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

Concentrations of the natural radionuclide Po-210 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 milli), 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 Po-210 was supported by decay of the Pb-210 parent (Po-210/Pb-210 activity ratios were 15, 134 and 5.9 respectively for the three species), indicating that direct uptake of Po-210 into the liver balances losses from excretion and radioactive decay. The radiation dose from Po-210 in the livers accounted for between 88% and 99% of the total internal absorbed dose received by the fish species. The activity of Po-210 in sea water from the study area was 0.9-2.2 mBq L-1, yielding concentration factors for Po-210 in liver tissue in the range 3 x 103 to 100 x 103. No significant monophasic relationships were observed between the Po-210 results and the measured concentrations of the elements Cd, Cu, Fe, Mn, Zn and Pb, except that Pb and Po-210 were correlated (r = 0.511) in C. kumu.