【作者】 丁腾达；

【导师】 张志剑； 张建英；

【作者基本信息】 浙江大学 ， 环境工程， 2014， 博士

【摘要】 砷(Arsenic, As)因其价态与结合态的多样性而呈现差异显著的污染行为,成为水体生态风险研究热点的代表性类金属元素。本论文研究毒性最强的三价砷[As(Ⅲ)]在淡水硅藻中的吸附吸收行为及其毒性作用,选取水质指示生物硅藻为藻类生物介质代表,通过氢化物原子吸收光谱(Hydride generation-atomic absorption spectrometry, HG-AAS)、傅里叶红外光谱(Fourier transform infrared spectroscopy, FTIR)和X射线光电子能谱(X-ray photoelectron spectroscopy, XPS)等技术,探究三价砷在淡水硅藻中的吸附吸收行为、机制、以及多不饱和醛(Polyunsaturated aldehydes, PUAs)与硅(Silicon, Si)的介导作用；运用透射电镜(Transmission electron microscope, TEM)和原子力显微镜(Atomic force microscope, AFM)等超微表征技术,探索三价砷和二甲基砷(Dimethylarsinic acid, DMA)对硅藻的毒作用及细胞微形态。主要研究结论如下：(1)淡水硅藻对As(Ⅲ)的生物吸收主要是胞内吸收,其对As(Ⅲ)的吸收作用强于硅藻硅壳对As(Ⅲ)的表面吸附。在0.05-20mg L-1As(Ⅲ)浓度下,代表性淡水硅藻Navicula sp和海洋硅藻Phaeodactylum sp分别在5.0和10.0mg L-1As(Ⅲ)下达到最大吸收效率,分别为55.64±4.5%和99.4+0.1%。随着As(Ⅲ)浓度增大,淡水硅藻Navicula sp的吸收效率先上升后下降,20mg L-1As(ⅡⅠ)下其生长完全受到抑制而使其吸收效率下降为21.9+3.5%,经过对胞内和细胞壁结合砷浓度分析,发现胞内砷浓度远远高于细胞壁结合砷浓度,表明了其对As(Ⅲ)的胞内吸收强于其硅壳对As(Ⅲ)的表面吸附。(2)As(Ⅲ)与DMA复合污染对淡水硅藻Nitzschia sp具有相加和拮抗效应,其毒性效应取决于暴露浓度。在0.04-45.32mg L-1DMA与016-0.49mg L-1As(Ⅲ)暴露浓度下,其复合污染对硅藻的联合作用表现为相加效应,硅藻生长速率呈现明显的下降,同时其细胞膜也受到较严重的破坏,通过细胞膜形成速率分析表明该处理组中细胞膜形成速率最快。而随As(Ⅲ)浓度的升高,DMA与0.58-1.26mg L-1As(Ⅲ)暴露浓度下的复合污染对硅藻具有拮抗效应,硅藻生长和细胞膜损伤都有所恢复。经过对胞内巯基水平分析,发现0.58-1.26mg L-1As(Ⅲ)与DMA复合污染处理组中巯基含量明显升高,表明了As(Ⅲ)在该浓度下会诱导硅藻胞内解毒机制而减弱As(Ⅲ)的毒性。(3)淡水硅藻对As(Ⅲ)的生物吸收量因界面多不饱和醛(PUAs)的介导而增加。淡水硅藻Cymbella sp和Navicula sp对5mg L-1As(Ⅲ)的生物吸收效率分别为36.1+2.9%和12.4+2.7%,而增加PUAs会使两种硅藻对As(Ⅲ)的生物吸收效率升至47.6+5.2%和23.7±1.3%。PUAs对硅藻吸收As(Ⅲ)的介导机制可能是由于其与As(Ⅲ)的亲核加成反应而减弱了As(Ⅲ)毒性。通过PUAs对As(Ⅲ)的吸附行为分析,发现PUAs对As(Ⅲ)的吸附效率为20.0±2.5%。通过毒性分析表明,两种硅藻生长速率在0.1μMPUAs下分别会上升49.0±10.5%和23.1±12.4%。经AFM分析表明,PUAs能减弱As(Ⅲ)对硅藻硅壳的破坏,其吸附As(Ⅲ)后滞留硅藻表面孔径中而阻止As(Ⅲ)进入硅藻胞内引起细胞性损伤。(4)淡水硅藻硅壳对As(Ⅲ)的吸附效率会因氨基和巯基官能团的介入而得到显著提高。硅藻硅壳对As(Ⅲ)的吸附作用并不显著,其对12mg L-1As(Ⅲ)的吸附效率在pH7条件下仅为13.8±1.4%,而pH4条件下其吸附效率能达到最高值20.5+0.6%,但通过人工模拟过程将氨基和巯基引入失活硅藻表面后,其吸附效率能提升65.5+1.3%。As(Ⅲ)在改性的失活硅藻表面的动力学行为和吸附等温线分别能用准二阶动力学方程和Langmuir-Freundlich模型进行良好描述,同时其热力学行为中得到的负自由能△G0和吸附焓△H0表明As(Ⅲ)在改性失活硅藻上的吸附行为是自发放热的过程。更多还原

【Abstract】 Arsenic (As) is a ubiquitous metalloid in the environment with toxicity dependent on its various species. Among the four arsenic oxidation states (+Ⅴ,+Ⅲ,0,-Ⅲ), the more toxic trivalent arsenic [As(Ⅲ)] in multi-phases mediums has received more attention. This focused study on the effect of As(Ⅲ) on algae is anticipated to provide valuable information about the risk of arsenic in aquatic ecosystem and the development of related arsenic criteria. The objective of this dissertation was to study the effects of arsenic on the several diatom species as the representative bio-indicator for their sorption and toxic effects of As(Ⅲ) on algae. The sorption mechanism of As(Ⅲ) on diatoms was examined by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The influence of dimethylarsinic acid (DMA) and polyunsaturated aldehydes (PUAs) on the As(Ⅲ) behavior was also studied. Changes of algal ultrastructure were studied by a transmission electron microscopy (TEM), and the variations on diatom frustules were observed with an atomic force microscopy (AFM). The results are concluded as follows:(1) As(Ⅲ) sorption on diatoms is mainly intracellular uptake, which is higher than the amount of the cell wall-bound. The absorption efficiency also changes with As(Ⅲ) concentrations, which varies among diatom species. Toxicity and biosorption responses to As(Ⅲ) were examined in a72-h exposure study using typical freshwater diatom Navicula sp. and marine diatom Phaeodactylum sp. Results indicated that in the range of0.05-20mg L-1As(Ⅲ), two diatoms could reach their maximum absorption efficiency of55.6±4.5%and99.4±0.1%at5.0and10.0mg L-1As(Ⅲ), respectively. With the increase of As(Ⅲ) concentration, the absorption efficiency of freshwater diatom Navicula sp. increased at the low concentration range of As(Ⅲ). At higher concentrations, absorption decreased with increasing As(Ⅲ) concentration. The algal growth was completely inhibited at20mg L-1As(Ⅲ) with the absorption efficiency decreasing to21.9±3.5%. The analysis of the intracellular and cell wall-bound arsenic content indicated that the intracellular uptake of freshwater diatom on As(Ⅲ) was significant. (2) The mixed effects of As(III) and DMA on the growth of diatom Nitzschia sp. presented additive and antagonism effects at different arsenic concentrations. At the exposure of0.04-45.32mg L-1DMA and0.16-0.49mg L-1As(Ⅲ), the combined effects were found to be additive. The growth rate of diatom decreased significantly, and the diatom frustule was destructed heavily. It was also verified by the analysis of the formation rate of frustules, which was faster in these treatments. However, with the As(Ⅲ) concentration increased, the combined toxicity of DMA and0.58-1.26mg L-As(Ⅲ) showed to be antagonistic, which the decrease of growth rate and the destruction of diatom frustule was improved. Results also indicated that the thiols increased in the treatment of0.58-1.26mg L-1As(Ⅲ) and DMA, suggesting that the detoxification mechanism in diatom was activated to reduce the As(Ⅲ) toxicity.(3) The efficiency of As(Ⅲ) sorption by diatoms increased with the addition of polyunsaturated aldehydes (PUAs). The absorption efficiency of Cymbella sp. and Navicula sp. for As(Ⅲ)(5mg L-1) was36.1±2.9%and12.4±2.7%, respectively. But after the addition of PUAs, they increased further to47.6±5.2%and23.7±1.3%. The modulation mechanism of PUAs on uptake of As(Ⅲ) on diatoms may be caused by the reactions between PUAs and As(Ⅲ) that reduced the As(Ⅲ) toxicity. The analysis of PUAs adsorption for As(Ⅲ) indicated that PUAs could adsorb20.0±2.5%As(Ⅲ). The toxicity analysis also demonstrated that the growth rate of two diatoms increased49.0±10.5%and23.1±12.4%at0.1μM PUAs, respectively. The AFM observations suggested that PUAs could mitigate the destruction of diatom frustule by As(Ⅲ). The adsorbed As(Ⅲ) by PUAs was proved to enter into pores on diatom frustules, and thus the As(Ⅲ) toxicity on intracellular organelles could be mitigated.(4) As(Ⅲ) adsorption on freshwater diatom silica shells increased significantly following the surface modification through addition of amino and thiol groups. The adsorption of As(Ⅲ) on raw and modified non-activated diatom was examined at varying pHs. Results indicated that the adsorption efficiency of As(Ⅲ) on non-activated diatom was small, sorption reached only13.8±1.4%under the12mg L-1As(Ⅲ) at pH7, and the highest sorption of20.5±0.6%occurred at pH4. However, after the introduction of amino and thiol groups onto diatom surface, the adsorption efficiency was improved by65.5±1.3%. The adsorption kinetics and isotherms could be described by psedo-second-order kinetic model and Langmuir-Freundlich model, respectively. Meanwhile, the negative values of Gibbs free energy A G0and enthalpy A H0indicate the spontaneous and exothermic nature of the adsorption.更多还原