Toluene sorption behavior on soil organic matter and its composition using three typical soils in China

The effect of soil organic matter (SOM) content and composition on sorption behavior of toluene for fluvo-aquic, red and black soils in China was investigated in batch experiments. Tested SOM was fractionated into two primary sorptive domains (‘soft’ and ‘hard’) to explain the dependence of sorption behavior on SOM composition. All the tested soils exhibited similar sorption kinetics and nonlinear sorption isotherms. Soils with high SOM content possessed a high sorptive capacity. Clay minerals also contributed to the sorptive capacity, especially for fluvo-aquic and red soils with low SOM content. In comparison, after removing most ‘soft’ SOM fraction from soils through hydrogen peroxide treatment, the residual ‘hard’ SOM fraction of three soil samples exhibited a slower sorption rate and a less sorption capacity compared to the untreated soil samples. The nonlinear degree of sorption was positively correlated with the content of ‘hard’ SOM for all soil samples. This is explained by the combined effect of SOM content and the composition on toluene sorption rates, sorption capacity and nonlinear degree of sorption of three typical soils in China.     

Influence of the sample history and the moisture status on the thermal behavior of soil organic matter

Recent studies indicate that glassiness represents a characteristic feature of soil organic matter (SOM). It is however unknown, to which extent the transitions detected in humic substances and whole soil samples correspond to common models of synthetic polymers providing the theoretical basis for explaining their glass transition characteristics. Physical aging associated with structural relaxation of amorphous substances below their glass temperature is one fundamental basis for the glass transition behavior of synthetic polymers. According to the results of this study, aging processes also occur in SOM. In whole soil samples, this process can be observed by the shift of glass transition-like step transitions to higher temperatures within the time scale of years. Not only the structural relaxation of the macromolecular organic substances, but also interactions with water molecules, which may exhibit both plasticizing and antiplasticizing properties, influence the aging process of SOM. Especially under moistening or drying conditions, a differentiation between the effects of water and of alterations of the SOM structure in the course of time on the rigidity of the macromolecular network is difficult.     

Models of natural organic matter and interactions with organic contaminants

Adsorption of organic contaminants onto soils, sediments and other particulates has the potential to be a major controlling factor in their bioavailability, fate and behavior in the environment. Models for estimating the amount and stability of sorbed organic contaminants based on the fraction of organic carbon in a soil or sediment can oversimplify the process of sorption in the environment. In order to help understand sorption of organic contaminants in soils and sediments, we modeled various components of natural organic matter (NOM) that are possible substrates for sorption. These substrates include soot particles, lignin, humic and fulvic acids. The molecular scale interactions of selected aromatic hydrocarbons with different substrates were also simulated. Results of the simulations include the 3-D structures of the NOM components, changes in structure with protonation state and solvation and the sorption energy between PAH and substrate. This last parameter is an indicator of the amount of contaminant that will sorb and the energy required to free the contaminant from the substrate. Although the simulation results presented in this paper represent a first-order examination of NOM and contaminant interactions, the findings highlight a number of essential features that should be included in future molecular models of NOM and contaminant sorption.     

Influence of humic acid on the sorption of pentachlorophenol by aged sediment amended with rice-straw biochar

Black carbon (BC), especially biochar, is a potential material for the remediation of hydrophobic organic compounds (HOCs) pollution in soils and sediments. Recent studies have reported that the adsorption capability of BC in sediment was reduced as time increased. It was hypothesised that this behaviour was caused by the presence of natural organic matter (NOM), but few systematic studies have examined the influence of NOM on the sorption ability of BC in sediment (S). The results of this study revealed that a humic acid (HA) coating changed the surface properties, blocked the micropores, and decreased the sorption capacity of rice-straw biochar (RBC) towards pentachlorophenol. With increasing aging time, the reductions in the sorption capacity of the S + RBC and S + HA + RBC systems occurred more rapidly than in the S + HA/RBC (HA-coated RBC) system, and the sorption curves became closer to that of the S + HA/RBC system, indicating that HA may play a primary role in reducing the sorption capacity of RBC in the sediment. With higher HA contents, the sorption capacity of the complex sediments was lower and decreased more rapidly.     

有机组分土-水分配系数的确定(英文)

有机组分的土水分配系数(Kd)是描述有机组分在地下系统中吸附特征的重要参数。同时,它也是物质运移模拟和环境评价中的主要参数之一。影响Kd的因素可概括为三个方面:土壤性质、有机组分本身特征及水相的物理化学性质。一般而言,对于非极性和弱极性有机组分,土壤中的有机质含量(foc )是影响Kd的最主要因素。但是,对于极性有机组分(POCs), 特别是在土壤有机质含量较低的情况下,土壤中矿物的种类和含量、水化学组分特征(pH、离子力等)经常在吸附过程中起重要作用。实验室内测定Kd的方法包括批实验和柱实验方法。批实验法适用于研究Kd较高情况下的吸附。在Kd较低的情况下,如低有机质土壤对极性有机污染物的吸附,土柱色谱法(SCC)是更适宜的选择。另外,可用土柱色谱法快速了解各种因素对吸附过程的影响,并获取详细的吸附和解吸信息。应用土柱色谱法时应当注意非平衡吸附和可能的柱堵塞问题。很多文献中提到结合柱实验和已有的吸附数据来预测土壤有机碳标准化的分配系数Koc(=Kd/foc)。但是,如果没有考虑吸附中特定的作用过程(如矿物吸附),对极性有机组分Koc的预测将会产生很大的误差。在环境评价中,将从一种土壤测定的Koc 应用到不同性质的土壤中,可能会导致错误的认识。在进行室内实验时,应把标准土(如Eurosoi     

Comparison of the structural,spectroscopic and phenanthrene binding characteristics of humic acids from soils and lake sediments

The structural, spectroscopic and phenanthrene binding characteristics were compared for humic acids (HA) extracted from two different sources: eight soils and six lake sediments. The elemental analysis revealed that HA from sediments had higher H/C, N/C, and (N + O)/C ratios compared to HA from soils, reflecting a lower degree of humification and more autochthonous organic input upon the formation of the HA for lake sediments versus soil environments. HA from soils exhibited a higher content of aromatic carbon structures than the sediment HA based on ¹³C NMR results. The source of HA was easily distinguished by comparing the synchronous fluorescence spectra of each HA group. The presence of a protein like fluorescence was prominent for the HA from sediment while it was minor for the HA from soil. Irrespective of the HA source, however, humification index (HIX) exhibited a common positive correlation with the aromatic content, and a negative correlation with O-alkyl carbon structures of the HA. The correlations were consistent with the general structural trends of humification processes, suggesting that HIX may serve as a source independent predictor to describe the structural information and humification degree of terrigenous HA. Aromatic carbon structures did contribute to enhancing the phenanthrene binding for both sources of HA. However, the primary structures associated with non-ideal phenanthrene binding (i.e., non-linear sorption isotherm) appear to differ by the HA source because the opposed correlations were obtained between aromaticity and the isotherm linearity for the two HA groups. Our results suggest that the HA structural function associated with specific non-linear sorption for hydrophobic organic contaminants (HOCs) may be more strongly governed by the HA source than by the apparent physico-chemical properties.     

Mechanistic roles of soil humus and minerals in the sorption of nonionic organic compounds from aqueous and organic solutions

Mechanistic roles of soil humus and soil minerals and their contributions to soil sorption of nonionic organic compounds from aqueous and organic solutions are illustrated. Parathion and lindane are used as model solutes on two soils that differ greatly in their humic and mineral contents. In aqueous systems, observed sorptive characteristics suggest that solute partitioning into the soil-humic phase is the primary mechanism of soil uptake. By contrast, data obtained from organic solutions on dehydrated soil partitioning into humic phase and adsorption by soil minerals is influenced by the soil-moisture content and by the solvent medium from which the solute is sorbed.     

Contribution of lipids to the nonlinear sorption of polycyclic aromatic hydrocarbons to soil organic matter

The sorption isotherms of benzene, naphthalene, fluorene and phenanthrene for a suite of whole and lipid-extracted soils are presented. The sorption of benzene to two different peats displays linear characteristics which are consistent with the partitioning model of sorption. The sorption of the PAHs to three different mineral soils show marked nonlinear character. The nonlinear sorptive character of the soil organic matter can be described by site specific sorption occurring within the soil organic matrix. Removal of the lipids via Soxhlet extraction increases the nonlinear character of the sorption isotherms as well as doubles the sorptive capacity of the mineral soils for the PAHs studied. This indicates that the lipids naturally present in the soil strongly compete for hydrophobic sorption sites present in the soil organic matter matrix.     

煤中干酪根的成熟度与菲的吸附行为间的关系

将云南先锋褐煤采用热模拟的实验方法制得一组成熟度不同的煤,并将煤中的干酪根用于对菲的吸附研究.结果表明:随着干酪根成熟度的增加,有机质结构变得紧密、刚硬,还原性和芳香性增强.不同成熟度干酪根的内部结构和性质与菲的吸附行为间存在一定的关系.随着干酪根内部结构的刚性和芳香性的增强,吸附等温线的非线性逐渐增强.对于成熟度相对较低的干酪根,随着成熟度的增加,吸附容量逐渐增大,而对于成熟度相对较高的干酪根,随着成熟度的增加,吸附容量却减小.     

Influence of HCl/HF treatment on organic matter in aquifer sediments: A Rock-Eval pyrolysis study

Rock–Eval pyrolysis is increasingly used for the routine characterization of natural organic matter in soils and sediments. In this work the bulk composition of sedimentary organic matter (SOM) in sandy aquifer sediments is studied, as well as purified samples (isolation of SOM) by HCl/HF treatment. This treatment is necessary to avoid detection limit problems for samples with low SOM contents, but the results presented here indicate that this treatment influences the organic geochemistry of the aquifer sediment samples. The FID and CO₂/CO pyrograms show a shift of 10–40 °C of the major peak to a lower temperature. Organic matter alteration or removal of components containing O-bearing groups may explain this. It is also suggested that destruction of the mineral matrix may lead to the reduced retention of the material. For the change of the CO₂/CO pyrograms of the RC fraction only organic matter alteration seems to be likely. Concentrated organic matter samples may also accelerate the release of exothermic energy and influence the pyrograms. Results indicate that the organic matter concentration in the sample influences the measured total organic matter (TOM) content and the T_max of the FID pyrogram, while the sample loading (absolute organic matter amount) up to 80 mg in the Rock–Eval apparatus does not. The FID pyrograms can be deconvoluted into four subpeaks, which allows comparison of samples at various depths. Rock–Eval pyrolysis may only be routinely applied to characterize SOM in aquifer sediments when such systematic and analytical phenomena are taken into account.     

Sorption of monoaromatic compounds to heated and unheated coals,humic acid,and biochar: Implication for using combustion method to quantify sorption contribution of carbonaceous geosorbents in soil

Batch sorption isotherms of two nonpolar compounds (1,3-dichlorobenzene and 1,3,5-trichlorobenzene) and two polar compounds (1,3-dinitrobenzene and 1,3,5-trinitrobenzene) to heated (at 375 °C for 24 h) and unheated coals (lignite and anthracite) were compared with those to a soil humic acid and a maize stalk derived biochar. For all test compounds, unheated lignite and anthracite exhibited much stronger sorption than humic substances (the organic carbon-normalized distribution coefficient was up to 2–3 orders of magnitude larger), but lower sorption than biochar. This sorption trend is consistent with the degree of sorbent condensation (biochar > coal > humic acid). The results indicate that sorption of the test sorbates (regardless of the difference in polarity) to soils would be dominated by carbonaceous geosorbents. Notably, the organic carbon contents of the coals were pronouncedly lowered by the heat treatment, from 47.4% to 7.3% for lignite, and from 80.1% to 58.1% for anthracite. Moreover, the heat treatment markedly decreased organic carbon-normalized distribution coefficient to coals (up to one order of magnitude), attributable to the decreased hydrophobicity of sorbents due to increased O-containing groups from oxidation. An important implication is that heat treatment, which is commonly used to quantify the content of carbonaceous geosorbents in soil and sediment, may cause significant underestimation of sorption contribution of carbonaceous geosorbents due to the combined effect of reduced organic carbon content and decreased hydrophobicity of less graphitized carbonaceous geosorbents (coals). This was illustrated using a widely adopted dual-component model that combines linear partition to humic substances (represented by humic acid) and nonlinear adsorption on condensed geosorbents (represented by biochar and coal).     

Depositional environments of the Senonian chert, phosphorite and oil shale sequence in Israel as deduced from their organic matter composition

In the Upper Cretaceous sequence of the Negev (southern Israel) the organic matter in phosphorites and cherts differs from that associated with oil shales in its higher content of humic substances and lower kerogen content, and in its more intensive microbial alteration. The n-alkane distribution pattern of the oil shales, phosphorites and cherts indicates that marine biota, probably algae, are the main organic precursors of their organic matter. In some of the oil shales, however, some contribution of terrestrial organic matter is also evident. Similar high phytane/pristane ratios indicate that the organic matter in the oil shales as well as in the phosphorites and cherts accumulated under reducing conditions. The main differences in the organic matter composition are attributed to early diagenetic processes rather than to different biotic precursors or to late modifications due to temperature-induced maturation. The depositional model suggested for the sequence involves upwelling conditions at the boundary between the deep Tethys and the shallow shelf, which induced high organic productivity deep into the inner shelf. Bottom water circulation enabled intensive microbial alteration of the organic matter, followed by a winnowing process leading to phosphorite formation. Since humification is considered an oxygen-consuming reaction, these processes favoured the formation of oxygen-enriched humic substances and the oxidation of humic substances already present. These humic substances are relatively resistant to further alteration and their conversion into kerogen is thus retarded. Subsequently, syndepositional tectonic activity resulted in the introduction of less saline water, restriction of bottom-water circulation and the establishment of a density stratification in the water body. Consequently, aeration of the bottom layer and the sediments was inhibited, microbial alteration was reduced and later winnowing processes were prevented. Such conditions favoured the formation of kerogen directly, rather than through humic substances, and also favoured the preservation of most of the organic matter in the form of oil shale deposits instead of phosphorites.     

Effects of water chemistry and concentrations of dissolved organic matter on its fluorescence characteristics and molecular conformation

Previous studies showed that water chemistry and concentrations of dissolved organic matter (DOM) could affect its molecular conformation and binding characteristics with hydrophobic organic contaminants (HOCs). However, the conformational change of DOM resultant from water chemistry and concentrations of DOM was not extensively investigated; therefore, the contradictory reports regarding the binding property with HOCs were available in literature. In this study, the effects of ionic strength, pH and DOM concentrations on the fluorescence properties of two humic acids (HA), namely Fluka HA and Amherst HA, were investigated by three-dimensional excitation-emission matrix fluorescence spectroscopy (3DEEM) and steady-state fluorescence polarization (FP) techniques. The results not only corroborated previous observations obtained by other investigators, but revealed some new information about the fluorescence properties and molecular conformation of the humic acids under different water chemistry and DOM concentration conditions, which could shed light on its binding mechanisms and binding properties with HOCs.     

Fate and Transport of Hydrophobic Organic Chemicals in the Lower Passaic River: Insights from 2,3,7,8-Tetrachlorodibenzo-p-Dioxin

The fate and transport of hydrophobic organic chemicals (HOCs) is particularly complex in estuaries because of bidirectional longitudinal currents, density stratification, the tendency to trap sediments, and significant dilution in the downstream bay or ocean. Investigations of HOCs in estuaries are further complicated because HOCs typically enter from multiple sources. The distribution of contaminants in estuarine sediment beds reflect a time integration of a complex balance of time- and space-variable fate and transport processes and loading history. A unique opportunity to study HOC fate and transport exists in the Lower Passaic River (LPR), where a pesticide manufacturer was the dominant source of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) to the estuary and the distribution of this “tracer of opportunity” provides insights about fate and transport processes in estuarine systems. This paper presents observed sediment 2,3,7,8-TCDD patterns within the LPR and the adjacent Newark Bay, and interprets them in terms of fate and transport processes that likely distributed the contaminant from its dominant source, drawing upon other physical datasets as needed. Major observations include that estuarine transport processes have distributed 2,3,7,8-TCDD approximately 18 km upstream of the source and downstream across Newark Bay, and that, generally, HOC trapping processes within the LPR have been highly effective, particularly near the 2,3,7,8-TCDD source and in downstream areas. The present LPR surface sediment 2,3,7,8-TCDD distribution indicates spatially variable recovery, which appears broadly driven by historical net sedimentation patterns, though the dominant processes may be shifting as the system continues to evolve.     

Mössbauer spectroscopic studies of iron in organic material from natural sedimentary environments

⁵⁷Fe Mössbauer spectra have been obtained from samples of humic acid, fulvic acid and kerogen and from the organic material extracted from bituminous chalk with benzene-methanol. The spectra indicate that iron occurs in a trivalent form in the silicate residue of the humic acid fraction, as hydrated ferrous ions associated with the fulvic acid fraction, as pyrite in kerogen and in a form not detectable by Mössbauer spectroscopy in the benzene-methanol extract.     

红壤中矿物表面对腐殖质吸附萘的影响

矿物表面可改变土壤腐殖质对疏水性有机污染物的结合能力。采用红壤和高岭石分别与胡敏酸结合制备得到的两种复合体对萘的吸附等温线非线性显著,其n=0.76或0.74,并且有机碳归一化吸附分配系数的实验值Koacds是采用Kow计算得出的理论值Koc的5倍以上,表明红壤、高岭石均对腐殖质吸附萘有强化作用,且红壤较之高岭石对腐殖质吸附萘的影响稍强些。主要原因是,红壤中除了高岭石外,还有与腐殖质结合力很强的铁氧化物,而且很可能是吸附态腐殖质组成结构形态发生了有利于对萘吸附的改变。     

Effect of pH on binding of pyrene to hydrophobic fractions of dissolved organic matter (DOM) isolated from lake water

In order to better understand the compositional and structural complexity of dissolved organic matter (DOM) macromolecules and provide mechanistic information on the binding of hydrophobic organic contaminants (HOCs) to DOM, we fractionated large amounts of lake water into three hydrophobic DOM-fractions. The variation of the partitioning coefficients (K _DOC) of pyrene at different pH levels was examined by florescence quenching titration. Results show that, relative to the more polar acidic DOM-fractions, the hydrophobic neutral fraction exhibits a higher sorption ability to pyrene. Generally, the sorption of pyrene to the three hydrophobic fractions is strongly pH-dependent. The K _DOC values of pyrene generally increase with decreasing pH levels, which is especially obvious in the sorption of pyrene to the fulvic acid fractions, suggesting that the binding is controlled by hydrophobic interactions. The mechanisms underlying the binding of pyrene to the hydrophobic fractions were also discussed. Our data are beneficial to further understanding the binding of HOCs to DOM and how it has been affected, which may result in more accurate predictions of K _DOC.     

Characteristics and distributions of humic acids in two soil profiles of the southwest China Karst area

Characteristics and distributions of humic acid (HA) and soil organic matter (SOM) in a yellow soil profile and a limestone soil profile of the southwest China Karst area were systematically investigated to reveal their evolutions in different soils of the study area. The results showed that characteristics and distribution of SOM along the two soil profiles were notably different. Total organic carbon (TOC) contents of soil samples decreased just slightly along the limestone soil profile but sharply along the yellow soil profile. TOCs of the limestone soils were significantly higher than those of the corresponding yellow soils, and C/N ratios of SOMs showed a similar variation trend to that of TOCs, indicating that SOM can be better conserved in the limestone soil than in the yellow soil. The soil humic acids were exhaustively extracted and further fractionated according to their apparent molecular weights using ultrafiltration techniques to explore underlying conservation mechanisms. The result showed that C/N ratios of HAs from different limestone soil layers were relatively stable and that large molecular HA fractions predominated the bulk HA of the top soil, indicating that HA in the limestone profile was protected while bio and chemical degradations were retarded. Combined with organic elements contents and mineral contents of two soils, we concluded that high calcium contents in limestone soils may play a key role in SOM conservation by forming complexation compounds with HAs or/and enclosing SOMs with hypergene CaCO₃ precipitation.     

The nature of metals—sediment—water interactions in freshwater bodies,with emphasis on the role of organic matter

A review with 227 references of the title subject is presented. It is divided into two main sections, viz., nature and properties of humic matter, and water—metal—sediment interactions.The first section deals with the essential properties of organic matter which occurs naturally in drainage sediments and waters. Discussion of the basic molecular structure of humic and fulvic acids is followed by some details of the chemical nature of functional groups within these structures which are important in metal-ion adsorption and complexing reactions which these materials can undergo. Information is also presented for colloidal and polyelectrolyte properties, complexation properties, and finally a summary discussion of metal-ion—humic-acid, metal-ion—fulvic-acid stability constants for both single ligand and mixed ligand systems completes the section.The second section comprises discussions of some specific aspects of interactions between metals, sediments and waters, including metal and organic speciation studies; sorption interactions between organic matter, clays and humic acids; chemical reaction between humic acids, heavy-metal minerals, clays and other silicate minerals; metal-ion adsorption—desorption studies, oxidation—reduction reactions between metal ions and humic acids; effects of sulphide ion on some of the above interactions and finally a summary of some relevant field geochemical dispersion studies.This second section describes both laboratory and field studies for each aspect.     

A laboratory batch study on arsenic sorption and desorption on guava orchard soils of Baruipur,West Bengal,India

Groundwater contaminated with arsenic (As), when extensively used for irrigation, causes potentially long term detrimental effects to surface soils. Such contamination can also directly affect human health when irrigated crops, such as rice, vegetable and fruits, are used for human consumption. Therefore, an understanding of the sorption and desorption behavior of As in surface soils is of high importance, because these processes regulate the bioavailability of As in the soil environment. In this study, we have collected soils from guava orchards of Baruipur, West Bengal, and characterized soil chemistry and batch sorption and desorption behavior in the laboratory. The sorption and desorption behavior of As in the soils were examined using the Langmuir and Freundlich sorption equation. Regression analysis of the soil chemical characteristics and sorption equation parameters were also performed. The results suggest that the sorption behavior of arsenate is highly dependent on soil characteristics, specifically organic carbon, clay and Al₂O₃ content of the soils. Whereas desorption behavior is critically influenced by the presence of high concentrations of amorphous and/or crystalline Fe₂O₃ in the soils. Retention of the significant portion of As in the soils (~ 84% of the total) suggests that As in the orchard soils may not be highly bioavailable to plants for uptake. However, more detailed studies will be required to ascertain the role of individual soil components on the As sorption and desorption processes.