Polonium-210 in mussels and fish from the Baltic-North Sea estuary

Polonium-210 has been measured in Danish fish meat caught in the North Sea, the Kattegat and the Baltic in 1991–1994. Average values of 0.35, 0.65 and 0.96 Bq 210Po kg−1 fresh weight were observed for cod, herring and plaice fillets, respectively. The difference between species is statistically significant, whereas no effect of salinity could be observed. There is a high variation giving SD values in the range 70–100%. Mytilus edulis soft parts were analysed for 210Po from 11 Danish locations ranging from full North Sea salinity to Baltic 8% water. Significantly increasing 210Po concentrations with a decreasing ‘condition index’ were observed. Concentrations at two former phosphate industry sites were not statistically different from the other locations. The average 210Po concentration in the M. edulis soft parts was 149 Bq kg−1 dry ±55% SD (n = 41). The present levels of 210Po in fish and mussels may represent a natural baseline.