IMHE OpenIR  > 山地表生过程与生态调控重点实验室
可溶性有机质与汞的络合及氧化/还原作用机制
Alternative TitleMercury oxidation-reduction and Complexation with Dissolved Organic Matter
卞永荣
Subtype博士
Thesis Advisor朱波
2018
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline土壤学
Keyword 甲基汞 可溶性有机质 水稻 有机肥
Abstract汞(Hg)是毒性最强的重金属元素之一,以多种形态赋存,其中易于在厌氧环境中转化产生的甲基汞毒性最强。水稻作为我国南方地区主要的粮食作物,其长期淹水的缺氧环境为厌氧菌的汞甲基化提供了条件。由于稻米对甲基汞具有富集特性,食用受甲基汞污染稻米是当地居民甲基汞的主要暴露途径。有机肥在水稻生产过程中大量施用导致可溶性有机质(Dissolved Organic Matter, DOM)在稻田系统中广泛存在,而DOM对环境中汞的形态分布、生物有效性至关重要,并影响甲基汞的形成。因此,探究稻田土壤中DOM对汞转化的影响机制,探讨农艺措施特别是施用有机肥与矿物-有机复合肥对水稻籽粒中甲基汞累积效应的影响与机理,对保障人体健康具有重要的理论与实际意义。本文采用室内批处理实验,模拟稻田厌氧环境,研究了厌氧与有氧条件下DOM对Hg(II)的还原反应与速率,分析影响Hg(II)还原的因素;研究了厌氧与有氧条件下DOM对Hg(0)诱导氧化络合作用及反应速率,推断其反应机制;采用温室盆栽实验,研究了干湿交替和厌氧腐熟有机肥对水稻土中汞的形态转化及水稻不同部位汞/甲基汞累积的影响;分析了海泡石和厌氧腐熟矿物-有机复合肥对水稻土中汞的形态转化及降低水稻不同部位汞/甲基汞累积效应。主要研究结果与结论如下:1. DOM对Hg(II)的还原反应结果表明:(1)还原态DOM(还原态胡敏酸和还原态富里酸)的还原容量高于氧化态DOM。还原态胡敏酸和富里酸对Hg(II)还原的最佳浓度分别是0.2 mg L-1和1.5 mg L-1。低于最佳浓度时,Hg(II)还原量均随还原态DOM浓度的增加而增加;而高于最佳浓度时,由于发生巯基竞争性络合作用,Hg(II)还原量均随还原态DOM浓度的增加而减少,胡敏酸浓度在5 mg L-1时不能将Hg(II)还原成Hg(0)。可见,还原态胡敏酸和富里酸对Hg(II)还原和络合过程中扮演双重角色。(2)还原态DOM对Hg(II)的还原反应动力学表明:可溶性有机碳(DOC),低摩尔比(DOC:Hg(II)= 400:1)时,还原反应速率胡敏酸大于富里酸;高摩尔比(DOC:Hg(II) = 10000:1)时,胡敏酸对Hg(II)的还原反应停止,甚至向相反方向进行。2. 还原态DOM与Hg(0)的相互作用研究表明:腐殖酸浓度增加时,Hg(0)含量减少;当胡敏酸和富里酸浓度分别增加至5 mg L-1和10 mg L-1时,样品中未检测到Hg(0)。回收率实验表明,还原态DOM与Hg(0)发生诱导氧化络合反应。氧化态DOM对Hg(0)氧化作用相对较弱,含量达到40 mg L-1时,仅消耗20% Hg(0)。还原态胡敏酸和Hg(0)的反应动力学符合假一级动力学,反应速率胡敏酸大于富里酸。在pH = 7.0和3.5时,胡敏酸与Hg(0)的反应容量分别是3.5 μmol g-1和1.6 μmol g-1。还原态胡敏酸和Hg(0)相互作用,发生巯基或双硫键诱导性氧化络合作用,其对稻田汞的形态转化、氧化还原过程及生物可利用性具有重要意义。3. 干湿交替和有机肥对水稻土中汞形态转化及水稻中汞/甲基汞累积影响的研究表明:(1)干湿交替(AWD)和1%豆饼粉有机肥(BOM1)增加了汞的土/气交换,1%鱼粉肥(FOM1)、2%豆饼粉肥(BOM2)和2%鱼粉肥(FOM2)减弱汞的土/气交换,水稻土总汞损失为:AWD (43%) > BOM1 (41%) > Control (38%) > FOM1 (33%) > BOM2 (26%) > FOM2 (25%);有机肥施用导致水稻土的甲基汞含量显著增加,各处理的土壤甲基汞为:AWD(7.41 μg kg-1) < Control(10.43 μg kg-1) < BOM1(16.80 μg kg-1) < FOM1(24.10 μg kg-1) < BOM2(33.53 μg kg-1) < FOM2(38.46 μg kg-1);施用鱼粉有机肥的水稻土甲基汞含量显著高于施用豆饼肥的水稻土,可能因鱼粉有机肥含硫量高,促进水稻土的硫还原菌生长,增加水稻土中汞甲基化所致;同时,施用有机肥增加了水稻土的甲基汞/汞比例。(2)有机肥施用后,水稻不同部位总汞累积差异显著,根部最高(2812.83 μg kg-1),其次是糙米(336.78 μg kg-1)和茎叶(300.44 μg kg-1)。施用豆饼粉肥(1%、2%)与鱼粉肥(1%、2%)对水稻籽粒富集总汞差异不显著。施用有机肥后,水稻不同部位累积甲基汞的能力不同,表现为籽粒(180.06 μg kg-1) >根(59.71 μg kg-1) >茎叶(38.97 μg kg-1)。不同类型有机肥施用均增加籽粒中甲基汞含量,与对照相比分别增加BOM1 (16.1%) < FOM1 (19.3%) < BOM2 (41.5%) < FOM2 (57.9%),鱼粉有机肥增加幅度大于豆饼粉肥,可能鱼粉肥中含有较多巯基化合物,腐熟后形成大量巯基小分子氨基酸,同时巯基丙氨酸是植物体内蛋白的基本组成,其与甲基汞结合将甲基汞转运到稻米中,同时稻米中甲基汞浓度与水稻土中甲基汞含量呈正相关。4. 海泡石和矿物-有机复合肥(海泡石与有机肥堆制而成)施用对水稻土汞赋存形态与水稻汞/甲基汞累积及其分配的对比研究表明:(1)矿物和矿物-有机复合肥减少水稻土中汞的土/气交换,总汞浓度最高是2%鱼粉矿物-有机复合肥,其次是1%鱼粉矿物-有机复合肥、2%豆饼粉矿物-有机复合肥、1%豆饼粉矿物-有机复合肥和海泡石,与仅施用有机肥相比,矿物-有机肥增加水稻土中总汞持留5~10%,降低水稻土甲基汞含量5%~25%,其中,鱼粉矿物-有机复合肥降幅最大,可能矿物与巯基化合物结合降低甲基汞迁移性。(2)矿物-有机复合肥施用,水稻不同部位总汞浓度为:根(1473.67 μg kg-1) >籽粒(282.33 μg kg-1) >茎叶(217.83 μg kg-1),与仅施用有机肥对比,根部总汞浓度显著降低50%。此外,水稻不同部位甲基汞含量为:糙米(114.79 μg kg-1) >根(34.83 μg kg-1) >茎叶(18.17 μg kg-1),说明矿物-有机肥显著降低了水稻对甲基汞的富集,矿物-有机鱼粉肥对糙米中甲基汞浓度降低最明显,比对照降低50%,与仅添加有机肥相比,2%鱼粉矿物-有机复合肥效果最好,籽粒中甲基汞浓度降幅达65%;糙米中甲基汞浓度与土壤中甲基汞浓度呈现负相关关系,这可能由于施用矿物-有机复合肥后,降低了水稻土中甲基汞迁移性,进而减少稻米对甲基汞的富集。
Other AbstractMercury (Hg), as one of the most toxic heavy metals, exists in various species in the environment. Methylmercury (CH3Hg+), which is easily converted in anaerobic environment, is the most toxic. Rice (Oryza sativa L.) is the major cereal crop in southern China, and rice fields, usually long-term flooded during most of growing seasons, have provided continuously anoxic conditions for the anaerobes to produce CH3Hg+ . Moreover, due to the bioaccumulation ability of rice to methylmercury, the rice grains, which are in high contents of CH3Hg+, are the main exposure pathway of CH3Hg+ for local residents. The application of the organic fertilizers in the process of rice production has increased the content of dissolved organic matter (DOM) in paddy field system. The species distribution, the bioavailability of Hg and the transformation process to CH3Hg+ were all significantly influenced by DOM. Hence, it has important theory and practical significance for the protection of human health to explore the mechanism of DOM on the transformation of mercury in paddy soil, and investigate the effects and the mechanisms of agrotechnology, especially the application of the organic fertilizers and mineral organic fertilizers, on the accumulation of CH3Hg+ in rice grains.In this study, indoor batch experiments were performed with the simulation of anaerobic environment in paddy field to study the reduction and reaction rates of Hg(II) by anaerobic and aerobic DOM, and explore the affects factors. Moreover, the induced oxidative complexation and reaction rate of Hg(0) by DOM under anaerobic and aerobic conditions was explored and elucidate the detailed mechanisms. Greenhouse pot experiment was conducted to study the effects of alternating wet and dry conditions and anaerobic organic fertilizer application on the transformation of Hg in paddy soil and the accumulation of Hg and CH3Hg+ in various organs of rice, and the effects of sepiolite and anaerobic decomposed organic mineral fertilizers application on the transformation of Hg in paddy soil and the reducing of Hg/CH3Hg+ accumulation in diverse organs of rice. The main conclusions of our study are listed as follows:1. The results of the reduction of Hg(II) by DOM: (1) Compared to oxidized DOM, the reduction capacity of the reduced DOM (reduced humic acid and fulvic acid) for Hg(II) were higher. The optimal concentrations of the reduced humic acids and fulvic acids to reduce Hg(II) into Hg(0) were 0.2 mg L-1 and 1.5 mg L-1, respectively. The reduction quantity of Hg(II) was enhanced with the increased concentration of the reduced DOM at a lower concentration than optimal concentration, while the reduction quantity of Hg(II) was decreased with the increasing concentration of the reduced DOM at a higher concentration than optimal concentration due to the occurrence of thiol-competitive complexation. There was no the reduction of Hg(II) occurred at the concentration of humic acid at 5 mg L-1. Therefore, reduced humic acid and fulvic acid played dual roles on the reduction process of Hg(II). (2) The kinetics results of the reduction of Hg(II) by reduced DOM demonstrated that the reduction rates of humic acid were higher than fulvic acid at low molar ratio (DOC: Hg(II) = 400:1). And, the reduction of Hg(II) by the reduced humic acid would stopped, or even processed in the opposite direction, at the condition of high molar ratio (DOC: Hg(II) = 10000:1). 2. The results of the interaction between reduced DOM and Hg(0) indicated that: the quantities of Hg(0) has been decreased with the increasing humic acid concentration. And, as the concentration of humic acid and fulvic acid were increased to 5 mg L-1 and 10 mg L-1, respectively, there were no detectable Hg(0) in the samples. The experiment of the recovery confirmed that reduced DOM can react with Hg(0). For the oxidized DOM, up to 40 mg L-1, only 20% of Hg(0) were consumed. The reaction process between reduced humic acid and Hg(0) could be fitted by the pseudo first-order kinetic equation successfully. And, the reaction rate of humic acid was higher than fulvic acid. At pH = 7.0 and 3.5, the reaction capacities between humic acid and Hg(0) were 3.5 μmol g-1 and 1.6 μmol g-1, respectively. Additionally, reduced humic acid and Hg(0) could lead to induce oxidative complexation with sulfhydryl or disulfide bonds, which is important to the forms transformation, redox process and bioavailability of mercury in rice fields. 3. The effects of alternating wet-dry conditions and organic fertilizers application on Hg forms transformation and the accumulation of Hg and CH3Hg+ in various organs of rice indicated that: (1) alternation of wetting and drying (AWD) and 1% bean organic fertilizer (BOM1) application enhanced the Hg air/soil exchange; on the contrary, the application of 1% fishmeal organic fertilizer (FOM1), 2% bean organic fertilizer (BOM2) and 2% fishmeal organic fertilizer (FOM2) reduced the Hg air/soil exchange. The total Hg loss was ordered by : AWD(43%) > BOM1(41%) > Control (38%) > FOM1(33%) > BOM2(26%) > FOM2 (25%) in paddy soil. In addition, a significant increase in CH3Hg+ content was observed as : AWD(7.41 μg kg-1) < Control(10.43 μg kg-1) < BOM1(16.80 μg kg-1) < FOM1(24.10 μg kg-1) < BOM2(33.53 μg kg-1) < FOM2(38.46 μg kg-1) in paddy soil. Compared to the bean organic fertilizer, the application of fishmeal organic fertilizer has result in significantly higher CH3Hg+ content in paddy soils. It is might because of the high sulfur content of fishmeal organic fertilizer, which promoting the growth of sulphur reducing bacteria and increasing Hg methylation in paddy soil. In addition, the application of organic fertilizer increased the ratio of CH3Hg+ to Hg in paddy soil. (2) After organic fertilizer application, the total Hg accumulation in various organs of rice was rather different, with the highest content observed in root (2812.83 μg kg-1), followed by brown rice(336.78 μg kg-1) and stem (300.44 μg kg-1). Application of bean organic fertilizer (1%, 2%) and fishmeal organic fertilizer (1%, 2%) had no significant difference in total Hg concentration in rice grains. After the application of organic fertilizer, the ability to accumulate CH3Hg+ in different organs of rice was different and the results was showed as grain (180.06 μg kg-1) > root (59.71 μg kg-1) > stem and leaf (38.97 μg kg-1). Additionally, the application of different organic fertilizers increased the content of CH3Hg+ in rice grains, compared with the control treatment, which was listed as: BOM1 (16.1%) < FOM1(19.3%) < BOM2(41.5%) < FOM2(57.9%). The increasing extent of fishmeal organic fertilizer is larger than that of bean organic fertilizer, which was partly owing to the higher content of sulfydryl compounds in fishmeal organic fertilizers. After being decomposed, a large amount of sulfhydryl small molecule acid is formed in fishmeal organic fertilizers. Meanwhile, the sulfhydryl alanine is the basic composition of protein in plants, and it will be combined with CH3Hg+. The combined component would transport CH3Hg+ to the rice grains, and lead to the positively correlated with of CH3Hg+ concentration in rice grains and the initial CH3Hg+ content in paddy soil thereafter.4. The effects of the application of the sepiolite and mineral organic fertilizer, obtained from the compost of the sepiolite and mineral organic fertilizer together, on the form transformation of Hg in paddy soil and the Hg/CH3Hg+ accumulation in the different organs of rice showed: (1) With the addition of mineral and mineral organic fertilizers, the Hg soil/air exchange in paddy soil was decreased, the highest total Hg concentration treatment was the application of 2% fishmeal mineral organic fertilizers, followed by 1% fishmeal mineral organic fertilizers, 2% bean mineral organic fertilizers, 1% bean mineral organic fertilizers and sepiolite. Compared with only addition of organic fertilization, the mineral organic fertilizers increased the total Hg concentration in paddy soil (5%~10%), and decreased the CH3Hg+ concentration in paddy soil (5%~25%), especially under the fishmeal organic mineral fertilizers treatment. It is might because of the limits of CH3Hg+ transfer, which result from the combination of mineral and sulfhydryl compound. (2) Under the application of organic mineral fertilizers, the total Hg concentration in different organs of rice was: root (1473.67 μg kg-1) > grain (282.33 μg kg-1) > stem and leaf (217.83 μg kg-1). Compared with the only application of organic fertilization, total Hg was significantly reduced (50%) in root. In addition, the CH3Hg+ concentration in different organs of rice was: brown rice (114.79 μg kg-1) > root (34.83 μg kg-1) > leaf (18.17 μg kg-1), which indicated the significantly decrease of the accumulation of CH3Hg+ in rice with the addition of organic mineral fertilizers. The mineral fishmeal organic fertilizer performed best in decreasing the concentration of CH3Hg+ in brown rice, which was decreased by 50% than that of the control treatment. Compared with the treatment of only addition of organic fertilizer, the 2% fishmeal mineral fertilizer treatment decreased the CH3Hg+ content in rice grains by about 65%. The concentration of CH3Hg+ in brown rice is negatively correlated with the initial content of CH3Hg+ in soil. Organic mineral fertilizer may be applied to reduce the migration of CH3Hg+ in paddy soil and thus reducing the enrichment of CH3Hg+ in rice. 
Pages101
Language中文
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/24771
Collection山地表生过程与生态调控重点实验室
Affiliation中国科学院成都山地灾害与环境研究所
First Author Affilication中国科学院水利部成都山地灾害与环境研究所
Recommended Citation
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卞永荣. 可溶性有机质与汞的络合及氧化/还原作用机制[D]. 北京. 中国科学院大学,2018.
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