The spent adsorbents that remain after being used to purify As-contaminated water constitute waste containing a large amount of As. These spent adsorbents, after being disposed, are likely to come into contact with silicic acid leached from the soil or cementitious solidification materials. Thus, it is crucial the evaluate the effects of silicic acid on spent adsorbents. In this study, the effects of silicic acid on spent Ca-based (CaO and Ca(OH)(2)) adsorbents with arsenite were investigated. The As leaching ratio for the spent adsorbents decreased with an increase in the initial concentration of silicic acid in the liquid. Under the tested conditions, the As leaching ratio decreased from 8-9% to less than 0.7% in the presence of silicic acid at an initial Si-normalized concentration of 100 mg/L. The primary mechanism behind the inhibition of As leaching by silicic acid was determined to be re-immobilization via the incorporation of arsenite during the formation of calcium silicates. In the presence of silicic acid, spent Ca-based adsorbents with arsenite had a lower As leaching ratio than those with arsenate. Therefore, spent Ca-based adsorbents with arsenite were found to have a higher environmental stability than those with arsenate.

<title>Abstract</title>This work developed a model for predicting the volatilization flux from the unsaturated soil contaminated by volatile chemical substances (VCSs) such as mercury and benzene. The model considers a series of phenomena under the unsaturated condition such as multi-phase flow consisting of a non-aqueous phase liquid, water, and gases together with the permeation of rainfall into the surface soil, the volatilization/condensation of VCSs, and the adsorption/desorption of VCSs. On this basis, this work clarified a mechanism for the generation of a volatilization flux at the ground surface. In addition, the effects of various transport phenomena in the surface soil on the magnitude and seasonal changes in this flux due to variations in weather factors such as rainfall level, temperature, and air pressure were quantitatively evaluated. This newly developed prediction model can be utilized to estimate dynamic variations in the flux under real-environmental conditions.

Chloroethenes are common soil and groundwater pollutants. Their dechlorination is impacted by environmental factors, such as the presence of metal ions. We here investigated the effect of ferrous iron on bacterial reductive dechlorination of chloroethenes and on methanogen community. Reductive dechlorination of tetrachloroethene was assayed with a groundwater sample originally containing 6.3 × 103 copies mL-1 of Dehalococcoides 16S rRNA gene and 2 mg L-1 of iron. Supplementation with 28 mg L-1 of ferrous iron enhanced the reductive dechlorination of cis-dichloroethene (cis-DCE) and vinyl chloride in the presence of methanogens. The supplementation shortened the time required for complete dechlorination of 1 mg L-1 of tetrachloroethene to ethene and ethane from 84 to 49 d. Methanogens, such as Candidatus 'Methanogranum', Methanomethylovorans and Methanocorpusculum, were significantly more abundant in iron-supplemented cultures than in non-supplemented cultures (P < 0.01). Upon methanogen growth inhibition by 2-bromoethanesulfonate and in the absence of iron supplementation, cis-DCE was not dechlorinated. Further, iron supplementation induced 71.3% dechlorination of cis-DCE accompanied by an increase in Dehalococcoides 16S rRNA and dehalogenase vcrA gene copies but not dehalogenase tceA gene copies. These observations highlight the cooperative effect of iron and methanogens on the reductive dechlorination of chloroethenes by Dehalococcoides spp.

© 2020 Elsevier Ltd The Tohoku region of Japan is geologically diverse, with a long agriculture and mining history; however, little information about the origins and distribution mechanisms of elements in this region has been reported. This study aims to provide fundamental insights into the effects of geological features and anthropogenic activities on various elements, including toxic elements and rare-earth elements (REEs), in the Tohoku region. A geochemical database (2007, AIST) consisting of data for 53 elements in 485 river sediment samples from the region was used, and a data-driven method combining principal component analysis (PCA) was applied for analysis. GBs for numerous types of areas, including general areas (GGB), natural environments (NGB), high anthropogenic-influenced areas (AGB) and mineralised areas (MGB) were established; especially, MGB was newly proposed in this study to illuminate the role of ore deposits. Both PCA and GBs comparison results show that geological features (especially igneous rock distribution) were the most important factor affecting elemental distribution, rather than anthropogenic activities. In the PCA, the first principal component showed that REE resources were commonly associated with the distribution of granitic rocks and REE-bearing minerals. Anthropogenic contaminations from mining, urban, and anthropogenic areas played important roles as the origin of some toxic elements (e.g. Ni, Pb, Sb). Comparisons between these GBs effectively elucidated the enrichment of certain toxic elements (e.g., Hg, Sb) in ore deposit areas. This data-driven study not only clarified the origins of toxic elements, but also revealed the location of potential REE mineral resources in the Tohoku region.

<p>陰イオン交換基として第四級アンモニウムカチオン-N(CH₃)₃^＋を有する市販の陰イオン交換樹脂カラムを用いて，亜ヒ酸－ヒ酸分離手法に関する研究を行った。そして，無機ヒ素の価数分離を行う際の最適条件の選定及び共存する陰イオンの影響について実験的に検討した。亜ヒ酸とヒ酸の第一解離定数に基づいた計算によって，ヒ素（As）の価数分離に最適な検液のpHは4.3～7.1と見積もられた。このpH 範囲内に調整された検液を本カラムに通液すると，亜ヒ酸は陰イオン交換樹脂に吸着されないが，ヒ酸は吸着されるため，検液中のAs を適切に価数分離できることが実証された。また，陰イオン交換樹脂に吸着したヒ酸は，HCl あるいはHNO₃の使用によって容易にほぼ全てを回収することができた。さらに，As の回収率に及ぼす共存陰イオンの阻害影響の強さは，CH₃COO^－＜＜Cl^－＜NO₃^－＜SO₄^2－であることを明らかにした。本研究で提案する亜ヒ酸－ヒ酸分離手法は，本試験条件において，実験誤差6％程度で亜ヒ酸及びヒ酸を良好に分離回収できることが示された。</p>

<p>汚染水からのヒ素除去やヒ素汚染土壌の不溶化を目的としたヒ素吸着材として、マグネシウム（Mg）系及びカルシウム（Ca）系吸着材が期待されている。しかしながら、ヒ素汚染水中にケイ酸が共存している場合、Mg系吸着材に関しては、そのヒ素吸着能がケイ酸によって著しく低下させることが既往の研究によって報告されており、Ca系吸着材に関しても同様のヒ素吸着能の低下が懸念された。そこで、本研究では、Ca系吸着材（酸化カルシウムCaO及び水酸化カルシウムCa(OH)2）を対象とし、模擬ヒ素汚染水としてケイ酸を共存させたヒ酸溶液を用いたヒ酸除去試験を実施し、Ca系吸着材のヒ酸吸着能に及ぼすケイ酸の影響を実験的に検討した。その結果、ケイ酸の存在はCa系吸着材のヒ素吸着能を向上させることが明らかになった。</p>

The stability and dispersion of naturally occurring As have been receiving increasing attention, because As is toxic and its contamination is a widespread problem in many countries. This study investigated As fractionation and speciation in organic sediments collected from different depositional settings to elucidate the existence of stable As in humic substances. Eleven organic sediment samples were collected from marine and terrestrial alluvial regions in Hokkaido prefecture, Japan, and the chemical fraction of As and species of humic substances were identified by sequential extraction. In addition, stable As bound in organic matter was evaluated by FT-IR spectroscopy. The As fraction mainly comprised inorganic substances, especially sulfur, iron, and manganese, and terrestrial sediments (lacustrine and inland deposits) were rich in sulfides and Fe and Al (hydr)oxides. When the residual fraction was excluded, the organic fraction of As was higher in seawater sediments than in terrestrial sediments. Among humic substances, cellulose, humic acid, and hydrophilic fulvic acid were clearly associated with As accumulation, and As speciation showed that the As was of organic origin. Cellulose, an organic compound of plant origin, was abundant in As=S and As (III)=O bonds, and As accumulation was higher in sulfur-rich peat sediments, corresponding with the physiological activities of As in plants. Hydrophilic fulvic acid and humic acid in these sediments, originating from small animals and microorganisms in addition to plants, denote higher As contents and abound in As (III, V)=C and C-H, CH3 bonds even in sulfur-rich sediments. The methylated As bonds reflect the ecological transition of organisms.

Characterizing the mechanisms by which natural microorganisms in soil decompose gasoline hydrocarbons is of fundamental importance for a better understanding of natural attenuation and/or for predicting contaminant transport and fate in soils. To examine whether and how gasoline hydrocarbons can be decomposed under general environmental conditions, the decomposition of 10 major components generally contained in commercially available gasoline was analyzed in three arbitrarily selected Japanese soil samples. Gasoline hydrocarbons, especially aromatic hydrocarbons, are easily adsorbed by the tested Japanese soils, with straight chain hydrocarbons decomposing faster than branched hydrocarbons. Saturated monocyclic hydrocarbons were less easily decomposed than unsaturated monocyclic hydrocarbons. Enhancement of microbial decomposition of gasoline hydrocarbons requires a continuous supply of oxygen together with nutrients for the microorganisms.

ヒ素吸着材のひとつとしてカルシウム系吸着材が期待されているが，汚染水中のヒ素を除去した吸着材は，それ自体が多量のヒ素を含有するため，適切な処理を行わずに環境中に廃棄された場合，ヒ素溶出による二次的な環境汚染を引き起こす懸念がある．本研究では，土壌やセメント系固化材等から溶出する可能性のあるケイ酸成分が使用済Ca系吸着材の環境安定性に及ぼす影響を評価するために，ケイ酸溶液を用いた振とう試験を実施した．その結果，CaO及びCa(OH)₂を母材とした使用済Ca系吸着材では，試験溶液に含まれるケイ酸の初期濃度が高いほどヒ素の溶出率が低下することが明らかになった．これは，ケイ酸成分が使用済吸着材から溶出したカルシウム成分と反応してケイ酸カルシウム種を生成する際に，使用済吸着材から溶出したヒ酸成分を取り込むためと考えられた．また，生成したケイ酸カルシウムの平均化学組成は，試験溶液の初期Si濃度によって異なり，25 mg/L付近ではCa₂SiO₄，50～100 mg/LではCaSiO₃が推測された．一方，初期Si濃度が比較的低い場合（約5 mg/L）では，使用済吸着材表層へケイ酸成分がイオン交換反応あるいは化学吸着反応によって直接的に吸着する反応が優勢であると推察された．

1,4-ジオキサンは，環境動態が科学的に未解明であるため，従来のVOCsに比べて土壌汚染調査が困難である．本研究では，真砂土，黒ボク及び黒泥を対象として，土壌中の固相及び液相中の1,4-ジオキサンの分配の基礎的な検討を行った．各種分配試験（pH依存性，土壌含水比及び保水性）の結果では，分配試験初期に与えた1,4-ジオキサン濃度とほぼ同値の濃度となり，固相への分配割合は0.1～数％であった．しかし，高アルカリ条件では，1,4-ジオキサンが20％固相へ分配される可能性がある．土壌の保水性に着目すると1,4-ジオキサンは，有機分の少ない土壌で間隙水による希釈の影響によって濃度変化する可能性がある．このことから，特殊な環境（高アルカリ，低保水性）に移行しない限り，環境中に放出された1,4-ジオキサンは，間隙水または地下水へ移行することが示された．

汚染水中のヒ素を除去した吸着材は，それ自体が多量のヒ素を含有するため，適切な処理を行わずに環境中に廃棄された場合，ヒ素溶出による二次的な環境汚染を引き起こす懸念がある．本研究では，土壌等から溶出したケイ酸がマグネシウム系使用済吸着材の環境安定性に及ぼす影響を評価するために，ケイ酸溶液を用いた振とう試験を実施した．その結果，Mg(OH)₂及びMgCO₃系使用済吸着材では，ケイ酸濃度の増加に伴いヒ素の溶出量が増大することが明らかになった．一方，MgO使用済吸着材では，ヒ素の再溶出はほとんど生じず，ケイ酸に対しても非常に高い環境安定性を持つことが示された．それゆえ，土壌やセメント系固化材等からのケイ酸成分の溶出が想定される条件下で使用するヒ素吸着材として，MgOが最も優れていると結論付けられた．

Tsunami deposits accumulated on the Tohoku coastal area in Japan due to the impact of the Tohokuold earthquake. In the study reported in this paper, we applied principal component analysis (PCA) and cluster analysis (CA) to determine the concentrations of heavy metals in tsunami deposits that had been diluted with water or digested using 1 M HCl. The results suggest that the environmental risk is relatively low, evidenced by the following geometric mean concentrations: Pb, 16 mg kg(-1) and 0.003 ml L-1; As, 1.8 mg kg(-1) and 0.004 ml L-1; and Cd, 0.17 mg kg(-1) and 0.0001 ml L. CA was performed after outliers were excluded using PCA. The analysis grouped the concentrations of heavy metals for leaching in water and acid. For the acid case, the first cluster contained Ni, Fe, Cd, Cu, Al, Cr, Zn, and Mn; while the second contained Pb, Sb, As, and Mo. For water, the first cluster contained Ni, Fe, Al, and Cr; and the second cluster contained Mo, Sb, As, Cu, Zn, Pb, and Mn. Statistical analysis revealed that the typical toxic elements, As, Pb, and Cd have steady correlations for acid leaching but are relatively sparse for water leaching. Pb and As from the tsunami deposits seemed to reveal a kind of redox elution mechanism using 1 M HCl. (C) 2015 The Authors. Published by Elsevier Ltd.

It is important to understand the distribution mechanism of heavy metal elements in environmental systems, because the toxicities of various metals and metalloids significantly affect health risks. The heavy metals concentrations are controlled by a wide of variety environmental factors. This study aims to clarify main influence factors on the heavy metal distribution in sediment, soil, river in the Natori River, Sendai City. We firstly produced geochemical maps for heavy metal concentrations (As, Pb and Cr) of river sediment, neighboring soil (bulk component, soluble component in 1N HCl and in pure water) and river water. The heavy metals concentrations in river water increase from upper stream to down stream, whereas heavy metal concentrations in river sediments and soil vary little from upper stream to downstream. There are no anomalous distributions of heavy metals in the studied area, although many anthropogenic materials are found in sediment, soil and river water. The correspondence analysis was applied to investigate relationships of heavy-metal concentrations between sediment, soil and river water. The results indicate that the heavy metals (As, Pb Cr and Zn) in sediment, soil and river water are dominantly controlled by natural sedimentary processes, such as denudation and sedimentation. The proposed method could be further applied for other pollutants in various environment systems. From a viewpoint of risk assessment of heavy metals, it is suggested by the presence of closer relationship of heavy metals that contains the risk information of heavy metals.

製鋼スラグの利用用途で，腐植物質との混合による磯焼け回復技術が注目されているが，製鋼スラグから溶出する重金属等の環境影響を検討する必要がある．本研究では純水による検討に加えて，海域利用を想定し，実海水を用いて振とう試験および浸漬式のシリアルバッチ試験を実施した．さらに，海域利用において要求される環境安全品質の考え方に基づき，海域利用への適合性について考察を行った．試験結果より，Cd，Pb，Cr，Bは，試験条件を変えた場合に，溶出濃度が港湾用途溶出量基準を超過することは確認されず，製鋼スラグ及び腐植物質の相互作用により，重金属類の溶出濃度は減少傾向を示した．また，本研究で想定した海域利用の環境安全品質を設定し，本試験結果を適用した結果，重金属類による海域汚染の原因となる可能性は低いことが示唆された．

The great tsunami that followed the 2011 off the Pacific coast of Tohoku Earthquake caused derangement of superficial sediments in coastal areas of Sendai Plain and Sendai Bay. Tsunami deposits were transported with flooded seawater in the form of mud, sand, or granules, and were deposited in the coastal region. These deposits record important information that facilitate determining the age and frequency of past tsunami events. The origins of tsunami deposits and the derangement of marine sediments are studied based on a chemical composition analysis of tsunami deposits, marine sediments, and samples of subsurface soil collected before the earthquake. The solubility of chemical components, such as of chromium, iron, nickel, copper, zinc, arsenic, and lead, in 1 M HCl was much higher for tsunami deposits than subsurface soils. The metal speciation and correlation of chemical composition indicate that the main origins of tsunami deposits are coastal marine sediments. The transformation of marine sediments to the coastal side, except Arahama offing, is also confirmed from active regional shifts of bacteria. These imply that the tsunami had a large effect on mobilizing marine sediments in the northern area of Sendai Bay, Nanakita River offing, Arahama offing, and Hiroura offing based on the extent of bacterial activity shift and chemical compositions of organic materials.

This study involved measurement of concentrations of dissolved and particulate radiocesium (Cs-134 and Cs-137) in river water, and determination of the quantitative relations between the amount of deposited Cs-137 and Cs-137 concentrations in river waters after the Fukushima Daiichi nuclear power plant accident. First, the current concentrations of dissolved and particulate Cs-134. Cs-137 were determined in a river watershed from 20 sampling locations in four contaminated rivers (Abukuma, Kuchibuto, Shakado, and Ota).
Distribution characteristics of different Cs-137 forms varied with rivers. Moreover, a higher dissolved Cs-137 concentration was observed at the sampling location where the Cs-137 deposition occurred much more heavily. In contrast, particulate Cs-137 concentration along the river was quite irregular, because fluctuations in suspended solids concentrations occur easily from disturbance and heavy precipitation. A similar tendency with dissolved Cs-137 distribution was observed for the Cs-137 concentration per unit weight of suspended solids.
Regression analysis between deposited Cs-137 and dissolved/particulate Cs-137 concentrations was performed for the four rivers. The results showed a strong correlation between deposited Cs-137 and dissolved Cs-137, and a relatively weak correlation between deposited Cs-137 and particulate Cs-137 concentration for each river. However, if the particulate Cs-137 concentration was converted to Cs-137 concentration per unit weight of suspended solid, the values showed a strong correlation with deposited Cs-137. (C) 2014 Elsevier Ltd. All rights reserved.

We developed a rapid method for concentrating and measuring radiocesium (Cs-134 and Cs-137) dissolved in fresh water using nonwoven fabric impregnated with Prussian blue (PB) as a radiocesium absorber in combination with gamma-ray spectrometry using a germanium (Ge) detector. Utilizing this method, dissolved radiocesium in a 20-100 L freshwater sample could be concentrated within a period of 20-60min by passing the sample through 10-12 columns, connected in series, that had been fitted with nonwoven fabric disks impregnated with PB. Laboratory tests using water samples containing known amounts of radiocesium confirmed that the overall recovery rate of the isotope was 100%-108%, and that the first six columns recovered 84%-97% of the isotope. The detection limit of this method was determined to be 0.002 Bq/L with a sample of 100 L and measurement time of 43,200s. In comparison with traditional methods using ion-exchange resin, co-precipitation with ammonium phosphomolybdate, etc., our method has the advantages of reduced cost and a significantly shorter concentration time. Since water samples can be treated in short periods of time, it is now possible to conduct radiocesium pre-concentration in situ, thus eliminating the need to transport large-volume water samples to laboratories.

The steel slag/compost fertilizer containing soluble form of iron has been evaluated for restoring barren coastal ground. While humic substances in the compost have been believed to be carriers for supplying iron to such coastal land, they become coagulated and/or flocculated in seawater. Thus, the focus of the study was on seawater extractable organic matter (SWEOM) from the compost that could function as a chelator of iron. Structural features of a novel organic fraction from the compost, SWEOM, were characterized by TMAH-py-GC/MS and the result were compared with those for humic (HA) and fulvic (FA) acids from the same origin. The TMAH-py-GC/MS analyses provided information on the structural characteristics for HA, FA and SWEOM. FA contained high amount of nitrogen-containing pyrolysate compounds, which were likely derived from saccharides and RNA. The large amounts of methoxybenzenes and hydroxybenzenes, which were originated from lignin, were also identified in the HA. For SWEOM, the percentages of fatty acid pyrolysate compounds were significantly larger than the corresponding values for HA and FA. An acidic functional group analysis indicated that the levels of carboxylic groups in SWEOM were lower than those in HA and FA, suggesting that the fatty acid pyrolysate compounds were produced as the result of the cleavage of ester-linkages. (C) 2012 Elsevier B.V. All rights reserved.

Alterations in the structural features of humic acids (HAS) in a steel slag-compost fertilizer for supplying soluble Fe(II) to barren ground in coastal areas were monitored during a 6-month period of fertilization. HAs, the major organic fractions in the fertilizer, were extracted at different periods of time (2, 4 and 6 months) in the absence and presence of steel slag. To focus on the polymeric structure of the HA-backbone and the organic fractions, which are sorbed onto the HA-polymeric matrix (e.g., lipids), the extracted HA samples were analyzed by pyrolysis-gas chromatography/mass spectrometry under conditions where the sample is methylated with tetramethylammonium hydroxide (TMAH-py-GC/MS). The structural features analyzable by TMAH-py-GC/MS for the HA were dramatically altered in the presence of steel slag during the fertilization period. The major modification involved a decrease in phenolic moieties and a significant increase in the sulfur-containing pyrolysate compounds. These results indicate that the steel slag has a significant effect in altering the structure of HA in the fertilizer. TMAH-py-GC/MS analysis of the HAs indicated that the sulfur in the HAs was present in an organic form and not as elemental sulfur. Significant increases in the levels of biomarker fatty acids (iso- and anteiso-C-15:0 and C-17:0 carboxylic acids), which are related to the activity of sulfate reducing bacteria, suggests that the significant alterations in the HA structures in the presence of steel slag can be attributed to the sulfurization of organic matter in the fertilizer to form hydrogen polysulfides by the reduction of sulfate ions in seawater and/or steel slag via microbial processes. (C) 2012 Elsevier B.V. All rights reserved.

Understanding the transport and fate of gasoline components in soils is of fundamental importance for protecting human health from possible risks. A series of column experiments were performed to investigate the effects of soil organic matter, on the transport of total petroleum hydrocarbons (TPH) and the paraffin (n-paraffin and isoparaffin), olefin, naphthene, and aromatic (PONA) components in 2 typical Japanese soils. The results of this study illustrated the following observations: 1) The remaining mass of regular gasoline in a soil is time-dependent. 2) The major degradation mechanism of regular gasoline in soils would be volatilization. 3) The sorption of regular gasoline by soil organic matter might be one of the major reasons that causes regular gasoline remaining in Kuroboku soil. 4) Aromatic and isoparrafine components are tended to remain in soils. © 2012 Nova Science Publishers, Inc.

In order to determine whether natural attenuation of chlorinated ethenes by microbial activity occurs in aquitards, sediments at a site contaminated with tetrachloroethene were vertically studied by drilling. The distribution of microbes (Dehalococcoides group and anaerobic hydrogen producers) and the ability of the sediments to sustain microbial dechlorination were determined in an aquitard as well as in an aquifer. Close-spaced sampling revealed the existence of large populations of Dehalococcoides and H(2)-producing bacteria, especially in the organic-rich clayey aquitard rather than in the aquifer. The vinyl chloride reductase gene was also detected in the clay layer. Furthermore, incubation experiments indicated that the clay sediment could sustain transformations of tetrachloroethene at least to vinyl chloride. In contrast, no significant transformation was observed in the aquifer sand. Our results indicate that dechlorination of tetrachloroethene by bacteria can take place in an organic-rich clayey aquitard, and that organic-rich clay may also be important in the natural attenuation in an adjacent aquifer, possibly supplying a carbon source or an electron donor. (C) 2011 Elsevier B.V. All rights reserved.

The combination of steel slag and humic acids has an important role that the migration of essential elements, particularly iron and nutrients can be promoted in the aquatic environment. Humic substances such as fulvic acid and humic acids have functions of the formation of chemical complex with metal elements in the environment. Especially in the structure of fulvic acid, iron and humic matter have relatively strong linkage to form a chemical structure of iron-fulvic substances which can dissolve in water phase and be easily taken in plants and organisms as an essential element of iron. A kind of humic substances is considered to be very effective to rehabilitate the ecological situation around coastal environment. In this paper we present the methodology of chemical analysis for complex formation between divalent iron and humic substances, obtained from soils, sediments, plants, woods and coal materials. The necessary conditions of eluting humic substances into aquatic environment were experimentally examined using the natural substances modified by pH and Redox control. The properties of long-term stability of humic substances were also investigated under the condition of fresh water and sea water environments. In addition a trial of risk assessment using the original assessment tool was carried out to reveal safer features of this technology. Thus the acceptability of the technology using steel slag and humic substances is discussed on the basis of experimental and risk assessment results.

Understanding the volatilization properties of gasoline components in soils is of fundamental importance in the field of geoenvironments. A series of experiments were performed to investigate the effects of temperature, soil water content, soil organic matter content, as well as mean particle size on volatilization rate of total petroleum hydrocarbons (TPH) and the paraffin (n-paraffin and isoparaffin), olefin, naphthene, and aromatic (PONA) components in four typical Japanese soils. The results of this study can be summarized as follows. (1) Volatilization rate of gasoline in a soil is concentration-dependent; extensive volatilization occurs above a certain threshold, while volatilization becomes very slow below this threshold. (2) Compared to other factors, temperature and soil organic matter content have greater effects on volatilization rate of gasoline in soils. The volatilization rate is proportional to temperature, but inversely related to soil organic matter content. (3) The characteristics of time-dependent decreases of TPH and PONA components in soils are similar. The volatilization rate of olefin is higher than those of other components. In addition, volatilization of olefin is also more sensitive to temperature as well as organic matter content.

There is no question about the importance of understanding the fate of oil pollutants and the risks of individual components of gasoline to human health. To investigate the effects of major environmental factors on the volatilization of regular gasoline from unsaturated soils, a series of experiments were organized and performed on four typical Japanese soils under different temperature, soil organic matter content, and water content conditions. Quantitative assessment of risks of each residual gasoline component to human health was pioneered using the experimental results and a self-developed software program, Geo-Environmental Risk Assessment System (GERAS). Results of this study illustrated that (1) temperature and soil organic matter had significant effects on volatilization and thus on the residual concentrations of gasoline components remaining in unsaturated soils. These residual concentrations were positively related to the amount of soil organic matter, but inversely related to temperature. (2) Risks of residual gasoline components remaining in soils depended on exposure pathway, gasoline component, and carbon numbers. Risks of respiratory exposure due to vapor inhalation were generally higher than the risks of oral exposure due to intake of crops and water. (3) Although residual concentrations of gasoline components remaining in soils with high organic matter contents were high, their risks to human health were low. This is because high organic matter content has strong sorptivity for gasoline components, resulting in less vapor inhalation, less intake from water, and low bioavailability for crops.

Non-destructive measurements of contaminated soil core samples are desirable prior to destructive measurements because they allow obtaining gross information from the core samples without touching harmful chemical species. Medical X-ray computed tomography (CT) and time-domain low-field nuclear magnetic resonance (NMR) relaxometry were applied to non-destructive measurements of sandy soil core samples from a real site contaminated with heavy oil. The medical CT visualized the spatial distribution of the bulk density averaged over the voxel of 0.31 x 0.31 x 2 mm(3). The obtained CT images clearly showed an increase in the bulk density with increasing depth. Coupled analysis with in situ time-domain reflectometry logging suggests that this increase is derived from an increase in the water volume fraction of soils with depth (i.e., unsaturated to saturated transition). This was confirmed by supplementary analysis using high-resolution micro-focus X-ray CT at a resolution of similar to 10 mu m, which directly imaged the increase in pore water with depth. NMR transverse relaxation waveforms of protons were acquired non-destructively at 2.7 MHz by the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence. The nature of viscous petroleum molecules having short transverse relaxation times (T2) compared to water molecules enabled us to distinguish the water-saturated portion from the oil-contaminated portion in the core sample using an M (0)-T2 plot, where M (0) is the initial amplitude of the CPMG signal. The present study demonstrates that non-destructive core measurements by medical X-ray CT and low-field NMR provide information on the groundwater saturation level and oil-contaminated intervals, which is useful for constructing an adequate plan for subsequent destructive laboratory measurements of cores.

It is demanded more convenient survey methods for soil pollution by oils and techniques for toxicity evaluation of petroleum hydrocarbons. The quantitative bioassay using luminous bacteria has not been established. The accumulation of data obtained under scientific condition setting is required.<BR>Firstly, methanol, ethanol and n-propanol which are both moderate hydrophilic and oleophilic, were examined whether they are adequate as the extraction solvent for soil polluted by oils. From the results in bioassay test using luminous bacteria, methanol was selected as the most suitable extraction solvent from them.<BR>Secondly, the acute toxicity evaluation and the detection limit of gasoline, heating oil, light oil, benzene, toluene, n-hexane and carbon disulfide were experimentally examined. The severity of toxicity on luminous bacteria by each 100 vol% of them (without solvent) except n-hexane was carbon disulfide > toluene > gasoline > benzene > methanol > heating oil > light oil. Although the toxicities of 100 vol% of heating oil, light oil and n-hexane were weaker than that of methanol, the use of methanol as the solvent improved the detection sensitivity for them and was possible to detect the toxicity of them by luminous bacteria. The appropriate reaction time for toxicity evaluation or screening may be 15 to 45 minutes. The severity of toxicity on luminous bacteria evaluated using methanol solvent was gasoline > n-hexane > heating oil > toluene > carbon disulfide > benzene > light oil. Also, this study showed potential for quantitatively evaluating in the ranges of 0.02 to 1 vol% of gasoline and heating oil, 0.1 to 5 vol% of light oil and carbon disulfide, 0.2 to 5 vol% of benzene, 0.1 to 1.0 of toluene and 0.05 to 0.5 vol% of n-hexane in methanol solvent (extractant).

本報告では, 支流域に多くの鉱床・熱水変質帯が分布する北海道長流川流域を調査対象地域として, 鉱床・熱水変質帯が深度50cmほどまでの表層土壌中の重金属類濃度にどのような影響を与えているのか調査, 検討を行った. 各鉱床・熱水変質帯には亜鉛, 砒素, 鉛, 銅, ニッケルなどの重金属類に富む岩石が多量に分布した. 変質帯からの重金属類の影響は各支流域に分布する表層土壌には少なく, 河川堆積物を母材とする下流域で砒素の溶出率が高い表層土壌が確認された. 砒素はその物理化学特性から河川を介して溶解と変質鉱物への吸着・沈殿を繰り返しながら移動しうる. ところが供給源となる変質帯から河川への砒素の流出ポテンシャルは変質帯の性状および露頭環境に依存して異なり, 本調査地域では河川沿いの露頭に褐鉄鉱鉱床変質帯の分布する紫明川, 弁景川でのみ高濃度の流出を示した.

土壌と地下水の汚染が人の健康に与えるリスクを評価するための手法を開発した。種々の要素研究を基盤として、評価システム全体を最適に構成した。このため、分野融合型の研究計画を立案して、要素研究の実施からリスク評価システムの開発までを行い、さらに産業や社会で利用可能な形にした。本報告では、研究開発において採用した要素技術の統合と構成のシナリオ、リスク評価の実践におけるスパイラル的な研究展開を中心に、目標達成に至るまでのプロセスについて論じる。

鉱物油等による油汚染が深刻な問題となっており、その浄化が進められている。油浄化について微生物分解を利用するバイオレメディエーションが有効であるが、分解による人の健康に対するリスク変化に関する検討は行われていない。本研究では、土壌汚染のリスク評価システムを用いて、鉱物油成分の微生物分解によるリスク変化の把握を試みた。

鉱物油による汚染土壌浄化における土壌微生物による油成分分解挙動の把握のため、黒ボク土にガソリンないし軽油を混合して模擬汚染土壌を作成し、分解実験を行った。鉱物油の多様な成分の変化に対応するため、TPHおよび芳香族炭化水素・脂肪族炭化水素・BTX（ベンゼン・トルエン・キシレン）の定量分析を行い、炭素数の違いによる分解速度を評価した。

The degradation behavior of chlorinated solvents were difference between each sites and classified in three types; (A) degradation with by-products, (B) degradation without by products, (C) non-degradation. The chemical components in the groundwater of the degradation type (A) showed lower redox potential (ORP), dissolved oxygen (DO) and higher heavy metals such as iron and manganese. These anaerobic reducing ambient is suitable for the bacteria concerned with the reductive dechlorination. Further, there is a possibility that chlorinated solvents are dechlorinated by catalysis, for example pyrite, containing within the soil. The chemical components in groundwater showed higher ORP, DO (degradation type (13)). Since the contaminant at the site YO was PCE which was not degraded by aerobic microorganisms, the reason for the natural attenuation might be dispersion or dilution. Although the higher ORP, DO were detected at degradation type (C), the VOC (TCE) was not attenuated at the site HK. This suggest that the dense non-aqueous phase liquids (DNAPLs) exist in the soil or groundwater, or the biochemical activity is low in this condition due to lower temperature.

Experimental studies of dehalogenation for chlorinated benzenes were conducted using iron sulfide (FeS2) at 25 degrees C in pure water. Chlorinated benzenes are used as a model sample of persistent organic pollutants (POPs) and evaluate the dechlorination ability of natural metallic minerals for POPs. A total of 90% of chlorinated benzenes are dechlorinated after a mere 10 days for mono-, di-, tri-chlorobenzenes and 1,2,3,4-, 1,2,3,5-tetrachlorobenzenes. Their dechlorination abilities are not sensitive to the difference in isomers. The other 1,2,4,5-tetrachlorobenzene, pentachlorobenzene and hexachlorobenzene are also dechlorinated at about 10 to 30% after 10 days. This dehalogenation is only utilized in the dissolution of natural metallic minerals. Metallic minerals such as iron sulfide are expected to have sufficient remediation ability not only for chemical treatment but also as a natural depollution mineral.

Methane hydrate is one of the potential resources of natural gas in the near future, because a large amount of reservoir exists in marine sediments and permafrost regions worldwide. It is very important to investigate physical phenomena in hydrate reservoirs, especially for developing an extraction system for gas hydrates, and in considering the environmental impacts by the development.<BR>In this study, we carried out an experimental research on hot water injection process as one of the thermal stimulation methods, using a special-type apparatus designed for simulating hydrate reservoir. As a result of the experiments, it was found that the dissociation process by hot water injection consisted of the following four stages, such as (1) displacement of free methane gas due to water injection, (2) additional hydrate formation at downstream zone due to migration of dissociated gas and water, (3) actual dissociation, (4) completion of dissociation. In addition, the permeability of the hydrate reservoir was observed as a function of time that, tended to decrease during the additional hydrate formation period and increase during the actual hydrate dissociation period. Based on experimental data of temperature distribution during dissociation, the reservoir could be divided into three zones from upstream edge, and dissociation zone was extremely narrow area depending on the dissociation rate. Furthermore, we discussed the effect of injected water temperature, reservoir pressure and hydrate saturation on the movement of dissociation front and gas production behavior.

In order to obtain fundamental data for the evaluation of permeability in methane hydrate reservoir, we have conducted experimental and analytical studies on the behavior of formation and dissociation of methane hydrate in porous media and the change in permeability in the process of formation and dissociation. The experimental apparatus for permeability measurement was originally designed and manufactured. Very uniform methane hydrate reservoir was achieved by the method of gas injection into sand column. The artificial sample of sand column with methane hydrate was satisfactory for the experiment of absolute permeability measurement. As a result of the experiment, it was found that the formation rate of methane hydrate in porous media depends on the particle size distribution of sands composing porous media. The interfacial condition between methane gas and pore water was an essential parameter of formation. In an experiment of dissociation of hydrate by the injection of hot water, the increase of permeability in methane hydrate reservoir was observed as a function of time. The large decrease in permeability was also obtained as a result of reformation due to flow of dissociated gas in porous media. The apparent absolute permeability drastically decreased as the hydrate saturation in sand column becomes lower. The values of the permeability in the case of hydrate saturation 40 % were 1/30 to 1/50 compared with the original values without any hydrate formation in porous media.

The influence of high concentrations of ferric ions on the biochemical activity of Acidithiobacillus ferrooxidans was studied using intact cells. The specific oxidation rate of ferrous ions decreased with increasing ferric ion concentration. Lineweaver-Burk plots revealed typical competitive inhibition kinetics, because the slopes varied with the ferric ion concentration. A linear relationship between the slope and the square of the ferric ion concentration revealed that the iron-oxidizing enzyme system of A. ferrooxidans was competitively inhibited by about two molecules of ferric ion. The kinetic equation based on this inhibition model agreed with the experimental observation at a high ferric ion concentration where the bacterium is usually exposed in bioleaching and biooxidation plants.

The exposure rates, the distribution of exposure paths and the risk level of inorganic arsenic containing in soil and groundwater in Japan have been evaluated by using originally developed risk assessment model.<BR>Major exposure path for human to arsenic in Japan was food intake. The average total exposure rate was estimated about 4×10^-1 to 5×10^-1 (95% confidence interval (CI)), which revealed that the skin cancer risk resulting from oral intake was about 6×10^-4 to 7×10^-4 (95%CI) and the lung cancer risk resulting from inhalation intake was about 2×10^-4 to 2×10^-3 (95%CI). The total exposure rates from soil and groundwater paths were about 3×10^-3 to 5×10^-2 (95%CI), which revealed that the average oral and inhalation cancer risk (95%CI) was evaluated at 4×10a^-6 to 8×10^-5 and 1×10^-5 to 2×10^-4, respectively.<BR>The contaminated area where soil concentration was higher than Japanese criteria of total content in soil (150mg/kg) had the oral cancer risk more than 5×10^-4 to 1×10^-3 (95%CI) and the inhalation cancer risk 2×10^-3. The risk level of contaminated area exceeded groundwater criteria (10μg/l ) was estimated at about 3×10^-5 to 8×10^-5 (95%CI).

We have developed the geo-environmental risk assessment model for heavy metals, which are considered both soil properties and exposure factors specific to Japanese situations. The exposure rates, the distribution of exposure paths and the risk level of soil content to the human have been evaluated by using this model.<BR>Since the Japanese soil have the specific properties, i.e. high pH, high fraction of organic carbon content and high fraction of clay content, it is difficult to transport into the groundwater and the crops in comparison with other kinds of soil. The exposure rates of children are higher than those of adults. Especially, infants aged 1 to 2 are much exposed to the heavy metals. The major exposure paths of the human are different due to the kind of heavy metal. The human are mainly exposed to lead and chromium from direct ingestion of soil, whereas they are mainly exposed to selenium and cupper from intake of drinking water. The soil contents of exposure limit are estimated at 37 mg / kg for arsenic, 26 mg / kg for cadmium, 620 mg / kg for chromium, 4,600 mg / kg for cupper, 4.0 mg / kg for mercury, 120 mg / kg for lead and 1.6 mg / kg for selenium.

The reduction reaction of selenate ion by TiO₂ photocatalyst in the presence of sulfate ion was studied. Sodium selenate solution was used in the experiments. The selenium concentration of this solution was 10 to 100 ppm as selenium (1.27×10^-1 to 1.27 mmol / dm³), and 1.27 to 1.27×10 mmol / dm³ of sodium sulfate and 2.5×10 mmol / dm³ of formic acid were added to it.<BR>The rate of the reduction reaction of selenate ion by the TiO₂ photocatalyst became smaller by the presence of the sulfate ion. However, the reduction reaction of selenate ion proceeded until the remaining total selenium concentration became under 0.1 ppm. Reduced selenate ion became hydrogen selenide via amorphous selenium, and trapped by the CuSO₄ solution gas trap. On the contrary, sulfate ion was not reduced by the TiO₂ photocatalyst. The rate of the reduction reaction of selenate ion to amorphous selenium depended on the amount of adsorbed selenate ion (C_SeA) and was expressed as a dimensional function of C_SeA. The amount of adsorbed selenate ion on the TiO₂ photocatalyst was decreased with increase of the amount of sulfate ion, and was expressed as the competitive Langumuir isotherm. This is the reason why the rate of the reduction of selenate ion becomes smaller by the presence of sulfate ion.

Biochemical activities of Thiobacillus ferrooxidans in the presence of activated carbon were studied under the shaking and stationary conditions using the 9K medium at pH 1.5. In the shaking condition, the biochemical activities of the bacterium were lower in the presence of activated carbon than in the absence. On the contrary, the activities were higher under the stationary condition. In the shaking condition, the bacteria were adsorbed onto the activated carbon according to the Langmuir isotherm. The adsorbed cells became inactive with regard to their ferrous ion-oxidizing and growth. Under the stationary condition, the oxidation rate of ferrous ion was higher in the presence of activated carbon than in the absence, because the cells gathered to the gas-liquid interface in the presence of activated carbon.<br>

This paper describes an inhibition of oxidation and growth of Thiobacillus ferrooxidans by chloride ion and the effect of diatomaceous earth against its inhibition. <br> Ferrous ion oxidation experiment in the absence of nutrient salts was carried out with various amount of chloride ion. The assay solution of this experiment contained only ferrous sulfate and magnesium sulfate (pH 1.5), and no bacteria grew in this condition. The oxidation of ferrous ion was inhibited by the chloride ion, and was subjected to the competitive inhibition from the Lineweaver-Burg plot. The addition of the diatomaceous earth in assay solution had no effect on the bacterial oxidation.<br> The growth of T. ferrooxidans in 9 K medium was also inhibited by the chloride ion. The growth kinetics of this bacterium in the presence of chloride ion were described with the modified Monod type equation including the term of inhibitor concentration. The growth inhibition reduced by the addition of diatomaceous earth in the medium. The oxidation rate in the presence of diatomaceous earth was much faster than that in the absence of it in high concentration of chloride ion. The growth inhibition constant of adsorbed bacteria was about 60 % larger than that of free bacteria, which was the reason the oxidation of ferrous ion in the presence of diatomaceous earth was faster. <br> The adsorption amount of T. ferrooxidans onto the diatomaceous earth was almost constant in this experimental range of the chloride ion. <br>

Diatomaceous earth is an effective carrier with a large surface area on which Thiobacillus ferrooxidans adsorbs, and enhances the oxidation rate of ferrous ions by the bacterium. The adsorption of T.ferroxidans on diatomaceous earth was expressed by the Henry isotherm, and reached equilibrium within five minutes. The enhancement was due to an increase in the growth rate of the adsorbed cells, which were so active that their specific growth rate calculated using a Monod-type equation was higher than that of the free cells in the liquid phase.