Bioaccumulation of 137Cs and 60Co in freshwater plants

Contamination of the aquatic environment by the heavy metals and radionuclides has become a serious concern in the world. In our study, gamma-spectrometry of freshwater plants Bacopa monnieri and Egeria densa growing in cultivation media spiked with 137CsCl and 60CoCl2 was used for quantitative determination of bioaccumulation kinetic and distribution Cs+ and Co2+ ions in plant tissues. We found, that bioaccumulation of Cs and Co by fully immersed B. monnieri in Hoagland media (HM) was dependent on ion concentration in medium. Approx. 5-times lower Cs uptake 2.9 nmol/g (d.w.) was obtained in plants cultivated in 20% HM than from deionized water. The maximal Co uptake was 4-times higher than cesium uptake at the same conditions. Both Cs and Co were localized mainly in roots. The highest immobilization from roots to shoots was found in the case of Co uptake from deionized water with concentration ratio [Co]leaves : [Co]stem : [Co]root = 1.00 : 5.33 : 56.8. Cesium uptake by submerged plant E. densa was also strongly dependent on nutrients concentration in medium. However, in the case of cobalt uptake this dependence was less pronounced. Nutrients concentration also had a significant influence on distribution of Cs between stems and leaves of E. densa. Cesium was localized in leaves, however with increasing of nutrients concentration in cultivation media Cs was localized for account of stem. On the other hand, cobalt was immobilized mainly in leaves in whole range of nutrients concentration. Obtained data can serve as a models for understanding of phytoaccumulation of radionuclides from open water ponds and water channels in the vicinity of nuclear power plants and monovalent and bivalent metals from industrial sources of contamination.