Records of the riverine discharge of 129I in riverbank sediment after the Fukushima accident.

Although 129I discharge from watersheds is fundamental for assessing long-term radiation effects on aquatic ecosystems, 129I originating from the Fukushima nuclear accident is yet be evaluated. This study investigated the transport behavior of 129I by riverbank surveys conducted from 2013 to 2015 in a watershed where the 129I/137Cs activity ratio is low in the mountainous area and high in the plain as of 2011. Until 2015, the 129I/137Cs activity ratio of the levee crown in the studied watershed was similar to that of the surrounding area in 2011. However, the 129I/137Cs ratios of the surface riverbank sediments were all low, indicating that radionuclides transported from the mountainous area were deposited on the riverbank in the plain. The vertical distribution of the 129I/137Cs ratio in the riverbank sediments indicated that some 129I and 137Cs deposited during the accident remained in the lower layers, but most were eroded immediately after the accident. Based on the 129I/137Cs ratios of sediments deposited on the riverbank, which remained constant until 2015 after the accident, the amount of 129I discharged to the ocean was determined from the previously evaluated 137Cs discharge. It was calculated that 1.8 × 105 Bq and 1.2 × 107 Bq of 129I were discharged with sediment from the studied watershed and the contaminated river watersheds (Abukuma River and Fukushima coastal rivers, including the study river), respectively. This amount of 129I was 0.3% of the 129I released from the Fukushima Dai-ichi Nuclear Power Plant into the ocean immediately after the accident. Furthermore, a comparison of the 129I/137Cs ratio showed that the continuous 129I and 137Cs discharge from the river contribute little to their amount in the seafloor sediments along the Fukushima coast.

Simulation study on 3H behavior in the Fukushima coastal region: Comparison of influences of discharges from the Fukushima Daiichi and rivers.

The release of tritium (3H) to the ocean is planned on the coastal environment in the Fukushima coastal region from Spring or Summer of 2023. Before its release, we evaluate the effect of 3H discharges from the port of Fukushima Daiichi and rivers in the Fukushima coastal region using a three-dimensional hydrodynamic model (3D-Sea-SPEC). The simulation results showed that discharges from the port of Fukushima Daiichi dominantly affected the 3H concentrations in monitoring points within approximately 1 km. Moreover, the results indicate that the effect of riverine 3H discharge was limited around the river mouth under base flow conditions. However, its impact on the Fukushima coastal regions under storm flow conditions was found, and the 3H concentrations in seawater in the Fukushima coastal region were formed around 0.1 Bq/L (mean 3H concentrations in seawater in the Fukushima coastal region) in the near shore.

Thirty-year simulation of environmental fate of 137Cs in the Abukuma River basin considering the characteristics of 137Cs behavior in land uses.

The Fukushima Daiichi Nuclear Power Plant accident caused a radioactive contamination of deposited radionuclides, including 137Cs, on the land surface. Cesium-137 deposited on the land surface was strongly adsorbed on soil particles and was then washed off through soil erosion. Trends of temporal variation of 137Cs wash-off varied greatly depending on land use. Therefore, it is important to reflect the characteristics of 137Cs migration processes in each land use to clarify the long-term fate of 137Cs. In this study, a 30-year simulation of environmental fate of 137Cs was conducted using a distributed radiocesium prediction model, taking into account the characteristics of the 137Cs behavior in each land use. Overall, in the Abukuma River basin, the 137Cs transported into the ocean for 30 years was estimated to correspond to 4.6 % of the initial deposition in the basin, and the effective half-life of 137Cs deposited in the basin was estimated to be 3.7 years shorter (by 11.6 %) than its physical half-life. These results suggested that 137Cs deposited from the accident could still remain for decades. Based on the analysis of the 137Cs behavior in land use, in 2011, the contribution of 137Cs export to the ocean from urban lands was estimated to correspond to 70 % of the total 137Cs export. Meanwhile, from 2012 to 2040, the contribution of 137Cs export from agricultural lands was estimated to correspond to 75 % of the total 137Cs export. The reduction ratios excluding radioactive decay of 137Cs remained in areas with and without human activities for 30 years after the accident, defined as the ratios of the total outflow to the initial deposition, were estimated to be 11.5 %-17.7 % and 0.4 %-1.4 %, respectively. These results suggested that human activities enhance the reduction of 137Cs remaining in land in the past and future.

Effect of radioactive cesium-rich microparticles on radioactive cesium concentration and distribution coefficient in rivers flowing through the watersheds with different contaminated condition in Fukushima.

Radioactive cesium-rich microparticles (CsMPs) derived from the Fukushima Daiichi Nnuclear Power Plant accident were detected from soils and river water around Fukushima Prefecture, Japan. Because CsMPs are insoluble and rich in radioactive cesium (RCs), they may cause the overestimation of solid-water distribution coefficient (Kd) for RCs in the water. Previous studies showed the proportion of RCs derived from CsMPs on RCs concentration in soils collected from areas with different contaminated levels. Because the proportion of RCs concentration derived CsMPs to the RCs concentration of soils in the less contaminated areas is higher than that in the highly contaminated areas, the effect of CsMPs on particulate RCs concentration in river water may be larger in the less contaminated areas. However, the difference in the effects of CsMPs on the particulate RCs concentration and Kd in river water flowing through watersheds with different contaminated levels has not been clarified. In this study, we investigated the effect of CsMPs on the particulate RCs concentration and Kd in two rivers, Takase River and Kami-Oguni River, flowing through the watersheds with different RCs contaminated levels in Fukushima Prefecture. CsMPs might enter rivers due to soil erosion because they were detected only in some samples collected from both rivers during flood events. CsMPs accounted for more than half of particulate RCs concentration in some water samples collected in the flood condition. In particular, the proportion of CsMPs in particulate RCs for the Kami-Oguni River was greater than that for the Takase River. However, when evaluating for the entire water sampling in the flood condition, a proportion of RCs concentration derived from CsMPs in the average RCs concentrations per unit mass of SS in both river waters collected in the flood condition was not large. CsMPs might temporarily increase the particulate RCs concentration and Kd in the flood event, but CsMPs did not significantly affect them when evaluated throughout the event.

CESIUM-RICH MICROPARTICLES RUNOFF DURING RAINFALL: A CASE STUDY IN THE TAKASE RIVER.

Cesium-rich microparticles (CsMPs) with high cesium-137 (137Cs) concentrations were released and deposited in surface soil after the Fukushima Daiichi Nuclear Power Plant accident. Radioactive materials on the soil surface layer enter rivers owing to soil erosion during rainfall. In this study, we investigated CsMPs runoff through the river via soil erosion during rainfall in the Takase River watershed in Namie Town, Fukushima Prefecture, Japan. CsMPs were rarely detected in suspended solids (SS) in water samples collected during four rainfalls between February and July 2021. Furthermore, the proportion of 137Cs concentration derived from CsMPs to 137Cs concentration in the form of SS (particulate 137Cs) in the water was ~6% on average, which suggests that 137Cs runoff in the form of CsMPs from the forest to the Takase River was not large.

A new approach to extracting biofilm from environmental plastics using ultrasound-assisted syringe treatment for isotopic analyses.

Plastics are one of the ubiquitous and artificial types of substrates for microbial colonization and biofilm development in the aquatic environment. Characterizing plastic-associated biofilms is key to the better understanding of organic material and mineral cycling in the "Plastisphere"-the thin layer of microbial life on plastics. In this study, we propose a new method to extract biofilms from environmental plastics, in order to evaluate the properties of biofilm-derived organic matter through stable carbon (δ13C) and nitrogen (δ15N) isotope signatures and their interactions with radionuclides especially radiocesium (137Cs). The extraction method is simple and cost-effective, requiring only an ultrasonic bath, disposable plastic syringes, and a freeze drier. After ultrasound-assisted separation from the plastics, biofilm samples were successfully collected via a sequence of syringe treatments, with less contamination from plastics and other mineral particles. Effective removal of small microplastics from the experimental suspension was satisfactorily achieved using the method with syringe treatments. Biofilm-derived organic matter samples (14.5-65.4 mg) from four river mouths in Japan showed 137Cs activity concentrations of <75 to 820 Bq·kg-1 biofilm (dw), providing evidence that environmental plastics, mediated by developed biofilms, serve as a carrier for 137Cs in the coastal riverine environment. Significant differences in the δ13C and δ15N signatures were also obtained for the biofilms, indicating the different sources, pathways, and development processes of biofilms on plastics. We demonstrate here a straightforward method for extracting biofilms from environmental plastics; the results obtained with this method could provide useful insights into the plastic-associated nutrient cycling in the environment.

Migration processes of radioactive cesium in the Fukushima nearshore area: Impacts of riverine input and resuspension.

It is essential to evaluate secondary migration caused by riverine input and resuspension from seabed sediments to estimate the future distribution of radioactive cesium (137Cs) in the coastal area off Fukushima Prefecture. In particular, the inflow from rivers cannot be ignored because most of the 137Cs inflow from rivers is deposited on the coast without elute into seawater. Two mooring systems were installed near the Ukedo River's mouth (Fukushima Prefecture) from February 2017 to February 2018. The first contained a sediment trap system, collecting sinking particles during the period. The second comprised a turbidity sensor and a current sensor. The contribution of resuspension and inflow from the river to the mass flux was quantitatively evaluated using multiple regression equations. The results showed that resuspension caused 79%-83% of secondary 137Cs migration in nearshore areas, whereas the influence of riverine 137Cs input on the sediment was only 7% per year.

Remobilisation of radiocaesium from bottom sediments to water column in reservoirs in Fukushima, Japan.

Reservoir sediments generally act as a sink for radionuclides derived from nuclear accidents, but under anaerobic conditions, several radionuclides remobilise in bioavailable form from sediments to water columns, which may contribute to the long-term contamination of aquatic products. This study systematically investigated the 137Cs activities of sediment-pore water, providing a direct evidence of the remobilisation of bioavailable 137Cs from sediments in two highly contaminated reservoirs affected by the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. We observed that the dissolved 137Cs activity concentration of pore water (3.0-65.8 Bq L-1) was one to two orders of magnitude higher than that of reservoir water. Moreover, the distribution coefficient (Kd) values for the 137Cs of sediment-pore water (2.6-14 × 103 L kg-1) decreased with depth. The Kd values were significantly and negatively correlated with the concentration of the major 137Cs competing cation NH4+. Our results strongly indicate a competitive ion exchange process between 137Cs and NH4+ via a highly selective interaction with the frayed edge sites of phyllosilicate minerals, which is the major reason for the variability of Kd values of sediment-pore water, even in the Fukushima case. Additionally, the sediment accumulation rates were relatively high, and the annual depositional rate of exchangeable 137Cs prevailed over the annual diffusive flux of 137Cs from the sediment to the overlying water. This finding indicates that even after 10 years since the FDNPP accident, the bioavailable 137Cs is still continuously supplied from the catchment covered by mountainous forests, and reservoir sediments are a long-term important source of bioavailable 137Cs in the riverine system. Our findings provide important parameter values for mid- and long-term assessments of the radiation impact of radionuclide discharges to freshwater environments.

Visualization of radiocesium distribution in surface layer of seafloor around Fukushima Daiichi Nuclear Power Plant.

Large quantities of volatile radionuclides were released into the atmosphere and the hydrosphere following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on March, 2011. Monitoring of radiocesium in sediment is important for evaluating the behavior of radiocesium in the environment and its effect on aquatic organisms. In this study, the radiocesium distribution in the surface sediment around the FDNPP was visualized as a radiocesium concentration map using periodical survey data from a towed gamma-ray detection system. The uncertainty of the radiocesium map was evaluated via comparison with a large amount of sediment core sample data. The characteristics of the radiocesium distribution were examined considering the seafloor topography and a geological map, which were obtained via acoustic wave survey. The characteristics of the formation of 137Cs anomaly at the estuaries were analyzed using a contour map of 137Cs concentration combined with water depth. Validation of the created map showed that it was comparable with actual sediment core samples. The map generated using the towed radiation survey depicted the 137Cs concentration distribution as the position resolution of a 1 km mesh. Finally, the 137Cs concentration decreased with time in consideration of such uncertainty.

Leaching characteristics of 137Cs for forest floor affected by the Fukushima nuclear accident: A litterbag experiment.

In forest ecosystems, forest litter is considered an active medium for radiocesium (137Cs). To understand discharge mechanisms of highly bioavailable dissolved 137Cs from forests to river systems, we investigated the characteristics of 137Cs leaching from forest litter as observed from litterbag experiments. Leaching experiments with conifer needle and deciduous broadleaf litters were then conducted. After soaking conifer needles and broadleaf litters for 20 min, 140 min, and 1 day, the mean values of the 137Cs leaching ratios were 0.13-2.0% and 0.81-6.6%, respectively, indicating that 137Cs leaching ratios are different between forest litter types. To elucidate the factors affecting 137Cs leaching from forest litter, a multi-regression analysis of 137Cs leaching ratios was conducted against antecedent mean precipitation and temperature before sampling the litterbag and accumulated temperature during the litterbag experiments. The 137Cs leaching ratios showed a negative correlation to the antecedent mean precipitation for both litters and the accumulated temperature for broadleaf litters, whereas it exhibited a positive correlation with the antecedent mean temperature for both litters and the accumulated temperature for conifer needle litters. It was proposed that the fraction of 137Cs in labile sites in forest litter increased/decreased due to litter decomposition by antecedent/accumulated temperature, and that this fraction can be washed off by the antecedent precipitation. The different effects of accumulated temperature on 137Cs leaching from conifer needles and broadleaf litters could be due to their different decomposition rates. Our results contribute further the understanding of the mechanisms associated with dissolved 137Cs discharge from forested catchments.

Reservoir sediments as a long-term source of dissolved radiocaesium in water system; a mass balance case study of an artificial reservoir in Fukushima, Japan.

Because of their large mobility and high bioavailability, it is necessary to elucidate the origins and dynamics of dissolved radionuclides in river and reservoir systems to assess the transfer of those radionuclides from water to crops and aquatic organisms. Elution from contaminated reservoir sediments, a potential source of dissolved radionuclides, presents a long-term concern, particularly for long-lived radionuclides. In this study, we systematically investigated caesium-137 (137Cs) concentrations using a time-series suite of input and output water samples collected from 2014 to 2019 from the Ogaki Dam Reservoir, which has a catchment with a high 137Cs inventory due to the Fukushima Dai-ichi Nuclear Power Plant accident. The results of our study showed that dissolved 137Cs concentration was significantly higher in the output water than that in the main input water, and that the effective ecological half-life of dissolved 137Cs in the output water was longer than in the main input water. We quantitatively evaluated the mass balance of dissolved 137Cs in the reservoir to elucidate how much dissolved 137Cs from the rivers and production from reservoir sediments contribute to 137Cs in the reservoir output. The annual output of dissolved 137Cs was significantly higher than the total input of dissolved 137Cs, with approximately 32%-40% of the dissolved 137Cs in the output water presumably being produced from reservoir sediments. Consequently, the estimated dissolved 137Cs fluxes from reservoir sediments to overlying water were 0.57-1.3 × 104 Bq m-2 y-1. This implies that approximately 0.04%-0.09% of 137Cs accumulated in the sediments was released through elution to the overlying water each year. Reservoir sediments containing high 137Cs levels may thus become even more important as sources of bioavailable dissolved 137Cs in the future.

Radiocesium distribution in the sediments of the Odaka River estuary, Fukushima, Japan.

Radiocesium that originated from the Fukushima Daiichi Nuclear Power Plant accident was deposited on the ground surface and has been transported via fluvial discharge, primarily in the form of particulates, to downstream areas and eventually to the ocean. During transportation, some of the radiocesium accumulated on the riverbed. In this study, we quantified the radiocesium deposition on the riverbed in the Odaka River estuary and investigated the radiocesium sedimentation process of the river bottom. Our results show that the radiocesium inventory in the seawater intrusion area is larger than those in the freshwater and marine parts of the estuary. Moreover, the particle-size distribution in the seawater intrusion area shows a high proportion of silt and clay particles compared with the distribution in other areas. The increased radiocesium inventory in this area is attributed to the sedimentation of fine particles caused by hydrodynamic factors (negligible velocity of the river flow) rather than flocculation factor by salinity variation.

Mineral composition characteristics of radiocesium sorbed and transported sediments within the Tomioka river basin in Fukushima Prefecture.

The deposited radiocesium in the Fukushima river basin is transported in the river systems by soil particles and redistributed in the downstream areas. Although predicting the behaviors of minerals that adsorb radiocesium and of radiocesium dissolved in river water within the river systems is essential, the dominant mineral species that adsorb radiocesium have not yet been comprehensively identified. We identify herein such mineral species by investigating the 137Cs distribution and the mineral species in each size fraction that are found in the bedload sediments from an upstream reservoir to an estuary within the Tomioka river basin located east of Fukushima Prefecture in Japan. In the fine sand sediment, which is the dominant fraction in terms of the 137Cs quantity in the river bedload, the 137Cs concentrations of the felsic and mafic minerals are comparable to that of micas. The mafic minerals contain 62% of the 137Cs in the fine sand fraction in the upstream area, while the felsic minerals contain the highest quantities of 137Cs in the downstream area. These results suggest that the quantification of the mineral species and the 137Cs concentration of each size fraction are critically important in predicting the behaviors of the minerals and radiocesium within the Fukushima river basin in the future.

Factors controlling dissolved 137Cs concentrations in east Japanese Rivers.

To investigate the main factors that control the dissolved radiocesium concentration in river water in the area affected by the Fukushima Daiichi nuclear power plant accident, the correlations between the dissolved 137Cs concentrations at 66 sites normalized to the average 137Cs inventories for the watersheds with the land use, soil components, topography, and water quality factors were assessed. We found that the topographic wetness index is significantly and positively correlated with the normalized dissolved 137Cs concentration. Similar positive correlations have been found for European rivers because wetland areas with boggy organic soils that weakly retain 137Cs are mainly found on plains. However, for small Japanese river watersheds, the building area ratio in the watershed strongly affected the dissolved 137Cs concentration. One reason for this would be because the high concentrations of solutes, such as K+ and dissolved organic carbon, discharged in urban areas would inhibit 137Cs absorption to soil particles. A multiple regression equation was constructed to predict the normalized dissolved 137Cs concentration with the topography, land use, soil component, and water quality data as explanatory variables. The best model had the building land use as the primary predictor. When comparing two multiple regression models in which the explanatory variables were limited to (1) the land use and soil composition and (2) the water quality, the water quality model underestimated the high normalized dissolve 137Cs concentration in urban areas. This poor reproducibility indicates that the dissolved 137Cs concentration value in urban areas cannot be solely explained by the solid-liquid distribution of 137Cs owing to the influence of the water quality, but some specific 137Cs sources in urban areas would control the dissolved 137Cs concentration.

A modeling approach to estimate the 137Cs discharge in rivers from immediately after the Fukushima accident until 2017.

We developed a simple model to evaluate and predict the 137Cs discharge from catchments using a tank model and the L-Q equation. Using this model, the 137Cs discharge and discharge ratio from the Abukuma River and 13 other rivers in the Fukushima coastal region were estimated from immediately after the Fukushima accident up to 2017. The 137Cs discharge (and discharge ratio to the deposition inventory in the catchment) of the Abukuma River and 13 other rivers in the Fukushima coastal region during the initial six months after the accident were estimated to be 18 TBq (3.1%) and 11 TBq (0.79%), respectively. These values of 137Cs discharge ratio were 1-2 orders of magnitude higher than those observed after June 2011 in previous studies (Ueda et al., 2013; Tsuji et al., 2016; Iwagami et al., 2017a), indicating that the initial 137Cs discharge from the catchments through the rivers was significant. The simulated initial 137Cs discharge rates for the initial six months after the Fukushima accident were about 9-30 times larger in each catchment than those after that point until 2017, though initial 137Cs concentration in river water was derived from an extrapolation of data based on a two exponentially decreasing fitting. However, it was found that the impact on the ocean from the initial 137Cs discharge through the rivers can be limited because the 137Cs discharge from the Abukuma River and the 13 other rivers in the Fukushima coastal region (29 TBq) was two orders of magnitude smaller than the direct release from Fukushima Dai-ichi Nuclear Power Plant (FDNPP) into the ocean (3.5 PBq) and from atmospheric deposition into the ocean (7.6 PBq) (Kobayashi et al., 2013). This model is expected to be useful to evaluate and predict 137Cs discharge from catchments in future water management and in the estimation of 137Cs discharge into reservoirs and the ocean.

Trend of 137Cs concentration in river water in the medium term and future following the Fukushima nuclear accident.

It is a critical to examine the migration behavior of radiocesium derived from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in river systems to predict the future contamination status and propose effective countermeasures to reduce exposure. We conducted a three-year-long observation (April 2015-March 2018) of the 137Cs concentration in two rivers which located surrounding the FDNPP. The result revealed a declining trend for the dissolved and particulate 137Cs concentration in river water from four to seven years after the FDNPP accident. The dissolved and particulate 137Cs concentrations for both rivers had similar temporal patterns and showed declining trends with time. However, the dissolved 137Cs concentration had longer half-life than the particulate 137Cs concentration and large seasonal variations related to water temperature. The environmental half-life for the dissolved 137Cs concentration was longer than previous reported values within three years after the accident, suggesting that the declining trend for the dissolved 137Cs concentration is gradually decreasing with time. The temperature dependency of the dissolved 137Cs concentration became weaker year by year. From the D10 equation we proposed, the dissolved 137Cs concentration will likely remain at the same level for several decades. The results of the present study promote our understanding of both the medium- and long-term impacts of the FDNPP accident on river systems.

Distribution and fate of 129I in the seabed sediment off Fukushima.

In this study, seabed sediment was collected from 26 stations located within 160 km from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) during the 2 years which followed the FDNPP accident of March 2011 and the concentrations of 129I and 137Cs were measured. By comparing the distribution of these two radionuclides with respect to their different geochemical behaviors in the environment, the transport of accident-derived radionuclides near the seafloor is discussed. The concentration of 129I in seabed sediment recovered from offshore Fukushima in 2011 ranged between 0.02 and 0.45 mBq kg-1, with 129I/137Cs activity ratios of (1.9 ±â€¯0.5) × 10-6 Bq Bq-1. The initial deposition of 129I to the seafloor in the study area was 0.36 ±â€¯0.13 GBq, and the general distribution of sedimentary 129I was established within 6 months after the accident. Although iodine is a biophilic element, the accident-derived 129I negligibly affects the benthic ecosystem. Until October 2013, a slight increase in activity of 129I in the surface sediment along the shelf-edge region (bottom depth: 200-400 m) was observed, despite that such a trend was not observed for 137Cs. The preferential increase of the 129I concentrations in the shelf-edge sediments was presumed to be affected by the re-deposition in the shelf-edge sediments of 129I desorbed from the contaminated coastal sediment. The results obtained from this study indicate that 129I/137Cs in marine particles is a useful indicator for tracking the secondary transport of accident-derived materials, particularly biophilic radionuclides, from the coast to offshore areas.

Evaluation of sediment and 137Cs redistribution in the Oginosawa River catchment near the Fukushima Dai-ichi Nuclear Power Plant using integrated watershed modeling.

The Oginosawa River catchment lies 15 km south-west of the Fukushima Dai-ichi nuclear plant and covers 7.7 km2. Parts of the catchment were decontaminated between fall 2012 and March 2014 in preparation for the return of the evacuated population. The General-purpose Terrestrial Fluid-flow Simulator (GETFLOWS) code was used to study sediment and 137Cs redistribution within the catchment, including the effect of decontamination on redistribution. Fine resolution grid cells were used to model local features of the catchment, such as paddy fields adjacent to the Oginosawa River. The simulation was verified using monitoring data for river water discharge rates (r = 0.92), suspended sediment concentrations, and particulate 137Cs concentrations (r = 0.40). Cesium-137 input to watercourses came predominantly from land adjacent to river channels and forest gullies, e.g. the paddy fields in the Ogi and Kainosaka districts, as the ground in these areas saturates during heavy rain and is easily eroded. A discrepancy between the simulation and monitoring results on the sediment discharge rate following decontamination may be explained by fast erosion occurring after decontamination. Forested areas far from the channels only made a minor contribution to 137Cs input to watercourses, total erosion of between 0.001 and 0.1 mm from May 2011 to December 2015, as ground saturation is infrequent in these areas. The 2.3-6.9% y-1 decrease in the amount of 137Cs in forest topsoil over the study period can be explained by radioactive decay (approximately 2.3% y-1), along with a migration downwards into subsoil and a small amount of export. The amount of 137Cs available for release from land adjacent to rivers is expected to be lower in future than compared to this study period, as the simulations indicate a high depletion of inventory from these areas by the end of 2015. However continued monitoring of 137Cs concentrations in river water over future years is advised, as recultivation of paddy fields by returnees may again lead to fast erosion rates and release of the remaining inventory.

Amine/Hydrido Bifunctional Nanoporous Silica with Small Metal Nanoparticles Made Onsite: Efficient Dehydrogenation Catalyst.

Multifunctional catalysts are of great interest in catalysis because their multiple types of catalytic or functional groups can cooperatively promote catalytic transformations better than their constituents do individually. Herein we report a new synthetic route involving the surface functionalization of nanoporous silica with a rationally designed and synthesized dihydrosilane (3-aminopropylmethylsilane) that leads to the introduction of catalytically active grafted organoamine as well as single metal atoms and ultrasmall Pd or Ag-doped Pd nanoparticles via on-site reduction of metal ions. The resulting nanomaterials serve as highly effective bifunctional dehydrogenative catalysts for generation of H2 from formic acid.