Estimated lifetime effective dose to hunters and their families in the three most contaminated counties in Sweden after the Chernobyl nuclear power plant accident in 1986 - A pilot study

LARCalc, a tool to estimate sex- and age-specific lifetime attributable risk in populations after nuclear power plant fallout

A tool called LARCalc, for calculating the radiological consequences of accidental large scale nuclear power plant releases based on estimates of 137Cs ground deposition, is presented. LARCalc is based on a previously developed models that has been further developed and packaged into an easy-to-use decision support tool for training of decision makers. The software visualises the radiological impact of accidental nuclear power plant releases and the effects of various protective measures. It is thus intended as a rapid alternative for planning protective measures in emergency preparedness management. The tool predicts projected cumulative effective dose, projected lifetime attributable cancer risk, and residual dose for some default accidental release scenarios. Furthermore, it can predict the residual dose and avertable cumulative lifetime attributable risk (LAR) resulting from various protective measures such as evacuation and decontamination. It can also be used to predict the avertable collective dose and the increase in cancer incidence within the specified population. This study presents the theoretical models and updates to the previous models, and examples of different nuclear fallout scenarios and subsequent protective actions to illustrate the potential use of LARCalc.

Cancer incidence in a male adult population in relation to estimated protracted colon dose - A nested case control study in Northern Sweden after the Chernobyl Nuclear Power Plant accident

INTRODUCTION

Uncertainty in the dose-response of low dose radiation raised concern of an increased cancer incidence in Sweden after the Chernobyl Nuclear Power Plant (NPP) accident.

MATERIAL AND METHODS

A closed cohort was created of all males ≥18 years of age living in the Northern Sweden in 1986. In total 826,400 individuals were enrolled including 40,874 hunters. A nested case-control design was used with five controls randomly selected for each cancer case matched on year of diagnosis and year of birth. Individual absorbed colon dose was calculated 1986 to 2015. Allowing for a 5-year latency period Hazard Ratios (HR) per mGy with 95% Confidence Intervals (95% CI) were calculated in a conditional logistic regression adjusted by rural/non-rural living, length of education and pre-Chernobyl cancer incidence 1980 to 1985. A total of 127,109 cancer cases occurred from 1 January 1991 to 31 December 2015. Cancer was classified in: 1) Organ-specific (stomach, colon, liver, lung, prostate, urinary bladder, thyroid and leukaemia), 2) Other and 3) Not previously associated to ionizing radiation.

RESULTS

The average colon dose in cases was 1.77 mGy compared to controls 1.73 mGy. Hunters average colon dose was 2.32 mGy. Organ-specific cancers showed the highest HR per mGy both in the full cohort, adj HR 1.019 (1.014-1.024) and the hunter subcohort, adj HR 1.014 (1.001-1.027) during follow-up 1991 to 2015. Other cancer and Not previously associated with ionizing radiation showed lower HR per mGy. Therefore, the adj HR per mGy for Total cancer, 1.013 (1.009-1.017) was explained by Organ-specific cancer. Increased adj HR per mGy was seen in stomach, colon and prostate cancer, respectively in the full cohort and lung cancer in hunters.

CONCLUSIONS

Some cancer sites previously associated with ionizing radiation showed a positive adjusted HR per mGy both in the full cohort and in the hunter subcohort.

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.

Longitudinal Verification of Post-Nuclear Accident Food Regulations in Japan Focusing on Wild Vegetables

Focusing on the importance of wild vegetables for local residents, this study aims to validate the effects of food regulations under the current criteria (e.g., 100 Bq/kg for general foods) established approximately a year after the Fukushima Dai-ichi Nuclear Power Plant accident. Over 2,500,000 monitoring tests were performed under the criteria until fiscal year (FY) 2020. We estimated changes in internal exposure dose using test results. The effective dose was estimated using the radioactive concentration randomly sampled from the results, food intake, and dose conversion factor. As a new attempt, dose estimation reflecting the intake of wild vegetables that may have irreplaceable value for local residents was conducted. The median, 95th, and 99th percentile of the estimated dose without reflecting the wild vegetables’ intake were 0.0485, 0.183, and 10.6 mSv/year, respectively, in the estimation with all test results (no regulation) and 0.0431, 0.0786, and 0.236 mSv/year, respectively, in the estimation with results within the standard limits (regulated) in FY2012. These doses decreased with time. Although estimated doses with or without the reflection of wild vegetables’ intake were similar, estimation that is more plausible is possible, particularly for a high percentile, by reflecting the wild vegetables’ intake. Radiation doses (regulated) were significantly less than 1 mSv/year in different FYs. In Japan, food regulation measures benefit food safety.

Exposure of German hunters and their family members to the radioactive nuclide 137Cs due to their eating habits

The radioactive nuclide ¹³⁷Cs that was released during the Chernobyl accident in 1986 is still present in the environment of wide parts of Middle Europe. It causes internal radiation exposure of people who incorporate this radionuclide when eating contaminated food, in particular boar meat and certain kinds of wild mushrooms. This study investigates the exposure of German hunters and their family members, which are supposed to consume these kinds of food more frequently than the general population. For this purpose, the body activity of ¹³⁷Cs was measured in 58 hunters and their family members mostly from Southern Germany and it was compared with body activities from 1729 measurements of 251 members of the general population. Significantly higher ¹³⁷Cs body activities were found in the hunters and their family members compared to the references after matching both groups for sociodemographic factors and the time of the measurement (factor of 2.4 between the geometric means, p-value ≪ 0.001). Within the hunters and their family members, an adjusted exponential regression showed significant associations of the activity and of mushroom picking (factor 2.6, 95% confidence interval 1.5-4.6) and of the frequency of having boar meat as part of the diet (factor 1.4 per meal per week, 95% confidence interval 1.1-1.8). No significant association was found for the ¹³⁷Cs surface contamination at the hunting grounds. Within families, mostly similar results were found in terms of activity concentrations. For the hunter with the highest measured activity (1050 Bq), an annual contribution to the effective dose of 35 μSv was calculated, showing that also in hunters and their family members ¹³⁷Cs is expected to cause only small contributions to the total effective dose from environmental exposure.

Levels of 137Cs in game and soil in Opole Anomaly, Poland in 2012-2020

Once deposited, radiocesium remains in the environment for a long time, and constantly enters the food chain. Over time, game species tend to accumulate ¹³⁷Cs by two orders of magnitude more than farm animals. This occurs especially in places heavily contaminated, thus meat products made out of local game should be treated with caution. One of such areas, known as the Opole Anomaly, is located in South-Western Poland and represents one of most ¹³⁷Cs contaminated regions across Europe after the Chernobyl accident. The aim of the study was to find out the ¹³⁷Cs activity in soil and local game, the value of the soil-to-game aggregated transfer factor and to assess the effective dose of the ionising radiation (E_eff) received by consumers of local game meat in years 2012-2019. We examined meat of three common game species: red deer, roe deer and wild boar for ¹³⁷Cs activity. ¹³⁷Cs activity in meat samples ranged from 0.14 to 592 Bq kg^-1. The aggregated transfer factor (T_ag) in game ranged from 0.006 to 0.01 m² kg^-1 f.w. for wild boar, 0.005-0.008 m² kg^-1 f.w. for roe deer, and 0.003-0.004 m² kg^-1 f.w. for red deer. The effective dose received by people who regularly consume local game meat ranged from less than 14.2 µSv y^-1 to 134 µSv y^-1, depending on the amount of differently contaminated game meat consumed annually. Even those for whom game is the only source of meat, consumption of wild boar along with local mushrooms and bilberries will, since 2012, not exceed the regulation limit of ¹³⁷Cs at the level of 1 mSv y^-1. By the best of our knowledge this is the first study regarding ¹³⁷Cs activity in game and risk assessment from the most contaminated "post-Chernobyl" area in Poland.

Increased cancer risk in male hunters compared to the general male population in Northern Sweden after the Chernobyl Nuclear Power Plant accident?

Male hunters in Swedish counties with high fallout of ¹³⁷Cs after the Chernobyl Nuclear Power Plant (NPP) accident have higher radiation exposure due to higher consumption of game compared with the general population.

Methods

Cancer incidence in Sweden was studied in 9 counties with different ¹³⁷Cs fallout after the Chernobyl NPP accident in 1986. In total, 9,267 cancer cases occurred in hunters and 138,909 cancer cases in non-hunters to 31 December 2015. Incidence rate ratios (IRR) with 95% confidence intervals (CI) were calculated using unexposed hunters, or non-hunters, as reference to study internal radiation exposure or hunter life style, respectively.

Results

Directly age standardized total cancer incidence showed an increasing trend in non-hunters. For hunters, the total cancer incidence was significantly lower up to 2001 when the total cancer incidence crossed over the weaker non-hunter trend and remained higher for the following 15 years. IRRs for total cancer in hunters versus non-hunters for each county did not show any clear exposure response pattern. IRRs for hunters versus non-hunters were higher regardless of rural/non-rural status with slightly higher risk estimates for the rural settings. The IRR for hunters was 1.06 (95% CI 1.04-1.08) 1986-2015, representing an excess of 531 cancer cases in hunters.

Conclusion

An increased total incidence of cancer was identified for male hunters compared with male non-hunters. No obvious association between cancer and ¹³⁷Cs from the Chernobyl NPP accident could be identified, although the exposure classification was too crude to exclude such an association.

Modelling the effective dose to a population from fallout after a nuclear power plant accident-A scenario-based study with mitigating actions

The radiological consequences of a nuclear power plant (NPP) accident, resulting in the release of radionuclides to the environment, will depend largely on the mitigating actions instigated shortly after the accident. It is therefore important to make predictions of the radiation dose to the affected population, from external as well as internal exposure, soon after an accident, despite the fact that data are scarce. The aim of this study was to develop a model for the prediction of the cumulative effective dose up to 84 years of age based on the ground deposition of 137Cs that is determined soon after fallout. The model accounts for different assumptions regarding external and internal dose contributions, and the model parameters in this study were chosen to reflect various mitigating actions. Furthermore, the relative importance of these parameters was determined by sensitivity analysis. To the best of our knowledge, this model is unique as it allows quantification of both the external and the internal effective dose using only a fallout map of 137Cs after a nuclear power plant accident. The cumulative effective dose over a period of 50 years following the accident per unit 137Cs deposited was found to range from 0.14 mSv/kBq m-2 to 1.5 mSv/kBq m-2, depending on the mitigating actions undertaken. According to the sensitivity analysis, the most important parameters governing the cumulative effective dose to various adult populations during 50 years after the fallout appear to be: the correlation factor between the local areal deposition of 137Cs and the maximum initial ambient dose rate; the maximum transfer from regional average fallout on the ground to body burden; the local areal deposition of 137Cs; and the regional average 137Cs deposition. Therefore, it is important that mapping of local 137Cs deposition is carried out immediately after fallout from a nuclear power plant accident, followed by calculations of radiation doses for different scenarios using well-known parameters, in order to identify the most efficient mitigation strategies. Given this 137Cs mapping, we believe our model is a valuable tool for long-term radiological assessment in the early phase after NPP accidents.

A model for estimating the total absorbed dose to the thyroid in Swedish inhabitants following the Chernobyl Nuclear Power Plant accident: implications for existing international estimates and future model applications

The time-integrated absorbed dose to the thyroid gland in the years after a fallout event can indicate the potential excess number of thyroid cancers among young individuals after a radionuclide release. Typical mean values of the absorbed dose to the thyroid have been calculated previously using reported data on radioiodine obtained from air sampling and dairy milk surveys in Sweden after the Chernobyl fallout, not including the contribution from ¹³⁴Cs and ¹³⁷Cs. We have developed a model for Swedish conditions taking these additional dose contributions into account. Our estimate of the average time-integrated absorbed dose to the thyroid, D _th,tot, during the first 5 years after fallout ranged from 0.5-4.1 mGy for infants and from 0.3-3.3 mGy for adults. The contribution to D _th,tot from ¹³¹I through inhalation and milk consumption varied considerably among different regions of Sweden, ranging from 9%-79% in infants, and from 4%-58% in adults. The external irradiation and exposure from the ingestion of ^134,137Cs in foodstuffs accounted for the remaining contributions to D _th,tot (i.e. up to 96% for adults). These large variations can be explained by the highly diverse conditions in the regions studied, such as different degrees of fractionation between wet and dry deposition, different grazing restrictions on dairy cattle, and differences in ^134,137Cs transfers through food resulting from differences in the local fallout. It is our conclusion that the main contribution to D _th,tot from nuclear power plant fallout in areas subjected to predominantly wet deposition will be from external exposure from ground deposition, followed by internal exposure from contaminated food containing the long-lived fission product ¹³⁷Cs and the neutron-activated fission product ¹³⁴Cs. The contribution from ^134,137Cs to the thyroid absorbed dose should thus be taken into account in future epidemiological studies.