Short- and long-term patterns of ¹³⁷Cs in fish and other aquatic organisms of small forest lakes in southern Finland since the Chernobyl accident

We summarize the patterns of ¹³⁷Cs activity concentrations and transfer into fish and other biota in four small forest lakes in southern Finland during a twenty-year period following the Chernobyl accident in April 1986. The results from summer 1986 showed fastest accumulation of ¹³⁷Cs into planktivorous fishes, i.e. along the shortest food chains. Since 1987, the highest annual mean values of ¹³⁷Cs have been recorded in fish occupying the highest trophic levels, for perch (Perca fluviatilis) 13,600 Bq/kg (ww) and for pike (Esox lucius) 20,700 Bq/kg (ww). At the same time, activity concentrations of ¹³⁷Cs in crustacean zooplankton and Asellus aquaticus have ranged between 1000 and 19,500 Bq/kg (dw). In 2006, 5-28% of the 1987 ¹³⁷Cs activity concentration levels were still present in perch and pike. Since 1989 their ¹³⁷Cs activity concentrations in oligohumic seepage lakes have remained significantly higher than in polyhumic drainage lakes due to the increased transfer of ¹³⁷Cs into fish in the seepage lakes with lower electrolyte concentrations, longer water retention times and lower sedimentation rate.     

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.     

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.     

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.     

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.     

Pu/Cs ratios in the water column of the North Pacific: a proxy of biogeochemical processes

Anthropogenic radionuclides in seawater have been used as transient tracers of processes in the marine environment. Especially, plutonium in seawater is considered to be a valuable tracer of biogeochemical processes due to its particle-reactive properties. However, its behavior in the ocean is also affected by physical processes such as advection, mixing and diffusion. Here we introduce Pu/¹³⁷Cs ratio as a proxy of biogeochemical processes and discuss its trends in the water column of the North Pacific Ocean. We observed that the ^239,240Pu/¹³⁷Cs ratio in seawater exponentially increased with increasing depth (depth range: 100–1000 m). This finding suggests that the profiles of the ^239,240Pu/¹³⁷Cs ratios in shallower waters directly reflect biogeochemical processes in the water column. A half-regeneration depth deduced from the curve fitting the observed data, showed latitudinal and longitudinal distributions, also related to biogeochemical processes in the water column.     

Inventory and vertical migration of ¹³⁷Cs in Spanish mainland soils

In this study the total activity of ¹³⁷Cs deposited per unit area over the Spanish peninsular territory was analysed using a 150 × 150 km² mesh grid, with samples taken from 29 points. The deposited activities ranged between 251 and 6074 Bq/m². A linear relationship was obtained between these values and the mean annual rainfall at each sampling point which allowed a map to be drawn, using GIS software, which shows the distribution of total deposited ¹³⁷Cs activity across the Spanish mainland. At twelve of these sampling points the vertical migration profile of ¹³⁷Cs was obtained. These profiles are separated into two groups with different behaviour, one of which includes clay and loam soils and the other containing sandy soils. For both groups of profiles the parameters of the convective-diffusive model, which describes the vertical migration of ¹³⁷Cs in the soil, v (apparent convection velocity) and D (apparent diffusion coefficient) were calculated.     

Radioactivity measurements in moss (Hypnum cupressiforme) and lichen (Cladonia rangiformis) samples collected from Marmara region of Turkey

The present study was conducted to compare the ¹³⁷Cs, ⁴⁰K, ²³²Th, and ²³⁸U activity concentrations in epigeic moss (Hypnum cupressiforme) and lichen (Cladonia rangiformis). The activity levels in 37 moss and 38 lichen samples collected from the Marmara region of Turkey were measured using a gamma spectrometer equipped with a high purity germanium (HPGe) detector. The activity concentrations of ¹³⁷Cs, ⁴⁰K, ²³²Th, and ²³⁸U in the moss samples were found to be in the range of 0.36-8.13, 17.1-181.1, 1.51-6.17, and 0.87-6.70 Bq kg⁻¹ respectively, while these values were below detection limit (BDL)-4.32, 16.6-240.0, 1.32-6.47, and BDL-3.57 Bq kg⁻¹ respectively in lichen. The average moss/lichen activity ratios of ¹³⁷Cs, ⁴⁰K, ²³²Th, and ²³⁸U were found to be 1.32 ± 0.57, 2.79 ± 1.67, 2.11 ± 0.82, and 2.19 ± 1.02, respectively. Very low ¹³⁷Cs concentrations were observed in moss and lichen samples compared to soil samples collected from the same locations in a previous study. Seasonal variations of the measured radionuclide activities were also examined in the three sampling stations.     

Ra and Ra in scale and sludge samples and their correlation with the chemical composition

In order to contribute to a future waste management policy related to the presence of technologically enhanced natural occurring radioactive material (TENORM) in the Brazilian petroleum industry, the present work presents the chemical composition and the ²²⁶Ra and ²²⁸Ra content of sludge and scales generated during the offshore E and P petroleum activities in the Campos Basin, the primary offshore oil production region in Brazil.The ²²⁶Ra and ²²⁸Ra content on 36 sludge and scales samples were determined by gamma-spectrometry. Based on X-ray diffractometry results, a chemical analysis schema for these samples was developed. The results have shown that scales are 75% barium and strontium sulfates, with a mean ²²⁶Ra and ²²⁸Ra content of 106 kBq kg⁻¹ and 78 kBq kg⁻¹, respectively. On the other hand, sludge samples have a much more complex chemical composition than the scales. The ²²⁶Ra and ²²⁸Ra content in sludge also varies much more than the content observed in the scales samples and ranged from 0.36 to 367 kBq kg⁻¹ and 0.25 to 343 kBq kg⁻¹, respectively.     

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.     

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.     

Cesium accumulation by fish following acute input to lakes: a comparison of experimental and Chernobyl-impacted systems

An uptake parameter u (L kg⁻¹ d⁻¹) and a loss rate parameter k (d⁻¹) were estimated for the patterns of accumulation and loss of ¹³³Cs by three fish species following an experimental ¹³³Cs addition into a pond in South Carolina, USA. These u and k parameters were compared to similar estimates for fish from other experimental ponds and from lakes that received ¹³⁷Cs deposition from Chernobyl. Estimates of u from ponds and lakes declined with increasing potassium concentrations in the water column. Although loss rates were greater in the experimental ponds, the times required to reach maximum Cs concentrations in fish were similar between ponds and lakes, because ponds and lakes had similar retentions of Cs in the water column. The maximum Cs concentrations in fish were largely determined by initial Cs concentrations in the water column. These maximum concentrations in fish and the times required to reach these maxima are potentially useful indicators for assessments of risks to humans from fish consumption.     

Time-dependency of the Cs contamination of wild boar from a region in Southern Germany in the years 1998 to 2008

Following the Chernobyl accident, ¹³⁷Cs contamination levels of wild boar in some districts of Southern Germany are still exceeding thousands of Bq kg⁻¹. While the long term ¹³⁷Cs concentration in forest plants, mushrooms, and roe deer meat has decreased significantly, for wild boar it has remained constant during the last decade. Between 1998 and 2008, we analysed the muscle meat of 656 wild boars shot in the district (“Landkreis”) Ravensburg. The ¹³⁷Cs activity concentration showed considerable variability from less than 5 up to 8266 Bq kg⁻¹ and it followed a seasonal pattern, which is attributed to changes in dietary habits, fodder availability, meteorological conditions and specific behaviour of ¹³⁷Cs in wild boar organism. T_ag values for wild boars from the district Ravensburg varied from 0.008 to 0.062 m² kg⁻¹ during 2000–2008.     

Cs in a raised bog in central Sweden

The vertical distribution of ¹³⁷Cs activity in peat soil profiles and ¹³⁷Cs activity concentration in plants of various species was studied in samples collected at two sites on a raised bog in central Sweden. One site (open bog) was in an area with no trees and only a few sparsely growing plant species, while the other (low pine) was less than 100 m from the open bog site and had slowly growing Scots pine, a field layer dominated by some ericaceous plants and ground well-covered by plants. The plant samples were collected in 2004–2007 and were compared with samples collected in 1989 from the same open bog and low pine sites. Ground deposition of ¹³⁷Cs in 2005 was similar at both sites, 23?000 Bq m⁻². In the open bog peat profile it seems to be an upward transport of caesium since a clear peak of ¹³⁷Cs activity was found in the uppermost 1–4 cm of Sphagnum layers, whereas at the low pine site ¹³⁷Cs was mainly found in deeper (10–12 cm) layers. The migration rate was 0.57 cm yr⁻¹ at the open bog site and the migration centre of ¹³⁷Cs was at a depth of 10.7, while the rate at the low pine site was 0.78 cm yr⁻¹ and the migration centre was at 14.9 cm. Heather (Calluna vulgaris) was the plant species with the highest ¹³⁷Cs activity concentrations at both sites, 43.5 k Bq⁻¹ DM in 1989 decreasing to 20.4 in 2004–2007 on open bog and 22.3 k Bq kg⁻¹ DM in 1989 decreasing to 11.2 k Bq⁻¹ DM by the period 2004–2007 on the low pine site. ¹³⁷Cs transfer factors in plants varied between 0.88 and 1.35 on the open bog and between 0.48 and 0.69 m² kg⁻¹ DM at the low pine site.     

Analytical results and effective dose estimation of the operational Environmental Monitoring Program for the radioactive waste repository in Abadia de Goiás from 1998 to 2008

This paper presents the results of the Environmental Monitoring Program for the Radioactive waste repository of Abadia de Goiás, which was originated from the accident of Goiania, conducted by the Regional Center of Nuclear Sciences (CRCN-CO) of the National Commission on Nuclear Energy (CNEN), from 1998 to 2008.The results are related to the determination of ¹³⁷Cs activity per unit of mass or volume of samples from surface water, ground water, depth sediments of the river, soil and vegetation, and also the air-kerma rate estimation for gamma exposure in the monitored site.In the phase of operational Environmental Monitoring Program, the values of the geometric mean and standard deviation obtained for ¹³⁷Cs activity per unit of mass or volume in the analyzed samples were (0.08 ± 1.16) Bq.L⁻¹ for surface and underground water, (0.22 ± 2.79) Bq.kg⁻¹ for soil, and (0.19 ± 2.72) Bq.kg⁻¹ for sediment, and (0.19 ± 2.30) Bq.kg⁻¹ for vegetation. These results were similar to the values of the pre-operational Environmental Monitoring Program.With these data, estimations for effective dose were evaluated for public individuals in the neighborhood of the waste repository, considering the main possible way of exposure of this population group.The annual effective dose obtained from the analysis of these results were lower than 0.3 mSv.y⁻¹, which is the limit established by CNEN for environmental impact in the public individuals indicating that the facility is operating safely, without any radiological impact to the surrounding environment.     

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.     

Recent changes in Red Lake (Romania) sedimentation rate determined from depth profiles of Pb and Cs radioisotopes

This work presents a first estimation of the sedimentation rate for the Red Lake (Romania). The sediment accumulation rates were determined by two well-known methods for recent sediment dating: ²¹⁰Pb and ¹³⁷Cs methods. Both techniques implied used the gamma emission of the above-mentioned radionuclides. The ²¹⁰Pb and ¹³⁷Cs concentrations in the sediment were measured using a gamma spectrometer with a HpGe detector, Gamma-X type. Activities ranging from 41 ± 7 to 135 ± 34 Bq/kg were found for ²¹⁰Pb and from 3 ± 0.5 to 1054 ± 150 Bq/kg for ¹³⁷Cs. The sediment profile indicates acceleration in sedimentation rate in the last 18 years. Thus, the sedimentation process for the Red Lake can be divided in two periods, the last 18 years, and respectively, the period before that. Using the Constant Rate of ²¹⁰Pb Supply method values between 0.18 ± 0.04 and 1.85 ± 0.5 g/cm² year (0.32 ± 0.08 and 2.83 ± 0.7 cm/year) were obtained. Considering both periods, an average sedimentation rate of 0.87 ± 0.17 g/cm² year (1.17 cm/year) was calculated. Considering an average depth of 5.41 m for the lake and the sedimentation rate estimated for the last 18 years, it could be estimated that the lake will disappear in 195 years.     

Foliar uptake of Cs from the water column by aquatic macrophytes

A transplant experiment was performed to determine the relative importances of root uptake from the sediments and foliar uptake from the water column in determining the accumulation of ¹³⁷Cs by aquatic macrophytes. Uncontaminated individuals of three species, Brasenia schreberi, Nymphaea odorata and Nymphoides cordata, were transplanted into pots containing either contaminated sediments (i.e. 1.2 Bq ¹³⁷Cs g⁻¹ dry mass) or uncontaminated sediments (i.e. < 0.1 Bq g⁻¹ dry mass) and immersed in Pond B, a former reactor cooling pond where ¹³⁷Cs concentrations in surface waters range from 0.4 to 0.8 Bq liter⁻¹. The plants in uncontaminated sediments rapidly accumulated ¹³⁷Cs from the water column and after 35 days of immersion had ¹³⁷Cs concentrations in leaves that were: (1) not statistically significantly different from those for plants in contaminated sediments; and (2) similar to those for the same species growing naturally in Pond B. The similarity in ¹³⁷Cs concentrations between naturally-occurring plants and those in pots with uncontaminated sediments suggests that foliar uptake from the water column is the principal mode of Cs accumulation by these species in Pond B.     

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.     

Bioaccumulation of 137Cs in pelagic food webs in the Norwegian and Barents Seas

Knowledge and documentation of the levels of radioactive contamination in fish stocks important to Norwegian fisheries is of major importance to Norwegian consumers and fish export industry. In the present study, the bioaccumulation of caesium-137 ((137)Cs) has been investigated in marine food webs in the Barents and Norwegian Seas. The contents of (137)Cs in the different organisms were generally low (<1 Bq kg(-1) wet weight), but a marked bioaccumulation was apparent: The concentration of (137)Cs was about 10-fold higher in the harbour porpoise Phocoena phocoena, representing the upper level of the food web, than in the amphipod Themisto sp., representing the lower level of the food web. The Concentration Factors (CF=Bq kg(-1) wet weight/Bq l(-1) seawater) increased from 10+/-3 for a mixed sample of krill and amphipods to 165+/-5 for harbour porpoises.