Transfer of radioactive caesium from soil to vegetation and comparison with potassium in upland grasslands

The distribution and transfer of caesium and potassium between soils and vegetation has been investigated by field sampling and experimental studies on soils and vegetation typical of upland grassland in north west England. Total (137)Cs content to a depth of 0.05 m below root matt ranged from 13 000 to 18 000 Bq m(-2). This caesium content derives from three sources: the Windscale accident of 1957, weapons-testing fallout which peaked in the early 1960s, and the Chernobyl accident in May 1986. From 2200 to 6200 Bq m(-2) is attributed to the first two sources, and the remainder to Chernobyl. In December 1986, 23-78% of pre-Chernobyl (137)Cs was associated with soil underlying root matt and 0.5-5.5% was associated with vegetation. Plant/soil concentration ratios for pre-Chernobyl (137)Cs were in the range 0.5-6.5, the lowest values being associated with patches of Festuca/Agrostis turf. At the same time, 4-19% of (137)Cs deposited from Chernobyl was associated with vegetation, although higher values appeared in conjunction with the moss, Polytrichum commune. Corresponding total potassium contents were in the range 9.6-22 mg m(-2) to 0.05 m soil depth. Lower values were found at the wetter sites where, on average, 5.7% of the total potassium was present in vegetation. At drier sites the potassium content was higher and, on average, 8.9% was present in vegetation. Plant/soil concentration ratios ranged from 2.2 to 9.2. During accelerated growth of vegetation, on monoliths in glasshouse conditions over the winter of 1986/87, (137)Cs was transferred from soil and root matt to new growth, such that concentrations in fresh growth were similar to or higher than those observed in the field during December 1986. Removal of caesium by successive cuts resulted in up to 25% of the original estimated total being removed over a 240 day period. Increased concentrations coincided with the emergence of Carex sp. and Trichophorum caespitosum, as well as the development of Agrostis sp. and Festuca ovina. Observed Cs/K discrimination ratios, particularly for (137)Cs deposited from Chernobyl, were higher than previously reported in the literature. The experimental results were confirmed by field observations during spring 1987 and it is concluded that caesium deposited as a result of the Chernobyl accident will continue to be recycled in organic and low potassium soils.     

Laboratory analyses of 137Cs uptake by sunflower, reed and poplar

The 137Cs uptake by three plant species (Phragmites australis L., Heliantus annus L., Populus simonii L.) was analyzed in a hydroponic medium (14 MBql(-1); 0.5 mM CsCl) during cultivation. The radioactivity disappearance from the medium was measured after 2, 4, 8, 16 and 32 days of cultivation. Radioactivity distribution within the plant was determined by autoradiography. We did not find differences between uptake of radioactive and stable caesium isotopes. Relations between the uptake of 137Cs and concentration of potassium and ammonium ions in medium were also tested. The highest uptake of radiocaesium by sunflower was obtained for medium with 1 mM K2SO4 (14.2%) and in case of ammonium ions for concentration ratio 6 mM NH4Cl : 3 mM NH4NO3 (13.2%). The obtained results make it possible to compare the capability and rate of 137Cs phytoremediation of different plant species.     

The occurrence and bioavailability of radioactive 137Cs in small forest lakes in Southern Finland

Following the Chernobyl accident in late April 1986, central Finland was subjected to considerable radioactive fallout. The radioactive isotope of caesium, (137)Cs, was potentially the most harmful isotope in the fallout because of its long half-life (30 years). (137)Cs activities remained unexpectedly low within the biota (algae, zooplankton, aquatic moss, fish) of some humic forest lakes in southern Finland compared to the clear water lakes within the same district. This observation suggested that humic substances, by binding (137)Cs chemically, may reduce its bioavailability in lake water. Our laboratory experiments (throughflow systems; gel chromatography) demonstrated that binding of (137)Cs by humic substances was negligible in untreated lake waters; only when most of the alkali metals had been removed with an ion exchange resin was any binding of (137)Cs by low molecular humic fractions apparent. Instead, the concentrations of cations (especially potassium) were of overwhelming importance for the bioavailability of (137)Cs within the lacustrine ecosystems. The concentrations of (137)Cs within food chains are expected to stay at a high level for many years especially in lakes with long water renewal times.     

The influence of season and leaf age on concentrations of radiocaesium (137Cs), stable caesium (133Cs) and potassium in Agrostis capillaris

The transfer of radioactive caesium from soils to plants has been well researched. In contrast there is limited knowledge on natural stable 133Cs and its potential role as a predictor for radiocaesium behaviour. In a pot experiment with Agrostis capillaris close correlations were found between plant 137Cs and plant 133Cs concentrations (R2 90-96%). Season and leaf age had significant effects with concentrations increasing 10-30-fold between June and December. Simultaneously the plant concentrations of K, the nutrient analogue of Cs, decreased to around one third. In the soil the exchangeable fractions of K and 137Cs declined. No clear relationships were found between 137+133Cs in the plant and exchangeable K in the soil. However, at the end of the experiment the K content of the above-ground biomass was higher than the exchangeable pool in the soil, suggesting that depletion of soil K could be a key factor in the observed increase of plant 137+133Cs over time.     

Earthworms and radionuclides, with experimental investigations on the uptake and exchangeability of radiocaesium

The potential influence of earthworm activity on the mobility of radionuclides in soils and their subsequent availability for uptake by plants and transfer to higher trophic levels is briefly reviewed. The accumulation of caesium by the earthworm Aporrectodea longa from soil and from plant litter was investigated in laboratory experiments, as was the effect of reworking (through burrowing and ingestion) soil and soil with added organic material, on the extractability of caesium (ammonium acetate extraction). Soil was spiked with (134)Cs, organic matter with (137)Cs. In soil-fed worms, most of the radioactivity measured was eliminated with the gut contents; 5-25% of the ingested radioactivity was retained or assimilated. Loss of caesium from soil-fed worms followed a two component curve, with an initial rapid loss due to gut clearance (half-life of loss (Tb1/2) of about 0.2-0.6 days) and a slower loss of assimilated caesium (Tb1/2 of 15-26 days). Loss rates of assimilated caesium from worms fed on fragmented apple leaves were found to have half-lives of 18-54 days. Assimilation of caesium from apple leaves was higher than from soil, ranging from 55-100% of the activity measured before gut clearance. Dry weight transfer factors (concentration in worm tissue/concentration in substrate) for worms cleared of their gut contents were similar for the two substrates 0.04 and 0.04 for two loss experiments with worms fed on radioactive soil, and 0.03 and 0.05 for worms fed on apple leaves. After three months of reworking soil and soil/organic mixtures, A. longa was found to have no measurable effect on the extractable fraction of caesium. If earthworms have any subtle effects they were masked by changes in availability that occurred when the spiked soil and organic substrates were mixed together. Only about half of the extractable fraction in soil was recovered when soil was mixed with organic material suggesting that some of the labile fraction in soil had become complexed with organic material. This exchange occurred in substrate mixtures with and without worms. The limitation of chemical extraction procedures is discussed and suggestions for further work are presented.     

Distribution of fission products in dust samples from the region of Thessaloniki, Greece, after the Chernobyl nuclear accident

The distribution of the fission products (95)Zr, (95)Nb, (103)Ru, (106)Ru (determined through (106)Rh), (125)Sb, (129m)Te, (134)Cs, (137)Cs, (140)Ba, (140)La, (141)Ce and (144)Ce has been determined in dust samples from the region of Thessaloniki, Greece, after the nuclear accident at Chernobyl. The samples studied also included (110m)Ag, not belonging to the products of (235)U fission. Samples showing higher concentrations of radionuclides also show a higher content in clay minerals, whereas samples having low concentrations of radionuclides usually contain large amounts of quartz and feldspars. Desorption and leaching experiments using solutions of chlorides of sodium, potassium, calcium and magnesium (0.5 N), as well as distilled and tap water, were also performed. Sodium and potassium chloride solutions were found to be efficient in desorbing and/or leaching of caesium and ruthenium isotopes to an extent of about 30%.     

Radiocaesium activity concentrations in potatoes in Croatia after the Chernobyl accident and dose assessment

Systematic investigations of (137)Cs and (134)Cs activity concentrations in potatoes (Solanum tuberosum) for the post-Chernobyl period (1986-2005) in the Republic of Croatia are summarized. The correlation between (137)Cs activity concentrations in fallout and potatoes, has been found to be very good, the correlation coefficient being r = 0.88 with P(t) < 0.001 for 18 degrees of freedom. As the radiocaesium levels in potatoes decreased exponentially, the mean residence time of (137)Cs in potatoes was estimated by fitting the measured activity concentrations to the exponential curve. The mean residence time was found to be 6.8 +/- 1.1 years, the standard deviation being estimated by the Monte Carlo simulations. The initial observed (134)Cs:(137)Cs activity ratio in potatoes has been found to be quite variable, but slightly lesser than the theoretically predicted value of 0.5, calculated by applying the known inventory of these radionuclides in the Chernobyl reactor to the equation for the differential radioactive decay. This can be explained by presence of the pre-Chernobyl (137)Cs in soil that originated from nuclear fallout. The annual effective doses received by (134)Cs and (137)Cs intake due to consumption of potatoes estimated for an adult member of the Croatian population were found to be very small, as the per caput Dose for the entire 1986-2005 period was calculated to be about 2.9 microSv, (134)Cs accounting approximately for 1/3 of the entire dose. Therefore, after the Chernobyl accident consumption of potatoes was not the critical pathway for human intake of radiocaesium from the environment in Croatia.     

Caesium concentration factors in wild herbivores and the fox (Vulpes vulpes L)

A selection of wild animals was sampled in the winter of 1986/87. The sites chosen for sampling were based on information obtained from survey carried out by The Institute of Terrestrial Ecology in the spring and autumn of 1986. Animals included deer, grouse, hares and rabbits, and foxes which were collected as a top carnivore in the food chain. Variation in concentration of caesium between species from the same area was unpredictable; rabbits, for instance, never exceeded 200 Bq kg(-1) (fresh wt) of (137)Cs in their flesh, even when adjacent to deer forests with over 1000 Bq kg(-1) in the venison. The greatest complication grose from areas of peaty uplands where the pre-Chernobyl (137)Cs from weapons-testing was much higher than expected. This pre-Chernobyl contribution amounted to 630 Bq kg(-1) in a red grouse from the Pennines, and 650 Bq kg(-1) in a roe deer from near the Borders, being c. 60% of the total. Concentration factors were calculated using values from freshly ingested vegetation and tissues from individual animals. Significant differences in concentration factors were found depending on species, food, sex, breeding condition and age. Contrasting the decrease of the two caesium isotopes in roe deer from forestry on peat with those from woodlands on mineral soils, it appeared that after an initial fall in concentration, the only decrease thereafter occurred on the mineral soils. Nowhere were radiocaesium concentrations high enough to cause concern amongst consumers of game and other wild animals, even when levels exceed 3000 Bq kg(-1) (fresh wt) as they did in red deer, red grouse and the blue hare.     

Dynamic equilibrium of radiocesium with stable cesium within the soil-mushroom system in Turkish pine forest

Mushrooms and soils collected from pine forests in Izmir, Turkey were measured for radiocesium and stable Cs in 2002. The ranges of (137)Cs and stable Cs concentrations in mushrooms were 9.84+/-1.67 to 401+/-3.85Bqkg(-1) dry weight and 0.040+/-0.004 to 11.3+/-1.09mgkg(-1) dry weight, respectively. The concentrations of (137)Cs and stable Cs in soils were 0.29+/-0.18 to 161+/-1.12Bqkg(-1) dry weight and 0.14+/-0.004 to 1.44+/-0.045mgkg(-1) dry weight, respectively. Even though different species were included, the concentration ratios of (137)Cs to stable Cs were fairly constant for samples collected at the same forest site, and were in the same order of magnitude as the (137)Cs to stable Cs ratios for the organic soil layers. The soil-to-mushroom transfer factors of (137)Cs and stable Cs were in the range of 0.19-3.15 and 0.17-12.3, respectively. The transfer factors of (137)Cs were significantly correlated to those of stable Cs.     

Accumulation history of radionuclides in the lichen Stereocaulon vesuvianum from Mt. Vesuvius (south Italy)

The fruticose lichen Stereocaulon vesuvianum, growing on the slopes of Mt. Vesuvius (south Italy), was used as a biomonitor of 134Cs, 137Cs, 103Ru and 106Ru derived from the April 26 1986 Chernobyl nuclear reactor accident. Samples were taken at five different quotes (370, 490, 580, 780 and 960 m a.s.l.) and four successive dates (October 1986, December 1986, October 1987 and May 1999). At the first sampling, the concentrations (as Bq kg(-1) dry weight) ranged between 460 and 1020 for 134Cs, 1330 and 2500 for 137Cs, 90 and 200 for 103Ru and 360 and 710 for 106Ru, values generally lower in respect to those measured in soil and higher plants. Of the total 137Cs measured only 14% was due to 1950s and 1960s nuclear weapons tests fallout. Highest average activities of all nuclides were observed at the quote of 960 m and significant correlation (0.7相似文献   

Uptake of 134Cs in the shoots of Amaranthus tricolor and Amaranthus cruentus

Amaranthus tricolor L. and Amaranthus cruentus L. were grown in pots containing 7.5 kg soils artificially contaminated with three levels of 134Cs activity: 5.55 x 10(5) Bq pot-1, 1.11 x 10(6) Bq pot(-)1, and 1.665 x 10(6) Bq pot(-1), respectively. Forty-nine days after sowing and growth, plants were harvested. The plants growing in soils with increasing 134Cs concentrations showed increasing concentration of this radionuclide in shoots. There were significant differences in uptake of 134Cs applied to soils between and within the plant species, depending on the initial 134Cs concentrations. The plant species showed different responses to the addition of (NH4)2SO4 to soils. Biomass production of both species was reduced in pots treated with (NH4)2SO4. (NH4)2SO4 application decreased the uptake of 134Cs by A. tricolor but increased the accumulation of 134Cs by A. cruentus, showing that chemicals with the highest efficiency to enhance the desorption of 134Cs might play an unexpected role in transferring the radionuclide to shoots.     

Radioactive isotopes in atmospheric aerosols over Russia and the Sea of Japan following nuclear accident at Fukushima Nr. 1 Daiichi Nuclear Power Station in March 2011

Artificial radionuclides, such as iodine-131 (¹³¹I), cesium-134 (¹³⁴Cs), and cesium-137 (¹³⁷Cs), as well as natural isotopes of beryllium-7 (⁷Be) and potassium-40 (⁴⁰K) have been registered in atmospheric aerosols over Vladivostok selected from 11 March to 17 June 2011. Additionally, ¹³⁴Cs and ¹³⁷Cs were detected in atmospheric aerosols over Tomsk selected from 16 March to 17 June 2011. Artificial radionuclides were also discovered in atmospheric wet depositions sampled in Vladivostok from 3 to 17 May 2011. Moreover, these radionuclides have been registered in atmospheric aerosols over the sea surface of the Sea of Japan selected from 3 to 31 May 2011 during an expedition of the “Nadezhda” sailing ship. From 18 March to 15 April, an increase in concentrations of atmospheric aerosols over Vladivostok from 108.8 to 321.5 μg/m³ has been registered. It was accompanied by increased activity concentrations of ¹³⁴Cs, ¹³⁷Cs, and the ¹³¹I. During the period from 18 March to 15 April, activity concentrations of ¹³⁷Cs and ¹³⁴Cs in atmospheric aerosols increased 100 times compared with the minimum detectable concentration (MDC) level and peaked in the weekly sample gathered from 8 to 15 April (145.0 and 105.3 μBq/m³, respectively). Variability of concentrations of natural isotopes of ⁷Be and ⁴⁰K was not greater than 1 order of magnitude throughout the sampling period. Maximal values of ¹³⁷Cs and ¹³⁴Cs concentrations (1,281.5?±?141 and 384.4?±?42.3 μBq/m³, respectively) in Tomsk were reached in samples taken from 1 to 2 April. For the atmospheric aerosol samples from the Sea of Japan, the largest concentration of ¹³¹I (392.3?±?215.7 μBq/m³) was detected from 13 to 19 May, while all other samples had much lower concentration values. Synoptic analysis of back trajectories movement of air masses showed that the radioactive cloud came to Vladivostok from the regions of Siberia and northeastern part of China. Synoptic analysis for Tomsk showed that during the period of maximal activity concentrations (1–9 April), air masses were arriving from the European part of Russia and north of Kazakhstan.     

Ecological half-life of caesium in roe deer (Capreolus capreolus)

Biological half-lives for various radionuclides have been determined for many animals kept in the laboratory or under controlled conditions. Only occasionally has been it possible to determine the ecological half-lives of radionuclides in wild animals, where the contamination has occurred in their natural habitats. Following the fallout from the Chernobyl accident and its subsequent ingestion by wildlife, no one knew how long it would take the wild animals to eliminate the radionuclides, and in particular radiocaesium, from their bodies. In this study of roe deer (Capreolus capreolus), bucks (males)were shot at weekly/fortnightly intervals from mid-May till the end of July, as part of the annual cull on an area, which included some young forestry (Stone Chest-National Grid Reference NY48090), planted in 1971/72. The ration of 137Cs:134Cs, typical of the Chernobyl fallout, was seldom observed in these animals due to the highly variable concentrations of 137Cs originating from bomb fallout. Therefore, 134Cs was used instead because its presence was almost entirely due to the Chernobyl fallout. After using log10 transformation of the 134Cs concentrations, a significant (p < 0.01) regression was obtained which accounted for 85% of the variation. From the regression, the ecological half-life for 134Cs was found to be 28.3 days.     

Uptake of radionuclides by vegetation at a High Arctic location

Radionuclide levels in vegetation from a High Arctic location were studied and compared to in situ soil concentrations. Levels of the anthropogenic radionuclide 137Cs and the natural radionuclides 40K, 238U, 226Ra and 232Th are discussed and transfer factor (TF) values and aggregated transfer (Tag) values are calculated for vascular plants. Levels of 137Cs in vegetation generally followed the order mosses > lichen > vascular plants. The uptake of 137Cs in vascular plants showed an inverse relationship with the uptake of 40K, with 137Cs TF and Tag values generally higher than 40K TF and Tag values. 40K activity concentrations in all vegetation showed little correlation to associated soil concentrations, while the uptake of 238U, 226Ra and 232Th by vascular and non-vascular plants was generally low.     

生物对137Cs的吸收和富集

螺蛳等供试生物能很快地吸收水体中的＾１３７Ｃｓ,并随着时间的延长而不断增加,吸收过程可用直线方程来表达,螺蛳、喜旱莲子草和金鱼藻可以用来净化被＾１３７Ｃｓ的吸收较少,其中稗草和喜旱莲子草较高;由于Ｋ＾＋与Ｃｓ＾＋之间的拮抗作用,帮可用施钾肥方法减少作物以土壤中＾１３７Ｃｓ的吸收。     

Constraints on the use of 137Cs as a time-marker to support CRS and SIT chronologies

CRS and SIT are two (210)Pb-based models widely used in the radiometric dating of recent sediments. (210)Pb chronologies should be validated using at least one independent tracer, such as (137)Cs. This paper demonstrates that simple methods based on the identification of (137)Cs fallout peaks cannot provide a definitive support for CRS and SIT chronologies. Two main arguments will support this assertion: Firstly, the (137)Cs time-marks cannot support a CRS or SIT chronology if the derived sedimentation rates cannot explain the whole (137)Cs activity profile without postulating mixing. Secondly, the support by the (137)Cs time-marks for a given CRS or SIT chronology cannot be considered as definitive if other dating models can equally explain the whole set of data, thereby producing a different chronology. Several case studies selected from the literature are used to support the present discussion.     

Excess plutonium in soil near the Nevada Test Site,USA

Two soil profiles were collected from undisturbed areas near the Nevada Test Site (NTS). The activity of 137Cs in the surface layer of the downwind Queen City Summit profile is three times higher than at the upwind site at Searchlight, NV (41.1+/-0.6 mBq/g vs. 13.0+/-0.4 mBq/g), and the 239,240Pu activity is 100 times greater (51+/-2 mBq/g vs. 0.52+/-0.03 mBq/g). An examination of the literature suggests that the 137Cs/239,240Pu and the 239,240Pu/238Pu activity ratios in soils and sediments from the northern hemisphere, due to fallout from atmospheric atomic weapons testing, have generalized values of 36+/-4 and 30+/-4, respectively (as of 1 July 1995). Deviations from these values may indicate possible contamination by sources other than fallout. Data from the surface soil of the downwind Queen City Summit profile yield a 137Cs/239,240Pu ratio of 0.81+/-0.02 and a 239,240Pu/238Pu ratio of 78+/-6. Clearly, an increase in 239,240Pu relative to 137Cs or 238Pu can account for these observations. There is compelling evidence that this "excess" 239,240Pu came from activities at the NTS during the aboveground testing of nuclear devices, more than likely from safety tests, some 40 years ago, and/or during the interim by the wind-driven resuspension of contaminated surface soil on the NTS and its transport off-site. Moreover, the two concentration profiles show that high percentages of both of these elements are retained for decades in the upper few centimeters of soil in Nevada's desert environment.     

Effects of Cd and Zn waterborne exposure on the uptake and depuration of 57Co, 110mAg and 134Cs by the Asiatic clam (Corbicula fluminea) and the zebra mussel (Dreissena polymorpha)--whole organism study

Groups of zebra mussels (Dreissena polymorpha) and asiatic clams (Corbicula fluminea) were exposed to cadmium and zinc with the aim of studying the effect of these metals on the 57Co, 110Ag and 134Cs uptake and depuration by these freshwater bivalves. In the presence of zinc, the 57Co concentration factor for the whole organism of the two species was halved, notably because of a decrease of the uptake parameter. Conversely, Zinc and the Cd + Zn mixture increased the 110mAg uptake process by clams and mussels. The two metals also increased the depuration of this radionuclide in mussels, whereas this phenomenon was only observed in clams exposed to cadmium. In comparison with 57Co and 110mAg, the 134Cs bioconcentration was 5-10 times lower in D. polymorpha and not detected in C. fluminea. This weak contamination by this radionuclide resulted from a lower uptake and a higher depuration parameters.     

Effect of ectomycorrhizae and ammonium on 134Cs and 85Sr uptake into Picea abies seedlings

Microorganisms play an important role in the fixation of radionuclides in forest soils. In particular, fungi have the capacity to absorb and translocate radionuclides. The role of the ectomycorrhizal fungus Hebeloma crustuliniforme in the uptake of radiocaesium (134Cs) and radiostrontium (85Sr) into seedlings of Norway spruce (Picea abies) was investigated in a pouch test system. Inoculated and non-inoculated seedlings; seedlings inoculated during 8 and 15 weeks; seedlings exposed during 2 and 3 weeks to the radioactive solution; and seedlings grown under low and high ammonium conditions prior to the application of the radionuclides were compared. The final 134Cs and 85Sr activity was determined in fine-roots, main-roots, stems and needles. The results showed that ectomycorrhizae reduced the uptake of 134Cs and 85Sr. The degree of ectomycorrhization was of crucial importance and seemed to be governed by the period during which ectomycorrhizae were allowed to develop and by the ammonium concentration in the nutrient solution. The radionuclide uptake increased with increasing exposure time. Both radionuclides were predominantly accumulated in fine-roots. However, needles proved to describe best the result of net root uptake and translocation to the shoot. The uptake-and and translocation-rates of 85Sr were smaller than those of 134Cs. It is assumed that the translocation is coupled with the intensity of water fluxes through the xylem and that 85Sr is more readily adsorbed into mycelium or plant tissue relative to 134Cs. The effect of high ammonium growth conditions was overcome by the effect of ectomycorrhization, except in needles with a very large biomass which behaved as a strong sink and led to a high accumulation of 134Cs.     

Radiocaesium from Chernobyl in Swedish moose

The (137)Cs activity concentrations of muscle samples taken from moose collected from the central part of Sweden were determined. Pre-Chernobyl samples had a mean (137)Cs activity concentration of 23 Bq kg(-1). Samples collected during the hunting season (mainly October) had, on average, 760 Bq kg(-1) in 1986 and 664 Bq kg(-1) in 1987. No significant differences between various muscles (neck, thigh and leg) could be seen. The correlation between ground deposition of (137)Cs and activity concentration in moose muscle was significant. There seems, however, to be other important parameters. One is the percentage of farmland within the home range of the moose-less farmland gives higher (137)Cs activity concentrations.