The Biological Effects Of Rare Earth Yttrium And Its Response To Ore Leaching Ammonium Sulfate

Increasing concerns have being raised to the pollutions caused in the dealing processes of rare earth such as mining, smelting, purification and so on. Consequently, fundamental researches on biological effects of rare earth elements as well as their potential influences to environment are needed urgently, especially with the increasing demand and development of rare earth elementals. Among researches, the rare earth accumulation and their biological effects in soil are paid more and more attention. In the present work, we carried out systematic study of biological effects of Yttrium on rice and earthworms, respectively. The sources of investigated Yttrium include exogenous Y(NO3)3, Longnan yttrium-rich rare earth ore mining soil and (NH4)2SO4contained yttrium-rich rare earth soil. Through modern analysis techniques, we studied chemical speciations of Y and their contents in soil and enrichment of Y in biology. Furthermore, via technique of enzyme biological labeling, biological effects of yttrium under presence of (NH4)2SO4and concerning mechanism and response relationships were investigated and discussed. The study provide fundamental understanding of the toxicity and biological effects of yttrium-rich rare earth ore mining soil and benefit the environmental protection and friendily application of rare earth elements1. Through study of biological effects of exogenous Yttrium, it was found that suitable concentrations of Y in soil promote the growth of rice, improves the trend of rice biomass, chlorophyll, protein content, enhance the activity of antioxidant enzymes (SOD, POD and CAT), and decreases the content of malondiahyde (MDA). However, high concentrations of Y inhibit the growth of rice and even have toxic effects on the growth of rice. The most suitable concentration of Y(NO3)3is100mg/kg. There existed a linear relationship between the enrichment of yttrium in rice and the content of yttrium in soil, and the correlation coefficient R2is0.9982.2. Study of acute toxicity of Y on earthworms (Eisenia) indicated that values of LC50were0.18g/L and1.08g/kg obtained from approaches of contact filter paper test and natural soil test, respectively. Therefore, the toxicity of Y(NO3)3to earthworms is in low level, and the toxicity of yttrium nitrate in natural soil test is lower than that of filter paper test. ICP-AES analysis indicates that there are correlated relationships among concentration of yttrium nitrate and duration of contamination, mortality rate of earthworms, and the bioaccumulation.3. Study of biological effects of Yttrium with the presence of (NH4)2SO4demonstrated that content of (NH4)2SO4has certain relationships with the biological effects of yttrium. Under the stress of (NH4)2SO4, low concentrations of exogenous Y can increase the activities of antioxidant enzymes (SOD, POD and CAT), reduce the content of MDA, thus alleviate the stress of (NH4)2SO4to rice. The best concentration of Y is100mg/kg, under which conditions the all index properties of rice increased to maximum except the height of plant; while if the concentration increased to500mg/kg, the total weight of rice, height of plant and weight of the roots all decreased. Under the stress of (NH4)2SO4, the enrichment of yttrium in rice is slightly higher than the relatively cleaner soil group, which also has a linear relationship with the concentration of Y in soil with a correlation coefficient R2of0.9884.4. The leaching agent (NH4)2SO4in mine soil has negative effects to rice biomass, contents of chlorophyll and protein; it also inhibits activities of rice antioxidant enzyme (SOD, POD, CAT) and increases malondialdehyde content. When the content of (NH4)2SO4was increased to3.0g/kg, rare earths contents in these four chemical speciations, enrichment of rare earth in both whole rice and rice roots all reached to maximum, indicating the detrimental effects of (NH4)2SO4to the growth of rice.