Rapid remobilisation of plutonium from estuarine sediments

Plutonium remobilisation experiments, using contaminated Esk Estuary sediments and uncontaminated River Esk and North Sea waters, have successfully reproduced the observed non-conservative behaviour of dissolved Pu in the Esk Estuary, Cumbria, UK. Remobilisation is greatest at low salinites (<4%) and, under these conditions, Pu(III, IV) and Pu(V, VI) are released into solution in similar absolute amounts. The remobilisation process appears to be associated with a rapid (equilibrium achieved in 15 min) exchange reaction involving competition between Pu species, protons and major cations for the available surface sites. The experimental results show a systematic variation in distribution coefficients (i.e. K_d) for total Pu (7·2 × 10⁴−4·1 × 10⁶), Pu(III, IV) (1·0 × 10⁵−5·8 × 10⁶) and Pu(V, VI) (6·4 × 10³−5·5 × 10⁵).     

Measurement of transuranic elements,chiefly 237Np (by neutron activation analysis), in the physical and biological compartments of the French shore of the English channel

The behaviour of transuranic elements in the marine environment has been studied via both in situ sampling and laboratory tracer experiments. In particular, the radionuclide ²³⁷Np was investigated and techniques for its quantitative determination are described. In the field investigations, a preliminary separation of Np from samples was performed prior to neutron activation analysis, with subsequent γ-ray spectrometry of ²³⁸Np. In the laboratory studies, ²³⁷Np was determined by a radiochemical method followed by α-spectrometry. The results obtained from the in situ study in the English Channel (sea water, seaweed, molluscs) and from laboratory-uptake experiments (water and mussels) are described. Levels of Pu, Am and Np are compared and the characteristics of neptunium transfer to molluscs are discussed.     

UO22+-humate interactions in soft,acid, humate-rich waters

Few analytical techniques are sensitive enough to detect environmental concentrations of uranium in waters where humic acids are present. One objective of this study was to devise a technique for measuring humic-complexed and uncomplexed uranium at these concentrations. Three techniques were combined to determine the binding capacity and conditional stability constant of uranium with Aldrich^® humic acid. Free UO₂²⁺ was separated from bound by chelating resin; the CC bonds were destroyed by photo-oxidation and UO₂²⁺ was quantified by laser fluorometry. The binding capacity (BC) of 3·5 mg C liter⁻¹ Aldrich humic acid solution was estimated to be 1·14 × 10⁻⁶MUO₂²⁺ with an asymptotic standard error of 5·0 × 10⁻⁸MUO₂²⁺. UO₂²⁺ was bound to humic acid by a continuum of sites with different strengths. The frequency distribution of these sites was log-normal. A Gaussian-Scatchard model was used to estimate the overall conditional stability constant for uranium concentrations of 5·25 × 10⁻⁸Mto 2·1 × 10⁻⁷M in the presence of 3·5 mg liter⁻¹ humate (1·14 × 10⁻⁶M = φ). The estimates of the mean and standard deviation for the log of the stability constants were 6·5 and 0·8, respectively. When these mean and standard deviations were used to determine the mole-average number of binding sites at three points on the Gaussian distribution, the estimators of log-stability constants were found to be: K₁ = 5·2, K₂ = 6·5 andK₃ = 7·7 with mole fractions of the total number of binding sites associated with each region of 0·21, 0·55 and 0·21, respectively. The thermodynamic, geochemical simulation model GEOCHEM and the three-component Gaussian-Scatchard estimates allowed accurate prediction of the relative proportion of UO₂²⁺ bound to humates for a soft water pond across the entire range of metal-ligand ratios studied. Approximately 22% of the UO₂²⁺ was predicted to be associated with dissolved organic carbon.     

The transfer of 60Co from feed into vitamin B12 in cow liver,milk and beef

The transfer of the radionuclide ⁶⁰Co from feed to milk, meat and the organs of a cow and its incorporation into vitamin B12 were studied in order to determine the transfer coefficient of ⁶⁰Co into vitamin B12 in cattle. Upper limits of transfer coefficients for ⁶⁰Co organically complexed into vitamin B12 were determined to be 6·0 × 10⁻⁵ days/litre in milk and 3·9 × 10⁻⁵ days/kg in meat, based on values measured after 140 days in bovine liver.     

The distribution of plutonium,Americium and curium isotopes in pond and stream sediments of the Savannah river plant,South Carolina,USA

The concentrations of ²³⁸Pu, ^239,240Pu, ²⁴¹Am and ²⁴⁴Cm were determined in sediment samples from five streams and two ponds on the Savannah River Plant (SRP) and in four sediment samples from the Savannah River above and below the plant site. The following concentration ranges were determined: ²³⁸Pu, 0·07–386 fCi g⁻¹; ^239,240Pu, 0·37–1410 fCi g⁻¹; ²⁴¹Am, 0·1–4360 fCi g⁻¹; ²⁴⁴Cm, <0·01–392 fCi g⁻¹. Comparisons of the elemental and isotopic ratios of the sediments show that the majority of the sediments studied have been impacted upon by plant operations and that sediments outside the plant boundary in the Savannah River have only been influenced by aerial releases. Atom ratios of ²⁴⁰Pu/²³⁹Pu indicate that up to 86% of the Pu in these sediments is derived from plant operations. However, comparisons of the concentration data with values for other impacted sediments near nuclear facilities indicate that the levels are relatively small. Finally, <13% of the Pu, Am or Cm in pond sediments is associated with humic or fulvic acids, indicating that little of the material should be remobilized in oxic environments through organic complexation.     

Plant uptake of neptunium-237 and technetium-99 under field conditions

Plant uptake of ⁹⁹Tc freshly added to soils was compared with uptake of ⁹⁹Tc ‘aged’ in soil for more than a decade. A combination of alkaline soil and freshly added ⁹⁹Tc resulted in elevated uptake into radish foliage (plant/soil concentration ratios ranged from 37 to 46). Neptunium-237 was freshly added to all soils. Neptunium uptake via plant roots into foliage was strongly affected by soil pH. Neptunium uptake was greatest from acidic soils. The observed plant/soil concentration ratios for ²³⁷Np under field conditions were approximately 10⁻² from acidic soils (pH 5·6–5·7) and were comparable to field concentration ratios for ²³⁹Pu, that is 10⁻³, from a basic soil (pH 7·5).     

Environmental radioactivity around tokai-works after the reactor accident at chernobyl

Following the reactor accident at Chernobyl, environmental samples of air, rain water and agricultural and marine products were collected and analyzed by gamma- and alpha-spectrometry. The highest concentrations of ¹³¹I in the environmental samples were as follows: 1·0×⁻¹ Bqm⁻³ (aerosol-associated in air); 3·0×10⁻¹ Bqm⁻³ (gaseous in air); 2·1×10² bq kg⁻¹ (plants); 1·4×10¹ Bq litre⁻¹ (milk). Other nuclides such as ⁹⁵Zr, ⁹⁵Nb, ¹⁰³Ru, ¹⁰⁶Ru, ¹²⁵Sb, ^129mTe, ¹³²I/¹³²Te, ¹³⁴Cs, ¹³⁷Cs, ¹⁴⁰Ba/¹⁴⁰La, ¹⁴¹Ce and ¹⁴⁴Ce were also observed in various environmental samples. ^110mAg was only detected in marine products such as cephalopoda and shellfish, ^239,240Pu and ²⁴¹Am originating from the accident were not identified.Based on the monitoring results at one dairy farm, we have derived an equation to model the transport of ¹³¹I from pasture grass to milk. This equation was then applied to the data from two other farms around Tokai-Works and the calculated ¹³¹I activities in milk were compared with those measured. The equation shows good predictive capabilities for quantification of the peak concentrations of ¹³¹I in milk but underestimates longer-term activities.     

Gamma radioactivity in the Iberian Marine environment closest to the NEA dumping site

The distributions of caesium-137 and some naturally occurring gamma-emitters in a range of environmental samples, collected along the north-west Iberian coastline during April 1984, are presented. Samples, including surface waters, algae, sediments and fish, have been analyzed to establish accurate baselines for that region of the continental shelf closest to the NEA dumping site. Results indicate that caesium-137 levels were a factor of three lower than those typical of waters off the west coast of Ireland and are consistent with those expected from global fallout prior to the Chernobyl accident. The mean caesium-137 concentration in sea water at six well-separated stations near the coast was 3·85 ± 0·19 Bq m⁻³, whilst caesium-137 levels in widely consumed species of fish were in the range 1·1–6·2 Bq kg⁻¹ (dry wt). It is estimated that caesium-137, through one year's ingestion of fish and shellfish, generates a collective dose equivalent commitment to the adult Galician population of 0·78 man-Sv, which is approximately 3% of the total annula collective dose equivalent from non-medical sources of radiation.     

The distribution and inventory of fallout plutonium in sediments of the Ligurian Sea near La Spezia,Italy

Pu concentrations in surface sediments of the Ligurian Sea are about ten times higher than in adjacent river sediments and are highly correlated with sediment porosities. The integrated inventory of ^239,240Pu in a sediment core is calculated to be 3·5 mCi km^?2, nearly twice the average input from fallout at these latitudes, apparently because Pu is removed from seawater by particle scavenging.The sedimentation rate is calculated from the depth of the ^239,240Pu maximum to be 0·52 ± 0·06 cmy^?1.     

Experimental studies on the bioaccumulation of plutonium from sea water and a deep-sea sediment by clams and polychaetes

The bioavailability of ²³⁷Pu in the (III + IV) and (V + VI) oxidation states from sea water and a NE Atlantic deep-sea sediment has been studied for clams (Venerupis decussata) and polychaete worms (Hermione hystrix). After 22 days' exposure in sea water transfer factors (TF) had not reached equilibrium, and were 74 ± 5 and 61 ± 1 for clams and 370 ± 10 and 275 ± 11 for polychaetes, for Pu (III + IV) and Pu (V + VI) respectively. Depuration rates after sea water exposure followed a single exponential form ($\text{T}{}_{\mathrm{<mtext>b</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{= 50}\text{days}$) for clams, and for polychaetes at least a two component from with $\text{T}{}_{\mathrm{<mtext>b</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{= 1·3}\text{days}$ and 54 days. TF values for ²³⁷Pu bioaccumulation from sediments were very low, 6 × 10^?3 and 5 × 10^?2 for clams and polychaetes, respectively, after 20 days' exposure.Plotonium appears to be about 50% more bioavailable to the same species than americium as measured by laboratory experiments using a similar deep-sea sediment. Depuration experiments with clams after 40 days' exposure to labelled sediment indicated loss followed a single exponential form with a $\text{T}{}_{\mathrm{<mtext>b</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{= 24}\text{days}$. Significant differences in the behaviour of Pu introduced into the uptake and loss experiments in different oxidation states were not observed in general.     

Transfer of 241Am and 237Pu from euphausiid moults to a carbonate-rich marine sediment

Concentrations of ²⁴¹Am and ²³⁷Pu adsorbed onto moulted exoskeletons from the euphausiid Megancytiphanes norvegica decreased exponentially with 50% retention times of 3–7 d when moults were incubated in filtered seawater with small amounts of a carbonate-rich sediment. Over 95% of sediment weight was present as < 43 μm silt particles and 91 ± 4% of radioactivity lost from moults was recovered in this size fraction. Adsorption of both actinides (atoms μm⁻²) was greatest in the medium-fine sand fraction which had the highest carbonate content. These particles constituted <0·4% of total sediment dry weight but their reactivity (atoms μm⁻² surface: atoms μm⁻³ in solution) was 10³–10⁴ times higher than similar quotients for <43 μm particles. The enrichment shows that non-homogeneous distributions may arise between particle types when actinides such as ²⁴¹Am and ²³⁷Pu sorbed to surfaces of organic particles are transferred to sediments.     

99Tc in the sub-arctic food chain Lichen-Reindeer-man

The deposition, migration and annual variations of ⁹⁹Tc fallout in carpets of lichen collected during the period 1956–1981 have been investigated. The transfer of ⁹⁹Tc to reindeer and man has also been studied. Technetium showed a shorter mean residence time than ¹³⁷Cs in the lichen carpet. The activity ratio ⁹⁹Tc/¹³⁷Cs was generally lower than the theoretical fission ratio of 1·43 × 10⁻⁴. The maximum concentration of ⁹⁹Tc in lichens occurred in 1967 (ca. 60 mBq kg⁻¹) but in 1975 higher values were found than would have been predicted from fallout. The average depth integrated concentration of ⁹⁹Tc at 62·3°N, 12·4° E in 1972 was 540 ± 100 mBq m⁻². The studies of reindeer tissues show that technetium has a short mean residence time in the muscle tissues (ca. 5 days) and is not accumulated like ¹³⁷Cs. The committed dose equivalent from ⁹⁹Tc to the local Lapp population engaged in reindeer breeding is negligible.     

Activity concentrations of 226Ra, 228Ra, 210Pb, 40K and 7Be and their temporal variations in surface air

Activity concentrations of the long-lived natural radionuclides ²²⁶Ra, ²²⁸Ra, ²¹⁰Pb, ⁴⁰K and of ⁷Be in surface air were measured twice monthly at a semi-rural location 10 km north of Munich (FRG) for at least three years. For the time interval 1983–1985, all values were found to be distributed log-normally, with geometric means (in μBq m⁻³) of 1·2 for ²²⁶Ra, 0·5 for ²²⁸Ra, 580 for ²¹⁰Pb, 12 for ⁴⁰K and 3500 for ⁷Be. Reflecting their common origin, the activity concentrations of ²²⁶Ra and ⁴⁰K are correlated with surface air dust concentrations (geometric mean 59 μg m⁻³). Seasonal variations of ²¹⁰Pb and ⁷Be air activity concentrations are established for the time interval 1978–1985.The contribution of local soil activity to the air activity concentrations of these radionuclides and of natural uranium is discussed. Resuspension factors are found to be of the order of 10⁻⁹m⁻¹.     

Aspects of the uptake of radionuclides by sheep grazing on an estuarine saltmarsh. 2. Radionuclides in sheep tissues

The transfer ¹³⁷Cs, ²³⁸Pu, ^239/240Pu and ²⁴¹Am to sheep which graze a saltmarsh in the Esk estuary, 7 km south of the sellafield reprocessing plant in west Cumbria (UK), has been estimated.The concentrations of gamma-emitting radionuclides and of ²³⁸Pu, ^239/240Pu and ²⁴¹Am were measured in liver, lung, muscle, kidney and bone from saltmarsh ewes and lambs. ¹³⁷Cs concentrations in the soft tissues were similar in liver, lung and muscle but were consistently higher in kidney and much lower in bone. The highest concentration of the transuranics was found in liver.Transfer coefficients and concentration factors were calculated for both ewes and lambs. The concentration of ¹³⁷Cs in the tissues of 5-month old lambs was higher than in those of their mothers. Therefore, a higher transfer coefficient was obtained for lamb muscle (1·8 × 10^?1 d kg^?1) than for ewe muscle (6·4 × 10^?2 d kg^?1). Concentration factors were consistently higher for ¹³⁷Cs than for the transuranics.     

Americium adsorption on the surface of macrophytic algae

Data are presented on the rates at which americium (Am) deposits upon blade surfaces of three benthic algal species (Ulva rigida, Fucus vesiculosus and Gigartina stellata) following short-term exposures (1–6 h). Am is taken up in direct proportion to the ambient radionuclide concentration in sea water. Uptake by the green alga was 3 to 5 times greater than that for the brown and red species. Experimental evidence indicated that Am accumulation is a passive process and that adsorption takes place mainly on the thin outer organic coating of the seaweed. The Am transport coefficients (0·9–4·1 × 10?⁵ Bq cm?² s?¹ per Bq ml?¹ sea water) are quite similar to that previously found for the naturally occurring α-emitter ²¹⁰Po, but are an order of magnitude lower than a plutonium transport coefficient reported in the literature. Release of labelled extracellular products associated with the algal surface coating is considered to be responsible for the rapid loss of Am observed previously in macroalgae and may in fact serve as a mechanism for transferring Am to filter feeding zooplankton.     

Accumulation of 210Po in Baltic invertebrates

This paper presents the results of an investigation of the ²¹⁰Po contents of Baltic marine invertebrates. The ²¹⁰Po concentrations fall within the range 11·3–78·9 Bq kg⁻¹ (dry wt), the higher values relating to polychaeta, priapulida and malacostraca and the lower levels to bivalvia. It is demonstrated that ¹⁰Po is non-uniformly distributed within the isopod Mesidotea entomon and the bivalve Mya arenaria. The ²¹⁰Po contents of the internal organs decreasing in the order-hepatopancreas > alimentary tract > gill > muscle. Moreover, the results indicate the dominant role of the digestive organs of these invertebrates in controlling absorption and elimination of ²¹⁰Po.     

222Rn and 210Pb in the Arctic summer air

As part of an extensive air chemistry programme, during summer 1980, on board the Swedish ice-breaker ‘Ymer’, levels of ²²²Rn (radon) and its long-lived daughters ²¹⁰Pb and ²¹⁰Po were measured. The radon was trapped on charcoal and the long-lived daugther products sampled on filters on a daily basis. In addition, short-lived progenies were followed continuously on the filters in order to achieve a time resolution of about one hour. The concentrations of radon and ²¹⁰Pb in the Arctic summer air north of latitude 75° N averaged 75 ± 21 (1 sd) and 0·075 ± 0·028 mBqm⁻³, r respectively. During a two week period of persistent polar winds, the mean radon concentration was 19 ±5 mBq m⁻³. During such ‘Arctic background’ conditions, radon exhalation from the sea may contribute significantly to the measured radon-in-air concentration. It is shown that steady-state equilibrium models, applied to an air mass over the sea, overstimate the aerosol residence-time calculated from activity ratios. Time-dependent calculations indicate a mean aerosol residence time of 4 to 7 d in Arctic air. Good agreement is observed between radon levels and the time since the air mass left larger areas. Both the ²²²Rn and the long-lived daughter measurements are insensitive to contamination from ship and local settlement.     

Migration of radium from the thorium ore deposit of Morro do Ferro,Poços de Caldas,Brazil

A large thorium ore deposit is located in Morro do Ferro, a hill in the Poços de Caldas Plateau, Minas Gerais, Brazil, which contains an estimated 30 000 t of Th and 100 t of U in a highly weathered matrix exposed to erosion and leaching. ²²⁸Ra and ²²⁶Ra were analyzed in surface waters collected at various points in the drainage basin and in groundwaters from wells drilled through and around the ore body. The concentrations in groundwater demonstrated that radium is markedly leached by rainwater percolating through the ore body. In its transit underground, radium is removed from groundwater by sorption on soil particles and this natural process greatly reduces the radium discharged to the environment. In dry weather, the concentration of dissolved ²²⁸Ra in the main stream draining the Morro do Ferro is 7·0 ± 1·1 mBq litre⁻¹ and in a control stream 1·6 ± 0·3 mBq litre⁻¹. The estimated ²²⁸Ra mobilization rate by solubilizations is of the order of 10⁻⁷ y⁻¹.     

Speciation patterns of actinides in natural waters: a laboratory investigation

The results of laboratory investigations of actinide speciation in ground waters of varying compositions are summarized, re-evaluated and further interpreted, with the inclusion of additional data. Actinide speciation (solubility, oxidation state distributions) in these water samples exhibits great variability at 10⁻¹⁰ to 10⁻⁸ M total actinide concentrations. Americium solubility appears to be controlled by the formation of radiocolloids. neptunium is predictably oxidized and soluble in these water samples, with only a few exceptions. Plutonium exhibits widely varying oxidation state distributions—and hence solubility— despite the presence of 6 mg liter⁻¹ dissolved oxygen in all experiments. Plutonium solubility is enhanced by carbonate and fluoride but is diminished by sulfate in reducing waters. In general, these results are compatible with the limited information available for actinide speciation from previous in-situ investigations but they emphasize the paucity of accurate thermodynamic data to describe these systems.     

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.