Changes in 137Cs concentrations in soil and vegetation on the floodplain of the Savannah River over a 30 year period

(137)Cs released during 1954-1974 from nuclear production reactors on the Savannah River Site, a US Department of Energy nuclear materials production site in South Carolina, contaminated a portion of the Savannah River floodplain known as Creek Plantation. (137)Cs activity concentrations have been measured in Creek Plantation since 1974 making it possible to calculate effective half-lives for (137)Cs in soil and vegetation and assess the spatial distribution of contaminants on the floodplain. Activity concentrations in soil and vegetation were higher near the center of the floodplain than near the edges as a result of frequent inundation coupled with the presence of low areas that trapped contaminated sediments. (137)Cs activity was highest near the soil surface, but depth related differences diminished with time as a likely result of downward diffusion or leaching. Activity concentrations in vegetation were significantly related to concentrations in soil. The plant to soil concentration ratio (dry weight) averaged 0.49 and exhibited a slight but significant tendency to decrease with time. The effective half-lives for (137)Cs in shallow (0-7.6 cm) soil and in vegetation were 14.9 (95% CI=12.5-17.3) years and 11.6 (95% CI=9.1-14.1) years, respectively, and rates of (137)Cs removal from shallow soil and vegetation did not differ significantly among sampling locations. Potential health risks on the Creek Plantation floodplain have declined more rapidly than expected on the basis of radioactive decay alone because of the relatively short effective half-life of (137)Cs.     

Ecological half-life of 137Cs in plants associated with a contaminated stream

Ecological half-life (Te) is a useful measure for studying the long-term decline of contaminants, such as radionuclides, in natural systems. The current investigation determined levels of radiocesium (137Cs) in two aquatic (Polygonum punctatum, Sagittaria latifolia) and three terrestrial (Alnus serrulata, Myrica cerifera, Salix nigra) plant species from a contaminated stream and floodplain on the U.S. Department of Energy's Savannah River Site. Current 137Cs levels in plants were used in conjunction with historical data to determine Te of 137Cs in each species. Median concentrations of 137Cs were highest in S. latifolia (0.84 Bq g(-1)) and lowest in M. cerifera (0.10 Bq g(-1)). Te's ranged from 4.85 yr in M. cerifera to 8.35 yr in S. nigra, both terrestrial species. Te's for all aquatic (6.30 yr) and all terrestrial (5.87) species combined were very similar. The Te's of the two aquatic primary producers (P. punctatum and S. latifolia) in the Steel Creek ecosystem were somewhat longer than Te values previously reported for some consumers from this ecosystem.     

The influence of a whole-lake addition of stable cesium on the remobilization of aged 137Cs in a contaminated reservoir

To document the short-term dynamics of Cs, 4 kg of (133)Cs were introduced into an 11.4-ha, 157 000 m(3) reservoir previously contaminated with (137)Cs from past reactor operations at the US Department of Energy's Savannah River Site near Aiken, South Carolina, USA. The (133)Cs addition resulted in an increase of 6.1 MBq of (137)Cs (1.9 mug (137)Cs) in the water column over the following 260 days. Possible sources for the increased (137)Cs included (1) release from the sediments, (2) release from the approximately 26 000 kg of aquatic macrophytes that occupied 80% of the reservoir, and (3) wash-in from the pond's watershed. Data are presented to indicate that release from the sediments was the principal source of the (137)Cs increase. The fraction of (137)Cs released from the sediments (0.7%) is consistent with laboratory measurements of (137)Cs desorption from neighboring ponds on the Savannah River Site.     

Distribution of 137Cs in soil along Ta-han River Valley in Tau-Yuan County in Taiwan

Environmental 137Cs contamination was suspected from accidents at spent fuel storage pits of a research reactor site in the Ta-han River valley in Taiwan. In order to further characterize this contamination, soil samples were collected and measured by a gamma-spectroscopy system in 1999. It was found that 137Cs contamination is distributed up to 4 km from the reactor in an area covered mostly by rice and plant fields. 137Cs concentration in the topsoil ranged up to about 1000 Bq kg-1, as compared with soil beyond the contaminated area, which does not exceed 15 Bq kg-1. Spatial distribution of 137Cs was characterized by strong non-uniformity, which complicated our understanding of the distribution pathway of the radionuclides. The highest concentrations of 137Cs, up to more than 1000 Bq kg-1, were found within a few rice fields. The relative location of these rice fields and the water supplies from local streams suggested that the 137Cs was distributed along water pathways in the valley.     

The current content of artificial radionuclides in the water of the Tobol-Irtysh river system (from the mouth of the Iset River to the confluence with the Ob River)

Data on content of (90)Sr, (137)Cs, (239,240)Pu and (3)H in water of the Tobol-Irtysh part of the Techa-Iset-Tobol-Irtysh-Ob river system (through which the "Mayak" PA radioactive wastes are transported) are presented and discussed. The data were received in 2004-2005 under the ISTC project on radioecological monitoring of the Tobol and Irtysh rivers. Monthly observations of (137)Cs, (90)Sr and (3)H content in water in the area of the Tobol and Irtysh confluence have been conducted starting from May 2004. To obtain information on the investigated river system as a whole, the radioecological survey of the Tobol and Irtysh rivers at the section from the mouth of the Iset River to the confluence with the Ob River was carried out in 2004. It is shown that the impact of "Mayak" PA waste transport by (90)Sr is distinctly traced as far as the area of the Irtysh and Ob confluence.     

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.     

Land use influence on 137Cs levels in perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.)

The environmental influence on Chernobyl-derived 137Cs levels in perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.) was revealed using partial least-squares regression (PLS). The 53 environmental predictors used describe land use in catchment areas, various catchment area and lake characteristics, lake water chemistry, and fish stock composition. The study showed a profound effect of land use on the 137Cs levels in fish. Radiocaesium deposited on arable land was retained in the soil to a greater extent than was 137Cs deposited on wetlands, which more easily leached out to the lake ecosystems. The 137Cs deposition close to the lakes had a more pronounced effect on 137Cs levels in the fish than did more distant deposition. The radiocaesium bioavailability is mainly governed by lake water cation content, as hardwater lakes had significantly lower 137Cs content in fish. Resuspension of 137Cs contaminated sediments only had a limited influence on the observed levels in fish.     

Numerical simulation of 137Cs and (239,240)Pu concentrations by an ocean general circulation model

We simulated the spatial distributions and the temporal variations of 137Cs and (239,240)Pu concentrations in the ocean by using the ocean general circulation model which was developed by National Center of Atmospheric Research. These nuclides are introduced into seawaters from global fallout due to atmospheric nuclear weapons tests. The distribution of radioactive deposition on the world ocean is estimated from global precipitation data and observed values of annual deposition of radionuclides at the Meteorological Research Institute in Japan and several observed points in New Zealand. Radionuclides from global fallout have been transported by advection, diffusion and scavenging, and this concentration reduces by radioactive decay in the ocean. We verified the results of the model calculations by comparing simulated values of 137Cs and (239,240)Pu in seawater with the observed values included in the Historical Artificial Radionuclides in the HAM database, which has been constructed by the Meteorological Research Institute. The vertical distributions of the calculated 137Cs concentrations were in good agreement and are in good agreement with the observed profiles in the 1960s up to 250 m, in the 1970s up to 500 m, in the 1980s up to 750 m and in the 1990s up to 750 m. However, the calculated 137Cs concentrations were underestimated compared with the observed 137Cs at the deeper layer. This may suggest other transport processes of 137Cs to deep waters. The horizontal distributions of 137Cs concentrations in surface water could be simulated. A numerical tracer release experiment was performed to explain the horizontal distribution pattern. A maximum (239,240)Pu concentration layer occurs at an intermediate depth for both observed and calculated values, which is formed by particle scavenging. The horizontal distributions of the calculated (239,240)Pu concentrations in surface water could be simulated by considering the scavenging effect.     

AFCF and clinoptilolite use in reduction of (137)Cs deposition in several days' contaminated broiler chicks

The objective of this study was to investigate the binding efficiency of AFCF and clinoptilolite, mixed to the feed and administered orally using gastric tube to chronically (137)Cs alimentary contaminated broiler chicks. Seventy-five male Hybro broiler chicks, between 35 and 47 days of age were divided into five groups (15 birds per group) reared in cages (five birds in a cage) and fed a standard diet. Every day during 13 days of the experimental period all chicks received orally 1 ml CsCl water solution with activity of 1310 Bq ml(-1)(137)Cs (gastric tube). Group 1 was the control group and received no binders. The experimental groups received the binders. Group 2 received 0.2 g of AFCF in the form of water solution (gastric tube); group 3 received 0.2% AFCF in the feed; group 4 received 2g clinoptilolite in the form of water suspension (gastric tube) and group 5 received 2% clinoptilolite in the feed. Five chicks from each group were sacrificed on days 4, 10 and 13 of the experimental period. Using gamma spectrometric methods specific activity of (137)Cs was determined in the samples of breast meat, liver and gizzard. The results obtained showed that administering binders to the chronically contaminated broiler chicks significantly (p<0.01) reduced (137)Cs transfer and deposition in breast meat, liver and gizzard. Decreasing deposition of (137)Cs in breast meat and internal organs increased with time of contamination and binders' administration. With AFCF as a cesium binder, on day 13 of measuring the (137)Cs activity in breast meat was 80-83% lower than that in the control group, 89% in liver and 83-84% in gizzard. Natural clinoptilolite demonstrated lower binding efficiency. On day 13 of measuring the (137)Cs activity in breast meat was 53-69% lower than that in the control group, 67-60% in liver and 59-71% in gizzard.     

Evaluation of 137Cs fallout from the Chernobyl accident in a forest soil and its impact on Alpine Lake sediments, Mercantour Massif, S.E. France

The Boréon area in the Mercantour Massif, S.E. France, was contaminated by radionuclides after the Chernobyl accident in the first days of May 1986. Sediments from a small mountain lake in this area were collected, as well as forest soils in its vicinity, in order to obtain 137Cs and 210Pb profiles. Calculated from the 210Pb inventory in a soil of a horizontal area, the flux is high in the area (0.06 Bqcm(-2)y(-1)) probably because of the great frequency of rain and uranium ores outcropping in the massif. The comparison of the 137Cs soil inventories and the unsupported 210Pb suggests that the 137Cs fallout due to the Chernobyl accident in the study site (Boréon) was at least 3.5 Bqcm(-2), more probably the double. The recent lake sediments still undergo a rather strong contamination by 137Cs and the sediment profiles show that the residence time of 137Cs in the catchment area is long. The study area is frequented by many inhabitants of the city of Nice and other cities at the Mediterranean coast during week-end and during summer and winter holidays. Thus the 137Cs external exposure impact was evaluated at 2 mSvy(-1) for 2002 in the most contaminated point.     

Current contamination by 137Cs and 90Sr of the inhabited part of the Techa river basin in the Urals

Previous discharges of radioactivity from the Mayak Production Association plant in the Urals have resulted in considerable radionuclide contamination of the Techa River, and consequent high radiation doses during the late 1940s and 1950s to residents of villages along the Techa river. The most contaminated villages close to the site were evacuated in the period 1954-1962. The objective of this recent study was to conduct a preliminary assessment of the current radioactive contamination of soil, vegetation and foodstuffs in the two remaining villages closest to the Mayak site, Muslyumovo and Brodokalmak. The highest contamination levels in soil were found in the floodplain at 5.5 MBq m(-2) for 137Cs and 1.0 MBq m(-2) for 90Sr. Radionuclide contamination in soil of the villages was much lower, but exceeded that expected from global fallout. Data from 1207 measurements of 137Cs in milk and 1180 for 90Sr in milk for the period 1992-1999 were collated. There was no change with time in the 90Sr or 137Cs activity concentration in milk over the measured period. There were significantly higher 137Cs activity concentrations in milk sampled during the housed winter period in Muslyumovo compared with the grazing summer period, but compared to that for Brodokalmak or for either settlement for 90Sr. The highest measured activity concentrations in food products of 137Cs and 90Sr were found in river fish, waterfowl, poultry and milk. The measured activity concentrations of 137Cs and 90Sr in some animal products were higher than that expected from soil and vegetation from fields and pasture in the villages (not including the floodplain) confirming that the highly contaminated floodplains are contributing to contamination of some animal products.     

Screening plant species native to Taiwan for remediation of 137Cs-contaminated soil and the effects of K addition and soil amendment on the transfer of 137Cs from soil to plants

This study aims to screen plant species native to Taiwan that could be used to eliminate (137)Cs radionuclides from contaminated soil. Four kinds of vegetables and two kinds of plants known as green manures were used for the screening. The test plants were cultivated in (137)Cs-contaminated soil and amended soil which is a mixture of the contaminated one with a horticultural soil. The plant with the highest (137)Cs transfer factor was used for further examination on the effects of K addition on the transfer of (137)Cs from the soils to the plant. Experimental results revealed that plants cultivated in the amended soil produced more biomass than those in the contaminated soil. Rape exhibited the highest production of aboveground parts, and had the highest (137)Cs transfer factor among all the tested plants. The transfer of (137)Cs to the rape grown in the soil to which 100 ppm KCl commonly used in local fertilizers had been added, were restrained. Results of this study indicated that rape, a popular green manure in Taiwan, could remedy (137)Cs-contaminated soil.     

Discharge of 137Cs and 90Sr by Finnish rivers to the Baltic Sea in 1986-1996

The total amounts of 137Cs and 90Sr transported from Finland by rivers into the Gulf of Finland, Gulf of Bothnia and Archipelago Sea since 1986 were estimated. The estimates were based on long-term monitoring of 137Cs and 90Sr in river and other surface waters and on the statistics of water discharges from Finnish rivers to the above sub-areas of the Baltic Sea. The total amounts of 137Cs and 90Sr removed from Finland into the Baltic Sea during 1986-1996 were estimated to be 65 and 10 TBq, respectively. The results show that, although the deposition of 137Cs was much higher than that of 90Sr after the Chernobyl accident, the amount of 137Cs removed from Finland is only six times as high as that of 90Sr. This emphasizes the importance of 90Sr while considering radiation doses from surface waters and 137Cs while estimating doses via pathways from catchment soil, lake sediments and biota after a fallout situation.     

Assessment of state-of-the-art models for predicting the remobilisation of radionuclides following the flooding of heavily contaminated areas: the case of Pripyat River floodplain

The performances of models are assessed to predict the wash-off of radionuclides from contaminated flooded areas. This process should be accounted for in the proper management of the aftermath of a nuclear accident. The contamination of the Pripyat River water following the inundation of a floodplain heavily contaminated by (90)Sr and (137)Cs of Chernobyl origin is used as the basis for modelling. The available experimental evidence demonstrated that remobilisation of radiostrontium is an important process implying a significant secondary radioactive load of water flowing over the contaminated floodplain. On the contrary, there is no empirical evidence of a similar behaviour for radiocaesium. In general, state-of-the-art models properly predicted the remobilisation of strontium, whereas they significantly overestimated radiocaesium concentrations in water. The necessary model improvements for a more accurate prediction of radiocaesium contamination levels include a reassessment of the values of the model parameters controlling the remobilisation process.     

Radiocesium in North San Francisco Bay and Baja California coastal surface waters

Radiocesium, 137Cs, and rare earth elements (REEs) were determined in suspended material and dissolved fractions of waters across the salinity gradient in North San Francisco Bay (estuary). We describe the variation of this conservative isotope tracer with salinity and sediment load. REE data are used to differentiate marine and terrigenous source terrains for suspended material and dissolved fractions. We estimate that about 1-4 x 10(10) Bq of 137Cs migrates annually on suspended material through the North Bay. In addition, 137Cs concentrations were measured in surface waters off Baja California. Combined in situ water density (sigma(t)) and 137Cs data distinguish between California Current and Gulf of California water, and delineate areas of upwelling, where nutrient-rich, deep Pacific Intermediate water, with little or no 137Cs, is brought to the surface off promontories along Baja California.     

Radionuclide tracing of water masses and processes in the water column and sediment in the Algerian Basin

Caesium-137 and (239,240)PU were analysed in the water column along the Algerian coast. The (137)Cs activity concentration in surface water increased from the west to the east from 1.6 to 3.3 mBq L(-1), documenting a presence of Modified Atlantic Water (MAW) in the region. Higher concentrations observed in deep waters may be due to an intrusion of Levantine Intermediate Water (LIW), which has been carrying higher levels of (137)Cs from Chernobyl accident. The (239,240)Pu sub-surface concentration peaked at about 250 m water depth as a result of biogeochemical processes in the water column. The observed (239,240)Pu/(137)Cs activity ratio at the surface (0.003) was significantly lower than that in global fallout (0.04). This decrease exceeds that expected from radioactive decay of (137)Cs, and confirms that Pu due to its adsorption on sinking particles is more effectively removed from surface layers than is (137)Cs. An increase of the (239,240)Pu/(137)Cs activity ratio with depth suggests that (239,240)Pu, similarly as (137)Cs, should be also transported by advection to maintain the observed ratios in deep waters. An intrusion of LIW may enhance therefore both the (137)Cs and (239,240)Pu concentrations in deep waters. The average (238)Pu/(239+240)Pu activity ratio in seawater was 0.03+/-0.02, confirming a global fallout origin of Pu in the Algerian Basin. Caesium-137 and (239,240)Pu inventories in the water column were estimated to be from 2.7+/-0.5 kBq m(-2) to 3.8+/-0.7 kBq m(-2), and from 13.8+/-2.6 Bq m(-2) to 41+/-7B qm(-2), respectively. The (137)Cs massic activities in surface sediment were almost constant, the average activity was 9.0+/-0.8 Bq kg(-1). Sedimentation rates obtained using the (210)Pb method were from 0.1 to 0.7 cm y(-1), and resulting penetration depths of (137)Cs in the sediment cores were from 15 to over 40 cm. The (137)Cs peaks found in the sediment cores were associated with the Chernobyl accident (1986) and global fallout (1964). The (137)Cs inventories in the sediment were increasing from the west (180 Bq m(-2)) to the east (350 Bq m(-2)).     

137Cs and 40K in the terrestrial vegetation of the Yenisey Estuary: landscape, soil and plant relationships

Plant species, forming important components of Arctic food chains and of interest from a monitoring perspective, were studied at 36 plots representing flood plain and terrace landscapes of the Yenisey River and Estuary from its upper delta to the gulf. (137)Cs contamination densities at the plots varied from 0.35kBq/m(2) (central delta, sandy riverside plot) to 88kBq/m(2) (the upper delta plot) indicating both global and regional sources of anthropogenic pollution. Cs-137 levels in plants were within the range expected from global fallout inputs and varied from 31 to 140Bq/kg d.w. increasing in dominant groups in the order: grasses相似文献   

Frequency distributions of 137Cs in fish and mammal populations

We collected fish and mammals in several radioactively contaminated locations in the Chornobyl Exclusion Zone and analyzed them for 137Cs content. Frequency distributions were built for populations of channel catfish, yellow-necked mice and bank voles. We combined our data with similar data from several other studies to demonstrate the relationship between the standard deviations and means of 137Cs of fish and mammal populations. The frequency distributions of 137Cs in populations of fish and mammals are not normal, as indicated by the strong relationship between standard deviation and mean. Distributions for mammals are more skewed than those for fish. Fish and mammals probably use their environments in fundamentally different ways. The highest concentrations and thus greatest risks are therefore confined to relatively few individuals in each population.     

Geochronology of Pb and Hg pollution in a coastal marine environment using global fallout 137Cs

Global fallout 137Cs was used for dating sediment cores and estimation of recent sedimentation rates (up to 1 cm/y) in the Thane Creek, which lies in the southern part of the Deccan belt of India. The residence time of 210Pb in the Thane Creek water was calculated to be 0.7 years. Further, the concentrations of Pb (up to 70 microg/g) and Hg (up to 10 microg/g) in sediment profiles were measured to assess the anthropogenic input of contaminants due to large-scale industrialization, which has taken place in this area over the last two decades. The depth-wise concentration profile of Hg shows positive evidence of continued fresh input into the Creek.     

Estimation of radiation doses from (137)Cs to frogs in a wetland ecosystem

Currently, there is no established methodology to estimate radiation doses to non-human biota. Therefore, in this study, various dose models were used to estimate radiation doses to moor frogs (Rana arvalis) in a wetland ecosystem contaminated with (137)Cs. External dose estimations were based on activity concentrations of (137)Cs in soil and water, considering changes in habitat over a life-cycle. Internal doses were calculated from the activity concentrations of (137)Cs measured in moor frogs. Depending on the dose model used, the results varied substantially. External dose rates ranged from 21 to 160 mGy/y, and internal dose rates varied between 1 and 14 mGy/y. Maximum total dose rates to frogs were below the expected safe level for terrestrial populations, but close to the suggested critical dose rate for amphibians. The results show that realistic assumptions in dose models are particularly important at high levels of contamination.