Migration And Distribution Of Radionuclide In Uranium Tailing Soil And The Effects Of Radionuclide On Soil Microbial Diversity

With the support of National nuclear facilities decommissioning and radioactive waste management key scientific research projects (14ZG6101), we choose the whole soil beach face in some big uranium tailings of China as study object. Fix on a regular basis to collect soil samples in different sites seven times a year. Soil uranium, thorium, radium and potassium contents are analyzed so as to study the concentration distribution characteristics and the migration patterns of these four radionuclides in soils. We subdivide study area according to the concentration of uranium, analyze the effects of uranium tailings on soil quality by using soil physics and chemistry nature, soil enzyme activity, soil respiration, microbial numbers and microbial diversity and analyze the adaptive mechanism of soil microbial under radioactive environment by using metagenomic technique. Scores of soil evaluation indices are weighted according to multivariate statistical analysis which are used to comprehensive evaluate soil quality in different blocks and depths. So we can screen and build evaluation system of radionuclide environment in uranium milling in order to provide the basis for radionuclide migration, governance and safety evaluation of uranium tailings.The main conclusion as follows:(1) Concentrations of uranium and thorium in different blocks in uranium tailings are more than the standard values. Correlation of thorium and radium is significant difference (PCC= 0.69, p=0.04) and correlation of radium and potassium is also significant difference (PCC= 0.88, p<0.01). Concentrations of thorium, radium and potassium in soil outside uranium tailings are close to natural background levels and national average levels and slow down with the distance between sampling sites and uranium tailings increase.(2) Soil pH in different blocks is all acidic; Soil organic matter contents increase with the concentration of uranium decrease; Soil total carbon contents increase with the concentration of uranium increase; Cation exchange capacity of soil increase with the concentration of uranium decrease; Nutrient characteristic in soil increase with the concentration of uranium decrease; Soil respiration and enzyme activity increase with the concentration of uranium decrease and the differences are significantly (P<0.05). Under the effect of special ecological environment and complex pollutants, soil environmental quality gets worse increase with the concentration of uranium.(3) The order of microbial population in moderate and low concentration block is bacteria> actinobacteria> fungi while the population of actinobacteria in high concentration block is less, the order of microbial population in this block is bacteria> fungi> actinobacteria. Soil microbial quantity increases with the concentration of uranium decrease. The microbial population in different concentration blocks was different with seven domain strains in low and moderate block, and four in high block. Furthermore, in each sample site, Proteobacteria was the most dominant flora according to GenBank database. For diversity analyses, Actinobacteria and Proteobacteria were the dominant phyla in radioactive soils by metagenomic library which proved radionuclide can have a significant impact on microorganism. Soil microbe quantity and diversity have a big change with the concentration of uranium increase which can provide reference for uranium tailings safety evaluation.(4) Proportion of metabolism of other amino acids (e.g. beta-alanine, taurine and hypotaurine) was significant lower in radioactive soils than in uncontaminated soils, whereas membrane transport was the opposite which might be two of reasons causing heavier uranium contamination. Additionally, KOs was mostly enriched in ABC transporters, carbon metabolism and two-component system which might be associated with the probable mechanism of bacteria that could tolerate or degrade the radioactive substance.(5) The average weighted of each soil evaluation index in uranium is soil physicochemical properties index>microbial adaptation mechanism index>microbial activity index> pollutant distribution index>microbial diversity according to from big to small. These results suggest that soil physicochemical properties index and microbial adaptation mechanism index in pollution environment can be environmental risk assessment factors to effectively evaluate soil quality in uranium milling. The results is C1>C2>C3>A1>A3>A2 after comprehensive sequencing of indicators which indicated radionuclide has significant effects on soil quality. Soil quality gets worse sharply with the increase of radionuclide. Surface soil quality is better than soil in middle and subsurface soil in different block. Soil quality gets worse with radionuclide moving downward.