An experimental study of the uptake and loss of Ra-226 by the tissue of the tropical freshwater musselVelesunio angasi (Sowerby) under varying Ca and Mg water concentrations

Freshwater musselsVelesunio angasi (Sowerby) from Magela Creek, Alligator Rivers Region, Northern Territory, Australia, experimentally exposed to mean elevated Ra-226 water concentrations ranging between 0.95 and 1.85 Bq 1^–1 for 28 days, accumulated Ra-226 in their tissue to mean concentrations ranging from 2.8 to 4.8 Bq per gram of dry tissue. The Ra-226 (log₁₀) was accumulated in a linear pattern over exposure periods of 28 and 56 days. Mussel size and sex had little or no effect on the rates of uptake of Ra-226 per gram of tissue.Increased Ca and Mg water concentrations, both in combination and singly, reduced the rate of uptake of Ra-226 by mussel tissue. The experimental data are consistent with Ra-226 accumulation being inversely proportional to both Ca and Mg water concentrations; for Ca the constant of proportionality i.e. is unity; for Mg it is about 0.1.The results indicate competitive inhibition of the uptake of Ra-226 by Ca, i.e. that the mussel treated Ra-226 as a metabolic analogue of Ca; however, there are other possible interpretations of these results that need not invoke competitive inhibition. For Mg the results suggest involvement of some other mechanism(s) apart from or in addition to competitive inhibition of Ra-226 by Mg.Exposure of mussels that had accumulated Ra-226 under field and laboratory conditions to radium-free water for up to 286 days resulted in no significant loss (P > 0.05) of Ra-226 from the tissue. This indicates a very long biological half-life for Ra-226 in the tissue ofV. angasi.