Long-term combined impact of 90Sr and Pb2+ on freshwater cladoceran

The effect of Pb2+ (0.01 and 0.1 mg l-1) and 90Sr (2E+01; 2E+03 and 2E+05 Bq l-1) in conditions of long-term two-factor experiment had a negative impact practically upon all biological parameters of freshwater cladoceran Daphnia magna shown in decrease of the productional characteristics, delay of growth rate and reduction of lifetime. The level of radiotoxical effect positively correlated with the contents in water of the researched agents and their combinations. At combined impact of the radiating and chemical factors the positive modifying effect of radionuclide on toxic influence of lead ions in range of 90Sr activity 2E+01-2E+03 Bq l-1 is registered. It is supposed, that at exposure of ionising radiation in doses 7-70 cGy at daphnia occurs stimulation of protective reactions of organism, interfering realisation of damaging effect of the radiating factor. It is supposed that one of the radioprotective mechanisms is the activation of glutathione system and increase of level of sulfhydric groups of endogenous glutathione, having the important significance for oxidation-reduction reactions and in fermentative reparation of damages. However besides of radioprotective function glutathione takes part in synthesis of metalthioneins, which by chelation are capable to remove heavy metals from a biochemical exchange. Thus, metabolic changes, initially directed on realisation of radioprotective effect, at combined impact of the radiating and chemical factors can carry multifunctional character, being shown in positive modification of toxic influence caused by ions of heavy metals. (author)