Radionuclide bioaccumulation by freshwater organisms can be modified by the presence of Cd or Zn.
Garnier-Laplace J., C. Adam, B. Fraysse, O. Ausseil and A. Boudou
12th annual meeting of SETAC Europe , Vienne (Autriche), 12-16 mai 2002.
Should realism of radioecological assessments be enhanced by taking into account the deleterious influence of stable pollutants on aquatic organisms which can be physiologically stressed, and therefore modify their response to radionuclide bioaccumulation? Direct transfer experiments on a bivalve (Dreissena polymorpha) and a fish (Oncorhynchus mykiss) involved metals (Cd, Zn) and radionuclides (radioactive isotopes of Co, Cs, and Ag). Chronic metallic waterborne exposures (1-4 µg/L Cd and/or 170-250 µg/L Zn) led to a decrease in radionuclide bioaccumulation with respect to the reference group (110mAg and 137Cs for fish with respectively –60% and –30%; 57Co for bivalve with –50%, on average); while no effect was noticed with other radionuclide/organism pairs (Co for fish, Cs and Ag for bivalve).
Some explanations are given
(1) to link the stable pollutant-induced stress in organisms (especially biomarkers of oxidative stress and protein synthesis) and the modification of the radionuclide bioaccumulation level and kinetics,
(2) to provide evidence of the mechanisms involved.
Illustration will be mainly given for the bivalve for which the inhibiting effect of Zn on the 57Co uptake rate was clearly evidenced and explained with:
(1) a net decrease in 57Co input through biological barriers,
(2) a cellular redistribution of 57Co with a decrease of the cytosolic fraction and an increase of the storage in the form of mineral granules,
(3) a modification of the 57Co tissue distribution with a storage in the form of granular deposits in the mantle and the excretory organs.
These biomineralisation processes playing a fundamental role in bivalves could explain the marked difference of effect between the two biological models.