Accumulation of 210Po by spiny dogfish (Squalus acanthias), elephant fish (Callorhinchus milii) and red gurnard (Chelodonichthys kumu) in New Zealand shelf waters

Abstract

Concentrations of the natural radionuclide ²¹⁰Po in the livers of 81 individual specimens of three fish species collected from waters of the Otago continental shelf, New Zealand, have been measured: spiny dogfish (Squalus acanthias), 4·2 ± 1·8 Bq kg^-1 wet weight (mean ± standard deviation, n = 48); elephant fish (Callorhinchus milii), 136 ± 39 Bq kg^-1 (n = 7); and red gurnard (Chelodonichthys kumu), 38 ± 13 Bq kg^-1 (n = 26). Separate measurements showed that only a negligible fraction of the ²¹⁰Po was supported by decay of the ²¹⁰Pb parent (²¹⁰Po/²¹⁰Pb activity ratios were 15, 134 and 5·9 respectively for the three species), indicating that direct uptake of ²¹⁰Po into the liver balances losses from excretion and radioactive decay. The radiation dose from ²¹⁰Po in the livers accounted for between 88% and 99% of the total internal absorbed dose received by the fish species. The activity of ²¹⁰Po in sea water from the study area was 0·9–2·2 mBq L^-1, yielding concentration factors for ²¹⁰Po in liver tissue in the range 3 × 103 to 100 × 103. No significant monophasic relationships were observed between the ²¹⁰Po results and the measured concentrations of the elements Cd, Cu, Fe, Mn, Zn and Pb, except that Pb and ²¹⁰Po were correlated (r = 0·511) in C. kumu.