稀土元素的低剂量混合暴露已成为一种普遍现象。但对水体中稀土元素混合物的联合毒性作用机制仍认识不清，对其水质基准的制定和生态风险评估的瓶颈效应日益突显。项目以镧、铈和镝及其二元和三元混合物为研究对象，以莱茵衣藻为受试生物，开展稀土元素混合物的联合毒性效应研究。利用单细胞ICP-MS研究藻细胞内稀土元素的累积及浓度分布，阐明稀土元素混合物对莱茵衣藻的生物有效性。研究混合物对莱茵衣藻的生长、光合效率、脂质过氧化、抗氧化酶活性及基因表达的效应，分别建立基于生物有效态的外暴露剂量和内暴露剂量与毒性的定量关系，应用CA和IA模型评价混合物毒性。同时开展实际水体毒性实验，多角度系统揭示稀土元素混合物对莱茵衣藻的联合毒性效应及作用机制。所获成果基于金属的生物有效性，从细胞和分子水平研究混合物的毒性，更加准确揭示稀土元素的联合毒性作用机制，为稀土元素水质基准的建立、生态风险评估及污染控制提供科学依据。

The exposure of rare earth elements (REEs) mixture with low concentration has become a universal phenomenon in environment. However, little information is available on the joint toxicity of mixture of REEs and mechanism, which has hampered the development of water quality criteria and assessment of ecological risk of REEs. In the present project, the toxicity of lanthanum, cerium and dysprosium and the joint toxicity of their binary and ternary mixtures to Chlamydomonas reinhardtii will be investigated. The bioaccumulation and distribution of concentration in cells will be determined by using the single cell ICP-MS and bioavailability of REEs mixture will be illustrated. We will investigate the effects of REEs mixture on growth rate, photosynthesis efficiency, lipid peroxidation, activity of antioxidant enzymes, and expression level of genes of the microalga, and develop the media exposure dose and internal exposure dose-effects relationships, respectively. Then the concentration addition model and independent model will be used to assess the joint toxicity of mixtures based on the toxicity data with single element. The toxicity experiments with the water collected in field polluted by REEs will also be conducted. Based all of the results together, the joint toxicity of REEs mixture and mechanism to Chlamydomonas reinhardtii will be systematically revealed. In this project, the toxicity is expressed by using bioavailable species of metals, and studied at the cell and molecular levels, in which the mechanism of joint toxicity of REEs can be revealed accurately. The results will provide reliable basis for development of water quality criteria, regional ecological risk assessment and pollution control of REEs.