Temporal and spatial variation in ¹³⁷Cs concentrations in wild boar (Sus scrofa) from Sweden

This study investigates temporal and spatial variation in ¹³⁷Cs activity concentrations in Swedish wild boar between 2011 and 2024 to assess long-term ecological impacts of radiocaesium of anthropogenic origin. Data from a total of 5844 meat samples collected across 39 municipalities in six counties were analysed. Average ground deposition of ¹³⁷Cs in these municipalities in 1986 ranged from 1.84 to 51.55 kBq m^-2. The average ¹³⁷Cs concentration in wild boar meat was 1679 Bq kg^-1, with 27.5% of samples exceeding the sales limit of 1500 Bq kg^-1. Seasonal variation in ¹³⁷Cs activity concentrations in wild boar meat was evident, with levels peaking in winter and early spring and declining nearly fivefold in late summer and early autumn, across all locations. On average, younger boars (≤1 year) exhibited 25% higher concentrations than older individuals, with the greatest differences observed in winter and no differences in autumn. No sex-specific differences in concentrations were detected. A weak but statistically significant correlation was observed between meat radioactivity and average ground deposition across all counties, with a slightly weaker correlation in Gävleborg and Uppsala. Overall, ¹³⁷Cs deposition remained the primary factor explaining the observed levels of meat contamination. A twofold increase in ¹³⁷Cs deposition resulted in an almost proportional increase in ¹³⁷Cs activity concentrations in wild boar meat, whereas the ¹³⁷Cs transfer factor (T_ag) remained largely unchanged. The geometric mean T_ag for wild boar was 0.052 m² kg^-1, while the effective half-life (T_eff) of ¹³⁷Cs varied widely among municipalities (2-3 to >30 years); no T_eff could be estimated for the study area as a whole due to the absence of a consistent decline in ¹³⁷Cs activity concentrations.