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PubMed2003

Using selected operational descriptors to examine the heterogeneity within a bulk humic substance.

The heterogeneity within a bulk humic substance (HS) was investigated for ultrafiltration (UF) fractions of purified Aldrich humic acid (PAHA) using specific ultraviolet absorbance (SUVA), weight- and number-average molecular weights (MWw and MWn), and organic carbon-normalized pyrene binding coefficients (Koc). As expected, variations in these selected operational descriptors were found for the PAHA UF fractions, but the variations were smaller than the ranges observed for a small subset of different aquatic and terrestrial HS. In general, correlations among the operational descriptors for the different HS failed to predict the correct trends for the PAHA UF fractions. More variation in Koc was observed for the different HS versus the PAHA UF fractions despite comparable molecular weight ranges, suggesting that the extent of pyrene binding is more strongly influenced by HS source and chemical structure than merely by physical structural features. Size-exclusion chromatography (SEC) confirmed the structural stability of PAHA UF fractions, as demonstrated by a near-identical mathematical reconstruction of the original bulk chromatogram from a weighted summation of the individual UF fraction chromatograms. An ideal mixture model accurately predicted some operational descriptors of PAHA properties (i.e., SUVA and MWw), but failed to predict the PAHA reactivity for pyrene binding. Our Koc results at pH 4 and 7 suggest that the relative contribution of two mechanisms, partitioning and specific interactions, may account for the interactions between HS and pyrene.

Chromatography, Gel↗

PubMed2006

Dissolved and particulate humic substances in water channels in the historic centre of Venice.

The presence of humic substances, both in solution and as particulate, was studied in channels of the historic centre of Venice. The amount of particulate, its composition (organic and inorganic fraction) and the ratio between organic matter and humic substances were also considered. The sampling campaign was planned in 2001-02 from November to May. Three samplings in 20 stations representative of a large typical urban area were performed. The results obtained show that the composition of the particulate is variable, whereas the concentration of both dissolved and particulate humic substances is relatively homogeneous. Fulvic acids present in particulate are less homogeneous than dissolved forms; furthermore, the humification rate of organic matter is variable. Humic acids are absent, both in particulate and in dissolved forms.

Humic Substances↗

PubMed2004

[Influence of humic substance in solids on CODMn of the Yellow River].

Experiments were carried out to study the influence of humic substance in solids (Loess soil) on CODMn in the Yellow River. Several significant results were abtained from the study: (1) The total CODMn of water sample including liquid and solid phases increased significantly with the increase of solid content; The CODMn of liquid phase of water sample under pre-treatment with acid (LPWSPC) also increased significantly with the increase of solid content while that without pre-treatment did not increased significantly. (2) With the increasing of solid content, the total BOD5 of water sample increased much slower than the total CODMn and the CODMn of LPWSPC. (3) The humic substances with the content of 0.76% in solids (Loess soil) contributed greatly to the total CODMn of water sample. When the solid contents were 7.5 g/L and 15.0 g/L, the humic substances in solids accounted for 15.9% and 21.7% of the total CODMn of water sample, respectively. (4) When solid contents were 7.5 g/L and 15.0 g/L, fulvic acid,one of the main compositions of humic substance contributed to 23.6% and 50.6% of the CODMn of LPWSPC, respectively. Since the fulvic acid can hardly be biologically oxidized under natural conditions, the CODMn of LPWSPC in water quality monitoring exaggerates the oxygen-consuming organic contamination of the Yellow River.

China↗

PubMed2003

NMR diffusion analysis of surfactant-humic substance interactions.

Surfactants can be introduced into the environment through wastewater or by direct contamination. Understanding the fate and transport of surfactants in the environment is important in assessing their role as pollutants. Humic substances are complex heterogeneous mixtures of decomposition products of natural organic materials. They are environmentally important because they are known to solubilize and transport organic pollutants. Therefore humic substances are likely to affect the environmental fate of surfactants. Diffusion coefficients measured with pulsed-field gradient nuclear magnetic resonance spectroscopy are used in this study to examine the intermolecular interactions of the surfactants sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) in the presence of various humic substances. These results indicate that humic substances enhance the aggregation of SDS prior to micellization with a more pronounced effect observed for the more hydrophobic humic materials. The positively charged surfactant CTAB forms stable ion pairs with the humic substances.

Journal Article↗

PubMed1991

Organic compounds adsorption onto activated carbon: the effect of association between dissolved humic substances and pesticides.

The quantitative determination of pesticide binding to dissolved humic substances is relevant to both water treatment operation using activated carbon adsorption process and the application of transport models that predict the environmental distribution patterns of a given hydrophobic contaminant. In this study and in a first set of experiments, the extent of binding between (i) three pesticides of environmental concern, aldicarb, lindane and pentachlorophenol, and (ii) dissolved commercial humic acid and soil extracted fulvic acid, was determined using dialysis experiments and water solubility enhancement tests. In a second set of experiments, the influence of dissolved humic substances or pesticide on the retention of the other co-adsorbate onto activated carbon was investigated in binary systems. It was found that association was negligible for aldicarb and that the pesticide sorption onto activated carbon was not affected by humic acid (8.5 mg liter(-1) DOC). The association constants K for lindane and pentachlorophenol were identical in the presence of fulvic acid (logK=4.1) but lower than that observed with humic acid. In the presence of humic acid, binding affinity for pentachlorophenol (logK=4.6) was higher than the one observed for lindane (logK=4.4), despite its much higher water solubility. This observation suggests that the aromatic character of the pentachlorophenol molecule contributes to association interactions with humic acid. From co-adsorption experiments onto activated carbon it was found that fulvic acid (7.7 mg litre(-1) DOC) slightly enhances sorption kinetics of pentachlorophenol. Lindane (1 mg litre(-1)) does not affect sorption kinetics for fulvic acid but markedly enhances both the sorption kinetics and adsorptive capacity for humic acid. Activated carbon retention of dissolved humic substances or pesticide appears to be enhanced by the association potential that exists between these co-adsorbates in some binary systems.

Journal Article↗

PubMed2005

Molecular structure in soil humic substances: the new view.

A critical examination of published data obtained primarily from recent nuclear magnetic resonance spectroscopy, X-ray absorption near-edge structure spectroscopy, electrospray ionization-mass spectrometry, and pyrolysis studies reveals an evolving new view of the molecular structure of soil humic substances. According to the new view, humic substances are collections of diverse, relatively low molecular mass components forming dynamic associations stabilized by hydrophobic interactions and hydrogen bonds. These associations are capable of organizing into micellar structures in suitable aqueous environments. Humic components display contrasting molecular motional behavior and may be spatially segregated on a scale of nanometers. Within this new structural context, these components comprise any molecules intimately associated with a humic substance, such that they cannot be separated effectively by chemical or physical methods. Thus biomolecules strongly bound within humic fractions are by definition humic components, a conclusion that necessarily calls into question key biogeochemical pathways traditionally thought to be required for the formation of humic substances. Further research is needed to elucidate the intermolecular interactions that link humic components into supramolecular associations and to establish the pathways by which these associations emerge from the degradation of organic litter.

Humic Substances↗

PubMed2003

Humic substances in drinking water and the epidemiology of thyroid disease.

Thyroid diseases are common in all populations but the type and frequency depends on environmental factors. In Denmark geographical differences in iodine intake are caused by different iodine contents of drinking water, which varies from < 1 to 139 microg iodine per litre. Comparative epidemiologic studies have demonstrated considerable differences in type and occurrence of thyroid disease with more goitre and hyperthyroidism in Aalborg with water iodine content around 5 microg/L, and more hypothyroidism in Copenhagen with water iodine around 20 microg/L. In Denmark, iodine in ground water is bound in humic substances, which have probably leached from marine sediments in the aquifers. Interestingly, humic substances in water from other parts of the world have goitrogenic properties, especially humic substances from coal and shale. Humic substances are heterogeneous mixtures of naturally occurring molecules, produced by decomposition of plant and animal tissues. The effect of humic substances in drinking water on the epidemiology of thyroid disease probably depends on the source of aquifer sediments.

Chelating Agents↗

PubMed2002

Fast quantification of humic substances and organic matter by direct analysis of sediments using DRIFT spectroscopy.

A simple method based on diffuse reflectance coupled with infrared Fourier transform spectroscopy (DRIFTS) has been developed for the quantification and the characterization of sedimentary (or soil, peat, etc.) humic substances. Under optimized conditions, the quantification of humic substances or total organic matter is possible with DRIFTS at a frequency of 2930 cm(-1) using whole dry sediment samples. A study of the operational parameters that affect the DRIFTS signal shows the importance of normalizing analysis conditions, especially the diffuse reflectance accessory alignment, the particle size and compaction, and the homogeneity of the powdered samples, to obtain reproducible quantitative analyses. The quantification of total humic substances by DRIFTS correlates well with the concentrations determined using classical extraction methods. DRIFTS analysis requires only a few minutes instead of tedious extractions of humic substances. Moreover, the distribution of total organic matter and of fulvic acids, humic acids, and humin can also be obtained. Analysis of natural samples indicates that a calibration using humic material representative of the studied area provides the most accurate quantification. The fast screening of organic matter fractions by DRIFTS on intact natural samples provides useful quantitative and qualitative information that can be used in environmental or monitoring studies.

Algorithms↗

PubMed2005

Evidence from surface tension and fluorescence data of a pyrene-assisted micelle-like assemblage of humic substances.

Surface activity and fluorescence of humic substances (HS) and HS/pyrene solutions were monitored under various pH conditions. For HS alone the surface tension of the solutions decreased with increasing acidity, with a minimum at around pH 4. This effect, which is a consequence of an increase in the amphiphilic character of structures, is much more pronounced in humic (HA) than in fulvic acids (FA). The addition of pyrene (0.1 micromolL(-1)) results, for HA, in a marked reduction in the migration of amphiphilic species to the solution surface. FA profiles are not modified in presence of pyrene at that concentration. A decrease in the pyrene I1/I3 ratio in HS solutions shows that below pH 9 pyrene molecules react progressively to the change to a more hydrophobic environment, the greatest effect being observed at around pH 6 to 7. These signals are followed by a significant increase in the pyrene excimer fluorescence (lambda(exc)/lambda(em)=334 nm/450 nm), which is a consequence of the proximity of pyrene molecules. For FA, the I1/I3 decrease is less significant and no excimers develop. This set of effects is explained in view of conformational adjustments of HS, mainly HA, which become arranged in micelle-like domains in aqueous solution, the aromatic moieties being assembled around the pyrene molecules.

Benzopyrans↗

PubMed2003

Electrospray ionization mass spectrometry of terrestrial humic substances and their size fractions.

Electrospray ionization mass spectrometry (ESI-MS) was used to evaluate the average molecular mass of terrestrial humic substances, such as humic (HA) and fulvic (FA) acids from a soil, and humic acid from a lignite (NDL). Their ESI mass spectra, by direct infusion, gave average molecular masses comparable to those previously obtained for aquatic humic materials. The soil HA and FA were further separated in size-fractions by preparative high performance size exclusion chromatography (HPSEC) and analyzed with ESI-MS by both direct infusion and a further on-line analytical HPSEC. Unexpectedly, their average molecular mass was only slightly less than for the bulk sample and, despite different nominal molecular size, did not substantially vary among size-fractions. The values increased significantly (up to around 1200 Da) after on-line analytical HPSEC for the HA bulk sample, at both pH 8 and 4, and for the HA size-fractions when pH was reduced from 8 to 4. It was noticed that HA size-fractions at pH 8 were separated by on-line HPSEC in further peaks showing average masses which progressively increased with elution volume. Furthermore, when the HA and NDL bulk samples were sequentially ultracentrifuged at increasing rotational speed, their supernatants showed mass values which were larger than bulk samples and increased with rotational speed. These variations in mass values indicate that the electrospray ionization is dependent on the composition of the humic molecular mixtures and increases when their heterogeneity is progressively reduced. It is suggested that the dominance of hydrophobic compounds in humic supramolecular associations may inhibit the electrospray ionization of hydrophilic components. Our results show that ESI-MS is reasonably applicable to humic substances only after an extensive reduction of their chemical complexity.

Humic Substances↗

PubMed2002

Sorption and desorption of Co(II) on alumina: mechanisms and effect of humic substances.

The effects of pH, ionic strength and humic substances on the sorption and desorption of Co(II) on alumina and silica were, respectively investigated by using radiotracer 60Co. The distribution coefficients, the breakthrough curves and the displacement curves were experimentally determined in the batch and the column experiments. The pH and the humic substances influenced the sorption of Co(II) on alumina greatly as compared with the sorption of Co(II) on silica. It was found that the sorption characteristics of Co(II) onto alumina and silica are distinctly different, that the strong chemical bonds are formed between the bare alumina surface and Co(II) and between the coated alumina surface and Co(II), and that a transition from the adsorption to the surface-induced precipitation of Co(II) on the bare alumina surface takes place.

Journal Article↗

PubMed2001

Humic substances as catalysts in condensation reactions.

Humic substances (HS) demonstrate appreciable impact on the rate of the condensation reactions as shown in the example of the reaction between hydrazine and 4-(dimethylamino)-benzaldhyde in an aquatic environment. The catalytic activity of HS has also been demonstrated in Knoevenagel and Claisen-Schmidt reactions for condensation of carbonyl compounds with CH acids. The aquatic fulvic acids are the most active in these reactions. The velocity of the studied reactions also depends on pH, temperature, the concentration and origin of HS used. A possible micellar and acid-base catalysis mechanism in aquatic media has been suggested.

Benzopyrans↗

PubMed1985

The occurrence of copper, iron, zinc and other elements and the nature of some copper and iron complexes in humic substances from municipal refuse disposed of in a landfill.

Municipal refuse was allowed to decompose in a simulated landfill for 20 months. Three different models were studied in which the refuse, in 40 m3 lots, was either compacted or mixed 2:1 with sewage sludge, the latter being studied in both uncompacted and compacted states. At 2, 6, 12 and 20 months, humic substances were extracted from samples with 0.1 M Na2P4O7 and 0.1 M NaOH, and humic acids isolated by precipitation after acidification with HCl. The humic substances were examined by electron paramagnetic resonance (EPR) to determine the free radical content and the nature of some of the metal complexes present. The principal form of copper was present in either a square planar or a tetragonally-distorted octahedral environment, probably coordinated to two nitrogen and two oxygen atoms. Fe3+ was present in at least three different environments. In one, it was probably in a complex with rhombic symmetry; another showed Fe3+ in an axially-symmetric environment, most likely as a ferric porphyrin. No distinctions could be made between the concentrations or forms of metals present in the refuse humic substances as a result of adding sewage sludge, but the additions increased the yield of humic substances, particularly in the uncompacted landfill. Humic substances in the refuse retain metal elements in complexed forms which will restrict their release from the landfill.

Carbon↗

PubMed2002

Minimizing biofilm in the presence of iron oxides and humic substances.

Based upon circumstantial evidence linking elevated coliform bacteria counts in drinking water distribution systems with unlined cast iron pipe, it was hypothesized that adsorption of humic substances by iron oxide containing corrosion products (CPs) can stimulate and/or support biofilm development. Using porous media consisting of iron-oxide-coated glass beads (IOCBs) or actual iron CPs, experiments were performed to evaluate the effectiveness of different corrosion control and disinfection treatments in reducing biofilm when humic substances were the carbon source. Free chlorine was the most effective treatment in minimizing biofilm. Addition of phosphate alone did not significantly reduce biofilm using the CPs, but there was weak evidence it did using the IOCBs. The combination of free chlorine and phosphate was more effective at minimizing biofilm than free chlorine alone when CPs were the media. The presence of humic substances was a major factor when considering biofilm minimization based on results of experiments using both types of iron oxide media. The combination of humic substances and CPs led to an increase in biofilm biomass when free chlorine was not present, similar to conditions that could occur at distribution system dead-ends. Treatment to raise the pH to 9 did not reduce biofilm in experiments using both media, and actually increased biofilm in the experiment using CPs under the conditions tested.

Bacteria↗

PubMed2003

Evaluation of toxicity of the pesticides, chlorpyrifos and arsenic, in the presence of compost humic substances in aqueous systems.

An improved understanding of pesticide toxicity in natural systems can have important consequences for pesticide management and remediation strategies for contaminated areas. The interaction between humic substances extracted from compost natural organic matter and both organic and inorganic pesticides was evaluated for its effect on the toxicity of pesticides in the aqueous phase. The toxicity of contaminants was measured using the Microtox toxicological bioassay. Solutions containing concentrations ranging from 2 to 42 mg C/l of humic substance extracted from a South Texas compost were added to concentrations of the organic pesticide, chlorpyrifos, and toxicity reduction ranging from 50 to 100% was demonstrated. Different concentrations of arsenic ranging from 0.5 to 5 mg/l were also associated with three different concentrations of humic substances and the arsenic toxicity was consistently reduced by a factor of 100%. These results demonstrate a significant relationship between humic substance interactions with organic and inorganic pesticides, and pesticide toxicity in natural systems, and may also suggest a mechanism for pesticide toxicity reduction in natural waters through compost humic addition for contaminated groundwaters and surface waters.

Arsenic↗

PubMed1999

High Pressure Size Exclusion Chromatography (HPSEC) of humic substances: molecular sizes, analytical parameters, and column performance

High Pressure Size Exclusion chromatography (HPSEC) is increasingly used to evaluate molecular sizes of humic substances from different sources. Asymmetry factors (As), number of theoretical plates (N), coefficient of distribution (k(d)), and column resolution (Rs) were determined for two different HPSEC columns (TSK G3000SW and Biosep S2000) and polysaccharides of known molecular weights were used as standards. Calibration curves were equivalent for both columns whereas analytical parameters revealed that the TSK column was only slightly more efficient in separating polysaccharide standards. Mw and Mn values for humic substances differed according to the molecular weight range of each column but relative standard deviation never exceeded 5% for both columns. Variations between columns were attributed to intrinsic humic properties such as the stability of conformational structures. These results suggested that humic substances in solutions are loosely-bound association of small molecules that may be consistently dispersed by diffusion through size-exclusion pores. HPSEC is confirmed to represent a highly precise method to evaluate the relative molecular-size distribution of dissolved humic substances.

Journal Article↗

PubMed1992

Rapid method for separation of bacterial DNA from humic substances in sediments for polymerase chain reaction.

The polymerase chain reaction (PCR) was used to amplify an Escherichia coli 16S ribosomal gene fragment from sediments with high contents of humic substances. Total DNA was extracted from 1 g of E. coli seeded or unseeded samples by a rapid freeze-and-thaw method. Several approaches (use of Bio-Gel P-6 and P-30 and Sephadex G-50 and G-200 columns, as well as use of the Stoffel fragment) were used to reduce interference with the PCR. The best results were obtained when crude DNA extracts containing humic substances were purified by using Sephadex G-200 spun columns saturated with Tris-EDTA buffer (pH 8.0). Eluted fractions were collected for PCR analyses. The amplified DNA fragment was obtained from seeded sediments containing fewer than 70 E. coli cells per g. Because only 1/100 of the eluted fractions containing DNA extracts from 70 cells per g was used for the PCR, the sensitivity of detection was determined to be less than 1 E. coli cell. Thus, DNA direct extraction coupled with this technique to remove interference by humic substances and followed by the PCR can be a powerful tool to detect low numbers of bacterial cells in environmental samples containing humic substances.

Chromatography, Gel↗

PubMedDate not supplied

[Study of humic substance transformation in phosphatic soil in terms of nucleophilicity and electrophilicity].

The applicability of the nucleophilicity/electrophilicity concept to the explanation of mechanisms of formation and transformation of humic substances was considered. Sequential time changes in the structure and properties of humic substances in phosphatic soil have been revealed. Different elemental composition of humic and fulvic acids at different stages of humus transformation was due to different patterns of electron density distribution in phosphorus-modified fragments of humic molecules. The important role of metals and phosphorus in realization of different pathways of humic substance transformation was demonstrated.

Benzopyrans↗