Preliminary evaluation of (135)Cs/(137)Cs as a forensic tool for identifying source of radioactive contamination

Ratios of the fission products (135)Cs and (137)Cs were determined in soil and sediment samples contaminated from three different sources, to assess the use of (135)Cs/(137)Cs as an indicator of source of radioactive contamination. Soil samples from the Chernobyl exclusion zone were found to have to be heavily depleted in (135)Cs ((135)Cs/(137)Cs approximately 0.45), indicative of a high thermal neutron flux at the source. Sludge samples from a nuclear waste treatment pond were found to have a (135)Cs/(137)Cs ratio of approximately 1, whereas sediment collected downstream from a nuclear reactor was highly variable in both (137)Cs activity and (135)Cs/(137)Cs ratio. Comparison of these preliminary results of variability in radiocaesium isotope ratios with reports of Pu isotope ratios suggests (135)Cs/(137)Cs similarly varies with fuel and reactor conditions, and may be used to corroborate other methods of characterizing radioactive contamination.     

Evidence of the radioactive fallout in the center of Asia (Russia) following the Fukushima Nuclear Accident

It was recently reported that radioactive fallout due to the Fukushima Nuclear Accident was detected in environmental samples collected in the USA and Greece, which are very far away from Japan. In April-May 2011, fallout radionuclides (¹³⁴Cs, ¹³⁷Cs, ¹³¹I) released in the Fukushima Nuclear Accident were detected in environmental samples at the city of Krasnoyarsk (Russia), situated in the center of Asia. Similar maximum levels of ¹³¹I and ¹³⁷Cs/¹³⁴Cs and ¹³¹I/¹³⁷Cs ratios in water samples collected in Russia and Greece suggest the high-velocity movement of the radioactive contamination from the Fukushima Nuclear Accident and the global effects of this accident, similar to those caused by the Chernobyl accident.     

Global Radioactive Contamination Background in Terrestrial Ecosystems 13 Years after the Chernobyl Accident

The contents of ¹³⁷Cs in the soil, plant, and animal samples collected in the ecosystems of protected areas from the White Sea to the Black Sea in 1999 slightly differ from those in the period between 1980 and 1984. As a result of global fallout after the Chernobyl accident, the content of radioactive cesium in the soil has increased only on the territory of the Biological Station of Moscow State University at the White Sea, whereas that in the litter and plants has increased in virtually all areas studied. The isotope content in animals is actually equal to that recorded between 1980 and 1984. The mobility of ¹³⁷Cs in the soil–plant link has increased, which may be due to fallout after the accident. The duration of a complete radionuclide cycle in ecosystems decreases from 10 half-life periods in northern regions to 2.5 half-life periods in the southern regions. The Chernobyl disaster has caused no significant changes in the global radioactive background in the European part of the Russian Federation.     

Transfer of Chernobyl-derived 134Cs, 137Cs, 131I and 103Ru from flowers to honey and pollen

The activity concentrations of ¹³⁷Cs, ¹³⁴Cs, ¹³¹I and ¹⁰³Ru were determined separately in honey and pollen samples collected from a single bee colony during several months after the deposition of Chernobyl fallout. The source of each honey and pollen sample was determined by pollen analysis. Although the activity concentrations in honey and pollen varied with time, the concentrations of ¹³⁷Cs and ¹³⁴Cs were, in general, higher in pollen than in honey. For ¹⁰³Ru and ¹³¹I, these differences were comparatively small. The mean ¹³¹ I/¹³⁷Cs and ¹⁰³Ru/¹³⁷Cs ratios were about one order of magnitude higher in honey than in pollen. The mean ¹³¹I/¹⁰³Ru ratio was about the same for honey and pollen. This observation, in the light of the corresponding nuclide ratios found in the deposition, suggests that ¹³⁷Cs, ¹³⁴Cs, ¹³¹I and ¹⁰³Ru were taken up by the plant leaves and transported to nectar and pollen. The higher activity concentrations of ¹³⁷Cs and ¹³⁴Cs in pollen, relative to honey, indicate that these radionuclides behave analogously to potassium, which is also found in higher quantities in pollen.     

Arctic cushion plants as fallout ‘monitors’

The internal distribution of fallout ¹³⁷Cs was determined for arctic cushion plants Dryas integrifolia, Silene acaulis and the bryophytes Rhacomitrium lanuginosum and Polytrichum juniperinum collected at various latitudes in the Canadian Arctic. The results indicate that these plants have functioned as biological monitors of radioactive fallout and it is suggested that analysis of the internal distribution of ¹³⁷Cs could serve as a model for other airborne contaminants.     

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.     

Fallout in the New York metropolitan area following the chernobyl accident

In the metropolitan New York area, maximum concentrations in air of radioactive aerosol and gaseous debris from the Chernobyl accident of April 1986 were much lower than those measured in Europe. The observed maxima were: for gaseous ¹³¹I, 23mBq m⁻³; for aerosol samples, 20mBq m⁻³ of ¹³¹I and 9·mBq m⁻³ of ¹³⁷Cs. The data suggest that little gas-to-particle transformation of iodine occurred during transport of the radioactive cloud from the Ukraine to New York. The ratios of ¹⁰³Ru and other refractories to ¹³⁷Cs were low in the first debris sampled, debris which probably was emitted from Chernobyl in late April during the early stages of the accident. In subsequent samples these ratios were higher, presumably because debris from the later, hotter stages of the fire had reached our sampling sites. A significant fraction (25–40%) of the deposition of ¹³¹I and ¹³⁷Cs into our samplers and on grass was by dry deposition. The total deposition of Chernobyl ¹³⁷Cs in the area was <1% of that already present in the soil from fallout from past nuclear weapon tests. The highest concentration of ¹³¹I measured in fresh milk was about 1.5 B1 liter⁻¹, <0.1% of the US action level. The dose to the thyroid of a six-month-old infant who had fresh milk as a sole food source would be about 70 μGy (7 mrad).     

The simulation of long-range transport of ¹³⁷Cs from East Asia to Japan in 2002 and 2006

To evaluate the quantities of ¹³⁷Cs from past nuclear tests being transported to and deposited in Japan by naturally-occurring phenomena, the authors developed long-range transport models for ¹³⁷Cs considering Asian dust. The simulation using these models backed the observed recent increase of ¹³⁷Cs deposition along the coast of the Sea of Japan in early spring. For the sake of public safety, it is vital to ascertain whether an increase of radioactive deposition is caused by natural phenomena or a nuclear accident. The observations in recent years have suggested that dust and soil containing ¹³⁷Cs is transported from the regions around Inner Mongolia to Japan by the wind. In this paper, using observation data from the early spring of 2002 and 2006, the authors have found good agreement between the simulations and the measurements. The simulations reproduced the entrainment of ¹³⁷Cs and subsequent transport to Japan caused by strong winds associated with low pressure areas around the Inner Mongolian grasslands. The most likely cause of high-level ¹³⁷Cs deposition over northern Japan during March 2002 was ¹³⁷Cs associated with particles transported at low-altitude (1 km) and subjected to precipitation on the 22nd to 24th.     

C, δC and total C content in soils around a Brazilian PWR nuclear power plant

Nuclear power plants release ¹⁴C during routine operation mainly as airborne gaseous effluents. Because of the long half-life (5730 years) and biological importance of this radionuclide (it is incorporated in plant tissue by photosynthesis), several countries have monitoring programs in order to quantify and control these emissions. This paper compares the activity of ¹⁴C in soils taken within 1 km from a Brazilian nuclear power plant with soils taken within a reference area located 50 km away from the reactor site. Analyses of total carbon, δ¹³C and ¹³⁷Cs were also performed in order to understand the local soil dynamics. Except for one of the profiles, the isotopic composition of soil organic carbon reflected the actual forest vegetation present in both areas. The ¹³⁷Cs data show that the soils from the base of hills are probably allocthonous.     

Adsorption models of Cs radionuclide and Sr (II) on some Egyptian soils

Distribution of cesium (¹³⁴Cs and ¹³⁷Cs) and strontium (Sr-II) between soil/water phases depends on many factors such as concentration of these ions between phases, the cation exchange capacity (CEC) of the soil as well as its clay content, chemical composition (especially Na, K, Ca, and Mg ions), grain size distribution, calcite, iron oxide content, and organic coatings. Distribution coefficients (Kd) of cesium (labeled with ¹³⁷Cs) and strontium were measured on the grain size distributions ≥32 μm of four soil samples. These soils were obtained from four different locations within Inshas site in Egypt and three groundwater samples were obtained from the same site locations. X-ray diffraction showed that the soil samples consisted mainly of quartz mixed with the minor amounts of kaolonite and clay minerals. Sorption experiments were carried out at strontium aqueous concentrations range 10⁻⁷ to 10⁻⁴ mol l⁻¹. The CEC and Kds for cesium and strontium were measured at the same metal concentrations range. Distribution coefficients of cesium were found to be influenced by the composition of the soil, while the distribution coefficients of strontium were found to depend on calcium concentrations in the soil/groundwater system. The aim of this study was to determine the safety assessment of disposal ¹³⁷Cs radionuclide and Sr(II) in the aquifer regions inside the Inshas site. Sequential extraction tests showed that, strontium was associated with the carbonate fractions and majority of cesium was sorbed on the iron oxides and the residue.     

Recent levels of radionuclides in lichens from southwest Poland with particular reference to 134Cs and 137Cs

Analyses of Umbilicaria species collected from southwest Poland in August 1986 have shown there to be significant increases in levels of various radionuclides since previous analyses based on fieldwork in 1978–1979. The composition and ratio of the various radionuclides, particularly in respect of ¹³⁴Cs and ¹³⁷Cs, exhibit a characteristics signature consistent with contamination derived from the accident at the Chernobyl nuclear reactor in April 1986. Intraspecific variation in levels of ¹³⁷Cs in Umbilicaria is related to such factors as location, altitude and, to a lesser degree, aspect; interspecific variation in levels is related to ecological requirements and geographical pattern, and hence the same factors, although morphological differences in thalli may be implicated.     

Concentrations of long-lived artificial radionuclides in the moss-lichen cover of mountain plant communities

Specific features of⁹⁰Sr and¹³⁷Cs accumulation in individual lichen species and in the moss-lichen cover of plant communities were studied in some mountain ranges of the Polar and Northern Urals. The results showed that the amounts of radionuclides in lichens and mosses of mountain plant communities are at the level characteristic of the moss-lichen cover of flat ecosystems, and their accumulation depends on⁹⁰Sr and¹³⁷Cs input with the global radioactive fallout. The radionuclide contents in lichens and mosses sampled from different mountain rocks, slopes, and elevations fluctuate around this level. The differences depend both on the structural and functional properties of plants and on the climatic and ecological features of their environment.     

Concentrations of (137)Cs in summer pasture plants that reindeer feed on in the reindeer management area of Finland

Samples of summer pasture plants that reindeer feed on were collected in order to study ¹³⁷Cs concentrations in different plant species and in species nested in certain site types, and to study the regional distribution of ¹³⁷Cs in the Finnish reindeer management area. Plant species were categorized by the site types of mineral soil forest (xeric heath forest and mesic heath forest) and peatland. A third category called ’other plant species’ included plants with various site types, poorly determined species and species with poor statistics. The ¹³⁷Cs concentrations in different site types differed significantly. The mean ¹³⁷Cs concentrations of the whole reindeer management area in the xeric heath forest plant species was 44 ± 27 Bq/kg dw, in the mesic heath forest plant species 75 ± 59 Bq/kg dw and in the peatland plant species 219 ± 150 Bq/kg dw. The peatland species uptake ¹³⁷Cs more efficiently than plant species of mineral soil forests. A particularly efficient collector of ¹³⁷Cs was Trichophorum sp. It is suggested that Trichophorum sp. could be used as an indicator species for reindeer summer fodder plants. The highest concentrations of ¹³⁷Cs were found in Southern Lapland and the lowest in Northern Lapland. Today, the concentrations of ¹³⁷Cs in summer pasture plants that reindeer feed on in Finland are at such a level that there is no need to avoid any plant species. In the case of future nuclear fallout, reindeer grazing in peatlands would increase concentrations of ¹³⁷Cs in reindeer meat.     

Vertical distributions of (99)Tc and the (99)Tc/(137)Cs activity ratio in the coastal water off Aomori, Japan

Using a sector-field ICP-MS the vertical distributions of the ⁹⁹Tc concentration and ⁹⁹Tc/¹³⁷Cs activity ratio were measured in the coastal waters off Aomori Prefecture, Japan, where a spent-nuclear-fuel reprocessing plant has begun test operation. The ⁹⁹Tc concentrations in surface water ranged from 1.8 to 2.4 mBq/m³, no greater than the estimated background level. Relatively high ⁹⁹Tc/¹³⁷Cs activity ratios (10-12 × 10⁻⁴) would be caused by the inflow of the high-⁹⁹Tc/¹³⁷Cs water mass from the Japan Sea. There is no observable contamination from the reprocessing plant in the investigated area. The ⁹⁹Tc concentration and the ⁹⁹Tc/¹³⁷Cs activity ratio in water column showed gradual decreases with depth. Our results implied that ⁹⁹Tc behaves in a more conservative manner than ¹³⁷Cs in marine environments.     

Fukushima fallout in Northwest German environmental media

Traces of short- and long-lived fallout isotopes (¹³¹I, ¹³⁴Cs and ¹³⁷Cs) were found in environmental samples collected in Northwest Germany (rain water, river sediment, soil, grass and cow milk) from March to May 2011, following the radioactivity releases after the nuclear accident in Fukushima, Japan. The measured concentrations are consistent with reported concentrations in air, amount of rainfall and expected values applying simple radioecological models. The [¹³⁴Cs]/[¹³⁷Cs] ratio reported for air (about 1) allows for discrimination between “recent” and “old” ¹³⁷Cs. Expected ¹³⁶Cs values fell below the detection limits of the instrumentation, despite large sample masses and long counting times.     

Dynamic model for radionuclide uptake in lichen

Samples of atmospheric particulate material and terrestrial plants, including lichens, were collected in New Brunswick, Canada between 1980 and 1983 and analyzed for a wide range of artificial and naturally-occuring radionuclides, including fission products (¹⁴¹Ce, ¹⁴⁴Ce, ¹⁰³Ru, ¹⁰⁶Ru, ⁹⁵Zr and ¹³⁷Cs) derived from the 16 October 1980 Chinese nuclear test. Activity ratios of some of the short-lived fission products in air particulates and lichens are in reasonable agreement with those predicted from fission product yields for nuclear weapons tests, indicating that only minor fractionation occurred for these radionuclides during their transport through air particulate and lichen environmental phases. The ⁷Be inventories measured in a suite of lichen (Cladonia rangiferina) samples were used to calibrate each lichen plant for its collection efficiency for atmospheric particulates and fallout radioactivity.A lichen model has been developed to predict lichen inventories of radioactivity for different lichen growth functions and bio-elimination rates. Assuming that lichen growth results in a linear increase in surface area with time, the experimental results yield biological residence times of 1–2 years for ²¹⁰Pb and Pu and 5–8 years for ¹³⁷Cs. The more efficient retention of ¹³⁷Cs is probably due to its physiological uptake in lichen plants as a proxy for potassium, as evidenced by an observed, inverse relationship between ¹³⁷Cs and ⁴⁰K activities in lichen.     

Radioactivity in surface air and precipitation in Japan after the Chernobyl accident

Radioactive plumes from the Chernobyl reactor accident first passed over Japan on 3 May 1986. Measurements of ¹⁰³Ru, ¹³¹I and ¹³⁷Cs in rainfall and airborne dust collected at Chiba near Tokyo show that, in fact, at least two or more kinds of plume arrived during May. Their altitudes were calculated to be about 1500 m in early May and 6300 m in late May.Radionuclides detected in 33 precipitation samples collected by the network of prefectural radiation monitoring stations from 1 to 22 May were ⁷Be, ⁸⁹Sr, ⁹⁵Sr, ⁹⁵Zr, ⁹⁵Nb, ¹⁰³Ru, ¹⁰⁶Ru, ^110mAg, ¹²⁵Sb, ^129mTe, ¹³¹I, ¹³²Te, ¹³²I, ¹³⁴Cs, ¹³⁶Cs, ¹³⁷Cs, ¹⁴⁰Ba, ¹⁴⁰La, ¹⁴¹Ce and ¹⁴⁴Ce, the measurements being made using germanium detectors and low-background GM counters after radiochemical separation. The radiation was characterized by higher levels of the volatile nuclides, such as ¹⁰³Ru (in the form of RuO₂), ¹³²Te, ¹³¹I and ¹³⁷Cs, than fallout levels in nuclear weapons testing, and by activity ratios of 0·48 and 14 for, respectively, ¹³⁴Cs/¹³⁷Cs and ⁸⁹Sr/⁹⁰Sr, as on 26 April. The fallout activity was higher in northwestern Japan, the average depositions of ⁹⁰Sr and ¹³⁷Cs in Japan from 1 May (or 30 April) to 22 May being 1·4 Bq m⁻² and 95 Bq m⁻², inventories which are 14 and 550 times higher than the pre-Chernobyl values.     

Foliar uptake of Cs from the water column by aquatic macrophytes

A transplant experiment was performed to determine the relative importances of root uptake from the sediments and foliar uptake from the water column in determining the accumulation of ¹³⁷Cs by aquatic macrophytes. Uncontaminated individuals of three species, Brasenia schreberi, Nymphaea odorata and Nymphoides cordata, were transplanted into pots containing either contaminated sediments (i.e. 1.2 Bq ¹³⁷Cs g⁻¹ dry mass) or uncontaminated sediments (i.e. < 0.1 Bq g⁻¹ dry mass) and immersed in Pond B, a former reactor cooling pond where ¹³⁷Cs concentrations in surface waters range from 0.4 to 0.8 Bq liter⁻¹. The plants in uncontaminated sediments rapidly accumulated ¹³⁷Cs from the water column and after 35 days of immersion had ¹³⁷Cs concentrations in leaves that were: (1) not statistically significantly different from those for plants in contaminated sediments; and (2) similar to those for the same species growing naturally in Pond B. The similarity in ¹³⁷Cs concentrations between naturally-occurring plants and those in pots with uncontaminated sediments suggests that foliar uptake from the water column is the principal mode of Cs accumulation by these species in Pond B.     

Inventories of Pu, Cs, and excess Pb in sediments from freshwater and brackish lakes in Rokkasho, Japan, adjacent to a spent nuclear fuel reprocessing plant

We investigated the vertical profiles of ^239+240Pu, ¹³⁷Cs, and excess ²¹⁰Pb (²¹⁰Pb_ex) in sediment core samples obtained from two freshwater lakes and two brackish lakes situated near the first commercial spent nuclear fuel reprocessing plant in Rokkasho, Japan, before the final test of the plant using actual spent nuclear fuel. The inventory of ^239+240Pu in those lakes was larger than that in soil in Rokkasho, which indicated the inflow of ^239+240Pu from the catchment area in addition to direct deposition on the lake surfaces. The ¹³⁷Cs inventory in sediments of the brackish lakes was lower than that in the soil, which showed that part of the ¹³⁷Cs was removed from the sediments by the brackish water or that it was not deposited into the sediments, because of the high solubility of Cs in brackish water. The ¹³⁷Cs inventory in sediments of the freshwater lakes was higher than that of the brackish lakes, and comparable with that in soil except for one core sample out of four. The ^239+240Pu/¹³⁷Cs ratio in freshwater lake sediments was higher than that in soil, and that indicated that part of the ¹³⁷Cs was lost from the sediments. The low inventory of ¹³⁷Cs may be attributable to competition for absorption sites in sediments with ammonium ions formed in the reducing environment which occurs from summer to fall in the sediments. Those data will be used as background data on the artificial radionuclides in the lakes to assess the effect of released radionuclides on their concentrations.     

Correlations between potassium, rubidium and cesium ((133)Cs and (137)Cs) in sporocarps of Suillus variegatus in a Swedish boreal forest

An analysis of sporocarps of ectomycorrhizal fungi Suillus variegatus assessed whether cesium (¹³³Cs and ¹³⁷Cs) uptake was correlated with potassium (K) or rubidium (Rb) uptake. The question was whether intraspecific correlations of Rb, K and ¹³³Cs mass concentrations with ¹³⁷Cs activity concentrations in sporocarps were higher within, rather than among, different fungal species, and if genotypic origin of sporocarps within a population affected uptake and correlation. Sporocarps (n = 51) from a Swedish forest population affected by the fallout after the Chernobyl accident were studied. The concentrations were 31.9 ± 6.79 g kg⁻¹ for K (mean ± SD, dwt), 0.40 ± 0.09 g kg⁻¹ for Rb, 8.7 ± 4.36 mg kg⁻¹ for ¹³³Cs and 63.7 ± 24.2 kBq kg⁻¹ for ¹³⁷Cs. The mass concentrations of ¹³³Cs correlated with ¹³⁷Cs activity concentrations (r = 0.61). There was correlation between both ¹³³Cs concentrations (r = 0.75) and ¹³⁷Cs activity concentrations (r = 0.44) and Rb, but the ¹³⁷Cs/¹³³Cs isotopic ratio negatively correlated with Rb concentration. Concentrations of K and Rb were weakly correlated (r = 0.51). The ¹³³Cs mass concentrations, ¹³⁷Cs activity concentrations and ¹³⁷Cs/¹³³Cs isotopic ratios did not correlate with K concentrations. No differences between, within or, among genotypes in S. variegatus were found. This suggested the relationships between K, Rb, ¹³³Cs and ¹³⁷Cs in sporocarps of S. variegatus is similar to other fungal species.