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.

A Batch Experiment of Cesium Uptake Using Illitic Clays with Different Degrees of Crystallinity

Radiocesium released by the severe nuclear accident and nuclear weapon test is a hazardous material. Illitic clays play a key role in the spatial distribution of radiocesium in groundwater environments due to selective uptake sites at the illite mineral, such as frayed edge sites. However, the cesium uptake capabilities of illitic clays are diverse, which could be associated with the illite crystallinity. This study was performed to determine the cesium uptake of illitic clays and evaluate the crystallinity effects on cesium uptake using statistical approaches. A total of 10 illitic clays showed various crystallinity, which was parameterized by the full width at half maximum (FWHM) at 10 Å XRD peak ranging from 0.15 to 0.64. The uptake behavior of illitic clays was well fitted with the Freundlich model (i.e., r2 > 0.946). The uptake efficiency of illitic clays increased with the decrease in dissolved cesium concentrations. The cesium uptake was significantly correlated with the FWHM and cation exchange capacity, suggesting that the uptake becomes higher with decreasing crystallinity through expansion of the edge site and/or formation of ion-exchangeable sites.

COMPARATIVE STUDY OF THE CESIUM UPTAKE ABILITY BETWEEN HEU-TYPE (CLINOPTILOLITE-HEULANDITE) ZEOLITIC TUFF AND PURE HEULANDITE

Specific continuous layers of zeolitic tuff in Ntrista stream location of Petrota area of Evros region (NA11) and pure natural crystals of heulandite (HEU1) from the collection of the Department of Mineralogy-Petrology-Economic Geology, School of Geology, Aristotle University of Thessaloniki, have been investigated. The X-Ray Diffraction analyses showed that the sample NA11 consists of 86 wt% HEU-type zeolite, 4 wt% micas+ clay-minerals, 4 wt% quartz, 2 wt% christobalite and 4 wt% feldspars, while the sample HEU1 is pure heulandite crystal. The mineral-chemistry was determined by SEM-EDS microanalyses. The zeolite of the NA11 sample is Ca-rich clinoptilolite and its chemical formulae is Ca1.8K1.0Mg0.7Na0.5Al6.4 Si29.5O72·21H2O, while the zeolite of the sample HEU1 is heulandite and its chemical formulae is Ca3.6Na1.0Κ0.2Sr0.2Ba0.1Al8.1Si27.6O72·21H2O. The uptake ability of the samples was measured by the AMAS method (Ammonium Acetate Saturation). The two examined materials show high uptake ability. The measured value for the zeolitic tuff NA11 is 231 meq/100g, while for the heulandite crystal (HEU1) is 296 meq/100g. For the determination of the cesium sorption a CsNO3 solution (concentration 500 mg/L), labelled with small activity of 137Cs, and pH 2-12 was used. The sorption of the cesium by the two materials, was determined by measuring the gamma radiation emitted by the 137Cs tracer. The zeolitic tuff presents higher uptake ability of radioactive cesium than the pure heulandite crystal, whereas the sorption of radioactive cesium is not significantly affected by the pH values of the initial solutions in the range pH 2-12.The clinoptilolitic zeolitic tuff NA11 is suitable material for various environmental, agricultural and industrial applications.