砷矿区食物链中砷的生物富集与转化特征

Arsenic is ubiquitous in the environment and biota. Arsenic can be accumulated in food chain, rendering potential hazards to ecological system and human health. The toxicities of arsenic depend largely on arsenic speciation, which is, mostly related to the biotransformation. Arsenic tend to be accumulated in the lower level of food chain, while whether methylated arsenic may be increasingly accumulated along the food chain is not determined; in addition, biota can uptake and retain arsenobetaine and arsenocholine inside their bodies, however whether they are the products of arsenic metabolism remained unknown. In this project, the Shimen arsenic mine will be chosen to be the investigated area. Comparison of the food web between high arsenic level area and the control area (arsenic clean) will be conducted, especially on the bioaccumulation and biotransformation characteristics in the typical food chains. The systematic identification of fauna, incorporating with nitrogen and carbon isotope classification method, will be used to determine the trophic levels in the food chains. Keynote species will be analyzed using the “Ecopath with Ecosim” software, and a two sources of carbon isotope mixing model will be used to trace the food sources of the biota. Arsenic bioaccumulation and biotransformation will be characterized in the typical food chains containing keynote species in the field. Laboratory experiments employing the same or similar invertebrates as the keynote species will be conducted to further analyze the arsenic accumulation, transformation, the antioxidant responses as well as index of arsenic toxicities, e.g., glutathione and metallothionein contents. Finally, data obtained from field survey and laboratory experiments will be combined to elucidate the characteristics of arsenic bioaccumulation and biotransformation in the typical food chains in the arsenic mining area. The results are expected to contribute to understanding the sources of various arsenic species in terrestrial organisms with the relationship of arsenic transformation and bioaccumulation within food chains.

砷在地表环境和生物体中普遍存在，并可在食物链中不断富集，对生态系统和人群健康产生危害。砷的毒性很大程度上决定于其存在形态，并与生物转化作用紧密相关。砷更多地富集于食物链的底端，但甲基砷是否会由于其亲脂性而沿食物链向上不断富集，仍不确定；生物可通过捕（摄）食存留砷甜菜碱和砷胆碱于体内，但其是否可由陆生生物体内生物转化而来也不清楚。本项目选择石门雄黄矿区，通过高砷与清洁对照区对比、典型食物链砷富集与转化迁移行为对比、动物系统分类结合氮同位素食物链营养级精确定级、食物链关键种分析、食物链生物碳同位素混合模型食源分析、典型食物链关键种室内模拟实验研究、生物体砷胁迫反应参数测定等多种技术途径展开深入研究，围绕以关键种为代表的典型食物链，以生物体内的砷的生物甲基化为重点，阐明砷污染区典型食物链中砷的生物富集与生物转化行为。成果有望揭示陆生生物体内不同形态砷的来源及其与生物转化与食物链富集之间的关系。

砷是一种有毒有害并致癌的元素，而砷在陆生生物体沿食物链中的生物富集与转化行为知之甚少。本项目通过对石门雄黄矿区陆地和河湖水系环境与生物多介质采样，应用碳氮稳定同位素确定生物营养级，构建陆地与水生食物链，同时结合室内高效液相色谱-等离子质谱和同步辐射X射线吸收光谱进行砷形态分析，初步揭示了砷在陆地生态系统和水生生态系统食物链中的富集与转化过程。结果表明：受到砷矿的开采和冶炼活动的影响，矿中心区和尾矿堆积区附近砷污染最为严重，随着离开中心区距离的增加砷污染程度明显降低。陆地生态系统中，除超富集植物蜈蚣草和大叶井口边草外，不同介质中的砷含量基本表现为：土壤>蚯蚓>植物和凋落物。土壤、蚯蚓和凋落物三者之间的砷含量两两显著正相关，显示砷矿区陆生生态系统砷的循环富集关系。植物和凋落物中的砷形态基本一致，主要为无机砷，并含有少量的有机砷，指示植物分解后砷形态的继承关系。蚯蚓中的砷除无机砷外，仅含有少量的AsB。而土壤、植物和凋落物中基本不含有AsB，由此推断蚯蚓体内AsB主要来自于蚯蚓自身对砷的转化作用。本研究中鸟类和家养鸡中的砷含量明显高于其他研究报道，说明长期的砷污染仍会导致高等生物也一定程度地富集砷。水生生物，包括淡水鱼类、底栖无脊椎生物、两栖类青蛙等，砷含量范围为0.60-45.75 mg/kg，受到多种因素的影响。生物体中的砷含量水平随着水体砷含量的增加而增加。且不同水生生物对砷的富集能力不同，底栖生物>淡水鱼类。对淡水鱼类而言，鱼皮中的砷含量高于肌肉组织中的砷含量。水生生物中的δ13C值变化范围为-30.59‰— -15.07‰，且同种生物在不同区域的δ13C差异较大，反映矿区水生生物食物来源有较大的区域差异性。水生生物的δ15N值变化范围为4.31‰-12.98‰，表现为滤食性<植食性<杂食性<肉食性，与食物链生物营养级一致。水生生物中砷含量与δ15N无显著相关关系，指示水生生物对砷的富集并无放大效应。水生生物中主要以有机砷为主（49-100%），包括大量未知的有机砷形态。水生生物中无机砷As(III)和As(V)的比例均与砷含量呈明显的正相关关系。甲基砷比例与δ15N呈正相关关系，表明水生食物链高营养级生物具有较高的砷转化能力。