Study On Effects Of External Rare-earths On Aquatic Ecosystem

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...