Bioaccumulation of 137Cs and 60Co by Helianthus annuus

The 60Co and 137Cs bioaccumulation by Helianthus annuus L. was measured during 9 day cultivation at 20 š 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.