黄、东海多氯联苯从源到汇：关键界面的通量、过程与机制

The industrial emissions of unintentionally produced polychlorinated biphenyls (PCBs) are sharply augmented due to the rapid industrialization and urbanization in China, leading to the enlarged contribution to the globally biogeochemical cycling of PCBs. The Yellow Sea (YS) and East China Sea (ECS) are deeply influenced by the continentally outflowed pollutants via long-range atmospheric transport and deposition. The ECS is prone to the controlling influence of the inputs from the Yangtze River and other regional large rivers as well, while the YS is basically free of the restrictions from the direct discharges of large rivers. This research project targets on the ECS and YS with substantial differences of input pathway for pollutants and sedimentary dynamic environments, and takes the pivotal interfaces as entry points to study the land-sea exchange. The main objectives of this application are to assess the air-sea exchange fluxes (volatilization or deposition), latitudinal fractionation and mechanisms related with seasonal source to sink exchange for PCBs in the ECS and YS based on the measurements of air and water samples collected seasonally from large-scale cruise surveillances in combination with small island-based intensive monitoring of atmospheric deposition, and to reveal the special processes and mechanisms for PCBs from the source to sink in the ECS and YS, coupled with sedimentary dynamic environments, on the basis of estimations of exchange fluxes at the key interfaces, including air and sea, large river discharge into the sea and burial mass in the seabed. This study features both regional specialty and universal application with great scientific significance.

我国工业化和城市化导致了非故意工业生产多氯联苯释放量大幅增加，对全球多氯联苯生物地球化学循环的贡献日益增大。黄、东海深受我国陆源大气污染物离岸传输和沉降的强烈影响；东海同时受到长江及局地大河多氯联苯输入的控制性影响，而黄海基本不受大河直接输入制约。本申请选择污染物输入途径和沉积动力环境差异显著的黄海和东海为靶区，以对陆-海交换起着控制作用的关键界面为切入点，通过大范围航次大气和海水样品的季节性采集与分析，结合该海域小岛大气沉降强化观测，评估黄海与东海大气-海水界面多氯联苯输入/挥发通量、季节性源-汇转换机制及纬度差异；在估算黄、东海关键界面（大气-海水、大河入海与海底埋藏）交换通量的基础上，与沉积动力环境相耦合，揭示黄海与东海多氯联苯从源到汇的特色过程与机制。研究兼具区域特色与普适意义，具有重要的科学价值。

本课题以对陆-海交换起着关键作用的界面为切入点，揭示黄、东海多氯联苯从源到汇的特色过程与机制，取得如下主要成果：1）发现不同生命周期持久性有机污染物（POPs）在长江口海域海-气界面存在显著不同的源/汇交换动力学过程与机制，新型POPs-BDE-209海-气气体交换通量全年呈现净沉降，其量与干湿沉降通量相当；传统POPs-多氯联苯呈现强烈的海-气界面气态净挥发，为长江口海域海-气界面多氯联苯交换的主导过程，可持续向大气再挥发释放多氯联苯。2) 发现因陆地输入减少，多氯联苯的海-气交换动力学已从大气主导模式转变为环境参数控制模式。冬季由于赋存较高浓度多氯联苯的沿岸流和长江冲淡水向东南传输，多氯联苯的海-气气体交换呈现净挥发。夏季，多氯联苯的海-气气体交换呈现净挥发，通量总体低于冬季；夏季东海台湾暖流占主导，海水中赋存较低的多氯联苯浓度，致使东海仅具有低的挥发通量，而在黄海北上的苏北沿岸流和长江冲淡水在绿潮作用下诱导了多氯联苯的较高挥发。3）首次强调了大河输入、大气沉降和陆架沉积过程对东中国边缘海非故意生产多氯联苯（UP-PCBs）与传统商用多氯联苯（IP-PCBs）归宿的耦合约束机制，揭示东海多氯联苯的埋藏通量远高于黄、渤海，黄海北部和南部中部泥质区以IP-PCBs为主，长江口泥质区和渤海以UP-PCBs为主导，闽浙沿岸表现为UP-PCBs和IP-PCBs的混合源，UP-PCBs的沉积通量在东中国边缘海已逐渐占据主导。4）东中国边缘海多氯联苯沉积通量在1950s-70s中期和1990s-至今出现两个明显的峰值，分别对应于中国多氯联苯的十年生产期（1965-1974年）和现代经济高速发展期（如水泥和钢铁的巨量生产）导致的UP-PCBs排放增加。5）东中国边缘海有机氯农药六六六和滴滴涕的沉积通量皆于1980s达到峰值，之后显著降低，与中国这两类污染物生产使用和禁用存在良好的响应关系。6）提出东海内陆架沉积物中低环数多环芳烃具有一定的可交换性，其可经沉积物-孔隙水间的分配解析至孔隙水，通过向沉积物-上覆水界面的扩散迁移，重新参与多环芳烃的生物地球化学循环过程。