Interaction Of Humic Acid Research Articles

Interactions of Humic Acid with Nanosized Inorganic Oxides

Adsorption of natural organic matter (NOM) on nanoparticles (NPs) is important for evaluating their transport, transfer, and fate in the environment, which will also affect sorption of hydrophobic organic compounds (HOCs) by NPs and thereby potentially alter the toxicity of NPs and the fate, transport, and bioavailability of HOCs in the environment. Therefore, the adsorption behavior of humic acids (HA) by four types of nano-oxides (i.e., TiO2, SiO2, Al2O3, and ZnO) was examined in this study to explore their interaction mechanisms using techniques including Fourier transform infrared (FTIR) spectroscopy and elemental, zeta potential, and surface area analyses. Adsorption of HA was observed on nanosized TiO2, Al2O3, and ZnO but not on nano-SiO2. Furthermore, HA adsorption was pH-dependent. HA adsorption by nano-oxides was mainly induced by electrostatic attraction and ligand exchange between HA and nano-oxide surfaces. Surface hydrophilicity and negative charges of nano-oxides affected their adsorption of HA. However, the maxima of HA adsorption on nano-oxides were limited by the surface area of nano-oxides. HA phenolic OH and COOH groups were responsible for its ligand exchange with nano-TiO2 and nano-ZnO, respectively, while either HA COOH or HA phenolic/aliphatic OH was responsible for its ligand exchange with nano-Al2O3. HA adsorption decreased the micropore surface area of nano-oxides but not the external surface area because of the micropore blockage. HA adsorption also decreased the zeta potential of nano-oxides, indicating that HA-coated nano-oxides could be more easily dispersed and suspended and more stable in solution than uncoated ones because of their enhanced electrostatic repulsion.

Adsorption interactions of humic acids with biocides

The chemical composition of humic acids from brown coal (Aldrich) was determined by element analysis, 13C NMR spectroscopy, and potentiometric titration. The adsorption ability of humic acids with different biocides (cyproconasol, propiconasol, tebuconasol, irgarol 1051, and DCOIT) was studied. The adsorption ability of a mixture of biocides in aqueous solutions was higher than that of the individual components. The limiting concentration of humic acids at which adsorption of biocides was maximum was determined. Adsorption constants were calculated by the Freundlich equation for each biocide in aqueous solution.

Interaction of humic acids with human DNA: Proposed mechanisms and kinetics

Human DNA quantification by quantitative real-time PCR (QRT-PCR) has gained great importance in forensic DNA and ancient DNA studies. However, in such samples, DNA quantification is impaired by the frequently present humic acid (HA). We have previously shown that the addition of synthetic HA inhibits QRT-PCR. In this study we investigated the possible mechanisms of HA interaction with human DNA, and kinetics of QRT-PCR inhibition. In QRT-PCR with pure human DNA and no HA added, VMAX was 40. With DNA sample containing 4 microg/mL of HA, VMAX was 30.30 while the addition of extra Taq polymerase to the same sample changed VMAX into 38.91, amplifying between 80 and 90% of input DNA. The KM/VMAX ratio in all the samples remained constant, indicating that the mechanism of HA inhibition of QRT-PCR is uncompetitive by nature. Moreover, HA shifts the human DNA melting temperature point (Tm) from 75 to 87 degrees C and inhibits DNase I-mediated DNA cleavage, most probably affecting the enzyme's activity.

Sorption of the Antibiotic Tetracycline to Humic‐Mineral Complexes

Humic substances, by altering the surface properties and/or competing for available reaction sites, can either suppress or promote sorption of organic compounds to mineral surfaces. Limited literature evidence points to the reduction in sorption of the antibiotic tetracycline to clay minerals in the presence of humic substances. We investigated the surface interaction of Elliott soil humic acid (ESHA) with hydrous Al oxide (HAO) and the effect of this association on tetracycline sorption. Strong interaction between ESHA and HAO led to ESHA-promoted dissolution of HAO and surface charge reversal. The ESHA-HAO sorption-desorption isotherms were successfully described using a modified Langmuir model that accounted for the heterogeneity of HAO surface and ESHA. Ligand exchange was proposed as the major interaction mechanism, and the edge Al atoms on HAO surface were considered as the sorption sites for ESHA macromolecules. ESHA was coated onto HAO to achieve two different organic content (foc) levels of 0.81 and 1.52%. Sorption results were compared for the binary ESHA-tetracycline and HAO-tetracycline systems, and the ternary ESHA-HAO-tetracycline system. The coating of ESHA on HAO significantly suppressed tetracycline sorption levels, attributable to altered HAO surface charge characteristics and/or direct competition between ESHA and tetracycline for potential sorption sites. Higher foc level, besides increasing the extent of sorption suppression, also resulted in greater ionic strength dependence and increased nonlinearity of sorption behavior. It, therefore, appears that the presence of humic substances, in both dissolved and mineral-bound forms, is likely to increase the environmental mobility of tetracycline compounds.

Behaviour of partially soluble humic acids in aqueous suspension

Solubility and dissociation of four various humic samples, including IHSS standard, in water are studied in this work. Obtained experimental data are compared with hypothesis of partial solubility of humic acids in aqueous solutions developed in our previous work. It was proved experimentally that behaviour of all used humic samples agrees with the multi-step mechanism of solid humic acids interaction with water, including partial equilibrium dissolution as well as direct equilibrium dissociation from the solid state. Experimental data further demonstrated that regardless the common mechanism, solubility and dissociation degree of various humic samples may be very different and can be estimated using parameters of model based on the proposed mechanism.

Atrazine Photodegradation in Aqueous Solution Induced by Interaction of Humic Acids and Iron: Photoformation of Iron(II) and Hydrogen Peroxide

The photochemical formation of Fe(II) and hydrogen peroxide (H 2O 2) coupled with humic acids (HA) was studied to understand the significance of iron cycling in the photodegradation of atrazine under simulated sunlight. The presence of HA significantly enhanced the formation of Fe(II) and H 2O 2, and their subsequent product, hydroxyl radical ( (*)OH), was the main oxidant responsible for the atrazine photodegradation. During 60 h of irradiation, the fraction of iron presented as Fe(II) (Fe(II)/Fe(t)) decreased from 20-32% in the presence of the Fe(III)-HA complex to 10-22% after adding atrazine. The rate of atrazine photodegradation in solutions containing Fe(III) increased with increasing HA concentration, suggesting that the complexation of Fe(III) with HA accelerated the Fe(III)/Fe(II) cycling. Using fluorescence spectrometry, the quenching constant and the percentage of fluorophores participating in the complexation of HA with Fe(III) were estimated by the modified Stern-Volmer equation. Fourier transform infrared spectroscopy (FTIR) offered the direct evidence that Fe(III)-carboxylate complex could be formed by ligand exchange of HA with Fe(III). Based on all the information, a possible reaction mechanism was proposed.

Competition and complexation of heavy metal ions and humic acid on zeolitic MCM-22 and activated carbon

Abstract Zeolitic MCM-22 and activated carbon have been used as adsorbents for removal of heavy metals (Cu2+ and Pb2+) and humic acid from aqueous solution. The adsorption behaviour has been investigated in single- and binary-adsorbate systems and the effect of humic acid on metal adsorption was obtained. It is found that the MCM-22 and activated carbon are effective in metal ion and humic acid adsorption. In single component system, the MCM-22 presents the adsorption capacities of Cu2+, Pb2+, and humic acid at 33, 94, and 78 mg/g, respectively, while the activated carbon exhibits the adsorption capacities of Cu2+, Pb2+, and humic acid at 12, 61, and 74 mg/g, respectively, lower than those on the MCM-22. Solution pH will significantly influence the adsorption. Cu2+ and Pb2+ adsorption will increase with increasing pH while humic acid shows a decreasing trend as pH is increased. In binary-adsorbate system, metal–humic acid interaction will affect the adsorption of metal and humic acid on the MCM-22 and activated carbon. On the MCM-22, Cu2+, Pb2+ will present competitive adsorption with humic acid. On the activated carbon, Pb2+ and humic acid also exhibit competitive adsorption, while Cu2+ and humic acid will have a complexation effect, resulting in an increase of Cu2+ adsorption on the activated.

Characterization of Mercury – Humic Acids Interaction by Potentiometric Titration with a Modified Carbon Paste Mercury Sensor

AbstractStability constant for mercury binding by commercial and natural humic acids (HA) were determined using a new potentiometric mercury(II) sensor based on dithiosalicylic acid modified carbon paste electrode. The sensor present a high selective and sensitive response to mercury(II) ions, and a low detection limit of 1.8×10−8 M. The potentiometric titrations curves of humic acids against mercury(II) ions were modeled. For 1.00×10−7 to 3.00×10−4 M mercury(II) ion concentration levels the results are consistent with the presence of two different binding sites in the humic acid macromolecule. The strongest binding sites (log K1 ranging from 10.1 to 6.8) are probably due to interaction with carboxylic acid and amine groups in the molecule, whereas weakest binding sites (log K2 ranging from 8.8 to 4.5) can be associated to phenolic groups.

Potentiometric investigations on the interaction of humic acid with Cu(II) and Eu(III) ions

The interaction of Cu(II) and Eu(III) ions with humic acid has been studied by potentiometry under normal atmospheric conditions at pH 6,I=0.1 M (NaClO4) at room temperature (23±2 °C). The investigation was performed for the Cu(II) ion directly by means of a Cu2+ion selective electrode, whereas for the Eu(III) ion it was indirectly based on competition reactions between the Cu(II) ion and the Eu(III) ion. The evaluation of the conditional formation constants, which was based on the charge neutralization model, resulted in as follows:logβ(Cu-HA(II)) = 5.6±0.3logβ(Eu-HA(III)) = 6.2±0.5

Fluorescence characterization of metal ion–humic acid interactions in soils amended with composted municipal solid wastes

Fluorescence spectroscopy has been used to probe the structural properties and Cu(II), Zn(II), Cd(II), and Pb(II)-binding behavior of humic acid (HA)-like fractions isolated from a municipal solid waste compost (MSWC) and HAs from unamended and MSWC-amended soils. The main feature of the fluorescence spectra, in the form of emission-excitation matrix (EEM) plots, was a broad peak with the maximum centered at an excitation/emission wavelength pair that was much shorter (340/437 nm) for MSWC-HA than for unamended and MSWC-amended soil HAs (455/513 and 455/512 nm, respectively). Fluorescence intensity for MSWC-amended soil HA was less than that for unamended soil HA. These results were indicative of more aromatic ring polycondensation and humification of soil HAs, and of partial incorporation of simple and low-humified components of MSWC-HA into native soil HA, as a result of MSWC amendment. Titrations of HAs with Cu(II), Zn(II), Cd(II), and Pb(II) ions at pH 6 and ionic strength 0.1 mol L(-1) resulted in a marked decrease of the fluorescence intensities of untreated HAs. By successfully fitting a single-site fluorescence-quenching model to titration data, the metal ion complexing capacities of each HA and the stability constants of metal ion-HA complexes were obtained. The binding capacities and stability constants of MSWC-HA were smaller than those of the unamended soil HA. Application of MSWC to soil slightly reduced the metal-ion-binding capacities and affinities of soil HAs.

Humic acid preparation, properties and interactions with metals lead and cadmium

Humic acid (HA) extracted from soil is investigated in terms of its cation exchange capacity (CEC), zero point of charge (zpc), oxygen containing functional group content, scanning electron microscope (SEM) images, and pH. The CEC of HA that was dried was approximately half the CEC of hydrated HA. Metal retention by HA was studied by conducting 24 h batch equilibrium tests with lead (Pb, as PbCl 2) and cadmium (Cd, as CdCl 2) and HA at pH 4 and 6, and with a mixture of HA, mackinawite and kaolinite. The reactivity of the HA towards Pb and Cd was reduced when it was combined with the mackinawite and kaolinite. The mackinawite raised the pH and dissolved some of the HA, until sufficient reactions between the metals and mixture lowered the pH enough for the dissolved HA to solidify and remove more metal from solution. HA bonding with the mackinawite and kaolinite reduced the HA sites available for metal uptake. The functional group content of the HA provided indications regarding the origin of the HA, the extent of humification and the presence of less decomposed fractions. The CEC of the HA could conservatively predict the amount of metal uptake. Low pH conditions are favorable for metal removal from solution by HA because the zpc of the HA was below pH 0.5 and because at higher pHs HA begins to dissolve. HA, especially in the hydrated phase, may represent an important material for metal removal from waters and wastewaters containing metals.

Effects of Urea, Humic Acid and Phosphate Interactions in Fertilizer Microsites on Ammonia Volatilization and Soil Ammonium and Nitrate Contents

Effects of Urea, Humic Acid and Phosphate Interactions in Fertilizer Microsites on Ammonia Volatilization and Soil Ammonium and Nitrate Contents

Modulating effects of humic acids on genotoxicity induced by water disinfectants in Cyprinus carpio

The use of chlorinated disinfectants during drinking-water production has been shown to generate halogenated compounds as a result of interactions of humic acids with chlorine. Such chlorinated by-products have been shown to induce genotoxic effects and consumption of chlorinated drinking-water has been correlated with increased risk for cancer induction in human populations. The aim of this work was to test the potential genotoxic effects on circulating erythrocytes of the fish Cyprinus carpio exposed in vivo to well-waters disinfected with sodium hypochlorite (NaClO), chlorine dioxide (ClO 2) or peracetic acid (CH 3COO 2H, PAA), in the absence or presence of standard humic acids (HA). The effects were measured by use of the micronucleus (MN) and the single-cell gel electrophoresis (Comet) assays at different sampling times after a 3-day exposure period. The exposure to chlorine disinfectants without the addition of HA produced a clear toxic effect. Significant cytogenetic damage (i.e. MN induction) was detected in fish populations exposed to both NaClO and ClO 2 with humic acids. In the Comet assay, a significant decrease of DNA migration was observed in erythrocytes of specimens after exposure to NaClO-disinfected water without HA. No effects were observed in any other experimental condition.

Solubility and dissociation of lignitic humic acids in water suspension

Behavior of humic acids (HAs) extracted from lignite in water suspension was studied by means of potentiometry. Although humic acids are operationally defined as that fraction of humic substances, which is not soluble under acidic conditions, it does not mean that solid preparation easily dissolves in water. Presented results suggest that dissolving of solid humic acids in water environment is more complex than conventional solubility behaviour of sparingly soluble solids. Multi-step mechanism of solid humic acids interaction with water, including partial equilibrium dissolution as well as direct equilibrium dissociation from the solid state, was proposed and proved experimentally. Only very small part of solid humic acids can be dissolved in water and not giving necessarily saturation at the same time. In contrast to common sparingly soluble solids, solid humic phase thus possesses non-constant chemical potential even under constant temperature and pressure and its activity does not equal to unity, in general.

Sorption of humic acid on zeolitic tuff: a preliminary investigation

This work involves a study of the interaction of humic acid (HA) with zeolitic (phillipsite+chabazite) Neapolitan yellow tuff (NYT). HA sorption isotherms were carried out on untreated as well as on Li +-, Na +-, K +-, NH 4 +-, Ca 2+-, Mg 2+-, or Ba 2+-enriched samples. Except for the Li-enriched sample, Langmuir sorption curves fitted the experimental data, allowing the calculation of the maximum HA sorbable amount, Q max, and the affinity constant between the sorbate and the sorbent, k. The Q max for the untreated sample was 8512±265 mg kg −1, with k=10.8±1.4 l kg −1. The experimental amounts of HA taken up by the Li-enriched sample were very small (183 to 2322 mg kg −1) and too scattered to be consistently fitted by any significant equation. For other cation enriched-samples, the HA- Q max amounts ranged from 6583±205 mg kg −1 for the K-treated tuff to 22 029±1065 mg kg −1 for the Mg-treated tuff, whereas the k values ranged from 8.0±1.7 l kg −1 for the Na-treated tuff to 81.4±17.5 l kg −1 for the Ba-treated tuff. The tuff samples enriched by divalent cations took up HA in amounts larger than those observed for the untreated sample; the opposite was true for the monovalent cation-enriched samples. The HA sorption curves on monovalent cation-enriched tuff were scarcely different, within experimental variance, from those observed for the untreated sample. On the contrary, both the Q max and the k values calculated for the HA sorption on the divalent cation-enriched samples were widely and significantly larger than those of the untreated sample, with the highest Q max for Mg- and Ca-enriched sample, and the highest k value for the Ba-enriched one. The results demonstrate that enrichment by divalent cations enhances the ability of Neapolitan yellow tuff to take up humic acid, whereas enrichment by monovalent cations reduces it; the results also show that humic acid sorption on tuff must be regarded as a complex phenomenon, occurring as a compromise between the ability of the cations to form stable bridges with the organic matter, and, on the other hand, their specific selective sorption by the tuff.

Evaluation of humic acid, chromium (VI) and TiO2 ternary system in relation to adsorptive interactions

Batch adsorption studies were carried out for the assessment of the adsorptive interactions of the system composed of humic acid, Cr(VI) and TiO2. These were preceded by a thorough investigation of the effect of the chromium ion concentration on the adsorption of humic acid onto TiO2. The adsorption equilibrium of total chromium, humic acid, and titanium dioxide in water were examined separately and in all combinations in order to distinguish the effects based on the interaction of the components. The adsorption data for the binary system as well as the ternary system were modeled with a simple Freundlich model and the model parameters were compared in terms of Cr(VI) and humic acid as expressed by Color436 (color forming moieties) and UV254 (UV absorbing centers) parameters.In binary systems composed of Cr(VI) and TiO2 no direct relationship could be assessed between adsorption capacity values (KF) and changes in chromium ion concentration. Chromium ion and humic acid interactions were followed by UV-Vis spectra. A minor change irrespective of added chromium ion concentration was observed for Color436 and UV254 parameters of humic acid (<5%). However, a significant alteration was observed at 365nm wavelength indicating the formation of chromate esters. In ternary systems comprising humic acid, Cr(VI) and TiO2, increasing Cr(VI) concentration five-fold did not cause drastic changes in the adsorption capacity values in terms of Cr(VI) concentration. On the other hand, the adsorption capacity values for color forming moieties as well as for UV absorbing centers of humic acid exhibited a decreasing trend with respect to increasing chromium ion concentration.

Sorption of natural organic matter fractions to goethite (α-FeOOH): effect of chemical composition as revealed by liquid-state 13C NMR and wet-chemical analysis

In order to quantify the potential influence of the chemical composition of natural organic matter (NOM) on the extent of its sorption to mineral surfaces, I compared the interaction with synthetic goethite (α-FeOOH) of 18 different NOM (hydrophilic and hydrophobic fractions, fulvic and humic acids) samples from soil and terrestrial surface waters. The chemical composition of NOM was characterised by elemental analysis, titration of acidity, wet chemical analyses of lignin and carbohydrate constituents, and liquid-state 13C NMR spectroscopy. The proportions of resonances due to carboxyl C ranged from 7 to 21% and signals for total aromatic C varied from 0 to 38%. Signals due to O,N-alkyl C comprised 5–65% of the spectral area. The sorption of all tested NOM was adequately described by the Langmuir model. In general, hydrophobic fractions and fulvic and humic acids rich in carboxyl and aromatic C, probably derived from lignin, sorbed much more strongly to goethite than the hydrophilic fractions which were characterised by high abundance of O,N-alkyl C, probably due to carbohydrates, and low abundance of aromatic C. A sample of fulvic acids rich in alkyl C sorbed more weakly than samples rich in aromatic C. Consequently, the strong sorption of the hydrophobic fractions and fulvic acids seemed to be caused by the presence of aromatic structures. Within the groups of samples, however, the major determinant of the extent of the sorption proved to be acidic groups, as revealed by the close relationship between maximum sorption and total acidity and the content of carboxyl C. The maximum sorption of hydrophobic, fulvic and humic acids was inversely related to the ratio of aromatic to carboxyl C, which suggests that the number (and probably the position) of acidic groups attached to aromatics controls the interactions of hydrophobic, fulvic and humic acids with goethite.

On the study of Th(IV)-humic acid interactions by competition sorption studies with silica and determination of global interaction constants

Summary The influence of humic acids (HA) on the retention of thorium (IV) onto the surface of silica colloids is investigated. Thorium is considered as an analogue of tetravalent actinides (U, Np, Pu), except for the fact that it has no f electrons. Silica (SiO2) is chosen as a model surface because it is a component of many minerals and because of its weak HA sorption properties. Retention experiments are performed by batch procedure at constant ionic strength (I = 0.1M NaClO4), at various pH (2 to 9) and HA concentrations (1–100mg/L). The sorption of Th(IV) onto colloidal amorphous silica is characterised using a surface complexation model. The ternary system (i.e. HA-Th-Silica) clearly shows the influence of HA on Th(IV) retention. This can lead to a strong reduction of the amount of Th(IV) sorbed onto silica in the presence of HA compared to silica colloids without HA, due to a predominant part of thorium present in solution as humic complexes. In a pH range where no organic coating onto silica occurs, there is a competitive reaction between Th(IV) sorption onto the silica surface and onto HA reactive functional groups. In this case, Schubert´s method is applied to obtain a global interaction constant for the Th(IV)-HA system. The large interaction constant values indicate a strong affinity of HA for Th(IV).

Influence of pH and ionic strength on removal processes of a sedimentary humic acid in a suspension of vermiculite

Understanding the interactions of humic acids and clay minerals is important for modeling the geochemical fate and transport of nutrients and pollutants in soil and natural waters upon changes of environmental parameters such as ionic strength and pH. This paper describes the adsorption/precipitation properties of a sedimentary humic acid under different conditions of pH and ionic strength in presence of the clay mineral vermiculite. The clay suspension was prepared to have a distribution of grain size composed mainly of particles <63 μm, which is believed to play a major role on transport and fate of adsorbed materials in aquatic environments. The pHs studied were 5.0, 6.0 and 7.0 (±0.1 pH units), in ionic medium of 0.002 and 0.020 mol l−1 KNO3, using initial HA concentrations from 0 to 100 mg l−1. The maximum removal of HA from solution occurred at pH 5.0 in medium of 0.020 mol l−1 KNO3. This removal is mostly due to precipitation, which occurred at similar rates in both ionic strength, so that the additional HA removal at higher ionic strength (0.020 mol l−1 KNO3) was attributed to adsorption. Adsorption processes intensified at higher ionic strength suggest the occurrence of chemical interactions between the interfaces since under these conditions the electrostatic interactions are minimized. A similar effect was observed at pH 6.0, but in this case adsorption prevailed as the removal mechanism in medium of 0.020 mol l−1 KNO3. At pH 7, adsorption is the predominant process removing HA from solution, with increase of adsorption upon decreasing the ionic strength, suggesting that electrostatic attractions play the major role in the adsorption mechanism under these conditions. Comparison of the results obtained using a re-precipitated commercial HA with low N content suggested that the presence of positively charged amine groups increase the adsorption and decrease desorption.

Supramolecular interactions of humic acids with organic and inorganic xenobiotics studied by capillary electrophoresis

Methodology based on capillary electrophoresis (CE) to study humic acids (HAs)–xenobiotics interactions is proposed. The interactions of HAs with organic and inorganic xenobiotics like paraquat, diquat, p,p ′-DDE, p,p ′-DDT, potassium ferrocyanide, potassium ferricyanide, chloride, 4-nitrocatechol and other organic compounds were studied. They were found to be of different kind depending on the structure of the xenobiotic molecule and on its charge (neutral, positive or negative). Ion binding, hydrogen bonding, van der Waals forces, ligand exchange, hydrophobic and hydrophilic adsorption, charge-transfer complexes and sequestration are some of the different mechanisms proposed to bind inorganic and organic compounds to HAs. It was also observed that some of the pollutants are strongly complexed (bound) only with some of the HA fractions forming quite stable entities of supramolecular kind, which can migrate independently. In addition, the stability constant of HA–Cl (negatively charged species) was estimated to be log k=3.1±0.95. In order to explain the interaction between negatively charged HAs and inorganic anions (like Cl −, [Fe(CN) 6] 3− and [Fe(CN) 6] 4−), it is proposed that macropolycyclic polyamine structures are present in HA supramolecules, and that they are responsible for such strong binding.