Radiocesium reaction with illite and organic matter in marine sediment.
ABSTRACT The mineralogical effect on the (137)Cs reaction with marine sediment has not been systematically studied yet, even though illite has been known to adsorb Cs preferentially on its frayed edge sites in a low Cs concentration. Ninety-three marine sediment samples were collected near Yangnam, Korea for quantitative X-ray-diffraction (XRD), gamma-ray, and total organic carbon (TOC) analysis. Illite content was in the range of 0-23 wt.% and those of (137)Cs and TOC were minimum detectable activity (MDA) approximately 7.19 Bq/kg-dry and approximately 3.32%, respectively. The illite content in the marine sediment showed a good relationship with the (137)Cs content (R(2)=0.69), but with an increase in the illite content, the relationship became less linear. This trend can be clearly shown in two groups of samples with different size fractions (< and >5Mdvarphi). For the samples of larger particle sizes (low contents of illite), the relationship is linear, but for the samples of the smaller particle sizes (high illite content) it is less linear with a decreased slope, indicating that increase in illite content does not significantly contribute to the fixation of (137)Cs in marine sediment. Rather, the TOC has a more linear relationship with (137)Cs content with no slope change in all particle size ranges. This may indicate that humic materials in marine sediment block the access of (137)Cs to the frayed edge site and reduces the adsorption of (137)Cs on illite and that the organic materials in marine sediment play more important roles in adsorbing Cs than illite.
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ABSTRACT: Two models of time-dependent 137Cs adsorption and fixation by soil were fitted to solution activity data from incubated organic upland soils, over a period of 709 days. Both model fits were highly (p < 0.01) or very highly (p < 0.001) significant. Both models differentiated between specifically adsorbed and nonspecifically adsorbed ‘labile' radiocesium. Transfer to a nonlabile pool was either by a kinetic step (model I) or a diffusive process (model II). Although fits for model II were comparatively worse in some soils, the second model had the dual advantage of being more mechanistic in structure and requiring fewer parameters. Parameters estimated for models I and II compared favorably with those derived experimentally; some dependence on soil mica was evident. Model I was used to predict the change in bioavail ability of radiocesium in soils following documented inputs from Windscale (1957), fallout from weapons testing (1960s), and the Chernobyl release (1986). For all but one of the five organic soils, long-term predic tions of relative bioavailability generated by model I were similar to the limited range of published values for 137Cs uptake by vegetation. It is concluded that the Cs fixation models presented account for a substantial part of the change in availability of 137Cs observed in field studies.Environmental Science and Technology 08/1996; 30(9). · 5.26 Impact Factor
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ABSTRACT: The Lena River is the second largest river that discharges into the Arctic Ocean. It is therefore important to determine not only the direct impact its discharge has on the 137Cs concentration of the Arctic, but also the potential its drainage basin has as a 137Cs source. 137Cs surface sediment concentrations and inventory values, which range from 4.97 to 338 Bq kg(-1) and 357 to 1732 Bq m(-2), respectively, were determined for the Lena River drainage basin lake samples, via gamma analysis. The average geochemical and mineralogical composition of a subset of samples was also determined using neutron activation analysis, X-ray diffraction and X-ray fluorescence spectrometry techniques. Results of these geochemical analyses allowed for the identification of key geochemical factors that influence the distribution of 137Cs in the Lena River drainage basin. 137Cs profiles indicate that Lena River drainage basin lacustrine sediments serve as a record of 137Cs fallout. Based on the downcore 137Cs, %illite, %smectite, %Al and %Mn distribution patterns, it was concluded that a small fraction of non-selectively bound 137Cs was remobilized at depth in some cores. Inconsistencies between the actual 137Cs fallout record and the 137Cs profiles determined for the lake sediments were attributed to 137Cs remobilization in subsurface sediments. In addition to establishing the agreement between the global atmospheric fallout record and the downcore 137Cs distribution patterns determined for these sediments, results indicate that 137Cs deposited during periods of maximum atmospheric release was buried and is not susceptible to surface erosion processes. However, mean 137Cs concentrations of the lacustrine surface sediments (125 Bq kg(-1)) are still significantly higher than those of the nearby Lena River estuary (11.22 Bq kg(-1)) and Laptev Sea (6.00 Bq kg(-1)). Our study suggests that the Lena River drainage basin has the potential to serve as a source of 137Cs to the adjacent Arctic Ocean.Science of The Total Environment 07/2000; 255(1-3):145-59. · 3.26 Impact Factor
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ABSTRACT: The strong correlation observed in situ between the bioavailability of radiocesium and soil organic matter content is paradoxical given the lack of coordination chemistry of cesium and its strong affinity for clay minerals. The aim of this work is to determine whether the adsorption of soil polymers, a protein and a polysaccharide, on reference clay minerals decreases cesium adsorption. Measurements were carried out in dilute suspensions of montmorillonite or illite, varying the initial polymer concentration, pH, and ionic strength. Planar clay surfaces were also blocked to elucidate the nature of the Cs adsorption sites affected. Both polymers caused a decrease in Cs adsorption, by up to an order of magnitude, particularly on illite and for trace concentrations of Cs. The effect increased with increasing polymer adsorbed on the clay surface but varied with experimental conditions so that there is no correlation between the quantity of polymer adsorbed and decreased Cs adsorption. Polymers appear to effect various Cs adsorption sites in different ways, by preventing clay layer collapse at frayed edge sites and by modifying the properties of regular exchange sites associated with planar surfaces. This indirect effect of adsorbed polymers may also modify the adsorption of other metals on clay minerals, in addition to the solubilizing effect of their coordination chemistry.Environmental Science & Technology - ENVIRON SCI TECHNOL. 06/2000; 34(14).