| 题名 | 区域环境中汞的污染特征及迁移转化过程研究 |
| 作者 | 孟梅 |
| 学位类别 | 博士 |
| 答辩日期 | 2015 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 江桂斌 |
| 关键词 | 汞 Mercury 污染特征 contamination characteristic 迁移转化 translocation and transformation 汞同位素 mercury isotope 质量分馏 mass-dependant fractionation 非质量分馏 mass-independent fractionation |
| 其他题名 | Contamination characteristics and environmental processes of mercury in Chinese typical regions |
| 中文摘要 | 我国是世界汞排放量最大的国家，而如此大量排放的汞在环境中的迁移转化过程尚不十分明确，因此，研究环境中汞的来源、生物地球化学过程以及归宿，具有重要的科学和实际意义。目前，水产品摄入和稻米食用已成为我国居民人体甲基汞暴露的重要途径，研究汞在水生食物链及水稻植株中的累积机制和途径，对于防治食物中汞污染和降低人体暴露风险具有重要意义。本论文综述了我国汞污染的现状和健康影响、汞的环境过程以及汞同位素研究进展，并针对汞在水稻中的累积过程、汞在我国近海沉积物中的分布及传输过程、汞在软体动物中的生物放大、以及海洋环境中汞同位素的分馏效应等开展了研究。 研究了汞矿区水稻植株不同部位（根、茎叶、稻米和稻壳以及根际土）中的汞含量和形态，探讨了无机汞和甲基汞在水稻中的累积机制。结果表明，尽管不同矿区汞污染程度明显不同，稻米对甲基汞都呈现最强的累积能力；无机汞和甲基汞在水稻植株中按不同机理进行累积；根际土中汞浓度与水稻各部位中汞浓度都呈显著相关性，且根际土中水溶态汞与各部位中甲基汞浓度相关性更为显著，表明水溶态汞在水稻累积甲基汞的过程中起了关键作用。 对我国四个海域220个表层沉积物和8个沉积物柱芯样品中的总汞含量、总有机碳和pH值进行了分析，研究了我国近海沉积物中汞的来源、分布和传输过程。表层沉积物中汞浓度范围是7.0-397.8 μg kg-1，平均值为63.7 μg kg-1。空间分布呈现随与沿岸距离增加而降低的趋势，垂直分布呈现从柱芯底部到表层波动增加的趋势。结果表明，沿岸人为排放和河流输入是我们近海沉积物中汞的主要来源，泥质区是汞的主要汇，而总有机碳、pH值、洋流和沉积物粒径大小对汞的累积、传输及分布起重要作用。总有机碳对汞浓度的影响比pH值更为显著。 对我国环渤海区域9种双壳类和2种螺类中的总汞、甲基汞、δ15N、δ13C和脂肪含量进行了分析，通过计算营养级、生物放大因子和生物累积因子，研究了汞在软体动物这种低营养级食物链中的生物累积和生物放大效应。结果显示，软体动物中THg和MeHg的浓度范围分别是27.2-461.1和2.1-295.5 μg kg-1，营养级范围是1.99-4.02。THg和MeHg均与营养级呈显著正相关，且生物放大因子均大于1，表明软体动物食物链中存在汞的生物放大。甲基汞是具有生物放大效应的主要汞形态，而无机汞则表现为营养级传递过程中的生长稀释效应。营养级对软体动物累积汞的影响明显高于脂肪含量。 研究了我国近海沉积物中汞同位素的质量分馏和非质量分馏特征，探讨了不同分馏特征在追踪沉积物中汞来源以及汞沉积前所发生环境过程中的应用。结果显示，沉积物中δ202Hg均为负值，其范围是-2.432‰~-0.092‰，Δ199Hg的范围是-0.076‰～+0.307‰。近岸河口与远海沉积物呈现完全不同的汞同位素分馏特征。人为活动影响较大的河口附近沉积物中δ202Hg值最高，最接近河口和周边城市土壤中δ202Hg值，而Δ199Hg几乎没有，表明近岸沉积物中汞同位素质量分馏主要来自于河流输送和陆源直接排放，可用于追踪沿岸人为排放源。而远海沉积物中Δ199Hg的值相对较高，其中黄海中部泥质区呈现最高程度的汞同位素非质量分馏，可能同时受到大气沉降和水体中汞光化学还原过程影响。pH值的降低和总有机碳的增加能显著提高非质量分馏的程度。 研究了汞在渤海食物链中的累积放大过程以及营养级传递过程中汞同位素值的质量分馏和非质量分馏特征。结果显示，δ202Hg的范围是-4.569‰～+0.528‰，Δ199Hg的范围是-0.007‰～+1.212‰。δ202Hg与营养级呈显著正相关，且营养级每增加1，δ202Hg值增加0.463‰，表明汞在食物链随营养级的传递过程会造成质量数较大汞同位素的富集。远海食物链与近海食物链相比呈现更高程度的汞同位素非质量分馏效应，可能与水体中MeHg的光致去甲基化过程有关。远海食物链和沉积物都呈现更高程度的汞同位素非质量分馏，与远海海域水柱特殊的物理和生物地球化学条件（如透光性）有关。 |
| 英文摘要 | China is the country with the largest anthropogenic mercury (Hg) emission. However, the complex translocation and transformation processes of the emitted mercury remain largely unclear. It is hence of great scientific and practical significance to unreval the sources, biogeochemical processes and sinks of mercury in the environment. The uptake of seafood and rice has become two major exposure pathways to humans. Investigating the accumulation mechanism of mercury in food webs and in rice plants is important for preventing mercury contamination and reducing human exposure risk. This paper reviewed the situation and health effect of mercury contamination in China, environmental processes of mercury and application progress of mercury isotope techeniques. Studies were carried out around the accumulation of mercury in rice plants, distribution and transport of mercury in Chinese coastal marine sediments, biomagnification of mercury in mollusks and mercury isotopic fractionation in marine environments. Accumulation pathways of inorganic mercury (IHg) and methylmercury (MeHg) were studied by analyzing concentrations and species of mercury in different tissues of rice plants (root, stalk&leaf, seed and husk) and paddy soils. Although the contamination degree of paddy fields where the rice plants grew were obviously different, rice seed showed the highest ability in MeHg accumulation. Accumulation of IHg and MeHg into rice plants followed different mechanisms. Concentrations of mercury in paddy soils were positively correlated with those in rice tissues, and water soluble mercury (Hg-w) in paddy soils showed more significant correlations with concentrations of MeHg in rice tissues, implying Hg-w may play a key role in the accumulation of MeHg. Distribution characteristics, souces, transport process and sinks of mercury in Chinese coastal marine sediments were studied by comprehensively analyzing mercury content, total organic carbon (TOC) and pH in 220 surface sediments and 8 sediment cores from Chinese marginal seas. Concentrations of mercury in surface sediments ranged from 7.0-397.8 μg kg-1, with an average value of 63.7 μg kg-1. Spatial distribution pattern showed a general offshore decreasing trend towards the outer continental shelf, and vertical distribution displayed a general increasing trend from bottom to surface layers, with slight fluctuation. Coastal anthropogenic discharge and riverine inputs are the main sources of mercury in sediment, and the mud deposits on the coastal shelves are the main sinks. TOC showed more important influence in mercury accumulation in sediments than pH. Ocean currents played a key role in the transport process of mercury in sediments and sediment particle size affected the re-distribution of mercury. Biomagnification of mercury in low trophic level mollusks was studied by comprehensively analyzing THg, MeHg, δ15N, δ13C and lipid contents in 9 species of bivalves and 2 species of gastropods, and further calculating the values of trophic levels (TLs) and trophic magnification factors (TMFs). The concentrations of THg and MeHg were in the range 27.2-461.1 and 2.1-295.5 μg kg-1, respectively. The TLs were in the range 1.99-4.02. Biomagnification of mercury existed during the trophic transfer of mercury in mollusks, and was confirmed by the significant positive correlations between Hg and TLs, and the TMFs values (>1). MeHg is the main mercury species magnifying in mollusks, while growth dilution occurs during the trophic transfer of IHg. TLs showed more effect on mercury accmulation in mollusks than lipid contents. Mass-dependent and mass-independent franctionation characteristics of mercury in coastal marine sediments were studied by analyzing mercury isotopic compositions. Application of tracing sources and processes of mercury in aquatic environments using different fractionation variations was also discussed. δ202Hg and Δ199Hg values were in the ranges -2.432‰～-0.092‰ and -0.076‰～+0.30 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/35205]  |
| 专题 | 生态环境研究中心_环境化学与生态毒理学国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 孟梅. 区域环境中汞的污染特征及迁移转化过程研究[D]. 北京. 中国科学院研究生院. 2015. |
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