汽油泄漏场地深层包气带土壤中苯系物的微生物降解机理

BTEX is a kind of commonly encountered hazardous compounds. During the past several decades, the aerobic microbial degradation mechanisms of BTEX has been a subject of extensive research in the world. However, BTEX contamination is often present in the anaerobic zones of the environment (i.e. sediment and groundwater). Therefore, microorganisms that degrade BTEX components in the absence of oxygen were also studied in recent years. However, the anaerobic microbial degradation mechanisms of BTEX still remain poorly understood in the coexistence of BTEX and other organic pollutants. This study will collect deep vadose zone soils from the petrol leaked sites, using the drilling sampling techniques. Here, combined molecular biology methods, routine laboratory analysis, and statistical analysis will be used to investigate the diversity and driving factors of the microbial diversity in deep vadose zone soils form the petrol leaked sites. This study will investigate the substrate interactions (individual substrate and BTEX combinations) during anaerobic biodegradation of BTEX (Benzene, toluene, ethylbenzene and xylenes) in the laboratory microcosms. This study will also investigate the effect of the site characterization factors(Nap, MTBE, Soil moisture, Nutrients) on the degradation of BTEX. The results of the study will improve the understanding of the microbial degradation mechanisms of BTEX in deep vadose zone soils form the petrol leaked sites, and provide some valuable theoretical basis for soil remediation in these sites.

苯系物(BTEX)是一类常见的有毒有害化合物，其好氧微生物降解机理的研究一直以来都是国际环境领域的热点。由于许多处于厌氧状态的沉积物和地下水中也存在BTEX污染问题。因此，近些年来BTEX的厌氧微生物降解也开始受到关注。尽管如此，在与其他有机污染物共存条件下BTEX的厌氧微生物降解机理的研究仍然较少。本项目拟以汽油泄漏场地深层包气带土壤为研究对象，采用地质钻探采样技术、实验室常规分析技术和现代分子微生物学手段，并结合数据统计分析方法，研究典型汽油泄漏场地深层包气带土壤中微生物多样性及驱动因子；采用室内厌氧培养方式，研究BTEX 厌氧降解过程中底物（苯、甲苯、乙苯和二甲苯）的相互作用，并考察场地特征因子(Nap、MTBE、土壤水分、营养物质)对BTEX降解的影响。研究结果有助于揭示汽油泄漏场地深层包气带土壤中BTEX的微生物降解机理，可以为汽油泄漏场地包气带土壤的修复提供理论依据。

该项目基于土壤DNA的提取，16S rDNA实时定量PCR和克隆文库的构建，分析了汽油泄漏场地土壤中微生物丰度及群落结构特征。实时定量PCR结果表明，表层土壤微生物丰度高于深层土壤约2个数量级，未污染的深层土壤中微生物丰度高于污染的深层土壤约2个数量级。RDP (Ribosomal Database Project) 分析结果表明，汽油泄漏场地表层土壤微生物种类较丰富，而深层土壤微生物组成较单一，且污染的深层土壤细菌群落多样性明显低于对照场地深层土壤。研究也发现，与汽油降解相关的微生物菌群 (如Beta-proteobacteria) 是深层污染土壤的主要微生物。对于深层汽油污染的土壤，经过180天厌氧培养后，添加硝酸盐电子受体处理的土壤中甲苯、乙苯、TPH（C6-C12）降解较为明显，且硝酸盐添加量越多，其降解率越高。尽管如此，其他单环芳烃如二甲苯、1,2,4-三甲苯、仲丁苯的降解并不明显。研究结果表明，土著微生物数量随着硝酸盐添加量增加而增加。此外，添加硝酸盐的处理中硝酸盐含量明显减少，并有一定量的亚硝酸盐生成，且硝酸盐和亚硝酸盐总量相对于第0天下降明显。这表明硝酸盐不仅促进了微生物数量的增加，且接受了电子受体，因此促进了甲苯、乙苯和TPH的厌氧降解。相对于硝酸盐来说，硫酸盐并未明显促进土壤中单环芳烃如甲苯、乙苯、二甲苯、1,2,4-三甲苯、仲丁苯及TPH（C6-C12）的降解。