137Cs Inventories Research Articles

Effects of Large-Scale Wildfires on the Redistribution of Radionuclides in the Chornobyl River System.

Wildfires in radiologically contaminated areas raise significant concerns due to potential radionuclides redistribution and increased public radiation exposure. This study examined the impact of the 2020 Chornobyl wildfire on the redistribution of radionuclides, specifically 137Cs and 90Sr, in the Chornobyl River system. We determined the quantities and speciation of 137Cs and 90Sr in charred residues and soil after wildfires and analyzed the riverine concentrations of these radionuclides based on long-term monitoring data. Our findings indicate that the inventories of 137Cs and 90Sr in the charred residues and soil decreased with increasing distance from the nuclear power plant, which is consistent with the initial deposition patterns. However, the transfer of 137Cs and 90Sr from soil to charred residues did not correspond to the distance, type of contamination source, or fire type. Speciation analysis revealed that the water-soluble fractions of 137Cs and 90Sr in the charred residues were significantly higher than those in the soil, implying increased mobility. Following the wildfires, no significant increase in 137Cs concentration was observed in a river catchment in Chornobyl. However, 90Sr concentrations showed a significant increase, exceeding the permissible levels in drinking water (2 Bq/L) in Ukraine. This increase is attributed to hydrologically driven mobilization processes: (1) during snowmelt in spring and (2) the transport of soluble 90Sr from charred residues and surface soil into the river during high suspended solid concentration events. Collectively, our findings highlight the importance of continuous monitoring of radionuclide dynamics in postwildfire environments to better assess potential radionuclide redistribution and radiation exposure risks. These results provide valuable insights into the behavior of 137Cs and 90Sr in river systems affected by wildfires, contributing to a more accurate understanding of their environmental impacts and potential countermeasures.

The Cross-Verification of Different Methods for Soil Erosion Assessment of Natural and Agricultural Low Slopes in the Southern Cis-Ural Region of Russia

The conventional measuring methods (runoff plots and soil morphological comparison) and models (WaTEM/SEDEM and regional model of Russian State Hydrological Institute (SHI)) were tested with regard to the Southern Cis-Ural region of Russia, along with data from rainfall simulation for assessing soil erosion. Compared with conventional methods, which require long-running field observations, using erosion models and rainfall simulation is less time-consuming and is found to be fairly accurate for assessing long-term average rates of soil erosion and deposition. In this context, 137Cs can also be used as a marker of soil redistribution on the slope. The data of soil loss and sedimentation rates obtained by using conventional measuring methods were in agreement with the data based on the used contemporary modeling approaches. According to the erosion model calculations and data on the fallout of radionuclides in the Southern Cis-Ural (54°50–25′ N and 55°44–50′ E), the average long-term annual soil losses were ~1.3 t·ha−1 yr−1 in moderate (5°) arable slopes and ~0.2 t·ha−1 yr−1 in meadows. In forests, surface erosion is negligible, or its rates are similar to the rate of soil formation of clay–illuvial chernozems. The rates of soil erosion and sediment deposition on the arable land obtained using different methods were found to be very close. All the methods, including the WaTEM/SEDEM, allowed us to measure both soil erosion and intra-slope sedimentation. The regional SHI model fairly accurately assesses soil erosion in the years when erosion events occurred; however, soil erosion as a result of snowmelt did not occur every year, which should be taken into account when modeling. The concentrations of 137Cs in the topsoil layer (0–20 cm) varied from 0.9 to 9.8 Bq·kg−1, and the 137Cs inventories were 1.6–5.1 kBq·m−2, with the highest values found under the forest. The air dose rate in the forest was higher than in open areas and above the average of 0.12 μSv·h−1 on the slope (0.1 μSv·h−1 in the meadow and 0.08 μSv·h−1 on the arable land), with the value increasing from the watershed to the lower part of the slope in all the areas. The γ-background level in the studied ecosystems did not exceed the maximum permissible levels.

Safety analysis of wind-induced resuspension of radioactive materials from the Techensky reservoir cascade coastline

The paper provides an assessment of the probability and consequences of external events capable of leading to an incident with a breach of established safety barriers restricting the spread of radioactive substances along the coastline of the Techensky reservoir cascade. The initiating events for such an incident could be adverse meteorological conditions resulting in a decrease in the water level in the cascade water bodies below the specified design levels. Drying out the surface of previously inundated sections of the coastline will create an extensive source of atmospheric contamination by technogenic radionuclides during wind-induced resuspension. The probable area of the dried-out sections will be 0.02 — 0.08 kml for reservoir V-3, 0.06 — 0.28 kml for reservoir V-4, 0.19 — 0.90 kml for reservoir V-10, and 0.47 — 2.19 kml for reservoir V-11. The cumulative inventory of 137Cs and 90Sr in the specified area exceeds 105 Bq/ml. The activity released into the atmosphere within an hour will range from 3.69∙108 to 8.48∙1011 Bq for the wind speeds of 5 m/s and 20 m/s, respectively. The probabilities of joint occurrence of strong winds and drought conditions are 6.8∙10-7 per year for a wind speed of 20 m/s and 2.1∙10-3 per year for a wind speed of 5 m/s. The highest values of effective dose for the population of the nearest settlements, reaching 1-3 μSv in the first 10 days and over 200 μSv in the first year, are achieved under extreme wind loads with wind speeds of 20 m/s or more.

The environmental consequences of rapid urbanization in central Florida reconstructed with high resolution 241Am and 210Pb dating in lake sediments

Throughout the 20th century, Florida was one of the fastest growing states in the US, putting unique environmental stress on the region. Accurately dated lake sediments can provide invaluable records of environmental change that extend beyond monitoring records. Here, we analyze profiles of americium-241 (241Am), cesium-137 (137Cs), lead (Pb), zinc (Zn), and uranium-series radionuclides in Lake Bonny in Lakeland, Florida. The 241Am peak is sharp in the sediment profile, while the 137Cs peak is broader and spread evenly across two layers. The measured 137Cs inventory of ~448Bq/m2 is less than half of the expected inventory from atmospheric deposition (accounting for decay since deposition), indicating significant losses. The reliability of 137Cs as a chronological tool can be complicated in environments with low quantities of 2:1 clays and low available potassium (K), characteristic of Florida and the U.S. southeast. Using a piecewise constant rate of supply 210Pb model verified by 241Am, we reconstruct sedimentation and chemical change in this lake. Highest sedimentation rates in the lake occur during decades of peak population growth in the mid-20th century. Uranium (U) and radium-226 (226Ra) inputs to the lake reach a maximum in the 1960s, consistent with expansion of local phosphate mines and elevated groundwater pumping during that time in response to drought conditions. Total Pb in the sedimentary record captures the rise and fall of the use of leaded gasoline, but Zn inputs to the lake remain nearly two orders of magnitude above background levels in the last decade. Our high-resolution chronology of the lake reveals regional impacts on water and lake quality in central Florida during a period of rapid population growth.

137Cs radiotracer in investigating influence of hillslope positions and land use on soil erosion and soil organic carbon stock—A case study in the Himalayan region

AbstractThe topography and land use/land cover (LULC) of the hillslope play a significant influence on soil erosion because of water, which is considered as a principal factor for the reduction of soil organic carbon content. Reliable information on the impact of erosion mechanism on soil organic carbon stock (SOCS) is essential for effectively accounting for the carbon flux that influences climate change. The main objectives of this study were to determine soil erosion based on the variation of 137Cs (Radiocesium) radionuclide activity at various hillslope positions and LULC in a hilly and mountainous region of the north‐western Himalayas. Additionally, the relationship between 137Cs concentration, soil erosion rate and SOCS were examined. Fallout radionuclide‐137Cs have emerged as a suitable method for assessing soil erosion in hilly and mountainous regions where rugged topography and extreme weather events restrain the conventional soil erosion assessment. The study revealed very high soil erosion rates of 32.89 and 30.70 t ha−1 year−1 in the lower hillslope positions with cultivated fields. The lowest soil erosion was obtained with a mean of 0.47 t ha−1 year−1 from the ridge with grassland, followed by the upper hillslope (5.50 t ha−1 year−1 under deodar forest and 14.07 t ha−1 year−1 under pine forest), and the middle hillslope (1.58 t ha−1 year−1 for deodar and 7.77 t ha−1 year−1 for pine forest). The soil erosion rates differ significantly between cultivated and forested regions, and there is also a significant difference between deodar and pine forests. Moreover, a significant difference was found between topographic positions concerning 137Cs, SOCS and soil redistribution rate. This difference was more pronounced at hillslope positions with different LULC. In both disturbed (cultivated) (r2 = .111) and undisturbed (forested and grassland) (r2 = .356) soils, positive and statistically significant (p < .005) poor relationships were found between SOCS and 137Cs inventory. This indicates the presence of various factors influencing the soil organic carbon stock (SOCS) mechanism or the indirect contribution of soil erosion‐induced carbon loss. This suggests that forest cover can enhance SOCS in the soil, mitigating the adverse effects of soil erosion and climate change. Consequently, 137Cs could be effectively used to quantify the SOC stock in soil redistribution over the hillslope affected by soil erosion. Statistical analyses indicated that the 137Cs inventory, SOCS and erosion were significantly affected by various hillslope positions and LULC types.

Downward migration of 137Cs promotes self-cleaning of forest ecosystem by reducing root uptake of Japanese cedar in Fukushima

Approximately 70 % of the area highly 137Cs-contaminated by the Fukushima Daiichi Nuclear Power Plant accident is forested. Decontamination works in most of these forests have not progressed, and the forestry industry remains stagnant. Although the long-term dynamics of 137Cs in the forest ecosystem will be controlled by the amount of 137Cs absorbed by roots in the future, temporal changes in 137Cs of tree roots have rarely been reported. In the present study, we monitored the depth distribution of 137Cs in the soil and absorptive very fine (VF) roots of 0.5 mm or less in a Japanese cedar forest from 2011 to 2023. As a result, the 137Cs inventory in the mineral soil increased over time due to the migration from the forest canopy and litter layers, whereas that in the VF roots tended to decrease since 2020, although there was a large variation. Temporal decrease in the exchangeable 137Cs fraction with fixation and temporal increase in VF root biomass with their growth were not clearly observed, the 137Cs concentration in the VF roots at 0–2 cm decreased with the decrease in 137Cs concentration in the litter layers. Although the 137Cs concentration in the VF roots below 2 cm tended to increase with increasing 137Cs concentration in the soil at the same depth, the downward migration of 137Cs within the soil can reduce the amount of 137Cs absorbed by roots because the VF root biomass decreases exponentially with depth. In other words, 137Cs can be removed from the long-term active cycles of forest ecosystems as they migrate deeper into the soil. This natural migration process can be regarded as a “self-cleaning” of the forest ecosystem, the green and sustainable remediation using such self-cleaning should be actively adopted for the future forest management.

Long-term behaviour of Cs-137, Cs-133 and K in beech trees of French forests

In the long-term after atmospheric deposit onto a forest ecosystem, Cs-137 becomes incorporated into the biogeochemical cycle of stable elements and progressively reaches a quasi-equilibrium state. This study aimed at determining to what extent Cs-137 activity distribution in tree vegetation could be predicted from that of stable caesium (Cs-133) and potassium (K), which are known to be stable chemical analogues and competitors for Cs-137 intake in tree organs. Field campaigns that focused on beech trees (Fagus sylvatica L.) were conducted in 2021 in three French forest stands with contrasted characteristics regarding either the contribution of global vs. Chornobyl fallouts, soil or climatic conditions. Decades after Cs-137 fallouts, it was found that more than 80% of the total radioactive inventory in the system remained confined in the top 20 cm mineral layers, while organic layers and beech vegetation (including roots) contributed each to less than 1.5%. The enhanced downward migration of Cs-137 in cambisol than podzol forest sites was presumably due to migration of clay particles and bioturbation. The distribution of Cs-137 and Cs-133 inventories in beech trees was very similar among sites but differed from that of K due a higher accumulation of Cs isotopes in roots (40–50% vs. < 25% for K). The aggregated transfer factor (Tag) of Cs-137 calculated for aerial beech organs were all lower than those reported in literature more than 20 years ago, this suggesting a decrease of bioavailability in soil due to ageing processes. Regarding their variability, Tags were generally lower by a factor 5 at the cambisol site, which was fairly well explained by a much higher value of RIP (radiocesium immobilisation potential). Cs-137 concentrations in trees organs normalized by the soil exchangeable fractions were linearly correlated to those of Cs-133 and the best fit was found for the linear regression model without intercept indicating that no more contribution of the foliar uptake could be observed on long term. Provided that the vertical distribution of caesium concentrations and fine root density are properly measured or estimated, Cs-133 was shown to be a much better proxy than K to estimate the root transfer of Cs-137.

High-resolution soil erosion mapping in croplands via Sentinel-2 bare soil imaging and a two-step classification approach

Erosion-induced lateral soil redistribution leads to spatially heterogenous soil composition, which can be captured through the distinctive spectral reflectance of soils under varying levels of erosion influence. This points to the potential of using remotely sensed soil spectra to detect severe erosion and deposition hotspots in exposed croplands and, importantly, further differentiate the intra-class spectral variability of moderate erosion that often occupies the largest proportion. Here, we aim to develop a two-step erosion classification and mapping approach based on multitemporal compositing of Sentinel-2 bare soil images of a typical agricultural region (11,500 km2) of northeast China. A random forest classifier was firstly trained against the ground-truth data derived from very high resolution (VHR) imagery in Google Earth, with an overall accuracy of 91 % that allowed for clear delineation of severe erosion and deposition areas based on their distinct topographic and spectral features particularly in the red and red-edge bands. In the second step, the remaining area of moderate erosion (60.30 %) was further differentiated using Iterative Self-Organizing cluster unsupervised classification to yield a five-class soil erosion map at 10 m spatial resolution. The accuracy of the predicted map was successfully validated by independent Caesium-137 (137Cs) and soil organic carbon observations at catchment and regional scales, as revealed by significant inter-class differences in soil redistribution rates estimated from 137Cs inventory. The severe erosion class had a soil loss rate of 5.5 mm yr−1, suggesting that previous assessments have underestimated erosion severity. The spatial accordance of crop growth with soil erosion intensity, particularly in localized settings, further highlighted the potential of bare soil imaging for mapping the spatiotemporal development of soil erosion and its response to targeted sustainable cropland management efforts.

Experience of using the portable gamma spectrometer MKS AT6101D for in situ measurements of the density of &lt;sup&gt;137&lt;/sup&gt;Cs soil contamination in the Bryansk region of Russia

We have tested applicability of the commercially available portable spectrometer-dosimeter MKS AT6101D (the manufacturer: ATOMTEX, Belarus) to measure the density of 137Cs soil contamination (inventory of 137Cs in soil) in situ. The study was performed in 2015–2020 at the territories of the Bryansk region of Russia contaminated due to the Chernobyl accident. The in situ measurements were performed in the 17 ground plots (7 grasslands and 10 kitchengargens) for which the 137Cs inventory and the mean migration depth of the radionuclide in soil was available from laboratory (ex situ) measurements of soil samples. It was found that the in situ data obtained with the method that was provided by the manufacturer of the instrument required additional correction on the vertical distribution of 137Cs in the soil. The correction procedure was developed; in 2020–2021, it has been successfully tested in 114 kitchengarden plots located at the settlements in the zones of radioactive contamination in the Bryansk region.

Accuracy and sensitivity of soil erosion estimation using 137Cs technology: A statistical perspective

Random spatial variation of the 137Cs inventory is the principal contributor to uncertainty in soil erosion estimation using 137Cs technology. A statistically sound sampling design is imperative for obtaining reliable soil erosion estimations. The objectives of this study are to: 1) characterize the effect of sample size on the estimates of mean inventories; 2) evaluate the sensitivity of the estimated soil redistribution to sample size using a new 137Cs model; 3) compare erosion detection limits among five conversion models; and 4) assess three spatial interpolation methods. Two small watersheds were sampled in an irregular grid design, and 30 samples were taken on a reference site. A moving window scheme was used to compute the 7-point and 11-point means of 137Cs inventories. The Welch’s modified t-test was used to test the mean estimates and to compute the detection limits for the replicated samples. Five models were selected to convert 137Cs inventories to soil redistribution rates. Since most single samples without replication yielded insignificant test results, the 137Cs technique cannot be used to estimate soil erosion at a single point due to random spatial variation. With 30 reference samples, 7 replicate samples on the sampling site provided reliable estimations of 137Cs inventories and soil redistribution. The spatial patterns of the estimated 137Cs inventories and soil redistribution became more regular and systematic as sample size increased, which agreed increasingly well with topography and surface hydrology. Replicate samples can be taken from each landform element or slope position where the erosion rate is expected to be uniform. Alternatively, a systematic grid sampling scheme can be used, and the nearest neighbors can be treated as replicates to calculate moving averages. The Type I and II errors with replicated samples showed that all sampling positions should be included in calculating watershed or area mean erosion rates even though the Type I errors indicated insignificant redistribution rates for some samples. Due to the lack of spatial autocorrelation, spline and inverse distance weighting methods performed better than kriging for interpolation. Detection limits and magnitudes of soil redistribution varied substantially with conversion models, depending on their sensitivities to changes in 137Cs inventories.

Unique transport paths of 137Cs from the Indian to Southern Oceans

To assess ocean-scale transport systems, we examined the latitudinal cross-sectional distribution of 137Cs activity concentrations in the Indian and Southern Oceans between December 2019 and January 2020 using low-background γ-spectrometry. At 0°–20°S, 137Cs concentrations exhibited a gradual decrease below the mixing layer (1–0.1 mBq/L). However, the concentrations steeply decreased toward the Southern Ocean along a transect of 30°–60°S (from 0.8 to 0.02 mBq/L) with minor vertical variation at each site. For the 137Cs inventories (0–800 m depth) from 15 to 600 Bq/m2, a maximum value was recorded at 30°S, indicating the downwelling of 137Cs as a reservoir for the Subantarctic Mode Water. The significantly low concentrations (0.02 mBq/L) at 60°S suggest minimal transport of 137Cs to the Southern Ocean. These findings assist in understanding 137Cs circulation patterns and provide valuable insights into the transport pathways of soluble contaminants.

Typhoon Chan-Hom (2015) induced sediment cross-shore transport in the mud depo-center of the East China Sea inner shelf

The erosion, transport, and deposition processes of sediments that are influenced by typhoons are significant constituents of the sedimentary source-sink processes in marginal seas. Nevertheless, the genesis of storm deposit layers in the continental shelf and their subsequent development and preservation after typhoons have not been comprehensively investigated. In this study, we have conducted a systematic investigation of the processes related to sediment transport and deposition, which were primarily induced by Typhoon Chan-Hom, and analyzed the evolution and preservation of storm deposits utilizing grain-size analysis, radionuclides (137Cs, 210Pbex and 7Be), and organic geochemistry (TOC, TN and δ13C). Sedimentary 137Cs, 210Pbex, and 7Be inventories measured three days after the typhoon suggest that the sediments in the water depth < 30 m were eroded, resuspended, and then transported offshore to deposit in the deeper areas (water depth > 50 m) of the Muddy Deposition Center of Zhejiang-Fujian Coast (MDC-ZFC), resulting in the formation of significant storm deposits (thickness of 8–16 cm) with high 210Pbex and 7Be. In addition to sediment transport, the offshore area also received organic matter generated by typhoon-induced phytoplankton blooms. Hence, in the present study area, the features of marine organic matter that possess high total organic carbon (TOC) content (>0.4%), low carbon to nitrogen (C/N) ratio (<7.5), and high δ13C value (> − 22‰) are crucial for identifying the storm deposit formed by cross-shore sediment transportation. In contrast, the commonly used indicators for identifying typhoon sedimentary records that rely on grain-size coarsening are not suitable for identifying storm deposits at the MDC-ZFC edge due to the influence of relict sands. Furthermore, the radionuclides and organic geochemical signals of the sediments revealed that no significant disturbance or transport of the storm sediments occurred three weeks after the passage of Typhoon Chan-Hom due to the high water depth, indicating that these storm deposits could be effectively preserved in this area. This study provides a valuable basis and reference for accurately identifying and interpreting typhoon sedimentary records in the MDC-ZFC.

The records of 239+240Pu and 137Cs of global fallout in Lake East Dongting Sediments and Responses to watershed environmental changes

Plutonium-239 + 240 and 137Cs in the environment can usually be used to track the impact of nuclear activities on the environment, and have become important tools in environmental geochemical studies. In this study, nine sediment cores (E1-E9) in Lake East Dongting were collected and measured for the activity concentration of 239+240Pu, 137Cs and the atomic ratio of 240Pu/239Pu, and then their vertical distribution characteristics were analyzed. The results show that: the activity concentrations of 137Cs and 239+240Pu in Lake East Dongting ranged from 5.26 ± 0.43 to 28.6 ± 2.23 Bq kg−1 and 0.29 ± 0.02 to 1.37 ± 0.09 Bq kg−1, with an average of 7.48 ± 0.68 Bq kg−1 and 0.39 ± 0.03 Bq kg−1, respectively. The atomic ratios of 240Pu/239Pu are 0.168 ± 0.012–0.211 ± 0.015, which are basically consistent with the global atmospheric deposition. The vertical profiles of 137Cs and 239+240Pu in sediment cores show obvious single-peak distribution in E1-E6 and bimodal distribution in E7-E9. The results of sedimentation rates calculated by 137Cs and 239+240Pu method ranged from 0.59 cm y−1 to 1.99 cm y−1 with a mean of 1.18 cm y−1 and 0.61 cm y−1 to 2.18 cm y−1 with a mean of 1.26 cm y−1. The inventories of 137Cs and 239+240Pu in nine sediment cores are 5.87–10.8 kBq m−2 and 307–545 Bq m−2, which are about 8–14 and 9–15 times the inventory in the global average atmospheric deposition at the same latitude respectively. Comparing the results of the sedimentation rates and the inventories from different sampling points indicates that extreme climatic events and human activities have a significant impact on sediment environment of Lake East Dongting.

137Cs inventories in soil in the Qaidam Basin, Tibetan Plateau

This paper presents measurements of cesium-137 (137Cs) in the Qaidam Basin during 2019 with 39 soil samples across the landscape. The aim here is to use the results of 137Cs inventories for the Qaidam Basin to subsequently estimate soil wind erosion. The 137Cs inventories in the surface soil vary from lower limit detection (LDD) to 1,072 Bq m−2, with a mean of 266 Bq m−2. Overall, the 137Cs inventories in the Qaidam Basin decreases from southeast to northwest. The highest 137Cs inventories was found in farmland, and the lowest was found in Gobi. Wetlands had higher 137Cs inventories than their neighboring sites.

Simulated inventory and distribution of 137Cs released from multiple sources in the global ocean

Radioactive cesium (137Cs) is distributed in the world's oceans as a result of global fallout from atmospheric nuclear weapons tests, releases from fuel reprocessing plants, and inputs from nuclear power plant accident. In order to detect future radionuclide contamination, it is necessary to establish a baseline global distribution of radionuclides such as 137Cs and to understand the ocean transport processes that lead to that distribution. In order to aid in the interpretation of the observed database, we have conducted a suite of simulations of the distribution of 137Cs using a global ocean general circulation model (OGCM). Simulated 137Cs radioactivity concentrations agree well with observations, and the results were used to estimate the changes in inventories for each ocean basin. 137Cs activity concentration from atmospheric nuclear weapons tests are expected to be detectable in the world ocean until at least 2030.

Explaining the variation in 137Cs aggregated transfer factor for wild edible plants as a case study on Koshiabura (Eleutherococcus sciadophylloides) buds

The aggregated transfer factor (Tag) is commonly used to represent the actual transfer of radiocesium from soil to wild edible plants, but the values have shown substantial variation since the Fukushima nuclear accident. To elucidate the factors causing this variation, we investigated the effects of spatial scale and vertical 137Cs distribution in the soil on the variation of Tag-137Cs values for one of the most severely contaminated wild edible plants, Eleutherococcus sciadophylloides Franch. et Sav. (Koshiabura). The variation in Tag-137Cs values was not reduced by direct measurement of 137Cs deposition in soil samples from the Koshiabura habitat, as a substitute for using spatially averaged airborne survey data at the administrative district scale. The 137Cs activity concentration in Koshiabura buds showed a significant positive correlation with the 137Cs inventories only in the organic horizon of soil from the Koshiabura habitat. The ratio of 137Cs inventories in the organic horizon to the total 137Cs deposition in soil exhibited substantial variation, especially in broad-leaved deciduous forests that Koshiabura primarily inhabits. This variation may be the cause of the wide range of Tag-137Cs values observed in Koshiabura buds when calculated from the total 137Cs deposition in soil.

Changes in air dose rates due to soil moisture content in the Fukushima prefecture forests

Radionuclides released and deposited because of the 2011 Fukushima Dai-ichi Nuclear Power Plant accident caused an increase in air dose rates in Fukushima Prefecture forests. Although an increase in air dose rates during rainfall was previously reported, the air dose rates in the Fukushima forests decreased during rainfall. This study aimed to develop a method to estimate rainfall-related changes in air dose rates, even in the absence of soil moisture data, in Namie-Town and Kawauchi-Village, Futaba-gun, Fukushima Prefecture. Moreover, we examined the relationship between preceding rainfall (Rw) and soil moisture content. The air dose rate was estimated by calculating the Rw in Namie-Town from May to July 2020. We found that the air dose rates decreased with increasing soil moisture content. The soil moisture content was estimated from Rw by combining short-term and long-term effective rainfall using half-live values of 2 h and 7 d and considering the hysteresis of water absorption and drainage processes. Furthermore, the soil moisture content and air dose rate estimations showed a good agreement with coefficient of determination (R2) scores >0.70 and >0.65, respectively. The same method was tested to estimate the air dose rates in Kawauchi-Village from May to July 2019. At the Kawauchi site, variation in estimated value is relatively large due to the presence of water repellency in dry conditions, and the amount of 137Cs inventory was low, so estimating air dose from rainfall remained a challenge. In conclusion, rainfall data were successfully used to estimate soil moisture and air dose rates in areas with high 137Cs inventories. This leads to the possibility of removing the influence of rainfall on measured air dose rate data and could contribute to the improvement of methods currently used to estimate the external air dose rates for humans, animals, and terrestrial forest plants.

Widespread Pb contamination in urban backyard soils for >100 years identified in soil cores constrained by 210Pb and 137Cs

Contaminated soil in urban residential areas is often overlooked as a source of childhood exposure to toxic levels of lead (Pb). We document mean Pb concentrations of 1200 ± 1000 mg/kg, three times the now outdated EPA soil hazard standard of 400 mg/kg, for 370 surface soils collected from 76 homes in the boroughs of Brooklyn and Manhattan of New York City. The mean Pb content of 250 ± 290 mg/kg Pb for 571 surface soils collected from tree pits and public parks was much lower. A subset of 22 surface samples analyzed by EPA Method 1340 extracted 86 ± 21 % (±1SD) of total soil Pb, indicating that it the Pb was highly bioavailable. To investigate the origin of backyard contamination, 49 cores were collected to an average depth of 30 cm from a subset of 27 homes. Twelve soil cores were analyzed for 210Pb and 137Cs to constrain processes that impact contaminant distribution and inventories (particle focusing, soil accumulation, loss, and mixing). Concentrations of Pb declined with depth in 60 % of the cores but usually did not reach background. Mean uncorrected Pb inventories of 340 ± 210 g/m2 Pb (mean ± 1SD, n = 12) were more than five times higher than the radionuclide corrected inventory of 57 g/m2 from Central Park soil cores. Average inventories of 210Pbxs (3.5 ± 0.9 kBq/m2) and 137Cs (0.9 ± 0.6 kBq/m2) corresponded to 71 ± 19 % and 50 ± 30 % of the predicted atmospheric inventories. Elevated Pb concentrations were found both in the fine (<1 mm) and coarse (>1 mm) fractions, the latter suggesting a local non-atmospheric source. This was confirmed by individual grains containing up to 6 % Pb and visible pieces of coal, bricks, and ash. Regardless of the source of contamination in backyard soils, systematic testing is needed to identify contaminated areas and reduce child exposure.

Effects of Wind-Water Erosion and Topographic Factor on Soil Properties in the Loess Hilly Region of China.

Wind and water erosion processes can lead to soil degradation. Topographic factors also affect the variation of soil properties. The effect of topographic factors on soil properties in regions where wind and water erosion simultaneously occur remains complicated. To address this effect, we conducted this study to determine the relationships between the changes in wind-water erosion and soil properties in different topographic contexts. We collected soil samples from conical landforms with different slope characteristics and positions in the wind-water erosion crisscross region of China. We examined the soil 137Cs inventory, soil organic carbon (SOC), total nitrogen (TN), soil particles, soil water content (SWC), and biomass. 137Cs was applied to estimate soil erosion. The results show that the soil erosion rate followed the order of northwest slope > southwest slope > northeast slope > southeast slope. The soil erosion rate on the northwest slope was about 12.06-58.47% higher than on the other. Along the slopes, the soil erosion rate decreased from the upper to the lower regions, and was 65.65% higher at the upper slope than at the lower one. The change in soil erosion rate was closely related to soil properties. The contents of SOC, TN, clay, silt, SWC, and biomass on the northern slopes (northwest and northeast slopes) were lower than those on the southern slopes (southeast and southwest slopes), and they were lower at the upper slope than at the lower one. Redundancy analysis showed that the variation in soil properties was primarily affected by the slope aspect, and less affected by soil erosion, accounting for 56.1% and 30.9%, respectively. The results demonstrate that wind-water erosion accelerates the impact of topographic factors on soil properties under slope conditions. Our research improves our understanding of the mechanisms of soil degradation in gully regions where wind and water erosion simultaneously occur.

Assessment of secondary radioactive contamination of a decontaminated land plot located on the territory of a recreation base in a wooded area

The article presents results of a long-term (1998–2021) radiological monitoring survey of a recreation base located in a wooded area in the zone of radioactive contamination after the accident at the Chernobyl nuclear power plant. Local mechanical decontamination of the soil had been made on the territory of the base in 1997. The evaluation of the secondary radioactive contamination of the decontaminated territory was performed by comparing dynamics of the radiological situation at the treated plot and the control, nondecontaminated, part of the base according to four main criteria: 1) dose rate of gamma radiation in the air from cesium radionuclides; 2) inventory of 137Cs in soil; 3) vertical distribution of 137Cs in soil; 4) activity concentration of 137Cs in plants and fungi. In 1998, the value of the 137Cs inventory in the upper 20 cm of soil in the control part of the territory of the base and in the decontaminated plot was 930 kBq/m2 and 143 kBq/ m2, respectively. By 2015, the value of the 137Cs inventory in the control area and the decontaminated plot had significantly decreased: by 35% and 36%, respectively. A decrease in the dose rate of gamma radiation in the air at the decontaminated plot and control area proceeded at the same rate, which is currently mainly determined by the decay of 137Cs. There was a gradual self-restoration of the forest ecosystem at the plot subjected to decontamination. Activity concentration of 137Cs in biota (pine, edible mushrooms) in the treated plot was many times lower than that in the control part of the recreation base. In general, there was no significant secondary radioactive contamination of the decontaminated plot in the 24 years after the intervention.