Y. Takahashi

Polysulfide reduction by Clostridium relatives isolated from sulfate-reducing enrichment cultures.

Sulfur is almost insoluble in water at ambient temperatures, and therefore polysulfide (S(n)(2-)) has been considered as a possible intermediate that is used directly by bacteria in sulfur respiration. Sulfur-reducing reductases have been purified and characterized from a few sulfur reducers. However, polysulfide reduction has only been confirmed in Wolinella succinogenes. In our previous study, the direct production of hydrogen sulfide from polysulfide was confirmed by an enrichment culture obtained from natural samples under sulfate-reducing conditions. The present study attempted to isolate and identify polysulfide-reducing bacteria from the enrichment cultures. Almost all the isolated strains were classified into the genus Clostridium, based on 16S rRNA gene sequence analysis. The isolates, and some closely related strains, were able to reduce polysulfide to hydrogen sulfide. During production of 1 mol of hydrogen sulfide, approximately 2 mol of lactate was converted to acetate. Thus, dissimilatory polysulfide reduction occurred using lactate as an electron donor. The ability to reduce elemental sulfur was also examined with the isolates and the related strains. Although elemental sulfur reducing strains can reduce polysulfides, not all polysulfide-reducing strains can reduce elemental sulfur. These results demonstrate that the conversion of elemental sulfur to polysulfide seems to be important in the reduction process of sulfur.

PIXE Analysis of Trace Heavy-Metals in River Waters Using an Ion-Exchange Cellulose Filter Paper

A simple but precise method for the PIXE analysis of trace heavy-metals in aqueous samples was developed, in which the PIXE targets were prepared by pre-concentrating heavy metals on a cellulose phosphate ion-exchange filter paper and no additional chemical treatment was required. Heavy metals in trace concentrations were quantitatively retained up to 16.7 μ-equivalent on a sheet of filter paper due to the excellent selectivity for heavy metals and ion-exchange kinetics of phosphate groups in cellulose matrix. Heavy metals of less than 1 μg on one filter paper are precisely and rapidly determined by PIXE analysis using 3-MeV proton beams. The present method is compared with the method preparing a PIXE target for each dissolved species of an element contained in aqueous samples. It will be resulted that the newly developed method enables an on-line PIXE analysis for river waters.

PIXE ANALYSIS OF TRACE HEAVY METALS IN RIVER AND TAP WATER USING AN ION-EXCHANGE CELLULOSE PHOSPHATE FILTER

An ion-exchange cellulose phosphate filter was used to prepare in-line PIXE targets for long-term monitoring of heavy metal concentrations in river and tap water. River water samples were taken every 30 minutes during 7 hours, and tap water samples every 5 hours during 150 hours. A PIXE target was prepared passing 300 ml of water sample and 2 ml of 20 ppm Y standard solution through a single sheet of the filter paper. Heavy metals (Mn, Fe, Cu, Zn, Pb and Hg) were detected by PIXE analysis with lower detection limits of 0.5-1.0 ppb. Analysis results show that the filter paper can trace concentration changes of heavy metals in a wide range.

THE POTENTIAL OF PIXE FOR ANALYTICAL WORK IN WATER POLLUTION

A method has been developed and tested for PIXE analysis of soluble and insoluble constituents in a variety of water samples in our surroundings. Insoluble components were filtered on a Nuclepore filter of 0.4-μm pores. For soluble fractions, a target of major components was made from a 0.15-ml filtrate evaporated on a user-made polycarbonate film, and in turn heavy metals in trace amounts were preconcentrated in a PIXE-target through the use of a combination of dibenzyldithiocarbamate-chelation with subsequent condensation into dibenzylidene-D-sorbitol gels. These three kinds of targets were analyzed with a PIXE system of 3-MeV proton beams. The widespread concentrations (several tenths of ppb to a few tens of ppm) of ~24 elements from Na to Pb were determined simultaneously in a precision sufficient to reveal the elemental distribution between the soluble and insoluble fractions of various aqueous samples such as river water, rain water and water leaking from disposal sites of industrial wastes. Hence, the methodology for preparing three types of targets promotes the PIXE analysis to a truly effective means for monitoring a water-pollution problem in our surroundings.

PIXE ELEMENTAL ANALYSIS OF DRINKING WATER SUPPLIES

In this study, we carried out PIXE analysis of raw and treated water at five water treatment plants as well as of tap water from several houses located in each supply route. We used a simple fast procedure for preparing thin uniform targets of inorganic components in both soluble and insoluble fractions of aqueous samples in combination with preconcentration of trace heavy metals; that is, Nuclepore filtration targets for coarse particles, preconcentration targets for heavy metal ions and deposit targets for fine particles and soluble major constituents. The target preparation and the PIXE measurement are not time-consuming, and a broad range of concentrations (several tenths of ppb to a few tens of ppm) of 19 elements from Na to Pb is determined simultaneously with a precision sufficient to reveal the elemental distribution in the soluble and insoluble fractions. Tap water quality was examined as a function of elemental distribution in untreated water at the plants. We confirmed the increase of insoluble components of some heavy metals in untreated water taken from river due to heavy rainfall and the elution of Cu, Zn and Pb in drinking water by corrosion of the piping in some part of the water distribution systems.

Polysulfide reduction using sulfate-reducing bacteria in a photocatalytic hydrogen generation system

A hydrogen generation process using photocatalytic reactions has been proposed. In this process, hydrogen sulfide is a source of hydrogen and is turned into polysulfide. In order to establish the cyclic operation of a photocatalytic hydrogen generation system, it is necessary to convert polysulfide back into hydrogen sulfide with a small energy input. This paper proposes the use of sulfate-reducing bacteria (SRB) for the regeneration of hydrogen sulfide. Batch cultivation of natural source SRB samples were carried out using a culture medium containing polysulfide as the only sulfur compound source. SRB produced hydrogen sulfide from several kinds of polysulfide sources, including a photocatalytic hydrogen generation-produces solution. Production lag phase and production rate of hydrogen sulfide were affected by initial polysulfide concentration. SRB activity was inhibited at high initial polysulfide concentrations. SRB enrichment culture T2, exhibited the highest hydrogen sulfide production rate, and was able to utilize several kinds of organic matter as the electron donor. The results suggest the possibility of using large biomass sources, such as sewage sludge and the raw garbage in a hydrogen generation system. We developed speculative estimates that an SRB based hydrogen generation system is feasible.

PIXE STUDY ON ABSORPTION OF ARSENATE AND ARSENITE BY ARSENIC HYPERACCUMULATING FERN (PTERIS VITTATA)

Pytoremediation using an arsenic hyperaccumulator, Petris vittata L., has generated an increasing interest worldwide due to both environmentally sound and cost effectiveness. However the mechanism of arsenic accumulation by this fern is not clear at this time. This study examined the uptake of arsenate (As(V)) and arsenite (As(III)) by a hydroponic culture of Pteris vittata using both in-air submilli-PIXE for different parts of the fern and in-air micro-PIXE for the tissue cells. These PIXE analysis systems used 3 MeV proton beams from a 4.5-MV single-ended Dynamitron accelerator at Tohoku University, Japan. The fern took up both arsenate and arsenite from hydroponic solutions which were spiked with 50 mg of arsenic per litter. Final amount of arsenic accumulation in the fern is 1,500 mg per kg (wet weight) of the plant biomass in arsenite treatment and 1,100 mg per kg in arsenate treatment. Arsenic accumulation was not observed at the root parts of the ferns. The in-vivo mapping of elements by submilli-PIXE analyses on the fern laminas showed the arsenic accumulation in the edges of a pinna. The micro-PIXE analyses revealed arsenic maps homogeneously distributed in cells of the lamina, stem and rhizome of the fern. These results indicate that arsenic, both arsenate and arsenite in a contaminated medium are translocated quickly from roots to fronds of Pteris vittata, and distributes homogeneously into tissue cells of the fern laminas.

PIXE ANALYSIS OF A MURINE FIBROSARCOMA TUMOR FOR PROTON THERAPY COMBINED WITH THE CHEMOTHERAPEUTIC AGENT CISPLATIN

Concentrations of the chemotherapeutic agent, cis-diamminedichloro-platinum(II) (CDDP) in NFSa fibrosarcoma tumors were investigated using a conventional PIXE analysis on the basis of an internal standard method to study enhancement of antitumor effects caused by proton therapy combined with CDDP treatment. Results of the PIXE analysis showed that platinum concentration of the tumors treated with CDDP at a single dose of 10 mg/kg was 2.0±0.1 µg/g and persisted at the level at least 6 hours after the administration. The present study demonstrated that the presence of CDDP in the tumor caused an enhanced therapeutic effect on tumor growth delay when CDDP treatment was combined with post proton-irradiation in comparison with CDDP treatment alone or proton therapy alone.

PIXE ANALYSIS OF PEANUTS PLANTED IN JAPAN AND IMPORTED FROM ABROAD

Elemental concentrations in Chinese peanuts have been analyzed and compared with those in Japanese peanuts by means of a PIXE (Particle Induced X-ray Emission) technique with an internal standard method to investigate traces of residual agricultural chemicals or toxic elements in them because frequent detection of excessive agrochemical residues in food imported from China has posed serious health concerns to Japanese people. We prepared the samples by separating the peanut seed into two cotyledons (seed leaves) and an embryo. Significant differences in elemental concentrations between Chinese and Japanese peanuts have not been observed as far as the peanut seeds used in the present measurement are concerned. The concentrations of the several elements in the embryo are higher than those in the cotyledon.

Useful Ingredients Recovery from Sewage Sludge by using Hydrothermal Reaction

Hydrothermal treatment of sludge from a sewage treatment plant was conducted to obtain useful ingredients for culture of specific microbes which can reduce polysulfide ion into sulfide ion and/or hydrogen sulfide. Several additives such as acid, base, and oxidizer were added to the hydrothermal reaction of excess sludge to promote the production of useful materials. After hydrothermal treatment, reaction solution and precipitation were qualitatively and quantitatively analyzed and estimated the availability as nutrition in cultural medium. From the results of product analysis, most of organic solid in sewage was basically decomposed by hydrothermal hydrolysis and transformed into oily or water‐soluble compounds. Bacterial culture of sulfate‐reducing bacteria (SRB) showed the good results in multiplication with medium which was obtained from hydrothermal treatment of sewage sludge with magnesium or calcium hydroxide and hydrogen peroxide.