Presentation Soil-soil solution partitioning coefficient of Mn-54 in Japanese agricultural fields

Uchida, Shigeo  ,  Tagami, Keiko  ,  Ishikawa, Nao

Manganese, an essential nutrient to plants, is observed to be deficient in some neutral and alkaline soils, while plants grown on some acid soils absorb the element to toxic levels. The uptake mechanisms through roots are well studied and the form is Mn(II). Thus the estimation of bioavailable Mn fraction is of important where deficient/excess Mn soil was observed. From radioactive waste management view point, Mn is of interest because radioactive Mn-54 (half-life: 312.1 d) is produced by neutron activation of iron in a nuclear power plant. When the radionuclide released to the environment, it is probable to be taken up by plants from soil. Therefore, it is necessary to provide environmental parameter for radiation dose assessment especially considering plant available form Mn, that is Mn(II). In this study, soil-soil solution partitioning coefficients (Kds) of Mn-54 were measured using 63 soil samples collected from rice paddy fields throughout Japan. Air-dried and sieved (<2 mm) soil samples were used; a 3-g of soil was transferred into a polypropylene bottle (50 mL) and 30 mL of Milli-Q water was added. After one day mixing in a shaker, the mixture was added with a known amount of Mn-54 and shook for 7 more days. The supernatant was taken and passed through a 0.45-µm filter then measured the radioactivity with an NaI(Tl) scintillation counter. The Kds were obtained by concentration of Mn-54 in soil (Bq/g) divided by that in soil solution (Bq/mL). The Kd values ranged from 140-140000; these data were used for statistical analysis to see the correlations between stable Mn concentrations in rice grain, soil and soil solutions. This work has been partially supported by the Agency for Natural Resources and Energy, the Ministry of Economy, Trade and Industry (METI), Japan.

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