Polonium-210 in cartilaginous fishes (Chondrichthyes) from south-eastern Australian waters

Abstract

A study was made of the concentration of the naturally occurring radionuclide polonium-210 in the livers of cartilaginous fishes (chondrichthyans) caught in the waters of Port Phillip Bay, Victoria, Australia in 1991. Five elasmobranch species had ²¹⁰Po concentrations in the range 1-31 Bq kg^-1 (wet weight) and one holocephalian species, the elephant fish (Callorhynchus milii), was exceptional with a ²¹⁰Po range of 60-270 Bq kg^-1 (n=3, mean 180 Bq kg^-1). Lead-210 was present at 0.1- 1.1 Bq kg^-1 and activity concentration ratios of ²¹⁰Po:²¹⁰Pb were all greater than 1, indicating that the ²¹⁰Po could not all have grown in from in situ decay of ²¹⁰Pb within the chondrichthyan liver. The concentration of ²¹⁰Po in the livers appeared to be species related. Concentrations of the trace metals Cu, Fe and Zn showed no correlation with the ²¹⁰Po and were not species-related. The mean concentration of ²¹⁰Po measured in Port Phillip Bay water was 0.32 mBq kg^-1. This yields concentration factors of 3.2 × 10³ to 8.4 × 10⁵ for unsupported ²¹⁰Po in the livers of the chondrichthyans. The total ²¹⁰Po (using Q=20) exposes the livers to a weighted absorbed dose of up to 140 mGy year^-1 (16µGy h^-1), which is >99% of the total internal dose and three orders of magnitude greater than the external dose based on estimated levels of ⁴⁰K.