微生物砷代谢机制的研究进展（Progress in Study of Mechanisms of Microbial Arsenic Transformation in Environment）

环境砷污染是一个全球性问题.研究砷的生物地球化学循环可以明确环境中砷的来源及其转化特征,为探索砷污染治理的方法提供参考.越来越多的研究表明,自然界中的微生物在砷的迁移转化过程中发挥了重要作用.根据微生物对砷的代谢机制不同将其分为:砷氧化微生物、砷还原微生物和砷甲基化微生物.砷氧化微生物可以将环境中的As(Ⅲ)氧化为毒性较弱并且容易被铁铝矿物吸附固定的As(Ⅴ),因此对降低环境中的砷毒性具有重要作用;微生物对砷的甲基化作用的产物通常为毒性较低的有机砷,因此也被认为是理想的修复环境砷污染的生物手段之一;然而在还原环境中,砷还原微生物却可以将游离态和结合态的As(Ⅴ)还原为毒性更强的As(Ⅲ),从而加重环境中的砷污染状况.由此可见,明确微生物的砷代谢机制及其对砷污染环境中砷迁移转化的影响,是实现生物修复砷污染环境的必要前提.论文总结了近年来国内外微生物砷代谢机制的研究进展,以期为深入研究微生物代谢砷的机理及其在砷污染治理中的应用提供参考.     

厌氧微生物作用下土壤中砷的形态转化及其分配

厌氧微生物作用下土壤中砷的形态转化及分配比例对砷的环境行为与归趋具有重要影响。实验利用张士污灌区土壤负载低浓度砷,研究了厌氧微生物作用下砷的形态转化过程,并通过磷酸盐及盐酸提取土壤中的砷、铁和硫,探讨了砷在土壤中结合形态的变化及土壤矿物结构转化与砷环境行为的关联。实验结果表明,微生物作用下土壤负载的砷被迅速还原为As(III)并释放进入液相,培养24h后液相累积的As(T)量达到16.9μmol·L-1,其中As(III)占液相总砷含量的91%以上;48h后释放的砷被再次固持,液相残留的As(III)浓度仅为1.5μmol·L-1。尽管微生物还原作用造成土壤中铁氧化物的活化,但固相中磷酸盐提取态与盐酸提取态砷所占的比例分别从载砷量的45.3%和49.8%降低到22.0%与0.22%,而体系中硫酸盐还原产生的硫离子的量与砷的释放量保持负相关。可见微生物还原作用下砷发生了活化,释放和再固定的过程,土壤负载的砷从溶解态、吸附态及铁氧化物结合态逐渐被转化为更稳定的硫化物结合态。此研究对于预测土壤中砷的行为与归趋及污染土壤修复具有一定意义。     

植物砷吸收与代谢的研究进展

砷(As)作为一种植物非必需的类金属元素广泛存在于自然界中,砷过量摄人不仅会对植物生长产生毒害作用,而且在植物的可食部位累积并通过食物链对人体健康构成威胁.生长介质中的砷酸盐(五价砷)一般是通过磷酸盐转运蛋白被植物吸收的,而亚砷酸(三价砷)和没有解离的甲基化砷则主要是通过质膜上的水通道蛋白被植物吸收的.在植物体内五价砷...     

集胞藻(Synechocystis sp. PCC6803)对砷吸收转化特性的初步研究

砷是一种广泛存在于环境中的有毒物质.集胞藻属于单细胞藻类,广泛分布在淡水生态环境中.采用营养液培养的方法探讨了集胞藻(Synechocystis sp.PCC6803)对砷的累积和转化特性.当集胞藻分别暴露于2和100 μM的无机As(Ⅲ)和As(Ⅴ)14 d后,体内的砷形态均以As(Ⅴ)为主,并且在100 μM浓度处...     

无机砷在植物和微生物体内的代谢机制研究进展

砷污染是全球的热点问题之一.土壤中的无机砷在植物中的积累可通过食物链传递,从而对人体健康构成严重威胁.了解微生物和植物对无机砷的代谢机制,对认识和控制土壤中砷的风险至关重要.近年来,微生物对无机砷的代谢机制研究已经比较深入,但是仍有一些问题亟待解决,如信号传导、抗砷基因筛选等.在植物对无机砷的摄取、还原机制等方面也取得了一定进展,但是植物体内砷的转运机制、排出机制等仍有待进一步研究.论文综述了微生物、植物体内无机砷的代谢过程中,砷摄取、转运、还原和排出机制的最新进展,并对今后的研究方向进行了展望.     

链霉菌的抗砷特性及其对蜈蚣草富集砷的作用

本文研究了链霉菌Streptomyces sp.的耐砷特性及其对蜈蚣草富集砷的影响。结果表明,Streptomyces sp.可在100mmo·lL-1的砷酸盐溶液中生长,具有较强的抗砷毒害能力,且在48h内对As(Ⅴ)的还原率达96.5%。施用Streptomyces sp.能促进植物对砷的吸收,蜈蚣草地上部砷浓度为930mg·kg-1,地上部砷累积量达到对照组的2.09倍。加入Streptomyces sp.后,能促进根际土壤中As(Ⅴ)还原成As(Ⅲ),大幅度降低根际土壤残渣态砷含量,从48.15mg·kg-1下降至28.75mg·kg-1。Streptomyces sp.通过影响蜈蚣草根际环境,提高根际土壤pH,增加DOC含量,促使砷形态变化,从而增加砷生物可利用性。该菌可作为强化蜈蚣草修复砷污染土壤的材料。     

锑和砷对固氮菌的毒性效应及其机制研究

锑作为一种具有毒性和致癌性的类金属,其不合理的开发造成了严重的生态环境污染,尤其是土壤中高浓度锑和砷污染导致了环境中多种营养元素的缺乏。其中,氮素的缺乏严重阻碍了环境的恢复。然而,固氮微生物不仅能为氮素匮乏环境提供稳定的氮素来源,而且其固氮潜能可以作为监测土壤金属污染的敏感指标。为此,该文通过乙炔还原法(ARA)微宇宙培养试验手段,研究了不同价态锑和砷(三价及五价)在不同质量浓度(100、200、500、1 000、2 500、5 000 mg·L^-1)水平下对棕色固氮菌固氮潜能的影响,同时进一步探究了土壤固氮菌群落固氮潜能对土壤中主要锑和砷价态[Sb(Ⅴ)和As(Ⅴ)]的响应机制。结果表明,锑和砷浓度与棕色固氮菌和土壤固氮微生物的固氮潜能均呈显著负相关,验证了以固氮微生物固氮潜能作为生物指示物的可行性。此外,Sb(Ⅴ)对土壤固氮微生物的毒性显著小于As(Ⅴ)。三价锑和砷污染对固氮菌固氮潜能的毒性高于五价[As(Ⅲ)>Sb(Ⅲ)>As(Ⅴ)>Sb(Ⅴ)],这可能是由于Sb(Ⅲ)和As(Ⅲ)对细胞的致裂性强于Sb(Ⅴ)和As(Ⅴ)。相较于Sb(Ⅴ)和As(Ⅴ)对于棕色固氮菌固氮潜能的抑制作用,其对土壤固氮菌群落的固氮潜能的影响相对较弱。这一差异可能是由于土壤复杂的理化性质以及微生物群落和功能多样性而导致的。     

铁循环微生物对环境中重金属的影响研究进展

铁循环微生物包括铁氧化菌(Fe(Ⅱ)-oxidizing bacteria,FeOB)和铁还原菌(Fe(Ⅲ)-reducing bacteria,FeRB),在由它们介导Fe²⁺(Fe³⁺)氧化(还原)的过程中,往往也伴随着一系列重金属元素的迁移转化,对重金属在环境中的生物有效性和迁移性方面有重要作用.本文综述了环境中的铁循环微生物,针对铁循环微生物驱动重金属迁移转化的作用机制,分别从铁氧化菌氧化亚铁生成铁矿物对重金属的固定,铁还原菌介导铁矿物还原溶解及次生矿物生成,以及铁循环微生物代谢耦合重金属形态转化方面进行阐述;进一步通过研究实例综述了铁循环微生物对环境中砷、镉、铬、铜、铅等重金属的作用及修复潜力;未来的研究可关注特定微生物的成矿机制,生物成矿对重金属固定的调控,以及重金属复合污染场地的铁循环微生物修复应用等方面.本文以期为基于铁循环微生物的重金属污染修复提供理论指导和应用依据.     

不同暴露条件下克氏原螯虾组织中砷的积累与转化

砷（As）可在水生食物链中积累转化,并通过食物链影响人体健康.克氏原螯虾（Procambarusclarkii）是一种生活在淡水底层的杂食性动物,能够从水和食物中吸收和转化无机砷.本研究探究了砷酸盐As(Ⅴ)在3种不同的暴露条件下（水相、食物相、水相与食物相）,克氏原螯虾不同组织中As(Ⅴ)的生物积累和转化.结果表明,其在水-食物两相体系中的砷积累浓度较高,而且水相暴露体系对总砷积累速率的贡献大于食物相暴露体系.砷在克氏原螯虾不同组织中的积累和转化具有显著的特异性,其富集浓度和积累速率如下：鳃>外壳>肌肉.克氏原螯虾对无机砷的生物转化途径是将部分As(Ⅴ)还原为As（Ⅲ）,部分转化为一甲基砷酸（MMA）、二甲基砷酸（DMA）和砷甜菜碱（AsB）.本文对了解底栖生物链中砷的积累和转化以及小龙虾的食用安全具有重要意义.     

抗氧化系统在蜈蚣草细胞砷解毒机制中的作用

砷超富集植物——蜈蚣草体内可以富集高浓度的砷且不表现出受害症状,暗示蜈蚣草细胞具有较强的砷解毒机制.为探讨抗氧化系统在蜈蚣草砷解毒机制中的作用,测定了0、0.5、1和2mmol/L的砷酸盐[As(Ⅴ)]、亚砷酸盐[As(Ⅲ)]和二甲基胂酸盐(DMA)处理下蜈蚣草愈伤组织的丙二醛(Malonyldiadehyde,MDA)含量、非酶类抗氧化物质含量和酶类抗氧化物质的活性.结果表明,0.5mmol/L As(Ⅴ)和DMA就可以诱导氧化胁迫的产生,浓度越高胁迫程度也越严重.而1mmol/L的As(III)仍未使蜈蚣草愈伤组织产生氧化胁迫.在As(Ⅲ)处理下,酸溶性巯基含量增加,叶绿素和类胡萝卜素含量不变,过氧化氢酶(Catalase,CAT)和过氧化物酶(Peroxidase,POD)活性增加.在As(Ⅴ)处理下,酸溶性巯基含量减少,叶绿素和类胡萝卜素含量略有上升;CAT和POD活性先增加后减少.在DMA处理下,酸溶性巯基含量减少,叶绿素含量降低而类胡萝卜素含量增加,CAT和POD活性先增加后减少.与As(Ⅴ)和DMA相比,As(Ⅲ)处理下高酸溶性巯基含量、高氧化酶活性和低MDA含量暗示As(Ⅲ)对蜈蚣草的毒性可能比As(Ⅴ)和DMA要小.这些结果表明,酸溶性巯基和酶类抗氧化物质(CAT和POD)在蜈蚣草细胞砷解毒机制中发挥着重要作用.图4参22     

The removal of arsenic from water with natural and modified clinoptilolite

The presence of increased arsenic concentrations in Eastern Croatia is a consequence of the geological composition of the soil. Because of its known harmful effects, arsenic removal is of high importance and adsorption represents an attractive and economically efficient approach to arsenic removal. The use of zeolites obtained from the Donje Jesenje deposit, Croatia (CZ) and the Zlatokop deposit in Vranjska Banja, Serbia (SZ) in Na- and Fe–Na-modified forms was investigated in order to effectively remove arsenate and arsenite from aqueous solutions. The adsorption kinetics of arsenic was studied as a function of the initial arsenate and arsenite concentrations (30–300 μg · L^?1), equilibration time (3–48 h), pH (5–10) and in the presence of sulfate and phosphate at initial concentrations of 0.2–0.5 mg · L^?1. In order to estimate sorption constants designating the sorption capacity and affinity of the zeolites samples, the experimental results were fitted to the Langmuir and Freundlich sorption isotherms. Desorption tests conducted with 1–3 mol · L^?1 HCl indicated that arsenate sorption was irreversible. The results obtained indicated that use of the Serbian zeolite in the Fe–Na-modified form (Fe–Na-SZ) was favourable for arsenate removal from water containing up to 30 μg As · L^?1.     

砷酸根在可变电荷土壤颗粒表面的配位吸附

研究了砷在3种可变电荷土壤颗粒表面的吸附对土壤胶体Zeta电位的影响及砷酸根吸附过程中羟基的释放特征.在酸性条件下,土壤胶体吸附砷酸根后土壤表面的负电荷增加,Zeta电位下降.这说明砷酸根在土壤颗粒表面发生了专性吸附,吸附的砷酸根离子进入土壤胶体双电层的紧密层中.亚砷酸根吸附对土壤胶体Zeta电位的影响很小,说明它在土壤颗粒表面主要通过形成外圈型表面络合物而发生非专性吸附.砷酸根在土壤颗粒表面的吸附过程中有羟基释放,说明砷酸根与表面羟基发生了配位交换反应.羟基释放量随砷酸根加入量的增加和pH值的升高而增加.动力学实验结果表明,砷酸根吸附量和羟基释放量随时间具有相似的变化趋势,在开始的20min内,二者均随时间迅速增加,随后变化较小.羟基释放量与砷酸根吸附量的摩尔比也随时间的增加而增加,说明羟基释放反应滞后于砷酸根吸附反应.土壤体系中羟基释放量与砷酸根吸附量的摩尔比小于针铁矿体系,说明除铁铝氧化物外,土壤的其它固相组分也参与了对砷的吸附反应.     

大同盆地富砷地下水的水化学与地球化学研究

为弄清大同盆地地下水中影响砷的迁移、富集的主要地球化学与生物地球化学过程,为区域供水安全提供指导作用,针对高砷地下水系统开展了水文地球化学与含水层沉积物全岩地球化学研究;并在此基础上探讨了研究区高砷地下水成因。结果表明,研究区高砷地下水为偏碱性、强还原环境,砷含量为0.31～452μg·L-1,主要以砷酸盐形式存在,地下水中砷与三价铁的浓度有显著的相关性。高砷含水层沉积物中有机质、铁与砷含量表现出显著相关性。以上结果说明,碱性还原环境有利于地下水中砷的富集;微生物参与下,沉积物相有机质的氧化和Fe氧化物/氢氧化物的还原过程是本区高砷地下水形成的主控因素。     

Biogeochemical cycling of ferric oxyhydroxide affecting As partition in groundwater aquitard

High arsenic (As) concentration in groundwater potentially poses a serious threat to the health of local residents in southwestern Taiwan. Although the As release to groundwater is responsible for the reducing bacteria-mediated reductive dissolution of As-rich Fe hydroxides, the influences of FeRB and different organic substrates on As and Fe mobility and transformation were rarely discussed. An experiment that involved As-adsorbed synthetic amorphous Fe(III) hydroxide (HFO) and the inoculation of in situ Fe-reducing bacteria (FeRB) was performed to evaluate the contribution of FeRB to the As mobility and transformation. The batched experiment of As-free HFO showed that the reducing bacteria rapidly induced the reduction of amorphous Fe oxyhydroxide to Fe(II) by reductive dissolution of HFO and formation of Fe-citrate complexation. For aqueous As(V) reduction experiment, arsenate was effectively reduced to As(III) by the facultative anaerobic bacterium in the cultured FeRB. In the experiment of As-containing HFO reduction, the aqueous As(V) acts as an electron acceptor and reduced to As(III) after the reductive dissolution of Fe(III) on HFO. However, the increase in the As(III) concentrations with time for various organic substrates in the As-adsorbed HFO-reducing experiment differ from the rates of As(V) reduction with various organic substrates in the As(V)-reducing experiment. The decrease in sorption sites by coupled reductive dissolution of HFO and the competitive desorption of small molecular organic carbon is apparently the important factor of As mobility. For large molecular organic carbon (i.e., citrate), the significant contribution of citrate on As mobility is the complexation of iron citrate. A working hypothesis model of As biogeochemical cycling is proposed to illustrate the relevant processes in the groundwater aquitard of southwestern Taiwan.     

The influence of solid matrices on arsenic toxicity to Corophium orientale

In marine ecosystems, benthic organisms are really important because they are the first step in the transfer of contaminants from environment to biota. To this end, this study focused on biological assays with the amphipod Corophium orientale exposed to two different molecules of arsenic: arsenate (As^V), the most abundant form in sediments, and dimethyl-arsinate (DMA), expected to be moderately toxic as an intermediate in the process of detoxification. The toxicity of arsenic compounds was measured after exposure to three different matrices: water, spiked natural sediment and inert spiked quartz sand. LC₅₀ values were calculated for each exposure, and the results confirmed the highest toxicity of As^V, in addition to underlining the importance of matrix of exposure. Water exposure was the matrix which presented the highest toxicity for inorganic arsenic (As^V LC₅₀=3.51 mg L^?1 vs DMA LC₅₀=54.65 mg L^?1), spiked natural sediment demonstrated its capability to chelate arsenate toxicity (As^V LC₅₀=34.27 mg kg^?1 vs. DMA LC₅₀=52.19 mg kg^?1) and spiked quartz sand presented intermediate values for As^V (LC₅₀=25.26 mg kg^?1), whereas for DMA a lower toxicity was registered (LC₅₀=872.35 mg kg^?1). This study can provide some useful data linked with chemical speciation of arsenic and exposure matrix, for improving the correct management of contaminated sediment.     

Species-level study on arsenic availability from dietary components

Arsenic (As) contaminated water and foodstuffs are of major concern. Samples of drinking–cooking water (n = 50), raw rice (n = 50), common vegetables (eight types), and common pulses (three types) were collected from households in the endemic region. The study found up to 70% As reduction by using safe water for cooking of rice and vegetables. Speciation study reflected more arsenate than arsenite and other organic arsenicals in all the types of samples. Male intake of 293 μg As through drinking water contained 38 μg arsenite and 246 μg arsenate, and female intake of 199 μg As contained 167 μg arsenate and 25 μg arsenite. In cooked rice, 108 μg As contained 69 μg arsenate and 17 μg arsenite with 9 μg dimethylarsonic acid (DMA). Total As consumption from cooked vegetables was 45 μg with 34 and 4 μg of arsenite and arsenate, respectively, and 5 μg of DMA. Data indicate that cooking with As-free water removes arsenic in already contaminated foodstuffs but without interconversion of the As species, from toxic inorganic to less toxic organic forms.