高浊度河口区胶体耦合作用对多环芳烃相态转化和沉降传输的影响研究

Nano-sized colloids are important absorption carriers for the migration and transport of polycyclic aromatic hydrocarbons (PAHs) in the estuarine waters. At present, most field studies still focus on dividing the water samples into “particulate phase” and “dissolved phase” based on the microporous fiber filters (with bore diameter of 0.45 to 1 μm) to explore the complex geochemical behaviors of PAHs in the estuary. Actually, the dissolved phase also includes “colloidal phase” which the particle size is smaller than fiber filter pore size, the neglect of “colloidal phase” could tend to cover up the importance of colloids in geochemical processes of PAHs, such as multiphase partitioning, phase transformation, and sedimentation transport. The applicant has recently found the deficiencies with the use of traditional two-phase separation to study the partitioning behavior and air-sea exchange of PAHs in the marginal seas of China. On the basis of these deficiencies, this project intends to separate the “colloidal phase” PAHs from the conventional “dissolved phase” to verify whether the study focusing on colloidal coupling contributes to a deeper understanding of the geochemical behaviors of PAHs such as multiphase partitioning, phase transformation, and sedimentation transport. Firstly, based on the effective separation of the “particulate phase”, “colloidal phase”, and “freely dissolved phase” PAHs using glass fiber filter coupling cross-flow ultrafiltration systems, we would conduct relevant research in the high turbidity Yangtze River estuary. On the one hand, we plan to construct a three-phase partitioning model of “particulate phase-colloidal phase-freely dissolved phase” of PAHs. Further, we systematically study the multiphase partitioning of PAHs coupled by colloids in combination with the spatial variation characteristic of PAH contents, partition coefficients of “particle phase and freely dissolved phase” (short as Kp-w) and “colloidal phase and freely dissolved phase” (Kc-w) and their corresponding organic carbon normalized partition coefficient (Kpoc and Kcoc) during entering the sea of Yangtze River dilute water. We further establish a linear relationship between Kpoc (or Kcoc) and octanol-water partition coefficient (Kow), and refine the multiphase distribution model of PAHs. Secondly, we focus on the correlation of multiphase partition coefficient with some environmental factors including salinity and temperature, concentrations of suspended particulate matters, particle or colloidal or dissolved organic carbon, and colloidal particle size and morphology, and their zeta electric potentials. We further emphatically explore the influence mechanism of hydrodynamic coupling of colloid and environmental multifactor on the phase transformation of PAHs. Thirdly, combining with multiscale mixing experiments of fresh and seawater, we want to establish the correlation between the salinity and clearance rate of PAHs coupled with colloids. Finally, based on the mass balance of PAHs before and after mixing, we can comprehensively evaluate the promotion of the colloid coupling on the sedimentation of PAHs. This project aims to provide an important scientific supplement for understanding the partition and fate of land-based PAHs during entering the sea.

河口水体中纳米尺寸的胶体是多环芳烃（PAHs）入海迁移的重要吸附载体。目前绝大多数现场研究仍基于微孔滤膜（0.45-1微米）将水样分为颗粒相和溶解相来探讨PAHs的河口地球化学行为。然而，实际上溶解相PAHs也包括了粒径小于滤膜孔径的胶体相PAHs，这往往掩盖了胶体在PAHs多相分配、相态转化和沉降传输等环境过程中的重要性。申请人近期研究也发现利用传统两相分离探讨我国近海海水中PAHs分配行为和海气交换存在一定问题。基于此，本项目拟将“胶体相”PAHs从“溶解相”中分离出来，进而验证胶体的耦合作用是否有助于更加深入地理解PAHs的多相分配、相态转化、沉降传输等地球化学行为。本项目在实现玻璃纤维滤膜和切向流超滤分别对“颗粒相”、“胶体相”和“自由溶解相”PAHs分离的基础上，以高浊度长江口为例，构建PAHs的“颗粒相-胶体相-自由溶解相”三相分配模型，结合长江口入海过程中PAHs含量和“颗粒相-自由溶解相”和“胶体相-自由溶解相”分配系数（Kp-w和Kc-w）及相应的有机碳归一化分配系数（Kpoc和Kcoc）等的空间变化特征，系统研究PAHs的多相分配规律，并进一步建立Kpoc（或Kcoc）与辛醇-水分配系数（Kow）线性关系，细化PAHs多相分配模型。另外，重点分析PAHs多相分配系数与温/盐度、悬浮颗粒物浓度、颗粒/胶体/溶解有机碳浓度、以及胶体粒度和形态、zeta电位等环境多因子的相关关系，探讨环境多因子调控下，胶体和PAHs耦合作用对PAHs相态转化的影响机制；结合现场淡/海水多比例混合模拟实验，并基于混合前后PAHs的质量守恒，建立PAHs清除率（由胶体絮凝引起）与混合盐度的非线性相关关系，全面评估长江口胶体和PAHs耦合沉降对表层海水PAHs垂直传输的促进作用。本项目旨在为深入理解陆源PAHs入海过程中的分配和归趋提供重要的科学补充。

天然水环境中悬浮颗粒物、胶体物质以及溶解有机碳等的耦合作用是影响痕量有机污染物的环境赋存、多相分配、迁移和埋藏的重要媒介。本研究建立和优化了固相萃取膜盘和切向流超滤两种手段实现水环境中痕量有机污染物的分离，并结合多粒径颗粒物过滤分离手段，实现了不同粒径颗粒物、超细胶体物、自由溶解物等多介质负载的痕量有机污染物分配规律模型的构建。通过对长江口不同季节水体以及南海北部近海海水中的大面积采样，认识了胶体耦合作用对痕量有机污染物分配和埋藏的重要作用。进一步，通过对颗粒物粒径和有机碳碳成分对痕量有机污染物的分配和埋藏的分析，表明细颗粒组分具有较强的疏水性有机污染物吸附能力，其可显著调节有机污染物的粒径分布和水-颗粒分配。不同温度梯度下的有机碳组分对有机污染物的粒径分布有明显不同的影响。高温热成因的有机碳组分是调控中高分子量有机污染物分配的主要因子。在悬浮颗粒物沉积和埋藏过程中，微生物对有机污染物的利用效率可能调控着疏水性迥异的单体化合物的埋藏趋势。本研究进一步阐明了痕量有机污染物在天然水体中的分配和埋藏机制，为模拟其他水生生态系统中颗粒结合的疏水性有机污染物的运输和埋藏机制提供了重要的参考。