Toshinari Shimokawa

Silver and other trace elements in a freshwater fish, Carasius auratus langsdorfii, from the Asakawa River in Tokyo, Japan.

The concentrations of silver (Ag) in a typical freshwater fish in Japan, Carasius auratus langsdorfii, and some other species have been determined to examine the Ag-contamination of fish and to specify the Ag accumulating species and part. They were dissected roughly into four parts, and analyzed by an instrumental neutron activation analysis. It was found that Ag was accumulated in the samples from the Asakawa River, and that the Ag concentration in the entrails of C. auratus langsdorfi reached 12 microg g(-1). The analysis of a C. auratus langsdorfii, which was dissected into 13 individual organs, showed that the Ag was accumulated highly in the liver, followed by the gallbladder and kidney. The inter-species and inter-part distributions of other trace elements have also been studied.

Physico-chemical speciation of trace elements in urban streams by size fractionation

Abstract Size fractionation methods have been used for the speciation of trace elements in several urban streams. Both filtration and ultrafiltration techniques were applied to separate the trace elements into various sizes and/or molecular weight ranges. The size distribution was determined for 39 elements by means of neutron activation analysis to estimate their chemical or physical forms. It was clarified that alkali and alkaline-earth elements, halogens and V, Mn, Co, Ni, Zn, As, Se, Mo, Sb, W, U etc., in the urban streams were mainly present in the dissolved phase, and that Sc, Fe, Ag, Al, Hf, Ta, Au and light rare-earth elements were predominantly associated with the suspended particles. The following conclusions could be drawn on the dissolved species of trace elements in the urban streams: (1) the dominant dissolved species for alkali and alkaline-earth elements, V, Mn, Al, Sb and Au are regarded as simple inorganic ions; (2) the elements Sc, Cr, Co, Ni, Zn, Se, Mo, W, Ir, U and heavy rare-earth elements lend to form soluble complexes with organic or inorganic ligands; (3) arsenic is divided between both species of simple inorganic ions and soluble complexes; and (4) the elements Fe, Ag, Ta and light rare-earth elements are mainly associated with organic or inorganic colloids.

Degradation of halogenated carbons in alkaline alcohol

Abstract 1,1,2-Trichloro-trifluoroethane, 1,2-dibromo-tetrafluoroethane, 2,3,4,6-tetrachlorophenol, 1,2,4-trichlorobenzene, and 2,4,6-trichloroanisole were dissolved in alkaline isopropyl alcohol and irradiated with 60 Co gamma rays after purged with pure nitrogen gas. The concentration of the hydroxide ions and the parent molecules decreased with the dose, while that of the halide ions and the organic products, with less halogen atoms than the parent, increased. Chain degradation will occur in alkaline isopropyl alcohol.

Improvement of sedimentation and dewatering of municipal sludge by radiation

Abstract As the promotion of sewerage system, the volume of municipal sludge in Tokyo has increased rapidly. Due to recent changes in the properties of the sludge, moreover, it has become difficult to thicken the liquid sewage sludge by sedimentation and to dewater the thickening sludge mechanically. The development of a new effective method for sludge treatment is necessary. Therefore, a study on the improvement of sedimentation and dewatering of sewage sludge by irradiation with 60Co gamma rays and electron beams was undertaken. Sedimentation tests and various dewatering tests were carried out for the waste activated sludge and anaerobically digested sludge. From the changes in the settling rate, capillary suction time, water content of the sludge cake, and the quality of separated water by irradiation, the optimum irradiation conditions for improving the sedimentation and dewatering of 2 types sludge were determined. The necessary dose for improving the sedimentation and dewatering was observed to be 1–3 kGy for the activated sludge and 5–10 kGy for the digested sludge. To confirm the cause of those changes by irradiation, the zeta potential and viscosity of the sludge were measured.

Chain Dechlorination of Organic Chlorinated Compounds in Alcohol Solutions by 60Co γ-Rays, (I)

Chlorinated benzenes dissolved in deoxygenated alkaline 2-propanol were dechlorinated by irradiating with 60Co γ-rays to produce the lower chlorinated benzenes and chloride ion. The yield of dechlorination was found to depend on the number of chlorine atoms on the benzene ring, the G (CI−)-values being, for instance, 6,500, 480 and 2.0 for 0.07 M penta-chlorobenzene, 1, 2, 4-trichlorobenzene, and monochlorobenzene, respectively, in 0.2 M KOH-2-propanol solution. In contrast, the values of G(C1−) differed little between the isomers of trichlorobenzene. The large difference in G (CI−) according to the number of chlorine atoms can be explained by considering the redox potential of the chlorinated benzenes and the ketyl radical ion. Trichlorobenzene is dechlorinated to dichlorobenzene and then to monochlorobenzene while producing potassium chloride and acetone, and consuming hydroxide ion. In the experiment, some chlorinated benzene derivatives were observed to be generated in the course of this process—proba...

Radiation treatment of municipal effluent

Abstract The recycling of municipal wastewater is an effective means of coping with the water shortage in Tokyo. After irradiation, the refractory organic substances in wastewater were decomposed. COD, light brown color, offensive odor and foaminess in the effluents were reduced with increasing dose. Inactivation efficiencies (D 10 ) of six microorganisms added to the secondary effluents and return sludge supernatant by irradiation were investigated. The survival curves of total bacteria, total coliforms and enterococci in the secondary effluents were compared. The number of total coliforms exponentially decreased with increasing dose and fell to undetectable levels at 0.5 kGy. The elimination of suspended solids in the secondary effluents is effective in diminishing the dose required to disinfect and prevent bacteria regrowth.

Radiation Decomposition of Humic Substances in Landfill Disposal Leachate

The leachate generated from landfill contains humic substances such as humic acid and fluvic acid. It shows, in general, high chemical oxygen demand (COD) and biological oxygen demand (BOD), and colors in dark brown. When the leachate collected on the No. 15 landfill in Tokyo Bay was irradiated by gamma-rays from a 60Co source in bubbling air, the total organic carbon (TOC) decreased with increasing dose and the brown color was bleached. The effects of pH, flow rate, and dose rate on the decrease of TOC, the variations of UV spectrum, and the formation of carbon dioxide by the irradiation were examined. The decreasing rate of TOC increased with an increase of the flow rate up to approximately 1l/min and showed a maximum value in the region of pH 4 approximately 6. It was also dependent on the dose rate and increased with a decrease of the dose rate. The radiation chemical yield, G(--TOC), reached 162 at low dose rate of 1.3 X10(4) rad/h. This result suggests that a radiation-induced chain reaction occurred. The amount of TOC decreased was almost equal to that of carbon dioxide formed. This result shows that the organic substances were decomposed by irradiation to carbon dioxide as a final product and it was ejected from the solution.