Heterogeneous aggregation of humic acids studied by small-angle neutron and X-ray scattering

Saito, Takumi*; Motokawa, Ryuhei; Okubo, Takahiro*; Miura, Daisuke*; Kumada, Takayuki

Environmental Science & Technology, 57(26), p.9802 - 9810, 2023/07

https://doi.org/10.1021/acs.est.3c02028

Cloudwater deposition process of radionuclides based on water droplets retrieved from pollen sensor data

Kaneyasu, Naoki*; Kutsuna, Shuzo*; Iida, Kenjiro*; Sanada, Yukihisa; Tajiri, Takuya*

Environmental Science & Technology, 56(17), p.12036 - 12044, 2022/09

https://doi.org/10.1021/acs.est.2c02051

Radionuclides released during the Fukushima Daiichi nuclear accident caused altitude-dependent surface contamination in the mountainous areas of Japan. To explore the possible cloudwater deposition that formed a distinctive contamination profile, data from pollen sensors deployed nationwide were analyzed. Utilizing the polarization of scattered light, Cedar pollen and water droplets were distinguished. On March 15, when surface contamination was simulated in previous studies, dense cloud with high droplet number density were observed outside the Cs surface deposition areas, indicating that the sensor sites were immersed amid cloud layers. In contrast, cloud droplets with moderate number density were measured at altitudes of approximately 570-840 m, which overlapped with the surface contamination areas. Considering the existing knowledge on vertical gradients of cloudwater composition, these suggest that contaminated cloud droplets were localized near the cloud base where a moderate number density of cloud droplets was measured. A formation process was proposed for the observed vertical distribution, that is, surface contamination occurred intensively at the contact line between the cloud base and mountain slopes via cloudwater deposition, and the descending cloud base formed the contamination zone. This study sheds light on the deposition processes of radionuclides which have not previously been clarified.

Stoichiometry between humate unit molecules and metal ions in supramolecular assembly induced by Cu and Tb measured by gel electrophoresis techniques

Nakano, Sumika*; Marumo, Kazuki*; Kazami, Rintaro*; Saito, Takumi*; Haraga, Tomoko; Tasaki-Handa, Yuiko*; Saito, Shingo*

Environmental Science & Technology, 55(22), p.15172 - 15180, 2021/11

https://doi.org/10.1021/acs.est.1c03993

Humic acid (HA) can strongly complex with metal ions to form a supramolecular assembly via coordination binding. However, determining the supramolecular size distribution and stoichiometry between small HA unit molecules constituting HA supramolecule and metal ions has proven to be challenging. Here, we investigated the changes in the size distributions of HAs induced by Cu and Tb ions using a unique polyacrylamide gel electrophoresis (PAGE) for the separation and quantification of HA complexes and metal ions bound, followed by UV-Vis spectroscopy and EEM-PARAFAC. It was found that the supramolecular behaviors of Cu and Tb complexes with HA collected from peat and deep groundwater (HHA) differed. Our results suggest that this supramolecular stoichiometry is related to the abundance of sulfur atoms in the elemental composition of HHA. Our results provide new insights into HA supramolecules formed via metal complexation.

Behavior of radiocesium in sediments in Fukushima coastal waters; Verification of desorption potential through pore water

Otosaka, Shigeyoshi*; Kambayashi, Shota*; Fukuda, Miho*; Tsuruta, Tadahiko; Misono, Toshiharu; Suzuki, Takashi; Aono, Tatsuo*

Environmental Science & Technology, 54(21), p.13778 - 13785, 2020/11

https://doi.org/10.1021/acs.est.0c05450

Concentrations of Cs in seawater, seabed sediment, and pore water collected from the area around Fukushima were investigated from 2015 to 2018, and the potential of coastal sediments to supply radiocesium to the bottom environment was evaluated. The Cs concentration in the pore water ranged from 33 to 1934 mBq L and was 10-40 times higher than that in the overlying water (seawater overlying within 30 cm on the seabed). At most stations, the Cs concentrations in the overlying water and the pore water were approximately proportional to those in the sediment. The conditional partition coefficient between pore water and sediment was 0.9-1410 L kg, independent of the year of sampling. These results indicated that an equilibrium of Cs between pore water and sediment has established in a relatively short period, and Cs in the pore water is gradually exported to seawater near the seabed. A simple box model estimation based on these results showed that the Cs in the sediment was decreased by about 6% per year by desorption/diffusion of Cs from the seabed.

Transport and redistribution of radiocesium in Fukushima fallout through rivers

Taniguchi, Keisuke*; Onda, Yuichi*; Smith, H. G.*; Blake, W.*; Yoshimura, Kazuya; Yamashiki, Yosuke*; Kuramoto, Takayuki*; Saito, Kimiaki

Environmental Science & Technology, 53(21), p.12339 - 12347, 2019/11

https://doi.org/10.1021/acs.est.9b02890

Activity of Sr in fallout particles collected in the difficult-to-return zone around the Fukushima Daiichi Nuclear Power Plant

Zhang, Z.*; Igarashi, Junya*; Satou, Yukihiko; Ninomiya, Kazuhiko*; Sueki, Keisuke*; Shinohara, Atsushi*

Environmental Science & Technology, 53(10), p.5868 - 5876, 2019/05

https://doi.org/10.1021/acs.est.8b06769

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released abundant radioactive particles into the surrounding environment. Herein, we analyzed the activity of Sr in these particles to estimate the contribution of this radionuclide to the overall radiation exposure and shed light on the processes that occurred during the accident. Seven radioactive particles were isolated from the dust and soil samples collected from areas surrounding the FDNPP, and the minimum/maximum Cs activities were determined as 224/4,100 Bq. Based on the size, specific activity, and Cs/Cs activity ratios, we concluded that six of the seven radioactive particles were released from the Unit 1 reactor, while one particle was released from the Unit 3 reactor by a hydrogen explosion. Strontium-90 was detected in all radioactive particles, and the minimal/maximal Sr activities were determined as 0.046/1.4 Bq. Cs/Sr activity ratios above 1000 were observed for all seven particles, that is, compared to Cs, Sr had negligible contribution to the overall radiation exposure. The Cs/Sr activity ratios of the radioactive particles were similar to those of terrestrial environmental samples and were higher for particles released from the Unit 1 reactor than for samples collected from the Unit 1 reactor building, which indicates possibility of additional Sr -rich contamination after release of the particles.

Effective removal of selenite and selenate ions from aqueous solution by barite

Tokunaga, Kohei*; Takahashi, Yoshio*

Environmental Science & Technology, 51(16), p.9194 - 9201, 2017/08

https://doi.org/10.1021/acs.est.7b01219

In the present study, we explore a new application of barite (BaSO) as a sequestering phase for selenite (Se(IV)) and selenate (Se(VI)) ions from aqueous solutions due to the low solubility and high stability of barite. The uptake of Se(IV) and Se(VI) during coprecipitation with barite was investigated through batch experiments to understand the factors controlling effective removal of Se(IV) and Se(VI) from polluted water to barite. The uptake of Se(IV) by barite is dependent on pH, coexistent calcium ion, and sulfate concentration in the initial solution, possibly due to their effects on the chemical affinity and structural similarity. On the other hand, the uptake of Se(VI) by barite was strongly dependent on sulfate concentration in the initial solution, which is only related to the structural similarity. This study provides a good estimate of its ability to effectively remove Se(IV) and Se(VI) from aqueous solutions (more than 80%) under optimized experimental parameters.

Tracking the fate of particle associated Fukushima Daiichi cesium in the ocean off Japan

Buesseler, K. O.*; German, C. R.*; Honda, Makio*; Otosaka, Shigeyoshi; Black, E. E.*; Kawakami, Hajime*; Manganini, S. M.*; Pike, S.*

Environmental Science & Technology, 49(16), p.9807 - 9816, 2015/08

https://doi.org/10.1021/acs.est.5b02635

A three year time-series of particle fluxes is presented from sediment traps deployed at 500 and 1000 m at a site 115 km southeast of Fukushima Daiichi Nuclear Power Plant (FDNPP). Results show a high fraction of lithogenic material, suggesting a lateral source of sediments. The accident-derived radiocesium were enhanced in flux peaks that, given variations in trap Cs/Pb ratios, are characteristic of material derived from shelf and slope sediments found from 120 to 500 m. The fluxes of radiocesium are an order of magnitude higher than a previously reported for the trap located 100 km due east of FDNPP. We attribute the large difference due to the position of our trap under the southeasterly currents that carry contaminated waters and resuspended sediments in to the Pacific. These higher sedimentary fluxes of radiocesium to the offshore are still small relative to the inventory of radiocesium currently buried nearshore.

Speciation of radioactive soil particles in the Fukushima contaminated area by IP autoradiography and microanalyses

Mukai, Hiroki*; Hatta, Tamao*; Kitazawa, Hideaki*; Yamada, Hirohisa*; Yaita, Tsuyoshi; Kogure, Toshihiro*

Environmental Science & Technology, 48(22), p.13053 - 13059, 2014/12

https://doi.org/10.1021/es502849e

no abstracts in English

Sorption of Eu(III) on granite; EPMA, LA-ICP-MS, batch and modeling studies

Fukushi, Keisuke*; Hasegawa, Yusuke*; Maeda, Koshi*; Aoi, Yusuke*; Tamura, Akihiro*; Arai, Shoji*; Yamamoto, Yuhei*; Aosai, Daisuke*; Mizuno, Takashi

Environmental Science & Technology, 47(22), p.12811 - 12818, 2013/11

https://doi.org/10.1021/es402676n

Eu(III) sorption on granite was examined by the combined microscopic and macroscopic approaches. Polished thin sections of the granite were reacted with solutions containing 10 M of Eu(III) and analyzed using EPMA and LA-ICP-MS. The Eu enrichment up to 6 wt.% was observed on most of the biotite grains. The Eu-enriched parts commonly lose K, which is the interlayer cation of biotite, indicating that the sorption mode is cation exchange in the interlayer. Batch Eu(III) sorption experiments on granite and biotite powders were conducted. The macroscopic sorption behavior of biotite was consistent with that of granite. The obtained sorption edges can be reproduced reasonably by the modeling considering single-site cation exchange reactions. Granite is complex mineral assemblages. However, the combined microscopic and macroscopic approaches revealed that elementary reactions by single phase can be representative for the bulk sorption reaction in complex mineral assemblages.