Aquatic Ecological Toxicity Studies Of Typical Rare Earth And Their Associated Elements

With the development and utilization of rare earth elements, which has been expanding its rare earth industry in China, but but existing in the development of rare earth industry in illegal mining, excessive exploitation, ecological environment destruction and problems such as wasting resources, rare earth reserves decline rapidly, the environmental pollution problem is increasingly outstanding in the process of production. Rare earth elements and their associated elements with the mineral exploration into the water ecosystem, inevitable damage to water ecological system, Because of the symbiosis of rare earth elements and thorium, the essay focuses on the research of rare earth element Ce and its associated elements Th to small crustacean in the water ecological system biological toxicity studies of Daphnia magna. Ce element is another form of rare earth nanomaterials CeO2 also more and more used in modern life, but also to the aquatic ecological toxicology of rare earth nanomaterials CeO2 were studied.The actinide, thorium(Th), and the lanthanide, cerium(Ce), are thought to be chemically similar and to have comparable toxic properties on organisms. In the present study, acute(24- and 48-h) and chronic(21 d) toxicity of Th(NO3)4 and Ce(NO3)3 to a freshwater crustacean Daphnia magna were investigated. In the exposure medium(modified reconstituted water, MRW), Ce was present as soluble ions, while all of Th was present as crystalline ThO2. EC50 values at 24 and 48 h were 7.3 and 4.6 μM for Th, and 16.5 and 10.5 μM for Ce, respectively, indicating that Th was more toxic to Daphnia magna than Ce regardless of their chemical forms and bioavailability. On the other hand, the chronic toxicity for Th, including clutch sizes, age at reproduction, and length of the first segments of the antenna of the exuviae for the three brood neonates were all similar to those for Ce. More attention should be paid on the potential detrimental effect of Th in the form of particulate ThO2. To the best of our knowledge, this is the first time to compare the aquatic toxicity of thorium and cerium according to their actual chemical species in the exposure medium.The wide use of nanomaterials may bring potential influence on the environment and human health. In accordance with the standard OECD Guidelines for the testing of chemicals(OECD 201 and 202), we studied the ecotoxicity of CeO2 nanoparticles(nCeO2) to the green algae(Chlorella pyrenoidosa) and water-flea(Daphnia magna). With the increase of concentration and time,the growth of chlorella cell was inhibited gradually under the stress of nCeO2, at the same time the level of chlorophyll decreased, while the ROS level increased. The 96 h EC50 of nCeO2 on the growth of Chlorella pyrenoidosa was 30.4 mg/L. In contrast, the 24 and 48 h-EC50 of nCeO2 on Daphnia magna were 430.2 and 142.7 mg/L, respectively. These results suggested that the sensitivity was different when exposed to nCeO2 among the different species, with chlorella cells being more sensitive than Daphnia magna. The majority of Ce in Daphnia magna was present as Ce(IV), of which 3% was transformed into Ce(III) approximately. Further research on the ecotoxicological mechanisms of such CeO2 nanoparticles is warranted in order to minimize the adverse ecological effects.