Motoki Terashima

Europium-binding abilities of dissolved humic substances isolated from deep groundwater in Horonobe area, Hokkaido, Japan

The binding of europium to dissolved humic substances (HSs), isolated from deep groundwater in the Horonobe area, Hokkaido, Japan, was evaluated by means of a three-dimensional fluorescence quenching technique. The Ryan and Weber model, extended by the charge neutralization model, was applied to the fluorescence quenching profiles to evaluate the conditional binding constants (K) at pH 5.0 and an ionic strength of 0.1. The K values for fulvic (FA) and humic acids (HA) in the Horonobe groundwater were comparable with each other regardless of the position of the fluorescence peaks. As compared with HSs from Lake Biwa, Aldrich, and Dando soil, the K values of the Horonobe groundwater HSs were the smallest, indicating that the Horonobe groundwater HSs have a lower affinity for the binding of europium compared to the HSs from surface environments. In addition, the results of the Aldrich-based comparison indicate that the Horonobe groundwater HSs have a lower binding affinity for trivalent lanthanides/actinides compared with other groundwater HSs obtained from different aquifer. These findings demonstrate that the characteristics and origin of deep groundwater HSs needs to be taken into consideration assessing the effects of HSs on the speciation of radionuclides in deep groundwater in geological disposal systems.

Characterization of an adsorbed humin-like substance on an allophanic soil formed via catalytic polycondensation between catechol and glycine, and its adsorption capability to pentachlorophenol.

An allophanic soil (AS) catalyzed the formation of dark-colored polymers via polycondensation reactions between catechol and glycine. The organic carbon content of the AS was increased from 0.16% to 1.3%, indicating that some of the dark-colored polymers had been adsorbed to the AS. The characteristics of the dark-colored polymers adsorbed on the AS were similar to those of a humin that is not extractable with an aqueous alkaline solution. Such a humin-like substance (HuLS) was separated from the AS by treatment with a mixture of HF and HCl. The HuLS and humic acid-like substance (HaLS), comprising the acid-insoluble fraction in the reaction mixture, were characterized by elemental analysis, size exclusion chromatography, pyrolysis-GC/MS and (13)C NMR. However, the structural features of HaLS and HuLS had many points in common. These results suggest that HuLS-AS can be regarded as an organo-clay complex formed by the strong adsorption of HaLS to the AS. The adsorption of pentachlorophenol (PCP) to AS and HuLS-AS was examined at pH 5.5. At this pH, the zeta potential of the HuLS-AS showed a negative value. It would, therefore, be expected that pentachlorophenolate anions would adsorb with difficulty to HuLS-AS because of electrostatic repulsion. Nevertheless, the adsorption coefficient for PCP to HuLS-AS, as estimated by the Freundlich isotherm, was seven times larger than that for AS. These results show that HuLS, when adsorbed on the AS surface, has the capability to enhance the adsorption of PCP.

Sorption and diffusion of Eu in sedimentary rock in the presence of humic substance

Abstract Sorption and diffusion behaviors of Eu in sedimentary rock in the presence of humic substance were investigated. The sedimentary rock collected from 500 m depth of HDB-6 bore hole at horonobe URL site of Japan and Aldrich humic acid (HA) were used in the present study. Sorption behaviors of Eu and the HA on the sedimentary rocks with and without the rock organic matter (ROM) were elucidated as a function of HA concentration. The HA reduced the sorption of Eu on the rock with the increase of HA. Eu and HA sorption on the rock with the ROM was larger than on the rock after removing the ROM, indicating that the ROM plays an important role on the sorption of Eu and HA. The diffusion of Eu in the presence of HA was examined as a function of HA concentration and molecular weight of the HA (∼150 kDa or below 10 kDa) by means of a reservoir depletion test method with the intact rock core of the sedimentary rock. Depletion of Eu concentration in the reservoir was reduced with the increase of HA concentration. On the other hand, slight depletion of HA concentration in the reservoir was observed, indicating that the larger HA molecule diffused less into the rock. From the depletion curve and in-diffusion profile of Eu in the rock, the effective diffusion coefficient, De, and distribution coefficient, Kd, in the intact system were estimated based on the profile fitting of the diffusion data with the conventional simple diffusion-sorption model. It was elucidated that the HA reduced the Kd and De of Eu in the intact system with the increase of HA. The contribution of the HA with smaller molecular weight to both the Eu sorption and diffusion was examined.

Degradation of bisphenol A by photo-fenton processes

The photo-Fenton reactions, which could yield hydroxyl radicals via the catalytic degradation of H2O2 by Fe(II), were focused as one of the abiotic degradation processes of bisphenol A (BPA) in surface waters. At pH 6, in the presence of H2O2 only, 32% of BPA was degraded after 120 min of irradiation. However, 97% of BPA was degraded in the presence of both H2O2 and Fe(II). Without light irradiation, no BPA degradation was observed even in the presence of Fe(II) and H2O2. These results show that photo-Fenton processes are effective in the natural attenuation of BPA in surface water. In addition, the presence of humic acids (HAs), which were of more aliphatic nature, resulted in enhancing BPA degradation via the photo-Fenton processes. Therefore, HAs can be one of the important factors in enhancing the degradation of BPA in surface water via the photo-Fenton processes.

Europium binding to humic substances extracted from deep underground sedimentary groundwater studied by time-resolved laser fluorescence spectroscopy

ABSTRACT Humic substances (HSs) are ubiquitous in various environments including deep underground and play an important role in the speciation and mobility of radionuclides. The binding of Eu3+, a chemical homologue of trivalent actinide ions, to HSs isolated from sedimentary groundwater at −250 m below the surface was studied by time-resolved laser fluorescence spectroscopy combined with parallel factor analysis (PARAFAC) as a function of pH and salt concentration. PARAFAC modeling reveals the presence of multiple factors that correspond to different Eu3+ species. These factors resemble those observed for Eu3+ binding to HSs from surface environments; however, detailed comparison shows that there are some particularities in Eu3+ binding to the deep groundwater HSs. The distribution coefficients (Kd) of Eu3+ binding to the HSs calculated from the PARAFAC modeling exhibits a rather strong salt effect. At 0.01 M NaClO4, the Kd values are relatively large and comparable to those to the surface HSs; they are decreaed at 0.1 M NaClO4 by more than an order of the magnitude. The Kd values are larger for the humic acid fraction of the deep underground HSs than the fulvic acid fraction over the entire range of pH and salt concentration investigated in this study.

Water Chemistry of the Middle Amur River

This chapter examines water chemistry in terms of iron, organic matter, and nutrients in river, drainage, and groundwater from the middle reaches of the Amur River, to ascertain the watershed environment of the Amur River Basin during 2005–2007. Nitrate-N concentration was 0.46 ± 0.38 mg/L for river water and 1.9 ± 5.0 mg/L for groundwater, corresponding respectively to 87 ± 11 % and 39 ± 42 % of total inorganic nitrogen. Dissolved iron concentrations were 0.10–1.08 mg/L for river water and 0.39 ± 0.26 mg/L on average. A positive correlation was found between dissolved organic carbon (DOC) and dissolved iron concentrations in river water. However, the groundwater had average iron concentrations of 4.9 ± 3.1 mg/L and 4.3 ± 9.9 mg/L of DOC concentration, and there was no correlation between DOC and dissolved iron concentrations. The results indicate that wetland and forest areas are important in the export of dissolved iron and organic matter in the middle reaches of the Amur River. In the groundwater system, sources of dissolved iron and organic matter are independent for each underground environment, because of differences in geologic media, groundwater flow, and redox conditions.

Sorption of Pentachlorophenol to Organo-Clay Complexes Prepared by Polycondensation Reactions of Humic Precursors

The surfactant-modified bentonite has been focused on the adsorption of hydrophobic organic contaminants in aqueous solutions, because the surfactant (e.g. quaternary alkylammonium salt) intercalation leads to the formation of highly hydrophobic domains. Humic substances (HSs) can serve as naturally occurring surfactants of higher affinity to hydrophobic organic contaminants, such as pentachlorophenol (PCP). However, HSs cannot be loaded into interlayer of montmorillonite in bentonite (Bent) because of their larger size. In the present study, the humin-like substance (HuLS) was loaded to the montmorillonite interlayer via polycondensation reactions of glycine and catechol as humic precursors. The montmorillonite basal spacing was expanded by forming the HuLS-bentonite complex (HuLS-Bent), showing the intercalation. The Freundlich adsorption coefficients of PCP for HuLS-Bent and Bent (K f) were evaluated at pH 4.0, 5.5 and 6.5. While K f values decreased with an increase in pH, K f values for the HuLS-Bent (83–1,220) were larger than the reported values for other organically modified clays (19–100 at pH 3–6). These results suggest that the prepared HuLS-Bent is effective in the removal of PCP from water.