【作者】 张怀静；

【导师】 翟世奎；

【作者基本信息】 中国海洋大学 ， 海洋地球化学， 2015， 博士

【摘要】 重金属是大气和水体中一类重要的污染物,它能通过食物链在动物和植物体内积累,最后进入人体对人类健康造成危害。汞是自然状态下唯一一种呈液态的重金属元素,具有极强的生理毒性,它可以通过大气的输送和河流的搬运进入湖泊、水库、河口直至海洋,其有机化合物甲基汞易于穿透生物膜富集在食物链中,对人体中枢神经系统产生危害。长江口及其邻近海域是世界上最有代表性的河海交汇区域,属于高浑浊河口并具有沿岸泥质区。其缺氧区和丰富有机质的存在为重金属的迁移转化,尤其是汞的甲基化作用提供了较为适宜的环境。重金属在长江口最大浑浊带内的通量研究和汞在长江口邻近海域的迁移转化及其环境效应的研究,不仅可以揭示包括汞在内的重金属在河口的输运和迁移转化规律,而且对海域环境保护,乃至国民食品安全和社会经济发展都具有重要意义。本论文以国家重点基础研究发展规划(973)项目第九课题(2002CB412409)和国家自然科学基金面上项目(41076022)为依托,分别在2003年6月“长江口及其邻近海域环境综合调查”和2012年6月国家自然科学基金项目“东海科学考察实验研究”春季航次中采集了悬浮物、海水和沉积物样品并获取了海水温度、盐度和叶绿素荧光以及海流等现场实测数据资料。完成了长江口最大浑浊带地区悬浮物浓度和重金属含量的分析测试,结合海水温度和盐度以及海流数据,分析了潮周期内悬浮物重金属含量的分布特征,估算了潮周期内各重金属的通量,探讨了重金属的运移规律。在此基础上,对闽浙沿岸海域汞的迁移转化及其环境效应进行了重点研究,完成了海水中的溶解态总汞浓度、悬浮物中的颗粒物浓度和总汞含量、沉积物中的粒度组成、210Pb测年、总汞、甲基汞、常量元素和有机碳含量以及孔隙水中的硫酸根离子浓度等相关项目的分析测试,在大量现场实测资料和系统的室内分析基础上,以悬浮颗粒物—水界面汞的分配为切入点,研究了河口-近岸环境中汞在悬浮颗粒态与溶解态之间的迁移转化规律,探讨了闽浙沿岸海域沉积物(表层沉积物和岩芯沉积物)中汞和甲基汞的含量分布和甲基化作用及其影响因素；结合21oPb测年,定量给出了泥质区沉积物中汞和甲基汞的年平均沉积通量,建立了汞的沉积记录,探讨了百年尺度汞的含量对人类活动的响应。论文主要成果包括：(1)在长江口最大浑浊带地区,潮周期内悬浮物重金属元素含量均值的大小顺序为：Zn>Ni>Pb>Co>>Cd,其含量分布特征为：落潮平均含量高于涨潮平均含量。悬浮物所携带的Zn、Pb、Co和Ni主要向东北偏东方向输运,主要为陆源,并且大部分沉降在离岸较近的区域,Cd受海源物质影响而向西北方向输运。影响悬浮物重金属元素含量分布的主要因素有重金属来源、水体盐度和悬浮物浓度。重金属含量与水体盐度呈正相关性,与悬浮物浓度呈负相关性。(2)闽浙沿岸泥质区海域悬浮物中总汞含量在1.20×105 ng/kg～16.5×106 ng/kg之间,溶解态总汞浓度在0.26 ng/L～2.69 ng/L之间。汞在悬浮颗粒态和溶解态之间迁移转化主要受控于悬浮颗粒物的吸附—解吸作用,同时还受到溶解态有机质的螯合、Cl-与Hg2+的络合作用、底层水氧化还原条件以及表层沉积物对其上覆水体释放汞过程的影响。溶解态有机质的螯合和高盐水的侵入可以促进汞由悬浮颗粒态向溶解态的转化过程。表层沉积物对其上覆水体释放汞的过程和底层水的氧化还原条件影响着汞在近底层水体和表层沉积物之间的迁移转化。(3)闽浙沿岸海域表层沉积物中汞和甲基汞含量分布大致表现为近岸含量高(杭州湾以南浙江沿岸),远岸含量低的特点。汞的甲基化作用主要发生在近表层较小的深度范围内(泥质区北部、中部和南部,其深度范围分别为0～15 cm、 0～8 cm和0-13 cm)。汞的原位甲基化是甲基汞的主要来源。在成岩过程中,埋深或其它环境条件的变化可以导致甲基汞的转移或再分配。影响沉积物中汞和甲基汞含量及甲基化作用强弱的因素主要包括人为污染、海流体系、粒度组成、有机质含量和硫酸盐还原菌活性等。人为污染是汞含量分布的主控因素；海流体系控制着汞含量近岸高、远岸低的分布格局；粒度组成影响着甲基汞的富集程度；有机质对表层沉积物中汞的甲基化作用影响不明显,在岩芯沉积物中,既可以促进汞的甲基化,也可以抑制汞的甲基化,主要取决于有机质的类型；硫酸盐还原菌的活化能力是汞甲基化作用的主控因素之一。(4)结合137Cs和210Pb测年结果,闽浙沿岸海域泥质区南部沉积物的平均沉积速率为0.11 cm/a,汞和甲基汞的年平均沉积通量范围分别为：6.63～60.96 ng/(cm2·-a)和15.86～272.45 pg/(cm2·a)。来自长江的汞在输运到闽浙沿岸海域时,大部分随悬浮颗粒物沉降在近岸狭长海域范围内。百年以来,闽浙沿岸海域沉积物中汞的含量分布和受污染程度与人类活动之间存在很好的正相关关系,即随着中国经济的快速发展,汞的含量逐渐增加,受污染程度日益严重。更多还原

【Abstract】 Heavy metals, as an important pollutant in water and atmosphere, can accumulate in the body of animals, plants and even human beings through the food chain, causing healthy problems in people. Mercury, the only kind of heavy metal element in liquid in nature, is one of the most toxic heavy metals commonly found in the global environments. It can be transported and deposited into lakes, reservoirs, estuaries and oceans by atmosphere and rivers. Methylmercury (MeHg), a sort of organic compound of mercury, is easy to penetrate the biofilm and accumulate in food chain, harming to human central nervous system. The Yangtze River Estuary, with high turbidity, and its adjacent mud area are the typical land-ocean interaction zones in the world. The low content of dissolved oxygen and abundant organic matter in this zone promoted the generation and transformation of mercury methylation. Systematical survey and discussion on the transformation and environment effects of mercury and some other heavy metals in the Yangtze River Estuary and its adjacent area can not only help to find the laws of the transformation and enrichment of heavy metals, but also have important significance to the protection of marine environment, national food safety and the development of our society and economy.This research is supported by the National Basic Research Program (973 program) of China (No.2002CB412409) and the National Natural Science Foundation of China (No.41076022). Two cruises, the cruise of synthetic investigation of Yangtze River Estuary environment and the spring cruise of National Natural Science Foundation, were carried out in June,2003 and 2012 respectively. During these two cruises, not only samples of suspended matters, seawaters and sediments were recovered, but also in situ data such as temperature, salinity and fluorescence of seawater and the speed of ocean current were measured. The concentration and heavy metal content of suspended matters were determined in the turbidity maximum zone around Yangtze River Estuary. Combining with the current speed, the temperature and salinity of seawater, the variation of heavy metal contents during a tidal cycle were analyzed and their fluxes were also estimated, at the same time, the influence factors were discussed.This thesis also focuses on the transformation processes and environment effects of mercury in the Min-Zhe coastal area. The bulk contents of mercury in seawater, suspended matter and sediment samples from three sites were determined and MeHg in surface and core sediment samples were also obtained. The vertical distribution profiles of dissolved and particulate Hg in the water column were demonstrated and the transformation mechanisms between them were discussed. Distributions of bulk mercury and MeHg in three core sediment samples from the Min-Zhe coastal area were also demonstrated and methylation mechanism of mercury and influencing factors were systematically analyzed. Combining with results of the 210Pb dating, the mean sedimentation rates and mean annual deposition fluxes of mercury and MeHg in mud area were estimated and the deposition record of mercury in the coastal mud area was established. Centennial-scale response of mercury to human activities was also explored.The main conclusions of the thesis are as follows:(1) For suspended matters from the turbidity maximum in Yangtze River Estuary, the average contents of heavy metals during a tidal cycle are in the order of Zn>Ni>Pb>Co>>Cd. Average contents in ebb tides are generally higher than those in flood tides. Zn、Pb、Co and Ni, mainly terrigenous, are transported towards east-northeast, settling down with the suspended matters in the alongshore area. Influenced by marine-derived materials, Cd is transported towards northwest. The source of heavy metals, the salinity of seawater and the concentration of suspended matters are the main factors controlling the distribution of heavy metals in suspended matters during a tidal cycle. There is a positive correlation between the content of heavy metals and the salinity of seawater, while the opposite correlation between the content and the concentration of suspended matter.(2) The content of bulk mercury in suspended matter samples from mud zones along the Min-Zhe coastal area is between 1.20×105ng/kg and 16.53×106 ng/kg and the dissolved concentration of mercury is from 0.26 ng/L to 2.69 ng/L. The transformation of mercury between particulate and dissolved phase is mainly controlled by the adsorption-desorption of suspended matters. At the same time, it is affected by the chelation of dissolved organic matters, the complexation of Cl-1 with Hg2+, the oxidation-reduction conditions near the bottom and the releasing of mercury from surface sediments to their overlying water. The chelation of dissolved organic matters and the inrush of the seawater with high salinity can promote the desorption of mercury from suspended particles. The releasing of mercury from surface sediment to its overlying water and the oxidation-reduction conditions near the bottom also have effect on the transformation of mercury between bottom water and surface sediment.(3) Mercury and MeHg are enriched in the sediment samples from the Min-Zhe coastal area (the alongshore area of Zhejiang to the south of Hangzhou Bay). Methylation in core sediments in mud zones mainly occurs in the shallow depth from surface (the depths are respectively 0～15 cm,0～8 cm and 0～13 cm in northern, middle and southern study areas). In Min-Zhe coastal mud area, MeHg mainly comes from in situ methylation. Downcore variations of environmental conditions can lead MeHg to be transferred or reassigned during the diagenetic process. Influencing factors of methylation and downcore distributions of bulk mercury and MeHg in sediments include sources of pollutions, bottom current patterns, grain-sizes of sediments, contents of TOC and activities of sulfate-reducing bacteria. Contaminant and circumfluence primarily control the distribution of mercury in the sediments. Grain-size affects the degree of enrichment of MeHg. The effect of TOC on the methylation is not obvious in surface sediments. In cores, the TOCs can not only promote the methylation, but also inhibit it, mainly depending on the type of organic matter in sediments. The activity of sulfate-reducing bacteria is one of the main controlling factors of mercury methylation.(4) Combining with results of the 137Cs and 210Pb dating, the mean sedimentation rate is estimated to be 0.11cm/a for the core DH7-2 (the southern mud zone in Min-Zhe coastal area). The mean annual deposition fluxes of mercury and methylmercury here vary from 6.63 ng/(cm2·a) to 60.96 ng/(cm2·a) and from 15.86 pg/(cm2·a) to 272.45 pg/(cm2·a) respectively. Most mercury transported by Yangtze River to the Min-Zhe coastal area, settled down in a narrow zone along the shore. In the past one hundred years, the mercury contents and contamination levels had a positive correlation with human activities. With the rapid development of Chinese economy, mercury content in the nearshore sediments gradually increases, and the degree of contamination increased seriously.更多还原