Correlation between the thyroid computed tomography value and thyroid function in hyperthyroidism: a retrospective study

OBJECTIVE

Radioiodine (I-131) therapy for hyperthyroidism is a well-established and safe treatment option. This study aimed to investigate the relationship between the computed tomography (CT) value and the function and volume of the thyroid gland by identifying the factors that induce changes in the CT value of patients with hyperthyroidism.

METHODS

This retrospective study evaluated 38 patients with Graves' disease and 10 patients with Plummer disease. To obtain the mean CT value and volume of the thyroid gland, the entire thyroid gland was set as the region of interest. A test dose of 3.7 MBq I-131 was administered before initiating I-131 therapy, and the radioiodine uptake (RIU) rate was assessed after 3, 24, 96, and 168 h. An approximate curve was plotted based on the RIU values obtained, and the effective half-life (EHL) was calculated. The correlation between the mean CT value and the volume of the thyroid gland, 24-h RIU, EHL, and the free triiodothyronine (FT3), free thyroxine (FT4), thyroid-stimulating hormone (TSH), and TSH receptor antibody (TRAb) levels was evaluated.

RESULTS

The CT value exhibited a significant positive correlation with EHL in patients with Graves' disease (r = 0.62, p < 0.0001) as well as patients with Plummer disease (r = 0.74, p < 0.05). However, it did not display any correlation with the remaining parameters.

CONCLUSION

The CT value is significantly correlated with EHL, suggesting that it reflects thyroid function and is mainly related to the factors associated with iodine discharge.

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.

Effective and environmental half-lives of radiocesium in game from Poland

For the first time changes in the ¹³⁷Cs activity in game throughout Poland, including its most contaminated part known as the Opole Anomaly, were analyzed. Due to its long physical half-life, ¹³⁷Cs continuously demonstrates high activity both in soil and biota. The species of game mammals, along with forest fruit and mushrooms, tend to accumulate this radionuclide, becoming one of the main sources of secondary contamination in people. In this study the ¹³⁷Cs activity in roe deer, wild boar and red deer muscle tissue samples, within the years of 1986-2019, were studied. The effective and environmental half-lives were determined for each of the mentioned species for four regions including NE Poland and the Opole Anomaly placed in SW Poland. In all examined species at least two different phases of changes in the ¹³⁷Cs activity were distinguished, therefore the values of effective half-lives for the researched period since the Chernobyl accident do not correspond with the values from within last ten years. It was proven for the first time that within the anomalous area, featuring the highest values of gamma surface activity in Poland, the ¹³⁷Cs activity increases with time in the muscle tissues of all three species. No intraspecies, nor interspecies differences of ¹³⁷Cs activity among the studied species were found. In the light of the collected data, monitoring game considering the ¹³⁷Cs activity appears to be valid, as, due to not completely clear trophic dependencies, this radionuclide currently increased its migration to the game species despite passing its physical half-life period.

Establishing historical 90Sr activity in seawater of the China seas from 1963 to 2018

Historical ⁹⁰Sr activity in seawater was established in the China seas from 1963 to 2018. Based on the exponential decrease in ⁹⁰Sr activity in seawater, the effective half-life (EHL) of ⁹⁰Sr was quantified to be 11.5 ± 1.6 a, 16.5 ± 2.4 a, 27.2 ± 6.2 a, and 26.7 ± 4.3 a in the Bohai Sea, Yellow Sea, East China Sea, and South China Sea, respectively. We found contrasting patterns in the EHL of ⁹⁰Sr and ¹³⁷Cs in the marginal seas and open oceans that were closely related to the subtly different pathways of ⁹⁰Sr and ¹³⁷Cs in marine environment. Additionally, we demonstrated that Fukushima-derived ⁹⁰Sr (<0.01 Bq/m³) would be difficult to identify in the China seas. Our study not only provided the key parameter of the EHL in marine models for predicting the ⁹⁰Sr activity in the China seas in the post-Fukushima era but also enhanced our understanding of ⁹⁰Sr behavior and its fate in marine environments.

Focus on radioiodine-131 biokinetics: the influence of methylprednisolone on intratherapeutic effective half-life of 131I during radioiodine therapy of Graves' disease

AIM

Radioiodine therapy (RIT) may trigger the development of Graves' ophthalmopathy (GO) or exacerbate pre-existing subclinical GO. Therefore, glucocorticoid administration is recommended for patients with pre-existing GO. Aim of this study was to analyze the influence of glucocorticoid therapy with methylprednisolone on intratherapeutic effective half-life (EHL) of radioiodine-131 in patients with Graves' disease (GD) as recent studies showed an effect for prednisolone.

METHODS

In a retrospective study, 264 patients with GD who underwent RIT without any additional antithyroid medication were evaluated. Intrathyroidal EHL was determined pre- and intratherapeutically. Patients with co-existing GO (n = 43) received methylprednisolone according to a fixed scheme starting 1 day prior to RIT, patients without GO (n = 221) did not receive any protective glucocorticoid medication. The ratios of EHL during RIT and during radioiodine uptake test (RIUT) were compared.

RESULTS

Patients receiving methylprednisolone showed a slight decrease of the mean EHL from 5.63 d (RIUT) to 5.39 d (RIT) (p > 0.05). A comparable result was obtained in patients without glucocorticoids (5.71 d (RIUT) to 5.47 d (RIT); p > 0.05). The ratios of the EHL between RIT and RIUT failed to show a significant difference between the two groups. EHL is therefore not significantly influenced by an additional protective treatment with methylprednisolone.

CONCLUSIONS

In the present study a decreased intrathyroidal EHL under glucocorticoid medication with methylprednisolone could not be detected. Therefore, co-medication with methylprednisolone in patients with GO may be preferred to avoid an intratherapeutic decrease of EHL by accompanying protective glucocorticoides.

A thermoluminescent method for the evaluation of the 131I effective half-life in the thyroid when treating Graves' disease

When planning treatment for Graves' disease with ¹³¹I, the effective half-life (T_eff) should be estimated individually as it depends on biological characteristics such as iodine uptake and excretion, which differ from an individual to another (Berg et al. 1996). All the methods to quantify T_eff described in the literature are quite complex and are difficult to be used in clinical routine. With the aim of optimizing this process, a simplified method is proposed here to evaluate T_eff of ¹³¹I during treatment of Graves' disease. The present study suggests improving the method of determining T_eff based on thermoluminescence dosimetry. This involves implementing a new method and includes reduction of TLD (Thermoluminescent Dosimeter) measurements. The proposed method was validated on patients with Graves' disease. The radiation dose delivered to the patients was determined using the MIRD (Medical Internal Radiation Dosimetry) formalism. The relative difference between T_eff obtained based on seven measurement intervals at [0-24 h, 24-48 h, 48-72 h, 72-96 h, 96-120 h, 120-144 h, 144-168 h] and based on three measurement intervals at [0-24 h, 72-96 h, 144-168 h] and [0-24 h, 120-144 h, 144-168 h] was 1.9% and 3.81%, respectively. Comparison of doses obtained based on a general T_eff and on a personalized T_eff gave a statistically significant difference with a correlation coefficient R²of 0.44. The T_eff obtained from just three measurements was found to be sufficiently accurate and easily applicable. The results obtained demonstrate the need to determine and use personalized T_eff values instead of using a fixed value of 7 days.

Long-term trends and speciation of artificial radionuclides in two submerged macrophytes of the Yenisei River: A comparative study of Potamogeton lucens and Fontinalis antipyretica

Long-term trends of artificial radionuclides, from 2003 to 2018, in two abundant species of macrophytes, shining pondweed, Potamogeton lucens, and water moss, Fontinalis antipyretica, have been analyzed to estimate the indicative reliability of these two species as biomonitors of radioactive contamination in a river system and to quantify the decrease in the content of artificial radionuclides in the Yenisei River. Time-dependent trends of artificial radionuclides in the biomass of these species were similar, resulting in estimates of effective half-lives for ⁵⁴Mn, ⁵⁸Co, ⁶⁰Co, ⁶⁵Zn, ¹³⁷Cs, and ¹⁵²Eu similar for both species. Concentrations of artificial radionuclides in biomass of shining pondweed and water moss correlated with annual discharges of the radionuclides to the Yenisei at different levels of significance, and the strongest (R² > 0.7) positive correlation (p < 0.05) was obtained for ⁶⁰Co, ⁶⁵Zn, and ¹⁵²Eu. Concentrations of ⁶⁰Co, ¹³⁷Cs, and ¹⁵²Eu in water moss were 2-7.5 times higher than in shining pondweed, and considerable percentages of those isotopes were recorded in extracellular particulate matter, which was largely represented by epiphytic diatoms. Higher concentrations of artificial radionuclides in the biomass of water moss can be considered as an advantage of water moss as a monitor of radioactive contamination of the Yenisei, while shining pondweed is more useful for estimation of annual deposits of radionuclides in vegetation of the Yenisei and spatial transfer of radionuclides downstream of the discharge site. Despite differences in concentrations of artificial radionuclides, both species can be considered as reliable indicators of radioactive contamination of the river on a long-term scale.

Trajectories of technogenic tritium in the Rhône River (France)

Tritium is a radioisotope of hydrogen with a half-life of 12.32 years and was used for its luminescent properties by the watchmaking industry from 1962 to the 2008. Tritiated luminescent salts were integrated in the paints applied on the index and dial of watches and clocks. French and Swiss watchmaking workshops used more than 28 000 TBq of tritium over this period of time and produced almost 350 million watches. Despite the end of tritiated salts use in watchmaking workshops in 1992 in France and 2008 in Switzerland, high level of organically bound tritium (OBT) are still observed in sediments of the Rhône River downstream the Lake Geneva. Contamination of the Rhône River by tritiated hot particles since 1962 up to nowadays remains poorly documented. In order to assess the long term behavior and fate of technogenic tritium in this river and its trajectories in the river system, two sediment cores were collected at the upstream (UC) and downstream (DC) part of the Rhône River in France and OBT contents were determined. For both sedimentary cores, maximum OBT contents were registered over the 1980s when tritium was intensively used by watchmaking industries. These residual OBT contents are 1 000 to 10 000 fold higher than current natural background levels in riverine sediments. The OBT contents progressively decreased since 1989 with close effective half-life in upstream and downstream area (5 ± 2 years). The OBT contents were lower in DC than in UC due to the dilution by uncontaminated sediments delivered by tributaries not affected by the watchmaking industries. Trajectories analysis indicates that the resiliency of the Rhône River system in regards to this contamination would be reached in 14-70 years and in 14-28 years respectively for the upstream and downstream part of the river.

Comparisons of effective half-lives of radiocesium in Japanese tea plants after two nuclear accidents, Chernobyl and Fukushima

The time-dependence of ¹³⁷Cs in new shoots of tea (Camellia sinensis (L.) Kuntze) following a¹³⁷Cs-deposition was analyzed and quantified in terms of effective half-lives. The underlying monitoring studies were performed after the accidents in the Chernobyl and the Fukushima Daiichi nuclear power plants for tea plants growing in Japan. The major transfer route for atmospherically deposited radiocaesium to the first new shoots sampled after the accidents were different: for the Fukushima accident, it was mainly translocation of radiocaesium deposited onto old leaves and twigs to the new growth, while direct deposition on the new leaves was the major source after the Chernobyl accident. The effective half-lives in new tea leaves representing the fast and slow components of the decline did not significantly differ between these accidents. Geometric means (ranges) of fast and slow effective half-lives of ¹³⁷Cs after the Chernobyl accident were 66 d (25-125 d) and 902 d (342-15900 d), respectively, and those after the Fukushima accident were 50 d (26-105 d) and 416 d (222-1540 d), respectively. From these results, ¹³⁷Cs declines in new tea leaves were similar although contamination conditions were different for these two accidents.

Long term investigation of 137Cs in chicken meat and eggs from northwest Croatia

This paper presents the results of long-term investigations of ¹³⁷Cs activity concentrations in chicken meat and eggs from northwest Croatia for the period 1987-2018. The research has been done as a part of monitoring program of radioactive contamination in Croatia. The highest activity concentrations in both of these foodstuffs were measured in 1987 and have been decreasing exponentially ever since. The Fukushima-Daiichi accident in 2011 did not cause any increase of ¹³⁷Cs activity concentrations. The ecological half-life for ¹³⁷Cs was estimated to be 8.0 and 8.4 years for chicken meat and eggs respectively. The correlation between ¹³⁷Cs in fallout and chicken meat as well as between ¹³⁷Cs in fallout and eggs is very good, the respective correlation coefficients being 0.79 and 0.72, indicating that fallout was the main source of ¹³⁷Cs contamination in both foodstuffs. The estimated effective doses received by adult members of the Croatian population due to the intake of radiocaesium by chicken meat and egg consumption for the overall observed period are very small, 2.0 and 0.6 µSv respectively. Therefore, chicken meat and chicken egg consumption was not a critical pathway for the transfer of radiocaesium to humans.

Lesion-Wise Comparison of Pre-Therapy and Post-Therapy Effective Half-Life of Iodine-131 in Pediatric and Young Adult Patients with Differentiated Thyroid Cancer Undergoing Radioiodine Therapy

Purpose

The effective half-life of radioiodine is an important parameter for dosimetry in differentiated thyroid cancer patients, particularly in children. We determined the pre-therapy and post-therapy effective half-life in different types of lesions, i.e., remnant, node, or lung metastases.

Methods

Of 84 patients recruited, 27 were < 18 years (group 1) and the remaining 57 were between 18 and 21 years (group 2). A total of 114 studies were conducted and 253 lesions were analyzed. Serial whole-body scans were acquired at 24, 48, and ≥ 72 h after administration of iodine-131. Region of interests was drawn over lesions to determine counts in the lesion. Time versus counts graphs were plotted and mono-exponentially fitted to determine effective half-life.

Results

The post-therapy effective half-life was found to be lesser than pre-therapy effective half-life in all types of lesions and in all groups. Median effective half-life was found maximum in intact lobe, minimum in the lung, and intermediate in remnant and nodes. In the assessment of all lesions together, pre- and post-therapy median and interquartile range (IQR) effective half-life were 59.8 (37-112) h and 48.6 (35.2-70.8) h (p < 0.0001) in group 1, 73.9 (46.2-112.7) h and 60 (57.4-85.9) h (p < 0.0001) in group 2, and 68.6 (41.53-112.36) h and 54.7 (36-80.6) h (p < 0.0001) in combined group, respectively. Importantly, the pre- and post-therapy median effective half-life serially dropped after each successive cycles of iodine-131.

Conclusions

There was a significant difference in pre-therapy and post-therapy effective half-life in all types of lesions. These results may have implications in calculating the correct therapeutic dose in children and in young adults.

Spatial assessment of radiocaesium in the largest lagoon in Fukushima after the TEPCO Fukushima Dai-ichi Nuclear Power Station accident

Radionuclides deposited on land by global fallouts and nuclear power station accidents spread over coastal environments through estuarine areas connecting land to ocean. In this study, we monitored activity concentration of radiocaesium in surface sediment and re-suspended particles in Matsukawa-ura lagoon, the largest lagoon in Fukushima, after the TEPCO Fukushima Dai-ichi Nuclear Power Station accident. Radiocaesium distribution in surface sediment varied spatiotemporally and irregularly due to the effect of tidal waves. The effective half-life was significantly shorter than physical half-life, suggesting some system of radiocaesium discharge in the lagoon. Sediment trap observation revealed re-suspended particles from sediment were transported to the ocean. For these reasons, it is suggested that re-suspension of particles in the lagoon and their transportation to the ocean by the seawater exchange process are important processes of radiocaesium discharge. Moreover, our results show that seawater exchange process contributes to the dispersion of radiocaesium in the ocean.

Behaviour of 137Cs in forest humus detected across the territory of the Czech Republic

The activity concentration of ¹³⁷Cs in samples of coniferous forest humus collected across the territory of the Czech Republic in 1995 and 2005 was analysed, and it was found significantly correlated with the surface deposition caused by the Chernobyl accident. The effective (12.8 y) and environmental (22.3 y) half-lives of radiocaesium in humus were calculated and compared with those in spruce bark. The impact of important forest stand factors, that is, precipitation, content of organic matter, age of trees and pH, on the behaviour of ¹³⁷Cs in humus was studied. It was observed that humus samples with a higher proportion of organic matter, higher pH(H2O) and pH(CaCl2) contained higher amounts of ¹³⁷Cs. Conversely, with the age of trees, the activity concentration of ¹³⁷Cs in humus is decreasing. Higher precipitation and humus acidity decrease the reduction rate of the ¹³⁷Cs in humus. These stand factors increase bioavailability of ¹³⁷Cs in humus. The transfer and retention of available ¹³⁷Cs in biomass of organisms living in humus for a long time can satisfactorily explain the longer residence time of ¹³⁷Cs in humus affected by the studied factors.

Thirty years after Chernobyl: Long-term determination of 137Cs effective half-life in the lichen Stereocaulon vesuvianum

It has been widely shown that nuclear fallout includes substances, which accumulate in organisms such as crustaceans, fish, mushrooms and lichens, helping to evaluate the activity concentration of contaminants accumulated on a long time. In this context, radiocaesium deposited in soil following the Chernobyl accident on 26 April 1986 is known to have remained persistently available for plant uptake in many areas of Europe. Studies on the lichen Stereocaulon vesuvianum show the plant's high capacity to retain radionuclides from the substrate and the air. After the Chernobyl accident, starting from September 1986, at the Radioactivity Laboratory (LaRa) of the University of Naples Federico II, four monitoring campaigns to evaluate the activity concentration of four isotopes of the two elements caesium and ruthenium (¹³⁴Cs, ¹³⁷Cs, ¹⁰³Ru and ¹⁰⁶Ru) were carried out until 1999. This study allowed the effective half-life of ¹³⁴Cs and ¹³⁷Cs to be estimated. Twenty-eight years after the accident, in December 2014, a further sampling was carried out; only ¹³⁷Cs was revealed beyond the detection limits, measuring activity concentrations ranging from 20 to 40 Bq/kg, while the other radionuclides were no longer observed due to their shorter half-life. The last sampling allowed more precise determination of the effective half-life of ¹³⁷Cs (6.2 ± 0.1 year), due to the larger dataset on a large time period.

Time series changes in radiocaesium distribution in tea plants (Camellia sinensis (L.)) after the Fukushima Dai-ichi Nuclear Power Plant accident

Radiocaesium ((134)Cs and (137)Cs) release following the accident at the Fukushima Dai-ichi Nuclear Power Plant, belonging to the Tokyo Electric Power Company caused severe contamination of new tea plant (Camellia sinensis (L.)) shoots by radiocaesium in many prefectures in eastern Japan. Because tea plants are perennial crops, there is the fear that the contamination might last for a long time. The objectives of this study were to reveal time series changes in the distribution of radiocaesium in tea plants after radioactive fallout and to evaluate the effect of pruning on reduction of radiocaesium concentrations in new shoots growing next year. The experimental tea field was located in Shizuoka, Japan, approximately 400 km away from the Fukushima Dai-ichi Nuclear Power Plant in a southwest direction. Time series changes in radiocaesium concentrations in unrefined tea, a tea product primarily produced for making Japanese green tea, from May 2011 to June 2013 and distribution of radiocaesium in tea plants from May 2011 to May 2012 were monitored. The radiocaesium concentrations in unrefined tea exponentially decreased; the effective half-lives for (134)Cs and (137)Cs were 0.30 and 0.36 y during the first 2 y after the accident, respectively. With time, the highest concentrations of (137)Cs moved from the upper to the lower parts of plants. Medium pruning 2-3 months after the accident reduced the concentration of (137)Cs in new shoots harvested in the first crop season of the following year by 56% compared with unpruned tea plants; thus, pruning is an effective measure for reducing radiocaesium concentration in tea.

Latitudinal variation and residence time of (137)Cs in Indian coastal environment

Anthropogenic (137)Cs activity concentration, in surface sea water along the western and eastern coast of India has been estimated using the in-situ pre-concentration approach. Activity levels of (137)Cs ranges from 0.09-1.30Bqm(-3) with an overall mean of 0.69±0.29Bqm(-3). Latitudinal variation and higher depletion in activity concentration of (137)Cs at few locations were observed. Temporal change of (137)Cs in sea water along Indian coast unveils a lower effective half-life of 13.8±0.7y in comparison to Asia Pacific regional sea water. The results prevailed that the spatial distribution confers no fresh input of (137)Cs in Indian coastal region.

Effective and ecological half-lives of 90Sr and 137Cs observed in wheat and rice in Japan

Published pre-Fukushima food monitoring data from 1963 to 1995 were used to study the long-term presence of ¹³⁷Cs and ⁹⁰Sr in rice and wheat. Effective half-lives (T_eff) were calculated for rice (¹³⁷Cs: 5.6 years; ⁹⁰Sr: 6.7 years) and wheat (¹³⁷Cs: 3.5 years; ⁹⁰Sr: 6.2 years), respectively. In rice, ¹³⁷Cs exhibits a longer T_eff because putrefaction processes will lead to the formation of NH₄⁺ ions that are efficient ion exchangers for mineral-adsorbed cesium ions, hence making it more readily available to the plant. Knowledge on the long-term behavior of radiocesium and radiostrontium will be important for Japanese food-safety campaigns after the Fukushima nuclear accident.

Transfer factors and effective half-lives of (134)Cs and (137)Cs in different environmental sample types obtained from Northern Finland: case Fukushima accident

The Fukushima NPP accident caused a small but detectable cesium fallout in northern Finland, of the order of 1 Bq/m(2). This fallout transferred further to soil, water, flora and fauna. By using modern HPGe detector systems traces of (134)Cs from the Fukushima fallout were observed in various samples of biota. In northern Finland different types of environmental samples such as reindeer meat, berries, fish, lichens and wolf were collected during 2011-2013. The observed (134)Cs concentrations varied from 0.1 Bq/kg to a few Bq/kg. By using the known (134)Cs/(137)Cs ratio observed in Fukushima fallout the increase of the Fukushima accident to the (137)Cs concentrations was found to vary from 0.06 % to 6.9 % depending on the sample type. The aggregated transfer factors (Tag) and effective half-lives (Teff) for (134)Cs and (137)Cs were also determined and then compared with known values found from earlier studies which are calculated based on the fallout from the Chernobyl accident. Generally, the Tag and Teff values determined in this study were found to agree with the values found in the earlier studies. The Teff values were sample-type specific and were found to vary from 0.91 to 2.1 years for (134)Cs and the estimates for (137)Cs ranged between 1.6 and 19 years. Interestingly, the ground lichens had the longest Teff whereas the beard lichen had the shortest. In fauna, highest Tag values were determined for wolf meat ranging between 1.0 and 2.2 m(2)/kg. In flora, the highest Tag values were determined for beard lichens, ranging from 1.9 m(2)/kg to 3.5 m(2)/kg.

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 (137)Cs concentrations in the tree tissue parts, i.e., fruits (flesh, skin and seeds), leaves and newly emerged branches, and then the effective half-lives (T(eff)) of (137)Cs 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 (137)Cs concentration with good adjusted contribution ratios of higher than ca. 0.7. The calculated T(eff) 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 (137)Cs data for persimmon fruits collected in Fukushima Prefecture were used to calculate T(eff) 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.

Effective half-life of caesium-137 in various environmental media at the Savannah river site

During the operational history of the Savannah River Site (SRS), many different radionuclides have been released from site facilities into the SRS environment. However, only a relatively small number of pathways, most importantly (137)Cs in fish and deer, have contributed significantly to doses and risks to the public. The "effective" half-lives (Te) of (137)Cs (which include both physical decay and environmental dispersion) in Savannah River floodplain soil and vegetation and in fish and white-tailed deer from the SRS were estimated using long-term monitoring data. For 1974-2011, the Tes of (137)Cs in Savannah River floodplain soil and vegetation were 17.0 years (95% CI = 14.2-19.9) and 13.4 years (95% CI = 10.8-16.0), respectively. These Tes were greater than in a previous study that used data collected only through 2005 as a likely result of changes in the flood regime of the Savannah River. Field analyses of (137)Cs concentrations in deer collected during yearly controlled hunts at the SRS indicated an overall Te of 15.9 years (95% CI = 12.3-19.6) for 1965-2011; however, the Te for 1990-2011 was significantly shorter (11.8 years, 95% CI = 4.8-18.8) due to an increase in the rate of (137)Cs removal. The shortest Tes were for fish in SRS streams and the Savannah River (3.5-9.0 years), where dilution and dispersal resulted in rapid (137)Cs removal. Long-term data show that Tes are significantly shorter than the physical half-life of (137)Cs in the SRS environment but that they can change over time. Therefore, it is desirable have a long period of record for calculating Tes and risky to extrapolate Tes beyond this period unless the processes governing (137)Cs removal are clearly understood.

Long-term behaviour of 137Cs in spruce bark in coniferous forests in the Czech Republic

Activity concentrations of (137)Cs were detected in more than 400 outer spruce bark samples collected at sites variably affected by Chernobyl fallout across the Czech Republic in 1995 and 2010. The temporal changes in the (137)Cs activities were found. The mean effective half-life (TEF) for (137)Cs in spruce bark was 9.6 years, and the mean environmental half-life (TE) was 14 years. The effective half-lives were significantly higher in areas with higher long-term annual precipitation sums. Coefficient a in linear regression y = ax + b of half-lives on precipitation sums was 0.015 y mm(-1) for TEF and 0.036 y mm(-1) for TE. The aggregated transfer factor of (137)Cs from soil to bark was determined and the pre-Chernobyl bark contamination related to year 2010 was estimated.