Plant uptake of radiocaesium from artificially contaminated soil monoliths covering major European soil types

Uptake of ¹³⁷Cs was measured in different agricultural plant species (beans, lettuce, barley and ryegrass) grown in 5 undisturbed soil monoliths covering major European soil types. The first cultivation was made three years after soil contamination and plants were grown during 3 successive years. The plant–soil ¹³⁷Cs transfer factors varied maximally 12-fold among soils and 35-fold among species when grown on the same soil. Single correlations between transfer factors and soil properties were found, but they varied widely with plant type and can hardly be used as a predictive tool because of the few soils used. The variation of ¹³⁷Cs concentrations in plants among soils was related to differences in soil solution ¹³⁷Cs and K concentrations, consistent with previous observations in hydroponics and pot trials. Absolute values of transfer factors could not be predicted based on a model validated for pot trials. The ¹³⁷Cs activity concentration in soil solution decreased significantly (11- to 250-fold) for most soils in the 1997–1999 period and is partly explained by decreasing K in soil solution. Transfer factors of lettuce showed both increasing and decreasing trends between 2 consecutive years depending on soil type. The trends could be explained by the variation in ¹³⁷Cs and K concentrations in soil solution. It is concluded that differences in ¹³⁷Cs transfer factors among soils and trends in transfer factors as a function of time can be explained from soil solution composition, as shown previously for pot trials, although absolute values of transfer factors could not be predicted.     

Predicting the transfer of radiocaesium from organic soils to plants using soil characteristics

A model predicting plant uptake of radiocaesium based on soil characteristics is described. Three soil parameters required to determine radiocaesium bioavailability in soils are estimated in the model: the labile caesium distribution coefficient (kd1), K+ concentration in the soil solution [mK] and the soil solution-->plant radiocaesium concentration factor (CF, Bq kg-1 plant/Bq dm-3). These were determined as functions of soil clay content, exchangeable K+ status, pH, NH4+ concentration and organic matter content. The effect of time on radiocaesium fixation was described using a previously published double exponential equation, modified for the effect of soil organic matter as a non-fixing adsorbent. The model was parameterised using radiocaesium uptake data from two pot trials conducted separately using ryegrass (Lolium perenne) on mineral soils and bent grass (Agrostis capillaris) on organic soils. This resulted in a significant fit to the observed transfer factor (TF, Bq kg-1 plant/Bq kg-1 whole soil) (P < 0.001, n = 58) and soil solution K+ concentration (mK, mol dm-3) (P < 0.001, n = 58). Without further parameterisation the model was tested against independent radiocaesium uptake data for barley (n = 71) using a database of published and unpublished information covering contamination time periods of 1.2-10 years (transfer factors ranged from 0.001 to 0.1). The model accounted for 52% (n = 71, P < 0.001) of the observed variation in log transfer factor.     

Kinetics of radiocesium released from contaminated soil by fertilizer solutions

(137)Cs is one of the major artificial radionuclides found in environments; but the mechanisms behind fertilizer-induced (137)Cs desorption from soil remain unknown. This study aimed to investigate the kinetics and mechanisms underlying the various cations and anions that cause Cs release from soil under acidic conditions. NH(4)H(2)PO(4) (1M), 0.5M (NH(4))(2)SO(4), 1M NH(4)Cl, 1M KCl or 1M NaCl solutions were added to (137)Cs-contaminated soil. The power function model well described the short term (137)Cs desorption with the solutions. The rate coefficients for (137)Cs release from soil in NH(4)H(2)PO(4), (NH(4))(2)SO(4), NH(4)Cl, and KCl solutions were 7.7, 7.3, 6.8, and 6.1 times higher than the rate observed in a NaCl solution, respectively. The NH(4)H(2)PO(4) and (NH(4))(2)SO(4) solutions induced significantly greater (137)Cs release from the contaminated soil than the NH(4)Cl, KCl and NaCl solutions. After four times repeated extractions with the fertilizer solutions, the total amount of (137)Cs extracted by (NH(4))(2)SO(4) and NH(4)Cl solutions reached equilibrium, while that extracted using an NH(4)H(2)PO(4) solution continued to increase. The combined effect of phosphate and protons was the major mechanism behind (137)Cs release from contaminated soils, when an NH(4)H(2)PO(4) solution was used.     

Leaching of nickel and copper from soil contaminated by metallurgical dust

The paper presents the results of the laboratory percolation experiment simulated soil contamination by emissions from a Ni-Cu smelter. Humus (Ao horizon) columns were transferred to lysimeters from an illuvial, humic, ferriferous forest podzol site. Fine metallurgical dust containing Ni and Cu was layered on the columns and irrigated with sulphuric acid solutions at pH 3, 4, 5, and 6. Irrigation for 19 months indicated that the leaching of metals down the humus column was greatest at pH 6. Calculations indicated that it would take 160-270 years for complete leaching of Ni from the Ao layer, and 100-200 years for Cu, depending on the dust composition. Natural decontamination of affected soils will take centuries.     

Analysis of radiocaesium in the Lebanese soil one decade after the Chernobyl accident

Fallout from the Chernobyl reactor accident due to the transport of a radioactive cloud over Lebanon in the beginning of May 1986 was studied 12 years after the accident for determining the level of (137)Cs concentration in soil. Gamma spectroscopy measurements were performed by using coaxial high sensitivity HPGe detectors. More than 90 soil samples were collected from points uniformly distributed throughout the land of Lebanon in order to evaluate their radioactivity. The data obtained showed a relatively high (137)Cs activity per surface area contamination, up to 6545Bqm(-2) in the top soil layer 0-3cm. The average activity of (137)Cs in the top soil layer 0-3cm in depth was 59.7Bqkg(-1) dry soil ranging from 15 to 119Bqkg(-1) dry soil. The horizontal variability was found to be about 45% between the sampling sites. The depth distribution of total (137)Cs activity in soil showed an exponential decrease. Estimation of the annual effective dose due to external radiation from (137)Cs contaminated soil for selected sites gave values ranging from 19.3 to 91.6 micro Svy(-1).     

A comparison of the soil migration and plant uptake of radioactive chlorine and iodine from contaminated groundwater

A 6-month soil column experiment was conducted to compare the upward migration and plant uptake of radiochlorine and radioiodine from shallow, near-surface contaminated water tables. Both fixed and fluctuating water tables were studied. After 6 months, (36)Cl activity concentrations were relatively uniform throughout the soil profile apart from an accumulation at the soil surface, which was especially marked under a fluctuating water table scenario. In contrast, (125)I (a surrogate for (129)I) tended to accumulate at the boundary between the anoxic conditions at the base of the column and the oxic conditions above, due to its redox-dependent sorption behaviour. The uptake of (36)Cl by perennial ryegrass was much greater than that of (125)I due to its greater migration into the rooting zone and its ready availability in soil solution. In the context of radioactive waste disposal, where these radionuclides may potentially be released into groundwater, (36)Cl would be expected to present a greater potential for contamination of the biosphere than (129)I.     

Phytoextraction for clean-up of low-level uranium contaminated soil evaluated

Spills in the nuclear fuel cycle have led to soil contamination with uranium. In case of small contamination just above release levels, low-cost yet sufficiently efficient remedial measures are recommended. This study was executed to test if low-level U contaminated sandy soil from a nuclear fuel processing site could be phytoextracted in order to attain the required release limits. Two soils were tested: a control soil (317 Bq 238U kg(-1)) and the same soil washed with bicarbonate (69 Bq 238U kg(-1)). Ryegrass (Lolium perenne cv. Melvina) and Indian mustard (Brassica juncea cv. Vitasso) were used as test plants. The annual removal of soil activity by the biomass was less than 0.1%. The addition of citric acid (25 mmol kg(-1)) 1 week before the harvest increased U uptake up to 500-fold. With a ryegrass and mustard yield of 15,000 and 10,000 kg ha(-1), respectively, up to 3.5% and 4.6% of the soil activity could be removed annually by the biomass. With a desired activity reduction level of 1.5 and 5 for the bicarbonate-washed and control soil, respectively, it would take 10-50 years to attain the release limit. However, citric acid addition resulted in a decreased dry weight production.     

Modelling the role of humic acid in radiocaesium distribution in a British upland peat soil

The significance of exchange sites on organic matter in the retention of radiocaesium in highly organic soils remains unclear. To quantify this retention, we measured the binding of 134Cs to a humic acid isolated from a British upland peat soil, under a range of chemical conditions. We interpreted our results using Humic Ion Binding Model V, a model of humic substance chemistry which simulates ion exchange by non-specific accumulation of cations adjacent to the humic molecules. Model V could simulate the humic acid-solution partitioning of Cs under all the solution conditions used. The model was used to estimate the contribution of organic matter to Cs sorption by the whole soil composite. An estimate of Cs sorption by illite frayed edge sites was also made. These simulations show that organic matter may play only a minor role in binding Cs. even in highly organic soils.     

A prognostic estimation of the area contaminated with alpha-emitting transuranium isotopes in Belarus following the Chernobyl accident

As a result of the Chernobyl accident, some regions of Belarus have been contaminated with the plutonium isotopes (238,239,240,241)Pu. Considering the importance of the environmental impact of the alpha-emitting radionuclides we have carried out a prognostic estimation of the area contaminated with (238,239,240)Pu and (241)Am (the latter being a decay product of (241)Pu) in Belarus. The calculations were made using measurements of (238,239,240)Pu activity concentrations in soil samples from about 600 settlements in the affected region, together with the estimated activity ratio A((241)Am)/A((238,239,240)Pu). The area contaminated with alpha-emitting transuranium isotopes predicted for the year 2006 has been compared with that estimated for 1986. The results show that by 2006, the area of inhabited districts where contamination with (238,239,240)Pu and (241)Am exceeds the threshold level of 740 Bq/m(2), will be 3.7 times larger, reaching approximately 3.5 x10(3)km(2). Of this, almost 20% will have a contamination level of 1850--3700 Bq/m(2).     

A blind test of the MOIRA lake model for radiocesium for Lake Uruskul, Russia, contaminated by fallout from the Kyshtym accident in 1957

This paper presents results of a model-test carried out within the framework of the COMETES project (EU). The tested model is a new lake model for radiocesium to be used within the MOIRA decision support system (DSS; MOIRA and COMETES are acronyms for EU-projects). This model has previously been validated against independent data from many lakes covering a wide domain of lake characteristics and been demonstrated to yield excellent predictive power (see H?kanson, Modelling Radiocesium in Lakes and Coastal Areas. Kluwer, Dordrecht, 2000, 215 pp). However, the model has not been tested before for cases other than those related to the Chernobyl fallout in 1986, nor for lakes from this part of the world (Southern Urals) and nor for situations with such heavy fallout as this. The aims of this work were: (1) to carry out a blind test of the model for the case of continental Lake Uruskul, heavily contaminated with 90Sr and 137Cs as a result of the Kyshtym radiation accident (29 September 1957) in the Southern Urals, Russia, and (2) if these tests gave satisfactory results to reconstruct the radiocesium dynamics for fish, water and sediments in the lake. Can the model provide meaningful predictions in a situation such as this? The answer is yes, although there are reservations due to the scarcity of reliable empirical data. From the modelling calculations, it may be noted that the maximum levels of 137Cs in fish (here 400 g ww goldfish), water and sediments were about 100,000 Bq/kg ww, 600 Bq/l and 30,000 Bq/kg dw, respectively. The values in fish are comparable to or higher than the levels in fish in the cooling pond of the Chernobyl NPP. The model also predicts an interesting seasonal pattern in 137Cs levels in sediments. There is also a characteristic "three phase" development for the 137Cs levels in fish: first an initial stage when the 137Cs concentrations in fish approach a maximum value, then a phase with relatively short ecological half-lives followed by a final phase with long ecological half-lives more or less corresponding to the physical decay of radiocesium.     

A study of radium uptake by the water-lily Nymphaea violacea (Lehm) from contaminated sediment

The rate and extent of radium-226 accumulation from sediment by the water-lily Nymphaea violacea (Lehm) were assessed. The plants were collected from Magela Creek, Northern Territory, Australia and grown in ²²⁶RaCl₂-labelled laboratory sediment over a period of 570 days. The nominal sediment activity of 5 Bq g⁻¹ dry weight was 100 times that of the naturally occurring concentration.In the roots and rhizomes, ²²⁶Ra accumulated on plant surfaces. This result was confirmed by autoradiographic studies which showed the presence of an iron-containing plaque on the surface of these tissues with which the radium was closely associated. Little radium reached the pith of the rhizomes and acropetal translocation was not detected. The average concentration ratio for growing rhizomes was 0·22. Assuming first order accumulation kinetics and likely incremental environmental concentrations, this Aboriginal dietary tissue could become dose-limiting within 50 years.The foliar accumulation of radium originating from the sediment was predominately due to contamination via the sediment-water-plant pathway. Differences in foliar radium concentrations in plants of different ages were due to differential biomass turnover rates. Plants with faster biomass turnover had higher average radium concentrations.     

Remediation strategies for rural territories contaminated by the Chernobyl accident.

The objective of the present paper is to derive remediation strategies for rural settlements contaminated by the Chernobyl accident in which annual doses to a critical group still exceed 1 mSv. Extensive radioecological data have been collected for 70 contaminated settlements. A dose model based on these data resulted in estimates that are on average close to and a bit less than the official dose estimates ('catalogue doses') published by the responsible Ministries of Belarus, Russia and Ukraine. For eight remedial actions that can be applied on a large scale, effectiveness and costs have been assessed in light of their dependence on soil type, contamination level and on the degree of previous application of remedial actions. Remediation strategies were derived for each of the 70 settlements by choosing remedial actions with lowest costs per averted dose and with highest degree of acceptability among the farmers and local authorities until annual doses are assessed to fall below 1 mSv. The results were generalised to 11 contamination/internal-dose categories. The total numbers of rural inhabitants and privately owned cows in the three countries distributed over the categories were determined and predicted until the year 2015. Based on these data, costs and averted doses were derived for the whole affected population. The main results are (i) about 2000 Sv can be averted at relatively low costs, (ii) the emphasis on reducing external exposures should be increased, (iii) radical improvement of hay-land and meadows and application of Prussian blue to cows should be performed on a large scale if annual doses of 1 mSv are an aim to be achieved, (iv) additional remedial actions of importance are fertilising of potato fields, distribution of food monitors and restriction of mushroom consumption, and (v) for inhabitants of some settlements (in total about 8600) annual doses cannot be reduced below 1 mSv by the remedial actions considered.     

The use of molecular techniques to characterize the microbial communities in contaminated soil and water

Traditionally, the identification and characterization of microbial communities in contaminated soil and water has previously been limited to those microorganisms that are culturable. The application of molecular techniques to study microbial populations at contaminated sites without the need for culturing has led to the discovery of unique and previously unrecognized microorganisms as well as complex microbial diversity in contaminated soil and water which shows an exciting opportunity for bioremediation strategies. Nucleic acid extraction from contaminated sites and their subsequent amplification by polymerase chain reaction (PCR) has proved extremely useful in assessing the changes in microbial community structure by several microbial community profiling techniques. This review examines the current application of molecular techniques for the characterization of microbial communities in contaminated soil and water. Techniques that identify and quantify microbial population and catabolic genes involved in biodegradation are examined. In addition, methods that directly link microbial phylogeny to its ecological function at contaminated sites as well as high throughput methods for complex microbial community studies are discussed.     

A phytochelatin-based bioassay in marine diatoms useful for the assessment of bioavailability of heavy metals released by polluted sediments

The aim of the present work was to develop a new bioassay involving the presence of phytochelatins (PCs), detoxifying intracellular metal-binding peptides, in microalgae as response to metal bioavailability in re-suspensions of metal-polluted marine sediments. For this purpose, the synthesis of PCs has been studied in laboratory cultures of three marine diatoms, namely Phaeodactylum tricornutum, Thalassiosira weissflogii and Skeletonema costatum, exposed to elutriates of sediments collected in a polluted coastal area in the province of Pisa (Tuscany, Italy). Short- and long-term incubations in the elutriates of two marine sediments (named A and B) exhibited an increase of PCs synthesis in all the phytoplanktonic species examined, when the elutriate concentration increased from 0% to 100%. Elutriate B, which was mainly contaminated by Cd, was shown to be more effective to induce PCs than elutriate A, which was richer in Cu and TOC. The results show that the PCs response, in the microalgae examined, was species-specific. Our data also show that the PCs synthesis occurred before the growth rate was affected, thereby indicating that PCs can be considered as an early warning response of metal exposure. The PCs response in exponentially growing cultures of T. weissflogii, which was found to be the most sensitive alga, increased when the initial cellular density decreased. Finally, the positive relationship obtained between the cellular PCs concentration in T. weissflogii and the degree of metal contamination of the elutriates from twelve sediments collected in a metal-polluted coastal area, confirmed that the PCs-induction test can be applied in field studies. In conclusion, the response of these marine microalgae suggests that these cellular peptides could represent an excellent biomarker of metal exposure, which is useful for the assessment of sediment toxicity, by carrying out PCs-induction tests on sediment elutriates.     

Annual variation in the levels of metals and PCDD/PCDFs in soil and herbage samples collected near a cement plant

In May 2000, the levels of a number of metals (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sn, Tl, V and Zn) and polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were determined in soil and herbage samples collected near a cement plant from Sta. Margarida i els Monjos (Catalonia, Spain). To determine the temporal variation in the concentrations of metals and PCDD/PCDFs, in May 2001 soil and herbage samples were again collected at the same sampling points and analyzed for the levels of metals and PCDD/PCDFs. In general terms, metal concentrations in soils did not change between May 2000 and May 2001, while significant decreases in the levels of Cr, Ni and V were found in herbage. On the other hand, no significant differences in the mean I-TEQ values of PCDD/PCDFs were found in soil and herbage samples. The results of this survey show that according to the annual variation in the levels of metals and PCDD/PCDFs the environmental impact of the cement plant on the area under its direct influence is not relevant.     

Sea-to-land transfer of technetium-99 through the use of contaminated seaweed as an agricultural soil conditioner

The use of seaweed as an agricultural soil conditioner gives rise to a potential pathway for the transfer of Technetium-99 ((99)Tc) from marine to terrestrial ecosystems and thence to man. However, to date there is little information on the extent of the release of (99)Tc from seaweed into soil and the mechanisms involved. This pot experiment has shown that (99)Tc is released fairly rapidly from Fucus vesiculosus into a sandy coastal soil. Despite low temperature conditions, 60% of the (99)Tc added with the seaweed had accumulated in the soil 15 weeks after addition. Concurrent CO(2) monitoring (used as a measure of microbial decomposition or catabolism) suggested that the initial (99)Tc release (up to 40% in the first 8 weeks) was due to leaching from the seaweed and that microbial decomposition was responsible for the release of the remaining (99)Tc in the latter phase (12-15 weeks).     

A simple and rapid method for analyzing radon in coastal and ground waters using a radon-in-air monitor

We have developed a simple and portable technique for measuring moderately high levels of 222Rn (t1/2=3.8d) in natural waters such as coastal water, groundwater, and river water. The water sample is carefully collected in a glass bottle, and the sample bottle is connected to a radon-in-air monitor in a closed air-loop mode. By purging air through the sample, radon is emanated from the water until a chemical equilibration is obtained between the two phases. The radon in the air loop is determined using the radon-in-air monitor. Then, the radon in water is calculated by a radon-partitioning factor between water and air for a measured water temperature. This technique is especially convenient for determination of 222Rn in natural waters on field sites, since it eliminates the preparation of He gas, cold traps, and alpha-scintillation cells and counter, which are required for traditional radon emanation methods.     

Development of a rapid method for direct detection of tet(M) genes in soil from Danish farmland

A method for direct detection of antibiotic resistance genes in soil samples has been developed. The tetracycline resistance gene, tet(M), was used as a model. The method was validated on Danish farmland soil that had repeatedly been treated with pig manure slurry containing resistant bacteria. The tet(M) gene was directly detected in 10-80% of the samples from the various farmland soils and could be detected in all samples tested after selective enrichment. To validate the obtained results, the method was applied to garden soil samples where lower prevalence of resistance was found. RESULT: A detection limit of 10(2)-10(3) copies of the tet(M) gene per gram of soil (in a Bacillus cereus group bacterium) was achieved. tet(M) gene was detected in soil samples with the highest prevalence on farmland treated with pig manure slurry.     

Effects of soil amendments on lead uptake by two vegetable crops from a lead-contaminated soil from Anhui, China

Previous studies have documented that phosphate compounds of lead (Pb) [e.g., pyromorphite Pb5(PO4)3-(X), where X=OH, F or Cl] are comparatively insoluble, and their formation in Pb-contaminated soil may be a means of reducing the bioavailability and chemical lability of Pb in soil. In this study, the effect of phosphate compound amendments on the bioavailability of Pb in a polluted alkaline soil was examined. A Pb-contaminated soil was treated with hydroxyapatite (HA), phosphate rock (PR), water-soluble P fertilizer (single superphosphate, SSP) and the combination of HA with SSP. The bioavailability of Pb was determined in plant uptake studies with vegetables (Brassica campetris L. var. communis, BC) and Brassica oleracea L. var. acephala, BO) and sequential extraction. The results indicated that the Pb concentrations in both shoots and roots of two vegetable plants decreased with increasing quantities of added P compound, and the HA treatment had the best effect at the level of 5000 mg of P kg(-1)as compared with other treatments in which the Pb concentrations in shoots of BO and BC decreased 51.9% and 65.5%, respectively, and the Pb concentrations in roots of BO and BC decreased 67.3% and 57.2%, respectively, as compared with the control treatment. The SSP treatment had little effect on the Pb concentrations in plant tissues. Sequential extraction results indicated that the addition of soil amendments transform soil Pb from nonresidual fractions to residual fraction substantially. The effect of treatments followed this order at the equivalent P addition: HA>PR>HA+SSP>SSP. The results suggested that HA amendments can lower the bioavailability and increase the geochemical stability of soil Pb, so it has the potential for in situ remediation in Pb-contaminated soils.