【作者】 胡勤海；

【导师】 朱荫湄；

【作者基本信息】 浙江大学 ， 环境工程， 2004， 博士

【摘要】 我国是世界上稀土储量最多（占世界稀土总储量的41.3％）、应用范围最广、应用量最大的国家。随着稀土在各个领域的广泛应用，稀土元素及其化合物势必将大量进入环境，特别是通过工业废水排放和农田地表径流等进入水体的稀土不断增加，对水生生态环境带来潜在的负面影响，并有可能通过食物链而影响人体健康。虽目前国内外已对稀土的水生态环境效应进行了一些研究，但重点主要集中在水体中稀土背景值、稀土海洋地球化学以及稀土对水生生物的毒理效应方面的研究，而有关稀土对水生生态系统生物群落结构及组分的影响、在水生态系统中迁移分配的动力学行为及食物链中的积累等生态效应研究仍较少。本论文通过实验室培养及模拟试验，就几种代表性外源稀土元素对淡水藻类种群结构和一些水生动植物生长的影响，以及外源稀土在水生态系统各组分中的迁移、分配和积累规律进行了试验研究，以期了解外源性稀土在水环境中的生态效应机制，为合理使用稀土、制订废水稀土排放标准及水环境质量标准等进一步提供科学的理论依据。论文主要研究结果如下： 1、外源稀土对水藻种群结构影响研究结果表明：（1）稀土元素对水藻种类数量、个体总数及代表性藻属（蓝纤维藻、舟形藻和小球藻等）的个体数量等均有一定的影响，并存在较一致的规律。其中轻稀土元素La、Nd及混合稀土在低浓度（1mg/L）处理时，试验初期（1～3d）对水藻种类数量、个体总数及代表性藻属的个体数量等略有刺激增长作用或与对照差异不大，但随处理时间的延长，其抑制作用逐渐呈现；而其较高浓度处理（5mg/L）及重稀土元素Y处理时，则抑制作用明显。（2）外源性稀土处理浓度与水样中藻类的多样性指数之间存在着较好的负相关性。（3）轻稀土元素La、Nd对藻类的毒性较重稀土元素Y要小；单一稀土元素对藻类的毒性略大于混合稀土元素。 2、外源稀土对小球藻（Chlorella ellipsoidea）及金鱼藻（Ceratophyllum demersum）生长生理影响研究结果表明：（1）中稀土元素Sm和重稀土元素Y处理浓度与小球藻生长量（以OD值间接表示）之间存在明显的负线性相关关系；在稀土一定处理浓度范围（Sm为2～40mg/L，Y为2～20mg/L）内，小球藻生长量随培养时间的动态变化符合多项式相关关系；统计计算得Sm和Y对小球藻的半致死浓度LC₅₀分别为41.36mg/L和22.57mg/L，表明Y对小球藻的毒性大于Sm。（2）La及混合稀土对小球藻叶绿素a含量的影响表现为短期内低浓度（成Zm岁L）的刺激增长作用及后期和高浓度的抑制作用;当稀土处理浓度)50 mg/L时，小球藻生长明显受阻，叶绿素a含量趋于下降;小球藻对稀土的安全耐受限值为Zm留L。（3） La和Nd对高等沉水植物金鱼藻叶绿素总量及抗坏血酸氧化酶、过氧化氢酶、过氧化物酶等酶活性有一定影响，表现为短期内低浓度（2 mg几一10m以L）的刺激促进作用和长期、高浓度（妻50m留L）的抑制作用;金鱼藻对低浓度稀土有较强的吸收富集能力，其富集量随时间变化的关系可由以下指数式表明:La为Y=123.04t0·!‘72（r=0.9644*），Nd为Y=117.o4t“·’388（厂0.9559**）。（4）电镜切片进一步揭示，sm和Y高浓度（分别为som以L和30m创L）处理情况下可进入小球藻细胞内部，对其叶绿体等结构影响显著，与对照组相比，明显可见其计十绿体片层结构显条索状排列或松散排列，细胞结构破坏;高浓度La和Nd（50m留L）对金鱼藻叶细胞叶绿体结构也有明显的破坏作用。 3、外源稀土在水一底泥中的环境化学行为研究结果表明:（l）进入水溶液的外源性稀土元素La可通过悬浮颗粒吸附、沉降等途径而迅速进入底泥中;水溶液中稀土元素La的衰减符合一级动力学方程:9.9呵ml处理组为Ct=Co砂29溯（卜0.5574*），47.6林g/ml处理组为et=e。e一o·’9，6‘（r=o.9739**）。（2）溶液pH对底泥中稀土La的溶出影响较大，试验初期，在酸性条件下La的溶出量最大，其次是碱性，最后是中性偏酸性;试验第四天起，溶出的La又重新沉积至底泥中去，但沉降速率明显趋缓。（3）在缺氧还原情况下（Eh落loomV），底泥中稀土La的溶出量明显高于一般（Eh二ZoomV）及好氧（Eh）250mV)状态，这主要与还原条件下铁锰氧化物结合态的稀土的还原溶解有关;溶出的La在实验第2天后又J「始重新沉积至底泥中去并渐趋平衡。（4）底泥中稀土La的存在形态按比例依次为:残渣态、铁锰氧化态、碳酸盐结合态、有机结合态、交换态和水溶态。 4、外源稀土在模拟水生态系统中分配动力学研究表明:（l）稀土元素La进入模拟水生态系统后，其水溶液中可溶态数量迅速减少，主要为悬浮物所吸附絮凝或水解络合而沉降，并被水生动植物及底泥所吸附、吸收。（2）金鱼藻（Ceratop妙llumdemersum）对La有较强的富集能力，主要通过枝计十表面吸附、吸收而富集;螺蜘 （Bella梢lya pur沂cala）对La也有一定的富集，并主要分布于肠、壳中，螺头（肉）中积累相对较少;草鱼（OenoPharyngodon idellus）对La的富集能力相对较弱，进入鱼体的La主要集中在鳃、内脏、鳞及头、骨中，肌肉中积累量较少;按质量计，刀叮l稀土元素La在模拟水生态系统各部分中的积累量依次为:底泥>金鱼藻>螺妙岭草鱼;各水生生物对稀土La的生物富集因子（BCF）依次为:金鱼藻>螺更多还原

【Abstract】 China ranks first in the world in rare earths reserves (make up 41.3 percent of the total reserves) and in usage areas, quantities of rare earths. Along with the extensive application of rare earths in many areas, a large quantity of rare earth elements and associated compounds enter the environment. The predominant pathway that rare earths enter the water is through from industrial discharge and runoff from farmland, which would bring the potential negative effects to aquatic ecosystem and health of human by means of food chain. Many studies on aquatic ecoeffects have been taken, mainly focus on background values of rare earths in water, marine geochemistry of rare earths and toxicology to hydrobioes, but few on effecs of rare earths on community of creatures and species of aquatic ecosystem, the distribution kinetics behaviour and accumulation in food chain of aquatic ecosystem. In this paper, it was studied that effects of some representative external rare earth elements on community of algae and some hydrobioes, and the rules of transportation and distribution of them in aquatic ecosystem by means of laboratory culture and simulation experiments. The main results are as follows:1. The effects of external rare earth on community of algaes were studied. The results indicated that the lower concentration (1mg/L) of La, Nd and mixed rare earths stimulate slightly the numbers of species and individuals of total algaes and some representative algaes in the early days (l~3d) of experiment, but which were inhibited apparently in the later period of experiment and as the concentration of rare earths increased or under treatment of Y. There were apparently negative interrelation between the concentrations of rare earths and the diversity index of algae. It was implicated that the toxicity of Y was greater than that of La and Nd, and the toxicity of individual rare earth element was slightly greater than that of mixed rare earths.2. The effects of external rare earth on growth and physiological of Chlorella ellipsoidea and Ceratophyllum demersum were studied. The results implicated that there were apparently negative linear interrelation between the concentrations of Sm, Y and the numbers (representated with OD) of Chlorella ellipsoidea, which would best be described as polynomial interrelation at 2-40 mg/L concentration range of Sm and 2-20mg/L of Y. The LC50 of Sm and Y was respectively 41.36 mg/L and 2.57 mg/L by statistics, which also indicated the toxicity of Y was greater than that of Sm. In the early period of experiment, it was shown that the lower concentration (<2 mg/L) of La and mixed rare earths also stimulated the chlorophyll(a) content increasing, but inhibited apparently in the later period of experiment and under higher concentration(50 mg/1) of rare earths, which implicated that the value of rare-earths-resisting of Chlorella ellipsoidea was 2 mg/L. It was also shown that the content of chlorophyll(a) and the activities of ascorbic acid oxidase, catalase, peroxidase of Ceratophyllum demersum would increase in early days of experiment under lower concentrations (2 mg/L~10 mg/L) of La and Nd, but inhibited apparently in the later period and under higher concentration(50 mg/1) of rare earths. The Ceratophyllum demersum had more stronger ability of accumulation to rare earths in lower concentration, and the relation of accumulated quantity of rare earths with time could be described as formula: Y=123.04 t 0.1172 (La) and Y= 117.04 t 0.1388 (Nd) . The electron microscope photogs further indicated that Sm and Y could enter inside of Chlorella ellipsoidea cell under higher concentration (respectively 50 mg/L and mg/L) and destroyed the ultrastructure of chloroplast apparently, which same as that of La and Nd under concentration of 50mg/L.3. The distribution of external rare earth element between water and benthic soil were studied. The results indicated that La was easy to deposit in benthic soil by adsorption and deposition of suspended particles in water, and decline of La in water solution conform更多还原