论文题目∶有害化学物质的水生食物网传递行为研究.doc

论文题目：有害化学物质的水生食物网传递行为研究作者简介：万祎，男， 1981年09月出生，2002年09月师从于北京大学胡建英教授，于2007年07月获博士学位。中 文 摘 要化学物质的安全评价是当今世界各国政府环境管理的主要组成。目前，全球合成使用的化学物质已超过1000万种，每年新登记注册并投放市场的超过1000种。为了有效管理众多商用化学品，美、日、欧盟等发达国家都有相关的化学物质管理法规，对已有的化学物质筛选控制，对新型物质进行危害性评估。作为化学品的重要指标之一，化学物质的生物放大性是标准制定和风险评价的主要依据。但是，由于影响物质生物放大行为的因素众多（食物吸收、代谢、排泄等）以及天然食物网的不可模拟性，生物放大的机理研究一直是环境科学领域无法解决的难题之一，导致了生物放大性的方法学研究无法实现突破性进展。由此，在对象物质的具体评价过程中，各国政府和国际协会只能根据污染物在生物和水之间的分配（辛醇与水分配系数（log Kow）和生物浓缩因子（BCF）来判断物质的生物放大性，这种方法忽视了污染物在生物体之间的传递过程和影响因素，很容易错误判断对象物质的生物放大性。典型例子如全氟辛烷磺酸盐类物质，无论从log Kow数值还是从实验室鱼类暴露实验判断都属于生物不放大的物质，但野外调查却发现这类物质在高等生物（鸟和哺乳动物）体内富集有很高的浓度。所以，仅仅依据log Kow或者水和生物间分配建立的生物富集预测模型是不准确的，需要进一步研究生物放大机理，找出主要影响因素，才能准确判断对象物质的生物放大性。针对生物放大研究目前存在的科学问题，本研究试图从药理动力学的角度解析生物放大性的机理，并建立相应的预测模型。渤海湾的海洋资源是京津地区主要的海产品来源，该区域多类有害化学物质的食物网传递行为研究有助于评价海洋污染对当地人群（最高营养级生物）的健康风险，为食品安全管理提供重要依据，也有助于北京和天津地区对化学物质生产和使用的管理。为此，本研究选取我国的半封闭内海（渤海湾）为研究区域，利用稳定同位素技术建立了渤海湾食物网主要生物种的营养和食物关系，以二噁英类物质为模型物质，通过对此类物质食物网传递动力学行为和高等生物体内的毒理动力学行为研究，尝试解析其食物网传递行为机理。基于此机理，并结合滴滴涕类、氯苯类和多环芳烃类物质的类似研究，建立了预测化学物质食物网传递行为的构效关系，进一步应用于多溴联苯醚类物质食物网传递行为的预测，并用实际调查验证预测结果。稳定的食物关系和相对封闭的环境是食物网研究的前提。本研究选取了我国唯一的内海（渤海湾）作为研究区域，在湾内采集了浮游动植物、5种无脊椎生物、8种鱼类、3种海鸟和鸟蛋，利用稳定碳同位素技术确定所采集的对象生物属于同一个食物网体系，并用稳定氮同位素技术建立了稳定同位素比值与营养层次的关系模型，定量计算得到浮游动植物、无脊椎生物、鱼类和海鸟的营养层次分别为1.46-2.10、1.91-3.32、2.55-4.23，2.98-4.28。同时，针对一些世界上经典的生物放大物质（滴滴涕类物质和六氯苯）进行，发现这类物质在渤海湾呈现明显的食物网放大行为，食物网放大系数（TMFHCB=2.96，TMFp,p-DDE=3.26，TMFDDMU=3.98）与世界上其他区域相近，证明了所建食物网适合有机污染物的食物网传递行为的研究。二噁英类物质（包括二噁英（PCDDs）、呋喃（PCDFs）和平板多氯联苯（co-PCBs）是一类亲脂性极强的物质，国际上普遍认为这类物质具有很高的生物放大性，将其纳入12种持久性有机污染物中的一大类物质。实际上，环境领域关于二噁英类物质生物富集和放大的研究仅仅局限于实验室内鱼类的暴露研究，还没有全面调查此类物质在天然食物网中的传递行为。本研究首先调查了渤海湾二噁英类物质的暴露状况。在渤海湾和天津地区一条主要排污河中，采集了三根柱状泥样。对泥样中的二噁英类物质、六六六类物质和六氯苯检测后发现，柱状泥各层都有二噁英类物质检出，说明渤海湾生物还处于二噁英类物质的暴露中。二噁英类物质的组成分析、以及与六六六类物质和六氯苯的行为研究表明，当地五氯酚钠生产是这些物质主要的污染来源。在此基础上，调查了二噁英类物质的食物网传递行为。结果发现二噁英类物质并非如人们想象的都呈现显著生物放大，其中PCDD/Fs和co-PCBs的食物网传递行为完全不同：co-PCBs的浓度随营养层次升高呈显著增加趋势，高氯和非2,3,7,8取代的PCDD/Fs的浓度随营养层次升高呈显著降低趋势，而低氯和中等分子量的PCDD/Fs的浓度随营养层次升高没有明显的升高和降低趋势。辛醇与水分配系数（log Kow）是衡量化学物质脂溶性的参数，在国际上被广泛应用于预测化学物质生物放大性高低的指标，因此本研究分析了二噁英类物质的食物网传递行为与log Kow的关系。值得注意的是，非2,3,7,8取代的PCDD/Fs、低氯取代的PCDD/Fs和co-PCBs的log Kow非常相似，但是这三类物质的食物网传递行为却完全不同，用log Kow不能准确判断二噁英类物质的生物放大性为了进一步研究二噁英类物质的食物网传递行为的机理，本研究以渤海湾高等生物（银鸥）为对象生物，调查了二噁英类物质在鸟体内的药代动力学行为。结果表明，PCDD/Fs在海鸟体内的器官分布也呈现出与co-PCBs不同的现象：PCDD/Fs主要富集在肝脏中，显示出很强的肝阻碍效应，而且该效应随物质log Kow的增加而增加。PCDD/Fs的肝阻碍比值与log Kow关系为这类物质的肝阻碍现象提供了结构与活性的定量关系。污染物在生物体内的半衰期是器官分布之外另一个重要的药代动力学参数，利用代谢逸度模型计算了二噁英类物质在银鸥体内的半衰期。对比二噁英类物质的肝阻碍效应、代谢速率和食物网传递行为，发现由于肝阻碍效应导致的不同代谢速率可能是二噁英类物质食物网传递行为的决定因子。在对二噁英类物质研究的同时，本研究调查了有机氯、六氯苯和多环芳烃类物质的食物网传递行为和高等生物体内的毒理动力学过程，得到了这些物质的食物网放大系数和代谢速率。为了建立预测化学物质食物网传递行为的预测方法，本论文尝试利用所有物质的代谢速率和脂溶性（log Kow），并采用概率密度分析方法，建立预测对象物质的生物放大性的构效关系。并将上述定性关系应用于目前的研究热点物质（多溴联苯类物质）的放大性预测。多溴联苯醚类物质的代谢速率是通过代谢模型计算获得，log Kow值采用了文献数据，预测结果表明这类物质在食物网中应该呈现生物放大。实际调查显示，多溴联苯类物质的浓度随营养层次确实呈现显著上升趋势，食物网放大系数为2.60-7.24，和预测结构是吻合的。本研究建立的预测模型对于国际上化学物质生物放大性评价具有重要的科学意义，所采用的研究体系为污染物的食物网传递行为研究提供了方法学的参考。关键词： 食物网动力学；药代动力学；代谢；肝阻碍；构效关系Trophodynamic Behaviors of Toxic Chemicals in Aquatic Food WebWan YiABSTRACTChemical management and control has become issues of great concern in the international communities, since more than one billion of chemicals were currently used in commerce in the world, and more than one thousand new chemicals appeared every year. With the aim of preventing damage to human health caused by pollution from existed or new chemical substances, all the developed countries have related national laws. Since biomagnification is one of the important criteria for chemical identification in laws, governments worldwide are currently trying to assess the biomagnification and hazards of substances. The mechanism of the biomagnification process is still unresolved since trophodynamics can be influenced by many factors including absorption, metabolism, excretion etc. and natural food web cannot be simulated in lab. Now, regulatory authorities judge the biomagnifation of substances mainly based on the chemicals log octanol-water partitioning coefficient (log Kow) or on organisms/water concentration ratios (bioconcentration factors (BCFs). However, trophic transfer of chemical in real food web is not solely lipid-water partitioning, the applicability of current regulatory criteria is only limited to small amount of substances. For example, perfluorooctane sulfonate (PFOS) should not biomagnify based either on the laboratory test with fish or log Kow value, but investigations show high degree of biomagnification through a food web in birds and mammals. So, there is a necessary to build a mechanism model to predict the biomagnification of substances. The present study tried to build a model for predicting the biomagnification potential of chemicals in aquatic food web by clarifying the mechanism using the pharmacokinetics of chemicals in organisms.Bohai Bay is an enclosed inner sea in north China, and highly polluted by the surrounded highly developed cities. Since most of the marine products in Beijing and Tianjin cities are from Bohai Bay, trophodynamics of various pollutants in this bay will help assess the health risks to people living these cities, provide basic data for food safety management, and also help the management of chemical usage and production in these areas. The present thesis firstly studied the trophic relationships among the main species in Bohai Bay by using the carbon and nitrogen stable isotope technologies. Then, the characterizations of trophic transfer for dioxins were investigated in the aquatic food web, and toxickinetics of dioxins in high trophic level animals were also studied to explore the mechanisms of biomagnification. Based on the mechanisms, a structure activity relationship (SAR) for prediction of trophodynamics was established using the trophic magnification factor (TMFs) and metabolism rates of 2-bis-(chlorophenyl)-1,1,1-trichloroethane (DDTs), hexachlorobenzene (HCB), polycyclic aromatic hydrocarbons (PAHs) and dioxins. Finally, the SAR was applied to predict the trophic magnification potential of polybrominated diphenyl ethers (PBDEs), and the prediction results were confirmed by the observed value.Since stable predator-prey interaction is the prerequisite for food web studies, Bohai Bay, the inner sea, was selected as the study area, where phytoplankton, zooplankton, five invertebrates species, eight fishes species and three seabirds were collected. According to the detected carbon isotope ratios, all collected species belong to one food web, and the enrichment factor of nitrogen isotopes ratios were used to construct an isotopic food web model to estimate the trophic levels of each species. According to this model, exact trophic levels of all organisms were estimated to be 1.46-2.10, 1.91-3.32, 2.55-4.23 and 2.98-4.28 for plankton, invertebrates, fishes, and seabirds, respectively. The concentrations of typical biomagnification chemicals (DDTs and HCB) increased significantly with trophic levels, and the TMFs (TMFHCB=2.96，TMFp,p-DDE=3.26，TMFDDMU=3.98) were similar with those reported in other places in the world, demonstrating that, the food web structure is suitable to test the TMFs of organic pollutants.Planar halogenated aromatic hydrocarbons (PHAHs) such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), non- and mono-ortho polychlorinated biphenyls (non- and mono-ortho PCBs) are a group of highly lipophilic contaminants, and belong to the twelve persistent organic pollutants (POPs). Since these chemicals with very high log Kow value were naturally considered to have high trophic magnification potential. However, biomagnification of dioxins were only assessed by laboratory exposure experiment of fish, no researches were conducted to investigate the trophodynamics of dioxin in natural aquatic food webs. In the present study, before the trophodynamic investigations in Bohai Bay, the levels, pollution sources and history of dioxins and organochlorines were studied in sedimentary cores from Bohai Bay (one core) and its adjacent river, the Nanpaiwu River (two cores). Dioxins were detected in all the samples especially in the top layers, indicating that organisms in the bay were still being exposed to the pollutants. And PCP was proved to be the main sources for dioxin based on the congener profiles of PCDDs, PCDFs and co-PCBs, and fates of HCB and HCHs in the three cores. Then, trophodynamics of dioxins in the marine food web were studied. Positive relationships were found between trophic levels and lipid equivalent concentrations of most coplanar PCBs. But lipid equivalent concentrations of low chlorinated 2,3,7,8-substituted-PCDD/Fs did not exhibit statistically significant trends with trophic levels, and lipid equivalent concentrations of high chlorinated 2,3,7,8-substituted-PCDD/Fs and three non-2,3,7,8-substituted-PCDD/Fs declined significantly with increasing trophic levels. Generally, food web magnification is significant for substances with log Kow approximately equal to 5 to 7. To investigate the effects of physicochemical properties on their bioaccumulation in the food web of Bohai Bay, the relationships between TMFs and log Kow were further studied. While no relationship between the TMFs and log Kow were found, the TMFs of non- and mono-ortho PCBs are greatly higher than those of PCDD/Fs. In addition, the TMFs for non-2,3,7,8-substitued PCDD/Fs are lower than those of 2,3,7,8-substituted PCDD/Fs with similar log Kow, indicating that log Kow can not be used as the sole criteria for assessing trophic magnification potential of substances.To clarify the trophodynamic mechanisms of dioxins in the food web of Bohai Bay, pharmacokinetics of dioxins were studied in wild herring gulls collected from Bohai Bay. Tissue distribution results showed preferential accumulation of PCDD/Fs in liver, and of co-PCBs in adipose. The liver/adipose concentration ratios for PCDD/Fs were found to increase significantly with log Kow, providing the quantitative relationship of structure-activity for hepatic sequestration of PCDD/Fs for the first time. As another important factor in pahrmacokinetic studies, the metabolic half-lives of dioxins in the herring gull were further estimated by a fugacity-based bioaccumulation model. The relationships among liver/adipose concentration ratios, half-lives and TMFs indicate that hepatic sequestration resulting in di