Influence of humic substances on sorption and methylation processes of inorganic- and organo-tin species

The influence of humic substances on sorption and methylation processes for inorganic- and organotin species is presented. Four sediment samples from different locations of the Rivers Elbe, Mulde and Spittelwasser, Germany, with different organotin and humic contents were selected to extract the humic and fulvic acids. The various fractions—the original sediment, the humic acid, the fulvic acid and the residual sediment—were analysed for their organotin content. The individual buyltin species show quite different distribution patterns. Monobutyltin is found mostly associated with humic acids. Dibutyltin shows a nonunique behaviour. At low total organotin content, dibutyltin is found bonded to humic and fulvic acids, whereas at high organotin content dibutyltin is distributed more with the residual sediment. Most of the tributyltin remains in the sediment unextracted; only small quantities of it are in the fulvic acid fraction. Tetrabutyltin is only in the humic acid fraction when it binds to humic matter; it mostly remains in the sediment. General observations indicate that ionic butyltin species bind to fulvic acids whereas the non-polar tetrabutyltin is not found in the fulvic acid fractions in any of the samples. The appearance of monomethyl- and dimethyl-tin species in the humic and fulvic acid fractions after the alkaline extraction was surprising. There is a correlation between the humic content of the sample and the formation of methyltin species. Evidence is provided by experiments that humic substances act as methylation agents.     

PHOTOPHYSICS OF A WELL CHARACTERIZED HUMIC SUBSTANCE

Abstract— The transient absorbance observed after flash excitation of a well characterized humic substance ("Armadale" fulvic acid) may be analyzed into three components. Two arise promptly (< 20 ps) and are assigned to a solvated electron (on the basis of decay and quenching) and its corresponding radical cation (on the basis of common origin). The third is a broad featureless band which arises only after a few ns and remains for long times. It is suggested to include triplets that may sensitize singlet oxygen.     

Influence of Pb(II) on the radical properties of humic substances and model compounds

The influence of Pb(II) ions on the properties of the free radicals formed in humic acids and fulvic acids was investigated by electron paramagnetic resonance spectroscopy. It is shown that, in both humic acid and fulvic acid, Pb(II) ions shift the radical formation equilibrium by increasing the concentration of stable radicals. Moreover, in both humic acid and fulvic acid, Pb(II) ions cause a characteristic lowering of the stable radicals' g-values to g = 2.0010, which is below the free electron g-value. This effect is unique for Pb ions and is not observed with other dications. Gallic acid (3,4,5-trihydroxybenzoic acid) and tannic acid are shown to be appropriate models for the free radical properties, i.e., g-values, Pb effect, pH dependence, of humic and fulvic acid, respectively. On the basis of density functional theory calculations for the model system (gallic acid-Pb), the observed characteristic g-value reduction upon Pb binding is attributed to the delocalization of the unpaired spin density onto the Pb atom. The present data reveal a novel environmental role of Pb(II) ions on the formation and stabilization of free radicals in natural organic matter.     

2H NMR study of dynamics of benzene-d6 interacting with humic and fulvic acids

Samples of three humic acids and one fulvic acid with 1% loading of benzene-d(6) in sealed glass tubes have been studied with solid-state deuterium quadrupole-echo nuclear magnetic resonance spectroscopy. Calculated spectra combining three motional models, two isotropic models and a third more restricted small-angle wobble (SAW) motional model, are fit to the experimental spectra. One isotropic motion (ISO(v)) is assigned to vaporous benzene-d(6) due to the small line width, short T(1), and the loss of this component by about -25 °C when the temperature is lowered. The remaining two motional components, ISO(s) and SAW, are sorbed by the humic or fulvic acid. Benzene-d(6) slowly interacts with the humic substances, progressively filling SAW sites as ISO(s) motion diminishes. Both the sorption and increase in percentage of SAW motion are for the most part complete within 200 days but continue to a lesser extent over a period of a few years. For the SAW motion there are at least two and most likely a series of T(1) values, indicating more than one adsorption environment. Enthalpies of sorption, obtained from application of the van't Hoff equation to the percentages of the different motional models derived from a series of variable temperature spectra, are comparable in magnitude to the enthalpy of vaporization of benzene. In Leonardite humic acid, ΔH and ΔS for the ISO(s) to SAW transition change from positive to negative values with age, implying a transition in the driving force from an entropic effect associated with expansion and deformation in the molecular structure of the humic substance to accommodate benzene-d(6) to an enthalpic effect of strong benzene-d(6)-humic substance interactions. In contrast, at advanced ages, Suwannee River humic and fulvic acids have small positive or near zero ΔH and positive ΔS for the ISO(s) to SAW transition.     

Separation and determination of dissolved and particulate humic substances in river water

Distribution of humic and fulvic acids in participate or dissolved form is studied by using simple leaching and sorption techniques. After filtration of water sample (100–200 ml), the filter along with suspended particles is treated with 5 ml of chloroform and 3 ml of 0.1 mol/l sodium hydroxide solution. The filter dissolves completely in the organic phase, while the suspended particles remain in the aqueous phase enabling a leaching of humic substances. The leaching is repeated once more with 2 ml of 0.1 mol/l sodium hydroxide solution. The humic and fulvic acids in the combined solution are fractionated at pH l by filtration, where the membrane filter is preliminarily coated with sodium dodecyl sulfate. On the other hand, dissolved humic substances are concentrated from a 50-ml filtered sample by sorption on a DEAE-cellulose column. They are desorbed with 5 ml of 0.1 mol/l sodium hydroxide solution and fractionated at pH 1. The spectrophotometric analysis of river water reveals that fulvic acid is predominant in suspended particles as well as in filtered samples. The concentration of dissolved humic and fulvic acids is approximately ten times that of suspended particles.     

胺基修饰大孔树脂对腐殖酸的吸附研究

研究了腐殖酸在胺基修饰大孔树脂D-301上的吸附行为,并与胺基修饰超高交联树脂NDA-99和大孔非极性树脂XAD-4作对比,结果表明,带有弱碱性基团的大孔亲水性树脂D-301对腐殖酸的吸附效果优于XAD-4和NDA-99,这主要得益于D-301树脂大孔结构和表面胺基修饰.探讨了溶液pH值和重金属离子对D-301树脂吸附腐殖酸的影响,并对作用机理进行了初步探讨.     

Electron Spin Resonance Analysis of Semiquinone Free Radicals of Aquatic and Soil Fulvic and Humic Acids

Abstract

We analyzed the solid state and aqueous solution electron spin resonance (esr) spectra of Oyster River and Podzol soil fulvic and humic acids. Because the aqueous solution esr spectra mimic the behavior of the model compound para-benzosemiquinone, we conclude that semiquinone free radicals predominate in fulvic acid. In addition a decrease in spin concentration at a potential of 0.20 volts (vs. SCE) demonstrates that the semiquinone radicals are at least partially responsible for the reducing capability of humic materials. From the above results we devised a quantitative semiquinone analysis for humic materials.     

土壤腐殖质各组分红外光谱研究

土壤腐殖质是土壤中所特有的一类特殊的高分子化合物,具有重要的肥力和环境调节功能。其中胡敏素的提取和纯化很困难,从而限制了对其性质和结构的研究。为揭示胡敏素的结构性质,本研究按Pallo分组,将胡敏酸(HA)分为焦磷酸钠提取的胡敏酸(HAP)、氢氧化钠提取的胡敏酸(HAS);富里酸(FA)分为焦磷酸钠提取的富里酸(FAP)和氢氧化钠提取的富里酸(FAS);胡敏素(HM)分为铁结合胡敏素(HMi)、粘粒结合胡敏素(HMc)和不溶性胡敏素(HMr)三个组分,采用红外光谱法对黑土、草甸土以及黑土底土加入大量玉米秸秆培养后腐殖质各组分的结构特征进行研究。腐殖质各组分按Pallo法分组。结果表明:铁结合胡敏素(HMi)、粘粒结合胡敏素(HMc)与胡敏酸(HA)、富里酸(FA)具有相似的光谱特征,但存在明显差异。黑土、草甸土中HMi和HMc的脂族性强于HA和FA;HMi与HMc相比,HMi具有较高的脂族性。黑土中氢氧化钠提取的胡敏酸(HAS)的脂族性强于焦磷酸钠提取的胡敏酸(HAP);NaOH提取的富里酸(FAS)的脂族性强于Na4P2O7提取的富里酸(FAP)。草甸土中HAP的脂族结构较多,而HAS脂族结构相对较少。在培养土中,新形成的FA脂族性强于HA、HMi和HMc组分。新形成的HMc脂族性强于HMi和HMc的脂族性强于HAP,而弱于HAS。     

Calcium binding by fulvic acids studied by an ion selective electrode an ultrafiltration method

The interaction between Ca(2+) and two well-characterized fulvic acids (Armadale and Laurentide FA) has been studied at 0.100 and 0.010M sodium nitrate using a fixed concentration of fulvic acid (100 ppm) and varying amounts of calcium (0.005-0.020 mmoles). Free calcium concentration was determined by in situ measurements employing a calcium electrode. For Armadale FA, free calcium was additionally determined via an ultrafiltration technique followed by atomic absorption measurements. For both fulvic acids, Ca(2+) binding was observed to be decreased by an increase in the ionic strength of the system. At the lower ionic strength the tendency for binding is dependent on the fulvic acid-to-metal ratio while at the higher ionic strength, the binding is insensitive to changes in the fulvic acid-to-metal ratio (an observation corroborating the contention that calcium binding to humic substances is primarily electrostatic). Comparison of the computed overall complex formation functions shows that values obtained from the ultrafiltration method were higher than those obtained using the calcium electrode. The binding of calcium was similar for the two fulvic acids.     

High-performance liquid chromatographic determination of humic acid in environmental samples at the nanogram level using fluorescence detection

A high-performance liquid chromatographic method for the determination of humic acid in environmental samples is presented. The humic acid is chromatographed as its sodium or calcium complex, eluting as a single, sharp peak. Coral skeletal matter, sea water, river water, soils and plant matter were successfully analysed. The detection limit is 15 ng. The relative standard deviation for a coral skeletal sample is 1.9%. Unusual chromatographic properties such as the occurrence of peak broadening with increased concentration appear to be due to a slow change in the equilibrium composition of humic acid. In solution, fulvic acid showed similar properties to humic acid.     

The methylation of inorganic tin by humic materials in an aquatic environment

This paper presents a study of methylation of inorganic tin (SnCl₄·5H₂O) by humic materials (humic and fulvic acids) isolated from the sediment of Tianjin Harbor, Tianjin, China, and the effects of pH, salinity, and the concentration of inorganic tin on the production of methyltin were investigated. These humic materials could methylate inorganic tin, and the methyltin product was mainly monomethyltin. Low molecular weight compounds of the humus fraction (i.e. fulvic acid) were more active in the methylation, which could be facilitated by salinity and affected by pH.     

Flocculation of humic substances with metal ions as followed by capillary zone electrophoresis

Humic and fulvic acids from various sources have been shown to give different electropherograms by capillary zone electrophoresis (CZE), depending on the pH of the electrolyte. This CZE work is extended here through investigations involving the titration of humic and fulvic acids with Fe(III) and Cu(II) cations. As increasing amounts of these cations were added to the humic substances (HUS), flocculation of metal-humic complexes occurred. This is believed to be caused by binding of the metal cations with negative carboxyl and phenolic sites on the HUS, resulting in a decrease of the repulsive forces that keep the HUS in a conformation more suitable for water solubility. The flocculated complexes were separated from the supernatant by centrifugation, and the supernatants were characterized as to total organic carbon (TOC) content, molecular weight (MW) using gel permeation chromatography, and average electrophoretic mobility (AEM) using CZE. The extent of flocculation correlated with both TOC and quantitative CZE measurements. The MW of the HUS remaining in solution actually decreased, presumably because of precipitation of larger molecules as they became insoluble because of reactions with the metals. Humic acids showed total precipitation of TOC with both metals at a concentration equivalent to their measured acidity. CZE demonstrated that certain fulvic acid fractions (low molecular weight phenolic acids) remained in solution even at high metal concentrations. In summary, changes in electrophoretic behavior of the soluble HUS could be related to changes in charge-to-mass ratios (charge densities) of both humic and fulvic acids with increasing metal cation concentration (neutralization). The copper treated HUS showed changes in their electrophoretic behavior even at low metal concentrations before flocculation, whereas the iron treated HUS flocculated uniformally over the range of added iron without significant changes in AEM. Thus these changes in CZE patterns illustrate different specific binding sites of the HUS for each metal.     

Flocculation of humic substances with metal ions as followed by capillary zone electrophoresis

Humic and fulvic acids from various sources have been shown to give different electropherograms by capillary zone electrophoresis (CZE), depending on the pH of the electrolyte. This CZE work is extended here through investigations involving the titration of humic and fulvic acids with Fe(III) and Cu(II) cations. As increasing amounts of these cations were added to the humic substances (HUS), flocculation of metal-humic complexes occurred. This is believed to be caused by binding of the metal cations with negative carboxyl and phenolic sites on the HUS, resulting in a decrease of the repulsive forces that keep the HUS in a conformation more suitable for water solubility. The flocculated complexes were separated from the supernatant by centrifugation, and the supernatants were characterized as to total organic carbon (TOC) content, molecular weight (MW) using gel permeation chromatography, and average electrophoretic mobility (AEM) using CZE. The extent of flocculation correlated with both TOC and quantitative CZE measurements. The MW of the HUS remaining in solution actually decreased, presumably because of precipitation of larger molecules as they became insoluble because of reactions with the metals. Humic acids showed total precipitation of TOC with both metals at a concentration equivalent to their measured acidity. CZE demonstrated that certain fulvic acid fractions (low molecular weight phenolic acids) remained in solution even at high metal concentrations. In summary, changes in electrophoretic behavior of the soluble HUS could be related to changes in charge-to-mass ratios (charge densities) of both humic and fulvic acids with increasing metal cation concentration (neutralization). The copper treated HUS showed changes in their electrophoretic behavior even at low metal concentrations before flocculation, whereas the iron treated HUS flocculated uniformally over the range of added iron without significant changes in AEM. Thus these changes in CZE patterns illustrate different specific binding sites of the HUS for each metal.     

The analytical concentration of humic substances from natural waters

The thermodynamics of the adsorption of humic and fulvic acids on the macroreticular polystyrene resin Amberlite XAD-2 have been investigated with a view to optimizing the conditions for its application to the analytical concentration of these compounds. Under the optimal conditions, recoveries of humic and fulvic acids of above 92 and 75%, respectively, were achieved. It has been shown that these compounds can be fractionated on a molecular weight basis during the desorption stage by serial elution at selected pH values.     

Spurenanalyse von huminstoffen im trinkwasser: The d.c. polarographic determination of traces of humic substances in potable waters

(The d.c. polarographic determination of traces of humic substances in potable waters) The inhibiting effect of a tri-n-butylphosphate layer adsorbed at the mercury drop on the polarographic wave of copper(II) is reduced by humic substances. This effect can be utilized to determine humic substances in the range 0.05–1 mg l^-1. The standard substance used was isolated from peaty water. Humic and fulvic acids are not differentiated but amino acids, peptides and polyhydroxy compounds do not interfere.     

Simultaneous spectrophotometric determination of humic acid and iron in water

A simple and rapid method for the determination of humic acid and iron in solution is described. Two absorbance measurements are required, one on an untreated sample aliquot, and the other on an aliquot treated to enhance iron absorptivity. The method requires sample volumes of less than 15 ml and is sensitive enough for direct application to most natural waters. Limits of detection for each component vary with concentration of the other, but 0.01 mg 1^?1 for humic acid and 0.04 μM for iron can be achieved. For six natural waters, determinations based on independent calibration curves for each component gave results 6–40$ higher for iron, and 6–29% higher for humic acid, than results obtained by the proposed method. The interference of fulvic acid and the use of different humic acid standards are examined.     

Use of the cation exchange equilibrium method for the determination of stability constants of Co(II) with soil humic and fulvic acids

The stability constants for tracer concentrations of Co(II) complexes with both the red earth humic and fulvic acids were determined at pH 5.9 and ionic strength 0.010 mol/l by using theArdakani-Stevenson cation exchange equilibrium method and the radiotracer⁶⁰Co. It was found that the 1:1 complexes of Co(II) with the red earth humic and fulvic acids were formed and that the average values of logβ (stability constant) of humic and fulvic acid complexes were 5.76±0.19 and 4.42±0.03, respectively.     

Iodine emission in the presence of humic substances at the water's surface

Humic substances that preferentially adsorb at the air/water interfaces of water or aerosols consist of both fulvic and humic acid. To investigate the chemical reactivity for the heterogeneous reaction of gaseous ozone, O(3)(g), with aqueous iodide, I(-)(aq), in the presence of standard fulvic acid, humic acid, or alcohol, cavity ring-down spectroscopy was used to detect gaseous products, iodine, I(2)(g) and an iodine monoxide radical, IO(g). Fulvic acid enhanced the I(2)(g) production yield, but not the IO(g) yield. Humic acid, n-hexanol, n-heptanol, and n-octanol did not affect the yields of I(2)(g) or IO(g). We can infer that the carboxylic group contained in fulvic acid promotes the I(2)(g) emission by supplying the requisite interfacial protons more efficiently than water on its surface.     

Sorption and desorption characteristics of Eu(III) on red earth

The batch method and the column method were simultaneously employed to study the sorption and desorption of Eu(III) on red earth as a function of pH (4.6–6), the presence of a well-characterized fulvic acid (FA) and the iron oxides content of red earth. The results from both methods were consistent qualitatively. The Eu(III) sorption showed significant dependences on pH and FA, the sorption was increased with increasing pH and by addition of FA to the solutions, while the iron oxides content of the red earth had a negative contribution to the sorption of Eu(III). Additionally, the sorption-desorption hysteresis of Eu(III) on red earth occurred at a pH range of 4.6–6. Therefore, the humic substance and high pH have a great tendency to immobilize Eu(III) on red earth.     

Adsorbability and photocatalytic degradability of humic substances in water on Ti-modified silica

From the viewpoint of development of a removal agent for humic substances, we prepared Ti-modified silica gel, SiO2-Ti, from titanium alkoxide and microsized silica gel. The prepared silica agent was investigated in adsorption and photocatalytic degradation of humic substances in water. In these experiments, four humic substances, commercially available Wako humic acid (Wako-HA), Nordic aquatic humic acid (Nordic-HA), Nordic aquatic fulvic acid (Nordic-FA), and Suwannee river fulvic acid (Suwannee-FA), were used, and Freundlich constants (KF and 1/n) and photodegradation rates were evaluated. Wako-HA, which has the highest aromaticity ratio [Ar-OH]/[COOH] and molecular weight, had the highest adsorbability (KF=17.5 (mg/g)(L/mg)(1/n), 1/n=0.67) but the lowest photodegradability (<80%). On the other hand, Suwannee-FA, which has the lowest aromaticity, [Ar-OH]/[COOH] ratio, and molecular weight, afforded lesser adsorbability (KF=7.1 (mg/g)(L/mg)(1/n), 1/n=0.39) but the highest photodegradability (>99%). Nordic-HA and Nordic-FA afforded adsorbabilities similar to that for Suwannee-FA, and medium photodegradabilities between those for Wako-HA and Suwannee-FA. Adsorption and photodegradation capacities of SiO2-Ti were improved with increased Ti content and phosphorescence emission amount, respectively. From XRD analysis, we found that the structure of anatase-type TiO2 features the Ti modifiers of SiO2-Ti. Therefore, humic substance molecules effectively interact with the Ti modifiers and are decomposed by OH radicals generated in situ. We hope that SiO2-Ti will be used as a photodegradation catalyst in water purification plants.