• 关键词：多环芳烃  巢湖  逸度  水体-沉积物扩散  炭黑  二次污染源

• 基金项目：国家自然科学基金（No.41390244）；中央高校基本科研业务费专项资金（No.2015HGCH0002）

• 刘大超
• 合肥工业大学资源与环境工程学院, 合肥 230009

• 徐秋萍
• 1. 合肥工业大学资源与环境工程学院, 合肥 230009;2. 合肥工业大学智能研究院, 合肥 230009

• 张浏
• 安徽省环境科学研究院, 合肥 230061

• 王继忠
• 合肥工业大学资源与环境工程学院, 合肥 230009

• 彭书传
• 合肥工业大学资源与环境工程学院, 合肥 230009

• 摘要：沉积物是污染物的一个重要汇区，同时亦可作为二次污染源释放污染物，因此，研究污染物在沉积物-水体界面的扩散过程对认识污染物的环境归趋及其迁移扩散具有重要意义.先前的研究结果表明，巢湖流域沉积物中高浓度多环芳烃（PAHs）来源于历史上工业废水排放，并且整个流域呈显著的空间差异性，但上层水体中PAHs浓度较为均匀.因此，有理由假设这些污染物在巢湖流域水体-沉积物间扩散交换呈明显的空间差异：即受工业废水污染的沉积物可能成为水体中PAHs的二次污染源，而其它区域沉积物则可能是这些污染物的重要汇.然而对于这些问题的研究目前仍然处于空白.本研究利用49个采样点的数据，通过逸度扩散模型，分别计算水体和沉积物中17种PAHs的逸度（f），并进一步计算它们的逸度分数（ff）值，依此全面认识这些污染物在水体-沉积物间的扩散趋势.结果显示，PAHs的ff值随环数增大而减小，即环数越高的PAHs越倾向于从水体向沉积物扩散.其中，低环（2~3环）PAHs和五环苝（Per）的ff均值都大于0.9，表示其从沉积物向上层水体扩散.多数采样点中、高环（4~6环）PAHs的ff值介于0.1~0.9，表示处于交换平衡，但受工业影响区域则呈现从沉积物向水体扩散的趋势.以Per和苯并[g，h，j]苝（BghiP）为例深入讨论了两种不同来源PAHs在巢湖流域水体-沉积物间扩散的差异性.对于Per而言，ff值空间差异较小，其普遍从沉积物向水体释放，说明沉积物-水体间扩散过程是上层水体中自然来源Per的重要来源.对于BghiP而言，ff值存在明显的空间差异性，受工业污染严重的地区，PAHs更易于从沉积物向水体扩散，而其它区域，BghiP则普遍处于平衡态甚至从水体向沉积物汇集.碳黑能促使PAHs向沉积物扩散，对PAHs的扩散有重要影响，且对高环（5~6环）PAHs扩散的影响更明显.当沉积物中碳黑含量为有机碳含量10%时，巢湖流域一半以上区域的PAHs扩散方向发生了改变.

• Abstract：Sediments are commonly considered as a sink of various contaminants in the aquatic environment,however,they might be the substantial secondary source of contaminants in the overlaying water. Thus studies on the diffusive process between water-sediment are important to understand the fate and transport of contaminants. In previous studies on Chaohu Lake watershed,we showed that high concentrations of PAHs was found to accumulate in the sediments as a result of industrial sewage,and significant spatial variation on PAHs contents were observed. However,uniform distribution of PAHs concentrations in water was found. It can therefore be hypothesized that the diffusive process of PAHs between water-sediment in Chaohu Lake watershed would show significant spatial variation. The information on the water-sediment diffusion of PAHs in Chaohu Lake watershed,however,is scarce. In the present study,the fugacity (f) and fugacity fraction (ff) values of 17 PAHs in water and sediment were calculated based on the data of PAHs for 49 sampling sites in Chaohu Lake watershed to understand the trends of diffusion between water-sediment. The results showed that ff values decreased with the molecular weight increase,suggesting the high molecular weight PAHs (5~6 rings) were inclined to transfer from water into sediment. Generally,ff values of low molecular weight (2~3 rings) PAHs and Per were greater than 0.9 for all sites,indicating that they were transported from sediment to water by molecular diffusion. PAHs with medium and high molecular weight PAHs (4~6 rings,excluding Per) achieved equilibrium between water-sediment for most sites. Taking Per and BghiP as examples,they show significant differences on the spatial variation of diffusive trends. Diagenesis derived Per had high ff values for all sampling sites,suggesting that sediment was the predominant source of Per in water. While BghiP which originated from anthropogenic activities was transported into water from sediment for the sites affected by industrial sewage. BighP exhibited equilibrium state between water and sediments in most sites located in rural area or less effected by industrial sewage. Thus these results indicated that sediment was the potential secondary source of anthropogenic activities related PAHs in water in Chaohu Lake watershed. Black carbon played an important role in the diffusive trends of PAHs,specially for high molecular weight PAHs. When the content of black carbon was set at 10% of organic carbon,the diffusive trends of PAHs in more than half sites were changed.

• Key words：polycyclic aromatic hydrocarbons  Chaohu Lake  fugacity  water-sediment diffusion  black carbon  secondary sources

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