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(M/EH126) Influences of K+ and Na+ concentrations on radiocesium bioaccumulation in two freshwater phytoplankters . Hagström, Jonas1, 1 ABSTRACT- The influences of cation concentrations (K+ and Na +) on radiocesium (137Cs) bioaccumulation in two freshwater phytoplankton species (Scenedesmus quadricauda and Chlamydomonas noctigama) were systematically investigated in batch-cultures monitored during two weeks. Both species were cultured at 9 muE m-2 s-1 constant illumination at 20°C. The exponential growth phase lasted for more than 100 hours (mu = 0.02 h-1 for C. noctigama and 0.03 h-1 for S. quadricauda). Over cation concentration ranges encountered in natural freshwaters ([K+] from 0.1 muM to 3 mM, [Na+] from 20 muM to 3 mM), a more than three order of magnitude variation was found for both uptake rate and observed bioconcentration factors (BCF) at apparent steady-state (from less than 10 3 to 10 6 L (kg C)-1). For both species, the major effector on BCF and uptake rate was external [K+], which was inversely proportional to these parameters over wide ranges (1 to 1000 muM for S. quadricauda and 0.1 to 300 muM for C. noctigama). At concentrations above these ranges K+ still reduced 137Cs biouptake, but less effectively. A minor influence of external [Na+] on 137Cs bioaccumulation was indicated for S. quadricauda, whereas no such influence was significant for C. noctigama. Key words: radiocesium, phytoplankton, K+, Na+ |
