40 Years after Chornobyl: New Insights into the Wild Boar Paradox

Wild boars in Central Europe exhibit an unexpectedly slow decline of radiocesium contamination originating from nuclear weapon test fallout (NWT) and the Chornobyl accident (CA), known as the wild boar paradox. Seemingly contradictory half-lives were published. Estimates based on Cs-135/Cs-137 ratios in wild boar suggested that: 1. older NWT radiocesium had migrated deeper into soils than the younger CA radiocesium and dominates the growth zone of deer truffles, a preferred wild boar food; and 2. NWT fallout contributes up to 99% (mean 31%) of radiocesium in wild boar. To test these hypotheses, soil cores from several Bavarian regions were analyzed for depth-dependent Cs-137 activity and in selected forest samples Cs-135/Cs-137 ratios were measured. A revised benchmark value for NWT-derived Cs-135/Cs-137 ratio of 3.3±0.3 (reference date: 2011.03.11) was determined, replacing the previously used 1.99±0.19. Cs-137 activities in soils decrease with depth, while Cs-135/Cs-137 ratios - thus NWT contribution - increase slightly, consistent with a compartment model. NWT radiocesium does not dominate the truffle growth zone. Applying the revised NWT-derived Cs-135/Cs-137 ratio reduces the maximum NWT contribution from 99% to 52% (mean 31% to 16%). This work contributes to resolving the wild boar paradox and reconciles reported seemingly incompatible ecological half-lives.