Simulation of 137Cs Migration over the Soil–Plant System of Peat Soils Contaminated after the Chernobyl Accident

A mathematical model was constructed to simulate the processes of ¹³⁷Cs migration in peat soils and its uptake by vegetation. Model parameters were assessed and the pattern of ¹³⁷Cs distribution over soil profile was predicted in case of peat soils, which are typical of the Russian regions contaminated after the Chernobyl accident. The ecological half-life of ¹³⁷Cs in the plant-root soil zone was calculated, and a long-term prognosis of the radionuclide uptake by plants was made.     

The Role of Floodplain Soils as a Barrier to Radionuclide Migration: An Example of the Techa–Iset' River System

The contents of ⁹⁰Sr and ¹³⁷Cs and the pattern of their redistribution in the soil and plant cover of floodplain ecosystems have been assessed. It is shown that the radionuclide distribution across the floodplain and along the river flow is determined by the formation of a barrier to their migration near the river channel, at which less mobile ¹³⁷Cs accumulates. The soil and plant cover of the central floodplain are enriched with ⁹⁰Sr. Differences in radionuclide migration in floodplain soils and their input into plants are determined by the relationship between the processes of their immobilization and migration with soil water.     

Uptake and loss of 134Cs and 60Co by the Baltic bivalve Macoma baltica in a laboratory microcosmos

Accumulation and clearance of ¹³⁴Cs and ⁶⁰Co by the Baltic bivalve Macoma baltica were experimentally investigated in a laboratory microcosmos. The nuclides were added to the water and the activities in bivalve flesh, shell, feces and sediment were determined at regular intervals. The uptake was quite rapid, 40% (Cs) and 55% (Co) of the final steady state values being attained after 24 h. The subsequent releases were also rapid, 50% (Cs) and 40% (Co), of the accumulated activity being lost within 6 days. The experiments demonstrated that the major intake route following short-term releases of activity will be from the water column and that the close relationship between activity in water and organism can thus be used for predictive purposes without the complication of radionuclide uptake from contaminated sediments. However, for longer periods, the subsequent intake of sediments will generate a significant exposure pathway for this deposit-feeding bivalve.     

Uptake and loss of Cs and Co by the Baltic bivalve Macoma baltica in a laboratory microcosmos

Accumulation and clearance of ¹³⁴Cs and ⁶⁰Co by the Baltic bivalve Macoma baltica were experimentally investigated in a laboratory microcosmos. The nuclides were added to the water and the activities in bivalve flesh, shell, feces and sediment were determined at regular intervals. The uptake was quite rapid, 40% (Cs) and 55% (Co) of the final steady state values being attained after 24 h. The subsequent releases were also rapid, 50% (Cs) and 40% (Co), of the accumulated activity being lost within 6 days. The experiments demonstrated that the major intake route following short-term releases of activity will be from the water column and that the close relationship between activity in water and organism can thus be used for predictive purposes without the complication of radionuclide uptake from contaminated sediments. However, for longer periods, the subsequent intake of sediments will generate a significant exposure pathway for this deposit-feeding bivalve.     

Review of Russian-language studies on radionuclide behaviour in agricultural animals: part 4. Transfer to poultry

Data on radionuclide transfer to domestic chickens and ducks obtained from research performed in the former Soviet Union were reviewed to provide transfer coefficient values (Ff) to poultry and edible egg contents. The majority of the data are from experiments with ⁹⁰Sr and ¹³⁷Cs, reflecting the importance of these radionuclides after global fallout and major radiation accidents. Data for ³H, ⁵⁴Mn, ⁵⁹Fe, ⁶⁰Co, ²²Na ⁶⁵Zn, ¹³¹I and U are also given. The values derived have been compared with those in the current IAEA Handbook of parameter values for the prediction of radionuclide transfer in temperate environments (TRS 364) and the recent revision which incorporates the values from this paper. The Russian-language data give improved estimates for many radionuclides and the revised handbook is now based on the better quality data given for chronic administration.     

A study of radium bioaccumulation in freshwater mussels, Velesunio angasi, in the Magela Creek catchment, Northern Territory, Australia

Freshwater mussels, Velesunio angasi, along Magela Creek in Australia’s Northern Territory were examined to study radionuclide activities in mussel flesh and to investigate whether the Ranger Uranium mine is contributing to the radium loads in mussels downstream of the mine. Radium loads in mussels of the same age were highest in Bowerbird Billabong, located 20 km upstream of the mine site. Variations in the ratio of [Ra]:[Ca] in filtered water at the sampling sites accounted for the variations found in mussel radium loads with natural increases in calcium (Ca) in surface waters in a downstream gradient along the Magela Creek catchment gradually reducing radium uptake in mussels. At Mudginberri Billabong, 12 km downstream of the mine, concentration factors for radium have not significantly changed over the past 25 years since the mine commenced operations and this, coupled with a gradual decrease of the ²²⁸Ra/²²⁶Ra activity ratios observed along the catchment, indicates that the ²²⁶Ra accumulated in mussels is of natural rather than mine origin. The ²²⁸Th/²²⁸Ra ratio has been used to model radium uptake and a radium biological half-life in mussels of approximately 13 years has been determined. The long biological half-life and the low Ca concentrations in the water account for the high radium concentration factor of 30,000-60,000 measured in mussels from the Magela Creek catchment.     

Factors affecting 210Po and 210Pb activity concentrations in mussels and implications for environmental bio-monitoring programmes

The activity of ²¹⁰Po and ²¹⁰Pb was determined in mussels of the same size (3.5-4.0 cm shell length) sampled monthly over a 17-month period at the Atlantic coast of Portugal. Average radionuclide concentration values in mussels were 759 ± 277 Bq kg⁻¹ for ²¹⁰Po (range 460-1470 Bq kg⁻¹ dry weight), and 45 ± 19 Bq kg⁻¹ for ²¹⁰Pb (range 23-96 Bq kg⁻¹ dry weight). Environmental parameters and mussel biometric parameters were monitored during the same period. Although there was no seasonal variation of radionuclide concentrations in sea water during the study period, the concentration of radionuclide activity in mussels varied seasonally displaying peaks of high concentrations in winter and low concentrations in summer. Analysis of radionuclide data in relation to the physiological Condition Index of mussels revealed that ²¹⁰Po and ²¹⁰Pb activities in the mussel (average activity per individual) remained nearly constant during the investigation period, while mussel body weight fluctuated due to fat storage/expenditure in the soft tissues. Similar variation of radionuclide concentrations was observed in mussels transplanted from the sea coast into the Tejo Estuary. However, under estuarine environmental conditions and with higher food availability throughout the year, transplanted mussel Condition Index was higher than in coastal mussels and average radionuclide concentrations were 210 ± 75 Bq kg⁻¹ (dry weight) for ²¹⁰Po and 10 ± 4 Bq kg⁻¹ (dry weight) for ²¹⁰Pb, therefore lower than in coastal mussels with similar shell length. It is concluded that the apparent seasonal fluctuation and inter-site difference of radionuclide concentrations were mostly caused by mussel body weight fluctuation and not by radionuclide body burden fluctuation. This interpretation can be extended to the apparent seasonal fluctuation in concentrations of lipophilic and lipophobic contaminants in mussels, and provides an explanation for occasional high concentrations of ²¹⁰Po and man-made contaminants measured in mussels far from pollution sources.     

Assessing the fate of radioactive nickel in cultivated soil cores

Parameters regarding fate of ⁶³Ni in the soil–plant system (soil: solution distribution coefficient, K_d and soil plant concentration ratio, CR) are mostly determined in controlled pot experiments or from simple models involving a limited set of soil parameters. However, as migration of pollutants in soil is strongly linked to the water migration, variation of soil structure in the field and seasonal variation of evapotranspiration will affect these two parameters. The aim of this work was to explore to what extent the downward transfer of ⁶³Ni and its uptake by plants from surface-contaminated undisturbed soil cores under cultivation can be explained by isotopic dilution of this radionuclide in the pool of stable Ni of soils. Undisturbed soil cores (50 cm × 50 cm) were sampled from a brown rendzina (Rendzic Leptosol), a colluvial brown soil (Fluvic Cambisol) and an acidic brown soil (Dystric Cambisol) using PVC lysimeter tubes (three lysimeters sampled per soil type). Each core was equipped with a leachate collector. Cores were placed in a greenhouse and maize (DEA, Pioneer^®) was sown. After 44 days, an irrigation was simulated at the core surfaces to supply 10 000 Bq ⁶³NiCl₂. Maize was harvested 135 days after ⁶³Ni input and radioactivity determined in both vegetal and water samples. Effective uptake of ⁶³Ni by maize was calculated for leaves and kernels. Water drainage and leaching of ⁶³Ni were monitored over the course of the experiment. Values of K_d in surface soil samples were calculated from measured parameters of isotopic exchange kinetics. Results confirmed that ⁶³Ni was strongly retained at the soil surface. Prediction of the ⁶³Ni downward transfer could not be reliably assessed using the K_d values, since the soil structure, which controls local water fluxes, also affected both water and Ni transport. In terms of ⁶³Ni plant uptake, the effective uptake in undisturbed soil cores is controlled by isotope dilution as previously shown at the pot experiment scale.     

The influence of hot particle contamination on Sr and Cs transfers to milk and on time-integrated ingestion doses

Most models for transfers of radionuclides through the food chain typically assume that the radioactivity is initially deposited in chemically available forms. It is known, however, that releases of radionuclides in the form of hot particles may significantly influence their environmental transfers and uptake to the food chain. This study presents models for time changes in ⁹⁰Sr and ¹³⁷Cs in milk which incorporate hot particle contamination using observed rates of hot particle dissolution following the Chernobyl accident. A general equation is presented for the influence of hot particles on overall ingestion doses. As expected from previous work, fallout of hot particles significantly influences time changes in radionuclide activity concentrations in foodstuffs. It is also shown that incorporation of radionuclides in hot particles influences time-integrated ingestion doses. For a situation in which a large proportion (90–100%) of fallout is in slowly dissolving hot particles, time-integrated ingestion doses from ⁹⁰Sr and ¹³⁷Cs are reduced by a factor of approximately two compared to the case where all radioactivity is deposited in bioavailable forms. However, the influence of rapidly dissolving hot particles on time-integrated ingestion doses is relatively minor. Remaining significant uncertainties in dose estimates are discussed.     

Deposition of artificial radionuclides from atmospheric Nuclear Weapon Tests estimated by soil inventories in French areas low-impacted by Chernobyl

Soil inventories of anthropogenic radionuclides were investigated in altitudinal transects in 2 French regions, Savoie and Montagne Noire. Rain was negligible in these 2 areas the days after the Chernobyl accident. Thus anthropogenic radionuclides are coming hypothetically only from Global Fallout following Atmospheric Nuclear Weapon Tests. This is confirmed by the isotopic signatures (²³⁸Pu/^239+240Pu; ¹³⁷Cs/^239+240Pu; and ²⁴¹Am/^239+240Pu) close to Global Fallout value. In Savoie, a peat core age-dated by ²¹⁰Pb_ex confirmed that the main part of deposition of anthropogenic radionuclides occurred during the late sixties and the early seventies. In agreement with previous studies, the anthropogenic radionuclide inventories are well correlated with the annual precipitations. However, this is the first time that a study investigates such a large panel of annual precipitation and therefore of anthropogenic radionuclide deposition. It seems that at high-altitude sites, deposition of artificial radionuclides was higher possibly due to orographic precipitations.     

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.     

Effect of cooking on radionuclide concentrations in waterfowl tissues

Twenty-four commercially raised mallard ducks (Anas platyrhynchos) were released at reactor radioactive leaching ponds in southeastern Idaho and subsequently collected 56 to 188 days later. Liver, gizzard and carcass were analyzed for radionuclide concentrations before and after cooking. Significant decreases (P < 0·05) in ¹³⁷Cs, ¹³⁴Cs, ⁶⁰Co and ^110mAg concentrations in carcass and liver samples occurred after cooking. Radionuclide concentrations in gizzard showed no significant change in radionuclide concentrations after cooking. Cesium-134 and ¹³⁷Cs concentrations decreased by 27% in carcass after cooking and reduced the dose commitment to man by that amount if only the carcass was consumed. No reduction in dose is expected if the carcass and juice were consumed.     

Distribution of 137Cs in the Tree Layer of Forest Ecosystems in the Zone of the Accident at the Chernobyl Nuclear Power Plant

Trends in ¹³⁷Cs distribution over the parts of coniferous (Pinus sylvestrisL.) and deciduous (Betula pendula Rocht.) trees are described. The trees have been selected in the stationary experimental plots located in southwestern Bryansk oblast, Russian Federation. The distribution of ¹³⁷Cs in the wood along the trunk height is shown to be nonuniform. The effects of ¹³⁷Cs content in the xylem sap on the accumulation of this radionuclide in the leaves and needles are assessed. The factors controlling ¹³⁷Cs accumulation in the components of woody plants are revealed, and their significance is estimated.     

Transfer parameter values in temperate forest ecosystems: a review

Compared to agricultural lands, forests are complex ecosystems as they can involve diverse plant species associations, several vegetative strata (overstorey, shrubs, herbaceous and other annual plant layer) and multi-layered soil profiles (forest floor, hemi-organic and mineral layers). A high degree of variability is thus generally observed in radionuclide transfers and redistribution patterns in contaminated forests. In the long term, the soil compartment represents the major reservoir of radionuclides which can give rise to long-term plant and hence food contamination. For practical reasons, the contamination of various specific forest products has commonly been quantified using the aggregated transfer factor (T_ag in m² kg⁻¹) which integrates various environmental parameters including soil and plant type, root distribution as well as nature and vertical distribution of the deposits. Long lasting availability of some radionuclides was shown to be the source of much higher transfer in forest ecosystems than in agricultural lands. This study aimed at reviewing the most relevant quantitative information on radionuclide transfers to forest biota including trees, understorey vegetation, mushrooms, berries and game animals. For both radiocaesium and radiostrontium in trees, the order of magnitude of mean T_ag values was 10⁻³ m² kg⁻¹ (dry weight). Tree foliage was usually 2–12 times more contaminated than trunk wood. Maximum contamination of tree components with radiocaesium was associated with (semi-)hydromorphic areas with thick humus layers. The transfer of radionuclides to mushrooms and berries is high, in comparison with foodstuffs grown in agricultural systems. Concerning caesium uptake by mushrooms, the transfer is characterized by a very large variability of T_ag, from 10⁻³ to 10¹ m² kg⁻¹ (dry weight). For berries, typical values are around 0.01–0.1 m² kg⁻¹ (dry weight). Transfer of radioactive caesium to game animals and reindeer and the rate of activity reduction, quantified as an ecological half-life, reflect the soil and pasture conditions at individual locations. Forests in temperate and boreal regions differ with respect to soil type and vegetation, and a faster decline of muscle activity concentrations in deer occurs in the temperate zone. However, in wild boar the caesium activity concentration shows no decline because of its special feeding habits. In the late phase, i.e. at least a few months since the external radionuclide contamination on feed plants has been removed, a T_ag value of 0.01 m² kg⁻¹ (fresh weight) is common for ¹³⁷Cs in the muscles of adult moose and terrestrial birds living in boreal forests, and 0.03 m² kg⁻¹ (fresh weight) for arctic hare. Radiocaesium concentrations in reindeer muscle in winter may exceed the summer content by a factor of more than two, the mean T_ag values for winter ranging from 0.02 to 0.8 m² kg⁻¹ (fresh weight), and in summer from 0.04 to 0.4 m² kg⁻¹. The highest values are found in the year of initial contamination, followed by a gradual reduction. In waterfowl a relatively fast decline in uptake of ¹³⁷Cs has been found, with T_ag values changing from 0.01 to 0.002 m² kg⁻¹ (fresh weight) in the three years after the contaminating event, the rate being determined by the dynamics of ¹³⁷Cs in aquatic ecosystems.     

Radioecological consequences of radioactive discharges into the Techa River on the Southern Urals

The sources and levels of radioactive contamination of the Techa River are analyzed. Dose assessments are made for humams and biota. The highest radionuclide concentrations in the river water were observed in the period 1950–1951. In 1951, at a distance of 78 km from the site of radioactive discharges, the content of ⁹⁰Sr in the water was 2.7 × 10⁴ Bq l⁻¹ and that of ¹³⁷Cs was 7.5 × 10³ Bq l⁻¹. Subsequently, the radionuclide activity in the river water decreased considerably. In the period 1991–1994, the average annual content of ⁹⁰Sr in the water varied between 6 and 20 Bq l⁻¹. The average annual content of ¹³⁷Cs in the river water varied from 0.06 to 0.23 Bq l⁻¹, i.e. was lower than that of ⁹⁰Sr approximately by two orders of magnitude. The concentration of ^239,240Pu in the water varied between 0.004 and 0.019 Bq l⁻¹. The radioactive contamination of the Techa floodplain is highly nonuniform. With increasing distance from the river sources, the contamination density of the floodplain decreases, remaining, however, considerably higher than the background values.At present, the average annual dose rates in contaminated areas are (0.1–2) × 10⁻³ Sv year⁻¹, which is considerably lower than in the periods of ‘acute’ exposure (1950–1951). The doses to aquatic biota were much higher than those to humans.     

Uptake and loss of technetium-95m in the crab Pachygrapsus marmoratus

The uptake and loss kinetics of ^95mTc in seawater have been investigated in the crab Pachygrapsus marmoratus. Both the uptake and loss kinetics can be represented as the sum of two exponential functions, one short-term ($\text{tb}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 16}\text{d}$) and one long-term ($\text{tb}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 63}\text{d}$), $\text{tb}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ being the biological half-time. The predicted steady state concentration factor was estimated to be about 18.No significant linear correlation between Tc uptake rate and animal weight was found during the accumulation phase. At the end of this phase, 77% of the Tc was found to be distributed in the digestive system and particularly in the hepatopancreas (56%); this organ also appeared to lose the radionuclide most quickly. During the loss phase, 90% of the incorporated radioactivity was eliminated in about three months. Therefore P. marmoratus does not appear to be a good bioindicator of Tc in the marine environment nor an important pathway for Tc contamination along marine food chains.     

Assessing field-scale migration of radionuclides at the Nevada Test Site: “mobile” species

Many long-lived radionuclides are present in groundwater at the Nevada Test Site (NTS) as a result of 828 underground nuclear weapons tests conducted between 1951 and 1992. In conjunction with a comprehensive geochemical review of radionuclides (³H, ¹⁴C, ³⁶Cl, ⁹⁹Tc and ¹²⁹I) that are presumably mobile in the subsurface, we synthesized a body of radionuclide activity data measured from groundwater samples collected at 18 monitoring wells, to qualitatively assess their migration at the NTS over distances of hundreds of meters and over timescales of decades. Tritium and ³⁶Cl showed little evidence of retardation, while the transport of ¹⁴C may have been retarded by its isotopic exchange with carbonate minerals in the aquifer. Observed local reducing conditions (either natural or test-induced) will impact the mobility of certain redox-sensitive radionuclides (especially ⁹⁹Tc) that were otherwise soluble and readily transported under oxidizing conditions. Conversely, strongly oxidizing conditions may impact the mobility of ¹²⁹I which is mobile under reducing conditions. The effect of iodine speciation on its transport deserves further attention. Indication of delayed transport of some “mobile” radionuclides (especially ⁹⁹Tc) in the groundwater at the NTS suggested the importance of redox conditions of the natural system in controlling the fate and transport of radionuclides, which has implications in the enhanced performance of the potential Yucca Mountain repository, located adjacent to the NTS, to store high-level nuclear wastes as well as management of radionuclide contamination in legacy nuclear operations facilities.     

A study of radionuclides, metals and stable lead isotope ratios in sediments and soils in the vicinity of natural U-mineralisation areas in the Northern Territory

Australian guidelines recommend that tailings materials from uranium (U) mining and milling be contained without any detrimental impact on the environment for at least 1000 years. Natural analogue sites are being investigated to determine if they can provide data on the rates of natural erosion processes which occur over these timescales, for input into predictive geomorphic computer models. This paper presents radionuclide, metal and stable lead (Pb) isotope data from sediment cores and surface soils in the vicinity of two mineralised areas in the Alligator Rivers Region.Surface scrapes from the natural Anomaly #2, south of the Ranger mineral lease, exhibit radiogenic ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb ratios, and elevated U and metal concentrations typical for a near surface U anomaly. In contrast, samples taken from the Koongarra mineral lease (KML) show radionuclide activity and metal concentrations similar to natural areas elsewhere in the Alligator Rivers Region and Pb isotope ratios are closer to present day average crustal ratios (PDAC), as the orebodies at KML are covered by surficial sand. A sediment core collected from Anbangbang Billabong, downstream of KML, exhibits small variations in Pb isotope ratios that indicate that approximately 1% of the upper sediments in the sediment core may be derived from material originating from the U anomaly at Koongarra.     

Radium-226 concentrations in faeces of snowshoe hares,Lepus americanus,established near uranium mine tailings

Samples of snowshoe hare faeces were collected near revegetated and chemically stabilized uranium mine tailings and at a control site. Washing the faecal pellets in water with concurrent ultrasonic agitation was ineffective in removing all traces of external contamination. Internal ²²⁶Ra levels in the faeces from the mine wastes were higher than controls. ²²⁶Ra levels in faeces are considered too low to constitute an important avenue for dispersing the radionuclide from the waste site.