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.     

Spatial and temporal distribution of Pu in the Northwest Pacific Ocean using modern coral archives

Historical ²³⁹Pu activity concentrations and ²⁴⁰Pu/²³⁹Pu atom ratios were determined in skeletons of dated modern corals collected from three locations (Chuuk Lagoon, Ishigaki Island and Iki Island) to identify spatial and temporal variations in Pu inputs to the Northwest Pacific Ocean. The main Pu source in the Northwest Pacific is fallout from atmospheric nuclear weapons testing which consists of global fallout and close-in fallout from the former US Pacific Proving Grounds (PPG) in the Marshall Islands. PPG close-in fallout dominated the Pu input in the 1950s, as was observed with higher ²⁴⁰Pu/²³⁹Pu atom ratios (> 0.30) at the Ishigaki site. Specific fallout Pu contamination from the Nagasaki atomic bomb and the Ivy Mike thermonuclear detonation at the PPG were identified at Ishigaki Island from the ²⁴⁰Pu/²³⁹Pu atom ratios of 0.07 and 0.46, respectively. During the 1960s and 1970s, global fallout was the major Pu source to the Northwest Pacific with over 60% contribution to the total Pu. After the cessation of the atmospheric nuclear tests, the PPG again dominated the Pu input due to the continuous transport of remobilised Pu from the Marshall Islands along the North Equatorial Current and the subsequent Kuroshio Current. The Pu contributions from the PPG in recent coral bands (1984 onwards) varied over time with average estimated PPG contributions between 54% and 72% depending on location.     

Plutonium concentration and 240Pu/239Pu atomic ratio in liver of squid collected in the coastal sea areas of Japan

Plutonium isotopes, 239Pu and 240Pu, were measured in liver samples from Surume squid using a sector-field high resolution ICP-MS after radiochemical purification. Surume squid samples were obtained from nine landing ports in Japanese inshore during fishery season from September to December 2002. Concentrations of 239Pu and 240Pu ranged from 1.5 to 28 mBq kg(-1) and 1.1 to 24 mBq kg(-1), respectively. Plutonium (239,240Pu) concentrations in liver were several thousand times higher than levels found in seawater. The concentration factor (CF) compared to seawater for 239,240Pu and 13 other elements ranged from 10(0) to 10(7). The CF values for 239,240Pu, V and Th were 10(2)-10(4). Pu had an intermediate CF between conservative and scavenged elements. 240Pu/239Pu atomic ratios in the squid liver ranged from 0.177 to 0.237 which were slightly higher than 0.178+/-0.014 for global fallout. The variations of 240Pu/239Pu atomic ratios in ocean currents with different source functions are important for interpreting high 240Pu/239Pu atomic ratios in Surume squid liver. It seems likely that Pu with high 240Pu/239Pu atomic ratio is continuously transported through the solubilization and seawater transport from the North Equatorial Current to Kuroshio and its branch, Tsushima Current. By assuming that Pu found in Surume squid liver is a mixture of global fallout Pu (0.178) and close-in fallout Pu with high 240Pu/239Pu atomic ratio (0.30-0.36) around Bikini Atoll, Pu contribution from Bikini close-in fallout Pu accounts for close to 35% of the whole plutonium in Surume squid liver. These results highlight that Surume squid is a useful organism for evaluating environmental Pu levels of larger sea area and facilitate the development of models to understand oceanic transport of close-in fallout Pu from Bikini Atoll.     

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.     

Characterization of Pu concentration and its isotopic composition in soils of Gansu in northwestern China

The total ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu atom ratios in surface soil samples (0–5 cm) in the Kumtag Desert in western Gansu Province, and in a soil core sample in Lanzhou were investigated using a sector-field ICP-MS. In the surface soil samples, ^239+240Pu activities in fine particles (<150 μm) were 1.3–2.1 times of those in coarse particles (150 μm–1 mm) which ranged from 0.005 to 0.157 mBq/g. Atom ratios of ²⁴⁰Pu/²³⁹Pu in the surface soils ranged from 0.168 to 0.192 with a mean of 0.182 ± 0.008. The mean ratio was similar to the typical global fallout value although the Kumtag Desert was believed to have received close-in fallout derived from Chinese nuclear weapons tests mainly conducted in the 1970s. Furthermore, the mean ²⁴⁰Pu/²³⁹Pu atom ratio observed in the soil core sample in Lanzhou was similar to the typical global fallout value. In the soil core sample, ^239+240Pu activities in the various layers ranged from 0.012 to 0.23 mBq/g, and the inventory of ^239+240Pu (32.4 Bq/m², 0–23 cm) was slightly lower than that expected from global fallout (42 Bq/m²) at the same latitude. Rapid downward migration of Pu isotopes was observed in Lanzhou soil core sample layers. The contribution of the 10-cm deep top layers of surface soils to total inventory was only 17%, while the contribution of deeper layers (10–23 cm) was as high as 83%. The ^239+240Pu activity levels and ²⁴⁰Pu/²³⁹Pu atom ratios in soils in Gansu Province, China are similar to those in atmospheric deposition samples collected in the spring in recent years in Japan.     

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.     

Resolving Chernobyl vs. global fallout contributions in soils from Poland using Plutonium atom ratios measured by inductively coupled plasma mass spectrometry

Plutonium in Polish forest soils and the Bór za Lasem peat bog is resolved between Chernobyl and global fallout contributions via inductively coupled plasma mass spectrometric measurements of 240Pu/230Pu and 241Pu/239Pu atom ratios in previously prepared NdF3 alpha spectrometric sources. Compared to global fallout, Chernobyl Pu exhibits higher abundances of 240Pu and 241Pu. The ratios 240Pu/230Pu and 241Pu/239Pu co-vary and range from 0.186 to 0.348 and 0.0029 to 0.0412, respectively, in forest soils (241Pu/239Pu = 0.2407 x [240Pu/239Pu] - 0.0413; r2 = 0.9924). Two-component mixing models are developed to apportion 239+240Pu and 241Pu activities; various estimates of the percentage of Chernobyl-derived 239+240Pu activity in forest soils range from < 10% to > 90% for the sample set. The 240Pu/230Pu - 241Pu/239Pu atom ratio mixing line extrapolates to estimate 241Pu/239Pu and the 241Pu/239+240Pu activity ratio for the Chernobyl source term (0.123 +/- 0.0007; 83 +/- 5; 1 May 1986). Sample 241Pu activities, calculated using existing alpha spectrometric 239+240Pu activities, and the 240Pu/230Pu and 241Pu/239Pu atom ratios, agree relatively well with previous liquid scintillation spectrometry measurements. Chernobyl Pu is most evident in locations from northeastern Poland. The 241Pu activities and/or the 241Pu/239Pu atom ratios are more sensitive than 240Pu/239Pu or 238Pu/239+240Pu activity ratios at detecting small Chernobyl 239+240Pu inputs, found in southern Poland. The mass spectrometric data show that the 241Pu activity is 40-62% Chernobyl-derived in southern Poland, and 58-96% Chernobyl in northeastern Poland. The Bór za Lasem peat bog (49.42 degrees N, 19.75 degrees E), located in the Orawsko-Nowotarska valley of southern Poland, consists of global fallout Pu.     

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.     

Studies of Np and Pu in the marine environment of Swedish-Danish waters and the North Atlantic Ocean

The long-lived anthropogenic radionuclides (237)Np, (239)Pu and (240)Pu were determined in marine environmental samples (seaweed and seawater) collected from Swedish-Danish waters and the North Atlantic Ocean at various locations on different occasions during the period 1991-2001. The measurements were performed with sector field Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and conventional alpha spectrometry. The (237)Np activity concentrations in Fucus vesiculosus and surface seawater from the Swedish west coast and Danish waters ranged from 0.16+/-0.02 to 1.02+/-0.09 mBq kg(-1) (dry weight) and 0.65+/-0.02 to 1.69+/-0.02 mBq m(-3), respectively, depending on the location and sampling year. Most of the (237)Np in these waters is believed to originate from the Sellafield nuclear reprocessing plant, with some contribution from global fallout. The (240)Pu/(239)Pu atomic ratios in F. vesiculosus samples are reported in this study with an overall average of 0.17+/-0.03. The (237)Np and (239)Pu activity concentrations observed in surface seawater collected in North Atlantic waters ranged from 0.16+/-0.01 to 0.62+/-0.08 mBq m(-3) and from 0.64+/-0.05 to 4.27+/-0.08 mBq m(-3), respectively, and the (237)Np/(239)Pu atomic ratios were a good indicator of conservative behaviour of Np in marine waters.     

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.     

Concentration and characterization of plutonium in soils of Hubei in central China

To study the Pu concentration and isotope ratio distributions present in China, the ^239+240Pu total activities and ²⁴⁰Pu/²³⁹Pu atom ratios in core soil samples from Hubei Province in central China were investigated using Accelerator Mass Spectrometry (AMS). The activities ranged from 0.019 to 0.502 mBq g⁻¹ and the ^239+240Pu inventories of 45 and ∼55 Bq m⁻² agree well with that expected from global fallout. The ²⁴⁰Pu/²³⁹Pu atom ratios in the soil ranged from 0.172 to 0.220. The ratios are similar to typical global fallout values. Hence, any close-in fallout contribution from the Chinese nuclear weapons tests, mainly conducted in the 1970s, must have either been negligible or had a similar ²⁴⁰Pu/²³⁹Pu ratio to that of global fallout. The top 10 cm layer of the soil contributes ∼90% of the total inventory and the maximum concentrations appeared in the 2-4 cm or 4-6 cm layers. It is suggested that climatic conditions and organic content are the two main factors that affect the vertical migration of plutonium in soil.     

Plutonium isotopes concentration in seawater and bottom sediment off the Pacific coast of Aomori sea area during 1991-2005

A radioactivity survey was launched in 1991 to determine the background levels of ^239+240Pu in the marine environment off a commercial spent nuclear fuel reprocessing plant before full operation of the facility. Particular attention was focused on the ²⁴⁰Pu/²³⁹Pu atom ratio in seawater and bottom sediment to identify the origins of Pu isotopes. The concentration of ^239+240Pu was almost uniform in surface water, decreasing slowly over time. Conversely, the ^239+240Pu concentration varied markedly in the bottom water and was dependent upon the sampling point, with higher concentrations of ^239+240Pu observed in the bottom water sample at sampling points having greater depth. The ²⁴⁰Pu/²³⁹Pu atom ratio in the seawater and sediment samples was higher than that of global fallout Pu, and comparable with the data in the other sea area around Japan which has likely been affected by close-in fallout Pu originating from the Pacific Proving Grounds. The ²⁴⁰Pu/²³⁹Pu atom ratio in bottom sediment samples decreased with sea depth. The land-originated Pu is not considered as the reason of the increasing ^239+240Pu concentration and also decreasing the ²⁴⁰Pu/²³⁹Pu atom ratio with sea depth, and further study is required to clarify it.     

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.     

Modelling the distribution of plutonium in the Pacific Ocean

An Oceanic General Circulation Model (OGCM) including a plutonium scavenging model as well as an advection-diffusion model has been developed for modelling the distribution of plutonium in the Pacific Ocean. Calculated 239, 240Pu water profile concentrations and 239, 240Pu inventories in water and sediment of the Pacific Ocean have showed a reasonable agreement with the experimental results. The presence of local fallout plutonium in central North Pacific waters has been confirmed. The observed 240Pu/239Pu mass ratios confirm that plutonium originating from local fallout from nuclear weapons tests carried out at Bikini and Enewetak Atolls is more rapidly removed from surface waters to deeper waters than plutonium originating from global fallout. The developed OGCM can be used for modelling the dispersion of other non-conservative tracers in the ocean as well.     

Comparison of Pu and (137)Cs as tracers of soil and sediment transport in a terrestrial environment

Following atmospheric nuclear weapons testing in the 1950s and 1960s significant quantities of (137)Cs and (239+240)Pu were deposited worldwide. In recent decades, (137)Cs has been commonly used as a tracer of soil erosion and sedimentation, particularly in the Northern Hemisphere where atomic deposition was three times as great as in the Southern Hemisphere. The relatively short 30-year half-life of this isotope means that its sensitivity as a tracer is rapidly decreasing. In contrast, with half-lives of 24,110 and 6561 years, the sensitivity of the two plutonium isotopes remains essentially the same as when it was deposited. Here we use the technique of Accelerator Mass Spectrometry to demonstrate the potential of anthropogenic Pu as an alternative to (137)Cs as a tracer of soil transport in Australia. We measure an average (137)Cs/(239+240)Pu activity ratio of 27.3+/-1.5 and an average (240)Pu/(239)Pu atom ratio of 0.149+/-0.003, both slightly lower than the global average.     

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/m²) and the Sulu Sea (1.38 Bq/m²). 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.     

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.     

Plutonium isotopes in the Hungarian environment

More than 50 soil samples were analysed from different parts of the country, the activity concentration of 239+240Pu was in the range of 0.01-0.84 Bq/kg dry soil with the average of 0.10 Bq/kg. 238Pu could be detected only in few moss samples and 238Pu/239+240Pu ratio determines the origin of plutonium. 241Pu was determined by liquid scintillation spectrometry. The activity concentration of this isotope in the soil is between 0.04 and 3.74 Bq/kg with the average of 0.82 Bq/kg, while in the moss is also similar 0.01-2.07 Bq/kg fresh mass with the average of 0.43 Bq/kg. Significant difference could not be observed between the different types of soils occurring in the country, but the results could be sorted according to the sampling carried out on undisturbed or cultivated area. The isotope ratios 241Pu/239+240Pu prove that the origin of the plutonium in Hungary is the global fallout determined by the atmospheric nuclear weapon tests.     

Distribution and flux of 238Pu, 239,240Pu, 241Am, 137Cs and 210Pb to high arctic lakes in the Thule district (Greenland)

Environmental samples (soil, sediment and lake water) in the Thule area (NW Greenland) have been studied to assess the contamination of radionuclides originating from a nuclear weapons accident (the Thule accident in 1968). Four lakes were chosen at different distances from the point of impact with the Thule air base community situated in between. The sedimentation rates in the lakes varied from 0.4 mm a(-1) (5 mg cm(-2) a(-1)) to 1.6 mm a(-1) (82 mg cm(-2) a(-1)). With these sedimentation rates, it is not possible to resolve the (239,240)Pu global fallout peak from a possible (239,240)Pu "accident" peak in the sediment depth profiles. However, the (239,240)Pu/(137)Cs and the (238)Pu/(239,240)Pu ratios agreed well with global fallout ratios, indicating that plutonium originating from the accident had not reached these lakes. This also indicates that the Thule air base community has probably only been exposed to radionuclides from the accident to a very limited extent. A limited study showed that (210)Pb could not be used as a normalizing nuclide to explain the transport of transuranic elements from the catchment area to the lake, i.e. (210)Pb has a different transport mechanism from that of the transuranic elements studied in this investigation.     

An assessment of the reported leakage of anthropogenic radionuclides from the underground nuclear test sites at Amchitka Island, Alaska, USA to the surface environment

Three underground nuclear tests representing approximately 15-16% of the total effective energy released during the United States underground nuclear testing program from 1951 to 1992 were conducted at Amchitka Island, Alaska. In 1996, Greenpeace reported that leakage of radionuclides, 241Am and 239+240Pu, from these underground tests to the terrestrial and freshwater environments had been detected. In response to this report, a federal, state, tribal and non-governmental team conducted a terrestrial and freshwater radiological sampling program in 1997. Additional radiological sampling was conducted in 1998. An assessment of the reported leakage to the freshwater environment was evaluated by assessing 3H values in surface waters and 240Pu/239Pu ratios in various sample media. Tritium values ranged from 0.41 Bq/l +/- 0.11 two sigma to 0.74 Bq/1 +/- 0.126 two sigma at the surface water sites sampled, including the reported leakage sites. Only at the Long Shot test site, where leakage of radioactive gases to the near-surface occurred in 1965. were higher 3H levels of 5.8 Bq/1 +/- 0.19 two sigma still observed in 1997, in mud pit #3. The mean 240Pu/239Pu for all of the Amchitka samples was 0.1991 +/- 0.0149 one standard deviation, with values ranging from 0.1824 +/- 1.43% one sigma to 0.2431 +/- 6.56% one sigma. The measured 3H levels and 240Pu/239Pu ratios in freshwater moss and sediments at Amchitka provide no evidence of leakage occurring at the sites reported by Buske and Miller (1998 Nuclear-Weapons-Free America and Alaska Community Action on Toxics, Anchorage, Ak, p.38) and Miller and Buske (1996 Nuclear Flashback: The Return to Anchitka, p.35). It was noted that the marine sample; 240Pu/239Pu ratios are statistically different than the global fallout ratios presented by Krey et al. (1976) and Kelley, Bond, and Beasley (1999). The additional non-fallout component 240Pu/239Pu ratio, assuming a single unique source, necessary to modify the global fallout 240Pu/239Pu ratio to that measured in the marine samples is on the order of 0.65 (Hameedi, Efurd, Harmon, Valette-Silver, & Robertson, 1999; Kelley et al., 1999). While this potentially suggests another plutonium source, such as high burn-up nuclear reactor fuel, rather than underground nuclear tests, the uncertainties in analyses and environmental processes need to be fully assessed before any conclusion can be reached. Further work is needed to evaluate these findings and to support any radiological assessment of the marine environment surrounding Amchitka. Based on geohydrological testing and modeling, leakage from the Amchitka Underground Nuclear Tests is projected to occur to the marine environment (Claassen, 1978; Fenske, 1972; Wheatcraft, 1995).