Studies On The Accumulated Characteristics And Toxicity Evaluation Of The Oxygen-containing Aromatic Hydrocarbons During The Remediation Process Of Contaminated Soil And The Degradation Characteristics Of Oahs Degrading Strains

Oxygen-containing aromatic hydrocarbons(OAHs)are present in various environmental systems and organisms,including water,soil and atmosphere.OAHs come from a variety of sources.In the environment,they mainly come from incomplete photolysis,chemical oxidation and biological transformation of benzene series and polycyclic aromatic hydrocarbons(PAHs)pollutants.In recent years,due to the increased risk of carcinogenesis and environmental risks in the remediation process,OAHs have attracted increasing attention.Results of medicine and toxicology indicate that most of the transformed OAHs are far more toxic than their parent rings.As so far,the successful remediation of soil contaminated with benzene series and PAHs only evaluate the removal efficiency of primary pollutants,while the toxicity of secondary pollutants accumulated by rapid transformation of parent compounds should also be considered.However,the accumulation characteristics and ecological toxicity of OAHs and further transformation and mineralization of these OAHs are seldom studied.The methods for toxicity assay of OAHs in soil are also rare.This study focuses on these issues.In this study,we firstly screened and identified typical strains for remediation of benzene series and PAHs contaminated soil.Then the accumulated characteristics of OAHs,transformed by this strain,were studied.The typical OAHs and its mixtures were obtained.On this basis,the method for toxicity assay of OAHs on soil ecology system was established.The method was applied to evaluate the ecological toxicity of OAHs mixtures.One strain,capable of degrading several typical OAHs,was isolated from OAHs contaminated soil.The metabolic characteristics of OAHs by this strain were studied and its molecular basis was also analyzed.The results are as follows:(1)One strain FF,which could efficiently degrade benzene series and PAHs in multiple pathways,was isolated from the crude oil polluted system and identified as Rhodococcus qingshengii.It could produce abundant OAHs during the degradation process.Fifty-two intermediates were extracted and identified in the remediation soil contaminated with phenanthrene,of which 55% were oxygen-containing aromatic hydrocarbons,and they are representative.38% of the intermediates were oxygen-containing chain hydrocarbons,indicating that strain FF also had strong capability in ring-cleavage.Strain FF could also secrete trehalolipids,which was one of the reasons for its rapidly degradation of PAHs.(2)The accumulated characteristics of OAHs produced by strain FF in liquid medium during the degradation process of phenanthrene were elucidated.Total of 29 intermediates were identified,of which more than 69% were OAHs,and the functional groups mainly included alcohol hydroxyl,phenolic hydroxyl,carboxyl and/or?-carboxylic acid.The degradation efficiency of phenanthrene in liquid system of the second day and the seventh day could reach about 30% and 90%,respectively,and the accumulation characteristics of OAHs in these two phases were remarkably different.Meanwhile,the inhibition of bio-luminescence to V.fischeri in these two phases were significantly different(about 45% and 90%,respectively).Thus,they could be used as typical OAHs mixtures for the soil ecological toxicity assay.(3)Combined with the accumulated and distributed characteristics of OAHs in the actual soil and their toxicity,1-hydroxy-2-naphthoic acid,1-naphthol and 9,10-anthraquinone were used as the typical OAHs to establish the method for ecological toxicity assay.The microbial diversity,catalase and invertase activity of soil,and wheat seed germination indexes were determined using as eco-toxicity evaluation indexes,and the effects of typical OAHs on soil ecology were elucidated.(4)OAHs mixture produced by strain FF during the degradation process in the second day and the seventh day were used as the aimed contamination to evaluate their effects on the ecology and function of farmland soil.The results showed that OAHs significantly or highly significant decreased microbial richness and evenness of farmland soil,varied the structure of bacterial community.Proteobacteria increased significantly,while Acidobacteria,Verrucomicrobia,and Chloroflexi decreased significantly.OAHs also significantly lowered the germinal length,root length or root number of wheat seed.PSL-PM analysis indicated that the changes of components of OAHs and soil bacterial community directly influenced the germination of wheat seed.(5)For further removing the accumulated OAHs in soil,one strain named Arthrobacter crystallopoietes NT16,was acclimated and screened.It could degrade1-hydroxy-2-naphthoic acid,1-naphthol and 9,10-anthraquinone through hydroxylation,decarboxylation and oxygenated ring-cleavage,and finally enter TCA cycle through salicylic acid or phthalic acid pathway.At the genomic level,it was found that both catechol-1,2-dioxygenase and catechol-2,3-dioxygenase genes existed in strain NT16,and there were 109 genes related to aromatic ring degradation in the genome,indicating that strain NT16 had both ortho-and meso-cleavage patterns,and had excellent capability of aromatic ring degradation.This thesis would lay a foundation for the establishment of evaluation methods for the safe utilization and reuse of remediation soil contaminated with benzene series,PAHs and other recalcitrant organic compounds,and also provide useful references for further decontamination of OAHs in soil.