Long-term trends of radiocaesium concentrations in moose (Alces alces) harvested in Sweden

This paper describes an analysis of data from long-term monitoring (28 years) of ¹³⁷Cs activity concentrations in muscle tissue from moose (Alces alces) harvested in east-central Sweden. Two data sets on activity concentrations in moose muscle samples from the adjacent municipalities of Heby (n = 3652; y 1986-2012) and Gävle (n = 11,511; y 1986-2008) were used. Geometric means of ¹³⁷Cs activity concentrations in moose have declined from 700 Bq kg^-1 in Heby and 1300 Bq kg^-1 in Gävle during 1986-1989 to around 300 Bq kg^-1 in Heby (2009-2012) and 700 Bq kg^-1 in Gävle (2005-2008). Based on annual geometric mean values of ¹³⁷Cs in the muscle samples, the effective ecological half-life of ¹³⁷Cs was calculated to be 16 years in both Heby and Gävle. The average ¹³⁷Cs activity concentrations in moose calves were 14 % higher in Heby and 18 % higher in Gävle compared to adults. No sex-specific difference in activity concentration was found. Mean aggregated transfer factors (T_ag) from soil to moose muscle tissue were calculated at 0.016 m² kg^-1 (range 0.010-0.036) in the Heby area and 0.023 m² kg^-1 (range 0.013-0.035) in the Gävle area. Using GIS software, mean deposition within a 1.7 km radius around each killing spot for moose harvested in Heby was calculated, resulting in individual T_ag values. On an individual level, this resulted in a minimum T_ag of 0.001 m² kg^-1 and a maximum T_ag of 0.104 m² kg^-1, distinctly reflecting the high variation of ¹³⁷Cs concentrations in moose. The proportion of samples exceeding the national intervention limit of 1500 Bq kg^-1 was 5 % in Heby and 25 % in Gävle during the study period.