| This study selected a mine tailings dam downstream of paddy soil and the surrounding soil as the research object, through the fixed-point collected in field soil samples in the study area, using laser-induced fluorometry for the analysis of distribution characteristics of uranium tailings in common long-lived radionuclides uranium content and the research of uranium in soil; using sequential chemical extraction for the analysis of the forms of uranium, on uranium speciation,using total prediction method and indicator plant method for the analysis of their bioaccessibility. The following results were obtained:(1)The uranium in Soil content distribution characteristic research shows that in the range of soil depth, uranium content in soil decreases with the increase of depth on the whole, average uranium content in surface soil was 15.73mg/kg; average uranium content in rhizosphere soil was 16.58mg/kg; average uranium content in 20 cm depth of soil was5.38mg/kg; average uranium content in the 40 cm depth soil was 4.44mg/kg; average uranium content in the depth of 60 cm soil was 4.05mg/kg; average uranium content in80 cm soil was 4.49mg/kg; average uranium content in 100 cm depth of soil was 3.61 mg /kg, the content uranium in the rhizosphere soil was highest; The distribution of uranium content in surface soil and rhizosphere soil is consistent, which is relatively close to the pollution source; in time, it shows that the first rhizosphere soil average uranium content(9.02 mg / kg)was higher than the second rhizosphere soil average uranium content(5.85 mg / kg) about 0.54 times.(2) The speciations of uranium in soil showed that in depth, different specimen or within the same sample, the speciation of uranium distribution characteristics are obvious differences,and rhizosphere soil of each speciation were significantly different from other levels of soil; in plane, the average percentage of all speciations of uranium in the surface soil was:residuals(31.07%) > carbonates(25.41%) > amorphous Fe Mn oxides /hydroxides(20.06%) > organic bounds(17.83%) > exchangeable(including water soluble)(3.69%) > crystal Fe Mn oxides / hydroxides(1.95%); the average percentage of all speciations of uranium in rhizosphere soil was:carbonates(30.30%) > residuals(24.12%) >organic bounds(21.09%) > amorphous Fe Mn oxides / hydroxides(16.47%) > exchangeable(including water soluble)(6.16%) > crystal Fe Mn oxides / hydroxides(1.87%), various speciations of surface soil and root rhizosphere soil of uranium content distribution trends are basically the same; in general, residuals(31.46%) >carbonates(25.34%) > organic bounds(19.02%) > amorphous Fe Mn oxides / hydroxides(16.58%) >exchangeable(including water soluble)(5.32%) > crystal Fe Mn oxides / hydroxides(2.3%);exchangeable(including water soluble) uranium, carbonates of uranium, organic bounds of uranium in rhizosphere soil than in nonrhizosphere soil higher and other speciations is lower than non rhizosphere soil.(3) Study on the bioaccessibility of uranium in soil samples shows that the activity of uranium accounted for 30.66% of the total uranium, the potential activity of uranium accounted for 35.60% of the total uranium, the inert state of uranium accounted for 33.76%of the total uranium, that is about 65% of the uranium on the environment constituted threats and potential threats, it mainly through the bioavailability factors,migration factors and conversion factors reflected the biological availability of uranium in the study area, the average bioavailability factors of the uranium in the soil of the study area was 55.40%, the average migration factors was 5.32% and the average conversion factors was 3.28%.Compared to the same sampling points, and the conversion factors of uranium was different in plant, the conversion factors of grass(3.13%) is higher than that of rice(1.70%). |
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