氯代烃厌氧降解过程中共存砷的形态转化及其对脱氯的影响

Arsenic (As) and chlorinated hydrocarbons are widespread groundwater contaminants due to natural processes and/or anthropogenic activities. Previous studies had demonstrated that biogeochemical conditions resulted from chlorinated solvents remediation can facilitate As reduction, dissolution and immobilization, but the consequences of these arsenic transformation processes on microbial dechlorination activity remain largely unexplored. In this proposal, microbial reductive dechlorination and As transformation processes will be stimulated in microcosms established using samples collected from sites impacted by As and chlorinated hydrocarbons. Changes in community structure and functional gene abundance relevant to As transformation will be investigated to unravel the mechanisms that govern As reduction and speciation under reductive dechlorination condition. A variety of arsenic compounds in different valences and forms will be tested in dechlorinating pure cultures and mixed cultures. The inhibitory effects of As transformation on chlorinated hydrocarbon degradation will be demonstrated by the changed in dechlorination performance, dechlorinating community structure and function, and reductive dehalogenase activity. The underlying inhibitory mechanisms of As transformation on reductive dichlorination will be explained at the ecosystem, organism and protein levels. The successful implementation of the project has significant values for effective risk control at arsenic and chlorinated hydrocarbon co-contaminated sites and enhanced biodegradation of chlorinated hydrocarbons.

氯代烃与砷是我国地下水中普遍检出的共存污染物。有研究显示氯代烃的还原性脱氯降解过程可引发固相砷的释放、还原与再固定等一系列复杂过程，但这些过程中砷的形态如何转化及对氯代烃降解产生什么样的影响，目前还鲜有报道。基于此，本项目以砷共存氯代烃污染地下水为研究对象，采集污染地下水和沉积物样品建立脱氯微宇宙系统，研究砷共存脱氯系统中砷的含量与形态、砷转化途径与相关功能基因的变化，探讨脱氯过程中砷的转化规律及影响因素；在脱氯菌纯培养和混合培养下，通过测试不同形态与价态的砷对氯代烃降解过程、脱氯菌种群结构与功能、以及还原性脱卤酶酶活的影响，明确不同形态的砷对关键脱氯菌种群的抑制效应，在生态系统、纯培养及功能蛋白水平的层面揭示砷转化对氯代烃降解的影响机制。项目的成功实施对于砷共存氯代烃污染风险有效控制及促进相关污染场地修复具有重要的理论和实践意义。

对于砷共存的氯代烃污染场地中，生物还原脱氯过程可以刺激砷、铁和硫等还原微生物活性，引起固定态As(V)的释放和转化，从而导致地下水砷的二次污染；另一方面，转化产生的不同形态砷可对脱氯菌种群和有机氯降解产生影响，最终决定氯代烃污染生物还原修复效果。本项目采集了沈阳细河（低硫）以及葫芦岛锌厂毗邻五里河流域（高硫）砷和氯代烃污染地区沉积物，发现污染程度不同，微生物群落组成差异明显，砷与绿弯菌门（专性脱氯球菌所在属）具有显著负相关。脱氯微生态系统研究发现脱氯过程可以引起As(V)释放、还原以及再固定；不同浓度硫的输入使砷的行为更为复杂，沉积物中的砷在固-液相之间会发生多次释放-固定过程，液相砷浓度随培养时间呈现“M”型变化趋势，中间可能有硫代砷化合物的生产。不同浓度和形态砷的输入不但引起脱氯速率的变化，也可以导致脱氯终点的改变，以及有毒中间产物二氯乙烯、一氯乙烯的积累。高通量测序结果显示不同形态砷对不同脱氯菌有不同的抑制效应；砷对非专性脱氯菌地质杆菌（Geobacter）的丰度影响不大，但显著降低了脱氯球菌（Dehalococcoides）的相对丰度。非专性脱氯菌地质杆菌SZ和硫磺单胞菌对As(V)和As(III)有较高的耐性；而脱氯球菌对As较为敏感，高浓度的As抑制脱氯速率和脱氯终产物，而且这种抑制是不可逆的。砷可以特异性的抑制脱卤关键酶活进而导致脱氯菌失活。此外，项目还尝试采用微生物成矿方式，把液相中的砷固定到硫酸盐还原菌成的黄铁矿中，进而解除其对脱氯菌的毒性，提高微生物修复效率。