¹³⁷Cs and ⁴⁰K in gray seals Halichoerus grypus in the southern Baltic Sea

This study presents levels of ¹³⁷Cs and ⁴⁰K concentrations in the placentas of seals gathered in the period 2007–2015. The mean activity of ¹³⁷Cs and ⁴⁰K was 5.49 Bq kg⁻¹w.w. and 136.6 Bq kg⁻¹ ww respectively. Statistically significant correlation was observed between the ¹³⁷Cs activities in placenta and in herring—the staple food for seals. The concentrations of ¹³⁷Cs and ⁴⁰K were also determined in other tissues (muscle, liver, lung, and brain) of wild seals. The concentrations of ¹³⁷Cs were from 2.59 Bq⁻¹ ww (lungs) to 24.3 Bq kg⁻¹ ww (muscles). The transfer factor values for ¹³⁷Cs (seal tissue/fish) ranged from 0.89 to 2.42 in the case of the placentas and from 1.35 to 8.17 in the case of the muscle. For adults seal, the effective dose from ¹³⁷Cs was 2.98 nGy h⁻¹. The mean external radiation dose to pup was 0.77 nGy h⁻¹ from ¹³⁷Cs and 6.69 nGy h⁻¹ from ⁴⁰K.