RCEES OpenIR  > 环境化学与生态毒理学国家重点实验室
砷与锑的赋存形态及转化机制研究
Alternative TitleCharacterization and Transformation of Arsenic and Antimony Species
叶丽
Subtype博士
Thesis Advisor景传勇
2020-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name理学博士
Degree Discipline环境科学
Keyword砷,锑,迁移转化 , 分子水平谱学手段 arsenic, Antimony, Transformation And Mobility, Molecular-level, Spectroscopy
Abstract

     砷( As)和锑 Sb)属同族元素,均为优先控制污染物,严重威胁人类健康。研究砷 /锑的迁移转化行为对理解砷 /锑污染来源和变化趋势具有重要意义。微生物在 As/Sb的生物地球化学循环中起着至关重要的作用,它们一方面直接决定As/Sb的赋存形态,另一方面通过改变以铁矿物为主的吸附介质性质 ,从而影响As/Sb的迁移转化。传统观念认为硫酸盐还原菌( SRB)导致 As/Sb固定 ,然而 我们的最新研究发现 SRB可以通过介导溶解态硫代锑酸盐的生成,进而促进 Sb的释放。为了理解微生物如何调控砷和锑的迁移转化过程,本文分为以下五个部分: 1)探索 ars基因介导砷解毒还原机制对零价纳米铁废泥中的砷的迁移转化影响; 2)研究砷还原菌和砷氧化菌共存时,吸附态砷的迁移转化过程 3)考察锑矿区的锑污染情况,并建立人体锑富集与环境变量的因果关系; 4)探索 SRB是否可以通过硫代锑酸盐的生成而促进锑的释放; 5)研究硫循环对砷和 锑的迁 移转化影响的区别。
     第一 ,发现 含 ars基因的好氧砷还原 菌, Pantoea sp. IMH更倾向于还原溶解态的 As(V),而非固相上吸附的 As(V),因此,其对砷的释放并未起到太大的促进作用。 μ-XRF和 As μ-XANES结果发现,零价纳米铁废泥中的砷和铁并非均匀分布,且 As和 Fe的分布显著相关。 穆斯 堡尔谱的结果发现 IMH使铁相的结 构发生了轻微扭曲。另外, Fe XANES拟合结果 证实 Fe3O4在 nZVI老化过程中 少量 会转化为水铁矿, IMH阻碍了铁相的转化,减慢了 nZVI的老化过程。
     第二,通过静态培养实验模拟了砷还原菌和砷氧化菌共存环境下,发现 砷氧 化菌主导着溶解态砷的形,中以 As(V)为主 ,即使 arsC基因表达量 几乎是 aioAB基因 的五倍。 As XANES结果表明砷氧化菌对固相吸附态 的形影响较小,而砷还原菌可将吸附态的 As(V)还原为了 As(III)。固相上 As形态的 改变使得少量砷的吸附构型由双齿双核向单齿双核变化。穆斯堡尔谱结果发现砷
氧化菌可以降低吸附载体针铁矿的结晶度,而砷还原菌的存在会削弱结晶度的降低程度。砷的吸附结构和针铁矿晶改变对释放影响不大.
     第三,考察了锑暴露导致人 体生物指示物(头发、指甲、尿液和唾液)中的锑积累 ,并建立了人体锑积累与环境因素的关系。 我们从湖南锡矿山的重锑污染 区域采集了 480个环境样品 ,发现 超过 70%的饮用水 (n=83)、80%的食物 (n=83)中的锑含量超过国际标准 。人体每日饮食摄取的锑 (11.7 μg/kg/d)超出建议值 (0.4 μg/kg/d)的三十倍,其中有 85-100%来自饮用水的摄入。人体对锑的摄取 造成锑 在生物指示物中积累,当地居民尿液 (95%, n=63),唾液 (44%, n=48),头发 (80%, n=51)和指甲 (83%, n=47)中的锑含量均超出正常值。 通过相关性分析发现人体每 日摄取锑含量仅与头发中的成正相关 (p=0.02),而与尿液 (p=0.05),唾液(p=0.52)和指甲 (p=0.85)没有显著相关性。相关性结果说明头发可能是最好的锑暴露的生物指示物。此外,摄取的锑在人体新陈代谢过程中发生了转化。摄取时主要是 以五价无机锑为主,而通过尿液和唾液排出时,主要以甲基锑为主, 表明 甲基化可能是人体对锑的解毒机制 。
     第四, SRB被普遍认为会通过生成硫化锑( Sb2S3)沉淀从而固定锑。与此认知相反, 本研究 发现 SRB显著促进了锑的释放 。厌氧条件下,硫酸盐还原菌 Desulfovibrio vulgaris DP4将吸附在针铁矿上的五价锑酸盐( SbV(OH)6-)转化为 硫代锑酸盐, 导致溶解态的锑浓度显著升高。硫代锑酸盐是释放出的锑的主要赋存形态。傅里叶变换离子回旋共振质谱( FT-ICR MS)被用来探索硫代锑酸盐的生成机制。 FT-ICR MS检测 到六配位和五硫代锑酸盐中间体。六配位硫代锑酸盐的存在表明第一步是巯基逐取代 SbV(OH)6-上的羟基,从而生成六配位硫 代锑酸盐。由于位阻效应,六配位 硫代锑酸盐并不稳定,它会进一步通 过脱去反 应,脱去一分子的硫化氢,生成五配位硫代锑酸盐。五配位 硫代锑酸盐会再次通 过脱去反应生成稳定的四配位硫代锑酸盐。 由 SbV(OH)6-生成硫代锑酸盐的过程 是 消耗质子的反应,因而pH依赖的反应。 硫化反应使得 Sb(V)由六配位八面
体结构转变为四配位 四面体结构。这种结构和形态的改变 使得 硫代锑 酸盐与铁氧 化物的亲和力不强,从而导致了锑释放到水体中。
     最后,由于 As与 Sb都可以在 SRB作用下生成溶解态硫代化合物,而二者 常常是共存于污染土壤中,我们推测两者对硫会有竞争关系。为了理解这种竞争作用以及竞争带来的对 As/Sb迁移转化 的影响,本研究探索了好氧 -厌氧转变时, 在土著微生物介导下硫循环是如何影响 As和 Sb的迁移转化过程。实验结果发 现砷在厌氧条件下被释放,而锑好。 As的释放不是由于铁还原作用,而是由于 SRB介导产生了溶解态的硫代砷酸盐。硫代砷酸盐的生成优于硫代锑酸盐的生成,因为有限的可利用的 S2-会优先与 As反应。由于硫代锑酸盐生成被抑制,硫循环对 Sb的迁移转化影响被减弱。 Sb的 迁移转化主要由锑氧化还原过程决定, Sb(III)氧化为 SbV(OH)6-成为 Sb释释放的主要原因.
 

Other Abstract

     Arsenic (As) and antimony (Sb) are in the same group, and both are listed as priority pollutant. Microorganisms play an important role in the biogeochemical cycle of As/Sb, by regulating As/Sb species or the transformation of adsorbent. Sulfate-reduing bacteria (SRB) is usually assumed to facilitate Sb immobilization via Sb2S3 precipitation. On the contrary, our recent study suggested that SRB mobilize Sb by the formation of thioantimony. To study the bio-transformation of As/Sb mediated by bacteria, the aims of the present work are: 1) to explore the effect of Pantoea sp. IMH with ars gene on As mobilization in spent nanoscale zero-valent iron (nZVI) waste residue; 2) to study the fate of adsorbed As mediated by coexisting arsenate-reducing and arsenite-oxidizing bacteria; 3) to investigate Sb intake of residents near an active mining area and Sb speciation in human biomarkers; 4) to study the effect of SRB on adsorbed Sb; 5) to compare the priority in the formation of thioarsenic and thioantimony, and the effect of microbial sulfate reduction on the mobility of As and Sb.
     Firstly, our incubation results showed that IMH preferentially reduces soluble As(V), not solid-bound As(V), and was innocent in elevating total dissolved As concentrations. μ-XRF and As μ-XANES spectra clearly revealed the heterogeneity and complexity of the inoculated and control samples. Nevertheless, the surface As local coordination was not affected by the presence of IMH as evidenced by similar As-Fe atomic distance (3.32-3.36 Å) and coordination number (1.9) in control and inoculated samples. The Fe XANES results suggested that magnetite in nZVI residue was partly transformed to ferrihydrite, and the IMH activity slowed down the nZVI aging process. IMH distorted Fe local coordination without changing its As adsorption capacity as suggested by Mössbauer spectroscopy. Arsenic retention is not inevitably enhanced by in situ formed secondary Fe minerals, but depends on the relative As affinity between the primary and secondary iron minerals.
     Secondly, Bacteria with arsenate-reducing (ars) and arsenite-oxidizing (aio) genes usually co-exist in aerobic environments, but their contrast impacts on arsenic (As)speciation and mobility remain unclear. To identify which bacteria, dominate As speciation under oxic conditions, we studied the biotransformation of adsorbed As on goethite in the co-existence of Pantoea sp. IMH with ars gene and Achromobacter sp. SY8 with aio gene. The incubation results show that SY8 dominated the dissolved As speciation as As(V), even though aio exhibited nearly 5 folds lower transcription levels than ars in IMH. Nevertheless, our XANES results suggest that SY8 showed a negligible effect on solid-bound As speciation whereas IMH reduced adsorbed As(V) to As(III). Our Mössbauer spectroscopic results suggest that the incubation with SY8 reduced the degree of crystallinity of goethite, and the reduced crystallinity can be partly compensated by IMH.
     Thirdly, to identify human biomarkers for Sb exposure, we analyzed 480 environmental samples from an active Sb mining area in Hunan, China. Elevated Sb concentrations exceeding the acceptable level were detected in drinking water (70% of n = 83 total samples), foods (80%, n = 188), urine (95%, n = 63), saliva (44%, n = 48), hair (80%, n = 51) and nails (83%, n = 47). Drinking water contributed 85%-100% of the average daily dose (ADD) of Sb, and the total ADD (11.7 μg/kg bodyweight/day) was up to thirty times higher than the oral reference dose (0.4 μg/kg bodyweight/day)  as recommended by USEPA. A distinct positive correlation was found between ADD and Sb content in hair (p = 0.02), but not in urine (p = 0.051), saliva (p = 0.52) or nails (p = 0.85), suggesting that hair is the best non-invasive biomarker. μ-XRF analysis indicated that Sb is distributed in discrete spots in hair and nails, and Sb distribution is correlated with other metals. Methylated Sb species were predominant in urine (46%-100%) and saliva (74%-100%) in collected samples, implying that the human metabolic system adopts methylation as an effective pathway to detoxify and excrete Sb.
      Fourthly, the biogenic sulfide is usually assumed to facilitate Sb immobilization via Sb2S3 precipitation. Here, to the contrary, we discovered that SRB mobilize adsorbed Sb(V). When SbV(OH)6--bearing goethite was incubated anaerobically with Desulfovibrio vulgaris DP4, elevated antimony was released due to the formation of thioantimonate which is the dominant Sb species in solution. Our fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis observed multiple six- or five-coordinate thioantimonate intermediates, suggesting stepwise ligand exchange of hydroxyl groups on SbV(OH)6- by biogenic sulfide. Direct H2S elimination reactions resulted in four-coordinate thioantimonate species as the stable end product, which was confirmed by our density functional theory (DFT) calculations. The thiolation of antimonate is pH-dependent and occurs in neutral environments. The thiolation changed Sb(V) from six-coordinate octahedral to four-coordinate tetrahedral coordination, weakening its affinity for iron oxides and thus facilitating its release into the aquatic environment.
     Finally, biogenic sulfide from microbial sulfate reduction under anaerobic conditions may enhance the release of coexisting As and Sb through the formation of labile thioarsenate (AsV-S) and thioantimonate (SbV-S). To understand the competition between As and Sb for thiolation and its effect on their mobility, we investigated the speciation and fate of As and Sb in the presence of indigenous microbiota in sediments during multiple oxic-anoxic cycles. Our incubation results indicated that As was released under anoxic conditions whereas Sb was mobilized during oxic cycles. The As release was not driven by the Fe(III) reductive dissolution, but by biogenic sulfide through the formation of soluble AsV-S. AsV-S formation outcompeted SbV-S because the limited available sulfide preferentially reacted with As rather than Sb. The Sb mobility was regulated by its redox transformation between antimonate (SbV-O) and antimonite (SbIII-O) where microbial SbV-O reduction resulted in Sb immobilization.
 

Pages144
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/43692
Collection环境化学与生态毒理学国家重点实验室
Recommended Citation
GB/T 7714
叶丽. 砷与锑的赋存形态及转化机制研究[D]. 北京. 中国科学院生态环境研究中心,2020.
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