Evaluation of 239+240Pu, 137Cs and natural 210Pb fallout in agricultural upland fields in Rokkasho, Japan

The background distributions of ^239+240Pu and ¹³⁷Cs fallout in agricultural soil were investigated in Rokkasho where Japan's first commercial nuclear fuel reprocessing plant is now being constructed. The mean inventories of ^239+240Pu and ¹³⁷Cs in three fields with non-yam-cultivation history were 116 Bq·m⁻² and 3.4 kBq·m⁻², respectively. The mean atomic ratio of ²⁴⁰Pu/²³⁹Pu for all studied fields was 0.18±0.04, and was similar to that of global fallout. The ^239+240Pu concentrations correlated very well with ¹³⁷Cs (r = 0.97) in spite of heavy disturbance of the soil, and the activity ratio of ^239+240Pu/¹³⁷Cs was 0.037±0.007, which is a typical value for global fallout. These results showed that the nuclides had similar behavior in agricultural upland fields in Rokkasho. Since ²¹⁰Pb is steadily deposited from the atmosphere to the land, this nuclide could be an index for the degree of disturbance of a field and of soil lost from the field. The ratio of excess ²¹⁰Pb inventory in the soil to the equivalent inventory of atmospheric ²¹⁰Pb deposition was 96%, and indicated that soil was not lost from the cultivated fields. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vertical Profiles, Inventories, and Activity Ratios of 239+240Pu and 137Cs in Sediments from Sagami Bay, Western Northwest Pacific Margin

Marine sediment cores were taken from Sagami Bay of the western Northwest Pacific and analyzed for ^239+240Pu and ¹³⁷Cs activities. A significant correlation was observed between ^239+240Pu and ¹³⁷Cs activities in sediment cores, i.e., their vertical profiles. The measured activities which were used to obtain the inventories of ^239+240Pu and ¹³⁷Cs in the sediment column, showed large variations, ranging from 36 to 474 MBq/km² for ^239+240Pu and 49 to 652 MBq/km² for ¹³⁷Cs. ^239+240Pu inventories in the sediment from one region in the Bay, Sagami Nada were 5–10 times greater than those predicted from atmospheric global fallout 42 MBq/km² at the same latitude. On the other hand, ¹³⁷Cs inventories, with a mean value of 297±168 MBq/km², were much less than predicted, 2040 MBq/km². The activity ratios of ^239+240Pu/¹³⁷Cs obtained, with a mean of 0.65±0.17, were significantly greater than the ratio predicted from fallout, 0.021. Furthermore, there was a clear relationship between both ^239+240Pu and ¹³⁷Cs inventories and the water content, indicating that higher inventories may be attributed principally to concentration in, and scavenging by, fine-grained particles.     

239+240Pu and 137Cs in Sediments from Tokyo Bay: Distribution and Inventory

Four sediment cores were collected from Tokyo Bay and analyzed for their ^239+240Pu and ¹³⁷Cs concentrations. Shallow nearshore sediments from Tokyo Bay have ^239+240Pu inventories which average 214±14 MBq/km². They are five times greater than the supply expected from the atmospheric global fallout at the same latitude of 42 MBq/km². The measured mean ¹³⁷Cs inventory of 433±93 MBq/km² is approximately one fifth the value expected from global fallout. Furthermore, the ^239+240Pu/¹³⁷Cs activity ratios, with a mean ratio of 0.50±0.14, are significantly greater than the ratio expected from the global fallout of 0.021. Excess ^239+240Pu inventories can be considered to have been introduced into Tokyo Bay as weathering products by soil erosion, transported via rivers and winds, and to be much more efficiently scavenged from seawater by particles resuspended at the sediment-water interface.     

Simultaneous analysis of 137Cs, 90Sr, 238Pu and 239+240Pu in Brazilian seawater

Methodologies for simultaneous analysis of ¹³⁷Cs, ⁹⁰Sr, ²³⁸Pu and ^239+240Pu were developed and applied to seawater samples. ¹³⁷Cs levels in Brazilian coastal seawater ranged from 0.12 to 4.7 Bq·m^-3, for ⁹⁰Sr from 2.0 to 8.6 Bq·m^-3, for ^239+240Pu from 0.8 to 4.5 mBq·m^-3 and for ²³⁸Pu it was of 1.9 mBq·m^-3. The artificial radioactivity levels in Brazilian seawater are typical values due to fallout deposition.     

Development of a bipolar electrolysis system for tritium accumulation in HTO

Due to the different ²⁴⁰Pu/²³⁹Pu atom ratios from different sources of Pu in the environment, Pu isotopes have been widely used for source identification of radionuclides in sediments. In this work, using sector-field ICP-MS, we investigated Pu inventory and its isotopic composition in a lacustrine sediment core collected in Chenghai Lake, SW China. The ²⁴⁰Pu/²³⁹Pu atom ratios in this sediment core ranged from 0.166 to 0.271 with a mean of 0.195±0.021, which was slightly higher than that of global fallout. The ^239+240Pu/¹³⁷Cs activity ratios ranged from 0.0155 to 0.0411, with a mean of 0.0215, and the ^239+240Pu inventory was 35.4 MBq/km²; both ^239+240Pu/¹³⁷Cs activity ratio and Pu inventory were close to those values of global fallout at 20–30 °N. Three peaks were observed for both ¹³⁷Cs and ^239+240Pu activities in the examined sediment core; they most probably indicated the maximum deposition of global fallout between 1963 and 1964, the fallout from a series of Chinese nuclear tests during the 1970s, and the deposition of resuspended Pu-bearing particles from the Chernobyl accident. Therefore, the vertical profile of Pu isotopes should provide useful time markers for rapid dating of recent sediments. These authors contributed equally to this work.     

Plutonium Isotopes in Sediments from the Sudanese Coast of the Red Sea

This paper presents the activity concentrations of Pu isotopes in surface marine sediments collected from the Sudanese coast of the Red Sea. The following concentration ranges were determined: ²³⁸Pu, 4.7–28.6 mBq/kg; ^239+240Pu, 53–343 mBq/kg dry weight. The average activity ratios of ²³⁸Pu/^239+240Pu (0.075±0.045 mBqk/kg) and ^239+240Pu/¹³⁷Cs (0.026±0.025 mBq/kg) are appropriately comparable to the literature values that are characteristic of the global fallout from the atmospheric nuclear weapon tests. However, ^239+240Pu/¹³⁷Cs ratio in sediments collected from the biologically rich fringing reef is an order of magnitude higher compared to other sampling locations.     

Current levels and distribution of 137Cs and Pu isotopes in soil on the Kazakhstan territory of the Kazakhstan-Chinese border: Semipalatinsk and Lob Nor nuclear test sites detonation

More than 100 soil samples were collected from 46 sites along roads and some settlements connecting Alma-Ata to Semipalatinsk City of the Kazakhstan-Chinese border and analyzed for ¹³⁷Cs and Pu isotopes (²³⁸Pu, ²³⁹Pu and ²⁴⁰Pu). The mean ¹³⁷Cs inventory at each site was within the range of 1,000-3,000 Bq/m² for most of the sites. The ^239,240Pu concentration and its inventories were observed in the wide range of 0.18-2.6 Bq/kg and 28-677 Bq/m², respectively. At the most northern sites in the areas studied, higher^239,240Pu inventories were found corresponding to the increase of ^239,240Pu fraction which was not leached by hot digestion with conc. HNO₃+H₂O₂. The ^239,240Pu/¹³⁷Cs activity ratios for the soil samples from the southern areas lie in the narrow range of 0.016–0.039 (most of data being 0.02–0.03), probably indicative of global fallout origin. On the other hand, a little or several higher ratios (0.05 to 0.22) were found for soil samples from the northern areas. These higher ratios demonstrate strongly that there was additional Pu input of local fallout due to the atomic explosions. From ²⁴⁰Pu/²³⁹Pu atomic ratios measured, contribution of local fallout ^239,240Pu, probably from the SNTS, was found to be higher (60–86%) in the sites around the northern areas than the southern ones. The present data might serve not only as a current baseline information on distribution and contamination levels of the long-lived fallout radionuclides in the Kazakhstan areas of the Kazakhstan-Chinese border, but also as a aid of selection of control area for epidemiological projects.     

Temporal variation of 137Cs inventory in the western North Pacific

The temporal variation of water column inventories of ¹³⁷Cs in the western North Pacific was examined. ¹³⁷Cs in seawater of the western North Pacific has originated mainly from global fallout from atmospheric nuclear weapons tests, which occurred in the early 1960's. In the western North Pacific, the water column inventories of ¹³⁷Cs were 5200 Bq·m^-2 in 1973 (GEOSECS station GX225) and 3400 Bq·m^-2 in 1983 (KH-84-3 station AN-1). In 1997, the ¹³⁷Cs inventory was 2600 Bq·m^-2 at station 1 of the IAEA'97 cruise. The global fallout at Tsukuba since 1945 was estimated to be 5600 Bq·m^-2 in 1973, 4600 Bq·m^-2 in 1983 and 3500 Bq·m^-2 in 1997. The water column inventories of ¹³⁷Cs were 93–74% of the estimated global fallout for the same latitude. The typical features of the temporal variation for three vertical profiles taken in 1973, 1983 and 1997 are the decrease of ¹³⁷Cs activity in the mixed layer and the gradual increase of ¹³⁷Cs activity in deeper layers. The proportion of the ¹³⁷Cs inventory in waters down to 1000 meters was 100% in 1973, 88% in 1983 and 75% in 1997. These findings suggest that large amount of the ¹³⁷Cs entering through sea surface would remain in the mixed layer for more than a few decades.     

Some aspects of environmental radioactivity around the former Soviet Union"""s Semipalatinsk nuclear test site: Local fallout Pu in Ust"""-Kamenogorsk district

The ¹³⁷Cs, ²³⁸Pu and ^239,240Pu activity concentrations were determined together with the atomic ratios of ²⁴⁰Pu/²³⁹Pu for the soil samples at 19 sites from the Ust"-Kamenogorsk district, located more than 300 km east of the Semipalatinsk nuclear test site (SNTS). The mean areal deposition of ¹³⁷Cs ranged from 1,500 to 4,100 Bq/m². However, some hot spot-like areas showing high concentrations of 5,500–7,700 Bq/m² were foundat some sites within the city. The ^239,240Pu levels ranged from <50 to 510 Bq/m², however most of them ranged between 120–200 Bq/m². These levels are nearly the same as those around the Semipalatinsk City. At most of the sites within the city and its adjacent areas, both nuclides were found in the soil layers up to a depth of 30 cm. A fraction of 20–50% of ^239,240Pu was not leached by hot digestion with concentrated HNO₃ containing a small amount of H₂O₂. Generally, such tightly bound fraction showed a trend to decrease with increasing distance from the SNTS. The fraction of these radionuclides that were deposited in Ust"-Kamenogorsk district from global and from SNTS fallouts have been determined using the ²⁴⁰Pu/²³⁹Pu atomic ratios in both Pu fractions: one which can be leached with hot HNO₃ + H₂O₂ and another that is a non-leacheable for each soil layer of core samples. As a result a fraction of 21–80% (mostly 30–60%) of total ^239,240Pu were found to be due to the local fallout of Pu from the SNTS debris. For ¹³⁷Cs, the contribution (mostly 10–20%) of local fallout from the SNTS were estimated to be far lower as compared to ^239,240Pu.     

Fallout of transuranium elements following the Chernobyl accident

The deposition of transuranium elements in Sweden following the Chernobyl accident was investigated through the analysis of carpets of lichen-and moss-samples and also air-filters and precipitation. The impact of transuranium elements was small compared to that of radiocesium. The deposition of^239+240Pu was, as for other actinides, inhomogeneously distributed and ranged from 0.1% to 100% of the inventory in 1986 from nuclear detonation tests. The activity ratio of^239+240Pu/¹³⁷Cs was between 10^–3 and 10^–6 in comparison to 10^–2 for nuclear test fallout. The activity ratios of²⁴¹Pu,²⁴²Cm,²³⁸Pu,^243+244Am and^239+240Pu were about 86, 14, 0.47, 0.14, and 0.13 respectively, but large variations were observed. The results from Sweden were compared with those found in South Finland, Denmark and Southern Europe. The deposition over Scandinavia originated from the initial explosion at Chernobyl, which contained relatively higher amounts of actinide elements than the second emission, which occurred a few days later and was a result of actions taken to bring the fire under control.     

Radioactivity of plutonium isotopes, <Superscript>137</Superscript>Cs and their ratio in sediment,seawater and biota from the east coast of Peninsular Malaysia

This study with sampling expeditions of marine sediment, seawater and biota were performed at 30 stations within Malaysian Exclusive Economic Zone (EEZ). A total of >400 samples were collected to determine the activity concentration of anthropogenic radionuclides (^239+240Pu, ¹³⁷Cs) and their activity ratio (^239+240Pu/¹³⁷Cs) in sediments, seawater and biota. The purpose of this study was to determine the concentration levels for these radionuclides and to evaluate any occurrence of radioactive contamination. Sediment cores were obtained using multicorer device, while water samples via co-precipitation techniques and biota was purchased from local fishermen. The activity concentrations of ^239+240Pu in sediment, seawater and biota were ranged 0.21–0.45 Bq/kg dry wt., 2.33–7.95 mBq/m³ and <0.008 Bq/kg fresh wt., respectively. Meanwhile, the values of ¹³⁷Cs were ranged <1.00–2.71 Bq/kg dry wt. in sediment, 3.40–5.89 Bq/m³ in seawater and <0.05–0.41 Bq/kg fresh wt. in biota, respectively. Activity ratios of ^239+240Pu to ¹³⁷Cs obtained seem to confirm that these artificial radioactivities were mainly due to global nuclear fallout.     

Distributions of Pu isotopes and 137Cs in soil from Semipalatinsk Nuclear Test Site detonations throughout southern districts

Soil samples collected mainly from the southern areas, including Kainar and Karaul settlements, around the Semipalatinsk Nuclear Test Site of the former USSR were analyzed for ¹³⁷Cs and Pu isotopes (²³⁸Pu,²³⁹Pu and ²⁴⁰Pu) by γ-ray and α-ray spectrometry and ICP-MS. The ¹³⁷Cs inventories varied widely from 170 to 13,600 Bq/m². The ^239,240Pu inventories, values of which are scare in the literature, also varied in the range of 34-2,050 Bq/m² (most of date being 100-300 Bq/m²). In the areas around Tailan, Sarzal and Karaul settlements where the radioactive cloud related to the first thermonuclear explosion passed through, higher inventories of these nuclides were observed and especially their ²³⁸Pu/^239,240Pu activity ratios (0.0064-0.0076) were markedly lower than those attributed to global fallout (0.03-0.04). The observed ratios might be used as a fingerprint to identify the Pu source of the first thermonuclear event. Most of the ²⁴⁰Pu/²³⁹Pu atomic ratios were lower than those of global fallout (0.18) commonly accepted. The contribution of local fallout ^239,240Pu was higher (more than 80-90%) in the areas around the Tailan, Sarzal and Karaul settlements than that (30-ca. 60%) in the other areas. This high Pu contribution was related to the Pu source from the first thermonuclear event. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Effect of Carbonate Soil on Transport and Dose Estimates for Long-Lived Radionuclides at a U.S. Pacific Test Site

The United States conducted a series of nuclear tests from 1946 to 1958 at Bikini, a coral atoll, in the Marshall Islands (MI). The aquatic and terrestrial environments of the atoll are still contaminated with several long-lived radionuclides that were generated during testing. The four major radionuclides found in terrestrial plants and soils are cesium-137, strontium-90, plutonium-239+240 and americium-241. Cesium-137 in the coral soils is more available for uptake by plants than ¹³⁷Cs associated with continental soils of North America or Europe. Soil-to-plant ¹³⁷Cs median concentration ratios (CR) (kBq·kg^-1 dry weight plant/kBq·kg^-1 dry weight soil) for tropical fruits and vegetables range between 0.8 and 36, much larger than the range of 0.005 to 0.5 reported for vegetation in temperate zones. Conversely, ⁹⁰Sr median CRs range from 0.006 to 1.0 at the atoll versus a range from 0.02 to 3.0 for continental silica-based soils. Thus, the relative uptake of ¹³⁷Cs and ⁹⁰Sr by plants in carbonate soils is reversed from that observed in silica-based soils. The CRs for ^239+240Pu and ²⁴¹Am are very similar to those observed in continental soils. Values range from 10^-6 to 10^-4 for both ^239+240Pu and ²⁴¹Am. No significant difference is observed between the two in coral soil. The uptake of ¹³⁷Cs by plants is enhanced because of the absence of mineral binding sites and the low concentration of potassium in the coral soil. Cesium-137 is bound to the organic fraction of the soil, whereas ⁹⁰Sr, ^239+240Pu and ²⁴¹Am are primarily bound to soil particles. Assessment of plant uptake for ¹³⁷Cs and ⁹⁰Sr into locally grown food crops was a major contributing factor in: (1) reliably predicting the radiological dose for returning residents and (2) developing a strategy to limit the availability and uptake of ¹³⁷Cs into locally grown food crops.     

239+240Pu and137Cs concentrations in salmon (Oncorhynchus keta) collected on the Pacific coast of Japan

Salmon (Oncorhynchus keta) samples were collected on the Pacific coast of Japan and analyzed for their^239+240Pu and¹³⁷Cs concentrations in six places, i.e., muscle, viscera, gill, gonad, skin and spine. The^239+240Pu concentrations in muscle ranged from 0.07 to 0.14 mBq/kg (wet) and had the lowest value among the six regions. The mean^239+240Pu concentrations in viscera, gonad and spine were more than 1 mBq/kg (wet_ while those in muscle and skin were one order of magnitude lower. The largest amounts of^239+240Pu were accumulated in gonad. The^239+240Pu/¹³⁷Cs activity ratios in all positions were lower than that of the global fallout ratio of 0.022, suggesting that¹³⁷Cs could be accumulated with greater ease than^239+240Pu in all positions and ratios of uptake differed remarkably from position to position. The total accumulations of^239+240Pu and¹³⁷Cs in salmon were 1.32 and 328 mBq/individual, respectively.     

238Pu, 239+240Pu, 241Am, 90Sr and 137Cs in mountain soil samples from the Tatra National Park (Poland)

Activity concentrations and inventory for ²³⁸Pu, ^239+240Pu, ²⁴¹Am, ⁹⁰Sr, and ¹³⁷Cs in soil from Tatra Mountains of Poland are presented. Soil samples were collected using 10 cm diameter cores down to 10 cm and sliced into 3 slices. Details of the applied procedure are described with the quality assurance program. The maximum activity concentrations found for various samples were: 1782±13 Bq/kg, 17.4±0.9 Bq/kg, 3.4±0.3 Bq/kg and 84±7 Bq/kg for ¹³⁷Cs, ^239+240Pu, ²⁴¹Am and ⁹⁰Sr, respectively. The maximum cumulated deposition of ^239+240Pu is 201±8 Bq/m². The origin of radionuclides is discussed, based mostly on the observed isotopic ratio of Pu. Significant correlations were found between ^239+240Pu, ²⁴¹Am and ¹³⁷Cs. The effective vertical migration rate seems to be in the order of: ⁹⁰Sr≫Pu>Am>Cs.     

Pu isotopes and137Cs in the surrounding areas of the former Soviet Union's Semipalatinsk nuclear test site

Field missions were sent to Semipalatinsk City and several settlements near the former Semipalatinsk nuclear test site to investigate the current radioactive contamination levels of the land coming from long-lived radionuclides. The soil was sampled at about 20 sites, including some settlements such as Mostik, Dolon and Chagan, forest and pasture areas, along the roads from Semipalatinsk City to Kurchatov City and to Korosteli settlement in the direction of the Altai District. The radioactivities of¹³⁷Cs,²³⁸Pu and^239,240Pu as well as²⁴⁰Pu/²³⁹Pu atomic ratios in the soil were determined by non-destructive γ-ray spectrometry and radiochemical separation followed by α-ray spectrometry and/or ICP-MS, respectively. The results showed a distinction of¹³⁷Cs and^239,240Pu inventories in soil depending on the site where we visited. While the overall¹³⁷Cs levels were as same as or slightly lower than the domestic global fallout level (3·10³–7·10³ Bq/m²),^239,240Pu levels at some sites were several to a few ten times higher than the domestic level (40–120 Bq/m²). The atomic ratios of²⁴⁰Pu/²³⁹Pu in the soil were in the range of 0.024–0.125, which were significantly lower than the value of 0.18 commonly accepted for global fallout Pu.     

Depth distribution of239,240Pu and137Cs in soils of South Korea

Depth distribution of^239,240Pu and¹³⁷Cs in the soils of South Korea have been studied. The average accumulated depositions were estimated roughly to be 54.8±32.1 Bq·m^–2 for^239,240Pu, 1.6±1.0 Bq· ·m^–2 for²³⁸Pu and 1982.8±929.1 Bq·m^–2 for¹³⁷Cs. The activity ratios of^239,240Pu/¹³⁷Cs in soils were found to be in the narrow range of 0.0153 to 0.0364 with a mean value of 0.0230±0.006. The concentrations of^239,240Pu and¹³⁷Cs in soils decrease exponentially with increasing the soil depth. A significant correlation was found between the concentration of^239,240Pu and that of¹³⁷Cs. The activity ratios of^239,240Pu/¹³⁷Cs tend to increase slightly with increasing soil depth.     

History of plutonium composition of fallout in the Northeastern U.S. from contemporary measurements

The analyses of lake sediments from the northeastern U.S. provide depositional histories of¹³⁷Cs and^239+240Pu from both global fallout and fallout from the Nevada Test Site (NTS) detonations in the 1950's. These results provide an independent verification and extension of the temporal trend of the²⁴⁰Pu/²³⁹Pu atom ration of global fallout to earlier times. This data supports the findings of other studies of fallout in the atmospheric and marine environment.     

Calculation of artificial radionuclides in the ocean by an ocean general circulation model

The concentrations of three artificial radionuclides (⁹⁰Sr, ¹³⁷Cs and ^239+240Pu) introduced into seawaters from global fallout were simulated from 1957 to 1994 by using an ocean general circulation model. The distributions of the calculated ¹³⁷Cs and ⁹⁰Sr concentrations were in good agreement with the observed concentrations. The vertical distribution of the calculated ^239+240Pu concentration in the South Pacific also agreed with the observed data. However, the calculated ^239+240Pu concentrations in the North Pacific water columns were significantly underestimated in comparison with the observed data, which strongly suggests the presence of additional sources of plutonium input to the North Pacific.     

The210Pb and137Cs profiles in sediment cores from Bay of Quinte,Lake Ontario

²¹⁰Pb,²²⁶Ra and¹³⁷Cs profiles have been measured for sediment cores from three locations in Bay of Quinte, Lake Ontario, Canada. Compaction of the sediment with depth of burial is taken into account in calculating recent sedimentation rates and age profiles at these locations from the excess²¹⁰Pb profiles. The rates are 1.803+0.592 cm·y^–1 (0.254±0.083 g·cm^–2·y^–1), 0.101±0.017 cm·y^–1 (0.036+0.006 g·cm^–2·y^–1), and 0.795±0.218 cm·y^–1 (0.076±0.021 g·cm^–2·y^–1). The corresponding fluxes of excess²¹⁰Pb to sediment/water interface are determined to be 1.652, 0.253, and 1.123 pCi·cm^–2·y^–1, respectively. The anomalies observed in the radionuclide concentration profiles are attributed to physical mixing. It is postulated that the significantly higher flux of²¹⁰Pb observed at one of the locations is due to inputs from Trent River which joins the Bay near this location.