Cancer incidence among Chernobyl cleanup workers from Estonia: A 34-year follow-up.

From 1986 to 1991, 4831 men from Estonia were sent to clean up radioactively contaminated areas near Chernobyl (Chornobyl). Their cancer incidence during 1986 to 2019 was compared to that of the male population of Estonia. The cohort of cleanup workers was linked to national population and cancer registers based on unique personal identification numbers. Nineteen (0.4%) workers could not be traced. A total of 4812 men contributing 120 770 person-years of follow-up were eligible for the analyses. Standardized incidence ratios (SIR) and adjusted relative risks (ARR, expressed as ratios of SIRs) with 95% confidence intervals (CI) were calculated. A total of 687 incident cancer cases were registered in the cohort (SIR 1.11, 95% CI 1.03-1.19). Presumptive radiation-related cancers combined were in excess, but not when smoking- and alcohol-related cancers were excluded (SIR 0.92, 95% CI 0.71-1.18). For smoking-related cancers, the SIR was 1.24 (95% CI 1.13-1.36) and for alcohol-related cancer the SIR was 1.53 (95% CI 1.31-1.75). Less educated workers had a higher risk of all cancers (ARR = 1.21, 95% CI 1.02-1.44) and smoking-related cancers (ARR = 1.42, 95% CI 1.14-1.76). An elevated risk of alcohol-related cancers was evident 15 to 24 years (vs <15 years) after return from the Chernobyl area. This updated register-based follow-up of Chernobyl cleanup workers from Estonia revealed an excess of radiation-related cancer sites combined, but the excess was not apparent after excluding cancers associated with smoking and alcohol.

Suicide and other causes of death among Chernobyl cleanup workers from Estonia, 1986 - 2020: an update.

Mortality was studied in a cohort of 4831 men from Estonia who participated in the environmental cleanup of the radioactively contaminated areas around Chernobyl in 1986-1991. Their mortality in 1986-2020 was compared with the mortality in the Estonian male population. A total of 1503 deaths were registered among the 4812 traced men. The all-cause standardized mortality ratio (SMR) was 1.04 (95% CI 0.99-1.09). All-cancer mortality was elevated (SMR 1.16, 95% CI 1.03-1.28). Radiation-related cancers were in excess (SMR 1.20, 95% CI 1.03-1.36); however, the excesses could be attributed to tobacco and alcohol consumption. For smoking-related cancers, the SMR was 1.20 (95% CI 1.06-1.35) and for alcohol-related cancers the SMR was 1.56 (95% CI 1.26-1.86). Adjusted relative risks (ARR) of all-cause mortality were increased among workers who stayed in the Chernobyl area ≥ 92 days (ARR 1.20, 95% CI 1.08-1.34), were of non-Estonian ethnicity (ARR 1.33, 95% CI 1.19-1.47) or had lower (basic or less) education (ARR 1.63, 95% CI 1.45-1.83). Suicide mortality was increased (SMR 1.31, 95% CI 1.05-1.56), most notably among men with lower education (ARR 2.24, 95% CI 1.42-3.53). Our findings provide additional evidence that unhealthy behaviors such as alcohol and smoking play an important role in shaping cancer mortality patterns among Estonian Chernobyl cleanup workers. The excess number of suicides suggests long-term psychiatric and substance use problems tied to Chernobyl-related stressors, i.e., the psychosocial impact was greater than any direct carcinogenic effect of low-dose radiation.

Recall of residential history and dietary habits during pregnancy and lactation in the distant past: reliability of questionnaire-based radiation doses for persons exposed in utero and early life.

This study evaluates the reliability of information obtained by standardized questionnaires used in by personal interviews for estimation of radiation thyroid doses of 1065 individuals in the Belarusian cohort of individuals who were exposed in utero and early life following the Chernobyl accident in April 1986. Data from two interviews conducted in 2012-2017 and in 2018-2022 with mothers, who were pregnant or gave birth shortly after the Chernobyl accident, were analysed. The most reliable answers dealt with various attributes related to residential history. In contrast, the reliability of answers regarding consumption rates of milk from privately owned cows or trade network was moderate, while the agreement in responses for consumption of milk products and leafy vegetables was fair. Information from the two interviews was used to calculate thyroid doses received by the cohort members. Specifically, 'model-based' thyroid doses due to 131I were estimated using input data on individual residential history and food consumption reported during the personal interviews and ecological data (131I ground deposition in the corresponding settlements). In addition, for a subset of cohort subjects (n = 205) whose mothers were measured for 131I thyroid activity, 'measurement-based' thyroid doses were calculated by adjusting the model-based dose using a scaling factor that is defined as the ratio of measured 131I thyroid activity to model-based 131I thyroid activity calculated for the date of measurement. A moderate agreement was observed for total (prenatal and postnatal) model-based thyroid doses due to 131I intake, the arithmetic mean ± standard deviation for the Jaccard similarity coefficient ([Formula: see text]) was 0.45 ± 0.34 (median = 0.39), while measurement-based doses showed a much better agreement with a [Formula: see text] of 0.78 ± 0.29 (median = 0.93). For model-based thyroid doses from external irradiation and from ingestion of 134Cs and 137Cs, [Formula: see text] was 0.82 ± 0.23 (median = 0.90) and 0.84 ± 0.24 (median = 0.96), respectively. Measurement-based doses due to ingestion of radiocaesium isotopes resulted in an almost perfect agreement, [Formula: see text] was 0.91 ± 0.19 (median = 1.0). The present findings suggest that long-term memory recall can be reliable, if a person is asked about unique or important life events, such as pregnancy and childbirth occurring around the time of a nuclear reactor accident. However, the substantial difference (more than 10 times) observed for model-bases doses calculated using the two questionnaires represents an important source of human factor uncertainties that needs to be considered in any dose response analyses. Other lessons learned from this study are that (i) individual measurements of radionuclides in the human body are the most valuable source of information for estimating radiation doses, and (ii) whenever a radiation accident occurs, a sample of affected people should be asked to keep a diary, if at all possible.

137Cs distribution on the territory of Romania 30 years after Chernobyl accident.

To estimate the contribution of Chernobyl 137Cs contamination, in 1993 and especially 2016, its total inventory was determined by gamma-ray high-resolution spectroscopy in 62 and respectively 747 soil samples covering the entire Romanian territory. This permitted to estimate the 137Cs inventory as varying between 0.4 and 187 as well as between 0.2 and 94.2 kBq/m2 for years 1993 and 2016, respectively. By representing the spatial distribution of 137Cs inventory in Voronoi polygons, it was possible to evidence a decrease of the total 137Cs inventory over entire Romanian territory with a factor of about 3 from about 3.6 TBq to less than 1.2 TBq, exceeding in this way the natural decay which suggests that a certain amount of 137Cs was washed out by precipitation and, at a lower extent, was incorporated into plants. At the same time, by evaluating the maximum contribution of 137Cs to the population exposure, in 1993 as well as in 2016, the supplementary annual effective dose did not exceed, in the majority of sampling points the value of 0.2 mSv/year.

Some observations on meaningful and objective inference in radioecological field studies.

Anthropogenic releases of radiation are of ongoing importance for environmental protection, but the radiation doses at which natural systems begin to show effects are controversial. More certainty is required in this area to achieve optimal regulation for radioactive substances. We recently carried out a large survey (268 sampled animals and 20 sites) of the association between environmental radiation exposures and small mammal gut-associated microbiomes (fungal and bacterial) in the Chornobyl Exclusion zone (CEZ). Using individual measurements of total absorbed dose rates and a study design and analyses that accounted for spatial non-independence, we found no, or only limited, association. Watts et al. have criticised our study: for not filtering candidate non-resident components prior to our fungal microbiome analyses, for our qualified speculations on the relative merits of faecal and gut samples, and for the design of our study which they felt lacked sufficient replication. The advantage of filtering non-resident-fungal taxa is not clear and it would not have changed the null (spatially adjusted) association we found between radioactive dose and mycobiome composition because the most discriminatory fungal taxa with regard to dose were non-resident taxa. We maintain that it was legitimate for us to make qualified discussion comments on the differences in results between our faecal and gut microbiome analyses and on the relative merits of these sample types. Most importantly, the criticism of our study design by Watts et al. and the designs and analysis of their recent studies in the CEZ show a misunderstanding of the true nature of independent replication in field studies. Recognising the importance of spatial non-independence is essential in the design and analysis of radioecological field surveys.

Modeling the Dynamic Behavior of Radiocesium in Grazing Reindeer.

Radiocesium contamination in Norwegian reindeer and the factors influencing contamination levels have been studied for more than 50 years, providing significant amounts of data. Monitoring contamination in reindeer is of utmost importance for reindeer husbandry and herders in Norway and will need to be studied for many years because of the persistent contamination levels due to the 1986 Chernobyl fallout. This paper presents a novel dynamic model that takes advantage of the large data sets that have been collected for reindeer monitoring to estimate 137Cs in reindeer meat at any given time. The model has been validated using detailed 137Cs data from one of the herds most affected by the fallout. The model basis includes detailed 137Cs soil data from aerial surveys, GPS-based knowledge of reindeer migration, and local soil-to-vegetation 137Cs transfer information. The validation exercise shows that the model satisfactorily predicts both short- and long-term changes in 137Cs concentrations in reindeer meat and suggests that the model will be a useful tool in estimating seasonal changes and evaluating possible remedial actions in case of a future fallout event.

Breast cancer risk in Ukrainian women exposed to Chornobyl fallout while pregnant or lactating: standardized incidence ratio analysis, 1998 to 2016.

The radiation-related risk of breast cancer among women following the Chornobyl accident remains uncertain. During pregnancy, there is rapid cell proliferation in the breast while radioactive iodine from fallout exposure can concentrate in lactating breast tissues. We conducted a standardized incidence ratio (SIR) analysis of breast cancer in a cohort of 2,631 women who were lactating and/or pregnant at any time during the 2-month period of radioiodine fallout (April 26, 1986-June 30, 1986). There were 37,151 person-years of follow-up, and 26 incident breast cancers were identified through linkage with the National Cancer Registry of Ukraine. Breast cancer rates among pregnant or lactating women were compared to the general population rates, and SIRs were adjusted for oblast, urban/rural, age, and calendar year. The SIR was not significant for women pregnant at the time of the accident (SIR = 0.75; 95% CI 0.44, 1.18) or for women lactating anytime within 2 months of the accident (SIR = 0.96; 95% CI 0.48, 1.68). However, there was a non-significantly elevated risk for women lactating at the time of accident (SIR = 1.30, 95% CI 0.40, 3.01). The increased SIR for breast cancer among lactating women is consistent with the results of a similar study in Belarus and indicates the need to quantify the radiation risk of breast cancer in a larger study of women lactating during the period of fallout exposure.

Risk of thyroid cancer in Ukrainian cleanup workers following the Chornobyl accident.

Although much is known about the radiation-related risk of thyroid cancer in those exposed at young ages, less is known about the risk due to adult exposure, particularly in men. We aimed to examine the association between thyroid radiation dose received during adulthood and thyroid cancer risk in men. We conducted a nested case-control study (149 cases; 458 controls) of male, Ukrainian cleanup workers who first worked in the Chornobyl zone between ages 18 and 59 years, with cases identified through linkage with the National Cancer Registry of Ukraine from 1988 to 2012. Individual thyroid doses due to external and internal exposure during the cleanup mission and during residence in contaminated settlements were estimated (total dose mean 199 mGy; range 0.15 mGy to 9.0 Gy). The excess odds ratio per gray (EOR/Gy) for overall thyroid cancer was 0.40 (95% CI: - 0.05, 1.48; p-value = 0.118). Time since exposure was borderline significant (p-value = 0.061) in modifying this association so that less time since exposure was associated with a stronger EOR/Gy. An elevated, but nonsignificant association was observed for follicular thyroid cancer (EOR/Gy = 1.72; 95% CI: - 0.25, 13.69; p-value = 0.155) based on a small number of cases (n = 24). Our findings for radiation-related overall thyroid cancer risk are consistent with evidence of increased risks observed in most of the other studies of adult exposure, though the magnitude of the effect in this study is lower than in the previous case-control study of Chornobyl cleanup workers.

Demonstrating the undermining of science and health policy after the Fukushima nuclear accident by applying the Toolkit for detecting misused epidemiological methods.

It is well known that science can be misused to hinder the resolution (i.e., the elimination and/or control) of a health problem. To recognize distorted and misapplied epidemiological science, a 33-item "Toolkit for detecting misused epidemiological methods" (hereinafter, the Toolkit) was published in 2021. Applying the Toolkit, we critically evaluated a review paper entitled, "Lessons learned from Chernobyl and Fukushima on thyroid cancer screening and recommendations in the case of a future nuclear accident" in Environment International in 2021, published by the SHAMISEN (Nuclear Emergency Situations - Improvement of Medical and Health Surveillance) international expert consortium. The article highlighted the claim that overdiagnosis of childhood thyroid cancers greatly increased the number of cases detected in ultrasound thyroid screening following the 2011 Fukushima nuclear accident. However, the reasons cited in the SHAMISEN review paper for overdiagnosis in mass screening lacked important information about the high incidence of thyroid cancers after the accident. The SHAMISEN review paper ignored published studies of screening results in unexposed areas, and included an invalid comparison of screenings among children with screenings among adults. The review omitted the actual state of screening in Fukushima after the nuclear accident, in which only nodules > 5 mm in diameter were examined. The growth rate of thyroid cancers was not slow, as emphasized in the SHAMISEN review paper; evidence shows that cancers detected in second-round screening grew to more than 5 mm in diameter over a 2-year period. The SHAMISEN consortium used an unfounded overdiagnosis hypothesis and misguided evidence to refute that the excess incidence of thyroid cancer was attributable to the nuclear accident, despite the findings of ongoing ultrasound screening for thyroid cancer in Fukushima and around Chernobyl. By our evaluation, the SHAMISEN review paper includes 20 of the 33 items in the Toolkit that demonstrate the misuse of epidemiology. The International Agency for Research on Cancer meeting in 2017 and its publication cited in the SHAMISEN review paper includes 12 of the 33 items in the Toolkit. Finally, we recommend a few enhancements to the Toolkit to increase its utility.

Association between exposure to radioactive iodine after the Chernobyl accident and thyroid volume in Belarus 10-15 years later.

BACKGROUND: While there is a robust literature on environmental exposure to iodine-131 (131I) in childhood and adolescence and the risk of thyroid cancer and benign nodules, little is known about its effects on thyroid volume. METHODS: To assess the effect of 131I dose to the thyroid on the volume of the thyroid gland, we examined the data from the baseline screening of the Belarusian-American Cohort Study of residents of Belarus who were exposed to the Chernobyl fallout at ages ≤18 years. Thyroid dose estimates were based on individual thyroid activity measurements made shortly after the accident and dosimetric data from questionnaires obtained 10-15 years later at baseline screening. During baseline screening, thyroid gland volume was assessed from thyroid ultrasound measurements. The association between radiation dose and thyroid volume was modeled using linear regression where radiation dose was expressed with power terms to address non-linearity. The model was adjusted for attained age, sex, and place of residence, and their modifying effects were examined. RESULTS: The analysis was based on 10,703 subjects. We found a statistically significant positive association between radiation dose and thyroid volume (P < 0.001). Heterogeneity of association was observed by attained age (P < 0.001) with statistically significant association remaining only in the subgroup of ≥18 years at screening (P < 0.001). For this group, increase in dose from 0.0005 to 0.15 Gy was associated with a 1.27 ml (95% CI: 0.46, 2.07) increase in thyroid volume. The estimated effect did not change with increasing doses above 0.15 Gy. CONCLUSIONS: This is the first study to examine the association between 131I dose to the thyroid gland and thyroid volume in a population of individuals exposed during childhood and systematically screened 10-15 years later. It provides evidence for a moderate statistically significant increase in thyroid volume among those who were ≥ 18 years at screening. Given that this effect was observed at very low doses and was restricted to a narrow dose range, further studies are necessary to better understand the effect.

Doses from external irradiation and ingestion of 134Cs, 137Cs and 90Sr of the population of Belarus accumulated over 35 years after the Chernobyl accident.

This study considers the exposure of the population of the most contaminated Gomel and Mogilev Oblasts in Belarus to prolonged sources of irradiation resulting from the Chernobyl accident. Dose reconstruction methods were developed and applied in this study to estimate the red bone-marrow doses (RBMs) from (i) external irradiation from gamma-emitting radionuclides deposited on the ground and (ii) 134Cs, 137Cs and 90Sr ingestion with locally produced foodstuffs. The mean population-weighted RBM doses accumulated during 35 years after the Chernobyl accident were 12 and 5.7 mGy for adult residents in Gomel and Mogilev Oblasts, respectively, while doses for youngest age groups were 20-40% lower. The highest mean area-specific RBM doses for adults accumulated in 1986-2021 were 63, 56 and 46 mGy in Narovlya, Vetka and Korma raions in Gomel Oblast, respectively. For most areas, external irradiation was the predominant pathway of exposure (60-70% from the total dose), except for areas with an extremely high aggregated 137Cs soil to cow's milk transfer coefficient (≥ 5.0 Bq L-1 per kBq m-2), where the contribution of 134Cs and 137Cs ingestion to the total RBM dose was more than 70%. The contribution of 90Sr intake to the total RBM dose did not exceed 4% for adults and 10% for newborns in most raion in Gomel and Mogilev Oblasts. The validity of the doses estimated in this study was assessed by comparison with doses obtained from measurements by thermoluminescence dosimeters and whole-body counters done in 1987-2015. The methodology developed in this study can be used to calculate doses to target organs other than RBM such as thyroid and breast doses. The age-dependent and population-weighted doses estimated in this study are useful for ecological epidemiological studies, for projection of radiation risk, and for justification of analytical epidemiological studies in populations exposed to Chernobyl fallout.

Spatial geochemical differentiation of the iodine-induced health risk and distribution of thyroid cancer among urban and rural population of the Central Russian plain affected by the Chernobyl NPP accident.

The main goal was to study the spatial distribution of thyroid cancer (THYC) among the population of urban and rural settlements of four regions of Russia, which were characterized by different contents of stable iodine in soils and exposed to radioactive fallout of 131I from the Chernobyl NPP. Using GIS technologies, zoning of territories for the deficiency of 127I and pollution with 131I was performed. The resulting risk maps were compared with the THYC distribution. The association between the spatial distribution of the total (natural and man-made) risk assessment and the incidence of THYC at the district level tended to have a higher positive correlation (r = 0.505, p < 0.001, n = 94) compared with the correlation of the latter parameter with a fallout density of 131I (r = 0.468, p < 0.001). After latent period, the incidence of THYC among residents of urban settlements of the Bryansk region was considerably higher than in rural, the difference increasing with time. The correlation between the assessed total risk and THYC distribution in risk zones was significant and higher in the rural areas than in the urban ones. A tendency for a negative significant correlation (r = - 0.55, p = 0.01) between daily iodine intake (based on the main components of the diet) and THYC cases among the rural population was found. A definite difference in the influence of geochemical environmental factors on the distribution of THYC among urban and rural populations deserves more detailed study to prevent this disease.

Lessons being learned from the Covid-19 pandemic for radiological emergencies and vice versa: report from expert discussions.

In order to examine what lessons radiological emergency management may offer for the management of the Covid-19 pandemic, and vice versa, a series of three online webinars were conducted with leading experts, scholars and practitioners from a wide range of disciplines essential for emergency management and long-term risk governance. The first webinar debated the lessons we are learning from the Covid-19 pandemic for radiological risk communication, the second explored issues around longer-term outcomes of a crisis and how to balance these with short-term actions whilst the third focused on the key challenges of the 'transition phase', using lessons learned from the Chernobyl (1986) and Fukushima Daichii (2011) accidents. This paper reviews the discussions and provides valuable lessons for the radiation protection community. Results of the discussions indicated that: (a) non-radiological and non-epidemiological consequences of emergencies, for example psychological (mental health), societal and economic, should not be underestimated; (b) multidisciplinary expertise is imperative for communication efforts and for effective emergency management, including decision-making in the application of protective measures; (c) stakeholder engagement, including the involvement of the potentially affected population, should be encouraged from an early stage; and (d) trust is increased if policy-makers and the main science agencies show a unified voice.

Breast cancer incidence in the regions of Belarus and Ukraine most contaminated by the Chernobyl accident: 1978 to 2016.

Even 30 years after the accident, an association between breast cancer incidence and ionizing radiation exposure from Chernobyl fallout remains uncertain. We studied breast cancer incidence in the most contaminated regions of Belarus (Gomel and Mogilev) and Ukraine (Kyiv, Zhytomyr and Chernihiv) before (1978-1986) and after (1987-2016) the accident. Breast cancer cases and female population size data were received from the national cancer registries and the state departments of statistics. The study included 85 132 breast cancers with 150 million person-years at risk. We estimated annual rayon (district)-average absorbed doses to the breast from external and internal irradiation of the adult female population over the period of 1986-2016. We studied an association between rayon-average cumulative absorbed breast dose with 5-year lag, that is, excluding the exposure in 5 years prior to breast cancer diagnosis, and breast cancer incidence using negative binomial regression models. Mean (median) cumulative breast dose in 2016 was 12.3 (5.0) milligray (mGy) in Belarus and 5.7 (2.3) mGy in Ukraine, with the maximum dose of 55 mGy and 54 mGy, respectively. Breast cancer incidence rates statistically significantly increased with calendar year and attained age, and were higher in urban than in rural residents. Adjusting for time, age and urbanicity effects, we found no evidence of increasing incidence with rayon-average 5-year lagged cumulative breast dose. Owing to ecological study design limitations, a case-control study covering this area with individually reconstructed absorbed breast doses is needed testing for association between low-dose protracted radiation exposure and breast cancer risk after Chernobyl.

Identification of the pigment and its role in UV resistance in Paecilomyces variotii, a Chernobyl isolate, using genetic manipulation strategies.

Fungi produce secondary metabolites that are not directly involved in their growth, but often contribute to their adaptation to extreme environmental stimuli and enable their survival. Conidial pigment or melanin is one of the secondary metabolites produced naturally by a polyketide synthesis (PKS) gene cluster in several filamentous fungi and is known to protect these fungi from extreme radiation conditions. Several pigmented or melanized fungi have been shown to grow under extreme radiation conditions at the Chernobyl nuclear accident site. Some of these fungi, including Paecilomyces variotii, were observed to grow towards the source of radiation. Therefore, in this study, we wanted to identify if the pigment produced by P. variotii, contributes to providing protection against radiation condition. We first identified the PKS gene responsible for synthesis of pigment in P. variotii and confirmed its role in providing protection against UV irradiation through CRISPR-Cas9 mediated gene deletion. This is the first report that describes the use of CRISPR methodology to create gene deletions in P. variotii. Further, we showed that the pigment produced by this fungus, was not inhibited by DHN-melanin pathway inhibitors, indicating that the fungus does not produce melanin. We then identified the pigment synthesized by the PKS gene of P. variotii, as a naptho-pyrone Ywa1, by heterologously expressing the gene in Aspergillus nidulans. The results obtained will further aid in understanding the mechanistic basis of radiation resistance.

Europe-Wide Atmospheric Radionuclide Dispersion by Unprecedented Wildfires in the Chernobyl Exclusion Zone, April 2020.

From early April 2020, wildfires raged in the highly contaminated areas around the Chernobyl nuclear power plant (CNPP), Ukraine. For about 4 weeks, the fires spread around and into the Chernobyl exclusion zone (CEZ) and came within a few kilometers of both the CNPP and radioactive waste storage facilities. Wildfires occurred on several occasions throughout the month of April. They were extinguished, but weather conditions and the spread of fires by airborne embers and smoldering fires led to new fires starting at different locations of the CEZ. The forest fires were only completely under control at the beginning of May, thanks to the tireless and incessant work of the firefighters and a period of sustained precipitation. In total, 0.7-1.2 TBq 137Cs were released into the atmosphere. Smoke plumes partly spread south and west and contributed to the detection of airborne 137Cs over the Ukrainian territory and as far away as Western Europe. The increase in airborne 137Cs ranged from several hundred µBq·m-3 in northern Ukraine to trace levels of a few µBq·m-3 or even within the usual background level in other European countries. Dispersion modeling determined the plume arrival time and was helpful in the assessment of the possible increase in airborne 137Cs concentrations in Europe. Detections of airborne 90Sr (emission estimate 345-612 GBq) and Pu (up to 75 GBq, mostly 241Pu) were reported from the CEZ. Americium-241 represented only 1.4% of the total source term corresponding to the studied anthropogenic radionuclides but would have contributed up to 80% of the inhalation dose.

70-Year Anthropogenic Uranium Imprints of Nuclear Activities in Baltic Sea Sediments.

A strongly stratified water structure and a densely populated catchment make the Baltic Sea one of the most polluted seas. Understanding its circulation pattern and time scale is essential to predict the dynamics of hypoxia, eutrophication, and pollutants. Anthropogenic 236U and 233U have been demonstrated as excellent transient tracers in oceanic studies, but unclear input history and inadequate long-term monitoring records limit their application in the Baltic Sea. From two dated Baltic sediment cores, we obtained high-resolution records of anthropogenic uranium imprints originating from three major human nuclear activities throughout the Atomic Era. Using the novel 233U/236U signature, we distinguished and quantified 236U inputs from global fallout (45.4-52.1%), Chernobyl accident (0.3-1.8%), and discharges from civil nuclear industries (46.1-54.3%) to the Baltic Sea. We estimated the total release of 233U (7-15 kg) from the atmospheric nuclear weapon testing and pinpointed the 233U peak signal in the mid-to-late 1950s as a potential time marker for the onset of the Anthropocene Epoch. This work also provides fundamental 236U data on Chernobyl accident and early discharges from civil nuclear facilities, prompting worldwide 233U-236U tracer studies. We anticipate our data to be used in a broader application in model-observation interdisciplinary research on water circulation and pollutant dynamics in the Baltic Sea.

3D simulations for evaluation of location factors in an urban environment: application of a novel methodology to calculate external exposure doses for evacuees from Pripyat.

This article presents a methodology for assessing the radiation doses in an urban environment due to external irradiation from radionuclides deposited on the ground and other surfaces as well as from a passing radioactive cloud. The approach was developed and applied to assess individual doses of residents of the town of Pripyat who were evacuated shortly after the Chernobyl accident. Typically, the so-called location factor is defined as the ratio of the dose rate at a point of exposure and the dose rate at an undisturbed lawn far from any buildings. The present study used a new definition of the location factor as a regular four-dimensional grid of ratios of air kerma rates indoors and outdoors distributed in space and time. The location factors were calculated for two scenarios: outdoor and indoor values for typical apartments and buildings in Pripyat. Indoor location factors varied within two orders of magnitude depending on the floor of residence and place of staying inside the apartment. Values of the indoor location factor differed during the daytime and night by a factor of 30-40 depending on the behaviour of an individual within the apartment. Both, outdoor and indoor location factors decreased with decreasing distances between buildings. It was shown that during the first 4 days after the accident, air kerma rates in Pripyat were governed by the radionuclides deposited on the ground surface, and not by radionuclides in the cloud. Specifically, the contribution of the radioactive cloud to air kerma rate was maximal (i.e., 2.3%) on the morning of 28 April 1986. The methodology and results of this study are currently being used to reconstruct the radiation gonadal dose for the subjects of the American-Ukrainian study of parental irradiation in Chernobyl cleanup workers and evacuees for investigating germline mutations in their offspring.

Thyroid doses in Ukraine due to 131I intake after the Chornobyl accident. Report II: dose estimates for the Ukrainian population.

This paper describes the revision of the thyroid dosimetry system in Ukraine using new, recently available data on (i) revised 131I thyroid activities derived from direct thyroid measurements done in May and June 1986 in 146,425 individuals; (ii) revised estimates of 131I ground deposition density in each Ukrainian settlement; and (iii) estimates of age- and gender-specific thyroid masses for the Ukrainian population. The revised dosimetry system estimates the thyroid doses for the residents of the settlements divided into three levels depending on the availability of measurements of 131I thyroid activity among their residents. Thyroid doses due to 131I intake were estimated in this study for different age and gender groups of residents of 30,353 settlements in 24 oblasts of Ukraine, Autonomous Republic Krym, and cities of Kyiv and Sevastopol. Among them, dose estimates for 835 settlements were based on 131I thyroid activities measured in more than ten residents (the first level), for 690 settlements based on such measurements done in neighboring settlements (the second level), and for 28,828 settlements based on a purely empirical relationship between the thyroid doses due to 131I intake and the cumulative 131I ground deposition densities in settlements (the third level). The arithmetic mean of the thyroid doses due to 131I intake among 146,425 measured individuals was 0.23 Gy (median of 0.094 Gy); about 99.8% of them received doses less than 5 Gy. The highest oblast-average population-weighted thyroid doses were estimated for residents of Chernihiv (0.15 Gy for arithmetic mean and 0.060 Gy for geometric mean), Kyiv (0.13 and 0.051 Gy) and Zhytomyr (0.12 and 0.049 Gy) Oblasts followed by Rivne (0.10 and 0.039 Gy) and Cherkasy (0.088 and 0.032 Gy) Oblasts, and Kyiv City (0.076 and 0.031 Gy). The geometric mean of thyroid doses estimated in this study for the entire Ukraine essentially did not change in comparison with a previous estimate, 0.020 vs. 0.021 Gy, respectively. The ratio of geometric mean of oblast-specific thyroid doses estimated in the present study to previously calculated doses varied from 0.51 to 3.9. The highest increase in thyroid doses was found in areas remote from the Chornobyl nuclear power plant with a low level of radioactive contamination: by 3.9 times for Zakarpatska Oblast, 3.5 times for Luhansk Oblasts and 2.9 times for Ivano-Frankivsk Oblast. The developed thyroid dosimetry system is being used to revise the thyroid doses due to 131I intake for the individuals of post-Chornobyl radiation epidemiological studies: the Ukrainian-American cohort of individuals exposed during childhood and adolescence, the Ukrainian in utero cohort, and the Chornobyl Tissue Bank.

Reliability of thyroid doses due to 131I intake exceeding 5 Gy in a cohort of Belarusian children exposed to Chernobyl fallout.

High thyroid doses due to Iodine-131 (131I) intake among individuals exposed in childhood and adolescence to Chernobyl fallout raise questions about their reliability and their impact on the analysis of the radiation-related risk of thyroid cancer and other thyroid diseases in the exposed population. In the present study, an in-depth examination was conducted of thyroid doses from 131I intake over 5 Gy calculated for 131 subjects of the Belarusian-American cohort of individuals exposed after the Chernobyl accident. Thyroid doses in this cohort study were estimated based on individual radiation measurements of 131I thyroidal activity and detailed questionnaire data on individual behavior and consumptions of locally produced foodstuffs. Therefore, these doses provide the best basis for assessing reliability. The analysis showed that the result of direct thyroid measurement was mistakenly assigned to three out of 131 study subjects (2.3% of the total), and, therefore, the instrumental thyroid dose for these individuals cannot be correctly estimated. This study confirmed with a high degree of confidence the reliability of thyroid doses due to 131I intake exceeding 5 Gy that were calculated for the Belarusian-American cohort members.