Assessment of the current contamination situation in wild boar in Germany. Final report

The wild boar (Sus scrofa) is, besides some fungal species, the only biomedium in Germany that can still show significantly elevated ${}^{137}$Cs activities due to the Chernobyl fallout. The ${}^{137}$Cs activity, which is deposited differently from region to region, acts as a base variable. The ${}^{137}$Cs contamination of wild boars is determined by several influencing factors and can vary by 3 orders of magnitude within months. Deer truffles (Elaphomyces spp.) and available fruit through tree mast play a special role. In this research project, the contamination situation of wild boars in 3 study areas from 2017 - 2020 was evaluated as an example. The study areas selected because of their ${}^{137}$Cs soil contamination and wild boar populations are Bodenmais / Bayerisch Eisenstein and Zusmarshausen and Dahn in Bavaria, in the Palatinate Forest. The investigations were divided into 3 work packages (AP1, AP2 and AP3). In the first work package, the body weight distribution of the wild boars was modeled on the basis of researched hunting data from the 3 study areas. For this purpose, forecasts were calculated according to two different population-ecological scenarios. The shooting data from all 3 study areas show a high percentage of killing weights up to 50 kg, which are predominantly wild boars up to 2 years of age. If the broad base of a wild boar population is formed by young animals, this indicates a growing population. The modeling was carried out for the two scenarios, "favorable conditions" and "unfavorable conditions". The weight distribution changes in the case of unfavorable living conditions, especially in the lower weight classes: In the "unfavorable conditions" scenario, the first three weight classes account for 34% of the huntings, and 45% in the "favorable conditions" scenario. The reason for this is that especially newborns put on less weight in unfavorable living conditions and the mortality rate is higher than under normal or optimal conditions. The weight distribution in the killings using the example of a sample population shows a peak in frequency (27.5%) for the 10 - 20 kg class. Thereafter, the frequency decreases continuously with each weight class. The topic of the second work package was the determination of the biomass and the ${}^{137}$Cs activity of deer truffles. For this purpose, the number and weight of fruit bodies on 4 square meters, down to a soil depth of 25 cm, were determined at 15 grid points in each study area. In Bodenmais, the biomass was significantly larger at an average of 319.9 g than in Zusmarshausen with 184.2 g and Dahn with 82.2 g. Most of the fruiting bodies were found in all 3 study areas in the soil area from 8-12 cm depth. In German forest ecosystems, the maximum of the ${}^{137}$Cs activity in the soil can often be found in this area. The ${}^{137}$Cs activity of a deer truffle (Elaphomyces granulatus) was measured for each grid point on high-purity Germanium detectors. The ${}^{137}$Cs activity of deer truffles varied significantly within one study area. The range of the measured values ranged in Dahn from 226 Bq•kg${}^{-1}$ to Bq•kg${}^{-1}$ FS, in Bodenmais from 941 Bq•kg${}^{-1}$ to 10,370 Bq•kg${}^{-1}$. In Zusmarshausen, the values were the furthest apart with 851 Bq•kg${}^{-1}$ to 16,908 Bq•kg${}^{-1}$. In the third work package, the ${}^{137}$Cs activity of wild boars was investigated. For this purpose, 451 samples were measured from the 3 investigation areas. As in the case of the deer truffles, the variability of the measured values was also very large in the wild boars, in each study area the ${}^{137}$Cs activity varied by 3 orders of magnitude. The span of all measured values ranged from 2 Bq•kg${}^{-1}$ (Dahn) to 17,326 Bq•kg${}^{-1}$ (Bodenmais / Bayerisch Eisenstein). Wild boars from Bodenmais / Bayerisch Eisenstein had significantly higher levels of ${}^{137}$Cs contamination with an average of 3,230 Bq•kg${}^{-1}$ than those from Zusmarshausen (663 Bq•kg${}^{-1}$) and Dahn (240 Bq•kg${}^{-1}$). However, there were also several wild boars in Zusmarshausen with significantly higher measured values: The maximum value was 10,290 Bq•kg${}^{-1}$. The ${}^{137}$Cs contamination of wild boars is controlled by several influencing factors. The level of soil contamination in the investigation areas acts as a basic disposition. The seasonal fluctuations in the measured values are significantly influenced by the food supply and the hunting strategies. In autumn, during fattening years, the wild boars mainly eat the fruits of beech and oak, which contain very little ${}^{137}$Cs activity. 2018 was a fattening year: In Zusmarshausen, the median value of ${}^{137}$Cs activity in wild boars during the fattening period was 16 Bq•kg${}^{-1}$. In the previous months, the median contamination was 6,869 Bq•kg${}^{-1}$, then 1,234 Bq•kg${}^{-1}$. Due to these peculiarities, the hunting strategies are of particular importance when interpreting the measured values: In Dahn and Zusmarshausen, wild boars are mainly hunted in autumn / early winter through group hunts, in Bodenmais / Bayerisch Eisenstein, however, all year round and predominantly through individual hunts. Therefore, 47.6% of all samples came from Zusmarshausen in the period from September 2018 to May 2019 (time of the very low ${}^{137}$Cs contamination), whereas only 9.3% from Bodenmais / Bayerisch Eisenstein. These relationships have a corresponding effect on the statistical results of the ${}^{137}$Cs measurement values.