Effect of NOM characteristics on brominated organics formation by ozonation

In this study, organic fractions, namely, humic acid, fulvic acid, hydrophobic base and neutral, and hydrophilic acid, base, and -neutral, were extracted from source water. First, the characteristics of the organic fractions, such as carboxylic acidity, phenolic acidity, ultraviolet absorbance, and aromatic content, were analyzed. Further, a systematic study was carried out to the by-products obtained when organic fractions, to which various amounts of bromide had been added, were oxidized with ozone. Samples after ozonation were analyzed for several brominated organics. The results indicate that the characteristics of the aquatic organic matter, including carboxylic/phenolic acidity, aromatic/aliphatic content, and ultraviolet absorbance, appear to affect the formation of halogenated organics. In general, hydrophobic organics having higher phenolic acidity, aromatic content, and ultraviolet absorbance have higher ozone consumption and produce higher concentrations of brominated organics than hydrophilic organics. It was also found that humic acid demonstrated the highest bromoform (CHBr(3)), dibromoacetic acid (DBAA), and 2,4-dibromophenol (2,4-DBP) formation, whereas hydrophilic neutral produced less CHBr(3) and 2,4-DBP than the rest of the organic fractions but produced the highest amount of dibromoacetone (DBAC) and dibromoacetonitrile (DBAN).     

Correlation of the partitioning of dissolved organic matter fractions with the desorption of Cd,Cu, Ni,Pb and Zn from 18 Dutch soils

Eighteen Dutch soils were extracted in aqueous solutions at varying pH. Extracts were analyzed for Cd, Cu, Ni, Pb and Zn by ICP-AES. Extract dissolved organic carbon (DOC) was also concentrated onto a macroreticular resin and fractionation into three operationally defined fractions: hydrophilic acids (Hyd), humic acids (HA) and fulvic acids (FA). In this manner, change in absolute solution concentration and relative percentage for each fraction could be calculated as a function of extraction equilibrium pH. The soils were also analyzed for solid phase total organic carbon and total recoverable metals (EPA Method 3051). Partitioning coefficients were calculated for the metals and organic carbon (OC) based on solid phase concentrations (less the metal or OC removed by the extraction) divided by solution concentrations. Cu and Pb concentrations in solution as a function of extract equilibrium pH are greatest at low and high pH resulting in parabolic desorption/dissolution curves. While processes such as proton competition and proton promoted dissolution can account for high solution metal concentrations at low pH, these processes cannot account for higher Cu and Pb concentrations at high pH. DOC increases with increasing pH, concurrently with the increase in Cu and Pb solution concentrations. While the absolute concentrations of FA and HA generally increase with increasing pH, the relative proportional increase is greatest for HA . Variation in HA concentrations spans three orders of magnitude while FA concentrations vary an order of magnitude over the pH range examined. Correlation analysis strongly suggests that HA plays a major role in increasing the concentration of solution Cu and Pb with increasing pH in the 18 soils studied. The percentage of the OC that was due to FA was nearly constant over a wide pH range although the FA concentration increased with increasing pH and its concentration was greater than that of the HA fraction at lower pH values (pH = 3-5). Thus, in more acidic environments, FA may play a larger role than HA in governing organo-metallic interactions. For Cd, Ni, and Zn, the desorption/dissolution pattern shows high metal solution concentrations at low pH with slight increases in solution concentrations at extremely high pH values (pH>10). The results presented here suggest that the effects of dissolved organic carbon on the mobilization of Cd, Ni, and Zn may only occur in systems governed by very high pH. At high pH, it is difficult to distinguish in this study whether the slightly increased solution-phase concentrations of these cations is due to DOC or hydrolysis reactions. These high pH environments would rarely occur in natural settings.     

Acid-base characteristics of organic carbon in the HUMEX lake Skjervatjern

The Humic Lake Acidification Experiment (HUMEX) was launched in 1988 to study the role of humic substances in the acidification of surface waters and the impacts of acidic deposition on the chemical and biological properties of humic substances. This subproject was designed to determine the contribution of organic acids to the acidity of Lake Skjervatjern (the HUMEX Lake) and the impacts of the acidification on the characteristics of organic carbon. In order to get an empirical measure for organic acidity, dissolved organic carbon (DOC) was fractionated, isolated, and base-titrated from each half of Lake Skjervatjern. Hydrophobic acids were the dominant organic carbon fraction; the total organic acid content was generally greater than 80% of the DOC. The reliability of the fractionation procedure was tested with synthetic acids and the Nordic Fulvic acid. The DOC fractions did not show high variation over the 1.5-y acidification period. Hydrophilic acids had consistently greater exchange acidities compared to hydrophobic acids, averaging 12.9 μeq/mg DOC vs. 10.9 μeq/mg DOC, respectively. The dissociation of organic acids during acid-base titrations clearly increased with increasing pH. The high organic anion contribution to the ion balances indicates that humic matter is an important acidity source in Lake Skjervatjern. There are slight signs that the contribution of organic acids to overall lake acidity has decreased since acidification was initiated.     

河流型水源地源水有机物种类分布特性及其与消毒副产物关系

研究了不同水文期条件下长三角某典型河流型水源地源水有机物种类分布特性及其与消毒副产物关系。结果表明，该水源地源水有机污染特性呈现出丰水期>平水期>枯水期的特点，水体腐殖化程度依次降低。经树脂富集分离后水样溶解性有机物(DOM)各组分占总有机碳(DOC)的比例有所不同。丰水期：疏水性有机酸(HPO A,38%)>亲水性有机物(HPI,26%)>过渡亲水性有机酸(TPI A,16%)>疏水性有机中性物质(HPO N,12%)>过渡亲水性中性物质(TPI N,8%)；平水期：HPO A(32%)>HPO N(22%)>TPI A(20%)>HPI(18%)>TPI N(8%)；枯水期：HPO A(28%)>TPI A(24%)>HPO N(20%)>HPI(19%)>TPI N(9%)。DOM中仅HPI组分比紫外吸光度值(SUVA)低于原水，其余均高于原水，其中HPO A组分SUVA值最高，是原水的177倍。各水文期条件下，疏水性有机物（疏水性有机酸和疏水性中性物质）对三卤甲烷和卤乙酸生成的贡献，分别超过全部有机物氯化后消毒副产物生成量的60%和65%，表明疏水性有机物是最主要的消毒副产物前体物，应当作为水处理工艺重点去除的有机物组分。各水文期源水有机物特性与消毒副产物生成潜能的关系变化不大，三卤甲烷生成潜能(STHMFP)与SUVA的线性相关度较高，卤乙酸生成潜能(SHAAFP)与SUVA的线性相关度一般。因此，可用水样SUVA值间接反映三卤甲烷生成潜能，以利于在实际生产中快速监控水中消毒副产物前体物的变化趋势     

Partition of iodine (¹²⁹I and ¹²⁷I) isotopes in soils and marine sediments

Natural organic matter, such as humic and fulvic acids and humin, plays a key role in determining the fate and mobility of radioiodine in soil and sediments. The radioisotope ¹²⁹I is continuously produced and released from nuclear fuel reprocessing plants, and as a biophilic element, its environmental mobility is strongly linked to organic matter.Due to its long half-life (15.7 million years), ¹²⁹I builds up in the environment and can be traced since the beginning of the nuclear era in reservoirs such as soils and marine sediments. Nevertheless, partition of the isotope between the different types of organic matter in soil and sediment is rarely explored. Here we present a sequential extraction of ¹²⁹I and ¹²⁷I chemical forms encountered in a Danish soil, a soil reference material (IAEA-375), an anoxic marine sediment from Southern Norway and an oxic sediment from the Barents Sea. The different forms of iodine are related to water soluble, exchangeable, carbonates, oxides as well as iodine bound to humic acid, fulvic acid and to humin and minerals. This is the first study to identify ¹²⁹I in humic and fulvic acid and humin. The results show that 30-56% of the total ¹²⁷I and 42-60% of the total ¹²⁹I are associated with organic matter in soil and sediment samples. At a soil/sediment pH below 5.0-5.5, ¹²⁷I and ¹²⁹I in the organic fraction associate primarily with the humic acid while at soil/sediment pH > 6 ¹²⁹I was mostly found to be bound to fulvic acid. Anoxic conditions seem to increase the mobility and availability of iodine compared to oxic, while subaerial conditions (soils) reduces the availability of water soluble fraction compared to subaqueous (marine) conditions.     

The molecular properties of humic substances isolated from a UK upland peat system: a temporal investigation.

The study concerns the possible changes in the molecular characteristics of humic materials isolated from the same source as a function of time. A great deal of data has been reported concerning the contrast in molecular characteristics of humic substances isolated from different environments. This has primarily been an attempt to identify source-specific molecular characteristics. However, data presented in this paper suggests that humic substances isolated from a single catchment have significant changes in molecular characteristics over time. Two naturally occurring peat pools (X and Y) situated upon a small organic catchment on Great Dun Fell, Cumbria, UK were sampled monthly between November 1994 and November 1996. Dissolved organic matter (DOM) from the pool water samples was fractionated using macroporous nonionic resins (XAD8 and 4), and the humic, fulvic and hydrophilic acids were collected. These fractions were analysed for elemental composition (C, H and N), weight average molecular weight, functional group content and adsorption (340 nm) of a 1 g l(-1) solution measured in a 1-cm spectrophotometer cell. The molecular characteristics were compared to those of natural DOM described by Scott et al. (1998). Scott et al. reported that drought conditions and seasonal climatic changes could have appreciable effects upon molecular characteristics of natural DOM. Results showed that the atomic H/C ratio of the humic substances increased immediately after strong drought conditions experienced in the summer of 1995. This change was temporary with atomic H/C ratio decreasing gradually over the following months. A similar decrease was observed in the carboxyl group content of the isolated compounds. The data set suggested that atomic H/C ratio in the fulvic and hydrophilic fractions exhibited seasonal characteristics of higher ratios during the late summer/early autumn months. This was not observed in the humic fraction. Humic acids exhibited a seasonal pattern of higher weight average molecular weight during the summer months. These trends were explained in terms of summer production of DOM in the catchment soils, their sequestering in the soil due to limited soil water movement during the summer months and their relative ease of dissolution when rainfall and soil water movement increased during the late summer/early autumn period. The results were found to support seasonal and long-term patterns observed in natural DOM as reported by Scott et al. (1998).     

Remobilisation of 109Cd, 65Zn and 54Mn from freshwater-labelled river sediments when mixed with seawater

A major fraction of trace metals transported by rivers is associated with sediments, especially during flooding, when erosion and resuspension increase sediment loads. Upon contact with seawater in estuaries, changes in ionic strength and pH may remobilise trace metals from sediment surfaces into more bioavailable forms. The objective of the present work was to investigate time-dependent interactions between trace metals and freshwater sediments and their potential remobilisation upon contact with seawater. Two river sediments (one organic and one inorganic) were labelled with 109Cd2+, 65Zn2+ and 54Mn2+ radioactive tracers for periods up to 6 months. Sorption of tracers occurred rapidly (> or = 80% sorption, < 1 h), followed by a slower approach to pseudoequilibrium. Kd(6 months) were estimated as 460, 480 and 2200 ml/g (inorganic sediment) compared to 5300, 4000 and 1200 ml/g (organic sediment) for 109Cd, 65Zn and 54Mn, respectively. Remobilisation of tracers from labelled sediments was studied using sequential extractions. Artificial seawater extracts simulated an estuarine environment. Subsequent extractions provided information about more strongly sorbed tracer fractions within sediments. Remobilisation of 109Cd by seawater was significant (> 65%) and least affected by sediment type or freshwater labelling time. Redistribution of Cd to strongly bound phases was minimal (4% and 1% of 109Cd in strongly oxidisable fractions). Seawater remobilisation of 65Zn was significantly greater from the organic sediment (54%) compared to the inorganic sediment (8%), where a large fraction of 65Zn (14%) became irreversibly bound. Similarly, more 54Mn was remobilised by seawater from the organic sediment than the inorganic sediment (66% and 3% remobilised, respectively), i.e., 54Mn became more strongly bound in the inorganic sediment. A simple three-box model, based on first-order differential equations, was used to describe the interaction between tracers in spiked freshwater and two operationally defined sediment fractions ("seawater exchangeable" and "seawater unexchangeable") up to 6 months of freshwater labelling. Model simulations were fitted to experiment data and apparent rate constants were calculated using numerical optimisation methods. Sorption ratios from modelling data (i.e., k1/k2) were greater for organic compared to inorganic sediments, while fixation ratios were higher in inorganic sediments. In conclusion, trace metals can be remobilised from sediments on contact with seawater in estuaries. High organic content in sediments increased initial sorption of tracers but inhibited redistribution to more strongly bound fractions over time, resulting in greater remobilisation of tracers when in contact with seawater.     

Identification of nonvolatile neutral organic compounds in tap water

Nonvolatile neutral organic compounds in tap water were examined by high-pressure liquid chromatography, infrared spectrometry, ¹H- and ¹³C-FT-NMR, gel permeation chromatography, elementary analysis, and field desorption mass spectrometry. Neutral organic compounds in 10 m³ of tap water were continuously extracted by the Amberlite XAD-2 resin column, and separated into four fractions by silica-gel column chromatography. Removal of volatile compounds in fraction 3 including polar oxygenated compounds was carried out with microdistillation column under high vacuum by using a diffusion pump. Nonvolatile organic compounds isolated from tap water were identified as poly(vinyl acetate) derivatives with molecular weights ranging from 300 to 1300.     

Vertical distribution and characteristics of soil humic substances affecting radionuclide distribution

The humic substances extracted from different soil depths are separated into humic (HA) and fulvic (FA) acids, and characterized for their chemical composition, proton exchange capacity, spectroscopic characteristics and binding properties to the europium ion. The chemical and spectroscopic results show that FA compared to HA has a relatively high O/C ratio, high acidic functional group contents and low aromatic contents. The synchronous fluorescence spectroscopic results show that the stability constant (K) of the soil humic substances with Eu(III) ion tends to increase as the soil depth becomes deeper, and HA has a slightly stronger binding ability than FA. The measured total site concentrations (C(L)) reveal that Eu(III) ion is loaded onto HA by 62-77% of the total acid sites, but FA is only approximately 50% covered by Eu(III) ion. Information could be useful in understanding the migration of radionuclides in soil layer.     

神农架大九湖泥炭地孔隙水溶解有机碳特征及其影响因素

溶解性有机碳（Dissolved Organic Carbon, DOC）是泥炭地碳循环的重要组成部分。以往的研究大多集中在北方泥炭地，而对亚热带季风区泥炭地DOC动力学的认识十分有限。利用紫外可见光光谱（UV-Vis）和三维荧光光谱结合平行因子分析法（EEM-PARAFAC）研究了神农架大九湖泥炭地孔隙水的DOC浓度与化学组成及其影响因素。EEM-PARAFAC的结果表明：大九湖泥炭地孔隙水DOC主要包含3种类腐殖质组分。紫外可见光和荧光指标表明，泥炭孔隙水DOC表观分子较小，而芳香度较高。深度剖面数据表明，泥炭孔隙水DOC浓度随深度降低，0~10 cm深度浓度最高为24.16 mg/L，150~160 cm深度浓度最低为9.72 mg/L，并且深层DOC以微生物代谢产生的新鲜有机物为主，具有较低的腐殖化度。此外，氧化还原电位（ORP）与DOC浓度及化学性质关系密切。以上结果表明，在亚热带泥炭地中，微生物来源或受微生物改造的有机物是泥炭孔隙水DOC的重要组成部分；垂向输送或选择性保存是影响该亚热带亚高山泥炭地DOC动力学的重要因素。     

Basic characterization of reference NOM from Central Europe — Similarities and differences

The FA and HA fractions represent 20 to 50% of the DOC of the original samples, depending on the origin, and serve as reference materials. The original aqueous samples and the aqueous solutions of the reference materials were characterized with methods suited for measuring samples at natural concentrations. The DOC normalized values of the spectral absorbances (λ = 254 nm; λ = 436 nm) in the original water samples were highest for the brown water and brown coal water and lowest for the secondary effluents. The FA fractions were similar in the UV-absorbance with the exception of the low-absorbing groundwater FA, reflecting a low density of double bonds. The DOC-normalized proton capacity of the FA fractions (10 to 20 μmol/mg) was highest for the brown coal, brown water, and soil-derived samples and again lowest for the groundwater FA. The high values are due to a higher contribution of the weak acids of phenolic type. Specific data for copper complexation capacity (0.5 to 2.5 μmol/mg) went parallel to the proton capacity. The characterization of the FAs by gel chromatography with organic carbon detection revealed three major fractions. The refractory part at short retention time dominated in the brown water and soil-derived samples, whereas the fractions for the lower molecular mass acids at long retention times were dominant in the secondary effluent and the brown coal isolate. Comparison with UV-detected chromatograms revealed a strong decrease in the specific absorbance of the secondary effluent. Up to 3% of the total mass of the FAs could be identified as hydrolyzable amino acids with the highest yield in the sample from secondary effluent and the lowest one in the groundwater sample. The nitrogen content was always higher in the FAs compared to the HAs of the same origin. The application of gel chromatography fluorescence and fluorescence decay time distribution analysis turned out to be a useful tool to differentiate between the different fractions of NOM, the isolates obtained by different methods (e.g., XAD-8, membrane separation) and the fractions of the samples from different origin and age. This is of special value, for the information can also be obtained for samples with natural NOM concentrations, even though further investigations required for full understanding of the data. This work is part of a multi-disciplinary research program (ROSIG: Refraktäre Organische Säuren in Gewässern), funded by the German Research Association (DFG).     

Simultaneous biological removal of endosulfan (alpha+beta) and nitrates from drinking waters using wheat straw as substrate

Nitrate and endosulfan (alpha+beta) removal was studied in an upflow biological denitrification reactor packed with wheat straw as carbon source and support particles for microorganisms. While almost complete nitrate elimination and between 65% and 70% endosulfan (alpha+beta) elimination occurred when the temperature was higher than 20 degrees C; below that value, nitrate removal efficiency decreased to about 10%. Nitrate, dissolved organic carbon (DOC), and endosulfan (alpha+beta) removal efficiencies decreased considerably at 1500 microg/l endosulfan concentration in the batch experiments. Although a high removal efficiency was observed for endosulfan (alpha+beta) and nitrate in the biological denitrification continuous reactor, the effluent water could not be used for drinking purpose because of the unacceptable levels of endosulfan (alpha+beta), colour and dissolved organic content. During the continuous study, 23.4% of the initial weight of wheat straw was lost and 24 g was consumed per gram of nitrogen removed. The results of the continuous study showed that 21.3% of the endosulfan removal was achieved by adsorption onto the wheat straw and 68.2% of the endosulfan removal occurred by biological activity and the remaining portion was detected in the effluent water.     

Basic characterization of Norwegian NOM samples — Similarities and differences

NOM (natural organic matter) samples, isolated by reverse osmosis (RO), and nine NOM samples, concentrated by low-pressure, low-temperature evaporation (EVA) from various origin in Norway, were characterized by different methods. The methods included elemental content of the freeze-dried samples (C, H, N, and O), elemental content of the redissolved samples (DOC, Na, Ca, Cu, Fe, and Mn), specific spectral absorbance at λ = 254 nm (A(254 nm)/DOC) and at λ = 436 nm (A(436 nm)/DOC), UV/Vis-spectra, specific fluorescence (excitation and emission spectra), proton capacity, Cu-complexation capacity, and content of hydrolysable amino acids and carbohydrates. In addition, chromatographic characterization by gel chromatography and reversed-phase chromatography was done. Studies on adsorption and flocculation abilities and the formation of trihalomethanes (THM) and organic halogens adsorbable on activated carbon (AOX) upon chlorination were also investigated. Comparison of the results showed that the samples were different according to the origin of the sample, isolation procedure, and time of sampling. The differences are not the same for all parameters used. Standardized procedures have to be applied to redissolve the organic material in water in order to compare data. For the samples investigated, it was shown that parameters like elemental analysis (H/C ratio), the specific spectral absorption in the UV range, proton capacity, complexation capacity and anionic particle charge, amount of hydrolysable amino acids and carbohydrates, adsorption behaviour on activated carbon, and the THM-FP are sensitive parameters to show differences concerning origin and isolation procedure.     

Role of the fungal mycelium in the retention of radiocaesium in forest soils

The aim of this work was to study possible binding of 137Cs to various organic components in the soil and fungi, by using various sequential extraction procedures. The retention and binding of 137Cs has been studied in two horizons Of/Oh and Ah/B of a Ukrainian forest soil. The exchangeable fractions 137Cs from soil (sum of H2O and 1 M NH4OAc fraction) were found to be 12% in the organic-rich layer (range 11-14%) and 23% in the organic-poor (range 20-29%). The hydrolysis with 10% H2SO4 resulted in an additional release of 30% of 137Cs from the organic-rich soil (range 30-35%) and 38% from the organic-poor soil horizon (range 27-53%). Extraction with 30% H2O2 released 11 and 15% of the 137Cs activity from organic-rich and organic-poor soil horizons. The corresponding values for treatment with 98.8% NaOCl were about 27% in both types of soil. About 11% of the total 137Cs activity was found in the humic acid fraction, about 5% in the fulvic fraction and 46% in the residue fraction. Relatively high level of 137Cs activity in soil (ca. 50%) was thus still left unsolved in the residue fraction. About 29% of 137Cs activity concentration in fungal mycelia was found as water soluble with a range of 11 to 41%. Additionally 24% of the 137Cs activity from mycelia was released by 1 M ammonium acetate extraction. Together, water and 1 M ammonium acetate extraction released about 53% of the total 137Cs activity in the mycelia. In fruit bodies of mycorrhizal fungi, 68% of the total 137Cs inventory was found to be water soluble at room temperature and 93% at 80 degrees C.     

三江源高寒草甸下溪流溶解性有机碳的季节性输移特征

溶解性有机碳（DOC）在生态系统中起着重要作用，但河流DOC输移动态及其对气候变化和多年冻土退化的响应还不清楚。对青藏高原三江源地区高寒草甸下8条小流域河流于2016年8月至2017年7月进行逐月采集水样，同步测定流量，在室内对DOC浓度进行分析，研究河流DOC浓度和输移通量的逐月变化规律以及对降雨和温度逐月变化的响应。结果表明：（1）DOC的年平均浓度介于4.05±1.20~6.55±2.86 mg·L-1之间，均值为5.30 mg·L-1；DOC平均浓度与流域内高寒沼泽草甸（ASM）覆盖面积比例呈显著线性负相关，而与高寒草甸（AM）呈显著线性正相关；此外，有多年冻土发育的流域内河流平均DOC浓度明显高于无多年冻土发育的流域。（2）DOC浓度随季节性气温的变化呈现较大的变异性，在-8~2℃气温回升的过程中，DOC平均浓度随气温的升高呈急剧上升的趋势，在随后2~13℃气温继续升高到最高的过程中，DOC平均浓度又急速降低，而在之后13~-8℃气温下降的过程中，DOC平均浓度呈一个缓慢降低的趋势，并在12月达到最低。（3）DOC平均输移通量也显示出较大的季节差异，其范围为0.006±0.000 5~3.01±0.74 kg·km-2·d-1，均值为1.12±0.81 kg·km-2·d-1；DOC输移通量与流域内平均径流量显著线性正相关，DOC的输移主要集中在春季融雪期和夏季丰雨期。气候变暖会导致多年冻土活动层厚度增加，因此，温度增加导致DOC输移增加的结果提示，气候变暖可能会增加青藏高原高寒草甸区河流对有机碳输移和释放。     

Characteristics of soil organic matter (SOM) extracted using base with subsequent pH lowering and sequential pH extraction

Humic substances from eight soils of varying properties were extracted by two different methods: (1) the traditional NaOH-extraction with subsequent acidification to different pH (approximately 1 to approximately 12) and sequential extractions using 0.01 M NaNO(3) at incremental pH (approximately 1 to approximately 11). Cumulative organic matter (OM) in the sequential extractions showed properties that were consistent with NaOH-extracted OM. The release of Al and Fe in the sequential extractions was closely related with the release of organic carbon (OC). The ratio of OC associated with humic acid (HA) and fulvic acid (FA) (the HA:FA ratio) varied widely among the soils indicating heterogeneity in their OM composition. However, a significant correlation between this HA:FA ratio and the NaOH extractable %OC content of the soils is indicative of the possible relationship between them. Between pH 5 and 7, which is a typical soil solution pH, a significant amount of HA-associated OC was soluble. In modeling metal speciation in soil solutions, it has been assumed that all dissolved organic carbon (DOC) that is active toward metal binding is associated with FA. The results of this study indicate that the validity of these assumptions based on model sensitivity alone is questionable.     

Detection of tritium sorption on four soil materials

In order to measure groundwater age and design nuclear waste disposal sites, it is important to understand the sorption behavior of tritium on soils. In this study, batch tests were carried out using four soils from China: silty clays from An County and Jiangyou County in Sichuan Province, both of which could be considered candidate sites for Very Low Level Waste disposal; silty sand from Beijing; and loess from Yuci County in Shanxi Province, a typical Chinese loess region. The experimental results indicated that in these soil media, the distribution coefficient of tritium is slightly influenced by adsorption time, water/solid ratio, initial tritium specific activity, pH, and the content of humic and fulvic acids. The average distribution coefficient from all of these influencing factors was about 0.1-0.2 mL/g for the four types of soil samples. This relatively modest sorption of tritium in soils needs to be considered in fate and transport studies of tritium in the environment.     

The effect of fire on soil organic matter--a review

The extent of the soil organic carbon pool doubles that present in the atmosphere and is about two to three times greater than that accumulated in living organisms in all Earth's terrestrial ecosystems. In such a scenario, one of the several ecological and environmental impacts of fires is that biomass burning is a significant source of greenhouse gases responsible for global warming. Nevertheless, the oxidation of biomass is usually incomplete and a range of pyrolysis compounds and particulate organic matter (OM) in aerosols are produced simultaneously to the thermal modification of pre-existing C forms in soil. These changes lead to the evolution of the OM to "pyromorphic humus", composed by rearranged macromolecular substances of weak colloidal properties and an enhanced resistance against chemical and biological degradation. Hence the occurrence of fires in both undisturbed and agricultural ecosystems may produce long-lasting effects on soils' OM composition and dynamics. Due to the large extent of the C pool in soils, small deviations in the different C forms may also have a significant effect in the global C balance and consequently on climate change. This paper reviews the effect of forest fires on the quantity and quality of soils' OM. It is focused mainly on the most stable pool of soil C; i.e., that having a large residence time, composed of free lipids, colloidal fractions, including humic acids (HA) and fulvic acids (FA), and other resilient forms. The main transformations exerted by fire on soil humus include the accumulation of new particulate C forms highly resistant to oxidation and biological degradation including the so-called "black carbon" (BC). Controversial environmental implications of such processes, specifically in the stabilisation of C in soil and their bearing on the global C cycle are discussed.     

Soil and soil water studies at the HUMEX site

Changes to natural organic compounds by acid deposition and subsequent effects on Al mobilization are not well understood. The HUMEX catchment-scale acidification experiment in western Norway offers a unique possibility for an integrated assessment of these interactions. In this report, the soil and soil water chemical data from the HUMEX site, from before and after the onset of experimental acidification, are used to characterize the catchment. Changes in soil water chemistry are discussed and controls on dissolved organic carbon are addressed in relation to Al mobilization. Decreases in the concentration of dissolved organic carbon (DOC) and organic Al fractions were found in soil water after the treatment started. These changes were related to an increase in soil water sulphate concentrations. The sulphate levels showed a significant increase (on a 95% level) in four of ten soil horizons while nitrate remained nearly unchanged. In organic soils, where the dissolved organic carbon content was high, the major control for monomeric aluminum concentration appeared to be the amount of exchangeable aluminum in the soil. In mineral soils, the gibbsite dissolution may govern inorganic Al concentrations in soil water, though substantial undersaturation was found when DOC was high.     

Effect of shelterbelt on two kinds of soils on the transformation of organic matter

The changes of the total nitrogen, average yearly concentration of ammonia, nitrate ions, urease activity, total amount of amino acids in humic acids (HA) and the structure of humic acids were monitored in relation to the effect of shelterbelt as biogeochemical barrier located on a mineral and mineral-organic soil. The transformation of different forms of nitrogen in the soil under shelterbelt was strongly connected with the humification process and the molecular structure of humic acids.