沉积物-海水界面重金属化学平衡模型的研究

The equilibrium partitioning process of heavy metals at the sediment-water interface is an important research topic in order to better understand the distribution, recycling processes, and fate of heavy metals in the ocean. The sediment-water chemical equilibrium model (SCEM) is a simplified model describing the metal equilibrium partitioning reaction at the sediment-water interface under oxic environments. SCEM is easy to apply, and it can help assess the possibility of the heavy metal re-contamination at the sediment-water interface, as well as predict the overlying water free metal ion activities based on sediment geochemical data. The key factor in the SCEM is the conditional binding constant (βSED*), however by far only the Cu's βSED* value has been determined. This project will firstly conduct the sediment-seawater isotherm adsorption experiment to determine the βSED* values for Pb、Zn、Cd, following the field observations and laboratory analysis on sediment and water samples collected in oxic environmental areas from Bohai Bay. Based on the observation data, this work will assess the correlations between sediment metal content and particulate organic carbon (POC) and determine the metal speciation in the overlying water column. This project will establish the SCEM in Bohai Bay for Cu, Pb, Zn and Cd, in order to better understand heavy metal lability, toxicity, equilibrium partitioning status and possibilities of re-contamination at the sediment-water interface. This work will be a foundation work for the development and application of the SCEM in the coming years.

重金属在沉积物-海底界面的平衡分配过程是掌握重金属在海洋中的分布、再循环和归宿的重要课题。沉积物-海水化学平衡模型（SCEM）是一个简化地描述重金属在有氧环境下沉积物-海水界面动态平衡分配规律的模型，它易于应用，可帮助判断重金属在海底界面产生二次污染的可能性，也可通过沉积物化学预测上覆水中的金属活度。SCEM的关键系数是条件络合常数（βSED*），但目前仅有Cu的βSED*值得到了测定，限制了该模型的应用和发展。本项目将首先通过沉积物-海水等温吸附实验确定Pb、Zn、Cd的条件络合常数（βSED*），再通过对渤海湾有氧环境区域中沉积物和上覆水的采样和测试工作，研究分析沉积物中重金属与有机碳的相关性、上覆水中金属的存在形态，然后在渤海湾建立Cu、Pb、Zn、Cd的SCEM模型，探讨这几种金属在渤海湾海底界面的活性、生物毒性、平衡分配状态和二次污染可能性，为未来SCEM的应用和发展奠定基础。

沉积物-海水化学平衡模型（SCEM）是一个简化的描述重金属在有氧环境下沉积物-海水界面动态平衡分配的模型。该模型易于应用，可帮助判断重金属在海底界面产生二次污染的可能性，也可通过沉积物化学预测上覆水中的金属活度。但SCEM中的条件络合常数（βSEM*）不易测定，目前只有Cu的βSEM*值得到了测定。本研究筛选了POC含量不同的表层沉积物样品，通过沉积物-海水等温吸附实验，确定了SCEM中Pb、Zn、Cd的βSEM*值，分别为6.1 ± 0.7，4.9 ± 0.5 和 3.8 ± 0.4，并根据实验数据探讨了POC作为SCEM中络合相代表的可行性。同时，通过在渤海和黄海的采样，测定了沉积物中金属总含量、POC、粒度等参数，以及海水中四种金属（Cu、Pb、Zn、Cd）的总溶解态含量和存在形态，并将测试数据应用到SCEM中，探讨了在黄渤海该模型的可适性。结果显示，上覆水中金属活度的预测值和实测值较为一致，说明SCEM在黄渤海确有其适用性。本研究的主要成果和意义有：1）确定了Pb、Zn、Cd的条件络合常数，为未来SCEM的应用提供了重要参数；2）在黄渤海实现痕量金属无污染采样并测定了底层海水中Cu、Pb、Zn、Cd的存在形态，结果显示几种金属都存在不同程度的有机络合，自由离子活度都未超过其毒性阈值；3）综合吸附实验和海水测试的结果，显示黄渤海沉积物对Cd的吸附相对较弱，Cd造成二次污染的可能性较大。