本期文章导读

正01水生生态系统中汞-硒相互作用研究进展作者:南雪娇,余晓平,郭金玲,郭亚飞,邓天龙*导读撰文:本刊编辑部汞极易在水生生物体内富集并发生甲基化,严重危害食物链顶端消费者健康。汞与硒相互作用的研究在过去半个世纪以来一直是汞(硒)环境化学和毒理学及相关学科研究的重要领域之一。近年来,国内外研究表明水体、沉积物和水生生物系统中汞硒比≤1时,可明显     

厌氧和有氧氛围切割沉积物样品中对甲基汞测定的影响

甲基汞是在自然界中广泛存在的毒性最强的汞化合物之一.在汞的生物地球化学循环中,由于甲基汞具有生物积累和生物放大的特点而特别受到关注.无机汞可以在生物和非生物甲基化作用下转化为甲基汞,导致毒性增强和对生物的危害加重.汞的甲基化作用受许多因素的影响,例如pH,温度,DOC,细菌活性等.汞甲基化作用主要发生在沉积物的表层,且由于该处微生物活性最强,汞甲基化速率最快.沉积物是水体甲基汞的一个源.     

稻田生态系统汞的形态转化及同位素分馏北大核心CSCD

水稻是甲基汞的超富集农作物,汞污染区稻米普遍含有较高含量的甲基汞。食用大米是我国南方内陆居民人体甲基汞暴露的主要途径。水稻甲基汞污染问题已经引起了国际社会的高度关注。国内外学者围绕稻田生态系统汞的生物地球化学循环开展了大量的研究工作,取得了一系列重要研究成果。本文总结了稻田土壤汞的关键形态转化过程研究现状及存在问题,对未来需要进一步开展的研究工作进行了展望,包括:稻田土壤中汞的甲基化过程、影响因素及参与汞甲基化的主要微生物群落;典型汞矿区稻田土壤中汞的形态分布特征与参与甲基化反应的主要汞形态的识别;稻田土壤中汞的还原过程及对甲基化的影响;稻田生态系统汞的同位素分馏特征及汞的生物地球化学过程定量识别。     

稻田生态系统汞的形态转化及同位素分馏

水稻是甲基汞的超富集农作物,汞污染区稻米普遍含有较高含量的甲基汞。食用大米是我国南方内陆居民人体甲基汞暴露的主要途径。水稻甲基汞污染问题已经引起了国际社会的高度关注。国内外学者围绕稻田生态系统汞的生物地球化学循环开展了大量的研究工作,取得了一系列重要研究成果。本文总结了稻田土壤汞的关键形态转化过程研究现状及存在问题,对未来需要进一步开展的研究工作进行了展望,包括:稻田土壤中汞的甲基化过程、影响因素及参与汞甲基化的主要微生物群落;典型汞矿区稻田土壤中汞的形态分布特征与参与甲基化反应的主要汞形态的识别;稻田土壤中汞的还原过程及对甲基化的影响;稻田生态系统汞的同位素分馏特征及汞的生物地球化学过程定量识别。     

湿地条件下无机汞—有机汞相互转化研究进展

汞（Hg）作为一种有毒重金属污染物，在全球范围内受到广泛关注。有机汞尤其是甲基汞的毒性比无机汞毒性更大，且易在食物链中积累，因此无机汞—有机汞的转化问题近年来备受关注。之前的研究多集中于海洋环境中的Hg甲基化问题，对于淡水环境尤其是湿地环境Hg甲基化的研究相对欠缺。而湿地环境的特殊性与复杂性使其成为突出的甲基汞产出单元，且生物积累作用明显。通过系统总结湿地中无机汞—有机汞转化的途径和机理以及其影响因素和相关生物作用，指出沉积物、颗粒有机碳和周丛生物是重要的甲基汞产生微环境，频繁密切的生物间相互作用成为湿地高甲基化潜力的保障。因此加强各类湿地Hg甲基化研究对保护湿地生态及居民健康具有重要意义。     

植物中汞的研究进展

植物生态系统中汞的环境过程是生物地球化学循环过程的重要组成部分，且与整个生态系统中各物种的生存和发展密切相关。本文介绍了植物中汞生物地球化学循环的进展，包括汞对植物的生物毒性、植物中汞的来源、分布与迁移转化、植物大气间汞的交换过程及其研究方法，以及植被在生态系统间汞循环中的重要作用，最后简要介绍今后的研究重点和热点。     

汞的环境地球化学研究进展

介绍了目前环境样品中总汞及其各形态汞的分析方法以及大气和水生生态系统中 研究进展，并指出，燃煤，汞齐法采金和人造水库等引起的环境汞污染问题以及汞在热带地区水生生态系统中的迁移转化规律等是目前的研究热点。     

持久性卤代有机污染物(PHCs)在食物网中的生物放大研究进展北大核心CSCD

持久性卤代有机污染物(PHCs)具有持久性、生物富集性和毒性,是对生态环境和人类健康有严重威胁的污染物。PHCs浓度会沿食物链在生物中逐营养级放大,对高等生物及人体产生毒性。本文综述了PHCs在食物网中生物放大的特征,总结了国内外对食物网中PHCs的营养级放大因子研究进展,探讨了生态和化学因素对PHCs沿食物链传递过程的影响。目前的研究多集中于水生生态系统中传统PHCs的生物放大,对PHCs的生物差异性代谢缺乏足够的了解,难以说明不同生态系统中复杂的气候、地理、生物种群特征对PHCs生物放大的影响,也给准确评估PHCs的生态风险带来了困难。PHCs的生物放大研究需要引入更多先进地球化学手段和准确构建不同生态系统的野生食物网,阐明PHCs的生物放大机制和影响因素。     

湿地汞环境过程研究进展

汞在湿地生态系统中的环境过程是汞全球循环的组成部分,并与人类的健康有着密切关系。分析了湿地环境过程研究的重要意义,综述了国内外湿地汞环境过程研究的进展情况,包括在湿地汞来源、含量、赋存形态,迁移、转化、界面反应等方面。指出由于湿地独特的水文过程和环境条件,汞的累积、迁移与转化过程具有与其它生态系统不同的特点。湿地能吸收大气沉降和地表径流的汞,是汞的汇。汞在湿地生态系统中呈富集状态。湿地具有较高的汞累积速率和甲基汞生产能力,湿地的氧化-还原条件和丰富的有机碳有利于汞的甲基化。湿地甲基汞通过食物链的"生物放大",威胁人类的健康。全球气候变暖、酸雨和臭氧层耗竭可能增加湿地汞的生态环境风险。提出应开展湿地特定环境条件下汞的循环及其在汞全球循环中作用的研究,并关注湿地对全球环境变化的响应。     

持久性卤代有机污染物(PHCs)在食物网中的生物放大研究进展

持久性卤代有机污染物(PHCs)具有持久性、生物富集性和毒性,是对生态环境和人类健康有严重威胁的污染物。PHCs浓度会沿食物链在生物中逐营养级放大,对高等生物及人体产生毒性。本文综述了PHCs在食物网中生物放大的特征,总结了国内外对食物网中PHCs的营养级放大因子研究进展,探讨了生态和化学因素对PHCs沿食物链传递过程的影响。目前的研究多集中于水生生态系统中传统PHCs的生物放大,对PHCs的生物差异性代谢缺乏足够的了解,难以说明不同生态系统中复杂的气候、地理、生物种群特征对PHCs生物放大的影响,也给准确评估PHCs的生态风险带来了困难。PHCs的生物放大研究需要引入更多先进地球化学手段和准确构建不同生态系统的野生食物网,阐明PHCs的生物放大机制和影响因素。     

唐山开滦煤矿区Se、Hg元素地球化学特征及其迁移循环规律研究

唐山开滦煤矿已有百余年的开采史。河北平原多目标区域地球化学调查在矿区内发现了以Se、Hg元素为主的多种微量元素土壤地球化学异常。本文利用地球化学方法,研究Se、Hg元素地球化学空间分布特征、赋存状态及其在表生环境中的迁移循环规律。结果表明,Se、Hg元素含量在大气降尘中高度富集,土壤异常区与煤田分布范围几乎一致。Se、Hg元素主要通过大气降尘及地表水系途径在煤-大气-土壤-水系体系内迁移,迁移过程中其赋存状态发生了改变,活化趋势明显。迁移范围遍及矿区外围1 200 km²区域及流经矿区的整个水系覆盖区域。     

环境中硒形态分析方法的研究进展

硒的形态研究是了解环境中硒的毒性、生物可利用性、迁移和生物地球化学循环等方面的基础,其研究方法一般分为直接和间接法。本文总结了环境中硒形态的研究方法,特别是对环境样品中常用的硒形态分析技术——连续化学浸提技术作了全面详细的讨论,并综述了其它硒形态分析方法的最新动态。     

The distribution, speciation and geochemical cycling of selenium in a sedimentary environment, Kesterson Reservoir, California, U.S.A.

The well-defined and intensively studied episode of Se contamination at Kesterson Reservoir (Merced County, California, U.S.A.) provided a unique opportunity to describe the distribution, speciation and geochemical transformations of Se in a variety of geochemical and ecological settings, ranging from permanent ponds to semi-arid grasslands and salt flats. Kesterson Reservoir comprises 500 ha of land contaminated with Se from agricultural drain water. In most places. Se was concentrated in surficial organic detritus and the surficial decimeter of mineral soil. At dry sites, selenate ion predominated below 20 cm depth. Elemental selenium (Se⁰) also was prominent. The amount of zero-valent Se increased slowly with time. Although selenate is thermodynamically stable in the vadose zone in the presence of oxygen, Se⁰ is an additional, metastable product of the mineralization of organic selenium. Thiols and inorganic sulfides dramatically increase the solubility of Se⁰. Decreasing pH inhibits the reaction, explaining the observed decrease in solubility and biological availability of Se in soil and aquatic systems at low pH. Adding thiols or methionine to soil increases the emission of volatile Se compounds several-fold, suggesting that thiols play a major role in the microbial cycling of Se in soil.     

Selenium speciation,distribution, and transport in a river catchment affected by mercury mining and smelting in Wanshan,China

Selenium (Se) is an important co-existing elemental component of the mineral matrix of mercury (Hg) ore deposits. The hazards associated with Se contamination of the aquatic ecosystems in Hg mining areas; however, are often overlooked by environmental researchers due to a preoccupation with Hg. Selenium may also pose a long-term risk to the local ecosystem, and further complicate the situation as Se may also play an important antagonistic role against Hg. Furthermore, most studies on Se pollution have focused only on total Se, whereas the toxicity, bioavailability, and bioaccumulation of Se in aquatic ecosystems is primarily determined by its site-specific individual species. In this study, the concentrations of total Se, inorganic Se (tetravalent and hexavalent), and organic Se were determined in water samples collected from 41 typical sites selected in rivers, tributaries, and springs in Wanshan, China, where Hg and Se co-occur due to historic Hg mining and retorting activities. Se concentrations were observed to decrease with distance from mine-waste calcines, which indicated that mine-waste calcines may be significant sources of the elevated Se in the rivers, especially in downstream areas within 8 km from the mine-waste calcines. The concentration of total aqueous Se throughout the study area was highly variable (3.8 ± 6.0 μg L⁻¹) and on average was one order of magnitude greater than that in natural river systems worldwide (0.1–0.3 μg L⁻¹). The majority of the Se was hexavalent (3.1 ± 4.9 μg L⁻¹; 65%), followed by tetravalent (0.53 ± 0.86 μg L⁻¹; 15%) and organic forms (0.85 ± 1.5 μg L⁻¹; 20%), possibly due to the generally alkaline conditions. Se concentrations in some sampling sites exceeded certain recommended limit of values. However, the existing criteria for Se in aquatic system are mainly based on total Se and the recommended limit of values in different countries or organizations are inconsistent with one another. Therefore, the need to consider Se speciation rather than only total Se is highlighted for future studies.     

Mercury methylation dynamics in estuarine and coastal marine environments — A critical review

Considerable recent research has focused on methylmercury (MeHg) cycling within estuarine and coastal marine environments. Because MeHg represents a potent neurotoxin that may magnify in marine foodwebs, it is important to understand the mechanisms and environmental variables that drive or constrain methylation dynamics in these environments. This critical review article explores the mechanisms hypothesized to influence aqueous phase and sediment solid phase MeHg concentrations and depth-specific inorganic Hg (II) (Hg_i) methylation rates (MMR) within estuarine and coastal marine environments, and discusses issues of terminology or methodology that complicate mechanism-oriented interpretation of field and laboratory data. Mechanisms discussed in this review article include: 1) the metabolic activity of sulfate reducing bacteria (SRB), the microbial group thought to dominate mercury methylation in these environments; 2) the role that Hg_i concentration and/or speciation play in defining depth-specific Hg_i methylation rates; and 3) the depth-dependent balance between MeHg production and consumption within the sedimentary environment. As discussed in this critical review article, the hypothesis of SRB community control on the Hg_i methylation rate in estuarine and coastal marine environments is broadly supported by the literature. Although Hg_i speciation, as a function of porewater inorganic sulfide and/or dissolved organic matter concentration and/or pH, may also play a role in observed variations in MMR, the nature and function of the controlling ligand(s) has not yet been adequately defined. Furthermore, although it is generally recognized that the processes responsible for MeHg production and consumption overlap spatially and/or kinetically in the sedimentary environment, and likely dictate the extent to which MeHg accumulates in the aqueous and/or sediment solid phase, this conceptual interpretation requires refinement, and would benefit greatly from the application of kinetic modeling.     

氢化物发生-原子荧光光谱法测定植物样品中汞硒砷

植物样品经硝酸-高氯酸一次湿法消解后,用氢化物发生-原子荧光光谱法同时测定汞、硒、砷。测定时加入消泡剂磷酸三丁酯,可有效消除泡沫,降低记忆效应,提高精密度。方法精密度(RSD,n=12)为汞2.96%,硒0.96%,砷2.49%。经加标回收试验和国家一级标准物质验证,测定结果与标准值吻合。     

云南腾冲热海高温地热水中汞的地球化学异常及其指示意义

汞是环境中典型有害组分,深部地热系统可能是环境中汞的重要来源之一,但当前地热成因汞的研究程度很低。本文以腾冲火山带热海水热区为研究区,开展了热泉中汞的水文地球化学研究。热海水热区内排泄的中性热泉含有异常高浓度的汞,但酸性热泉则绝大多数未检出汞。热海热泉中的汞与典型的岩浆来源组分氯相同,均主要来源于岩浆流体的混合。在中性热泉中,Hg(II)是汞的占优势地位的价态,Hg²⁺与不同形态硫化物的配合则是决定Hg(II)的形态分布的直接因素,但pH可通过控制水中硫化物的形态分布来影响Hg(II)的形态分布。Hg(II)不易挥发,故中性热泉中汞含量普遍较高;但酸性热泉中的汞受泉口氧化还原电位较高的影响,以Hg(0)为主要价态,且因Hg(0)易挥发而导致总汞含量极低。就中性热泉而言,其汞含量对水热区断裂分布有重要指示作用,原因为沿不同断裂上升的中性地热水经历的冷却方式不同,最终导致热泉汞含量也表现出显著差异。热泉汞含量对水热系统结构研究有借鉴意义。     

Speciation and weathering of selenium in upper cretaceous chalk and shale from South Dakota and Wyoming, USA

In geologic materials, petroleum, and the environment, selenium occurs in various oxidation states (VI, IV, 0, -II), mineralized forms, and organo-Se complexes. Each of these forms is characterized by specific chemical and biochemical properties that control the element’s solubility, toxicity, and environmental behavior. The organic rich chalks and shales of the Upper Cretaceous Niobrara Formation and the Pierre Shale in South Dakota and Wyoming are bentoniferous stratigraphic intervals characterized by anomalously high concentrations of naturally occurring Se. Numerous environmental problems have been associated with Se derived from these geological units, including the development of seleniferous soils and vegetation that are toxic to livestock and the contamination of drinking water supplies by Se mobilized in groundwater.This study describes a sequential extraction protocol followed by speciation treatments and quantitative analysis by Hydride Generation-Atomic Absorption Spectroscopy. This protocol was utilized to investigate the geochemical forms and the oxidation states in which Se occurs in these geologic units. Organic Se and di-selenide minerals are the predominant forms of Se present in the chalks, shales, and bentonites, but distinctive variations in these forms were observed between different sample types. Chalks contain significantly greater proportions of Se in the form of di-selenide minerals (including Se associated with pyrite) than the shales where base-soluble, humic, organo-Se complexes are more prevalent. A comparison between unweathered samples collected from lithologic drill cores and weathered samples collected from outcrop suggest that the humic, organic-Se compounds in shale are formed during oxidative weathering and that Se oxidized by weathering is more likely to be retained by shale than by chalk. Selenium enrichment in bentonites is inferred to result from secondary processes including the adsorption of Se mobilized by groundwater from surrounding organic rich sediments to clay mineral and iron hydroxide surfaces, as well as microbial reduction of Se within the bentonitic intervals. Distinct differences are inferred for the biogeochemical pathways that affected sedimentary Se sequestration during periods of chalk accumulation compared to shale deposition in the Cretaceous seaway. Mineralogy of sediment and the nature of the organic matter associated with each of these rock types have important implications for the environmental chemistry and release of Se to the environment during weathering.     

Interactions of mercury with different molecular weight fractions of humic substances in aquatic systems

Interactions of mercury (Hg) with different molecular weight fractions of humic substances (HS) play an important role in controlling distribution, diffusion, speciation, and bioavailability of Hg in natural systems. This study suggests that Hg prefers to associate with higher molecular weight fractions of HS and this association particularly predominates at low pH and high ionic strengths of the medium. The concentrations of aggregated HS (with higher molecular weight) become high at lower pH (acidic condition) and high ionic strength. Molecular weight of HS gradually decreases with the increasing pH (basic condition) and low ionic strength of the medium. The disaggregation property of HS which involves the release of monomers from the surface of the aggregates produces HSs of different intermediate molecular weight with different Hg complexing capacity. Distribution of Hg in different molecular weight fractions of HS is dependent on aggregational and disaggregational properties of HS in aquatic medium. Association of Hg with high molecular weight fraction of HS may alter distribution and bioavailability of Hg in a system as the bioreactivity of organic matter decrease along a continuum of size in aquatic medium.