The mass spectrometric determination of fallout 239Pu and 240Pu in marine samples

A thermal ionization mass spectrometric technique is presented for the detection of ²³⁹Pu and ²⁴⁰Pu in sea water, pore water, ocean sediments, sediment trap samples and coral samples. Both sample preparation and purification procedures, as well as the procedure used to detect Pu by mass spectrometry (m.s.), are presented. The m.s. technique proves to be over an order-of-magnitude more sensitive than traditional alpha-counting techniques for the detection of Pu in environmental samples. Also, the ratio of ²⁴⁰Pu/²³⁹Pu is obtained with this technique.     

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.     

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 nuclear bomb Pu in Nishiyama area, Nagasaki, estimated by accurate and precise determination of 240Pu/239Pu ratio in soils

Plutonium isotopes in forest soils collected in Nishiyama area, Nagasaki, were successfully determined by high resolution inductively coupled plasma mass spectrometry after the treatment with a microwave decomposition system. The (240)Pu/(239)Pu atom ratios observed in the samples in the Nishiyama area were obviously lower than the range of the global fallout. The low ratios (minimum 0.032) observed in Nishiyama area indicated the influence of detonation of the Pu nuclear weapon in 1945. Since the area is contaminated also by global fallout, the (240)Pu/(239)Pu atom ratio can be more sensitive indicator of bomb-derived Pu than Pu activity concentration.     

The inflow of (238)Pu and (239+240)Pu from the Vistula River catchment area to the Baltic Sea

The aim of the work was to estimate plutonium inflow from the Vistula River’s catchments area to the Baltic Sea. There were differences in plutonium activities depending on season and sampling site. The highest activities of ²³⁸Pu and ^239+240Pu were transported from the Vistula River watershed to the Baltic Sea in spring and the lowest in summer. Annually, the southern Baltic Sea is enriched via the Vistula River with 10.3 MBq of ²³⁸Pu and 89.0 MBq of ^239+240Pu. The enhanced concentration of plutonium in water from the Vistula River is the result of its runoff from the Vistula drainage area, mostly from snowmelt, enhanced rainfalls and leached materials from river bed.     

Environmental study of fall-out (239+240)Pu in soil samples in Iran

The result of a general survey on the concentration of fall-out (239+240)Pu in soil collected from several regions in Iran are presented. The samples represent mixed soil averaged over the depth of 0-50 mm. According to the results obtained by alpha spectrometry on 96 soil samples from 32 locations, the (239+240)Pu concentrations vary in the range 80-360 mBq kg(-1). Under normal operating conditions and present counting setup, the minimum detectable activity (MDA) was approximately 8 mBq kg(-1) for soil samples.     

Experimental values for 241Am and 239+240Pu Kd's in French agricultural soils

Experiments resulted in determination of K(d) values for (241)Am and (239+240)Pu in 6 soils whose characteristics are representative of agricultural soils found around French nuclear power plant sites. These experiments were conducted in stirred batch reactors and the sorption isotherms were plotted. For americium, the experimental K(d) values varied from 60 to 4000 Lkg(-1) (d.w.) and correlated well with soil pH, K(d) increased with increasing pH. As regards plutonium, the experimental K(d) values varied between 300 and 9600 Lkg(-1) and decreased with increasing total sand content. The estimation of the total residence time determined by using a particular and experimentally refined value for K(d)-with a model similar to those currently used for impact assessments-illustrates the importance of establishing values that are better suited to specific soils than generic values. Lastly, depending on the type of evaluation envisioned, it might be important to look for a specific value of K(d)-and even modelling-more suited to the specificity of the scenario studied, by performing more complex, or even in situ, experiments.     

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.     

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.     

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.     

Estimating the date corresponding to the horizon of the first detection of 137Cs and 239+240Pu in sediment cores

The anthropogenic bomb fallout nuclides 137Cs and plutonium isotopes (240Pu, 239Pu) are important chronometers for the determination of recent sediment accumulation rates using sediment cores collected from various water bodies. One of the crucial time horizons used to date sediment core profiles corresponds to the date of first detection of these nuclides. Although atmospheric nuclear testing began during the mid-1940s, the year corresponding to a nuclide's first detection when measured in 2006 depends on a number of factors including fallout history, radioactive half-life, gamma/alpha detection limits, geographic latitude and the accumulated thickness of the sediment section. This paper reports estimations of the year of first detection in sediment profiles of fallout 137Cs and Pu measured by gamma and alpha spectrometry, respectively. We find that for the latitude 30-40 degrees south of the equator the year of first detection for 137Cs is 1955. The date is earlier in the northern hemisphere due to higher fallout rates. Due to better measurement sensitivity first detection of Pu is generally earlier than 137Cs by 1-2 years.     

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.     

Fallout strontium and caesium transfer from vegetation to cow milk at two lowland and two Alpine pastures

Vegetation-to-milk transfer coefficients for 137Cs, 90Sr and stable strontium were determined for cows grazing on two intensively managed lowland pastures and two Alpine pastures in Austria. The 90Sr transfer coefficient at the four pastures ranged from 0.0005 to 0.0012 dl-1 and correlated with the stable strontium transfer coefficient (0.0006-0.0013 dl-1) with the lower values found on the intensively managed pastures. The 137Cs transfer coefficient ranged from 0.0009-0.0045 dl-1.     

The transfer of 60Co from feed into vitamin B12 in cow liver,milk and beef

The transfer of the radionuclide ⁶⁰Co from feed to milk, meat and the organs of a cow and its incorporation into vitamin B12 were studied in order to determine the transfer coefficient of ⁶⁰Co into vitamin B12 in cattle. Upper limits of transfer coefficients for ⁶⁰Co organically complexed into vitamin B12 were determined to be 6·0 × 10⁻⁵ days/litre in milk and 3·9 × 10⁻⁵ days/kg in meat, based on values measured after 140 days in bovine liver.     

90Sr, 238U, 234U, 137Cs, 40K and 239/240Pu in Emmental type cheese produced in different regions of Western Europe

A method is presented for the determination of (90)Sr and uranium in Emmental type cheese collected in dairy plants from different European countries. Results display a significant correlation (r = 0.708 Student t-test = 6.02) between the (90)Sr content of the cheese and the altitude of grazing. The highest (90)Sr activity is 1.13 Bq kg(-1) of cheese and the lowest is 0.29 Bq kg(-1). Uranium activity is very low with a highest (238)U value of 27 mBq kg(-1). In addition, (234)U/(238)U ratio shows a large enrichment in (234)U for every location. Without any significant indication of the geographic origin of the cheese, this enrichment is believed to be due to the geological features of the pasture, soil and underground water. These results tend to prove that the contamination of milk by uranium originates principally from the water that the cows drink instead of the forage. This finding may have a great importance in models dealing with dairy food contamination by radionuclides following a nuclear accident. Also, the (90)Sr content and to a lesser extent the (234)U/(238)U ratio could be used to trace the authenticity of the origin of the cheese. (137)Cs activity is lower than the detection limit of 0.1 Bq kg(-1) in all the samples collected (n = 20). Based on natural (40)K activity in cheese (15-21 Bq kg(-1)), the decontamination factor for the alkaline cations from milk to cheese is about 20. Plutonium activity stays below the detection limit of 0.3 mBq kg(-1).     

The transfer of different forms of 35S to goat milk

Sulphur-35 is released during the routine operation of UK gas-cooled reactors. An experiment to determine the rates of transfer of different forms of (35)S to goat milk is described. Lactating goats received (35)S orally as single administrations of sulphate, L-methionine, or grass contaminated either through root uptake of (35)S as sulphate or through aerial deposition of (35)S as carbonyl sulphide onto the grass. Transfer was higher for (35)S administered as methionine compared with (35)S administered as sulphate. Changes in activity concentrations in milk for all sources of (35)S demonstrated two components of loss. The first component had a half-life of circa 1 d for all sources, the second was longer in goats administered carbonyl sulphide (44 d) than in all of the other treatments (circa 10 d). The rate of transfer of (35)S to milk of a further group of goats receiving (35)S-sulphate daily appeared to reach equilibrium within 30 d. Extrapolation of transfer parameters derived to other dairy ruminants is discussed.     

The transfer of radionuclides from saltmarsh vegetation to sheep tissues and milk

Radionuclides released into the Irish Sea by the Sellafield reprocessing plant are deposited onto tide-washed pastures along the western coast of the United Kingdom. Many of these pastures are grazed by sheep or cattle. This paper describes a controlled feeding study, in which saltmarsh vegetation harvested from close to the Sellafield plant, was fed to lambs and adult female sheep for a period of 8 weeks. Activity concentrations of (60)Co, (95)Nb, (106)Ru, (134)Cs, (137)Cs, (238)Pu, (239,240)Pu and (241)Am were determined in edible tissues and transfer parameters estimated. The activity concentrations of some of the radionuclides will not have been in equilibrium with those in the diet. Nevertheless, the study was reasonably realistic in terms of agricultural management as the period of the study was similar to that for which lambs graze on the saltmarshes. A field study to determine the activity concentrations of (137)Cs and (239,240)Pu in the milk of ewes grazing a saltmarsh close to Sellafield is also described.     

Partitioning of polar and non-polar neutral organic chemicals into human and cow milk

The aim of this work was to develop a predictive model for milk/water partition coefficients of neutral organic compounds. Batch experiments were performed for 119 diverse organic chemicals in human milk and raw and processed cow milk at 37°C. No differences (<0.3 log units) in the partition coefficients of these types of milk were observed. The polyparameter linear free energy relationship model fit the calibration data well (SD=0.22 log units). An experimental validation data set including hormones and hormone active compounds was predicted satisfactorily by the model. An alternative modelling approach based on log K(ow) revealed a poorer performance. The model presented here provides a significant improvement in predicting enrichment of potentially hazardous chemicals in milk. In combination with physiologically based pharmacokinetic modelling this improvement in the estimation of milk/water partitioning coefficients may allow a better risk assessment for a wide range of neutral organic chemicals.     

137Cs and 90Sr transfer to milk in Austrian alpine agriculture

The alpine regions of Austria were among the most contaminated territories outside of the former USSR after the Chernobyl accident. In the investigated province of Salzburg the median (137)Cs surface deposition was 31.4 kBq m(-2) with maximum values exceeding 90 kBq m(-2) (May 1986). To quantify the transfer of (137)Cs and (90)Sr from vegetation to milk in these seminatural conditions nine seasonally grazed alps were identified and vegetation and milk sampled during summer 2002 and summer 2003. Mean+/-SD milk transfer coefficients (fm) for (137)Cs and (90)Sr were 0.0071+/-0.0009 d l(-1), and 0.0011+/-0.0004 d l(-1), respectively; which for (137)Cs is markedly higher than those fm values found in intensive agricultural systems. Transfer kinetics for (137)Cs into cow milk were approximated using a 2-compartment model with a short and a long-term component. Fitting the model to empirical data results in reliable estimates of the time constant of the short-term component, biological half-life 1.06+/-0.28 d, whereas the estimates of the long-term component are subject to high uncertainties.