| Soil contamination with polycyclic aromatic hydrocarbons (PAHs) poses a great threat worldwide to the agricultural food quality and human health, and calls for an immediate action to remediate the contaminated sites. The prospect of phytoreme-diation for soil organic contaminants is an attractive cost-effective alternative to traditional engineering approaches. However, the basic mechanisms involved are up-to-date not well elucidated. For PAHs are liable to be sorbed by soil solids, the plant and microbial availability of PAHs in soils is a major limiting factor of phytore-mediation efficiencies. The use of surfactants to enhance the apparent aqueous solubility, desorption of organic compounds from solids and microbial bioavailability of PAHs in soil solution has been well documented. However, to the best of our knowledge, there is a lack of experimental data to elucidate the rate and extent of plant uptake of hydrophobic organic compounds such as PAHs in the presence of surfactants. Little information is available on the surfactant-enhanced phytoremediation for organic contaminated soils.In this dissertation, the mechanisms of the phytoremediation for soil PAHs were evaluated based on the studies of plant uptake and accumulation of these compounds. The effects of surfactants on plant uptake and accumulation of phenanthrene and pyrene in surfactant-laden solution were investigated. The basic behaviors and mechanisms of surfactant-enhanced phytoremediation were studied. Based on the experimental results and data from literatures, the performance of a partition-limited model on the prediction of plant PAH contamination was evaluated. The main original conclusions are shown as follows.(1) Root concentrations and concentration factors (RCFs) of phenanthrene and pyrene in soils displayed significantly positive correlations with root lipid contents (p<0.05, n=12). Root and shoot concentrations of tested PAHs were positively correlated to their soil concentrations, whereas RCFs and SCFs (shoot concentration factors) showed negatively a correlation with their soil concentrations. Moreover, root concentrations and RCFs of pyrene were generally much higher, and TFs values of pyrene were significantly smaller than those of phenanthrene. The presence of vegetation evidently enhanced the remediation of phenanthrene and pyrene in soil environment. However, plant uptake and accumulation only accounted for less than 0.23% of the enhanced loss of these chemicals in vegetated versus non-vegetated soils. In contrast, plant-promoted microbial biodegradation was the dominant mechanism of the phytoremediation for soil phenanthrene and pyrene contaminants.(2) The presence of a nonionic surfactant (Tween80) can significantly enhanced plant uptake of two representative PAHs, phenanthrene and pyrene, from an aqueous solution with the initial phenanthrene of 1.0 mg/L and pyrene of 0.12 mg/L. Tween80 under a wide range of concentrations (0-105.6 mg/L) did not show any apparent phytotoxity toward the growth of ryegrass (Lolium multiflorum Lam) and red clover {Trifolium pretense L.). The presence of Tween80 with lower concentrations generally enhanced the plant uptake based on the plant concentrations, accumulated amounts and PCFs (plant concentration factors) of these two PAHs. The maximal plant uptake was observed at 6.6 mg/L Tween80, in which PAH concentrations, accumulation amounts and PCFs were ~216% of those in Tween80-free controls.(3) The basic behaviors and mechanisms of the surfactant-enhanced phytoremediation (SEPR) for soil pyrene were originally investigated. The amendment of Tween80 (<1000 mg/kg) or Brij35 (<600 mg/kg) significantly enhanced the phytoremediation efficiencies, whereas the addition of SDS would evidently inhibit the degradation of pyrene in soils. As the added concentration lower than 600 mg/kg, CTMAB would clearly promote pyrene dissipation. However, for CTMAB showed apparent phytotoxity toward the growth of tested plants, CTMAB was the last candidate to be utilized as the amendment. The dominant me...
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