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Birch tar was widely used since the Stone Age as adhesive, disinfectant, mosquito repellent etc. Despite of this, the chemical composition of the birch tar remains largely unknown. Here we implement the electrospray ionization ultrahigh resolution Fourier transform mass spectrometry for the determination of the molecular formulas of the birch tar constituents. It was found that in the positive ESI mode the compounds containing 2 nitrogen atoms dominates in the spectrum. Compounds containing 1 nitrogen atom were detected too but they are less abundant. In the negative ESI mode the compounds containing from 2 to 4 oxygen atoms were detected. Also, we used recently developed in-ESI source Hydrogen/Deuterium exchange approach for the structural characterization of the individual molecules. We observed the 1 H/D exchange for major O 3 compounds and did not observe H/D exchange for almost all O 2 compounds. Corresponding neutral molecules have 2 and 1 labile hydrogens and as a consequence –OH groups respectively.

In this study we successfully enhanced surface activity of natural humic substances (HS) with respect to mineral surfaces by functionalization with organosilanes. Of particular importance was that modification was conducted in water. Humates from coal and peat and 3-aminopropyl-triethoxysilane (APTES) were used as starting materials. Atomic force microscopy showed silanized HS produced self-assembled adsorption monolayers at the water–solid interface. These adlayers caused an increase in the surface hydrophobicity with contact angles equaling 56°. Application of silanized HS for treatment of different soil compartments including mineral soil separates and soil aggregates revealed an efficacy with respect to both re-assembly of soil aggregates and restoration of their water stability. Furthermore, field trials on the treatments of native sod-podzolic soil with silanized HS indicated improvements in soil structure as compared to non-treated soil or treatment with the non-functionalized humate. Results demonstrating the use of silanized HS as ecologically-safe, nature-inspired soil conditioners were promising.

The objective was to estimate suitability of humics-modified silica gels for adsorptive removal of the Direct Brown 1 trisazo dye from aqueous phase. The major advantage of the proposed adsorbents is that of an ecologically sound procedure of immobilizing silanized humic derivatives onto silica gel in aquatic solutions. The silanized humic derivatives, in turn, are obtained without a use of organic solvent by reacting natural humic materials from peat and coal with 3-aminopropyltriethoxyorganosilane in water. These silanized derivatives are surface active and are capable of self assembling into humic adlayers at the water solid interface. A use of this approach allows for immobilization of up to 220 mg of humic materials per 1 g of SiO2. The adsorption capacity of humics-modified silica gels with respect to the Direct Brown 1 trisazo dye varied from 3.5 up to 8.8 mg per 1 g of SiO2. The maximum sorption obtained for the silanized derivative with 50% modification degree was comparable to adsorption capacity of activated coal to this dye (7.5 mg g(-1)). The results of this adsorption study, warrant further studies of azo dye removal from aqueous environments.

Fourier transform ion cyclotron resonance mass spectrometry reveals substantial differences in the structural motifs of lignite and leonardite humates, which can be used for the standardization and molecular systematics of humic substances and for the directed design of humate-based products.

The problem of permeable reactive barrier (PRB) capture and release behavior is investigated by means of an approximate analytical approach exploring the invariance of steady-state solutions of the advection–dispersion equation to conformal mapping. PRB configurations considered are doubly-symmetric funnel-and-gate as well as less frequent drain-and-gate systems. The effect of aquifer heterogeneity on contaminant plume spreading is hereby incorporated through an effective transverse macro-dispersion coefficient, which has to be known. Results are normalized and graphically represented in terms of a relative capture efficiency M of contaminant mass or groundwater passing a control plane (transect) at a sufficient distance up-stream of a PRB as to comply with underlying assumptions. Factors of safety FS are given as the ratios of required capture width under advective–dispersive and purely advective transport for achieving equal capture efficiency M. It is found that M also applies to the release behavior down-stream of a PRB, i.e., it describes the spreading and dilution of PRB treated groundwater possibly containing incompletely remediated contamination and/or remediation reaction products. Hypothetical examples are given to demonstrate results.

a b s t r a c t In this study we explored a possibility for enhancing aqueous sorption of humic substances (HS) onto hydroxylated surfaces (e.g., silica gel) by increasing modification rate of their most abundant functional groups - carboxyls with mineral-adhesive alkoxysilyl moieties. The synthesis included treatment of dried humic material with 3-aminopropyl trimethoxy silane (APTS) capable of forming amide bonds with carboxyl groups of HS under anhydrous conditions. The reaction was run at six different HS to APTS ratio for achieving different modification degrees of the carboxyl groups in the humic backbone. The obtained derivatives were characterized using elemental analysis, 13C NMR Spectroscopy, Fourier transform infrared spectroscopy, and size exclusion chromatography that confirmed quantitative incor- poration of alkoxysilyl-moieties into HS structure. Aqueous adsorption was investigated in 0.028 M phosphate buffer using silica gel as a surrogate for mineral surface. Both distribution coefficients as well adsorption capacities paralleled the amount of alkoxysilyl-moieties incorporated into backbone of the parental HS. The adsorption capacity reached its maximum value of 210 mg of HS per g of SiO2 for the APTS derivative synthesized at the equimolar reagent ratio. This value was comparable to the amount of the same HS immobilized onto the APTS-treated silica gel (265 mg of HS per g of SiO2). Adsorption of alkoxysilyl-derivatives was found to be irreversible under conditions studied. Conclusively, we believe that the directed modification of HS by incorporating alkoxysilyl-moieties is well suited for producing humic derivatives with controllable affinity for aqueous sorption onto hydroxylated surfaces.

The effect of humic acids (HA) on neptunium redox behavior and sorption onto hematite, -Fe2O3, and goethite, -FeOOH, colloids was established in batch sorption experiments that were carried out in broad pH interval. The sorption isotherms were provided for two samples of HA: commercial sample of leonardite humic acid and its hydroquinone-enriched derivative obtained using formaldehyde copolycondensation. The distribution of Np fitted the distribution of hydroquinone-enriched HA at low pH values in case of both solids while the influence of parent HA on Np sorption was negligible. This is due to Np(V) reduction upon interaction with hydroquinone-enriched derivative having higher reducing capacity compared to the parent HA. The order of components addition was found to be significant for Np retention. © 2007 Elsevier B.V. All rights reserved.

Humic substances play an important role in the speciation of actinides in the environment due to complexing, redox and sorptive interactions. This work is devoted to plutonium(V) reduction studies in solutions containing different humic substances, eluted from Mollisol and Sod-podzolic soil samples, as compared to real Pu distribution is contaminated soils. On the basis of kinetic curve slopes, the reducing ability is increased in the order: HA < FA ∼ low molecular weight fraction. The data obtained show that the different humic compounds play different roles in Pu(V) migration ability due to differing reducing and complexing properties.

Alkoxysilylated humic derivatives were used to create covalently bound humic coatings on silica gel. The corresponding reaction was conducted in an aqueous milieu that was feasible due to the water solubility of these derivatives. The alkoxysilylated humic derivatives were obtained by alkoxysilylation of leonardite humic acid (HA) and hydroquinone-modified HA (HQ) with enhanced redox properties. The silica gel coated with covalently bound HA and HQ was tested for sequestration of aqueous Np(V) and Pu(V) under anaerobic conditions. Greater sequestration with respect to Pu(V) (up to 97%) as compared to Np(V) (up to 60%) was demonstrated for samples of silica gel coated with HA and HQ, whereas sorption of both actinides on pure silica gel did not exceed 20%. Results provide bench-scale proof that alkoxysilylated humic derivatives can be used as reagents for the in situ installation of permeable reactive barriers designed to remediate actinide-contaminated groundwater.

Natural humic materials are known to cause a reduction of penta- and hexavalent plutonium; however, contradicting results have been previously reported for neptunium. The goal of this study was to determine if incorporation of additional reducing centers into humic structure would yield material with enhanced reducing performance with respect to higher valent actinides, nominally, Pu(V) and Np(V). Hydroquinone-moieties were used as the redox centers. They were incorporated into humic structures using formaldehyde condensation at different monomer-to-humic ratios to obtain materials of different reducing properties. Reduction of model actinides by the hydroquinone-enriched humic materials was studied under both oxic and anoxic conditions at acidic and neutral pH values. Redox speciation of plutonium and neptunium was monitored using solvent extraction techniques and liquid scintillation counting. It was shown that both nonmodified leonardite humic acid and all the obtained derivatives were able to reduce Pu(V) quantitatively both at neutral and acidic pH and under oxic and anoxic conditions. The reduction rate increased with an increase in the degree of modification of the humic material and reached its maximum for HQ500 derivative. For neptunium, reduction was observed only under anoxic conditions at acidic pH. The hydroquinone-modified derivatives had much higher reducing performance when compared to nonmodified leonardite humic acid. The results obtained show good prospects for a use of hydroquinone-modified humic materials as reactive agents for remediation of actinide contaminated aquifers.

The spatial moments of a contaminant plume undergoing bio-attenuation are coupled to the moments of microbial populations effecting that attenuation. In this paper, a scalable inverse method is developed for estimating field-scale Monod parameters such as the maximum microbial growth rate (μmax), the contaminant half saturation coefficient (Ks), and the contaminant yield coefficient (Ys). The method uses spatial moments that characterize the distribution of dissolved contaminant and active microbial biomass in the aquifer. A finite element model is used to generate hypothetical field-scale data to test the method under both homogeneous and heterogeneous aquifer conditions. Two general cases are examined. In the first, Monod parameters are estimated where it is assumed a microbial population comprised of a single bacterial species is attenuating one contaminant (e.g., an electron donor and an electron acceptor). In a second case, contaminant attenuation is attributed to a microbial consortium comprised of two microbial species, and Monod parameters for both species are estimated. Results indicate the inverse method is only slightly sensitive to aquifer heterogeneity and that estimation errors decrease as the sampling time interval decreases with respect to the groundwater travel time between sample locations. Optimum conditions for applying the scalable inverse method in both space and time are investigated under both homogeneous and heterogeneous aquifer conditions.

An approach to the generation of size exclusion chromatographic (SEC) descriptors of humic substances (HS) is proposed. It implies a calculation of initial, central and normalised statistical moments and some of their ratios from the raw SEC-data. The proposed descriptors extend the pool of common molecular weight (MW) characteristics (average MW’s and their ratios) up to 20 parameters, which is important for the purposes of classification and prognostic modelling. Original software was developed to facilitate the computation of molecular weight distribution (MWD) and SEC-descriptors of HS from raw chromatographic data. The developed approach was applied to two model compounds and three humic materials. The discriminatory power of the calculated descriptors was roughly estimated on the example of three humic materials of different origin with the use of a multivariate variance analysis. Weight average MW and a ratio of the z- to weight average distribution coefficients were found to be the best discriminators, whereas the significance level of discrimination provided by the second moment and Mz/Mw-ratio was lower than 95%. ©2000 Elsevier Science B.V. All rights reserved.

Coal humic acids are successfully tested for the first time as new nontoxic agents for the preparation of core-shell iron oxide magnetic nanoparticles.

Size exclusion chromatography (SEC) is a powerful tool for the determination of molecular size of compounds. However, the conducted SEC analysis of 35 humic substances (HS) samples demonstrated, that it has some severe pitfalls for the molecular weight characterization of HS resulting from a lack of appropriate standards. To overcome this problem, a new approach to calculation of molecular weight from the SEC data was developed. It is based on the correction of the experimentally determined distribution coefficient ( K d ) values according to the predictive equations derived either from the data on charge density and hydrophobicity of the analyte or from the values of its characteristic structural parameters. Verification of both predictive equations using model compounds has displayed much better prognostic potential of the polynomial equation developed with a use of integral structural parameters of the analyte. Application of this predictive equation to synthetic polyelectrolytes gave satisfactory estimates for all the polymers with K d >0.15. The model calculation for an averaged sample of HS allowed to estimate a difference between the ideal and experimental values of K d (Δ K d ) by a value of 0.02. The correspondent correction of the SEC-data of 35 HS samples showed overestimation of the values of molecular weight of HS determined by the standard data handling technique. The obtained model estimations are to be verified along with the further development of the model based on the adjustment of the model assumptions to specific polyelectrolytic properties of HS.