Anthropogenic radionuclides in sediment in the Japan Sea: distribution and transport processes of particulate radionuclides

Distributions of anthropogenic radionuclides (⁹⁰Sr, ¹³⁷Cs and ^239+240Pu) in seabed sediment in the Japan Sea were collected during the period 1998–2002. Concentration of ⁹⁰Sr, ¹³⁷Cs and ^239+240Pu in seabed sediment was 0.07–1.6 Bq kg⁻¹, 0.4–9.1 Bq kg⁻¹ and 0.002–1.9 Bq kg⁻¹, respectively. In the northern basin of the sea (Japan Basin), ^239+240Pu/¹³⁷Cs ratios in seabed sediment were higher and their variation was smaller compared to that in the southeastern regions of the sea. The higher ^239+240Pu/¹³⁷Cs ratios throughout the Japan Basin were considered to reflect production of Pu-enriched particles in the surface layer and substantial sinking of particulate materials in this region. In the southern regions of the Japan Sea (<38°N), both inventories and ^239+240Pu/¹³⁷Cs ratios in sediment were larger than those in the other regions. In the southern Japan Sea, observations suggested that supply of particulate radionuclides by the Tsushima Warm Current mainly enhanced accumulation of the radionuclides in this region.     

Anthropogenic radionuclides in the Japan Sea: their distributions and transport processes

The anthropogenic radionuclides, (90)Sr, (137)Cs and (239+240)Pu, were measured in the water column of the Japan Sea/East Sea during 1997-2000. The vertical profiles of radionuclide concentrations showed: exponential decrease with depth for (90)Sr and (137)Cs, and surface minimum/subsurface maximum for (239+240)Pu. These results do not differ substantially from results reported previously. The area-averaged concentrations of radionuclides in the Japan Sea are higher than those found in the Northwest Pacific Ocean below surface layer showing the accumulation of the radionuclides in the deep waters in the Japan Sea. Concerning spatial distributions, the area of high (137)Cs inventory extends from the Japan Basin into the Yamato Basin. It is suggested that wintertime convection of water, occurring mainly in the Japan Basin, causes the radionuclides to sink. The nuclides then advect into the Yamato Basin after detouring around the Yamato Rise.     

Radioactivity concentrations of 40K, 134Cs, 137Cs, 90Sr, 241Am, 238Pu and 239+240Pu radionuclides in Jordanian soil samples

In November 2000, surface and core soil samples were collected from different regions of Jordan. The samples were analyzed by direct gamma spectrometry and combined radiochemical separation procedure to quantify (40)K, (134)Cs, (137)Cs, (90)Sr, (241)Am, (238)Pu and (239+240)Pu radioactivity. Concentrations (Bq.kg(-1) dry weight) have been observed to vary in the range 1.5-2.6 for (134)Cs, 2.8-11.4 for (90)Sr, and 0.13-0.48 for (241)Am, 0.016-0.062 for (238)Pu, 0.28-1.01 for (239+240)Pu and 155-543 for (40)K. The typical concentration of (137)Cs found in topsoils (0-2 cm) ranged in 7.5-576 Bq.kg(-1), dry weight. These values were greater than those observed in samples taken at greater depths (up to 32 cm). Activity ratios of (134)Cs/(137)Cs, (90)Sr/(137)Cs, (239+240)Pu/(137)Cs, (238)Pu/(137)Cs, (241)Am/(137)Cs, (239+240)Pu/(238)Pu and (241)Am /(238)Pu have mean values of 0.0049 (R=1), 0.29 (R=0.76), 0.41 (R=0.90), 0.39 (R=0.85), 0.41 (R=0.88), 7.72 (R=0.97) and 16.66 (R=0.98), respectively. The underlying concentrations were correlated and relatively higher than those reported in neighboring countries. One moss sample, as a biomonitor indicator, was measured and evaluated along with the soil samples. Its data showed higher concentrations of all measured radionuclides due to accumulations over years. The depth distribution of the fission product (137)Cs and the total deposition (Bq.m(-2)) were also studied in selected samples. Estimations of the annual effective dose equivalent due to (137)Cs-soil contamination showed values up to more than 200 microSv.     

Behaviour and transport of radionuclides in soil and vegetation of a sand dune ecosystem

A sand dune ecosystem in the vicinity of the British Nuclear Fuels reprocessing plant at Sellafield, Cumbria, UK was used to examine the spatial, temporal and depth distributions of 134Cs, 137Cs, 238Pu, 239 + 240Pu and 241Am in soil and in two species of vegetation (Festuca rubra, Ammophila arenaria). Core samples showed evidence of the accumulation of radionuclides derived mainly from sea-to-land transfer. Accumulated deposits of radioactivity (0-0.1 m) lie within the range: 1.1-3.4 Bq kg-1 (134Cs), 260-440 Bq kg-1 (137Cs), 31-40 Bq kg-1 (238Pu), 150-215 Bq kg-1 (239 + 240Pu) and 190-240 Bq kg-1 (241Am). Soil profiles showed greater activity concentrations in their deeper regions and this is attributed to leaching of radionuclides in percolating drainage water accentuated by the coarse texture, low organic matter and clay mineral content of coastal sands. Radionuclide activity concentrations in F. rubra and A. arenaria were similar, in the ranges 20-70 Bq kg-1 (137Cs), 1-5 Bq kg-1 (238Pu), 10-30 Bq kg-1 (239 + 240Pu) and 10-65 Bq kg-1 (241Am). Clear temporal and spatial variations were observed in both species of vegetation, reflecting the weather conditions antecedent to the sampling period and the influence of sea-to-land transfer. Concentration ratios (vegetation:soil) for activity concentrations in the two species were similar, in the ranges: 0.05-0.14 (137Cs), 0.025-0.097 (238Pu), 0.022-0.057 (239 + 240Pu) and 0.025-0.212 (241Am).     

137Cs and (239+240)Pu levels in the Asia-Pacific regional seas

137Cs and (239+240)Pu data in seawater, sediment and biota from the regional seas of Asia-Pacific extending from 50 degrees N to 60 degrees S latitude and 60 degrees E to 180 degrees E longitude based on the Asia-Pacific Marine Radioactivity Database (ASPAMARD) are presented and discussed. 137Cs levels in surface seawater have been declining to its present median value of about 3 Bq/m3 due mainly to radioactive decay, transport processes, and the absence of new significant inputs. (239+240)Pu levels in surface seawater are much lower, with a median of about 6 mBq/m3. (239+240)Pu appears to be partly scavenged by particles and is therefore more readily transported down the water column. As with seawater, (239+240)Pu concentrations are lower than 137Cs in surface sediment. The median 137Cs concentration in surface sediment is 1.4 Bq/kg dry, while that of (239+240)Pu is only 0.2 Bq/kg dry. The vertical profiles of both 137Cs and (239+240)Pu in the sediment column of coastal areas are different from deep seas which can be attributed to the higher sedimentation rates and additional contribution of run-offs from terrestrial catchment areas in the coastal zone. Comparable data for biota are far less extensive than those for seawater and sediment. The median 137Cs concentration in fish (0.2 Bq/kg wet) is higher than in crustaceans (0.1 Bq/kg wet) or mollusks (0.1 Bq/kg wet). Benchmark values (as of 2001) for 137Cs and (239+240)Pu concentrations in seawater, sediment and biota are established to serve as reference values against which the impact of future anthropogenic inputs can be assessed. ASPAMARD represents one of the most comprehensive compilations of available data on 137Cs and (239+240)Pu in particular, and other anthropogenic as well as natural radionuclides in seawater, sediment and biota from the Asia-Pacific regional seas.     

239+240Pu, 90Sr and 137Cs inventories in surface soils of Vietnam

Fallout 239+240Pu, 238Pu, 90Sr and 137Cs inventories in surface soils were measured for 20 locations in northern Vietnam yielding the mean values (+/- standard error) of 26.5+/-3.8 Bq m(-2) for 239+240Pu, 1048+/-143 Bq m(-2) for 137Cs and 212+/-28 Bq m(-2) for 90Sr. The concentrations of 137Cs and plutonium isotopes strongly correlate with each other resulting in a stable 239+240Pu/137Cs inventory ratio of 0.025+/-0.002. Among soil parameters, organic matter and fulvic acids strongly correlate with caesium and plutonium isotopes, especially in the 0-10 cm layer. 137Cs and 239+240Pu are distributed rather similarly over the 0-10 cm and 10-20 cm layers. At locations with high contents of sand (82-93%) along the South China Sea coast, the downward percolation by rainwater results in a higher accumulation of 239+240Pu and 137Cs in the 10-20 cm layer. The mean 137Cs/ 90Sr inventory ratio is 9.3+/-2.2, and the correlation is weak between these isotopes.     

Activity ratios of 137Cs, 90Sr and 239+240Pu in environmental samples

Both global and Chernobyl fallout have resulted in environmental contamination with radionuclides such as 137Cs, 90Sr and 239+240Pu. In environmental samples, 137Cs and 239+240Pu can be divided into the contributions of either source, if also the isotopes 134Cs and 238Pu are measurable, based on the known isotopic ratios in global and Chernobyl fallout. No analogous method is available for 90Sr. The activity ratios of Sr to Cs and Pu, respectively, are known for the actual fallout mainly from air filter measurements; but due to the high mobility of Sr in the environment, compared to Cs and Pu, these ratios generally do not hold for the inventory many years after deposition. In this paper we suggest a method to identify the mean contributions of global and Chernobyl fallout to total Sr in soil, sediment and cryoconite samples from Alpine and pre-Alpine regions of Austria, based on a statistical evaluation of Sr/Cs/Pu radionuclide activity ratios. Results are given for Sr:Cs, Sr:Pu and Cs:Pu ratios. Comparison with fallout data shows a strong depletion of Sr against Cs and Pu.     

Artificial radionuclides in sediments of the Don River Estuary and Azov Sea

The Don River Estuary-Azov Sea system is an extension of the shallow continental shelf area of the Black Sea. A large data set of artificial radionuclides in bottom sediments of the Azov Sea has been compiled in order to examine the storage and migration of radionuclides within this highly restricted inland sea and to estimate the annual dose received by individuals in the local population who regularly consume fish. In recent years (1997-1999), the radionuclide content of surface sediments has been: 137Cs < or = 0.5-100 Bq/kg d.w. (mean = 33.8 +/- 25.9 Bq/kg d.w., n = 57), 90Sr = 0.2-5.7 Bq/kg d.w. (mean = 2.1 +/- 1.4 Bq/kg d.w., n = 34) and 239,240Pu = 0.31-0.51 Bq/kg d.w. (n = 2). In general, 137Cs activities increase with distance from the mouth of the Don River and correlate negatively with sediment grain size (r2 = 0.77, n = 21). The annual 137Cs-derived dose received by an individual through the trophic chain water-fish-humans (approximately 10(-6) Sv/yr) is well below regulatory recommended limits, indicating that current levels of radioactivity in the environment pose no threat to commercial fisheries operations for the bordering nations of Russia and Ukraine.     

Radionuclide tracing of water masses and processes in the water column and sediment in the Algerian Basin

Caesium-137 and (239,240)PU were analysed in the water column along the Algerian coast. The (137)Cs activity concentration in surface water increased from the west to the east from 1.6 to 3.3 mBq L(-1), documenting a presence of Modified Atlantic Water (MAW) in the region. Higher concentrations observed in deep waters may be due to an intrusion of Levantine Intermediate Water (LIW), which has been carrying higher levels of (137)Cs from Chernobyl accident. The (239,240)Pu sub-surface concentration peaked at about 250 m water depth as a result of biogeochemical processes in the water column. The observed (239,240)Pu/(137)Cs activity ratio at the surface (0.003) was significantly lower than that in global fallout (0.04). This decrease exceeds that expected from radioactive decay of (137)Cs, and confirms that Pu due to its adsorption on sinking particles is more effectively removed from surface layers than is (137)Cs. An increase of the (239,240)Pu/(137)Cs activity ratio with depth suggests that (239,240)Pu, similarly as (137)Cs, should be also transported by advection to maintain the observed ratios in deep waters. An intrusion of LIW may enhance therefore both the (137)Cs and (239,240)Pu concentrations in deep waters. The average (238)Pu/(239+240)Pu activity ratio in seawater was 0.03+/-0.02, confirming a global fallout origin of Pu in the Algerian Basin. Caesium-137 and (239,240)Pu inventories in the water column were estimated to be from 2.7+/-0.5 kBq m(-2) to 3.8+/-0.7 kBq m(-2), and from 13.8+/-2.6 Bq m(-2) to 41+/-7B qm(-2), respectively. The (137)Cs massic activities in surface sediment were almost constant, the average activity was 9.0+/-0.8 Bq kg(-1). Sedimentation rates obtained using the (210)Pb method were from 0.1 to 0.7 cm y(-1), and resulting penetration depths of (137)Cs in the sediment cores were from 15 to over 40 cm. The (137)Cs peaks found in the sediment cores were associated with the Chernobyl accident (1986) and global fallout (1964). The (137)Cs inventories in the sediment were increasing from the west (180 Bq m(-2)) to the east (350 Bq m(-2)).     

Sources and distributions of Cs, Pu, Pu radionuclides in the north-western Barents Sea

Sediment deposits are the ultimate sink for anthropogenic radionuclides entering the marine environment. The major sources of anthropogenic radionuclides to the Barents Sea are fallout from nuclear weapons tests, long range transport from other seas, and river and non-point freshwater supplies. In this study we investigated activity concentrations, ratios, and inventories of the anthropogenic radionuclides, ¹³⁷Cs, ²³⁸Pu, ^239,240Pu in dated sediment cores collected along a north-south transect in the northwestern Barents Sea. The data were used to evaluate the influence of different sources on the derived spatial and temporal patterns of anthropogenic radionuclides in seafloor sediment deposits. Activity concentrations of ¹³⁷Cs ranged from <0.1 Bq/kg to 10.5 Bq/kg while ^239,240Pu ranged from <0.01 Bq/kg to 2.74 Bq/kg and ²³⁸Pu activity concentrations ranged from <0.01 Bq/kg to 0.22 Bq/kg. Total inventories of ¹³⁷Cs ranged from 29.5 ± 1.5 Bq/m² to 152.7 ± 5.6 Bq/m² and for ^239,240Pu inventories (6 sediment layers only) ranged from 9.5 ± 0.3 Bq/m² to 29.7 ± 0.4 Bq/m². Source contributions varied among stations and between the investigated radionuclides. The ²³⁸Pu/^239,240Pu ratios up to 0.18 indicate discharges from nuclear fuel reprocessing plants as a main contributor of plutonium. Based on ²³⁸Pu/^239,240Pu ratio, it was calculated that up to 19-27% of plutonium is supplied from sources other than atmospheric global fallout. Taking into account Atlantic current flow trajectories and that both activity concentrations and inventories of plutonium negatively correlate with latitude, Sellafield is a major source for the Barents Sea. Concentrations and inventories of ¹³⁷Cs correlate positively with latitude and negatively with distance from the Svalbard archipelago. The ¹³⁷Cs concentrations are highest in an area of intensive melting of sea ice formed along the Siberian coast. Thus, sea ice and supplies from Svalbard may be important source of ¹³⁷Cs to the Barents Sea seafloor.     

Distribution of Np and Pu in Swedish lichen samples (Cladonia stellaris) contaminated by atmospheric fallout

The activity concentrations of (237)Np and the two Pu isotopes, (239)Pu and (240)Pu, were determined in lichen samples (Cladonia stellaris) contaminated by fallout from atmospheric nuclear test explosions and the Chernobyl accident. The samples were collected at 18 locations in Sweden, from north to south, between 1986 and 1988 and analysed with high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) and alpha spectrometry. Data on the activity ratios (238)Pu/(239+240)Pu and (134)Cs/(137)Cs measured previously were also included in this study for comparison. The (237)Np activity concentration ranged from 0.08 +/- 0.01 to 2.08 +/- 0.17 MBq kg(-1), depending on the location of the sampling site and time of collection. The (239+240)Pu activity concentration ranged from 0.09 +/- 0.01 to 4.09 +/- 0.15 Bq kg(-1), with the (240)Pu/(239)Pu atomic ratio ranging between 0.16 +/- 0.01 and 0.44 +/- 0.03, the higher ratios indicating a combination of weapons test fallout and Chernobyl fallout. The (237)Np/(239)Pu atomic ratios ranged between 0.06 +/- 0.01 and 0.42 +/- 0.04, the lower ratios indicating combination of weapons test fallout and Chernobyl fallout. At a well-defined sampling site at Lake Rogen (62.32 degrees N, 12.38 degrees E), additional lichen samples were collected between 1987 and 1998 to study the distribution of Np and Pu in different layers. The concentrations of the two elements follow each other quite well in the profile.     

Radioactive contamination in the marine environment adjacent to the outfall of the radioactive waste treatment plant at ATOMFLOT,northern Russia

RTP "ATOMFLOT" is a civilian nuclear icebreaker base located on the Kola Bay of northwest Russia. The objectives of this study were to determine the distributions of man-made radionuclides in the marine environment adjacent to the base, to explain the form of the distributions in sediments and to derive information concerning the fate of radionuclides discharged from ATOMFLOT. Mean activity concentrations (d.w.) for surface sediment, of 63 Bq kg(-1 137Cs, 5.8 Bq kg(-1) 90Sr and 0.45 Bq kg(-1 239,240)Pu were measured. Filtered seawater activity levels were in the range of 3--6.9 Bq m(-3) 137Cs, 2.0-11.2 Bq m(-3) 90Sr, and 16-40 m Bq m(-3), 239,240Pu. Short-lived radionuclides were present at sediment depths in excess of 10cm indicating a high degree of sediment mixing. Correlations of radionuclide activity concentrations with grain-size appear to be absent; instead, the presence of relatively contaminated sediment appears to be related to the existence of radioactive particles.     

240Pu/239Pu atom ratios in seawater from Sagami Bay, western Northwest Pacific Ocean: sources and scavenging

Seawater samples were collected in Sagami Bay, western Northwest Pacific Ocean, and their (239+240)Pu activities and (240)Pu/(239)Pu atom ratios were determined by alpha-spectrometry and sector field high-resolution ICP-MS. A few samples also were analyzed for (137)Cs activities. The (239+240)Pu inventory of 41.1 Bq m(-2) was equivalent to the expected cumulative deposition density of atmospheric global fallout at the same latitude and this inventory was considerably lower than inventories in the underlying sediment columns. This result indicated that a significant amount of (239+240)Pu has been removed into the underlying sediments through enhanced scavenging from the water column by the high fluxes of particles in this region. The atom ratio of (240)Pu/(239)Pu showed no notable variation from the surface to the bottom; the average value was 0.234+/-0.004. This atom ratio was significantly higher than the mean global fallout ratio of 0.18, proving the existence of close-in fallout plutonium originating from the Pacific Proving Grounds (PPG). The relative contributions of the global stratospheric fallout and the PPG close-in fallout were evaluated by using the two end-member mixing model. The contribution of the PPG close-in fallout was estimated to be 15.2 Bq m(-2), which corresponded to 37% of the (239+240)Pu inventory in the water column. Thus (239)Pu and (240)Pu from the two sources of global fallout and close-in fallout have been homogenized in the water masses in the western Northwest Pacific margin during the past three decades.     

Residual radioactive contamination at the peaceful underground nuclear explosion sites "Craton-3" and "Crystal" in the Republic of Sakha (Yakutia)

In this paper, results are reported on the concentrations and activity ratios of 137Cs, 239+240Pu and 238Pu in soils, lichen and bottom sediments collected at the peaceful underground nuclear explosion sites "Craton-3" and "Crystal" (Republic of Sakha (Yakutia), North-East Siberia). At the "Craton-3" site, 239- 240Pu concentrations in the range 6.2 mBq/g to 5.9 Bq/g in surface soils (0-5 cm) and 239+240Pu concentrations up to 7.4 Bq/g in lichen were observed. The 137Cs concentration in measured soils range from 0.52 to 216 Bq/g for the near-plume and from 1.65 to 21.5 Bq/g for the far-plume. In lichen, 137Cs concentration varied from a global background level up to 251 Bq/g. Radioactive contamination at "Crystal" demonstrates an extremely irregular distribution of 239,240Pu and 137Cs in environmental samples taken at locations within 150 m radius of the site. Further work on compiling detailed maps of radioactive contamination of the territory around "Craton-3" and "Crystal" is discussed.     

Vertical distribution of radionuclides in soil of a grassland site in Chernobyl exclusion zone

Five soil profiles from a site about 8 km SE of the Chernobyl NPP were investigated for the vertical distribution of radionuclides. The average (137)Cs-inventory at the site is about 2.6 MBq/m(2) (reference date 1 May 1986). Apart from (137)Cs, the following radionuclides have been identified (their activity ratios to (137)Cs in brackets): (134)Cs (0.537), (125)Sb (0.068), (60)Co (0.0022), (154)Eu (0.016), (155)Eu (0.020), (94g)Nb (9.5E-5), (239/240)Pu (0.0088), (238)Pu (0.040), (90)Sr (0.30) and (241)Am (0.011). Apparent vertical migration velocities are between 0.14 and 0.26 cm/a, apparent dispersion coefficients range from 0.02 to 0.13 cm(2)/a. The rankings of the velocities v for different radionuclides are (Sr, Cs, Sb, Co, Pu)< Am < Eu and Sr < (Cs, Nb), for D, the following rankings have been found: (Nb, Sr, Cs) < Am < Eu, Cs相似文献   

Artificial radionuclides in the atmosphere over Lithuania

Measurements of airborne radioactive aerosol concentration were carried out on the basis of 1-3 days samples after the Chernobyl disaster and during the period of 1992-2003. Transport of "hot" particles of different composition resulted in the high activity concentrations of (137)Cs, (238)Pu, (239,240)Pu and (241)Am in the atmosphere in Vilnius at the end of April 1986. The (240)Pu/(239)Pu atom ratio showed clear evidence of non-global plutonium originating from the Chernobyl accident in the atmosphere over Lithuania. The (240)Pu/(239)Pu atom ratio ranged from 0.14 to 0.40 in monthly samples in Vilnius in 1995-2003. An increase in activity concentration of (137)Cs by a factor of 100 (up to 300 microBq/m(3)) was found following forest fires in the Ukraine and Belarus. However, no transport of the Chernobyl plutonium was observed and the (240)Pu/(239)Pu atom ratio in samples collected during the forest fires was found to be 0.229 and 0.185, respectively. The exponential decrease in the (240)Pu/(239)Pu atom ratio from 0.30 to 0.19 (mean values) was observed in 1995-2003.     

Cs, Pu concentrations and the Pu/Pu atom ratio in a sediment core from the sub-aqueous delta of Yangtze River estuary

A sediment core collected from the sub-aqueous delta of the Yangtze River estuary was subjected to analyses of ¹³⁷Cs and plutonium (Pu) isotopes. The ¹³⁷Cs was measured using γ-spectrometry at the laboratories at the Nanjing University and Pu isotopes were determined with Accelerator Mass Spectrometry (AMS), measurements made at the Australian National University. The results show considerable structure in the depth concentration profiles of the ¹³⁷Cs and ^239+240Pu. The shape of the vertical ¹³⁷Cs distribution in the sediment core was similar to that of the Pu. The maximum ¹³⁷Cs and ^239+240Pu concentrations were 16.21 ± 0.95 mBq/g and 0.716 ± 0.030 mBq/g, respectively, and appear at same depth. The average ²⁴⁰Pu/²³⁹Pu atom ratio was 0.238 ± 0.007 in the sediment core, slightly higher than the average global fallout value. The changes in the ²⁴⁰Pu/²³⁹Pu atom ratios in the sediment core indicate the presence of at least two different Pu sources, i.e., global fallout and another source, most likely close-in fallout from the Pacific Proving Grounds (PPG) in the Marshall Islands, and suggest the possibility that Pu isotopes are useful as a geochronological tool for coastal sediment studies. The ¹³⁷Cs and ^239+240Pu inventories were estimated to be 7100 ± 1200 Bq/m² and 407 ± 27 Bq/m², respectively. Approximately 40% of the ^239+240Pu inventory originated from the PPG close-in fallout and about 50% has derived from land-origin global fallout transported to the estuary by the river. This study confirms that AMS is a useful tool to measure ²⁴⁰Pu/²³⁹Pu atom ratio and can provide valuable information on sedimentary processes in the coastal environment.     

Depositional records of plutonium and (137)Cs released from Nagasaki atomic bomb in sediment of Nishiyama reservoir at Nagasaki

In a sediment core of Nishiyama reservoir at Nagasaki city, depth profiles of (240)Pu/(239)Pu isotopic ratio, (239+240)Pu and (137)Cs activities were determined. Sediments containing plutonium and (137)Cs, which were deposited immediately after a detonation of Nagasaki atomic bomb, were identified in the core. Observed below the sediments were macroscopic charcoals, providing evidence for initial deposit of the fallout of the Nagasaki atomic bomb. This is the first entire depositional records of plutonium and (137)Cs released from the Nagasaki atomic bomb together with those from atmospheric nuclear tests.     

Transuranic and fission product contamination in lake sediments from an alpine wetland, Boréon (France)

Transuranics and fission products have been measured in lake sediment samples, collected in an alpine wetland, to determine their vertical distribution and calculate inventories. The radionuclides considered are 90Sr, 137Cs, 238Pu, 239/240Pu and 241Am. From the results, a better knowledge of radionuclide accumulation mode and behaviour was obtained. In addition, the origins of the individual pollutants could be deduced from activity ratios. Analyses were made on different sediment cores. The sampling sites were chosen to enable future determination of the mass balances of the radiopollutants. As the selected study area is in a recreational area used by urban populations, a rough estimate was made of the mean external dose from 137Cs for comparison with the French regulation.     

Inventories of Pu, Cs, and excess Pb in sediments from freshwater and brackish lakes in Rokkasho, Japan, adjacent to a spent nuclear fuel reprocessing plant

We investigated the vertical profiles of ^239+240Pu, ¹³⁷Cs, and excess ²¹⁰Pb (²¹⁰Pb_ex) in sediment core samples obtained from two freshwater lakes and two brackish lakes situated near the first commercial spent nuclear fuel reprocessing plant in Rokkasho, Japan, before the final test of the plant using actual spent nuclear fuel. The inventory of ^239+240Pu in those lakes was larger than that in soil in Rokkasho, which indicated the inflow of ^239+240Pu from the catchment area in addition to direct deposition on the lake surfaces. The ¹³⁷Cs inventory in sediments of the brackish lakes was lower than that in the soil, which showed that part of the ¹³⁷Cs was removed from the sediments by the brackish water or that it was not deposited into the sediments, because of the high solubility of Cs in brackish water. The ¹³⁷Cs inventory in sediments of the freshwater lakes was higher than that of the brackish lakes, and comparable with that in soil except for one core sample out of four. The ^239+240Pu/¹³⁷Cs ratio in freshwater lake sediments was higher than that in soil, and that indicated that part of the ¹³⁷Cs was lost from the sediments. The low inventory of ¹³⁷Cs may be attributable to competition for absorption sites in sediments with ammonium ions formed in the reducing environment which occurs from summer to fall in the sediments. Those data will be used as background data on the artificial radionuclides in the lakes to assess the effect of released radionuclides on their concentrations.