イオウ セッカイセキフン コンゴウ ゾウリュウブツ オ モチイタ ハタチ アンキョ ハイスイ ノ ダッチツ ショリ

固体硫黄を用いた独立栄養脱窒(SLAD)法の問題点を改善した新しい脱窒資材である硫黄-石灰石粉混合造粒物(SC11)について脱窒温度特性の測定と畑地暗渠排水における現地脱窒実験を行い,次の結果を得た。1)SC11を用いた脱窒反応の温度特性では,15℃以上で脱窒が確認された。しかし20℃以下での脱窒能力の低下は著しく,実用には20℃以上が望ましい。2)SC11(2～50mm)を用いた暗渠排水脱窒実験では,硝酸性窒素の平均濃度75mg/lに対し,1日資材重量当たり2倍量(v/w)以下の流速,または1日資材1kg量当たり160mg以下の硝酸性窒素負荷量では99%以上の除去率が得られ,処理水中に亜硝酸性窒素は認められなかった。3)1日資材重量当たり2倍量以上の流速では,不完全な脱窒により処理水中に亜硝酸性窒素が残存した。このときの脱窒速度は,流速にかかわらずほぼ一定の値を示し,生成する硫酸の総量も一定であった。したがって流速を増すほど除去率は低下した。このことから硫黄を用いた脱窒処理は最適な流速の制御が重要であることが示された。4)処理水のpHはほぼ7.0±0.5の範囲に保たれ,生成する硫酸濃度に関係なく優れた中和応答を持続した。To improve the problem of the sulfur-limestone autotrophic denitrification (SLAD) process for treatment of nitrate-nitrogen contaminated water, novel material for denitrification bed was developed such as granulated sulfur-limestone mixture (SC11) which was made from sulfur and limestone of equal quantity in weight. The feasibility of the denitrification treatment by SC11 for underdrainage was studied. In batch experiments, the influence of temperature over the capacity of denitrification was examined with feed solution, SC11 and seed sediment. That capacity increased with the temperature in a range from 15℃ to 30℃. The decline of the denitrification ability was serious at lower temperatures. Therefore, the desirable temperature condition for SLAD process was higher than 20℃. In field experiment, nearly 100% of removal efficiency of NOx (NO_3^-+NO_2^-) was observed in the flow rate of twice as large as amount of SC11 (v/w) per day, on the effluent of the tile drain system, which contained approximately 75mg/l of NO_3^--N in average concentration. In this case, the maximum denitrification rate was 207mg of N per kilogram of SC11 per day. When the flow rate exceeded the level above, NO_2^- of the intermediate product was accumulated in the treated water, so that the removal efficiency of NOx decreased. Although the flow rate fluctuated, the pH level of the treated water was approximately neutral throughout the experiment period. The neutralization capacity of SC11 performed high responsibility independent of the concentration of SO_4^ which was produced in the process

The Maximal Protection by DMSO of Mammalian Cells Exposed to Very High LET Radiations

To understand indirect action for high linear energy transfer (LET), we examined the radioprotection effects of dimethylsulfoxide (DMSO) on the cell killing for cells irradiated with very high LET heavy ions. Exponentially growing Chinese hamster V79 cells were exposed to low- and high-LET radiations. We estimated that a maximal protectable fraction from a regression lines in the reciprocal plots degree of radical scavenger against the concentration from the cell survival curves. The contribution of indirect action decreased with increasing LET, but remained at the very high LET region. The contribution of indirect action in the cell killing were 52, 39 and 32% at LET of 797, 1298 and 2106 keV/mm, respectively. When cell survival curves were analyzed by the linear-quadratic equation, dependence of the DMSO concentration on the survival curve parameters were found. The quadratic (b) term depends on DMSO concentration in X-rays, and the linear (a) term depends on that in the very high LET radiation. The results suggest that an indirect action to cell killing results from a double-event mechanism in X-rays, and from a single-event mechanism in the very high LET radiation.13th international Congress of Radiation Researc

Contributions of Direct and Indirect Actions in Cell Killing by High-LET Radiations

Biological effects of radiation originate principally in damages to DNA. DNA damages by X-rays as well as heavy ions are induced by a combination of direct and indirect actions. The contribution of indirect action in cell killing can be estimated from the maximum degree of protection by dimethylsulfoxide (DMSO) which suppresses indirect action without affecting the direct one. Exponentially growing Chinese hamster V79 cells were exposed to high LET radiations of 20 to 2106 keV/micrometer in the presence or absence of DMSO and their colony survival was determined. The contribution of indirect action in cell killing decreased with the increase in the LET. However, the contribution did not reach to zero even at very high LETs and was estimated to be 32% at an LET of 2106 keV/micrometer. Therefore, even though the radiochemically estimated G value of OH radicals was nearly zero at an LET of 1000 keV/micrometer, indirect action by OH radicals contributed to a substantial fraction of biological effects of high LET radiations. A RBE determined at a survival level of 10% increased with LET, reaching a maximum value of 2.88 at 200 keV/micrometer, and decreased thereafter. When the RBE was estimated separately for direct action (RBED) and indirect action (RBEI), both of them exhibited a similar LET dependency as the RBE, peaking at 200 keV/micrometer. However, the peak value was much higher for RBED (5.99) than RBEI (1.89). Thus, direct action contributes more to the high RBE of high LET radiations than indirect action does

Radiosensitization by hyperthermia in the chicken B-lymphocyte cell line DT40 and its derivatives lacking nonhomologous end joining and/or homologous recombination pathways of DNA double-strand break repair

Hyperthermia has radiosensitizating effect, which is one of the most important biological bases for its use in cancer therapy with radiation. Although the mechanism of this effect has not been clarified in molecular terms, possible involvement of either one or both of two major DNA double-strand break (DSB) repair pathways, i.e., non-homologous end-joining (NHEJ) and homologous recombination (HR), has been speculated. To test this possibility, we examined chicken B lymphocyte cell line DT40 and its derivatives lacking NHEJ and/or HR: KU70-/-, DNA-PKcs-/-/-, RAD54-/- and KU70-/-/RAD54-/-. Hyperthermic radiosensitization could be seen in all of the mutants, including KU70-/-/RAD54-/-, which lacked both NHEJ and HR. Therefore, hyperthermic radiosensitization cannot be explained simply by the inhibitory effects, if any, on typical NHEJ and/or HR alone. However, in NHEJ-defective KU70-/- and DNA-PKcs-/-/-, consisting of two subpopulations with distinct radiosensitivity, the radiosensitive subpopulation, which is considered cells in G1 and early S, was not sensitized: substantial sensitization was seen only in the radioresistant subpopulation, which is considered cells in late S and G2, capable of repairing DSBs through HR. This observation did not exclude possible involvement of NHEJ in G1 and early S phases and also suggested some inhibitory effects of hyperthermia on HR. Thus, partial contribution of NHEJ and HR in hyperthermic radiosensitization, especially that depending on the cell cycle stages, remains to be considered