| Full understanding of the distribution and transformation behaviors of polycyclic aromatic hydrocarbons (PAHs) in soil humic fractions and mechanism investigations of plant availability ,have considerable benefits for risk assessment of crop contamination and subsequent human exposure and the development of phytoremediation.In this dissertation,the mechanisms and affecting factors of phytoremediation technique for organic pollutants ,especially for plant uptake were reviewed.Chosen phenanthrene as target contaminant and maize as test plant ,the main research content of the dissertation involves:Preliminary study on the distribution and transformation of phenanthrene humic fractions distilling from polluted soil in different equilibration times;Investigation of plant availability of phenanthrene conbined with humic fractions;Uptake,accumulation and translocation behavior of different concentrations of PAHs and affected by fulvic acid andβ-cyclodextrin in maize by using a hydroponic system.The main valuable conclusions are shown as follows:(1) Uptake and accumulated by roots and subsequently transported to shoots was the major pathway for maize uptake of PAHs.The maize showed inhibitory and toxicity effect in the presence of higher concentrations(above 5 mg L-1 ) of phenanthrene in culture.When the initial concentrations in solutions was 0.5-4.0mg L-1,the uptake and accumulation of phenanthrene in shoots and roots from hydroponic solution were elevated with the increase of their solution concentrations.The concentration of phenanthrene was generally much lower in shoots than in roots.The accumulation speed of phenanthrene in shoots of maize was increased with the concentrations in solutions,while the accumulation in roots was opposite.After several days ,the accumulation efficiency of phenanthrene in shoots and roots of maize under different concentrations tended to identical.(2) When the pollutant's concentration ranged from 5.2 mg kg-1 to 404.0 mg kg-1,the content of phenanthrene adsorbed by humic fractions distilling from soil was humin>humic acid>fulvic acid.It maybe relate to carbon content and structure of each humic fraction.It was a gragual process for fulvic acid and humic acid to combine with phenanthrene in soil. When the equilibrium time get to 8 weeks, concentrations of phenanthrene in fulvic acid and humic acid both reached to maximum.(3) When the initial polluted concentration was 5.2 mg kg-1,the percentage content of concentration of phenanthrene in soil after plant cultivation to pre-plant cultivation was 36.6%,41.2%,45.9%,as the equilibrium time reaching to 4 weeks ,8 weeks and 16 weeks. In the condition of pot experiment ,maize played good performance in remediation of soil polluted by phenanthrene.(4) In the condition of hydroponic system,the presence of fulvic acid with reletalively low concentrations promoted the plant uptake of phenanthrene.,whereas fulvic acid with higher concentrations would inhibit the plant uptake of the compound.The presence of 10.54mg L-1 fulvic acid generally displayed the highest promotion of the plant uptake of phenanthrene.It could be decuced that fulvic acid is a surface-active agent.Different concentions ofβ-cyclodextrin generally inhibited the plant uptake of phenanthrene from solution.The inhibited effect would become smooth with the increasing concentration ofβ-cyclodextrin.This could be related to the equilibrium of phenanthrene among the plant roots ,culture solution andβ-cyclodextrin system,and the structure of inclusion complexes formed with phenanthren andβ-cyclodextrin.
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