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

Caesium-137 in the muscles of game animals in 2015-2022 - levels and time trend

Introduction

Radioactive caesium-137 occurring in the environment may be taken up by plants and animals and pose a trophic threat to humans. Game animals living in forest ecosystems are very good bioindicators of the level of environmental contamination by ionising radiation. The main species measurably exposed to caesium-137 are the wild boar (Sus scrofa), the roe deer (Capreolus capreolus), and the red deer (Cervus elaphus). The study determined the levels of Cs-137 in muscle samples of these game animals in 2015-2022.

Material and Methods

Using gamma radiation spectrometry, 858 samples of game animal muscle tissue were examined: 508 wild boar, 145 roe deer and 205 red deer samples.

Results

Concentrations of Cs-137 varied widely (from minimum detectable activity (MDA) values to over 4,000 Bq/kg). In 63.4% of cases, the obtained concentrations exceeded the MDA. The permissible limit (600 Bq/kg for food) was exceeded in nine wild boar muscle samples, whereas it was not even exceeded once in roe or red deer muscle. The average concentration in wild boar was three times higher than in roe and red deer and amounted to 42.84 Bq/kg. The highest concentration of Cs-137 in wild boar muscle was 4,195 ± 372.0 Bq/kg, in roe deer muscle it was 111.5 ± 12.50 Bq/kg, and in red deer muscle was 86.70 ± 3.470 Bq/kg.

Conclusion

The seven years' data indicate that wild boar absorb the most caesium-137 among game animals. The concentrations of Cs-137 in the muscle of game animals in the years 2015-2022 were at a nearly constant level, a very slow diminution being noticeable over time in roe and red deer muscle.

Time dependence of 137Cs contamination in wild Japanese monkeys after the Fukushima Daiichi nuclear accident

Over the 10 years immediately after the Fukushima Daiichi nuclear accident, we measured the changes in the muscle ¹³⁷Cs concentration (Bq/kg) of wild Japanese monkeys living in Fukushima City, which is located approximately 70 km from the Fukushima Daiichi Nuclear Power Plant. The muscle¹³⁷Csconcentration, which was observed at a maximum of 13,500 Bq/kg immediately after the accident, had decreased to several hundred Bq/kg 10 years later. The muscle ¹³⁷Cs concentration was significantly related to the soil contamination levels (10,000-30,000, 30,000-60,000, 60,000-100,000, and 100,000-300,000 Bq/m²), sex, age class (immature, mature), body weight (> 5000 g, 5000-10,000 g, < 10,000 g), and seasons (the cold period from December to April, the warm period from May to November).The value of muscle ¹³⁷Cs concentration and the aggregated transfer factor (T_ag: calculated by dividing muscle ¹³⁷Cs concentration [Bq/kg] by soil ¹³⁷Cs deposition density at the capture site [Bq/m²]) apparently decreased with time for several years. However, post hoc pairwise comparisons showed no difference from 2017 to 2020, and the accumulation of ¹³⁷Cs in muscle may continue for some time.

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.

Monitoring of radioactive cesium in wild boars captured inside the difficult-to-return zone in Fukushima Prefecture over a 5-year period

Following the Fukushima Daiichi Nuclear Power Plant accident in 2011, tissue samples from wild boar (Sus scrofa) outside the evacuation zone (difficult-to-return zone, DRZ) tended to show high activity concentrations of cesium-137 (¹³⁷Cs). Understanding the ¹³⁷Cs dynamics of wild boar populations inside the DRZ is necessary because they affect ¹³⁷Cs dynamics and wild boar management in areas outside the DRZ. Since few detailed, long-term studies have been conducted inside the DRZ, we measured ¹³⁷Cs activity concentrations in 221 wild boar muscle samples obtained from wild boar caught inside the DRZ and surrounding areas over a 5-year period. Our results showed that the ¹³⁷Cs activity concentration in wild boar from inside the DRZ were higher than those in wild boar outside this zone. No significant difference was observed between muscle and soil ¹³⁷Cs levels, but significant correlations were observed between muscle ¹³⁷Cs activity concentrations and body length and body weight in the low-activity-concentration season, but not between all seasons and the high-activity-concentration seasons. It is considered that the size effects observed during the low-activity-concentration season may be due to factors related to metabolism and changes in food habit. This is the first long-term survey of ¹³⁷Cs in wild boar inside the DRZ.

Radiocaesium in wild boars in Novohradské (Gratzen) Mountains

The monitoring of radiocaesium in the ecosystems of particular areas in the Czech Republic is necessary even decades following the Chernobyl nuclear disaster. We report an evaluation of the radioactive contamination of the meat of wild boars hunted in the Novohradské (Gratzen) Mountains in the period of December 2012 to December 2019. Radionuclide 137Cs is surveyed for food safety as a source of food chain contamination and a possible risk for human health. Overall, 654 samples of game meat from wild boars were analysed for 137Cs activity. The 137Cs legal limit of 600 Bq·kg-1 was exceeded in 238 samples (36.4%) of hunted wild boar meat. Statistical analysis showed that 137Cs activities measured in wild boar muscle in March reached lower values compared to the period from June till November (P < 0.05). Higher values were reported in September (P < 0.05) as well as in August (P < 0.01) compared to December. A significant season-based 137Cs level was found (P < 0.000). Higher 137Cs activities in wild boar in the winter season (November to April) are related to decreasing access to a naturally occurring diet with a lower 137Cs content. The keepers of the wild boar in this area were ordered to comply with obligatory emergency veterinary precautions set by the Regional Veterinary Administration to analyse all hunted game meat for radiocaesium. All wild boars with an above-limit 137Cs value had to be excluded from the food chain by hunting ground keepers and disposed of safely.

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.

Effects of 137Cs contamination after the TEPCO Fukushima Dai-ichi Nuclear Power Station accident on food and habitat of wild boar in Fukushima Prefecture

After the Tokyo Electric Power Company Fukushima Dai-ichi Nuclear Power Station accident, wild boar was found to have greater radiocesium (¹³⁷Cs) activity concentrations in their bodies than other wild animals in Japan; however, the reason for this remains unknown. To understand the mechanism of ¹³⁷Cs transfer from the environment to wild boar, and the factors that affect variation in ¹³⁷Cs contamination in wild boar, we sampled muscle and stomach contents from wild boar captured in Fukushima Prefecture and analyzed the relationships among ¹³⁷Cs concentrations in muscle tissue and in the stomach contents, ¹³⁷Cs ground deposition at capture sites, and wild boar food habits. Significant positive relationships were observed among ¹³⁷Cs activity concentrations in muscle and stomach contents, as well as ¹³⁷Cs deposition density at capture sites. These results suggest that ¹³⁷Cs is transferred from the environment to plant and animal materials consumed by wild boar, and then from these foods to the bodies of wild boar through digestion. However, no correlation was observed between ¹³⁷Cs concentrations in stomach contents and the presence of any particular food item in stomachs of wild boar, including mushrooms. These findings suggest mushrooms and underground food items, which were found to affect ¹³⁷Cs concentrations in wild animals in Europe, were not important contributors to high levels of ¹³⁷Cs contamination in Japanese wild animals.

Improved field-portable system to measure Cs-137 in wildlife

We have developed an improved system to measure Cs-137 in wildlife at the Savannah River Site. This field-portable system consists of a shielded 5 cm by 10 cm by 40 cm NaI detector controlled by an Ametek Ortec Digibase. Measurement of an animal's radioactivity is made by placing the animal at a predefined location on the detector system for a one minute count-time. The counts, animal type, and animal weight are then used as inputs to an algorithm which calculates the amount of Cs-137 within the whole animal and within the edible meat portion of the animal. The results from these calculations are used to estimate the received dose from eating this animal and is included in the Savannah River Site's Hunter Dose Tracking System. This system has a detection limit of 0.60 pCi/g (22.20 Bq/kg) with a typical measurement uncertainty of less than 0.32 pCi/g (11.84 Bq/kg).

Seasonal variation of Cesium-137 concentration in Asian black bear (Ursus thibetanus) and wild boar (Sus scrofa) in Fukushima Prefecture, Japan

To elucidate and reduce the risk of radionuclide contamination in wildlife caused by the Tokyo Electric Power Company Fukushima Dai-ichi Nuclear Power Station accident, it is important to understand radionuclide variations in the wild animal population. Here, we used environmental monitoring data and muscle samples collected from Asian black bear (Ursus thibetanus) and wild boar (Sus scrofa) from May 2011 to March 2016 to examine seasonal variation in radiocesium (¹³⁷Cs) concentrations in muscle tissues (hereafter, muscle ¹³⁷Cs) of these important game species in Fukushima Prefecture. We measured muscle ¹³⁷Cs of bears and wild boars killed by hunters or in animal control culls. First, using a linear mixed model (LMM), we tested for a positive relationship between muscle ¹³⁷Cs and ¹³⁷Cs in the soil at the site of capture (hereafter, soil ¹³⁷Cs) estimated from a soil ¹³⁷Cs deposition map produced by the Japan Atomic Energy Agency. In the LMM, muscle ¹³⁷Cs was positively related to estimated soil ¹³⁷Cs, which corroborates the results of previous studies. The LMM regression coefficients differed between the two species, with wild boar muscle ¹³⁷Cs being higher than that of bears sampled at the same locations. We then employed a generalized additive mixed model (GAMM) to estimate seasonal variation in the muscle ¹³⁷Cs of the target species. GAMM showed that muscle ¹³⁷Cs varied seasonally and that this seasonal variation also differed between the two species. In bears, muscle ¹³⁷Cs decreased from spring to early autumn, before increasing in winter. Wild boar muscle ¹³⁷Cs remained low during spring and summer and was high during autumn and early spring. These patterns are likely influenced by differences in diet, habitat use, and physiology between these two species.

Radiocaesium contamination of wild boars in Fukushima and surrounding regions after the Fukushima nuclear accident

Analysis of radioactivity data obtained under the food monitoring campaign in Japan indicates that elevated ¹³⁴Cs+¹³⁷Cs activity concentrations in wild boar meat remained constant or slowly decreased in Fukushima and surrounding prefectures from 2011 to 2015. The activity concentrations in some samples are still over the regulatory limit of 100 Bq kg^-1 fresh weight, even in 2015. Activity concentrations of ¹³⁷Cs in muscle of wild boars we captured in 2011 were higher than those in kidney, liver, spleen, heart and lung. A food processing retention factor, F_r, was 0.5 or 0.6 for ¹³⁷Cs when the wild boar meat was boiled, suggesting that a parboiling process is effective for reduction of radiocaesium intake from wild boar meat.

The Time-Dependent Transfer Factor of Radiocesium from Soil to Game Animals in Japan after the Fukushima Dai-ichi Nuclear Accident

Since the Fukushima Dai-ichi accident, monitoring of tissues from hunted game animals ensures compliance with the standard food limits for radionuclides in Japan. We quantified the transfer of (137)Cs from contaminated land to game animals using the Aggregated transfer factor (Tag = activity concentration in meat [Bq kg(-1) fw]/amount in soil [Bq m(-2)]) of (137)Cs for Asian black bear, wild boar, sika deer, green pheasant, copper pheasant and wild duck, collected between 2011 and 2015. Open data sources were used from Fukushima, Miyagi, Ibaraki, Tochigi, and Gunma prefectures. Our initially compiled data showed that the maximum reported (137)Cs activity concentration in wild boar after the Fukushima Dai-ichi accident were lower than those reported after the Chernobyl accident. The geometric mean Tag values (m(2)kg(-1) fw) of (137)Cs in 2015 for Asian black bear, wild boar, sika deer and copper pheasant were similar (1.9-5.1) × 10(-3) while those for green pheasant and wild duck were about 1 order of magnitude lower at (1.0-2.2) × 10(-4). Effective half-lives were 1.2-6.9 y except for sika deer and copper pheasant where no decreases were found. In contrast to the Chernobyl accident, no seasonal change occurred in the meat (137)Cs activity concentrations of the wild animals during the study period.

Dietary items as possible sources of (137)Cs in large carnivores in the Gorski Kotar forest ecosystem, Western Croatia

The mountain forest ecosystem of Gorski Kotar is distant from any significant sources of environmental pollution, though recent findings have revealed that this region is among the most intense (137)Cs contaminated area in Croatia. Therefore, the aim of this study was to investigate (137)Cs and (40)K load in three large predator species in the mountain forest ecosystem. Radionuclides mass activities were determined by the gamma-spectrometric method in the muscle tissue of brown bear (47), wolf (7), lynx (1) and golden jackal (2). The highest (137)Cs mass activity was found in lynx (153 Bq kg(-1)), followed by brown bear (132 Bq kg(-1)), wolf (22.2 Bq kg(-1)), and golden jackal (2.48 Bq kg(-1)). Analysis of 63 samples of dietary items suggests that they are not all potentially dominant sources of (137)Cs for wildlife. The most important source of radionuclides for the higher parts of the food-chain from the study area were found to be the mushroom species wood hedgehog (Hydnum repandum), with a transfer factor TF of 5.166, and blueberry (Vaccinium myrtillus) as a plant species (TF=2.096). Food items of animal origin indicated higher mass activity of radionuclides and therefore are possible moderate bioindicators of environmental pollution. The results also revealed that possible unknown wild animal food sources are a caesium source in the study region, and further study is required to illuminate this issue.