Search

This study examined the radiocesium (RCs) interception potential (RIP), cation exchange capacity (CEC), total organic carbon (TOC) content, and adsorption species in soils and minerals by using extended X-ray absorption fine structure (EXAFS) spectroscopy. The RIP related to Cs(+) adsorption by frayed-edge site (FES) has often been used to measure the mobility and bioavailability of RCs in the environment. This study found that the presence of organic matter (OM) can reduce RIP to a certain extent. The adsorption amount (=Q(T)) in soil was obviously correlated to RIP at a small [Cs(+)] region, whereas a linear relationship between Q(T) and CEC was observed at a large [Cs(+)] region. Both the inner-sphere (IS) and outer-sphere (OS) complexes of Cs(+) were observed through EXAFS at a molecular scale. The linear correlation between log (RIP/CEC) and the ratio of the coordination number (CN) of IS (=CNIS) and OS (=CNOS) complexes noted as CNIS/(CNIS + CNOS) suggested that the ratio of CN is very sensitive to Cs(+) adsorption species with variable RIP and CEC. The adsorption species of Cs(+) in soil was mainly dependent on the clay mineral content of soil. RIP was affected not only by FES but also by other strong adsorption sites, such as the interlayers and cavities identified as the IS complex in EXAFS analysis. Findings indicated that the EXAFS approach is a powerful and efficient tool to explore the behavior of Cs(+) in a given environment., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The concentration of radiocesium ((134)Cs and (137)Cs) in agricultural fields around Fukushima Dai-ichi Nuclear Power Plant (FDNPP) was elevated after the accident in March 2011. Evaluation of soil properties that influence phytoavailability of radiocesium is important for optimal soil management to minimize radiocesium transfer to crops. In this study, soybean grain and soil samples (0-15 cm) were collected from 46 locations in Fukushima Prefecture in 2011, and (137)Cs concentrations were measured. (137)Cs concentration ranges were 11-329 Bq kg(-1)-dry in soybean grain samples, and 0.29-2.49 kBq kg(-1)-dry in soil samples. The radiocesium interception potential (RIP) values in the soil samples ranged from 0.30 to 8.61 mol kg(-1). RIP negatively correlated with total carbon content and oxalate-extractable Si and Al + 1/2 Fe in the soils, suggesting that soils rich in organic matter and poorly crystalline clays tended to have lower RIP in this region. The soil-to-plant transfer factor for (137)Cs, analyzed in relation with various soil characteristics, varied by two orders of magnitude and was significantly negatively correlated with RIP and exchangeable K concentration in soil. The results show that RIP is useful for evaluating the efficiency of radiocesium transfer from soil to plants in this region., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Direct deposition of radioactive material onto crops is one important pathway for safety assessment of radionuclides released from nuclear facilities. Foliar uptake of Cs by radish (Raphanus sativus L. cv. Redchim) was studied by applying droplets of Cs solution (CsCl or CsNO3) on an upper leaf surface. The uptake of Cs was strongly affected by counter anions of Cs in the applied solution. Approximately 80% of Cs was absorbed for CsCl solution, while only 20% was absorbed for CsNO3. The partition of absorbed Cs between leaf and root tuber was quite similar for both Cs compounds, which indicated that behavior of the absorbed Cs in radish was the same for both.

Following the Fukushima Daiichi Nuclear Power Plant accident, extensive research has been conducted on the dynamic distribution of radiocaesium in large reservoirs. However, studies on small ponds, particularly those used for rice cultivation, are limited. This study analyzed the vertical water quality profiles, including the bioavailable Caesium-137 (137Cs) in an irrigation small pond classified as discontinuous cold polymictic based on water mixing type, and subjected to a high (2.0 MBq m−2) deposition of 137Cs and evaluated their potential risk associated with agricultural use. During 2014–2015, the suspended and dissolved concentrations of 137Cs in the pond water ranged from 0.10 to 7.7 Bq L−1 and 0.03–0.88 Bq L−1, respectively. The elution of dissolved 137Cs from the bottom sediment occurred only during the summer when the water temperature exceeded 15 °C, NH 4 + increased, and dissolved oxygen decreased. Except during flood inflow mixing events, the activity concentration of dissolved 137Cs in the bottom layer did not increase in the surface layer at depths ≤ 1.0 m. In a 3 m shallow pond without a well-defined thermocline, a gradual density stratification primarily occurred in the lower layer during summer, limiting the transport of dissolved 137Cs from the bottom to the surface layer. About 5 % of 137Cs in the suspended solids and bottom sediment are exchangeable, indicating the mica-rich soils and geological conditions with a high fixation capacity of 137Cs reduce the risk of 137Cs elution. Even after three to four years of considerable depositions, the risk of radiocaesium absorption by paddy rice and subsequent increase in radiocaesium concentration in brown rice was negligible as long as the surface water of the pond was used for agriculture. [Display omitted] • NH 4 + and DO content in bottom layer control dissolved 137Cs elution during summer. • Gradual density stratification limits the surface transport of dissolved 137Cs. • Mixing influences seasonal frequency of increased dissolved 137Cs in surface layer. • Mica-rich soil with high 137Cs fixation capacity reduce the risk of 137Cs elution. • Under normal conditions, rice irrigated with surface water poses a low 137Cs risk. [ABSTRACT FROM AUTHOR]

Abstract: Although it is well known that phytoavailability of radiocaesium is gradually lost after its deposition on the ground by fixation to soil minerals, the decreasing rates during early period after the deposition is not yet quantitatively evaluated. In this study, stable Cs was added to 5 types of soil, including Andosols, a sand-dune regosol and a smectic lowland soil, in a laboratory soil incubation experiment to assess the aging effect of radiocaesium. Aliquots of a soil sample were put into pots and incubated in an artificial climate chamber. Orchardgrass or red clover was cultivated for 28 d in soil pots containing one of the allophanic Andosol samples seven times during about 1200 d using new pots for each cultivation. The soil-to-plant transfer factors of Cs declined exponentially until about 100 d and were almost constant thereafter. The extractabilities of Cs by water and 1 M NH4OAc solution from this allophanic Andosol soil sample also decreased with time and their decreasing patterns were similar to that of the transfer factor. The temporal changes of extractabilities of Cs in other soil samples were also examined 6 times during about 600 d. Rate of decline for the extracted yield of the added Cs by 1 M NH4OAc varied widely among all the soil types. Two allophanic Andosol samples showed relatively higher extractabilities in comparison with the other soils throughout the incubation experiment, which may be attributable to the lower contribution of Cs specific sorption sites to total cation exchange capacity of the allophonic Andosol soil samples. [Copyright &y& Elsevier]