水环境中铈的生物有效性和毒性研究

Cerium is the most widely used rare earth element, but the toxicity on organism will be shown in high concentration of cerium. In surface water affected by rare earth industry, hazard risk may occur in organisms due to the exposure of cerium. However, little information is available on bioavailability and toxicity of cerium in water environment, and in the limited studies, the toxicity thresholds were expressed as total cerium concentrations or nominal concentrations without considering the impact of chemical speciation and environment factor. In the present project, based on the experiments of cerium (Ⅲ) and freshwater alga Chlamydomonas reinhardtii, we will investigate the chemical speciation, bioavailability and toxicity of cerium (Ⅲ) to alga under different environment conditions. The impact of environmental factors, such as natural organic matter and competitive cations on chemical speciation and bioavailability of cerium (Ⅲ) will be illustrated, and the media exposure dose and internal exposure dose-effects relationship and toxicity values of cerium will be developed. The quantitative relationships between environmental factors and toxicity values will be established. According to the integrated information on chemical speciation, bioaccumulation and toxic effects, the bioavailability of cerium and the influence of environmental factor and interactive mechanisms will be revealed. The biotic ligand model based on bioavailable forms of cerium will be developed and will be validated and calibrated with the cerium toxicity data from experiments conducted in natural surface water. In this project, the chemical speciation, bioaccumulation and toxicity effect will be combined effectively, and the results will provide reliable basis for development of water quality criteria, regional ecological risk assessment and pollution control of cerium.

铈是应用最广泛的稀土元素，但高浓度铈对生物有毒性。在受稀土工业影响的水体中铈可能对生物存在毒害风险。但铈在水环境中的生物有效性和毒性还不清楚，有限的研究多以金属总量或名义浓度表示毒性值，没有考虑存在形态和环境因素的影响。本项目以三价铈为研究对象，莱茵衣藻为受试生物，研究不同环境条件下(天然溶解有机质和竞争性阳离子)铈的存在形态、生物有效性和毒性，阐明环境因素对铈的化学形态和生物有效性的影响，建立分别基于外暴露和内暴露铈的剂量-效应关系和毒性值及其与环境因素的定量关系，从化学形态、生物累积和毒性多角度揭示铈的生物有效性及环境因素的影响和作用机理。建立基于有效态铈的生物配体模型，利用实际水体中铈的毒性数据验证和优化模型的预测能力。所获成果将化学形态、生物累积和毒性效应有机地结合起来，可以更加准确地认识铈的生态毒性，为铈的水质基准制定、区域生态风险评估及污染控制提供科学依据。

铈是应用最广泛的稀土元素，但高浓度铈对生物有毒性。在受稀土工业影响的水体中铈可能对生物存在毒害风险。但铈在水环境中的生物有效性和毒性还不清楚，有限的研究多以金属总量或名义浓度表示毒性值，没有考虑存在形态和环境因素的影响。本项目以三价铈为研究对象，研究了不同环境条件下(天然溶解有机质和竞争性阳离子)铈的生物有效性和毒性，从化学形态、生物累积和毒性多角度揭示铈的生物有效性及环境因素的影响和作用机理。结果显示，pH为6的时候，莱茵衣藻对铈的最大吸收通量为1.17×10-14 mol cm-2 s-1，稳定常数为1.48×10-8 M。三种稀土元素以及Ca2+和Mg2+的添加显著降低铈的生物吸收通量，表明这些金属离子对铈的生物吸收均具有显著抑制作用，具有相同的吸收通道和机制，存在竞争作用。柠檬酸和胡敏酸含量的增加使得藻细胞内铈的含量降低，但是在Ce3+浓度较低的情况下生物吸收通量高于仅是自由离子存在的情况，说明有机酸络合物可能也具有生物有效性。在铈浓度为5×10-8 M时可以影响莱茵衣藻相关基因的转录水平，且共存金属存在影响。所获成果将化学形态、生物累积和毒性效应有机地结合起来，可以更加准确地认识铈的生态毒性，为铈的水质基准制定、区域生态风险评估及污染控制提供科学依据。