sp. DN11 was previously isolated from gasoline-contaminated groundwater as an anaerobic benzene-degrading bacterium. Genome analysis of strain DN11 revealed that it contained a putative
gene cluster ...(
), which was recently found to be involved in bacterial iodate (IO
) respiration. In this study, we determined if strain DN11 performed iodate respiration and assessed its potential use to remove and sequester radioactive iodine (
I) from subsurface contaminated aquifers. Strain DN11 coupled acetate oxidation to iodate reduction and grew anaerobically with iodate as the sole electron acceptor. The respiratory iodate reductase (Idr) activity of strain DN11 was visualized on non-denaturing gel electrophoresis, and liquid chromatography-tandem mass spectrometry analysis of the active band suggested the involvement of IdrA, IdrP
, and IdrP
in iodate respiration. The transcriptomic analysis also showed that
,
, and
expression was upregulated under iodate-respiring conditions. After the growth of strain DN11 on iodate, silver-impregnated zeolite was added to the spent medium to remove iodide from the aqueous phase. In the presence of 200 μM iodate as the electron acceptor, more than 98% of iodine was successfully removed from the aqueous phase. These results suggest that strain DN11 is potentially helpful for bioaugmentation of
I-contaminated subsurface aquifers.
We studied the adsorption behavior of radioactive cesium (Cs) by the non-mica minerals kaolinite, halloysite, chlorite, montmorillonite, mordenite, MnO
2
, TiO
2
, Al
2
O
3
, and FeOOH to elucidate ...the environmental behavior of radioactive Cs fallout from the Fukushima Daiichi Nuclear Power Plant in the Tohoku region of Japan. The adsorption and desorption experiments of Cs on the minerals were carried out at the Cs concentrations 1 × 10
−4
, 1 × 10
−5
, and 2 × 10
−9
mole L
−1
at pH 5.5. The desorption of Cs from the minerals was examined using 0.1 mole L
−1
LiCl, NaCl, KCl, RbCl, and CsCl solutions. The sequential desorption was examined using a 0.1 mole L
−1
LiCl solution, a 1 mole L
−1
KCl solution, and a 1 mole L
−1
HCl solution. The distribution coefficient (K
d
) for the minerals at the Cs concentration 10
−9
mole L
−1
was in the order of mordenite > illite > montmorillonite, sericite, MnO
2
, kaolinite, and halloysite > chlorite, TiO
2
, Al
2
O
3
, and FeOOH, differing from the order observed at higher Cs concentrations. After the sequential desorption by the three reagent solutions, the residual fraction of Cs was higher at the Cs concentration 10
−9
mole L
−1
than at higher concentrations. Approximately 40%, 40%, 50%, and 25% of the adsorbed Cs were residual in montmorillonite, mordenite, MnO
2
, and kaolinite, respectively, after the sequential desorption. These results strongly suggest that (1) radioactive Cs at 10
−9
mole L
−1
is more strongly associated with the non-mica minerals than at higher concentrations of 1 × 10
−4
and 1 × 10
−5
mole L
−1
, and (2) the non-mica minerals montmorillonite, mordenite, kaolinite, and MnO
2
contributed to the fixation of the radioactive Cs fallout on Fukushima soil.
Growth of the nuclear industry has encouraged us to look for techniques to treat large volumes of nuclear waste. 60Co is one of the most problematic radioactive wastes in the nuclear industry. In ...this study, a Mn slag-based geopolymer (MSG) was prepared, which exhibited better Co immobilization performance than the ordinary metakaolin-based geopolymer (MKG). Varying the mass ratio between water glass and NaOH (mw/mn) influenced the structure and chemical performance of the MSG samples, which consequently influenced their Co immobilization capacity. The optimized MSG was obtained at an mw/mn value of 1.5. After the 7-day leaching test, about 0.20% of the Co was released from MSG, which is less than two-thirds of the MKG sample. The chemical state of Co in the geopolymer matrix was characterized by X-ray photoelectron spectroscopy. Divalent Co remained in the MKG samples, while most of Co ions in MSG samples existed in the trivalent state. These results strongly suggest that divalent Co was oxidized to trivalent Co in the MSG matrix, resulting in enhanced Co solidification capacity compared to MKG. The results in this study indicate that the oxidation environment in the MSG played an important role in Co immobilization.
Display omitted
•A Mn slag-based geopolymer (MSG) was fabricated to immobilize Co.•The chemical performance of MSG is affected by the water glass/NaOH mass ratio.•Co released from MSG was much lower than the ordinary metakaolin-based samples.•The oxidation environment in MSG played an important role in Co immobilization.
The reversibility of cesium adsorption in contaminated soil is largely dependent on its interaction with micaceous minerals, which may be greatly influenced by various cations. Herein, we ...systematically investigated the effects of NH4 +, K+, Mg2+, and Ca2+ on the adsorption/desorption of Cs+ into different binding sites of vermiculitized biotite (VB). Original VB was initially saturated by NH4 +, K+, or Mg2+; we then evaluated the adsorption of Cs+ on three treated VBs, and the desorption by extraction with NH4 +, K+, Mg2+, or Ca2+ was further evaluated. Our structural analysis and Cs+ extractability determinations showed that NH4 + and K+ both collapsed the interlayers of VB, resulting in the dominant adsorption of Cs+ to external surface sites on which Cs+ was readily extracted by NH4 +, K+, Mg2+, or Ca2+ irrespective of their species, whereas Mg2+ maintained the VB with expanded interlayers, leading to the overwhelming adsorption of Cs+ in collapsed interlayer sites on which the Cs+ desorption was difficult and varied significantly by the cations used in extraction. The order of Cs+ extraction ability from the collapsed interlayers was K+ ≫ Mg2+ ≈ Ca2+ ≫ NH4 +. These results could provide important insights into Cs migration in soil and its decontamination for soil remediation.
Remnant nuclear fuel debris in the damaged nuclear reactors at the Fukushima Daiichi Nuclear Power Plant (FDNPP) has contacted the groundwater containing microorganisms for over ten years. Herein, we ...report the possibility of bacterial alteration of fuel debris. We investigated the physical and chemical changes of fuel debris simulants (FDS) in the powder and pellet forms via exposure to two ubiquitous bacteria,
Pseudomonas fluorescens
and
Bacillus subtilis
, which are not recognized as metal element-oxidative (e.g., iron-oxidative) bacteria under aerobic conditions. In the experiments using FDS composed of the powders of Fe(0), solid solution of CeO
2
and ZrO
2
, and SiO
2
, Ce, Zr, and Si were hardly dissolved, while Fe was dissolved, a fraction of the dissolved Fe was present in the liquid phase as Fe(II) and Fe(III), and the rest was precipitated as the nano-sized particles of iron (hydr)oxides. In the experiment using
P. fluorescens
and FDS pellet pieces prepared by melting the Fe(0) particles and solid solution of CeO
2
and ZrO
2
, the bacteria selectively gathered on the Fe(0) particle surface and made corrosion pits. These results suggest that bacteria in groundwater corrode the iron in fuel debris at FDNPP, change fuel debris into porous one, releasing the nano-sized iron (hydr)oxide particles into the water.
We investigated the sorption of Pu(IV) on biogenic Mn oxide, composed of Mn(IV) oxide and hyphae, produced by Mn(II)-oxidizing fungus. The sorption of Pu(IV) on biogenic Mn oxide was similar to that ...of U(VI) and different from that of Th(IV), possibly due to oxidation of Pu(IV) to Pu(VI). When Pu(IV) was sorbed on hyphae only, it was desorbed into the solution phase over time. Pu(IV) could be solubilized by complexation with organic ligands secreted by fungal cells. Furthermore, Pu(IV) desorption was observed especially under circumneutral pH conditions, indicating that Pu(IV) can be solubilized by microbial activity in most surface environments.
The surface reactivity of biogenic birnessite is attributed to its structure. However, structural control of heavy metal adsorption on biogenic birnessite is not well understood. Here a ...poorly-crystalline birnessite was produced by the fungus Paraconiothyrium sp. WL-2 strain under ambient pH and temperature conditions. The structure was characterized by X-ray absorption spectroscopy and X-ray diffraction. Sorption behaviors of Co2+ were compared with Zn2+. The primary product of the Mn bio-oxidation is hexagonal birnessite with a turbostratic structure. XAFS analysis demonstrated that the biogenic birnessite consists of octahedral sheets with Mn(IV) as the central metal and some vacant sites. Mn(III) atoms are coordinated to some of the vacant sites in the interlayer. The adsorption of Co2+ by the biogenic birnessite is higher than Zn2+. The excess adsorption of Co2+ than Zn2+ is nearly the same as the excess release of Mn from the biogenic birnessite. These results strongly suggested that the interlayer Mn(III) can oxidize the adsorbed Co2+ to Co3+, resulting in excess adsorption of Co2+ compared to Zn2+ by biogenic birnessite.
► The surface reactivity of biogenic birnessite is attributed to its structure. ► Paraconiothyrium sp. WL-2 strain produce birnessite containing no layer Mn(III) and some interlayer Mn(III). ► Interlayer Mn(III) possesses a higher sorption capacity for Co2+. ► Oxidation of the adsorbed Co2+ to Co3+ results in excess adsorption of Co2+ compared to Zn2+.
Anthropogenic radionuclides contaminate a range of environments as a result of nuclear activities, for example, leakage from waste storage tanks/ponds (e.g. Hanford, USA or Sellafield sites, UK) or ...as a result of large scale nuclear accidents (e.g. Chernobyl, Ukraine or Fukushima, Japan). One of the most widely applied remediation techniques for contaminated waters is the use of sorbent materials (e.g. zeolites and apatites). However, a key problem at nuclear contaminated sites is the remediation of radionuclides from complex chemical environments. In this study, biogenic hydroxyapatite (BHAP) produced by Serratia sp. bacteria was investigated for its potential to remediate surrogate radionuclides (Sr(2+) and Co(2+)) from environmentally relevant waters by varying pH, salinity and the type and concentration of cations present. The sorption capacity of the BHAP for both Sr(2+) and Co(2+) was higher than for a synthetically produced hydroxyapatite (HAP) in the solutions tested. BHAP also compared favorably against a natural zeolite (as used in industrial decontamination) for Sr(2+) and Co(2+) uptake from saline waters. Results confirm that hydroxyapatite minerals of high surface area and amorphous calcium phosphate content, typical for biogenic sources, are suitable restoration or reactive barrier materials for the remediation of complex contaminated environments or wastewaters.
Following identification of radioactive Cs microparticles (CsMPs) in aerosol samples from the Fukushima Daiichi Nuclear Power Plant (FDNPP), numerous reports on CsMPs have been published. This paper ...reviews recent progress in the measurement and characterization of CsMPs by advanced analytical techniques, including advanced transmission electron microscopy (TEM) and synchrotron X-ray analysis. These analyses revealed that the CsMPs contained Si, Fe, Zn, Cs, and minor quantities of U together with some fission products. Uranium in the CsMPs was identified as being in the form of uraninite and (U,Zr)O
2
. Detailed advanced TEM analysis has clarified some of the processes resulting in the alteration of constituents of the nuclear fuels and containment vessel materials during this severe accident. In addition, a detailed report on the elemental compositions and structures of the fuel debris fragments collected inside and outside of the primary containment vessel
25
highlighted the fact that the fuel debris fragments contained nanoparticles with the U and Zr components having similar structures to that of the CsMPs. This similarity in structures has stimulated further research on the structure and elemental constituents, especially for U and Zr in the CsMPs, and has opened up new avenues for studying the chemical characteristics of the fuel debris.
To understand the chemical durability of highly radioactive cesium-rich microparticles (CsMPs) released from the Fukushima Daiichi Nuclear Power Plant in March 2011, we have, for the first time, ...performed systematic dissolution experiments with CsMPs isolated from Fukushima soils (one sample with 108 Bq and one sample with 57.8 Bq of 137Cs) using three types of solutions: simulated lung fluid, ultrapure water, and artificial sea water, at 25 and 37 °C for 1–63 days. The 137Cs was released rapidly within three days and then steady-state dissolution was achieved for each solution type. The steady-state 137Cs release rate at 25 °C was determined to be 4.7 × 103, 1.3 × 103, and 1. 3 × 103 Bq·m−2 s−1 for simulated lung fluid, ultrapure water, and artificial sea water, respectively. This indicates that the simulated lung fluid promotes the dissolution of CsMPs. The dissolution of CsMPs is similar to that of Si-based glass and is affected by the surface moisture conditions. In addition, the Cs release from the CsMPs is constrained by the rate-limiting dissolution of silicate matrix. Based on our results, CsMPs with ∼2 Bq, which can be potentially inhaled and deposited in the alveolar region, are completely dissolved after >35 years. Further, CsMPs could remain in the environment for several decades; as such, CsMPs are important factors contributing to the long-term impacts of radioactive Cs in the environment.
Display omitted
•We report chemical durability of Cs-rich microparticle from Fukushima Daiichi.•The dissolution rate was estimated for various solution composition.•Cs-rich microparticles can remain in lung and environments for several decades.
PDF
