Particulate 137Cs Research Articles

Occurrence and partition ratios of radiocesium in an urban river during dry and wet weather after the 2011 nuclear accident in Fukushima

After the 2011 nuclear accident in Fukushima, radiocesium was released from the Fukushima Dai-ichi Nuclear Power Plant and contaminated waters in urban areas near Tokyo. By intensive field monitoring during 3 years, this study investigated the temporal trends and the occurrence of radiocesium during dry and wet weather, and analyzed the variations in radiocesium during rainfall events and factors controlling them. Concentrations of particulate radiocesium decreased rapidly from May 2012 to March 2013 and reached an equilibrium in 2014. Concentrations of particulate 137Cs during wet weather were almost double those during dry weather in the same period. In contrast to the small variations in 137Cs concentrations in the particulate phase on a suspended solids (SS) weight basis during events, those in the dissolved phase on a liquid-volume basis fluctuated greatly, resulting in variations in the partition coefficient (apparent Kd). The apparent Kd of 137Cs during wet weather ranged from 30 000 to 150 000 L kg−1 and showed a significant negative correlation with SS concentrations during wet weather. Specific surface area in solids contributed to the variations in apparent Kd.

Effects of radiocesium inventory on 137Cs concentrations in river waters of Fukushima, Japan, under base-flow conditions

To investigate the behavior of nuclear accident-derived 137Cs in river water under base-flow conditions, concentrations of dissolved and particulate 137Cs were measured at 16 sampling points in seven rivers of Fukushima Prefecture, Japan, in 2012 and 2013. The concentration of dissolved 137Cs was significantly correlated with the mean 137Cs inventory in the catchment area above each sampling point in both sampling years. These results suggest that the concentration of dissolved 137Cs under base-flow conditions is primarily determined by the 137Cs inventory of the catchment area above the sampling point. However, the concentration of particulate 137Cs did not show a clear relationship with either the mean 137Cs inventory or the dissolved 137Cs concentration, thus indicating that particulate and dissolved forms do not effectively interact in rivers. To evaluate the contribution of the 137Cs inventory within catchment areas, we analyzed relations between the 137Cs concentration and the mean 137Cs inventory over the area within certain flow path lengths that were traced along the river and slope above the sampling point. Coefficients of determination for dissolved 137Cs concentrations were highest for the longest flow path, i.e., the whole catchment area, and lower for shorter flow paths. Coefficients of determination for particulate 137Cs concentrations were only moderately high for the shortest flow path in 2012, whereas the values were quite low for all flow paths in 2013. These results suggest that dissolved 137Cs can originate from a larger area of the catchment even under base-flow conditions; however, particulate 137Cs did not show such behavior. The results also show that under base-flow conditions, dissolved and particulate 137Cs behave independently during their transport from river catchments to the ocean.

Cesium-137: Radio-Chemistry, Fate, and Transport, Remediation, and Future Concerns

In recent years, considerable interest has arisen with regard to the fate and transport of radionuclides such as iodine-131 (131I), cesium-134 (134Cs), and cesium-137 (137Cs) in aquatic environments. 137Cs is an important indicator of radioactive pollution in aquatic environments. The transport and fate of anthropogenic 137Cs is related to the chemical properties of ionic Cs (Cs+), which generally dictates a high degree of mobility and bioavailability of this radionuclide. The transport of 137Cs and its partitioning between abiotic and biotic components of aquatic ecosystems are complex processes that are considerably affected by a number of factors such as mineralogical composition of suspended and bottom sediments and the characteristic geochemistry of water. These factors influence sorption and desorption kinetics of 137Cs and the transport of particulate 137Cs. Nevertheless, substantial evidence suggests that direct biological 137Cs accumulation from the aquatic environment occurs readily in micro-organisms and aquatic plants. The evidence discussed in this work indicates that 137Cs is continuously re-circulated in biological systems for many years following a pulse of contamination. Possible remediation methods for the contaminated aquatic systems are also discussed. This review provides guidelines for future work plans for the study of the fate and transport of 137Cs in the aquatic environment in the wake of Fukushima Nuclear Power Plant disaster in 2011 and to provide answers to the urgent questions with respect to strategies for mitigating contamination and reducing radiation exposure for people living in the most affected regions of the world.

Sinking velocity of particulate radiocesium in the northwestern North Pacific

Sinking particles (SP) were collected by time series sediment traps at two depths in the northwestern Pacific before and after the Fukushima Daiichi Nuclear Power Plant accident, and accident-derived particulate radiocesium was measured. Radiocesium (137Cs) was first detected at 500 m (4810 m) about 2 weeks (1 month) after the accident. 137Cs of SP collected over 1 year revealed that the time lag between two depths was larger than that for the first 137Cs detection (about 2 weeks). We estimated the transient sinking velocity (SV) from the cumulative temporal 137Cs flux and the time lags at the two depths. Although the SV of SP collected in very early period was large, the estimated SV of most particulate 137Cs (about 80%) was about 50 m d−1. Based on comparison of 137Cs concentration in total SP with that in SP without organic materials, we suspect that most of the 137Cs was likely incorporated into aluminosilicates.

Distribution of dissolved and particulate radiocesium concentrations along rivers and the relations between radiocesium concentration and deposition after the nuclear power plant accident in Fukushima

This study involved measurement of concentrations of dissolved and particulate radiocesium (134Cs and 137Cs) in river water, and determination of the quantitative relations between the amount of deposited 137Cs and 137Cs concentrations in river waters after the Fukushima Daiichi nuclear power plant accident. First, the current concentrations of dissolved and particulate 134Cs·137Cs were determined in a river watershed from 20 sampling locations in four contaminated rivers (Abukuma, Kuchibuto, Shakado, and Ota).Distribution characteristics of different 137Cs forms varied with rivers. Moreover, a higher dissolved 137Cs concentration was observed at the sampling location where the 137Cs deposition occurred much more heavily. In contrast, particulate 137Cs concentration along the river was quite irregular, because fluctuations in suspended solids concentrations occur easily from disturbance and heavy precipitation. A similar tendency with dissolved 137Cs distribution was observed for the 137Cs concentration per unit weight of suspended solids.Regression analysis between deposited 137Cs and dissolved/particulate 137Cs concentrations was performed for the four rivers. The results showed a strong correlation between deposited 137Cs and dissolved 137Cs, and a relatively weak correlation between deposited 137Cs and particulate 137Cs concentration for each river. However, if the particulate 137Cs concentration was converted to 137Cs concentration per unit weight of suspended solid, the values showed a strong correlation with deposited 137Cs.

137Cs vertical distribution at the deep basins of the North and Central Aegean Sea, Greece

Large volume seawater samples were collected for the determination of 137Cs concentration along with depth in the deep basins of North and Central Aegean Sea. The vertical 137Cs distribution showed maximum concentration at the bottom of the basins, while the minimum values corresponded to the intermediate layer, where Levantine water exists. The surface 137Cs activity is found to lie between the two limits and is originated from the Black Sea waters. The typical oceanographic advection–diffusion balance model is modified to a diffusion-settling-decay balance model to better understand the vertical distribution and variation of the 137Cs concentration in the deep basins. In addition, the diffusivity of each basin, as well as the settling speed of particulate 137Cs is also estimated. The results are compared with theoretical approach as well as with previous data.

Global risk of radioactive fallout after major nuclear reactor accidents

Abstract. Major reactor accidents of nuclear power plants are rare, yet the consequences are catastrophic. But what is meant by "rare"? And what can be learned from the Chernobyl and Fukushima incidents? Here we assess the cumulative, global risk of exposure to radioactivity due to atmospheric dispersion of gases and particles following severe nuclear accidents (the most severe ones on the International Nuclear Event Scale, INES 7), using particulate 137Cs and gaseous 131I as proxies for the fallout. Our results indicate that previously the occurrence of INES 7 major accidents and the risks of radioactive contamination have been underestimated. Using a global model of the atmosphere we compute that on average, in the event of a major reactor accident of any nuclear power plant worldwide, more than 90% of emitted 137Cs would be transported beyond 50 km and about 50% beyond 1000 km distance before being deposited. This corroborates that such accidents have large-scale and trans-boundary impacts. Although the emission strengths and atmospheric removal processes of 137Cs and 131I are quite different, the radioactive contamination patterns over land and the human exposure due to deposition are computed to be similar. High human exposure risks occur around reactors in densely populated regions, notably in West Europe and South Asia, where a major reactor accident can subject around 30 million people to radioactive contamination. The recent decision by Germany to phase out its nuclear reactors will reduce the national risk, though a large risk will still remain from the reactors in neighbouring countries.

Hemispheric dispersion of radioactive plume laced with fission nuclides from the Fukushima nuclear event

Radioactivities of particulate 131I and 137Cs released from the Fukushima nuclear accident were monitored in a regional aerosol network including two high mountain sites (central Taiwan and Tibetan Plateau). The results were integrated with data measured elsewhere around the world, with special focus on the mid‐latitudes. The hemispheric transport of the Fukushima radiation clouds (FRCs) by the westerlies took ∼18 days, displaying an exponential‐like decrease eastward, with a dilution factor of at least five orders of magnitude following a full circuit around the globe. The initial two waves of FRCs may travel at different atitudes: the first one at ∼3–4 km, whereas the second one up to 5 km or more. 131I and 137Cs were fractionated during transport, with 137Cs concentrated in the shallower layer, susceptible to depositional removal, while 131I moving faster and higher. This accident may be exemplified to identify some atmospheric processes on the hemispheric scale.

Geochemical and radiochronological evidence of North Sea storm surges in salt marsh cores from The Wash embayment (UK)

The accumulation history of intertidal silty salt marsh sediments, from the northern shore of The Wash embayment (eastern UK), has been investigated along two cores, using a multiproxy approach involving visual logging, grain size measurements, as well as determination of particulate elements concentrations and 137Cs, 210Pb activities. The cores were collected in the high marsh area; one core was collected on the marsh platform, whilst the other was collected 5 m from the edge of a creek. Grain size distribution reveals two distinct silty sand layers within the lower parts of both cores. One of these is thought to represent the well-documented 1953 storm surge catastrophic event. A second silty sand horizon, found in the core located closer to the creek, is interpreted as being a later storm surge deposit produced in 1978. The redox states of both cores are similar and oxic conditions throughout are inferred from geochemical variations. The absence of a redox interface along the sediment column implies regular oxygen penetration during tidal cycles, thereby limiting the post-depositional mobility of 137Cs and 210Pb. The Caesium-137 distributions, in both of the cores, show a broad hump shape; these activities are interpreted as being largely affected by marine inputs from Sellafield. 210Pb dating is used as an independent chronometer that confirms 137Cs dating. Following the 1978 storm event, the mean accumulation rates, considering 137Cs and 210Pb radionuclide data and the discrete coarse-grained marker horizons, are 0.75 ± 0.09 g/cm2 per yr (nominally 1.00 ± 0.11 cm/yr) close to the creek edge and 0.46 ± 0.04 g/cm 2 per yr (nominally 0.74 ± 0.10 cm/yr) on the marsh platform. Storm erosion is followed by moderately high accumulation rates.

137Cs inventory in sediment near the Rhone mouth: role played by different sources

The low tidal range of the Mediterranean Sea and the high sediment load of the Rhone induce the formation of an important submarine delta. The 137Cs inventory in sediment on a 480 km 2 area near the Rhone mouth reached 19.6 TBq in 1990. The spatial distribution of both sediment accumulation rates and 137Cs concentrations in this area confirm the existence of a spatially well-delimited zone, i.e. the prodelta, where both parameters are the highest. Thus, 40% of the total amount of 137Cs stored in this 480 km 2 area was found within the prodelta (30 km 2) in the close vicinity of the river mouth. This attests to the efficiency of the 137Cs trapping by the prodelta sediments. A study on the part the different 137Cs sources in the Mediterranean Sea play in contributing to this inventory has been carried out. These sources are (i) direct deposition from both global fallout and the Chernobyl accident, (ii) indirect inputs arising from the erosion of surface soils of the Rhone catchment area that were also contaminated by the previous fallout, (iii) liquid effluents from the nuclear industry into the Rhone waters. Assuming that direct deposition is evenly distributed over the study area (480 km 2) and that the particulate 137Cs input from the Rhone is entirely trapped in this same area, these sources account for about 50% of the inventory. These hypotheses are unlikely in a coastal area subject to various physical disturbances but they are conservative enough to assess the lower limit of the nuclear liquid releases contribution to this inventory to be 50%.

Simulation of event‐based and long‐term spatial redistribution of Chernobyl‐derived radiocaesium within catchments using geographical information system embedded models

AbstractThe Chernobyl accident contaminated vast areas of Europe with radiocaesium (137Cs) in 1986. To evaluate long‐term and event‐based redistribution of Chernobyl‐derived 137Cs at the catchment scale, two geographical information system embedded models have been developed. The first model simulates 137Cs redistribution using a monthly time step based on a long‐term soil erosion model. The second model simulates lateral radiocaesium transport at the event scale based on the existing Limburg soil erosion model. This model accounts for surface runoff, soil erosion and deposition, and radiocaesium exchange between the topsoil layer, runoff water, and suspended sediment. Both models have been tested and applied to the Mochovce catchment, western Slovakia. The spatial distribution of 137Cs activity in soil simulated by the long‐term model was used as input for the event‐based model to assess the changes in 137Cs transport during rainfall events between 1986 and 2002. Soil erosion events in the first months after initial fallout input before ploughing caused a considerable decline in the 137Cs soil inventories, which were estimated at 8·9% of the total initial inventory. The majority of 137Cs transport during rainfall events occurs in particulate form. Both the absolute amounts of particulate 137Cs transport and the fraction of particulate 137Cs transport were shown to be positively related to suspended sediment transport. Between 1986 and 2002, dissolved 137Cs transport has declined by a factor of about 26, which can be largely attributed to the increased sorption to sediment particles. Particulate 137Cs transport has declined by a factor of about two, which can be largely attributed to the decrease in soil 137Cs. The 137Cs inventories in soil have decreased by a factor between three and four at the steep hillslopes, but have remained at about the same level as the initial fallout input at the valley bottoms. Copyright © 2003 John Wiley & Sons, Ltd.

Radioactive Contamination of the North-western Black Sea Sediments

The paper deals with the input and deposition of the man-made radionuclides 137Cs, 238 Pu, 239+240Pu and 241Am introduced to the north-western Black Sea, over the last few decades, as the result of atmospheric nuclear weapons testing and the Chernobyl nuclear accident. One approach taken was to retrieve the deposition records of these radionuclides in the sediments. The deposition chronology was compared with monitoring data of the post-Chernobyl input of 137Cs to the NW Black Sea sediments from the Danube River. The partitioning of 137 Cs between suspended matter and water was traced along the salinity gradient in the Danube mixing zone. In sediments deposited in the vicinity of the Danube delta and the Dniepr estuary, the activity of Chernobyl 137Cs had reached its maximum 5 and 10 years after the accident, respectively. The activity ratio of 137Cs to 239+240Pu and 241 Am revealed a higher mobility of 137Cs in the Danube River basin compared to plutonium and americium. The percentage of particulate 137Cs and its distribution coefficient vs salinity have allowed the estimation of sedimentary scavenging and desorption of caesium in the Danube mixing zone. Comparison of the post-Chernobyl 137Cs input from the Danube to the 137Cs inventory in the adjacent Black Sea sediments showed that more than 70% of this radionuclide was deposited in the Danube–Black Sea mixing zone.

Geochemical Associations of Sellafield-Derived Radionuclides in Saltmarsh Deposits of the Solway Firth

This paper describes a study of the geochemical associations of Sellafield waste radionuclides in saltmarsh sediments from south-west s]Scotland. The contaminant radionuclides are transported to this environment in association with particulate material and 137Cs was found to be predominantly (80-98%) non-extractable. In the case of 239+240Pu there was a redistribution from the oxalate extractable oxide fraction to the pyrophosphate extractable organic fraction as a consequence of on-shore transfer of contaminated sediment. The relatively aggressive nature of the chemical extractants required to remove the radionuclides from the sediments suggests that they were in a form which was unlikely to result in their being released into the aquatic environment or taken up by plants. Plutonium had a greater potential mobility or bioavailability than Cs. Values of KD for the desorption of 137Cs from the sediment by freshwater, groundwater and seawater were all approximately 105 L kg-1, confirming its immobility in this environment. The desorption KD values for stable 133Cs were all approximately 106 L kg-1, so the stable Cs did not have a significant influence on the radiocaesium in this sediment.

The history and source of particulate 137Cs and 239,240Pu deposition in sediments of the Ob River Delta, Siberia

This paper presents the first results of a project designed to examine the transfer of particle-associated artificial radionuclides down the Ob River in Siberia to its delta over the past 5 decades. The main sources include fallout from atmospheric nuclear weapons tests and weapons complexes and test sites of the Former Soviet Union in or near the Ob watershed. The approach is to measure the accumulation of the radionuclides in undisturbed delta sediments — obtaining a record of their deposition over time. These records were found in sediments of shallow lakes apart from, and connected to, the main channel. Sediment cores were collected in the summer of 1994 using a shallow draft catamaran to reach these lakes from a support ship in the main channel. Measurements are presented on the depth distributions of 137Cs and Pu isotopes and their inventories in a series of dated sediment cores — including one from a location in the Taz Estuary (which does not receive Ob River sediments). Sediment dating was carried out using the excess 210Pb technique. The results obtained are compared with known information on the temporal history of releases from the various sources and characteristics of the isotopic composition of the sources. The results show that good records of radionuclide deposition indicate that the major fraction of 137Cs and Pu isotopes deposited in these delta sediments comes from atmospheric nuclear weapons test fallout — both delivered directly from the atmosphere and from downstream transport of watershed sediments. No more than 25% of the observed inventories could be derived from other sources.

Discharge of dissolved and particulate 137Cs in the Kuji River, Japan

The discharge of fallout 137Cs in the water of the Kuji River was studied with the aim of understanding the migration behavior of 137Cs in the river watershed. Under normal flow conditions, the radioactivity of dissolved 137Cs in the water ranged from 0.05 to 0.12 mBq/l, while that of the particulate 137Cs ranged from 0.02 to 0.09 mBq/l. A large increase in the particulate 137Cs, up to 0.77 mBq/l, was observed under high flow conditions caused by a 40 mm precipitation event. It was found that the dominant speciation of 137Cs changed from the dissolved to the particulate mode according to the flow conditions related to the precipitation event. The annual budget of 137Cs in the watershed was estimated based on empirical relation between the load of 137Cs and the flow rate. The accumulated 137Cs in the watershed was evaluated as 4.2 × 10 3 MBq/km 2. On the other hand, the annual losses were 1.7 MBq/km 2 by the discharge into the river and 1 × 10 2 MBq/km 2 by radioactive decay. This budget has proved, qualitatively, that the surface soil acts as a significant adsorbant for atmospherically-derived 137Cs.