Effective Half-lives For 137Cs Research Articles

Effective half-lives for 137Cs in dairy milk from alpine ecosystems and the controlling factors

Alpine regions in the federal state of Salzburg (Austria) have been intensively contaminated by Chernobyl fallout, necessitating long-term monitoring programs. The sites predominately affected are those in areas with soil developed on silicate bedrock, as these soils tend to be acidic, favouring high transfer factors for 137Cs. In addition, nutrient deficiency, low mineral and high organic matter content, and tough climatic conditions are causing the slow migration of 137Cs in the soil, which are associated with long effective half-lives in the biosphere.As a quantitative measure for effective half-lives, milk has been collected at nine alpine seasonal stock farming sites since 1988; at four sites, the monitoring is still ongoing (2020). For the period between 1999 and 2020, the decrease of 137Cs can be reasonably fitted with one effective half-life describing the time-trend. The effective half-lives obtained by this procedure vary between 9.3 ± 0.9 years and 18.8 ± 3.4 years. The effective half-lives show a weak negative correlation with the half-value depth of 137Cs, defined as the depth of the upper soil layer containing half of the deposited fallout inventory. The majority of the inventory is bound in the rooting zone of 0–10 cm, which is reflected by the small half value depths in the range between 3.2 and 4.4 cm.The soils investigated are acidic with pH values between 3.78 and 4.88, showing a pronounced negative correlation with the effective half-lives of 137Cs in milk. The data indicate that in these soils rich in organic matter, which are also almost totally devoid of clay minerals and have a very low clay size fraction, pH may be the dominating factor influencing the effective half-lives of 137Cs plant uptake and the subsequent contamination of milk.

Exemplifying the “wild boar paradox”: dynamics of cesium-137 contaminations in wild boars in Germany and Japan

Wild boars (Sus scrofa) are notorious for accumulating high contamination levels of 137Cs in their meat. Publicly available data of 137Cs contamination levels in wild boars from 2011 to 2019 were used to determine some radioecological characteristics in Germany (affected by Chernobyl-fallout, 1986) and Japan (affected Fukushima, 2011). The effective half-life of 137Cs in wild boar meat was much longer in Germany (7.3 y) than in Japan (2.6 y), respectively. Wild boars in Germany thus show much more persistent contamination levels than other game or forest animals. This unusual behavior has been termed “wild boar paradox.” In German wild boars, the data sets reveal a distinct geographical and seasonal dependence with higher activity concentrations in winter than in summer. In Japan, contamination levels only exhibit a distinct decline behavior.

Environmental recovery from 137Cs contamination in Japanese coastal waters shown by comparison of temporal distributions with European seas

We compared the spatiotemporal distributions of 137Cs in the European Baltic Sea (semi-enclosed) and the North and Norwegian Seas (open to the ocean) after the Chernobyl Nuclear Power Plant (CHNPP) accident, with those in Japanese coastal regions, including the waters off Miyagi, Fukushima, and Ibaraki prefectures, open to the western North Pacific, after the Fukushima Nuclear Power Plant accident. The effective half-lives 1–9 years after each accident were shortest (1.6–4.7 y) in Japanese coastal waters, 4.9 y in the North Sea, and 14.4 y in the Baltic Sea, suggesting that decreases in 137Cs concentrations are largely dependent on the local geography, and that the dilution–diffusion effect of seawater was greater in the Japanese coastal waters. The effective half-lives of 137Cs in the surface waters of European seas, based on 30 years of data after the CNPP accident, became longer, ranging from 8.4 to 11.9 y. This may be due to the influence of rivers, and a delay in the decrease in 137Cs levels caused by the small difference in radioactivity concentrations between the seas and diluting waters. These results could contribute to the prediction of contamination levels in Japanese coastal waters in the future.

Eight-year variations in atmospheric radiocesium in Fukushima city

Abstract. After the Fukushima nuclear accident, atmospheric 134Cs and 137Cs measurements were taken in Fukushima city for 8 years, from March 2011 to March 2019. The airborne surface concentrations and deposition of radiocesium (radio-Cs) were high in winter and low in summer; these trends are the opposite of those observed in a contaminated forest area. The effective half-lives of 137Cs in the concentrations and deposition before 2015 (0.754 and 1.30 years, respectively) were significantly shorter than those after 2015 (2.07 and 4.69 years, respectively), which was likely because the dissolved radio-Cs was discharged from the local terrestrial ecosystems more rapidly than the particulate radio-Cs. In fact, the dissolved fractions of precipitation were larger than the particulate fractions before 2015, but the particulate fractions were larger after 2016. X-ray fluorescence analysis suggested that biotite may have played a key role in the environmental behavior of particulate forms of radio-Cs after 2014. However, the causal relationship between the seasonal variations in particle size distributions and the possible sources of particles is not yet fully understood. The current study also proposes an evaluation method of the consistency of a numerical model for radio-Cs resuspension and suggests that improvements to the model are necessary.

Dynamics of radionuclide activity concentrations in weed leaves, crops and of air dose rate after the Fukushima Daiichi Nuclear Power Plant accident

Data on reduction of radioactivity in plants are highly important for making decision on emergency response and remediation of contaminated areas. Dynamics of the 131I and 137Cs concentrations in the weed leaves sampled in the areas affected by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in Japan was assessed for the period March–December 2011. The effective half-lives for 131I and 137Cs of 3.8–4.2 days and 7.1–13.3 days in the weed leaves were calculated for the first two months after the deposition. The approach for assessment of the aggregated transfer factors based on the ambient dose equivalent rate was suggested and validated. The geometric means of the soil to the weed leaves aggregated transfer factors were estimated for June–December 2011. Soil to crop 137Cs- concentration ratios (buckwheat, brown rice and soybean) were estimated for 2011–2016. Soil to crop concentration ratios were found to decrease in the order of soybean > buckwheat > brown rice. The effective half-lives for 137Cs in these crops were estimated to be between 1 and 2.5 years for the period 2011 2016, and longer than 5–7 years after 2016. It was found that these data comply with the Chernobyl related data obtained for similar conditions and complement of international documents on radionuclide transfer in agricultural environment such as the IAEA TRS 472.

A long-term study of radionuclide concentrations in mushrooms in the 30-km zone around the Mining-and-Chemical Combine (Russia)

ABSTRACT137Cs concentrations were measured in mushrooms in an area affected by radioactive discharges of the Mining-and-Chemical Combine (MCC) (Rosatom, Russia) in 2002–2017. The sources of radionuclides in the study sites were global fallouts and waterborne and airborne radioactive discharges of the MCC. The mushroom species Suillus granulatus and S. luteus showed the highest 137Cs concentrations (140–7100 Bq kg−1) for this area. Over the entire monitoring period, no significant change in 137Cs concentration was observed in the Suillus spp. samples collected from the sites with the aerial deposition of radionuclides. In the floodplain site with the radionuclide deposition from water and air, a significant decrease in the average 137Cs concentration was observed in the period between 2004 and 2017: a three-fold decrease in Suillus spp. and a nine-fold decrease in Lactarius deliciosus. The effective half-lives of 137Cs in fruiting bodies of the mushrooms L. deliciosus and Suillus spp. in this site were 3.6 ± 0.6 and 9.2 ± 2.7 years, respectively.

Budget of 90Sr in the Gulf of Gdańsk (southern Baltic Sea)

Summary In the period from 2005 to 2011 the major source of 90Sr to the Gulf of Gdansk was the Vistula river. Its contribution was 99.7% of the total load. The main processes responsible for the decrease in 90Sr activity in the Gulf of Gdansk were: radioactive decay (87%) and sediment deposition (13%). Average increase in the activity of 90Sr in the Gulf of Gdansk during the study period was 5.0% (114 GBq), which was almost 2 times higher than the loss of 90Sr due to radioactive decay. In the years 1997–2015, the effective half-life of 137Cs was 9.1 years and that of 90Sr was 50.3 years. Assuming a further decrease in 137Cs and maintaining 90Sr concentrations at present level, it is expected that 90Sr will become the major anthropogenic isotope having impact on the level of radioactivity in the Gulf of Gdansk.

Retention of 137Cs in forest floor at three temperate coniferous forest stands in the Czech Republic diversely affected by fallout after the Chernobyl disaster in 1986

Distribution of the 137Cs activity concentrations, soil pH, content of organic matter and composition of mineral portion in humus were investigated in forest soils variably loaded by Chernobyl-derived fallout. Maximum in the 137Cs activity concentrations were found in the uppermost organic soil horizons. In forest humus the 137Cs activity concentrations was negatively related to pH and the content of organic matter. No significant content of clay minerals was detected in humus. Slow vertical migration (0.04–0.06 cm year−1) and effective half-life of 137Cs in humus about 20 years was found. The initial surface 137Cs activities in 1986 were estimated.

Activity Concentrations of <sup>137</sup>Cs and <sup>90</sup>Sr in Seawaters of East Sea, Korea

Background: This study was a long-term evaluation of 137Cs and 90Sr activity concentrations in seawater samples from the East Sea, Korea, in order to establish current activity levels. Results and long-term monitoring trends will be useful in the future monitoring of environmental radioactivity. Materials and Methods: Surface seawater samples were collected quarterly from Guryongpo and Jangho in the East Coast between 1998 and 2010 and the quarterly deep seawater samples were collected from three sites in the sea adjacent to Ulleung-do between 2012 and 2015. The activity concentrations of 137Cs were measured using a gamma-spectrometer. The activity concentrations of 90Sr and 90Y in a radioactive equilibrium state were measured using a gas flow proportional counter. Results and Discussion: We found the annual average activity concentrations of 137Cs in the surface seawater was 1.66-2.89 mBq∙kg-1 in Guryongpo and 1.68-2.43 mBq∙kg-1 in Jangho. The annual average activity concentrations of 90Sr in the surface seawater was 0.83- 1.98 mBq∙kg-1 in Guryongpo and 0.82-1.57 mBq∙kg-1 in Jangho. The annual average activity concentrations of 137Cs in the deep seawater sites were 1.51-1.73 mBq∙kg-1, 1.19-1.60 mBq∙kg-1 and 0.87-1.15 mBq∙kg-1 in TH, JD, and HP. The annual average activity concentrations of 90Sr in the same deep seawater sites were 1.00-1.94 mBq∙kg-1, 0.82-1.26 mBq∙kg-1, and 0.79-1.32 mBq∙kg-1. The effective half-life was calculated by analyzing change over time in the activity concentration in the surface seawater. The effective half-life of 137Cs was 15.3 ± 0.1 years in Guryongpo and 102 ± 3 years in Jangho. The effective half-life of 90Sr was 28.3 ± 4.3 years in Guryongpo and 16.6 ± 0.1 years in Jangho. The ratio of the average activity concentration (137Cs/90Sr) was 1.72 in the surface seawater, which is similar to the reported ratio of the global radioactive fallout. The ratio in the deep seawater was 1.24, which is somewhat low compared to the global ratio (1.6, 1.8). Conclusion: Activity concentrations of 137Cs and 90Sr in the seawaters of the East Sea were similar to the previously reported activity levels in the East Sea and northwestern Pacific as a result of global radioactive fallout following atmospheric nuclear weapon tests.

Long-term behavior of 90Sr and 137Cs in the environment: Case studies in Switzerland

We present long-term records of the 137Cs and 90Sr activity concentrations in soil, grass and milk from two lowland and two alpine pastures of Switzerland. The data is used for better understanding the long-term behavior of these radionuclides in the environment. Transfer factors between compartments are used as qualitative indicators of the magnitude of transfer and as a way to compare different elements (e.g. Cs and Sr) in similar conditions. The long-term behavior was quantified by means of the effective half-life which integrates all processes that cause a decrease of activity in a given medium such as leaching, fixation, erosion and radioactive decay. Our study shows that 90Sr is more likely transferred from alpine soil to grass than 137Cs. This is explained by a stronger fixation of Cs in the soils. We observed higher transfers of 90Sr to grass in soils with lower Ca concentrations, and vice versa. In contrast, the transfer of 137Cs to grass was not affected by the variations of the K content in the soil. We provide evidence that shows that 137Cs, after intake by dairy cattle, is more likely transferred to milk than 90Sr. However, as the 90Sr and Ca transfers to milk are influenced by parameters/processes that were not taken into account in our study, our result cannot be entirely validated. The effective half-lives of 137Cs and 90Sr in soil, grass and milk corresponded with previous estimates in alpine soils. We have found that processes other than radioactive decay are responsible for a major decrease of the 90Sr activity in soil. For 137Cs, on the other hand, radioactive decay is among the most relevant process. Our data shows to be of interest in studying the trends of behavior of radionuclides in alpine regions.

Effective half-lives of 137Cs in giant butterbur and field horsetail, and the distribution differences of potassium and 137Cs in aboveground tissue parts

Concentrations of 137Cs and 40K in different tissues of edible wild herbaceous plants, that is, leaf blade and petiole for giant butterbur (Petasites japonicas (Siebold et Zucc.) Maxim.), and leaf, stem and strobilus for fertile shoot of field horsetail (Equisetum arvense L.) were measured in 2012–2014 to clarify the effect in Japan from the Fukushima Daiichi Nuclear Power Plant accident. The concentrations of 137Cs decreased with time with effective half-lives of ca. 450 d and 360 d for giant butterbur and field horsetail, respectively. The ANOVA test revealed that 40K and 137Cs distributions in leaf blade and petiole for giant butterbur and leaf and stem for field horsetail were different. Therefore, other plants, leaf and stem for Japanese knotweed (Fallopia japonica (Houtt.) Ronse Decr.) and Canada goldenrod (Solidago canadensis L.), and leaf blade and petiole for gingko (Ginkgo biloba L.) and Someiyoshino cherry (Cerasus × yedoensis (Matsum.) A.V.Vassil. ‘Somei-yoshino’) were collected from the same sampling field and their 137Cs and 40K concentrations were compared to those in the giant butterbur and field horsetail parts. For 137Cs, concentrations in leaf blade and leaf parts were 1.1–6.0 times higher than those in petiole and stem parts for all six plants. On the other hand, 40K concentrations in leaf blade and leaf parts were 0.40–0.97 of those observed in petiole and stem parts. Discrimination ratios of 40K/137Cs of leaf blade to petiole or leaf to stem were then calculated and they ranged from 0.09 to 0.57. These results suggested that Cs and K did not behave similarly in these plants. Thus, to understand the radiocesium fate in plants, K measurement results should not be used as an analog for Cs behavior although Cs is known to have a similar chemical reactivity to that of K.

Time-dependence of 137Cs activity concentration in wild game meat in Knyszyn Primeval Forest (Poland)

Wild game meat samples were analysed from the region of the Podlasie province (Knyszyn Primeval Forest). 137Cs content in meat was determined by gamma spectrometry in 2003 (33 samples), 2009 (22 samples) and 2012 (26 samples). The samples were collected in the autumn of 2003, 2009 and 2012 and were compared with data from 1996. Mean concentrations of 137Cs in the respective years were as follow: 42.2 Bq kg−1, 33.7 Bq kg−1 and 30.5 Bq kg−1, respectively. On the basis of mean values of 137Cs in the meat samples of red deer (Cervus elaphus), roe deer (Capreolus capreolus) and wild boars (Sus scrofa) between 1996/2012, the effective half-life of 137Cs was determined for specific species. For red deer equaled 8.9 years, for roe deer 11.6 years while for wild boar it exceeded the physical half-life and equaled 38.5 years. Mean value CR obtained for all three species equaled 1.7 ± 1.5 out of 102 measurements in animals muscles.

Effective half-lives of 137Cs from persimmon tree tissue parts in Japan after Fukushima Dai-ichi Nuclear Power Plant accident

To estimate the radiocesium decreasing rates from persimmon trees during a period of about 3 y following the accident at Tokyo Electric Power Company's Fukushima Dai-ichi Nuclear Power Plant (FDNPP), we conducted measurements of tree tissue parts collected in 2011–2013. The sampling was carried out in Chiba, 220 km south of FDNPP; radioactive fallouts discharged from FDNPP had mainly been observed in March–April 2011 on the sampling site. We measured 137Cs concentrations in the tree tissue parts, i.e., fruits (flesh, skin and seeds), leaves and newly emerged branches, and then the effective half-lives (Teff) of 137Cs were calculated. Leaf samples were classified into two types by sampling months according to the growing stages, that is, immature (April–May) and mature (June–November) leaves. All these parts showed exponential declines in 137Cs concentration with good adjusted contribution ratios of higher than ca. 0.7. The calculated Teff values from all tissue parts were similar with the average of 229 d (range: 216–243 d). From these results, we concluded that each tree tissue was representative for the calculation of Teff. For comparison to these observation results, open source food monitoring data from 2011 to 2013 including 137Cs data for persimmon fruits collected in Fukushima Prefecture were used to calculate Teff for persimmon trees. Values of Teff were obtained for persimmon fruits grown in each local government area in Fukushima Prefecture and they ranged from 303 to 475 d.

Radiocaesium levels in game in the Czech Republic

The paper summarizes results of monitoring of 137Cs activities in game species roaming in the woods over the territory of the Czech Republic for the time interval of 1986–2012. Geometric means and other statistical characteristics were estimated from the data sets on the assumption of log-normal distribution of the data from the time interval 2004–2012 where the character of data distribution had displayed no significant change. Geometric means (in Bq/kg) in meat were: wild boar 5.1, red deer 1.9, roe deer 0.77 and feathered game 0.14. The mean value in the less frequent game amounted to 0.36 Bq/kg. The geometrical standard deviation (GSD) widely varied from 1.6 to 21 for the studied species.Based on mass activity dependence on time, we assessed the effective and environmental half-lives of activity decline. For red deer and roe deer, the effective 137Cs half-life was 2.9 and 3.2 years, and environmental half-life 3.2 and 3.6 years respectively. The effective half-life of 137Cs in wild boar of 38 years was determined with large uncertainty and it shows constant influx of 137Cs activity to the digestive tract of wild boars.A statistically significant season-based 137Cs level was found in red deer and wild boar. Higher winter and spring activities of 137Cs in wild boar are linked with decreasing access to naturally occurring food with lower 137Cs content (chestnuts, acorns, and beech nuts), making boar grub around for ground-deposited food (often for mushrooms with higher activity). Higher winter activities of 137Cs in red deer meat, most probably, are due to lower access to green diet in winter.The average annual committed effective dose for Czech population based on estimates of game species meat consumption between 2004 and 2012 was insignificant, only 0.03 μSv.

Website application for calculating cesium-137 ingestion doses from consumption of locally grown foods in the Marshall Islands

Fallout deposition from the US nuclear weapons test program at Bikini and Enewetak Atolls (1946–1958) resulted in widespread nuclear fallout contamination of the northern Marshall Islands. About 85–90 % of the nuclear test-related dose delivered to resident populations is derived from ingestion of cesium-137 (137Cs) contained in locally grown tree-crop food products. The Lawrence Livermore National Laboratory has developed a series of interactive internet applications to provide the public with an open access platform to learn more about radiological conditions in the Marshall Islands. The ingestion dose calculator application described here is one such feature whereby users can calculate hypothetical ingestion doses from 137Cs based on interactive user input matched to environmental data on the activity concentration of 137Cs contained in food plants such as coconut, breadfruit, Pandanus, and arrowroot. Users are asked to enter a date, an island and atoll location, a plant food type, and a daily intake amount (highlighted by the number of portions eaten per day in estimated gram equivalents). The application computes the user daily dose and the user equivalent annualized dose, and then compares the results with default settings based on dietary models developed for the Marshall Islands from independent dietary surveys. The default diets are based on a local plus imported food diet (or IA diet model) and an imported foods unavailable diet (or IUA diet model). Environmental data are decay corrected to the date entered by the user using an effective half-life of 137Cs of 8.5 years (http://marshallislands.llnl.gov).

Uptake and elimination of 137Cs by climbing perch (Anabus testudineus).

This work describes the uptake and retention/biological elimination of 137Cs by climbing perch (Anabus testudineus) under laboratory conditions. The accumulated 137Cs concentration in the whole body of the fish was measured at certain intervals up to 38 d. A significant accumulation of 137Cs was found, but a steady state accumulation of 137Cs was not achieved by the end of the experiment. The bioaccumulation factors and the distribution of the radionuclide in edible parts of the fish were determined. The effective half-life of 137Cs in the fish species was found to be approximately 147 d (average) for elderly and adult fishes and approximately 300 d for younger fishes. Accumulation of 137Cs in the edible parts of the fish was found to be approximately 77% of whole body accumulation.

Residence time and uptake rates of 137CS in lichens and mosses at temperature latitude (40°N)

The 137Cs concentrations in lichens and mosses were significantly high five years after the Chernobyl accident. In some species of foliose lichens and mosses, the uptake of 137Cs during the long period of time was dominant in respect of its natural removal. In some species of fruticose lichens, decrease of the 137Cs concentration was only observed with time passed, resulting in an effective half-life of 137Cs, averaging 2.6 y at latitude 40°N. Uptake rates of 137Cs in some species of foliose lichens were determined, varying from about 3 400 to 7 000 (average 4 800) Bq/kg·y.