Recent Cs deposition in sediments of Admiralty Bay, Antarctica

Cesium-137, radium-226 and lead-210 profiles of a 25 cm sediment core give an indication of recent changes in land-ocean interactions at a polar coastal environment (Admiralty Bay, King George Island, Antarctica). The linear sedimentation accumulation rate at the study site calculated from the unsupported ²¹⁰Pb profile was 6.7 mm/year from 1965 to 2005. A 3.5-fold increase in ¹³⁷Cs concentrations was observed in the top layer of this sediment core. This sharp increase seems to indicate a recent redistribution of fallout radionuclides previously deposited on soil, vegetation and snow. These results imply enhanced land-ocean interactions at this site likely as a result of climate change. Because our results are based on a single core, additional investigations are needed to confirm our observations.     

Concentrations of (137)Cs in summer pasture plants that reindeer feed on in the reindeer management area of Finland

Samples of summer pasture plants that reindeer feed on were collected in order to study ¹³⁷Cs concentrations in different plant species and in species nested in certain site types, and to study the regional distribution of ¹³⁷Cs in the Finnish reindeer management area. Plant species were categorized by the site types of mineral soil forest (xeric heath forest and mesic heath forest) and peatland. A third category called ’other plant species’ included plants with various site types, poorly determined species and species with poor statistics. The ¹³⁷Cs concentrations in different site types differed significantly. The mean ¹³⁷Cs concentrations of the whole reindeer management area in the xeric heath forest plant species was 44 ± 27 Bq/kg dw, in the mesic heath forest plant species 75 ± 59 Bq/kg dw and in the peatland plant species 219 ± 150 Bq/kg dw. The peatland species uptake ¹³⁷Cs more efficiently than plant species of mineral soil forests. A particularly efficient collector of ¹³⁷Cs was Trichophorum sp. It is suggested that Trichophorum sp. could be used as an indicator species for reindeer summer fodder plants. The highest concentrations of ¹³⁷Cs were found in Southern Lapland and the lowest in Northern Lapland. Today, the concentrations of ¹³⁷Cs in summer pasture plants that reindeer feed on in Finland are at such a level that there is no need to avoid any plant species. In the case of future nuclear fallout, reindeer grazing in peatlands would increase concentrations of ¹³⁷Cs in reindeer meat.     

Determining floodplain sedimentation rates using Cs in a low fallout environment dominated by channel- and cultivation-derived sediment inputs, central Queensland, Australia

Fallout ¹³⁷Cs has been widely used to determine floodplain sedimentation rates in temperate environments, particularly in the northern hemisphere. Its application in low fallout, tropical environments in the southern hemisphere has been limited. In this study we assess the utility of ¹³⁷Cs for determining rates of floodplain sedimentation in a dry-tropical catchment in central Queensland, Australia. Floodplain and reference site cores were analysed in two centimetre increments, depth profiles were produced and total ¹³⁷Cs inventories calculated from the detailed profile data. Information on the rates of ¹³⁷Cs migration through local soils was obtained from the reference site soil cores. This data was used in an advection–diffusion model to account of ¹³⁷Cs mobility in floodplain sediment cores. This allowed sedimentation rates to be determined without the first year of detection for ¹³⁷Cs being known and without having to assume that ¹³⁷Cs remains immobile following deposition. Caesium-137 depth profiles in this environment are demonstrated to be an effective way of determining floodplain sedimentation rates. The total ¹³⁷Cs inventory approach was found to be less successful, with only one of the three sites analysed being in unequivocal agreement with the depth profile results. The input of sediment from catchment sources that have little, or no, ¹³⁷Cs attached results in true depositional sites having total inventories that are not significantly different from those of undisturbed reference sites.     

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.     

Long-term investigation of anthropogenic and naturally occurring radionuclides at reference sites in western Sweden

In case of an accidental release of radioactive substances into the environment, it is important to quickly and reliably estimate the radiation dose received by people in the affected area, and to determine the extent of the contamination. Measurements of the extent of the release and the subsequent contamination can be facilitated if there are predetermined reference sampling sites with known background radiation and inventory of radionuclides. Since 1996, 34 reference sites for soil sampling, field gamma, and intensimeter measurements have been established in western Sweden. Time series data for dose rates and radioisotope inventory have been collected at these sites, allowing for the investigation of changes in these parameters over time. The mass activity densities for the uranium and thorium series elements varied approximately between 10 and 50 Bq/kg and between 10 and 40 Bq/kg, respectively. The mass activity density of ⁴⁰K was approximately in the range 300–800 Bq/kg. The radiation exposure due to ¹³⁷Cs was rather small in this area. The dose rates calculated from in situ measurement data showed that the contribution to the total dose rate was almost entirely due to naturally occurring radionuclides. The measured dose rate was about twice as high as the calculated rate, even after subtracting the contribution from cosmic radiation. This may be explained by the fact that intensimeters generally are calibrated to measure the quantity ambient dose equivalent, which should not underestimate the effective dose.     

Migration of Cs and Sr in undisturbed soil profiles under controlled and close-to-real conditions

Migration of ¹³⁷Cs and ⁹⁰Sr in undisturbed soil was studied in large lysimeters three and four years after contamination, as part of a larger European project studying radionuclide soil–plant interactions. The lysimeters were installed in greenhouses with climate control and contaminated with radionuclides in an aerosol mixture, simulating fallout from a nuclear accident. The soil types studied were loam, silt loam, sandy loam and loamy sand. The soils were sampled to 30–40 cm depth in 1997 and 1998. The total deposition of ¹³⁷Cs ranged from 24 to 45 MBq/m², and of ⁹⁰Sr from 23 to 52 MBq/m². It was shown that migration of ¹³⁷Cs was fastest in sandy loam, and of ⁹⁰Sr fastest in sandy loam and loam. The slowest migration of both nuclides was found in loamy sand. Retention within the upper 5 cm was 60% for both ¹³⁷Cs and ⁹⁰Sr in sandy loam, while in loamy sand it was 97 and 96%, respectively. In 1998, migration rates, calculated as radionuclide weighted median depth (migration centre) divided by time since deposition were 1.1 cm/year for both ¹³⁷Cs and ⁹⁰Sr in sandy loam, 0.8 and 1.0 cm/year, respectively, in loam, 0.6 and 0.8 cm/year in silt loam, and 0.4 and 0.6 cm/year for ¹³⁷Cs and ⁹⁰Sr, respectively, in loamy sand. A distinction is made between short-term migration, caused by events soon after deposition and less affected by soil type, and long-term migration, more affected by e.g. soil texture. Three to four years after deposition, effects of short-term migration is still dominant in the studied soils.     

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.     

A simplified 137Cs transport model for estimating erosion rates in undisturbed soil

(137)Cs is an artificial radionuclide with a half-life of 30.12 years which released into the environment as a result of atmospheric testing of thermo-nuclear weapons primarily during the period of 1950s-1970s with the maximum rate of (137)Cs fallout from atmosphere in 1963. (137)Cs fallout is strongly and rapidly adsorbed by fine particles in the surface horizons of the soil, when it falls down on the ground mostly with precipitation. Its subsequent redistribution is associated with movements of the soil or sediment particles. The (137)Cs nuclide tracing technique has been used for assessment of soil losses for both undisturbed and cultivated soils. For undisturbed soils, a simple profile-shape model was developed in 1990 to describe the (137)Cs depth distribution in profile, where the maximum (137)Cs occurs in the surface horizon and it exponentially decreases with depth. The model implied that the total (137)Cs fallout amount deposited on the earth surface in 1963 and the (137)Cs profile shape has not changed with time. The model has been widely used for assessment of soil losses on undisturbed land. However, temporal variations of (137)Cs depth distribution in undisturbed soils after its deposition on the ground due to downward transport processes are not considered in the previous simple profile-shape model. Thus, the soil losses are overestimated by the model. On the base of the erosion assessment model developed by Walling, D.E., He, Q. [1999. Improved models for estimating soil erosion rates from cesium-137 measurements. Journal of Environmental Quality 28, 611-622], we discuss the (137)Cs transport process in the eroded soil profile and make some simplification to the model, develop a method to estimate the soil erosion rate more expediently. To compare the soil erosion rates calculated by the simple profile-shape model and the simple transport model, the soil losses related to different (137)Cs loss proportions of the reference inventory at the Kaixian site of the Three Gorge Region, China are estimated by the two models. The over-estimation of the soil loss by using the previous simple profile-shape model obviously increases with the time period from the sampling year to the year of 1963 and (137)Cs loss proportion of the reference inventory. As to 20-80% of (137)Cs loss proportions of the reference inventory at the Kaixian site in 2004, the annual soil loss depths estimated by the new simplified transport process model are only 57.90-56.24% of the values estimated by the previous model.     

Plutonium as a chronomarker in Australian and New Zealand sediments: a comparison with Cs

The construction of high resolution chronologies of sediment profiles corresponding to the last 50-100 years usually entails the measurement of fallout radionuclides ²¹⁰Pb and ¹³⁷Cs. The anthropogenic radionuclide, ¹³⁷Cs, originating from atmospheric nuclear weapons testing can provide an important “first appearance” horizon of known age (1954-1955), providing much-needed validation for the sometimes uncertain interpretations associated with ²¹⁰Pb geochronology. However, while ¹³⁷Cs usually provides a strong signal in sediment in the northern hemisphere, total fallout of ¹³⁷Cs in the southern hemisphere was only 25% that of the north and the low activities of ¹³⁷Cs seen in Australian and New Zealand sediments can make its horizon of first appearance somewhat arguable. Low ¹³⁷Cs fallout also limited the size of the 1963-1964 fallout peak, a peak that is usually seen in northern hemisphere sediment profiles but is often difficult to discern south of the equator.This paper shows examples of the use of nuclear weapons fallout Pu as a chronomarker in sediment cores from Australia (3 sites) and New Zealand (1 site). The Pu profiles of five cores are examined and compared with the corresponding ¹³⁷Cs profiles and ²¹⁰Pb geochronologies. We find that Pu has significant advantages over ¹³⁷Cs, including greater measurement sensitivity using alpha spectrometry and mass spectrometric techniques compared to ¹³⁷Cs measurements by gamma spectrometry. Moreover, Pu provides additional chronomarkers associated with changes in the Pu isotopic composition of fallout during the 1950s and 1960s. In particular, the ²³⁸Pu/^239+240Pu activity ratio shows distinct shifts in the early 1950s and the mid to late 1960s, providing important known-age horizons in southern hemisphere sediments. For estuarine and near-shore sediments Pu sometimes has another significant advantage over ¹³⁷Cs due to its enrichment in bottom sediment relative to ¹³⁷Cs resulting from the more efficient scavenging of dissolved Pu in seawater by sediment particles.     

Use of (137)Cs technique for soil erosion study in the agricultural region of Casablanca in Morocco

Accelerated erosion and soil degradation currently cause serious problems to the Oued El Maleh basin (Morocco). Furthermore, there is still only limited information on rates of soil loss for optimising strategies for soil conservation.In the present study we have used the (137)Cs technique to assess the soil erosion rates on an agricultural land in Oued el Maleh basin near Casablanca (Morocco). A small representative agricultural field was selected to investigate the soil degradation required by soil managers in this region. The transect approach was applied for sampling to identify the spatial redistribution of (137)Cs. The spatial variability of (137)Cs inventory has provided evidence of the importance of tillage process and the human effects on the redistribution of (137)Cs. The mean (137)Cs inventory was found about 842 Bq m(-2), this value corresponds to an erosion rate of 82 tha(-1) yr(-1) by applying simplified mass balance model in a preliminary estimation. When data on site characteristics were available, the refined mass balance model was applied to highlight the contribution of tillage effect in soil redistribution. The erosion rate was estimated about 50 tha(-1) yr(-1). The aspects related to the sampling procedures and the models for calculation of erosion rates are discussed.     

Inventory and vertical migration of 90Sr fallout and 137Cs/90Sr ratio in Spanish mainland soils

In this paper the inventory of ⁹⁰Sr in 34 points distributed along the Spanish peninsular territory is presented. Obtained values range between 173 Bq/m² and 2047 Bq/m². From these data set and those ¹³⁷Cs data obtained in a previous work the ¹³⁷Cs/⁹⁰Sr activity ratio has been established, laying this value between 0.9 and 3.6. Also the migration depth of both radionuclides has been analysed obtaining for ¹³⁷Cs an average value 57% lower than that obtained for ⁹⁰Sr.Additionally, this paper presents the results obtained in 11 sampling points in which the activity vertical profile has been measured. These profiles have been analysed to state the behaviour of strontium in soils and after, by using a convective-diffusive model, the parameters of the model which governs the vertical migration of ⁹⁰Sr in the soil, v (apparent convection velocity) and D (apparent diffusion coefficient) have been evaluated. Mean values obtained are 0.20 cm/year and 3.67 cm²/year, respectively.     

Uptake of radionuclides and stable elements from paddy soil to rice: a review

The critical paths for radionuclides and the critical foods in Asian countries differ from those in Western countries because agricultural products and diets are different. Consequently, safety assessments for Asian countries must consider rice as a critical food. As most rice is produced under flooded conditions, the uptake of radionuclides by rice is affected by soil conditions. In this report, we summarize radionuclide and stable element soil-to-plant transfer factors (TFs) for rice. Field observation results for fallout ¹³⁷Cs and stable Cs TFs indicated that while fallout ¹³⁷Cs had higher TF than stable Cs over several decades, the GM (geometric mean) values were similar with the GM of TF value for ¹³⁷Cs being 3.6 × 10⁻³ and that for stable Cs being 2.5 × 10⁻³. Although there are some limitations to the use of TF for stable elements under some circumstances, these values can be used to evaluate long-term transfer of long-lived radionuclides in the environment. The compiled data showed that TF values were higher in brown rice than in white rice because distribution patterns for elements were different in the bran and white parts of rice grains.     

Cs,Co and K uptake by lettuce plants in two distributions of soil contamination

¹³⁷Cs and ⁶⁰Co, two of the radionuclides more representative of discharges from nuclear facilities, are of interest for radiological protections because of their great mobility in biosphere and affinity with biological systems. The aim of the present work is the investigation of the possible influence of the vertical distribution of ¹³⁷Cs and ⁶⁰Co in soil upon their uptake by lettuce as function of plant's growth. An experiment ad hoc has been carried out in field conditions. The results show that (i) the transfer of ¹³⁷Cs and ⁶⁰Co from soil to lettuce is independent by their distribution in soil, (ii) the soil–plant transfer factors of ¹³⁷Cs and ⁶⁰Co show a similar trend vs. growth stage, (iii) the ⁴⁰K transfer factor trend is different from those of anthropogenic radionuclides, and (iv) ¹³⁷Cs and ⁶⁰Co specific activities are about 1 Bq/kg, in the mature vegetable with soil activity from 9 to 21 kBq/m².     

Correlations between potassium, rubidium and cesium ((133)Cs and (137)Cs) in sporocarps of Suillus variegatus in a Swedish boreal forest

An analysis of sporocarps of ectomycorrhizal fungi Suillus variegatus assessed whether cesium (¹³³Cs and ¹³⁷Cs) uptake was correlated with potassium (K) or rubidium (Rb) uptake. The question was whether intraspecific correlations of Rb, K and ¹³³Cs mass concentrations with ¹³⁷Cs activity concentrations in sporocarps were higher within, rather than among, different fungal species, and if genotypic origin of sporocarps within a population affected uptake and correlation. Sporocarps (n = 51) from a Swedish forest population affected by the fallout after the Chernobyl accident were studied. The concentrations were 31.9 ± 6.79 g kg⁻¹ for K (mean ± SD, dwt), 0.40 ± 0.09 g kg⁻¹ for Rb, 8.7 ± 4.36 mg kg⁻¹ for ¹³³Cs and 63.7 ± 24.2 kBq kg⁻¹ for ¹³⁷Cs. The mass concentrations of ¹³³Cs correlated with ¹³⁷Cs activity concentrations (r = 0.61). There was correlation between both ¹³³Cs concentrations (r = 0.75) and ¹³⁷Cs activity concentrations (r = 0.44) and Rb, but the ¹³⁷Cs/¹³³Cs isotopic ratio negatively correlated with Rb concentration. Concentrations of K and Rb were weakly correlated (r = 0.51). The ¹³³Cs mass concentrations, ¹³⁷Cs activity concentrations and ¹³⁷Cs/¹³³Cs isotopic ratios did not correlate with K concentrations. No differences between, within or, among genotypes in S. variegatus were found. This suggested the relationships between K, Rb, ¹³³Cs and ¹³⁷Cs in sporocarps of S. variegatus is similar to other fungal species.     

Fukushima fallout in Northwest German environmental media

Traces of short- and long-lived fallout isotopes (¹³¹I, ¹³⁴Cs and ¹³⁷Cs) were found in environmental samples collected in Northwest Germany (rain water, river sediment, soil, grass and cow milk) from March to May 2011, following the radioactivity releases after the nuclear accident in Fukushima, Japan. The measured concentrations are consistent with reported concentrations in air, amount of rainfall and expected values applying simple radioecological models. The [¹³⁴Cs]/[¹³⁷Cs] ratio reported for air (about 1) allows for discrimination between “recent” and “old” ¹³⁷Cs. Expected ¹³⁶Cs values fell below the detection limits of the instrumentation, despite large sample masses and long counting times.     

Evidence of the radioactive fallout in the center of Asia (Russia) following the Fukushima Nuclear Accident

It was recently reported that radioactive fallout due to the Fukushima Nuclear Accident was detected in environmental samples collected in the USA and Greece, which are very far away from Japan. In April-May 2011, fallout radionuclides (¹³⁴Cs, ¹³⁷Cs, ¹³¹I) released in the Fukushima Nuclear Accident were detected in environmental samples at the city of Krasnoyarsk (Russia), situated in the center of Asia. Similar maximum levels of ¹³¹I and ¹³⁷Cs/¹³⁴Cs and ¹³¹I/¹³⁷Cs ratios in water samples collected in Russia and Greece suggest the high-velocity movement of the radioactive contamination from the Fukushima Nuclear Accident and the global effects of this accident, similar to those caused by the Chernobyl accident.     

Transport and distribution of artificial gamma-emitting radionuclides in the River Yenisei and its sediment

Discharges from the Krasnoyarsk Mining and Chemical Industrial Complex (KMCIC) near Krasnoyarsk resulted in radioactive contamination of sediments of the River Yenisei. Between 1999 and 2006, 16 sediment cores were collected at different positions 15-1500 km downstream from the discharge point. The concentration of artificial gamma-emitting radionuclides (¹³⁷Cs, ⁶⁰Co, ¹⁵²Eu, and ²⁴¹Am) was determined with the objective to analyze the migration processes leading to the transport of these radionuclides along the river and to their vertical distribution within the sediment. In cores taken in the vicinity of the reactors, the average activity concentration of ¹³⁷Cs, ¹⁵²Eu, and ⁶⁰Co was about 1000 Bq kg⁻¹, and the activity concentration of ²⁴¹Am was about 20 Bq kg⁻¹. Contamination levels of artificial radionuclides were decreasing with increasing distance downstream the KMCIC: The fastest decrease of average activity by a factor of 10 over a distance of 300 km was observed for ²⁴¹Am, whereas for ¹³⁷Cs this decrease occurred over a distance of 1100 km. Sequential extraction experiments revealed that in all depths and at all distances the studied radionuclides were tightly bound to the sediment.To investigate the mechanisms of transport of the ¹³⁷Cs and ⁶⁰Co contamination, mathematical models have been used to describe the contamination in the river water and within the sediments.     

Can 239 + 240Pu replace 137Cs as an erosion tracer in agricultural landscapes contaminated with Chernobyl fallout?

Erosion studies often use 137Cs from the global fallout (main period: 1953-1964) as a tracer in the soil. In many European countries, where 137Cs was deposited in considerable amounts also by the Chernobyl fallout in 1986, the global fallout fraction (GF-Cs) has to be separated from the Chernobyl fraction by means of the isotope 134Cs. In a few years, this will no longer be possible due to the short half-life of 134Cs (2 yr). Because GF-Cs in the soil can then no longer be determined, the potential of using 239 + 240Pu as a tracer is evaluated. This radionuclide originates in most European countries essentially only from the global fallout. The activities and spatial distributions of Pu and GF-Cs were compared in the soil of a steep field (inclination about 20%, area ca. 3 ha, main soil type Dystric Eutrochrept), sampled at 48 nodes of a 25 x 25 m2 grid. The reference values were determined at 12 points adjacent to the field. Their validity was assured by an inventory study of radiocaesium in a 70 ha area surrounding the field sampling 275 nodes of a 50 x 50 m2 grid. In the field studied, the activity concentrations of GF-Cs and Pu in the Ap horizon were not correlated (Spearman correlation coefficient R = 0.20, p > 0.05), and the activity balance of Pu differed from that of GF-Cs. Whereas no net loss of GF-Cs from the field was observed as compared to the reference site, Pu was more mobile with an average loss of ca. 11% per unit area. In addition, the spatial pattern of GF-Cs and Pu in the field differed significantly. The reason may be that due to their different associations with soil constituents, Pu and Cs represent different fractions of the soil, exhibiting different properties with respect to erosion/deposition processes. This indicates that both radionuclides or one of them may not be appropriate to quantity past erosion. When tracer losses are used to calibrate or verify erosion prediction models, systematic deviations may not only stem from model shortcomings but also from tracer technique.     

Distribution of fallout radionuclides (7Be, 137Cs, 210Pb and 239,240Pu) in soils of Taiwan

Depth profiles and cumulative deposition of four fallout radionuclides (7Be, 137Cs, 210Pb and 239,240Pu) were determined in presumably undisturbed soils in Taiwan. Inventories of these radionuclides in different areas correlate significantly with each other (except 7Be) and with mean annual rainfall, providing a necessary condition for the development of soil erosion studies in Taiwan. However, the data show very large spatial variability between and within landscape units, reflecting the steep topographic and meteorological gradients in the island. Thus, the application of fallout radionuclides to study soil conservation in Taiwan is expected to be a demanding task; it will call for dense sampling even at undisturbed reference sites.     

Accumulation of Cs in puddle sediments within urban ecosystem

The role of puddle sediments as a final depot of ¹³⁷Cs horizontal migration within the urban landscape is studied using the example of Ekaterinburg city, Russia. Radioactive contamination in the city appeared due to fallout after atmospheric testing of nuclear weapons and nuclear accidents. Contamination density of ¹³⁷Cs in the region was assessed from archive data to be about 5.1 kBq/m², of which the maximum activity concentration (<30 Bq/kg) is associated with the upper 15 cm soil layer. Results of the survey reported here indicate a mean ¹³⁷Cs activity concentration in puddle sediments of 80 Bq/kg, with a maximum value of 540 Bq/kg. It is estimated that horizontal migration has led to about a fourfold concentration of ¹³⁷Cs in puddle sediments.