Bioaccumulation of 137Cs and 60Co by Helianthus annuus

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