The Analysis Of Mechanisms And Efficiencies Of The Removal And Remediation Of Phenanthrene And Pyrene In Soil By Several Plants

Polycyclic aromatic hydrocarbons(PAils) are formed during the incomplete combustion of fossil fuel,wood,and other organic substances.They are persistent due to their recalcitrance to microbial degradation,high hydrophobicity,and ability to be absorbed strongly to soil particles.The partial breakdown products of PAHs degradation have toxic,mutagenic,and carcinogenic properties,and thus remediation is of great importance.Phytoremediation is a promising alternative approaches to soil remediation due to its convenience,cost-effectiveness and environmental acceptability.Full understanding of how plants uptake and accumulate organic contaminants like Polycyclic aromatic hydrocarbons(PAHs) have considerable benefits of risk assessment of crop contamination and subsequent human exposure and the development of phytoremediation.In this dissertation,the prospect of Phytoremediation for soil organic contaminants is an attractive cost-effective alternative to traditional engineering approaches.And the uptake,accumulation and translocation behavior of PAHs in plants was investigated using pot experiments.The potentials of six plant species on the degradation of phenanthrene(Phe) or pyrene(Pyr) in soil were investigated by pots experiments in a greenhouse,and the mechanisms and efficiencies of the removal and remediation of PAHs in soils by different planting patterns were also compared.The effects of earthworm activity on plant uptake and accumulation of PAHs in spiked soils were evaluated.) Based on these experimental results,a multi-process phytoremediation system composed of plants,soilfauna(earthworm) and aboriginal microbe was developed.The main original conclusions are shown as follows.1.Screening of twelve plant species for phytoremediation of phenanthrene or pyrene in soilsSix plant species were screened for their ability for the cleanup of PAH-spiked soil at their initial concentrations of ranging from 0 to 322 mg·kg^-1 by pots experiments in a greenhouse.The results of the screening experiment indicated that,at the end of the experiment (60d),the remaining respective concentrations of Phe or Pyr in spiked vegetated soils. The loss of Phe or Pyr in the vegetated soils was 52.82～82.27%and 42.27～75.4%of the added amounts of these contaminants,respectively.Among plants investigated, Ophiopogon japnicus and Festuca arundinacea caused a more significant decrease in the PAHs concentration in the planted soil than in the unplanted soil,and would be effective in the phytoremediation of PAH-spiked soils.Results also suggested that with the increment of their initial concentrations,the accumulations concentrations of Phe or Pyr in plant tissues monotonically increased,but RCFs(root concentration factors; defined as the ratio of PAHs concentrations in roots and in the soils on a dry weight basis) of these compounds gradually decreased.Under the same contamination level, PAHs concentrations in shoot and SCFs(shoot concentration factors;defined as the ratio of PAHs concentrations in shoots and in the soils on a dry weight basis) were always significantly lower than those concentrations in root and RCFs,and the concentrations of Phe in plants are always lower than those of Pyr.Plant uptake and accumulation 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 suggested a feasibility of the establishment of phytoremediation for soil PAHs contamination.2.Removal and remediation mechanisms of PAHs in soil by Festuca arundinaceaPot experiments were carried out to investigate the accumulation and removal mechanisms and efficiencies of PAHs by rock plant Tall rescue(Festuca arundinacea).The results showed that plantation of Tall fescue significantly removed phenanthrene and pyrene from soils at their initial concentrations of 0 to 322 mg·kg^-1. After 60 days plantation of Tall fescue,about 52.82%～82.27%(m=67.96%) of phenanthrene and 47.27%～75.4%(m=60.06%) of pyrene was removed from the soils of TD₃,respectively.Tall fescue removed averagely 45.41%of phenanthrene and 41.63% ofpyrene from the soils as compared to TD₁,and 62.89%ofphenanthrene and 57.5%of pyrene as compared to 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 larger than those for phenanthrene,and the BCFs for phenanthrene and pyrene in shoots were much lower than those in roots at same treatment.Despite the plantation of Tall rescue evidently enhanced the remediation of phenanthrene and pyrene in soils,contributions of biotic and abiotic factors to phytoremediation process displayed distinct diversity. Abiotic loss and plant accumulation accounted for 5.07%and 0.017%of the total removal of phenanthrene,and for 2.56%and 0.11%of pyrene from soils,respectively. In contrast,an average of 19.21%of the total removal of phenanthrene and 15.87%of pyrene were attributed to contributions of microbial degradation,and 62.87%of phenanthrene and 57.5%of pyrene to plant-microbial interactions.Thus microbial degradation and plant-microbial interactions are the main mechanisms of the remediation of soil PAHs pollution.3.Effects of multispecies phytoremediation on the fate of phenanthrene or pyrene in soilThe potentials of three plant species,rape and alfalfa,separately or jointly on the degradation of PAHs in soil were estimated by pots experiments in a greenhouse.The results showed that the presence of vegetation apparently enhanced the dissipation of PAHs in soils at their initial concentrations ranging from 0 to 322.06 mg·kg^-1,but the efficacy enhanced varied greatly among plant species and cropping patterns.At the end of the 60 d experiment,the extractable PAHs in soils with alfalfa and rape in mixed cropping were lower than that in monoculture.About 65.17%-83.52%of phenanthrene and 60.09%-75.34%of pyrene were removed from the soils in mixed cropping,respectively.As compared to monoculture with rape mixed cropping removed on average 43.26%of phenanthrene and 40.38%of pyrene from the soils and relative to monoculture with alfalfa,11.03%of phenanthrene and 16.29%of pyrene was removed.Alfalfa or rape did take up PAHs from the soils obviously; concentrations of PAHs in the root or shoot monotonically increased while ones in the soils were higher,and under the same treatment conditions,concentrations of PAHs in the root or shoot were lower in mixed cropping than that in monoculture,and in the shoot lower than in the root.Despite the presence of vegetation evidently enhanced the remediation of PAHs in soil environment,contributions of abiotic loss,plant accumulation and degredation was much lower than ones of microbial degradation and plant-microbial interactions in the process of phytoremediation.Thus plant-microbial interactions are the main mechanisms for the remediation enhancement of soil PAHs pollution under mixed cropping models.Results from this study 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.