Retrospective of radioactive fallout from data on sampled bottom sediments in closed water bodies

A method for identifying past radiation events from dated layers of bottom sediments in stagnant water bodies is described. Results of an experimental study (2005–2006) of the samples of bottom sediments in the pond of the Timiryazev dendropark in Moscow are considered. The sediment layers are dated with ²¹⁰Pb. The same radionuclide is used as a tracer for calculating the rate of sedimentation in the pond, which is estimated at 0.3–0.4 cm/year. The maximum ¹³⁷Cs values are detected in the 0–24 cm column at depths of 7 and 13 cm. The ¹³⁷Cs peak at a depth of 13 cm is dated as 1963, which reflects the maximum global fallout from the atmospheric nuclear weapon tests. A small peak of this radionuclide at 7 cm is dated as 1986. It appears to be attributed to the long-range fallout after the Chernobyl NPP accident. The origin of the ¹³⁷Cs maximum at a depth of 13–14 cm is confirmed by characteristic ratios of radionuclide pairs available in the global fallout in the Moscow region. The ratios of ⁹⁰Sr/¹³⁷Cs = 0.6 and ^239,240Pu/¹³⁷Cs = 0.03 in the 13–14 cm layer are characteristic of the global radioactive fallout from nuclear explosions. In the layers above this maximum, such ratios vary sharply toward the enhanced ¹³⁷Cs content in the fallout.     

Preliminary results of modeling studies on washout of stable and radioactive analogs of <Superscript>90</Superscript>Sr and <Superscript>137</Superscript>Cs from snow-covered areas

Experimental field and laboratory studies on washout of radionuclides from the snow cover during snow melting were carried out in the winter of 2005/06. In the field studies, a specially equipped runoff site was used. In the laboratory conditions, the experiments were conducted using prepared soil monoliths. In the winter of 2006, 25 g/m² of water-free cesium chloride (CsCl) and 25 g/m³ of strontium chloride (SrCl₂) were put onto the snow cover surface of the runoff site. The snow surface of the soil monolith was coated with a ¹³⁷Cs-bearing solution, then with SrCl₂. Under experimental conditions, practically no surface runoff from the runoff site was recorded. The experiments with the soil monoliths demonstrated that the coefficient of the liquid washout of ¹³⁷Cs normalized to the runoff layer was within 0.9 × 10^?6–1.2 × 10^?4 mm^?1, and that of ⁹⁰Sr normalized to the runoff layer was within 2 × 10^?–1.6 × 10^?4 mm^?1.     

Radiation monitoring in Bryansk Polesie twenty-one years after the Chernobyl NPP accident

Bryansk Polesie is the most ¹³⁷Cs-contaminated region of the Russian Federation after the Chernobyl NPP accident, where in 2007 (i.e., 21 years after the accident), the radiation monitoring was conducted within the Russia-Belarus Union State Program. The paper is based on the comparison of data obtained in the settlements and at the nearby landscape sites outside the villages. The ¹³⁷Cs content variability in the most spread in Polesie soils, the podzols, is considered using observations obtained at the monitoring sites in Svyatsk and Demenka. It is shown that ¹³⁷Cs is fixed at the surface, in the upper soil horizons, which is explained by a high soil sorption capacity. Vast crest-sink floodplains with the great contrast range of the hydromorphic features, which cause great variability of the ¹³⁷Cs vertical distribution, are typical for the Polesie landscape; this fact is confirmed by observations obtained at the monitoring sites located in Starye Bobovichi and Ushcherpie. It is shown that Polesie pine forest contamination maintains higher contamination density levels compared to the nearby settlements, pastures, and meadow lands in the fluvial plains. Extrapolation of the contamination density data obtained within the first decade after the accident as of 2007, performed with allowance for the correction for decay and the comparison of these estimates with the new data accumulated in the recent years, does not show any significant contradiction.     

Estimating by inverse modeling the release of radioactive substances (<Superscript>133</Superscript>Xe, <Superscript>131</Superscript>I,and <Superscript>137</Superscript>Cs) into the atmosphere from Fukushima Daiichi nuclear disaster

The estimate of the release of radioactive substances (¹³³Xe, ¹³¹I, and ¹³⁷Cs) into the atmosphere from the Fukushima Daiichi nuclear disaster is presented. It was obtained using the FLEXPART Lagrangian dispersion model and the data of local ground-based measurements of radiation dose rate. The computation period covers the active phase of the nuclear disaster that lasted 20 days after the tsunami. To get the quantitative characteristics of emissions of radioactive substances, the inverse modeling based on the Bayesian approach is used. The emissions were estimated for three altitudes. The total emissions are equal to 2.1 + 0.4 kg (14 000 + 2700 PBq) for ¹³³Xe, (3.8 + 0.4) x 10^-2 kg (174 + + 18 PBq) for ¹³¹I, and 5.7 + 1.2 kg (18 + 4 PBq) for ¹³⁷Cs that is consistent with the results of other studies. Retrieved emissions were used to provide the forward modeling for mapping the areas of radionuclide deposition. The developed method of retrieving the emission of radioactive substances makes a useful instrument that operationally estimates and localizes the areas of potential pollution in case of nuclear accidents and could be used for making decisions on the population evacuation.     

<Superscript>137</Superscript>Cs washout from the soil in winter and spring

Experimental investigations under field and laboratory conditions of ¹³⁷Cs washout from the periodically frozen and thawed soils were carried out. The experiments demonstrated that the amount of cesium washed out from the soil after freezing was much larger than from the non-frozen soils and by its intensity it corresponds to the washout under the influence of intensifiers. This fact allows recommending cheap and technologically simple measures for the in-snow runoff control to rehabilitate the contaminated lands.     

Assessment of possible mechanisms of decreasing <Superscript>137</Superscript>Cs concentrations in river waters affected by the Chernobyl NPP accident

The analysis of possible mechanisms of ¹³⁷Cs concentration changes in surface waters was performed in the process of preparation of reliable long-range forecasts of radioactive river contamination after the Chernobyl accident. The following mechanisms were considered: (1) radioactive decay; (2) advective transport with river waters; (3) irreversible sorption; (4) vertical migration deep into bottom sediments due to diffusion; (5) burial in clean bottom sediments. The data published on ¹³⁷Cs monitoring at Dobrush, on the Iput’ River in Belarus were used in the analysis. It is shown that the best agreement with the experimental results is achieved when the second, third, and fifth mechanisms are used in calculations. However, a dominating mechanism still cannot be chosen at the present stage of our study. Most probably, all of these mechanisms act simultaneously.     

Description of radiation conditions and evaluation of the date of <Superscript>137</Superscript>Cs release to the atmosphere using the radionuclide transfer model coupled with the forecasts by the mesoscale hydrodynamic model

The estimates of ¹³⁷Cs emissions from the accident happened in Elektrostal at the beginning of April 12, 2013 are presented. The transport of radionuclides and their dry and wet deposition on the surface are computed using the Lagrangian stochastic model of the NOSTRADAMUS software package worked out by Nuclear Safety Institute of Russian Academy of Sciences. Prognostic fields of wind (horizontal and vertical components) in the lower troposphere, precipitation, and vertical and horizontal turbulence diffusivity coefficients in the lower atmosphere (up to 4 km) were used as input data. Prognostic fields were obtained using the WRF-ARW numerical mesoscale model.     

Laboratory measurements of the <Superscript>12</Superscript>C/<Superscript>13</Superscript>C kinetic isotope effects in the gas-phase reactions of unsaturated hydrocarbons with Cl atoms at 298 ± 3 K

The carbon kinetic isotope effects (KIEs) in the reactions of several unsaturated hydrocarbons with chlorine atoms were measured at room temperature and ambient pressure using gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS). All measured KIEs, defined as the ratio of the rate constants for the unlabeled and labeled hydrocarbon reaction k ₁₂/k ₁₃, are greater than unity or normal KIEs. The KIEs, reported in per mil according to ^Cl ɛ = (k ₁₂/k ₁₃−1) × 1000‰ with the number of experimental determinations in parenthesis, are as follows: ethene, 5.65 ± 0.34 (1); propene, 5.56 ± 0.18 (2); 1-butene, 5.93 ± 1.16 (1); 1-pentene, 4.86 ± 0.63 (1); cyclopentene, 3.75 ± 0.14 (1); toluene, 2.89 ± 0.31 (2); ethylbenzene, 2.17 ± 0.17 (2); o-xylene, 1.85 ± 0.54 (2). To our knowledge, these are the first reported KIE measurements for reactions of unsaturated NMHC with Cl atoms. Relative rate constants were determined concurrently to the KIE measurements. For the reactions of cyclopentene and ethylbenzene with Cl atoms, no rate constant has been reported in refereed literature. Our measured rate constants are: cyclopentene (7.32 ± 0.88) relative to propene (2.68 ± 0.32); ethylbenzene (1.15 ± 0.04) relative to o-xylene (1.35 ± 0.21), all × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. The KIEs in reactions of aromatic hydrocarbons with Cl atoms are similar to previously reported KIEs in Cl-reactions of alkanes with the same numbers of carbon atoms. Unlike the KIEs for previously studied gas-phase hydrocarbon reactions, the KIEs for alkene–Cl reactions do not exhibit a simple inverse dependence on carbon number. This can be explained by competing contributions of normal and inverse isotope effects of individual steps in the reaction mechanism. Implications for the symmetries of the transition state structures in these reactions and the potential relevance of Cl-atom reactions on stable carbon isotope ratios of atmospheric NMHC are discussed.     

Concentration of <Superscript>18</Superscript>O in precipitation over Moscow in 2014

The series of δ¹⁸O values is presented for all precipitation events in Moscow in 2014. Precipitation samples were taken at the observation site of the Meteorological Observatory of Lomonosov Moscow State University (MSU MO), and the isotopic analysis was carried out in the isotopic laboratory of the Department of Geography of MSU. The concentration of stable ¹⁸O in precipitation over Moscow in 2014 varied from -0.09 to -26.29‰. The maximum amplitudes of δ¹⁸O were registered in March-April and October. The pronounced interrelation was revealed between the oxygen isotopic composition of precipitation and surface air temperature (the correlation coefficient is 0.85). The computation of back trajectories of air masses and the analysis of weather charts demonstrated that the most isotopically light precipitation is typical of relatively cold air masses slowly moving over the continent during the last five days before precipitation. In this case, the ongoing condensation leads to the progressive isotopic depletion of precipitation (more and more isotope-depleted precipitation is registered). On the contrary, fast air transport from the middle and even from high latitudes of the Atlantic Ocean leads to the relatively constant of δ¹⁸O values of precipitation.     

Radionuclides in soils at the Semipalatinsk test site 40 years after excavation nuclear explosions

Radionuclide composition of soils near craters produced by excavation explosions “1003” and “1004” in 1965 at the Semipalatinsk test site is characterized as of 2005. A conclusion is made that radionuclides ¹³⁷Cs, ¹⁵²Eu, ¹⁵⁴Eu, ¹⁵⁵Eu, ²⁴¹Am, and ⁶⁰Co do not penetrate deeper than the upper 2 cm of the chestnut solonetz-like soil. The patterns after the explosions studied can be traced over the terrain near the crater ejecta to present. Contamination levels rapidly decrease with the distance from the ground zero. It is demonstrated that technogenic soils in the region of nuclear tests in a dry-steppe zone can be a source of dust and secondary air contamination.     

Wet deposition of radionuclides derived from the Chernobyl accident

Chernobyl radioactivity in precipitation was measured at Tsukuba, Japan, as were both surface-air concentrations and particle-size distributions of Chernobyl-released radionuclides. To understand the wet removal processes of the Chernobyl radionuclides, i.e.¹³⁷Cs,¹⁰³Ru, and⁹⁰Sr, wet deposition velocities were calculated. The wet deposition velocities of the Chernobyl radioactivity for individual rainfall events varied largely. The wet deposition velocity is given as the product of washout ratio and rainfall rate. Typically, it was found that the washout ratios of⁹⁰Sr are systematically larger than those of¹³⁷Cs. In order to explain this fact, we examined the relationship between the washout ratios and particle sizes of radionuclide-bearing aerosols. A positive correlation between corrected washout ratios and particle size was found with a particle diameter range from 0.35 to 1.2 µm. The result strongly suggests that the factors controlling the wet removal of the Chernobyl radioactivity for individual rainfall events are surface air concentration, particle size, and rainfall rate, rather than precipitation amount, which is in agreement with previous understandings. This suggests that high contamination areas of radioactivity are formed during heavy rainfall events with high rainfall rates in the case of tropospheric injection such as the Chernobyl accident.     

Reference levels of radioactive contamination of water bodies based on the environmental criteria

Quantitative environmental criteria for the radiation protection of aquatic ecosystems, namely, reference concentrations of radionuclides in water are developed. If activity concentrations of radionuclides do not exceed these levels, aquatic biota can be considered completely protected from the negative effects of ionizing radiation. Reference concentrations of radionuclides in environmental objects can be compared directly with the measurement data on radioactive contamination parameters that allows using them for the monitoring data interpretation. Reference concentrations of anthropogenic radionuclides in the sea and fresh water are calculated using the environmental criteria and are compared to the values of reference concentrations computed using the hygienic criterion. It is demonstrated that the current levels of concentration of ⁹⁰Sr, ¹³⁷Cs, and tritium in the seas, rivers, and lakes of Russia are considerably lower than the values of reference concentrations of these radionuclides calculated using the environmental criterion.     

Global <Superscript>90</Superscript>Sr runoff from Eastern Fennoscandia catchments and water purification estimates

⁹⁰Sr runoff amounted to 0.22–0.67% of its budget in the catchment; the value is lower for high-latitude rivers running in the zone of frozen and seasonally frozen grounds. The ecological half-period of a decrease in the ⁹⁰Sr concentration in the river water of Eastern Fennoscandia amounted to 5.9–11.5 years in 1979–1985. The lake waters (Lake Ladoga and Lake Päijänne) were renewed approximately 4–5 times faster than the 90Sr content decreased in these lakes.     

The application of tree-rings and stable isotopes for reconstructions of climate conditions in the Russian Altai

We present new tree-ring width, δ¹³C, and δ¹⁸O chronologies from the Koksu site (49°N, 86° E, 2,200 m asl), situated in the Russian Altai. A strong temperature signal is recorded in the tree-ring width (June-July) and stable isotope (July-August) chronologies, a July precipitation signal captured by the stable isotope data. To investigate the nature of common climatic patterns, our new chronologies are compared with previously published tree-ring and stable isotope data from other sites in the Altai region. The temperature signal preserved in the conifer trees is strongly expressed at local and regional scales for all studied sites, resulting in even stronger temperature and precipitation signals in combined average chronologies compared to separate chronologies. This enables the reconstruction of June-July and July-August temperatures for the last 200 years using tree-ring and stable carbon isotopes. A July precipitation reconstruction based on oxygen isotopic variability recorded in tree-rings can potentially improve the understanding of hydrological changes and the occurrence of extreme events in the Russian Altai.     

Interpreting CO<Subscript>2</Subscript> Fluxes Over a Suburban Lawn: The Influence of Traffic Emissions

Turf-grass lawns are ubiquitous in the United States. However direct measurements of land–atmosphere fluxes using the eddy-covariance method above lawn ecosystems are challenging due to the typically small dimensions of lawns and the heterogeneity of land use in an urbanised landscape. Given their typically small patch sizes, there is the potential that CO₂ fluxes measured above turf-grass lawns may be influenced by nearby CO₂ sources such as passing traffic. In this study, we report on two years of eddy-covariance flux measurements above a 1.5 ha turf-grass lawn in which we assess the contribution of nearby traffic emissions to the measured CO₂ flux. We use winter data when the vegetation was dormant to develop an empirical estimate of the traffic effect on the measured CO₂ fluxes, based on a parametrised version of a three-dimensional Lagrangian footprint model and continuous traffic count data. The CO₂ budget of the ecosystem was adjusted by 135gCm⁻² in 2007 and by 134gCm⁻² in 2008 to determine the natural flux, even though the road crossed the footprint only at its far edge. We show that bottom-up flux estimates based on CO₂ emission factors of the passing vehicles, combined with the crosswind-integrated footprint at the distance of the road, agreed very well with the empirical estimate of the traffic contribution that we derived from the eddy-covariance measurements. The approach we developed may be useful for other sites where investigators plan to make eddy-covariance measurements on small patches within heterogeneous landscapes where there are significant contrasts in flux rates. However, we caution that the modelling approach is empirical and will need to be adapted individually to each site.     

Radioactive contamination of the Central Russian Upland and its surroundings 21 years after the Chernobyl NPP accident

The Chernobyl NPP accident resulted, due to the western atmospheric transfer, in the formation of a pattern crossing the Central Russian Upland and its surroundings in the latitudinal direction. A volatile long–lived dose-forming radionuclide 137Cs prevailed in the fallout. A peculiar character of the Central Russian Upland division by valleys and balkas could result in a 20–year period in radioactivity displacement down the slop to valleys. This article is devoted to checking the significance of such changes. The issue on revealing the differences between the measured contamination density values 21 years after the depositions and the expected values (calculated with the correction for 137Cs decay) is also under consideration.     

Winter precipitation isotope slopes of the contiguous USA and their relationship to the Pacific/North American (PNA) pattern

This study compares the synoptic-dynamic relationship between two phases of the Pacific/North American (PNA) pattern and winter precipitation isotopes at 73 sites across the contiguous USA. We use the spatial pattern of isotope slope—the rate of changes in precipitation isotope ratios with distance—to identify features in the seasonal precipitation isotope fields related to climatic patterns, PNA positive and PNA negative. Our results show relationships between zones of high isotope slopes and the spatial position of the polar jet stream and juxtaposition of air masses associated with the PNA pattern. During a positive PNA winter, zones of high isotope slope in the eastern USA shift southward. This change is coincident with a southward displacement of the polar jet stream in this region, which leads to a greater frequency of polar air masses and ¹⁸O-depleted isotope values of precipitation in the region. In the western USA, zones of high slope shift eastward during the positive PNA winter, associated with more frequent penetration of tropical air masses that bring ¹⁸O-enriched precipitation to the region. Differences in δ¹⁸O/temperature relationships between the PNA-positive and -negative winters and contrasting δ¹⁸O/temperature behaviors in the eastern and western USA provide support for the role of variation in moisture source and transport as a control on the isotopic patterns. These findings highlight the importance of synoptic climate driven by PNA pattern in determining the spatial patterns of precipitation isotopes and provide constraints on paleo-water isotope interpretation and modern isotope hydrological processes.     

The Hydrogen Kinetic Isotope Effects of the Reactions of <Emphasis Type="Italic">n</Emphasis>-Alkanes with Chlorine Atoms in the Gas Phase

The stable-hydrogen kinetic isotope effects (KIEs) for a series of n-alkanes in reaction with chlorine atoms in the gas phase were studied in a 25-L PTFE reaction chamber at 298 K. The time dependence of both the stable hydrogen isotope ratios and the concentrations was determined using a gas chromatography pyrolysis isotope ratio mass spectrometry (GC-P-IRMS) system. The following KIE values, in per mil (‰), were obtained: 39.6 ± 2.7 (n-butane), 28.2 ± 0.9 (n-pentane), 24.6 ± 1.0 (n-hexane), 24.0 ± 1.2 (n-heptane), 17.9 ± 3.3 (n-octane), 15.1 ± 0.7 (n-nonane), and 14.9 ± 1.8 (n-decane). The errors given are the ±1σ standard errors. These measured values were used to derive structure–reactivity relationship (SRRs), which allow for the calculation of the KIEs for the reaction of n-alkanes with Cl atoms. The results of the calculations agree with the measurements within few per mil or better. The site specific stable hydrogen isotope fractionation effects for methyl groups are approximately a factor of 3 larger than those for methylene group, a finding which is qualitatively similar to site-specific stable hydrogen isotope effects reported in literature for reactions of alkanes with the OH radical. Because n-alkanes with close to natural isotope ratios (i.e. neither artificially labeled, nor enriched or depleted) were used, the KIE data are directly applicable to atmospheric studies. Based on these KIE values, the impact of Cl-atom reactions of the stable hydrogen isotope ratio on alkanes are estimated for different levels of Cl-atom concentrations. On average in the troposphere, the impact of Cl-atom reactions of the stable hydrogen isotope ratio of n-alkanes will be small. However, in regions of the troposphere with high concentrations of Cl atoms, such as the tropospheric ozone depletion episodes during polar sunrise, the impact of Cl-atom reactions is substantial. An erratum to this article is available at .     

Exchange fluxes of VOSCs between rice paddy fields and the atmosphere in the oasis <Emphasis Type="Bold">of arid area</Emphasis> in Xinjiang,China

Investigations about VOSCs (volatile organic sulfur compounds) have been received increasing attention for their significant contribution to the nonvolcanic background sulfate layer in the stratosphere and the earth’s radiation balance and as a potential tool to understand the carbon budget. In this study, COS and CS₂ were always recorded throughout the entire rice cultivation season of 2014. COS fluxes appeared as emission in non-planted soil and as uptake in planted soil, the corresponding results were obtained as 2.66 and ?2.35 pmol·m^?2·s^?1, respectively. For CS₂, both planted and non-planted paddy fields acted as sources with an emission rate of 1.02 pmol·m^?2·s^?1 and 2.40 pmol·m^?2·s^?1, respectively. COS emission or uptake rates showed a distinct seasonal variation, with the highest fluxes at the jointing-booting stage. COS and CS₂ fluxes increased with increasing N fertilizer use because of improved plant and microbial growth and activity. Plots treated with both N and S reduced COS and CS₂ fluxes slightly compared with plots with only-N treatment. Light, soil moisture or temperature showed no significant correlation with COS and CS₂ fluxes, but revealed the important impacts on the magnitude and direction of gases fluxes. The results also showed that the (available) sulfur contents in soil and roots had a certain effect on VOSCs emission or uptake. Our results highlight the significance of biotic and abiotic production and consumption processes existing in the soil.