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Permeable Reactive Barriers (PRBs) is a passive in-situ technology, which is based on the interception and remediation of a contaminant plume through installation of reactive material in an aquifer. Groundwater and contaminant travel times for a given location in the aquifer to or from the PRB are important parameters in PRB design and performance monitoring. The approach taken is two-dimensional in the horizontal plane and based on existing flow field solutions for a series of PRB configurations. Transport is considered purely advective with a possible retardation between groundwater and contamination. The aquifer is assumed homogeneous and a dimensionless travel time is introduced for arbitrary magnitudes of ambient groundwater flow, confined aquifer thickness and porosity as well as contaminant retardation. Travel time is expressed in a general form by an integral along curved stream lines in the physical plane and transformed into an integral along a straight stream line in the complex potential plane, where a simple numerical integration method is applied to generate maps of isochrones. Travel times are seen to be rather uniformly distributed within capture/release zones with minor effects of local low flow zones (stagnation points). Funnel-and-gate systems show a stronger lateral growth of capture/release zones at early times than other PRB types. Drain-andgate PRBs possess closed isochrones and are identified as transitional configurations between classic PRBs and pump-and-treat systems.

An overview is given of the interactions encountered between humic substances (HS), ecotoxicants, and living organisms in the context of environmental remediation. The most important interactions identified include: binding interactions affecting chemical speciation and bioavailability of contaminants; interfacial interactions altering physical speciation or interphase partitioning of ecotoxicants; abiotic-biotic redox interactions that influence metabolic pathways coupled to pollutants; and finally direct and indirect interactions coupled to various physiological functions of living organisms. Because humics are polyfunctional, they can operate as binding agents and detoxicants, sorbents and flushing agents, redox mediators of abiotic and biotic reactions, nutrient carriers, bioadaptogens, and growth-stimulators. It is shown that these functions possess significant utility in the remediation of contaminated environments and as such humic-based reactions pertinent to permeable reactive barriers, in situ flushing, bioremediation, and phytoremediation are examined in detail. Finally, this chapter introduces the novel concept of “designer humics” which are a special class of customized humics of the reduced structural heterogeneity and of the controlled size. They are developed and deployed to carry out one or more of the above in situ functions in an optimum manner and for the purpose of enhancing the efficacy of one or more remediation technologies. Designer humics possess specified reactive properties obtained by chemical modification and cross-linking of the humic backbone. This new class of reactive agents portend new opportunities for achieving enhanced remediation and for quantifying remediation performance. The latter is described in the context of the passive flux meter technology developed for direct measuring fluxes of contaminants and biomass.

Preface. Introduction. Contributors. Part 1. Remedial properties of humic substances: general considerations and problems in addressing needs of environmental remediation. 1. Remediation chemistry of humic substances: theory and implications for technology I.V. Perminova, K. Hatfield. 2. Soil organic matter and protective functions of humic substances in the biosphere D.S. Orlov and L.K. Sadovnikova. 3. Chemical stoichiometry and molecular level mechanisms as support for future predictive engineering calculations, D.S. Gamble et al. Part 2. Complexing interactions of humic substances with heavy metals and radionuclides and their remedial implementation. 4. Interactions of humic substances with trace metals and their stimulatory effects on plant growth A. Kaschl, Y. Chen. 5. Influence of UV-oxidation on the metal complexing properties of NOM F.H. Frimmel et al. 6. Role of humic substances in the complexation and detoxification of heavy metals: case study of the Dnieper reservoirs P.N. Linnik, T.A. Vasilchuk. 7. Complexation of radionuclides with humic substances V. Moulin. 8. Humic acids as barriers in actinide migration in the environment S.N. Kalmykov et al. 9. The use of humates for detoxification of soils contaminated with heavy metals O.S. Bezuglova, A.V. Shestopalov. Part 3. Sorptive-partitioning interactions of humic substances with organic ecotoxicants and their implementation for remediation technologies. 10. Utilization of immobilized humic organic matter for in-situ subsurface remediation G.U. Balcke et al. 11. The use of aqueous humic substances for in-situ remediation of contaminated aquifers D.R. Van Stempvoort et al. 12. Advantages of in situ remediation of polluted soil and practical problems encountered during its performance J.F. De Kreuk. 13. Wastewater treatment using modified natural zeolites P. Princz et al. Part 4. Impact on physiological functions of living organisms and on microbial transformations ofecotoxicants. 14. Mitigating activity of humic substances: direct influence on biota N.A. Kulikova et al. 15. Cytogenetic effects of humic substances and their use for remediation of polluted environments A. Gorova et al. 16. Influence of metal ions on the activity of soil humics-enzyme complexes S. Jorobekova et al. 17. Microbial redox reactions mediated by humus and structurally related quinines J. A. Field, F.J. Cervantes. 18. Enhanced humification of TNT H. Thomas, A. Gerth. 19. Commercial humates from coal and their influence on soil properties and initial plant development O.S. Iakimenko. 20. Impact of humic substances on plants in polluted environments: implications for phytoremediation technologies M.M. Kharitonov et al. Part 5. Quantifying structure and properties of humic substances and example studies on design of humic materials of the desired properties. 21. Molecular level structural analysis of natural organic matter and of humic substances by multinuclear and higher dimensional NMR spectroscopy N. Hertkorn, A. Kettrup. 22. Understanding capillary electrophoretic separation processes to characterize humic substances and their interactions with pollutants Ph. Schmitt-Kopplin, A. Kettrup. 23. Ozone application for modification of humates and lignins M.M. Ksenofontova et al. 24. Synthesis, metal-binding properties and detoxifying ability of sulfonated humic acids M.V. Yudov et al. Author Index. Subject Index.

Recorded molecular weights (MWs) for humic substances (HS) range from a few hundred to millions of daltons. For purposes of defining HS as a specific class of chemical compounds, it is of particular importance to ascertain if this broad range of MWs can be attributed to actual variability in molecular properties or is simply an artifact of the analytical techniques used to characterize HS. The main objectives of this study were (1)to establish if a preferential range of MWs exists for HS and (2) to determine any consistent MW properties of HS. To reach the goal, we have undertaken an approach to measure under standardized conditions the MW characteristics of a large set of HS from different natural environments. Seventy-seven humic materials were isolated from freshwater, soil, peat, and coal, such that each possessed a different fractional composition: humic acid (HA), fulvic acid (FA), and a nonfractionated mixture of HA and FA (HF). Size exclusion chromatography (SEC) was used as the analytical technique to determine molecular weight characteristics. The MW distributions were characterized by number (Mn) and weight (Mw) average MW, and by polydispersity. The complete range of Mw values varied within 4.7-30.4 kDa. The maximum Mw values were observed for peat HF and soil HA, whereas the smallest weights were measured for river water HF. Maximum values of polydispersity (3.5-4.4) were seen for peat HF and soil HA, while much lower values (1.6-3.1) were found for all preparations isolated with XAD-resins. Statistical evaluation showed consistent Mw and Mn variations with the HS source, while polydispersity was mostly a function of the isolation procedure used. A conclusion was made that HS have a preferential range of MW values that could characterize them as a specific class of chemical compounds.

Partition coefficients for the binding affinities of atrazine to 16 different humic materials were determined by the ultrafiltration HPLC technique. Sources included humic acids (HA), fulvic acids (FA), and combined humic and fulvic fractions (HF) from soil, peat, and coal humic acid. Each of the humic materials was characterized by elemental composition, molecular weight, and composition of main structural fragments determined by 13C solution-state NMR. The magnitude of K(OC) values varied from 87 to 575 L/kg of C, demonstrating relatively low binding affinity of humic substances (HS) for atrazine. On the basis of the measured K(OC) values, the humic materials can be arranged in the following order: coal HA approximately = gray wooded soil HAchernozemic soil HA and HFsod-podzolic soil HA approximately = peat HFsod-podzolic soil FApeat dissolved organic matter. The magnitude of the K(OC) values correlated strongly with the percentage of aromatic carbon in HS samples (r = 0.91). The hydrophobic binding was hypothesized as the key interaction underlying the binding of atrazine to HS.

Effects of 27 different humic materials on the toxicity of polycyclic aromatic hydrocarbons (PAH) were studied for crustacean Daphnia magna. Sources included isolated humic acids, fulvic acids, and their combination from soil, peat, and freshwater. The PAH used were pyrene, fluoranthene, and anthracene. The observed reduction in toxicity of PAH in the presence of humic substances (HS) was shown to be a result of the detoxification effect caused by the chemical binding of PAH to HS and of the direct effect of HS on D. magna. An approach was developed to quantify the detoxifying impact of humic materials related to their chemical binding to PAH with a use of the "constant of detoxification" or "toxicological partition coefficient" K(oc)D. The latter was proposed to determine by fitting the experimental relationships of the detoxification effect versus concentration of HS. The obtained K(oc)D values were well tracked by the corresponding partition coefficients determined by the fluorescence quenching technique (K(oc)fq): K(oc)D=b x K(oc)fq, b (mean+/-Cl, n=26, P=95%)=2.6+/-0.3, 4.6+/-0.6, and 6.0+/-1.4 for pyrene, fluoranthene, and anthracene, respectively. The predictive relationships between the structure and detoxifying properties of humic materials in relation to PAH were developed. It was shown that the magnitude of the K(oc)D values correlated closely with the aromaticity of humic materials characterized with the 13C NMR descriptors (sigma(C)Ar, sigma(C)Ar/sigma(C)Alk) and atomic H/C ratio. The obtained relationships showed the highest detoxifying potential of the humic materials enriched with aromatics and allowed a conclusion on the chemical binding as the governing mechanism of the mitigating action of HS on the toxicity of PAH.

Natural polyelectrolytes, humic substances, are suggested to control in situ growth of feroxyhyte nanoparticles of a highly reduced mean size and with enhanced colloidal stability in salt solutions. The feroxyhyte is formed as 2–5 nm thick and 20 × 20 nm wide nanoflakes due to the blocking of developing facets of feroxyhyte and constraints caused by diffusion limitations of ionic constituents across partially charged branches of humic substances.

Self assembly of natural organic materials (e.g., humic substances) on mineral surfaces leads to the formation of adlayers with physically different domains. However, direct evidence to explain the molecular interactions responsible for the formation of these domains is still missing. Here, we developed alkoxysilanized humic probes capable of self-assembling onto hydroxylated surfaces. Using modified humic substances from vastly differed sources (peat, water, coal) and DNA array glass slides as a flat surrogate for mineral surfaces, we create humic adlayers under aqueous conditions and show them to be homogeneous on the macroscale, but consisted of nanosize domains in coal and water humics and submicron-size domains in peat humics. The surface charge and hydrophilic–lipophilic balance of humic associates were proposed as major molecular drivers of the self-assembly with the former causing the formation of thin adlayers composed of separated nanosize domains (e.g., coal humics) and the latter enhancing the formation of thicker adlayers composed of interconnected domains linked in chains up to the submicron-size (e.g., peat humic materials). To the best of our knowledge, this is the first time alkoxysilanized humic probes were used to examine how humic adsorbates and their molecular structure influences the surface morphology of assembled adlayers. In this fashion, the humic adlayer with molecularly-defined functional elements can be assembled on any hydroxylated surface in situ, at the water–solid interface.

Here, we report the application of a selective liquid-phase hydrogen/deuterium exchange (HDX) coupled to ultra-high resolution FTICR MS for structural investigations of individual constituents of humic substances (HS) isolated from three coal samples of different geographical origin. Selectivity was achieved by conducting reactions in DCl or NaOD solutions for catalyzing HDX in aromatic ring and side-chain positions with enhanced C-H acidity, respectively. FTICR MS analysis showed a significant overlap of molecular compositions in the HS samples under study, with 2000 common formulae. Using HDX, we demonstrated that the determined common formulae are presented by different structural isomers. We found that aromatic compounds varied both in the substitution pattern and the number of aromatic protons. Depending on the sample, lignin components with the same molecular formulae were composed of coumaryl, coniferyl or sinapyl moieties. Enumeration of HDX series for the 800 most abundant compounds showed that the results of HDX agreed well with the model structures suggested for humic components occupying a van Krevelen plot. In addition, we explored chemical transformations, which could connect individual constituents of coal HS. These transformations included hydrolysis of a guaiacyl moiety and reduction of a catechol unit, which corresponds to the conversion of a coniferyl fragment into a coumaryl unit. The obtained results were supportive of the hypothesis of the reducing humification pathway suggested for lignin transformation in the environment. The conclusion was made that the molecular ensemble of coal HS is composed of individual constituents produced at different humification stages.

Despite broad application of different analytical techniques for studies on organic matter of chondrite meteorites, information about composition and structure of individual compounds is still very limited due to extreme molecular diversity of extraterrestrial organic matter. Here we present the first application of isotopic exchange assisted Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) for analysis of alkali extractable fraction of insoluble organic matter (IOM) of the Murchison and Allende meteorites. This allowed us to determine the individual S-containing ions with different types of sulfur atoms in IOM. Thiols, thiophenes, sulfoxides, sulfonyls and sulfonates were identified in both samples but with different proportions, which contribution corroborated with the hydrothermal and thermal history of the meteorites. The results were supported by XPS and thermogravimetric analysis coupled to FTICR MS. The latter was applied for the first time for analysis of chondritic IOM. To emphasize the peculiar extraterrestrial origin of IOM we have compared it with coal kerogen, which is characterized by the comparable complexity of molecular composition but its aromatic nature and low oxygen content can be ascribed almost exclusively to degradation of biomacromolecules.