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At least 1,711 records · Page 95Linked to original sources
PubMed2003

Excess plutonium in soil near the Nevada Test Site, USA.

Two soil profiles were collected from undisturbed areas near the Nevada Test Site (NTS). The activity of 137Cs in the surface layer of the downwind Queen City Summit profile is three times higher than at the upwind site at Searchlight, NV (41.1+/-0.6 mBq/g vs. 13.0+/-0.4 mBq/g), and the 239,240Pu activity is 100 times greater (51+/-2 mBq/g vs. 0.52+/-0.03 mBq/g). An examination of the literature suggests that the 137Cs/239,240Pu and the 239,240Pu/238Pu activity ratios in soils and sediments from the northern hemisphere, due to fallout from atmospheric atomic weapons testing, have generalized values of 36+/-4 and 30+/-4, respectively (as of 1 July 1995). Deviations from these values may indicate possible contamination by sources other than fallout. Data from the surface soil of the downwind Queen City Summit profile yield a 137Cs/239,240Pu ratio of 0.81+/-0.02 and a 239,240Pu/238Pu ratio of 78+/-6. Clearly, an increase in 239,240Pu relative to 137Cs or 238Pu can account for these observations. There is compelling evidence that this "excess" 239,240Pu came from activities at the NTS during the aboveground testing of nuclear devices, more than likely from safety tests, some 40 years ago, and/or during the interim by the wind-driven resuspension of contaminated surface soil on the NTS and its transport off-site. Moreover, the two concentration profiles show that high percentages of both of these elements are retained for decades in the upper few centimeters of soil in Nevada's desert environment.

Cesium↗
PubMed1991

Environmental impact of the Chernobyl accident: mutagenesis in bank voles from Sweden.

An investigation was carried out in Sweden aimed at studying the possible genetic effects of the Chernobyl fallout on wild small mammals. The bank voles (Clethrionomys glareolus Schreb.) were obtained from three differently contaminated areas in Sweden and, for control, in an area with negligible contamination by fallout. Radionuclide determinations to assess the content of 137Cs and mutagenicity tests (bone marrow micronucleus test and sperm abnormality assay) were performed. The results obtained showed a positive correlation between the increase of micronucleated polychromatic erythrocytes (MPCE/1000 PCE) and both 137Cs content in muscle and in soil contamination. The estimated doses absorbed by the animals were far lower than those required for the same effect in laboratory experiments. An explanation of this discrepancy between dose and measured biological effect is not available, yet similar results have been repeatedly reported after the Chernobyl accident and should be a matter for further discussion. An increased frequency of micronucleated cells might occur at minimal dose gradients, and the micronucleus test appears to be a valid tool to show such effects.

Accidents↗
PubMed2006

Long-term mobility of fallout 90Sr in ploughed soil, and 90Sr uptake by wheat grain.

In this study, we evaluated the mobility of 90Sr in ploughed upland soil, which affects the residual amount in the soil and plant uptake on the basis of long-term monitoring data. Paired samples of soil and wheat grain were taken annually from 1961 to 1995 from 8 agricultural fields in Japan, and the concentrations of exchangeable 90Sr in soil and total 90Sr in wheat grain were determined. The concentration of exchangeable 90Sr in ploughed soil decreased exponentially with time. The environmental factor responsible for the decrease of exchangeable 90Sr in the ploughed layer, lambda(e), was determined from the monitoring data of exchangeable 90Sr in the ploughed soil and the amount of fallout-derived deposition. The lambda(e) was larger from 1970 to 1980 than it was from 1980 to 1995, suggesting that an easily removable fraction of 90Sr in soil was preferentially lost from ploughed soil. Among various soil properties that we investigated, the main factor controlling the long-term mobility of 90Sr from ploughed upland soil and 90Sr uptake by wheat grain was the cation-exchange capacity (CEC) of soil. Our experimental results indicate that the entrapment of 90Sr on a cation-exchange site retards the downward migration and wheat uptake of 90Sr from ploughed soil. The empirical parameters that we obtained based on the long-term observation of a wheat-cultivated upland field in Japan could be used as reference data in order to roughly estimate the mobility of 90Sr in ploughed soil and soil-borne 90Sr transfer to wheat grain in the humid Japanese climate.

Agriculture↗
PubMed1993

129I and 137Cs fission products in thyroids of animals, 1984-1991.

Iodine is intensely concentrated in the thyroid of animals, while 137Cs is not. In this study, 129I and 137Cs concentrations were determined in animal thyroids from selected areas during 1984-1991. The thyroids were from deer killed within the Savannah River Site (SRS) in South Carolina; from the environs of Oak Ridge (OR), Tennessee; West Tennessee; and Florida. Thyroids from sheep slaughtered routinely in Birmingham, England (UK), were also tested. The glands were analyzed by x-ray spectroscopy using a high-purity germanium well detector. 129I concentrations of 1 to 102 Bq 129I (g thyroid)-1 were found in 6.8% of deer thyroids from SRS. Eighty-nine percent of the thyroids from SRS and 38% of those from OR contained 129I concentrations of 0.01 to 1.0 Bq 129I g-1. No thyroids from West Tennessee or Florida had more than 4 mBq 129I g-1. Cesium was found to be distributed differently; 38% of the thyroids from SRS contained 0.1 to 0.65 Bq 137Cs g-1, and the highest concentrations appeared periodically, during November and December. Ten to 100 mBq of 137Cs were found in 60% of thyroids from SRS, 79% of those from Florida, 52% of those from OR, and 22% of those from West Tennessee. In thyroids from SRS and Florida, most of the 137Cs has been from worldwide fallout on sandy soil which permits 137Cs-rich vegetation; if a fraction of the 137Cs is from other sources, it has not been defined. The unique finding of this report is the high incidence and persistence of > 0.01 Bq 129I (g thyroid)-1 in deer from OR and SRS. 129I is a marker for fission products, but it is not a radiological hazard because of its very slow radioactive decay and its continual dilution by additions of nonradioactive iodine to the environment.

Animals↗
PubMed1998

Plutonium anomalies in attic dust and soils at locations surrounding the Nevada Test Site.

Attic dust and soil samples were collected during the Summer of 1996 and the Spring of 1997 in southern Nevada and southern Utah. Analysis of the samples for radiocesium and plutonium give activity ratios of radiocesium/plutonium that range from 0.7 +/- 0.1 to 27 +/- 2, well below the world-wide fallout ratio of 34 +/- 4 (as of 1 July 1997). This indicates anomalous plutonium throughout the region, including areas to the south of the Nevada Test Site (NTS), generally believed to have received only world-wide fallout. Safety tests and above-ground detonations that resulted in incomplete fission, conducted at the NTS during the 1950's and 1960's, are likely sources of this excess plutonium.

Cesium Radioisotopes↗
PubMed2006

Migration of fallout radiocaesium in a grassland soil from 1986 to 2001. Part II: evaluation of the activity-depth profiles by transport models.

The vertical migration of (134)Cs, deposited by the Chernobyl fallout (1986), and (137)Cs, deposited by the Chernobyl and the global fallout, in the soil of an undisturbed Bavarian grassland in Germany was investigated from 1986 to 2001. The activity-depth profiles of both isotopes at ten sampling dates were evaluated by the classical convection-dispersion equation and a random walk particle model. In both models, the apparent migration velocity v and the apparent dispersion coefficient D were assumed to be independent of time. However, optimized values of v and D were significantly different for the different locations sampled at different times. If nevertheless constant values of v and D were used, the simulated activity densities per soil layer were out of the range of the spatial variability of the observed activity densities determined in 2001. It is concluded that without further simultaneous investigations e.g. on bioturbation at the study site, migration parameters of radiocaesium determined by classical transport models based on convection and dispersion during the first years after the deposition of the activity cannot be used for predictive purposes.

Cesium Radioisotopes↗
PubMed2006

Soil-to-grain transfer of fallout 90Sr for 28 winter wheat cultivars.

In order to identify wheat cultivars with minimum soil-to-grain transfer of fallout 90Sr, 28 winter wheat cultivars were investigated at three different sites with different soil types in Upper Bavaria. Each cultivar was grown on an area of 10 m2 and harvested in August 1999. Mean soil-to-grain concentration ratios (C(r)) were 0.151 +/- 0.029, 0.205 +/- 0.035 and 0.060 +/- 0.012, respectively. The C(r) values obtained varied by factors of up to 2.6 for the different cultivars at a given site, and by factors of up to 5.0 for the different sites and a given cultivar. Site-averaged normalized concentration ratios (SANC(r)) ranged from 0.666 +/- 0.062 to 1.503 +/- 0.161. The cultivars Convent, Ludwig, and Semper, showed the lowest uptake of (90)Sr compared to the mean of all cultivars at each site. A cultivar that shows both minimum uptake of 90Sr and 137Cs could not be identified. The results suggest that 90Sr rather than 137Cs might be the limiting radionuclide concerning the use of contaminated land for wheat production. Thus, more efforts might be necessary identifying wheat cultivars with minimum 90Sr uptake.

Radiation Dosage↗
PubMed1999

Global distribution of Pu isotopes and 237Np.

Inventories and compositions of Pu isotopes and 237Np in archived soil samples collected in the 1970s from 54 locations around the world were determined to provide regional baselines for recognizing possible future environmental inputs of non-fallout Pu and Np. As sample sizes used in this work were small (typically 1 g), inhomogeneities in Pu and Np concentrations were easily recognizable and, as a result, we were able to determine that atypical debris in South America, from French testing in the South Pacific, is more widely and uniformly distributed than previously supposed. From our results we conclude that fallout 237Np/239Pu atom ratios are generally lower in the Southern Hemisphere (approximately 0.35) than in the Northern Hemisphere (approximately 0.47.) Moreover, 237Np/239Pu atom ratios are more device-dependent, hence more variable, than counterpart 240Pu/239Pu atom ratios. Given predictable trends caused by sample inhomogeneities, with only two exceptions, the Pu results of this work are entirely consistent with (and in several instances improve on) results previously reported for these same samples. However, unlike earlier interpretations used to explain these results, we recommend that fallout isotopic signatures be represented by mixing lines, rather than averages, to better reflect regional variations of stratospheric fallout inventories relative to tropospheric fallout inventories, and provide the theoretical basis for doing so. Finally, the Np results of this work constitute one of the largest single compilations of such data reported to date.

Geography↗
PubMed1992

Transfer characteristics of radiocaesium from soils to permanent pasture.

Depth profile measurements of 137Cs and 134Cs were carried out in 11 permanent pastures that had been exposed to fallout from the Chernobyl accident. In addition to gamma-ray spectrometric analysis, the selected pastures were characterized by several soil parameters, the influence of which on transfer was investigated. Sampling of soil and pasture grass was undertaken during a period extending from the Spring of 1987 to the Autumn of 1988. The results show that there has been limited downward migration of Chernobyl-derived caesium. In October 1988 more than 88% of the 137Cs attributable to Chernobyl was mainly confined to the top 10 cm of undisturbed soil, with 79% on average in the top 5 cm. The distribution of pre-Chernobyl caesium at the 11 sites was also evaluated. In an investigation of the influence of soil parameters on transfer to grass, a negative correlation with pH was observed in 1987. In April 1987 concentration ratios for 137Cs in grass ranged from 0.03 to 0.49. In general, comparison of the concentration ratio values showed a decreasing trend over the 18 months.

Accidents↗
PubMed2002

Global weapons' fallout 137Cs in soils and transfer to vegetation in south-central Chile.

The contamination and depth distribution of 137Cs in soil due to the fallout from atmospheric weapons' tests were measured at 29 sites in the 9th and 10th administrative regions in Chile located in the 40 degrees latitude in the southern hemisphere. The depth distribution in most of the sites follows no systematic pattern in the upper few centimetres, but below this depth an exponential decline could be deduced. The calculated relaxation depth appears to be a good indicator for estimating the long-term 137Cs distribution in these soil profiles. It ranges from 4.4 +/- 1.9 cm in Palehumults to 8.4 +/- 4.4 and 9.7 +/- 5.1 cm in Hapludands and Psamments, respectively. For these soil types the value for the relaxation depth tends to increase with decreasing clay content and increasing volume of coarse pores. 137Cs activity densities at the selected sites ranged from 450 to 5410 Bq m(-2) and correlate significantly (r = 0.791) with the mean annual rainfall rate of the sampling sites. 137Cs concentration ratios of prairie plants/soil were found to be in the range 0.008-2.3 and could be related to relaxation depths in undisturbed soils.

Cesium Radioisotopes↗
PubMed2003

Spatial variability of fallout-90Sr in soil and vegetation of an alpine pasture.

According to the soil-to-plant transfer concept generally used in dose assessment modeling, the plant uptake of a radionuclide should depend linearly on its concentration in the soil. In order to validate this concept for (90)Sr in a semi-natural ecosystem, plant and soil samples were taken at 100 plots of a 100 x 100 m(2) area within an alpine pasture near Berchtesgaden, Germany. At three plots, the vertical distribution of (90)Sr in the soil was determined in addition. A statistically significant correlation between the soil and plant concentration of (90)Sr was not detectable (Spearman correlation coefficient R=-0.116, p>0.05) within the range of the Sr-concentration covered (15-548 Bq kg(-1) dry soil and 17-253 Bq kg(-1) dry plant material). Thus, the prerequisite of the soil-to-plant transfer concept was not fulfilled for (90)Sr at this site. Organic carbon and total nitrogen were also determined in the soil samples. Both elements were highly correlated (R=0.912, p<0.001), their ratio being C/N=10.9+/-0.7. While C was positively correlated with the (90)Sr concentrations in the soil (R=0.342, p<0.001), negative correlations were observed for the plant concentrations (R=-0.286, p<0.01) and the concentration ratios (R=-0.444, p<0.001) of (90)Sr. These results are compared with those recently obtained for (137)Cs by Bunzl et al. (J Environ Radioactiv 48 (2000) 145).

Carbon↗
PubMed2002

Transport of fallout radiocesium in the soil by bioturbation: a random walk model and application to a forest soil with a high abundance of earthworms.

It is well known that bioturbation can contribute significantly to the vertical transport of fallout radionuclides in grassland soils. To examine this effect also for a forest soil, activity-depth profiles of Chernobyl-derived 134Cs from a limed plot (soil, hapludalf under spruce) with a high abundance of earthworms (Lumbricus rubellus) in the Olu horizon (thickness=3.5 cm) were evaluated and compared with the corresponding depth profiles from an adjacent control plot. For this purpose, a random-walk based transport model was developed, which considers (i) the presence of an initial activity-depth distribution, (ii) the deposition history of radiocesium at the soil surface, (iii) individual diffusion/dispersion coefficients and convection rates for the different soil horizons, and (iv) mixing by bioturbation within one soil horizon. With this model, the observed 134Cs-depth distribution at the control site (no bioturbation) and at the limed site could be simulated quite satisfactorily. It is shown that the observed, substantial long-term enrichment of 134Cs in the bioturbation horizon can be modeled by an exceptionally effective diffusion process, combined with a partial reflection of the randomly moving particles at the two borders of the bioturbation zone. The present model predicts significantly longer residence times of radiocesium in the organic soil layer of the forest soil than obtained from a first-order compartment model, which does not consider bioturbation explicitly.

Animals↗
PubMed2002

A millennium perspective on the contribution of global fallout radionuclides to ocean science.

Five decades ago, radionuclides began to enter the ocean from the fallout from atmospheric nuclear weapons tests. The start of the 21st century is an appropriate vantage point in time to reflect on the fate of this unique suite of manmade radionuclides--of which more than two-thirds arrived at the surface of the oceans of the planet. During these five decades much has been learned of the behavior and fate of these radionuclides and, through their use as unique tracers, of how they have contributed to the growth of basic knowledge of complex oceanic physical and biogeochemical processes. Some of the highlights of the ways in which fallout radionuclides have given new insights into these processes are reviewed in the historical context of technological and basic ocean science developments over this period. The review addresses major processes involved, such as physical dispersion and mixing, particle association and transport of reactive nuclides, biological interactions, and mixing and burial within ocean sediments. These processes occur over a range of scales ranging from local to global. Finally, an account is given of the present spatial distribution within the oceans of the various components of the fallout radionuclide suite.

History, 20th Century↗
PubMed1995

The variability in fallout content of soils and plants and the design of optimum field sampling strategies.

Sampling was carried out at an upland peat site in Ireland to assess the variability in 137Cs deposition to soils and activity concentration in individual vegetation species. A 3,600 m2 quadrat was laid out, and a soil core was extracted within each of sixteen 20 x 20 cm soil monoliths. The coefficient of variation values for 137Cs deposition and activity in individual soil horizons were in all cases greater than 30%, and the relative variability between corresponding horizons tended to increase with depth. Samples of Calluna vulgaris and Juncus squarrosus were taken at each soil sampling location and coefficients of variation for 137Cs activity in these species were 12 and 20%, respectively. The data was used to examine the relationship between the number of samples analyzed in a survey, the variability within those samples, and the way those two factors affect our ability to detect between-site differences in 137Cs contamination levels. A methodology is developed for detection of between-site differences in 137Cs contamination under different experimental criteria. The data show that, of the sample types examined, between-site differences could be detected most efficiently with C. vulgaris. Because of the variability associated with the 137Cs content of each sample type, between-site differences could be detected with fewer plant samples than soil samples. Plant-soil concentration ratios, transfer factors, and plant-plant ratios were calculated from the data, and the variability associated with each parameter was assessed. The variation among values for plant-plant ratios was less than among concentration ratios, and the greatest spread of values was associated with plant-soil transfer factors.

Analysis of Variance↗
PubMed2002

Fallout radiocesium in an Antarctic region: deposition history, activity densities and vertical transport in soils.

To improve the knowledge about the (137)Cs spatial distribution and vertical migration in soils of the Southern Hemisphere, the total areal activity density and the vertical transport parameters of this radionuclide were measured in an Antarctic region. For this purpose vegetation and incremental soil samples were collected at 21 representative sites located at 4 islands of the South Shetland Archipelago: King George, Robert, Greenwich and Snow (62-63 degrees S and 58-62 degrees W). The total (137)Cs activity density varied considerably from 118 to 662 Bq m(-2) (median 384 Bq m(-2), reference date 1995), with a high percentage of the total activity retained in the vegetation cover (5-98% in moss, 3-20% in lichen and 4-12% in grass). At most sites, the maximum activity density in soil was observed in the top layer from where it decreased continuously. To evaluate the transport parameters of (137)Cs from the activity-depth profiles, the classical convection-diffusion model was used based on the time-course of the annual deposition density of (137)Cs at the studied region. The values for the diffusion coefficient D(s) (median 0.043 cm(2) year(-1)) and the convection velocity v(s) (median -0.012 cm year(-1)) of radiocesium observed under a polar climate are small compared to the transport parameters determined in temperate zones. The data also indicate that at these sites the convectional transport of (137)Cs is almost negligible compared to the transport by diffusion. The high vulnerability of the Antarctic soils to (137)Cs deposition, as a consequence of its very slow transport due to the extreme climatic conditions at these latitudes, has been confirmed.

Antarctic Regions↗
PubMed2000

Calibration of a field-portable gamma detector to obtain in situ measurements of the 137Cs inventories of cultivated soils and floodplain sediments.

Over the past 10 years, a number of studies have exploited the potential for using measurements of fallout 137Cs inventories to document rates and patterns of soil erosion on cultivated land and to estimate rates of overbank sedimentation on river floodplains. Traditional procedures for applying the 137Cs technique involve the collection of soil or sediment cores from a study site and their subsequent transfer to the laboratory for preparation and analysis by gamma spectrometry. Such procedures are time consuming and there may be a considerable delay before the results are available. It is therefore difficult to obtain preliminary results, which could be used to guide the development of an ongoing sampling programme. The use of in situ gamma spectrometry measurements to quantify 137Cs inventories in soils and sediments offers a number of potential advantages over traditional procedures. However, in order to derive a reliable estimate of the 137Cs inventory for a measurement point, it is necessary to take account of the attenuation of 137Cs gamma rays by the soil matrix and information on the depth distribution of 137Cs in the soil or sediment is therefore required. In the present study, empirical relationships between in situ measurements of 137Cs activity and total 137Cs inventories have been established for soils from a cultivated field and for floodplain sediments, based on information on the vertical distribution of 137Cs in the soils and sediments provided by the forward scattering ratio derived from the field measured spectra. These relationships have been used to estimate 137Cs inventories from in situ measurements of 137Cs activity at other locations.

Cesium Radioisotopes↗
PubMed2003

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.

Diffusion↗