Modeling of cesium-137 and strontium-90 accumulation in the freshwater algae cells

Using the model object, freshwater Charophytae alga cells Nitella flexilis, the mechanisms of 137 Cs and 90 Sr uptake have been studied. The curves of radionuclide accumulation and washout in time have been measured, and the effects of uni- and divalent cations, pH of a solution, illumination, fulvic and humic acids on the curve pa­ rameters have been investigated. The results obtained have been interpreted on the basis of the currently known mechanisms of ion transport in plasmalemma: tT-ATPase pump, potassium channels, nonselective ion leakage, sur­ face charges and the apoplast - cation exchanging cell wall. It has been shown, that nuclides enter into a cell through potassium channels and nonselective ionic leakage. While a share of each pathway in a total l37 Cs influx is identical, the influx of 90 Sr is primarily through leakage. The basic ion transport mechanisms were assumed to be located separately on plasmalemma because of discrete nature of the molecule structures their forming, and can interact by superposition of local electric fields, generated by each of ion-transport mechanisms. So the intro-membrane electri­ cal field may be vary for different plasmalemma sites. Quantitative model based on above mentioned notions was developed and validated: it describes steady state distribution of l37 Cs and 90 Sr between cell and medium.