NUKLEONIKA 2005, 50(Supplement 1):S49-S52

The ⁶⁰Co and ¹³⁷Cs bioaccumulation by Helianthus annuus L. was measured during 9 day cultivation at 20 ± 2°C in hydroponic Hoagland medium. Previous starvation for K⁺ and for NH₄⁺ 2.2 and 2.7 times, respectively, enhanced ¹³⁷Cs uptake rate. Previous cultivation in surplus of K⁺ ions 50 mmol l^-1 has no effect on ¹³⁷Cs bioaccumulation rate. Both ¹³⁷Cs and ⁶⁰Co bioaccumulation significantly increase with dilution of basic Hoagland medium up to 1:7 for caesium and up to 1:3 for cobalt followed by mild decrease at higher dilutions. Root to shoot specific ¹³⁷Cs radioactivity ratio (Bq g^-1/Bq g^-1, fresh wt.) increased with dilution from 1.46 to 9.6–9.8. The values root to shoot specific radioactivity ratio for ⁶⁰Co were less dependent on the nutrient concentrations and were within the range 5.7 to 8.5. ¹³⁷Cs was localized mainly in young leaves (30%) and roots (39%) and ⁶⁰Co mainly in roots (67%) and leaves (20%). Obtained data showed less sensitivity of ⁶⁰Co uptake by sunflower on nutrient concentration in hydroponic media.