近海网箱养殖区不同来源溶解性有机质对汞形态转化的机理研究

Consumption of Hg-contaminated maricultural products has been regarded as one of the major Hg exposure pathways to human body. It is of great significance to investigate the environmental geochemistry of Hg in maricultural zone due to the fact that the situation of marine pollution caused by Hg is getting worse. Many studies have demonstrated that the dissolved organic matter (DOM) plays an important role in governing the behavior of Hg in the aquatic environment. However, influence of a large quantity input of organic matters, which enter the aquaculture zone from both interior and exterior sources, on the existing forms and transformation of Hg, has not been systematically studied yet. This project is to (1) investigate the difference of the in situ decomposition process of the three major organic matters frequently occurring at mariculture zone: unconsumed fish feed, fish excretes and dead algae; meanwhile the components and functional groups of DOM derived from the individual decomposition of three organic maters as well as the fingerprint of DOM fluorescence spectrum will be also characterized; (2) distinguish the contribution of the DOM components to the complexation, methylation and reduction/oxidation of Hg and the mechanism behind; (3) the coupled effect of decomposition of organic matters on the variation of physicochemical properties (e.g. pH value and Eh) as well as the microbial community; (4) quantify the contribution of three above mentioned organic matters during the decomposition to the DOM pool in the sediment beneath of the maricultural rafts in an attempt to identify their weight in transformation of Hg via 3-dimentional fluorescence image analyses. The outcomes from this project is hoped to facilitate the future study concerning how to mitigate Hg pollution in the mariculture zone and thus maintain the sustainable develop of mariculture industry.

食用汞污染的海产品是人体汞暴露的主要途径之一。随着海洋汞污染日益加剧，研究海洋养殖区汞的环境地球化学过程具有重要意义。研究表明溶解性有机质（DOM）对汞在水环境中的行为有极为重要的影响。但是海洋网箱养殖区大量多源性有机质高输入对汞的赋存形态及转化过程影响还缺乏系统研究。本项目以残饵、鱼排泄物和死亡藻体三种典型内源性和外源性有机物为对象，通过原位试验、树脂分离技术和红外光谱、核磁共振和荧光光谱等分析技术，以阐明①各有机质在原位腐解过程中生成的DOM主要组分、官能团组成比例的动态变化及其三维荧光特征指纹图谱；②各DOM组分对汞的络合、甲基化、氧化还原过程的影响及机理；③有机质腐解过程与沉积物理化性质以及微生物群落变化的耦合效应；④三种有机质对沉积物中总DOM的贡献度及其对汞形态转化的影响权重。以上研究结果对今后研究如何消减养殖区汞污染的健康风险、保障我国水产养殖产业的可持续发展提供科学依据。

本项目以浙江沿海渔业养殖区三种非同源有机物为研究对象，通过应用XAD大孔树脂与阴阳离子交换树脂串联技术将其DOM细分，从更微观的角度探究这些有机物在腐解过程中对汞甲基化的影响机理。结果表明：（1）经过树脂串联装置，可将鱼粪、鱼粮和藻体细分为6种亚组分，分别为亲水性酸、亲水性碱和亲水性中性物以及疏水性酸、疏水性碱和疏水性中性物（即HIA，HIB和HIN以及HOA、HOB和HON）。（2）未经腐解有机物的DOM中，疏水性有机亚组分占有主导地位，而且官能团组成结构和数量要比亲水性亚组分更加丰富。随着腐解的进行，疏水组分的总有机碳浓度降低，而亲水组分浓度略有增加。（3）在不同腐解时间对各有机物DOM对汞甲基化影响试验中，我们发现DOM亚组分对于汞甲基化的影响并非一成不变。疏水性亚组分在厌氧条件下会随着腐解时间的增加不断增强汞甲基化能力，尤其以HON和HOB为最强。（4）根据紫外可见吸收光谱，其中鱼粮的FI＞1.9，说明鱼粮的DOM主要是內源性的；而底泥和鱼粪和均介于1.4-1.9之间，所以这两种DOM的来源具有內源和外源双重特性；然而，海藻DOM的FI＜1.4，说明其主要是外源输入。本研究的科研成果可以为今后遭受汞污染鱼排区控制和降低汞污染健康风险提供科学依据。