Pu In Sediments Research Articles

Monitoring of 137Cs, 239+240Pu, and 90Sr in the marine environment of South Korea and their impact on marine biota: 10 years after the Fukushima accident

This study conducted an analysis of the behavior of radionuclides and assessment their radioactive risk based on seawater and seabed sediment samples gathered from the East, South, and Yellow Seas of South Korea over the period from 2011 to 2020. The distribution for each radionuclides in seawater obtained from the East, South, and Yellow Seas were similar. However, the concentrations of 137Cs and 239+240Pu in sediments from the East Sea were observed to be higher compared to those from the South and Yellow Seas. This variation can be attributed to differences in the ocean inflow, water column properties, and seabed characteristics among the seas around South Korea. There were no statistically significant differences between the radioactive concentrations of seawater and seabed samples collected before and after the Fukushima accident, and no areas with unusually high radiation levels were detected. Using the distribution coefficient (Kds) and the concentration ratio (CR) calculated from the 2011-to-2020 data, we evaluated the radiological impact on fish. The ERICA tool was utilized to assess these data, and indicated a negligible radiological risk from radioactivity in the seawater, seabed sediments, and marine biota in the South Korean Ocean.

Spatio-temporal distribution of 239+240Pu in sediments of the China sea and adjacent waters

Data of 239+240Pu activities and 240Pu/239Pu atom ratios in surface and core sediments of the China Sea and adjacent waters were collected. We examine a dataset of 239+240Pu activities and 240Pu/239Pu ratios determined from surface sediments at 516 sites and 84 core sediment mainly across the China Sea and adjacent waters. For the first time the spatial distributions of the 239+240Pu activities, the 240Pu/239Pu ratios and the Pacific Proving Ground (PPG) fraction in the China Sea and adjacent waters are fully presented at the same time. Four types of typical 239+240Pu distribution with depth are commonly summarized: non-peak, pseudo single peak, single peak and multi peaks, which are based on the comprehensive analysis of the vertical distribution of 239+240Pu in 84 sediment cores that had been studied in the China Sea and adjacent waters. Their occurrence probability are ∼15%, ∼4%, ∼67% and ∼11%, respectively. This is the dominant Pu source in seawater which was transported by the North Equatorial Current and Kuroshio Current and its extension into the China Sea and adjacent waters first from east to west, then from south to north. A sea area to the northeast of Taiwan Island and the Okinawa Trough, shows high 239+240Pu activities and 240Pu/239Pu atom ratios spatial distribution trends, which are related to the intrusion of the Kuroshio Current carrying 239+240Pu from the PPG nuclear weapon tests. The used two end-member mixing model suggests that global fallout and PPG close-in fallout are the main sources of Pu in most of the investigate areas. As the 240Pu/239Pu of global fallout is relatively constant, the change of 240Pu/239Pu ratios in surface sediments of the China Sea and adjacent waters are mainly controlled by the PPG close-in fallout input.

Evaluation of BenzoDODA grafted polymeric resin for rapid and reliable assaying of plutonium in sediment samples

The paper reports a new rapid radioanalytical procedure for the determination of plutonium (Pu) in sediments by solid phase extraction chromatography (SPEC) using Bis-(2-ethylhexyl) carbamoyl methoxy phenoxy-bis-(2-ethylhexyl) grafted resin, abbreviated as Benzodioxodiamide (BenzoDODA) grafted resin. The resin was synthesized and evaluated for its sorption behaviour towards Pu in batch and column mode to determine its efficacy for selective recovery of Pu from sediment samples. The analytical procedure was based on the radiochemical separation of samples by acid digestion, followed by preconcentration of actinides by co-precipitation with Fe(OH)3 and finally selective recovery of Pu by SPEC using a column filled with BenzoDODA grafted resin. Pu was then radiometrically assayed by preparing alpha disc sources with electro-deposition followed by alpha spectrometry. The method was further validated with IAEA reference materials. This method gives reliable and reproducible results for the activity concentration of Pu in sediment samples within 24 h.

Distinctive distribution and migration of global fallout plutonium isotopes in an alpine lake and its implications for sediment dating

This work investigated plutonium (Pu) isotopes in sediment cores collected from an alpine lake (Lake Heinongpo with 3779 m above sea level) in Southwestern China. 240Pu/239Pu atom ratios in all sediment samples showed the typical global fallout values of ∼0.18 without any influences from other Pu contaminant sources. 239+240Pu activities with surface and subsurface maximums followed by exponential decline with sediment depth were respectively observed in the two sediment cores. The distinctive depth distributions of 239,240Pu in the lake sediments was attributed to the very slow sediment deposition rate due to the lack of terrestrial sediment input, while the alpine snowmelt input was the primary source of Pu in the lake sediments in addition to the direct atmospheric deposition. The total Pu inventory was estimated to be 56.3 ± 1.4 and 63.9 ± 0.8 Bq/m2 respectively in the two sediment cores. The generally higher Pu inventory in the Lake Heinongpo compared with other reported lakes in similar latitude should be mainly attributed to their different Pu input passages. The advection-diffusion equation was further applied to evaluate the downward migration of Pu isotopes in the sediment cores and predict the future evolution of Pu distribution in the sediment cores. The fitted results indicated that the diffusion effect controlled the downward migration of Pu in the sediments, but this diffusive migration will not prevent the peak of global fallout Pu in undisturbed sediment cores from being a valuable time marker for sediment dating.

Reconstruction of temporal variations of metal concentrations using radiochronology (239+240Pu and 137Cs) in sediments from Kizilirmak River, Turkey

Sediment cores retrieved from rivers, lakes, and coastal marine environment have been widely utilized to reconstruct historical variations of anthropogenic pollutants. A sediment core was collected in the Kizilirmak River, Turkey during 2014 and analyzed for a suite of metals (Cu, Pb, Zn, Ag, Ni, Co, Mn, As, Cd, Sb, V, Cr, Hg and Se) to reconstruct their temporal variations. Chronology was attempted using excess 210Pb (210Pbxs), 137Cs and 239,240Pu in the sediment cores. The vertical profile of excess 210Pb indicates that this core is not datable using excess 210Pb method. The 137Cs-based linear and mass apparent accumulation rates were estimated to be 0.84 cm year−1 and 0.93 g cm−2 year−1, respectively. These values are in agreement with the 239+240Pu peak-based linear (0.88 cm year−1) and mass apparent accumulation (0.97 g cm−2 year−1) rates. There is considerable broadening in the peaks of both 137Cs and 239,240Pu, likely due to post-depositional mixing processes. The measured sediment inventories of 210Pbxs, 137Cs and 239+240Pu were 38, 29, and 0.42 dpm cm−2, respectively, which were generally higher than the expected inventories based on local atmospheric depositional inventories. We attribute these enhanced inventories to potential sediment focusing and additional watershed erosional input. The Al-normalized enrichment factors (ANEF) were used to evaluate the contribution from natural versus anthropogenic sources. The ANEF of Ag, Ni, As, Cd and Se were > 1.5, which suggests a significant contribution of anthropogenic sources for these trace metals varied between 226% and 1163%. The geoaccumulation index (Igeo) values of the sediment column suggest that Cu, Pb, Zn, Co, Mn, Sb, V and Hg were in an unpolluted level and the others were in a polluted level. Besides, both the ANEF and Igeo values of Cu, Pb, Zn, Ag, As, Se, Cd and Hg showed a peak at 28–30 cm layer (corresponds to 1978–1981), which is attributed to maximum metal release during 1970s.

Vertical distributions and source identification of the radionuclides 239Pu and 240Pu in the sediments of the Liao River estuary, China

Activity concentration of plutonium (Pu) and its isotopic compositions are extensively used for measuring transport processes of Pu and identifying its source. We investigated the spatial distribution characteristics of 239+240Pu activity concentrations and 240Pu/239Pu atom ratio in several sediment cores collected from the Liao River coastal zone. Additionally, we calculated the 239+240Pu inventories and based on the 240Pu/239Pu atom ratio to trace Pu source. The activity concentrations of 239+240Pu in surface sediments of the Liao River estuary ranged between 0.103 ± 0.008 and 0.978 ± 0.035 mBq/g, with an average of 0.294 ± 0.024 mBq/g. The 240Pu/239Pu atom ratios, ranging from 0.173 ± 0.047 to 0.215 ± 0.061 (mean: 0.188 ± 0.049 (1σ)), were consistent with global fallout value, which indicates the global atmospheric fallout is the main source of Pu in sediment cores from the both sides of Liao River estuary. As for the tidal flat core LT-2, the mean 240Pu/239Pu atom ratio, slightly higher than that of the global fallout value, was 0.217 ± 0.050. Such pattern of Pu isotopic compositions indicated that Pu on the tidal flat in the Liao River estuary is sourced from a combination of global fallout and close-in fallout from the PPG by ocean currents transporting. And by using a two end-member mixing model, the results indicate the relative contribution of the PPG close-in fallout to core LT-2 is round 27% and 73% can be attributed to global fallout and river input. Therefore, these results clearly indicate that the direct global fallout is the main source of Pu in the Liao River estuary.

Vertical distributions of Pu and radiocesium isotopes in sediments from Lake Inba after the Fukushima Daiichi Nuclear Power Plant accident: Source identification and accumulation

Radiocesium isotopes were released into the environment in the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, which resulted from the massive Tohoku earthquake in March 2011. Lake Inba is located in Chiba Prefecture about 200 km from the FDNPP site and the lake was contaminated by radioactivity from the accident. The present work was carried out in order to investigate the vertical distributions and accumulations of radiocesium and Pu in sediment cores collected during 2011–2015, and to study the migration behaviors of radiocesium and Pu isotopes in the sediments. The observed 134Cs/137Cs activity ratios in the core samples were approximately 1 (decay-corrected to 15 March, 2011), suggesting that sediment samples were contaminated by the FDNPP-released radiocesium. Compared with radiocesium inventories in soil in the area surrounding the Lake Inba, the calculated higher radiocesium inventories of the collected sediment cores indicated that most of the radiocesium was subsequently accumulated in the lake, and that the radiocesium input by atmospheric deposition and input from surrounding soil were greater than the output of the radiocesium. The 239+240Pu activities in the sediments were all within the background level seen before the accident. The atom ratios of 240Pu/239Pu ranged from 0.175 to 0.210, suggesting that Pu originated from global stratospheric fallout rather than from the FDNPP accident.

Uranium and plutonium in anoxic marine sediments of the Santiago River mouth (Eastern Pacific, Mexico)

The uranium (U) and plutonium (Pu) content with depth in a sediment core collected in the continental shelf off the mouth of the Santiago River in the Mexican Pacific was studied to evaluate the contamination effects of the effluent of the Santiago-Lerma River as it moves into the sea. The large mass of terrestrial detritus delivered by the river influences the physicochemical and geochemical processes in the seafloor. Abnormal concentrations of U and Pu in sediments were examined as indicative of the effects of anoxic conditions. One of the indicators of pollution of seawater is the bacterial activity of the shallow seabed layer; and among the prevailing bacteria, the magnetotactic ones induce the formation of euhedral and framboidal shapes (pyrite). These pyrite entities are by-products of anoxic environments loaded with decomposing detrital material and are very abundant in the surface layers of the sediment core analyzed. The pyrite formation is the result of a biochemical reaction between iron and organic sulphur reduced by bacteria, and the pyrite entities precipitate to the seafloor. In the same upper zone of the profile, 238U is readily immobilized, while 234U is oxidized and dissolved in seawater by the effect of hot atom chemistry. This may cause the activity ratio (AR) 234U/238U disequilibrium (near 0.41). Furthermore, in the shallow layer of the sediment core, an abnormally high concentration of 239+240Pu was detected. In this upper layer, the activity concentrations found were 3.19 Bq kg−1 for 238U, 1.32 kg−1 for 234U and 2.78 Bq kg−1 for 239+240Pu. In the lower fractions of the sediment core, normal values of AR 234U/238U (≈1) were found, with traces of 239+240Pu.

Radioactivity of plutonium isotopes, 137Cs 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.

Plutonium characteristics in sediments of Hiroshima Bay in the Seto Inland Sea in Japan

Sediment core samples were collected from Hiroshima Bay in the Seto Inland Sea, western Northwest Pacific Ocean, and their 239+240Pu activities and 240Pu/239Pu atom ratios were determined by sector field ICP-MS. The activities of 239+240Pu ranged from 0.556 ± 0.025 to 0.745 ± 0.023 mBq/g. The atom ratios of 240Pu/239Pu were almost constant within the whole depth; the average value was 0.227 ± 0.014. This atom ratio was significantly higher than the mean global fallout ratio of 0.18, proving the presence of close-in fallout Pu that originated from the Pacific Proving Ground (PPG). The water masses exchanges between the Kuroshio Current and the Seto Inland Sea brought the PPG source Pu to this area, then Pu was extensively scavenged into sediment particles supplied by the rivers around the bay. The relative contributions of the global fallout Pu and the PPG close-in fallout Pu were evaluated by the two end-member mixing model. The contribution of the PPG close-in fallout was 38–41% of the total Pu in sediment. The remaining 59–62% was attributed to direct global fallout and the land-origin Pu transported by the rivers around the Hiroshima Bay.

Characterization of plutonium in deep-sea sediments of the Sulu and South China Seas

Anthropogenic Pu isotopes are important geochemical tracers for sediment studies. Their distributions and sources in the water columns as well as the sediments of the North Pacific have been intensively studied; however, information about Pu in the Southeast Asian seas is limited. To study the isotopic composition of Pu, and thus to identify its sources, we collected sediment core samples in the South China Sea and the Sulu Sea during the KH-96-5 Cruise of the R/V Hakuho Maru. We analysed the activities of 239+240Pu and the atom ratios of 240Pu/ 239Pu using isotope dilution sector-field inductively coupled plasma mass spectrometry (SF-ICP-MS). The 240Pu/ 239Pu atom ratios in the sediments of both areas (inventory weighted mean: 0.251 for the South China Sea and 0.280 for the Sulu Sea) were higher than the global fallout value (0.178 ± 0.019), suggesting the existence of Pu from the Pacific Proving Grounds in the North Pacific. Low inventories of 239+240Pu in sediments were observed in the South China Sea (3.75 Bq/m 2) and the Sulu Sea (1.38 Bq/m 2). Most of the Pu input is still present in the water column. Scavenging and benthic mixing processes were considered to be the main processes controlling the distribution of Pu in the deep-sea sediments of both study areas.

Using sequential extraction techniques to assess the partitioning of plutonium and neptunium-237 from multiple sources in sediments from the Ob River (Siberia)

Sequential extraction techniques have been developed to assess partitioning of anthropogenic radionuclides ( 240Pu, 239Pu, and 237Np), originating from a variety of sources, as identified by using bulk sediment isotopic composition. Sediments were leached sequentially with a series of six chemical treatments designed to approximate different environmental processes that may occur or to selectively extract trace metals contained in different solid phases of the sediments (i.e., exchangeable, reducible, carbonate, organic, acid leachable, and refractory). Results indicate the majority of Pu and Np is similarly distributed within many of the extracted fractions, with the largest percentage (66–97%) of both elements being observed in sediments treated with buffered citrate dithionite (CDB), which targets easily reduced constituents such as Mn and Fe hydrous oxides. While these results do indicate an association of Pu and Np with redox sensitive elements, the environmental implications are unclear given that the CDB treatment is more extreme than naturally occurring conditions. Minor amounts of Np partition differently from Pu in sediments. The NH 4-acetate treatment, which is designed to liberate trace metals that are loosely adsorbed onto the surfaces of sedimentary materials such as hydrated iron oxides and humic substances, or present at exchangeable sites in clay minerals, mobilized ∼12% of the total Np while Pu levels were below detection. The H 2O 2 treatment, which is designed to liberate trace metals bound to organic matter, mobilized ∼8 and ∼1% of Np and Pu, respectively. These results indicate that a minor portion of the total Np may be affected by environmental conditions that have little or no effect on Pu. Between 7 and 24% of the Pu was observed in treatments designed to liberate Pu and Np that are tightly bound to lithogenic phases or refractory silicates. The 240Pu/ 239Pu observed in accessible and refractory fractions ranged between 0.11 and 0.18. With the exception of one sample, the 240Pu/ 239Pu isotope ratios measured in the refractory fractions are essentially identical having a mean ratio value of 0.123 ± 0.001 (1 σ). The 240Pu/ 239Pu ratios provide isotopic evidence that suggests a portion of non-fallout contamination has a refractory nature. The presence of similarly low 240Pu/ 239Pu ratios in refractory fractions of sediments from the Ob and Irtysh Rivers suggests the existence of a source of refractory Pu which is consistent with refractory “hot particles” derived from surface tests at the Semipalitinsk test site.

Plutonium isotopes in marine sediments and some biota from the Sudanese coast of the Red Sea

Measurements of (239+240)Pu and (238)Pu were carried out on marine biota as well as on sediments from the fringing reefs area extending towards north and south (Flamingo Bay) of PortSudan harbour. The analyses were performed using radiochemical separation and alpha spectrometry. The range of the activity concentrations in marine sediments, in mBq kg(-1) dry weight, was found to be from 5.10 to 82.00 for (239+240)Pu and from 0.89 to 8.63 for (238)Pu. Corresponding activity concentrations of (239+240)Pu and (238)Pu in sediments from the harbours at PortSudan and Sawakin were 53-301 and 8.29-28.6 (PortSudan) and 163-343 and 4.7 (Sawakin), respectively. The higher values for plutonium in marine algae suggest their suitability as an indicator species for monitoring purposes. The results obtained are generally lower than those found by other studies and show that the Red Sea environment is mildly affected by plutonium contamination. Activity ratios of plutonium isotopes confirm that the existence of plutonium in the Red Sea is mainly due to atmospheric global fallout.

Distribution of 137Cs, 238Pu and 239 + 240 Pu in sediments of the southeastern Brazilian shelf–SW Atlantic margin

In this work levels of 137Cs, 238Pu and 239 + 240 Pu as well as activity ratios of anthrophogenic radionuclides in sediment samples from the southeastern Brazilian shelf are presented. Instrumental gamma spectrometry was used to determine 137Cs and alpha spectrometry to determine 238Pu and 239 + 240 Pu after a radiochemical procedure. The levels ranged from 0.30 to 1.79 Bq kg − 1 for 137Cs, from 15 to 150 mBq kg − 1 for 238Pu and, from 18 to 117 mBq kg − 1 for 239 + 240 Pu. There was a bathymetric differentiation in the radionuclides distribution. 137Cs values were generally higher in the samples collected at water depths of less than 100 m. On the other hand, plutonium isotopes exhibit higher values at greater depths. The mean ratio of 239 + 240 Pu / 137Cs obtained was 0.112 ± 0.072 which is in agreement with the value reported for the Atlantic from atmospheric fallout of nuclear explosions in the past. The 238Pu / 230 + 240 Pu ratios varied widely (from 0.339 to 2.088) and showed the influence of the SNAP-9A accident in the 238Pu levels for this area. The main goal of this work was to present unpublished anthropogenic radionuclide levels and activity ratios related to the contamination of the southeastern Brazilian shelf.

Distribution and inventories of 90Sr, 137Cs, 241Am and Pu isotopes in sediments of the Northwest Pacific Ocean

Bottom sediments collected in the Northwest (NW) Pacific Ocean in 1997 were analysed for 90Sr, 137Cs, 239, 240Pu and 241Am contents to determine their distribution patterns, inventories and sources. Enhanced inventories of 239,240Pu and 241Am were observed in the latitudinal belts of 10–20°N and 30–40°N, which correspond to major areas of local (tropospheric) and global (stratospheric) fallout (with a contribution from local fallout), respectively. The sediment inventory of 239,240Pu near the Bikini Atoll exceeded its overlying water inventory, however, in the mid-latitudes, more than 70% of 239,240Pu still remains in the water column. 241Am inventories in sediments exceeded that of the water column for the entire NW Pacific Ocean. Higher 137Cs and 90Sr sediment inventories in the latitudinal belt of 30–40°N are due to global fallout, and they account for about 10% and less than 5% of the water column inventories, respectively. The observed activity ratios of 137Cs/ 90Sr, 238Pu/ 239,240Pu and 241Am/ 239,240Pu in sediment were at some stations higher than the global fallout ratios due to contributions from local fallout and due to specific processes in the water column. Two end-member mixing model based on the 240Pu/ 239Pu atom ratios observed in global and local fallout yielded ∼60% contribution of the local fallout in the bottom sediments near the Bikini Atoll. The upward decrease in the 240Pu/ 239Pu atom ratios in the sediment column indicates a decrease in the contribution of local fallout to the Pu inventory with time. 241Am and 241Pu dating of sediment layers was utilized to explain a hiatus in sediment accumulation in the deep seafloor.

Sources of the transuranic elements plutonium and neptunium in arctic marine sediments

Abstract We report here thermal ionization mass spectrometry measurements of 239 Pu , 240 Pu , 241 Pu , 242 Pu , and 237 Np isolated from oceanic, estuarine, and riverine sediments from the Arctic Ocean Basin. 238 Pu/ 239+240 Pu activity ratios are also reported for alpha spectrometric analyses undertaken on a subset of these samples. Our results indicate that the Pu in sediments on the Alaskan shelf and slope, as well as that in the deep basins (Amerasian and Eurasian) of the Arctic Ocean, has its origin in stratospheric and tropospheric fallout. Sediments from the Ob and Yenisei Rivers show isotopic Pu signatures that are distinctly different from those of northern-hemisphere stratospheric fallout and indicate the presence of weapons-grade Pu originating from nuclear fuel reprocessing wastes generated at Russian facilities within these river catchments. Consequently, sediments of the Eurasian Arctic Ocean, particularly those in the Barents and Kara Seas, probably contain a mixture of Pu from stratospheric fallout, tropospheric fallout, and fuel-reprocessing wastes of riverine origin. In particular, the 241 Pu/ 239 Pu ratios observed in these sediments are inconsistent with significant contributions of Pu to the arctic sediments studied from western European reprocessing facilities, principally Sellafield in the UK. Several other potential sources of Pu to arctic sediments can also be excluded as significant based upon the transuranic isotope ratios presented.

Marine radioactivity assessment of Mururoa and Fangataufa atolls

The International Atomic Energy Agency (IAEA) carried out an international project ‘The Study of the Radiological Situation at the Atolls of Mururoa and Fangataufa’ with the aim of assessing the present and future radiological situation at the atolls and making recommendations for either monitoring or remedial actions if they are deemed necessary. The paper concentrates on marine radioactivity aspects and gives an estimation of present radionuclide concentrations in water, sediment and biota of the Mururoa and Fangataufa lagoons and the surrounding ocean. The dominant radionuclide in both lagoons is Pu in sediments (the total inventory is approximately 30 TBq). A decline in radionuclide concentrations has been observed in recent years in lagoon water, with the exception of 3H and 90Sr, for which a contribution from underground sources is to be expected. Radionuclide concentrations in biota from the lagoons and the surrounding ocean are low and consistent with previous measurements. The observed radionuclide concentrations in both lagoons imply that no radiological risk exists for hypothetical inhabitants of Mururoa and Fangataufa Atolls.

Distribution and inventory of fallout Pu and Cs in the sediment of the East Sea of Korea

Sediment samples were collected from the Ulleung Basin in the East Sea of Korea and analyzed for 239, 240 Pu, 238Pu and 137Cs concentrations and excess 210Pb. The apparent sedimentation rate was estimated to be 0·069 cm year -1 for Station 1 sediment and 0·061 cm year -1 for Station 2 sediment. From depth profiles, the maximum concentrations of 239, 240 Pu and 137Cs appeared at 2–4 cm depth in sediments on the continental slope and at 2–3 cm depth in the Ulleung Basin, corresponding to the deposits laid down in the years 1950–1975. The inventories of 239, 240 Pu and 137Cs were estimated to be 59·4 and 338·6 Bq m -2 for Station 1 sediment and 65·5 and 247·4 Bq m -2 for Station 2 sediment. The activity ratios of 238Pu/ 239, 240 Pu in sediments were found to be within the narrow range of 0·028–0·052 with a mean value of 0·041. No significant changes in 239, 240 Pu/ 137Cs ratios occur with depth in the East Sea sediments. The activity ratios of 239, 240 Pu/ 137Cs in the surface sediment were higher than the ratio due to global fallout.

The annual cycle of plutonium in the water column of a warm, monomictic reservoir

An annual cycle occurs in the 239,240Pu inventories of the water column of Pond B, an 87-ha warm monomictic reservoir on the US Department of Energy's Savannah River Site in Barnwell Co., South Carolina. The pond has elevated concentrations of 238Pu and 239,240Pu in sediments due to releases from former reactor operations and continues to receive additional Pu input from atmospheric deposition. The 239,240Pu inventories in the water column display annual cycles that differ between surface waters (i.e. 0–6 m deep) and deeper waters ( i. e. > 6 m deep) that are anoxic in summer months. For surface waters, the 239,240Pu inventory increases following turnover in November to a maximum in March followed by a decline until later summer when minimum inventories occur. For deeper waters, the 239,240Pu inventories increase rapidly following turnover and reach maximum values in March. The inventories in deeper waters remain large from March until turnover. Maximum inventories for the entire water column occur in March with minimum inventories at turnover in October and November. Turnover results in a redistribution of Pu across water depth but no measurable Pu loss from the water column. Ratios of 238Pu: 239,240Pu indicate that the cycle involves primarily Pu from sediment sources with little influence from atmospheric sources. Thus, the cycle represents net remobilization of 239,240Pu from the sediments to the water column during the oxic, holomictic portion of the year followed by a net loss of Pu from the water column once stratification occurs.

Isolation and alpha-particle spectrometric determination of238Pu and239,240Pu in sediments

A simple method is described for the isolation and determination of plutonium isotopes in sediments. The method involves leaching of sample with nitric acid and subsequent separation of plutonium on an anion-exchange column. Major matrix elements and several potential radiochemical interferences are removed during 8M HNO3 sample loading on the column. Thorium is removed by thorough washing with 10M HCl. Plutonium (IV) is eluted with 4M HCl. Source for alpha-particle spectrometry is prepared by LaF3 coprecipitation technique at which stage a complete separation from uranium(VI) is also achieved. The entire analytical procedure is completed in about two days.