation mechanisms of PAHs in soil by Festuca rubraPot experiments were carried out to investigate the accumulation and removal mechanisms and efficiencies of PAHs by Lolium multiflorum Lam. It is showed that plantation of Festuca rubra significantly removed Nap and Pyr from soils at their initial concentrations of 0 to 300 mg-kg-1. After 55 days plantation of Festuca rubra, about 50.72%-83.17% of Nap and 44.34%～77.42% of Pyr were removed from the soils, respectively. The removal rates of Festuca rubra were averagely 46.40% of Nap and 43.53% of Pyr from the soils higher than that of control soils. PAHs were absorbed and accumulated by Festuca rubra. These results suggested that with the increase of their initial concentrations, the accumulations concentrations of Nap or Pyr in plant tissues monotonically increased, but BCFs (bio-concentration factors) of these compounds gradually decreased. It showed that accumulation of Nap and Pyr by Festuca rubra wasn't the main reason for their degradation. The removal rates of Nap by non-biotic factors, accumulation and degradation of macrobiotic were 4.98%,0.017%,18.77%, respectively. The removal rates of Pyr by non-biotic factors, accumulation and degradation of macrobiotic were 2.51%,0.11%,15.55%, respectively. However, the removal rates of Nap and Pyr by plant-microbial interactions were 61.53%,56.275%, respectively. It suggested that the plant-microbial interactions was the main reason for remove of Nap and Pyr.3. Multispecies phytoremediation of naphthalene or benzo(a)pyrene pyrene in soilsThe potentials of two plant species, Lolium multiflorum Lam. and Axonopus affinis, separately or jointly on the degradation of PAHs in soil were estimated by pots experiments in a greenhouse. It showed that the presence of vegetation and multispecies had little effect on their growth in soils at their initial concentrations ranging from 0 to 300 mg-kg-1. At the end of the 55 d experiment, the removal rate of Nap and Pyr in soils with Axonopus affinis and Lolium multiflorum in mixed cropping were 74.69%,68.16%, respectively, what were 43.92%,46.97%, 4.67%,16.32% higher than single cropping. PAHs were absorbed and accumulated by plant and the amount was positively related to the initial concentration of Nap and Pyr. Under the same contamination level, PAHs concentrations in shoot and SCFs (shoot concentration factors) were lower than those concentrations in root and RCFs (root concentration factors). The concentrations of Nap in plants are always lower than those of Pyr. In the plant-microbial system, the degradation of microorganism and plant-microbial interactions were the main reason for the removal of Nap and Pyr. These Results suggested a feasibility of the establishment of multispecies phytoremediation to improve the efficiency of bioaugmentation in decontaminating PAHs contaminated soils, decreasing crop accumulations to PAHs and reducing risks associated with PAHs.
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