Accumulation capability for cesium differs among bacterial species: A comprehensive study using bacteria isolated from freshwater and coastal sediment

The fate and behavior of radioactive cesium (Cs) in the water environment are of great concern. The involvement of bacteria regarding their accumulation capability for this element is the most fundamental factor that needs to be clarified even for exploring the interactions between many environmental factors that involve together in governing the transport and distribution of Cs. As the first systematical study that aimed to evaluate the accumulation capability of environmental bacteria for Cs, bacteria in the sediment of a freshwater reservoir and coastal water environment were isolated and multiplied for contact experiment with Cs under different temperature conditions (5, 25, and 35 °C). The accumulation concentration of Cs in bacteria from freshwater sediment varied in 3.95 × 10^-6 to 5.68 × 10^-4ng-Cs/cell, and that from coastal sediment in 1.52 × 10^-6 to 7.41 × 10^-4ng-Cs/cell, indicating obvious differences among bacterial species. Bacteria of coastal sediment possessed higher accumulation capability for Cs than bacteria from freshwater sediment, and temperature dependency was confirmed for bacteria from coastal sediment. The findings of this study have great reference value for better understanding and controlling the fate and behavior of radioactive Cs associated with bacteria in the water environment.

Efficient sampling of shiitake-inoculated oak logs to determine the log-to-mushroom transfer factor of stable cesium

Background

Stable cesium (¹³³Cs) naturally exists in the environment whereas recently deposited radionuclides (e.g., ¹³⁷Cs) are not at equilibrium. Stable cesium has been used to understand the long-term behavior of radionuclides in plants, trees and mushrooms. We are interested in using ¹³³Cs to predict the future transfer factor (TF) of radiocesium from contaminated logs to shiitake mushrooms in Eastern Japan. However, the current methodology to obtain a representative wood sample for ¹³³Cs analysis involves mechanically breaking and milling the entire log (excluding bark) to a powder prior to analysis. In the current study, we investigated if sawdust obtained from cutting a log along its length at eight points is as robust but a faster alternative to provide a representative wood sample to determine the TF of ¹³³Cs between logs and shiitake.

Methods

Oak logs with ready-to-harvest shiitake fruiting bodies were cut into nine 10-cm discs and each disc was separated into bark, sapwood and heartwood and the concentration of ¹³³Cs was measured in the bark, sapwood, heartwood, sawdust (generated from cutting each disc) and fruiting bodies (collected separately from each disc), and the wood-to-shiitake TF was calculated.

Results

We found that the sawdust-to-shiitake TF of ¹³³Cs did not differ (P = 0.223) compared to either the sapwood-to-shiitake TF or heartwood-to-shiitake TF, but bark did have a higher concentration of ¹³³Cs (P < 0.05) compared to sapwood and heartwood. Stable cesium concentration in sawdust and fruiting bodies collected along the length of the logs did not differ (P > 0.05).

Discussion

Sawdust can be used as an alternative to determine the log-to-shiitake TF of ¹³³Cs. To satisfy the goals of different studies and professionals, we have described two sampling methodologies (Methods I and II) in this paper. In Method I, a composite of eight sawdust samples collected from a log can be used to provide a representative whole-log sample (i.e., wood and bark), whereas Method II allows for the simultaneous sampling of two sets of sawdust samples—one set representing the whole log and the other representing wood only. Both methodologies can greatly reduce the time required for sample collection and preparation.

X-Nuclei NMR Self-Diffusion Studies in Mesoporous Silica Foam and Microporous MOF CuBTC

A standard X-observe NMR probe was equipped with a z-gradient coil to enable high-sensitivity pulsed field gradient NMR diffusion studies of Li+ and Cs+ cations of aqueous salt solutions in a high-porosity mesocellular silica foam (MCF) and of CO2 adsorbed in metal-organic frameworks (MOF). The coil design and the necessary probe modifications, which yield pulsed field gradients of up to ±16.2Tm-1, are introduced. The system was calibrated at 2H resonance frequency and successfully applied for diffusion studies at 7Li, 23Na, 13C and 133Cs frequencies. Significant reductions of the diffusivities of the cations in LiClac and CsClac solution introduced into MCFs are observed. By comparison of the diffusion behavior with the bulk solutions, a tortuosity of the silica foam of 4.5±0.6 was derived. Single component self-diffusion of CO2 and CH4 (measured by 1H NMR) as well as self-diffusion of the individual components in CO2/CH4 mixtures was studied in the MOF CuBTC. The experimental results confirm high mobilities of the adsorbed gases and trends for diffusion separation factors predicted by MD simulations.