Showing papers on "Humic acid published in 1994"

Molecular weight, polydispersity, and spectroscopic properties of aquatic humic substances.

Abstract: The number- and weight-averaged molecular weights of a number of aquatic fulvic acids, a commercial humic acid, and unfractionated organic matter from four natural water samples were measured by high-pressure size exclusion chromatography (HPSEC). Molecular weights determined in this manner compared favorably with those values reported in the literature. Both recent literature values and our data indicate that these substances are smaller and less polydisperse than previously believed. Moreover, the molecular weights of the organic matter from three of the four natural water samples compared favorably to the fulvic acid samples extracted from similar environments

Soil structure and carbon cycling

Abstract: Samples from the surface horizons of six virgin soils were collected and separated into density fractions. Based on the spatial distribution of organic materials within the mineral matrix of soil, the soil organic matter (SOM) contained in various density fractions was classified as: (a) free particulate OM, (b) occluded particulate OM, and (c) colloidal or clay-associated OM. The compositional differences noted among these three components of SOM were used to describe the changes that OM undergoes during decomposition when it enters the soil, is enveloped in aggregates and eventually is incorporated into microbial biomass and metabolites and associated with clay minerals. The occluded organic materials, released as a result of aggregate disruption, were in various stages of decomposition and had different degrees of association with mineral particles. Changes in the degree of association of occluded organic materials and mineral particles with decomposition are discussed and form the basis of a model which illustrates the simultaneous dynamics of microaggregates and their organic cores. This model indicates a major role for carbohydrate-rich plant debris in formation and stabilization of microaggregates.

Interaction of hydrophobic organic compounds with mineral-bound humic substances

Abstract: The sorption of hydrophobic organic compounds (HOC) on mineral-associated peat humic acid (PHA) was evaluated under different pH and electrolyte regimes. Relative size distribution measurements indicated that PHA was [open quotes]coiled[close quotes] in solution at high ionic strength (I) and elongated at low I. The sorption of PHA to hematite and kaolinite varied with I and electrolyte cation, suggesting that the configuration of the humic acid in solution influenced its structure on the mineral surface. The sorption maxima for PHA on kaolinite indicated that PHA occupies twice the mineral surface area at low I (0.005) as that observed at high I (0.1). HOC sorption to mineral-bound PHA in Na[sup +] electrolyte was greater at lower I, indicating that humate structure was a plausible determinant of HOC sorption. Freundlich isotherms of dibenzothiophene on the PHA-coated kaolinite did not display unit slope, regardless of pH, I, or cation. Carbazole and anthracene displayed competitive behavior for sorption onto PHA-coated kaolinite. Collectively, the experimental observations indicate that hydrophobic adsorption rather than phase partitioning was the dominant mode of HOC binding. 70 refs., 8 figs., 1 tab.

Micro-organization in dissolved humic acids.

Abstract: The proposed pseudomicellar character of five dissolved humic acids has been investigated by monitoring the fluorescence behavior of a pyrene probe added to the solutions. Fluorescence quenching by bromide in the presence of these humic acids was found to be consistent with a hydrophobic microenvironment. The presence of metal ions, with either quenching or nonquenching counterions, increased the pyrene fluorescence of several of the humic acids. The results indicate that cations have the property of increasing intramolecular micellization in these humic acids, thereby minimizing quenching interactions. The proposed mechanism involves enhanced shielding of the probe rather than its expulsion into the aqueous bulk as has been suggested previously

A humic acid improves growth of tomato seedling in solution culture

Abstract: The effects of humic acid (HA) on nutrient accumulation and growth of tomato seedlings were evaluated in a solution of limited nutrient availability in a greenhouse. HA additions were made to the nutrient solution at rates of 0, 640, 1280, or 2560 mg/L. The addition of 1280 mg/L HA produced significant increases in shoot accumulation of P, K, Ca, Mg, Fe, Mn, and Zn as well as increased accumulation of N, Ca, Fe, Zn, and Cu in roots. Fresh and dry weights of roots were also increased, However, on comparing nutrient accumulation in plants treated with 1280 mg/L HA and those given an additional supply of nutrients equivalent to those supplied by HA at the 1280 mg/L rate, shoots accumulated more N, P, K, Fe, and Cu, while roots accumulated more K and Ca. Therefore these increases do not appear to be associated with nutrients contained in HA. Eectrolyte leakage, as an indication of membrane permeability, did not differ as a consequence of HA additions. However, electrolyte leakage correlated positivel...

Efeito de doses crescentes de lodo de esgoto sobre fração da matéria orgânica e CTC de um latossolo cultivado com cana-de-açúgar

Abstract: A Typic Haplorthox in Guariba county, Sao Paulo State, Brazil, was limed and amended with mineral fertilizers or sewage sledge (4, 8, 16, or 32 t/ha) and cropped with sugar cane. Treatments with sewage sledge received potassium, as potassium chloride, to equalize the content of this element in all the fertilized treatments. Soil samples were collected soon before fertilization and at 77, 105, 140 168, 196, 230, and 473 days after planting the sugarcane. The samples were air dried and analysed for cation exchange capacity (CEC), total organic carbon, fulvic acid, humic acid and humin. Sewage sludge at 32 t/ha significantly increased total organic carbon and CEC. Sewage sludge organic carbon was quickly transformed into soil humin carbon, which was the predominant fraction in soil organic matter Humin was the fraction of the organic matter that more closely correlated with the soil CEC (r=0.59 *** ). The soil total organic carbon/soil humin carbon ratio decreased from planting to 230 days, faster in the first 140 days, an increased after sugar-cane harvesting. The soil humin carbon/soil humic matter carbon ratio showed a trend similar to that of the sugarcane plant biomass production; the soil organic fulvic acid/soil organic humic carbon ratio decreased in the first stage of the experiment and then tended to increase

Complexation of the Uranyl Ion with Aquatic Humic Acid

Abstract: The complexation of the uranyl(VI) ion with aquatic humic acid from Gorleben groundwater (Gohy-573) is studied in 0.1 M NaClO[sub 4] at pH 4 under argon atmosphere. The concentration range investigated is from 1 x 10[sup -7] to 1 x 10[sup -5] mol/l for the uranyl ion and from 1 x 10[sup -6] to 1.12 x 10[sup -5] mol/l for the humic acid. Three different experimental methods are applied to separate the uncomplexed uranyl ion from the uranyl humate complex, using differences of the two species in size by ultrafiltration at the pore size of about 1 nm, in charge by anion exchange separation and in spectroscopic properties by time resolved laser fluorescence spectroscopy (TRLFS). No reduction of U(VI) to U(IV) is observed in the course of the humate complexation process. The experimental results confirm that the prevailing complexation reaction is charge neutralization of the UO[sup 2+][sub 2] ion with two proton exchanging sites of humic acid. At pH 4 in 0.1 M NaClO[sub 4], where the hydrolysis of the uranyl ion appears negligible, the fraction of proton exchanging sites of the humic acid that can be occupied by the uranyl ion (called the loading capacity (LC) of the uranyl ion) is determined to be 0.185[+-]0.003. The complexation constant evaluated by taking the loading capacity into account is found to be log[beta] = 6.16[+-]0.13, which is a grand average of all values determined by the three experimental procedures under consideration. This value is valid for the humate complexation of the non-hydrolyzed uranyl ion, being independent of pH and ionic strength. (orig.)

Role of Soil Organic Acids in Mineral Weathering Processes

Abstract: The soluble organic acids in soils consist largely of complex mixtures of polymeric compounds referred to collectively as fulvic and humic acids. These compounds are relatively refractory, and are broken down only slowly by microorganisms. Low-molecular-mass acids (e.g., acetic, oxalic, formic) exist in dynamic balance: they are rapidly produced and consumed by microorganisms. Their concentrations may be quite high where rapid decomposition of plant material is taking place, and in microenvironments adjacent to roots and fungal hyphae, but are generally low (typically less than 1 mM) in bulk soil solution. Concentrations of organic acids are generally highest in the organic layer at the top of the soil profile and decrease with depth. Particularly high concentrations of dissolved organic acids occur in peatlands and waterlogged soils.

Mechanism of Atrazine Sorption by Humic Acid: A Spectroscopic Study

Abstract: Ultraviolet-visible, Fourier transform infrared, and electron spin resonance spectroscopy were applied to samples of representative soil humic acids reacted with atrazine for 4 days at 25 o C under environmentally relevant conditions (concentration, 140 μmol L -1 ; pH 2-6.5). The spectra obtained by the three methods indicated that a charge-transfer mechanism was not operative in the atrazine-humic acid interaction. The FTIR spectra gave evidence instead for a hydrogen-bonding or proton-transfer mechanism, especially at pH<4. The UV-visible spectra showed in addition that at pH<5 humic acid enhanced the rate of hydroxyatrazine formation, especially for pH <3

Modeling Carbon Storage Profiles in Temperate Forest Humic Loamy Soils of France

Abstract: In southwest France, thick humic acid soils have developed from Quaternary silty alluvial deposits. The objective of this study was to determine if specific patterns of carbon profiles occurred in these soils in order to evaluate total carbon storage using mathematical modeling and laboratory analys

Enzyme-mediated coupling of 3,4-dichloroaniline and ferulic acid : a model for pollutant binding to humic materials

Abstract: To investigate the incorporation of chloroanilines into humic substances, the reaction of ferulic acid with three different chloroanilines in the presence of a laccase of the fungus Rhizoctonia praticola was investigated. Under the reaction conditions used, chloroanilines alone were not transformed by the laccase, but in the presence of ferulic acid they formed cross-coupling products. The reactivity of anilines decreased with increasing chlorine substitution on the ring. Two dimeric compounds were isolated from the reaction assay of ferulic acid alone. The dimers were found to have phenylcoumaran and lactone structures

Characterization of organic matter in a forest soil of coastal British Columbia by NMR and pyrolysis-field ionization mass spectrometry

Abstract: Organic matter in the soil profile under a young Douglas-fir stand in coastal British Columbia was characterized by examining intact samples of fresh litterfall and organic horizons (LF, H), and fractions (floatables, humic acid [HA], fulvic acid [FA], humin [HU]) from the three mineral horizons (Ae, Bm, BC). Some 30–40% of the carbon in the mineral horizons was found in poorly-decomposed plant material floatable in water, a fraction whose characteristics changed little with depth, and which contained over 1% Fe. The proportion of soil C in HA plus FA was approximately 8%, but the ratio of C in FA/HA increased with depth. Solid-state 13C NMR spectra of litterfall, LH and H samples showed effects of decomposition, in particular a decrease in 0-alkyl C from litterfall to LH to H, and degradation of resolution from LF to H. For the mineral soil fractions, both floatables and de-ashed HU (‘HUd’ prepared by HCl/HF treatment) indicated high levels of the original plant biopolymers, including a large alkyl component. Solution 13C spectra of the HAs from mineral horizons showed little difference with depth, except that peaks due to lignin were more pronounced for the Bm HA. The NMR spectra of FAs were high in 0-alkyl and carboxyl C. Pyrolysis-field ionization mass spectrometry confirmed and extended the results from NMR and chemical analyses, in particular demonstrating the accumulation of suberin in some fractions and the leaching and decomposition of lignin components with increasing depth in the mineral horizons. The general features of the HA, FA and HUd from this forest soil, and the effects of decomposition and pedogenesis were similar to those widely found for agricultural and forest soils. However, the accumulation of suberin, and the leaching and decomposition of lignin are particularly associated with forest soils. The low proportion of soil C in HA and FA, and the high proportion in poorly decomposed, iron-rich plant fragments suggest that decomposition is somewhat limited at this site, which is classified as having low fertility. The high accumulations of alkyl C from suberin may also indicate, or contribute to inhibition of decomposition.

Molybdenum Adsorption by Aluminum and Iron Oxides and Humic Acid

Abstract: It is hypothesized that soil adsorption properties can be estimated from contents and adsorption properties of individual soil components (additivity principle), if the data are consistent. Therefore, adsorption of molybdenum(VI) by synthetic aluminum oxide, ferrihydrite, goethite, extracted humic acid and a sandy soil sample was determined as a function of Mo concentration (0-1.2 mmol/L) and pH (3.5-8). For each pH and adsorbent, the Langmuir adsorption maximum (adsorption capacity) was calculated. For the oxides, plots of these capacities against pH resulted in adsorption envelopes exhibiting maxima at pH 4-5, i.e., near the pK a1 and pK a2 for molybdenum acid

Hydrogen-bonding interactions between the herbicide glyphosate and water-soluble humic substances

Abstract: In this study, infrared spectroscopy (IR) was used to investigate the mechanism of interaction betw~n the widely used herbicide Giyphosate (N-(phosphonomelhyJ) glycine) and a water-soluble humic add (HA) obtained from a purified Leonardite. Aliquols of the purified humic solution were set to pH 4, 5, and 6, and added with Glyphosate volumes correspond­ ing {o increasing percentages of lotal acidity of the water-soluble HA_ The IR spectra of the HA-Glyphosate complexes showed two bands at 1,168 and, ,090 cm -I for the stretchings of the P=O and P-O- bonds, respectively, as they appear in the spec­ trum of Glyphosate alone where the phosphono group is involved in hydrogen bondings occurring in Glyphosate dimers. Con­ versely, When the complex solutions were brought back to the starting pH levels (4, 5, and 6), the two IR bands of the phosphono group were shifted to higher frequencies (1,195 and 1,134 cm -\, respectively), suggesting that the P-O bonds were no longer involved io hydrogen bondings. This behaviour supports the occurrence of hydrogen bondings in the Glyphosate-HA complex. In fact, the lR band shift in the herbicide-HA complex indiCates that, because the Glyphosate mOlecules are distributed along the humic macromolecule, they are too far apart to form the Glyphosate dimers again when the initial conditions are restored. The hydrogen-honding interaction between HA and Glyphosale evidenced in this study may well be responsible for the trans· port of Glyphosate in lower soil depths through the adsorption of Glyphosate on water·soluble humic substances.

Humic and fulvic acids: sink or source in the availability of metals to the marine bivalves Macoma balthica and Potamocorbula amurensis ?

Abstract: Humic acids (HA) and fulvic acids (FA) are common forms of organic matter in marine sedirnents, and are routinely ingested by depositand suspension-feeding animals. These compounds may be a sink for metals, implying that once metals are bound to humic substances they are no longer available to food webs. A series of experiments was conducted to quantitatively examine this premise using 2 estuarine bivalves from San Francisco Bay, USA: the suspension feeder Potarnocorbula arnurensis and the facultative deposit feeder Macoma balthica. HA and FA, isolated from marine sediments, were bound as organic coatings to either hydrous ferric oxides (HFO) or silica particles. Cd and Cr(II1) were adsorbed to the organic coatings or directly to uncoated HFO and silica particles. Pulse-chase laboratory feeding expenments using '\"'Cd and \"Cr(III) were then conducted to determine absorption efficiencies of Cd and Cr for individual specimens using each of the partlcle types. The results demonstrated that: (1) absorption of Cr(I1I) from all types of non-living particles was consistently low (< 11%). Ingested Cd showed greater bioavailability than Cr(IIl), perhaps due to differences in metal chemistry. (2 ) Bivalves absorbed Cd bound to uncoated HFO or silica particles (i.e. with no HA or FA present). (3) The presence of organic coatings on part~cles reduced Cd bioavailabhty compared with uncoated particles. (4) Both geochemical and biological conditions affected the food chain transfer of Cd. The data suggest that in marine systems inorganic and organic-coated particles are predominantly a sink for Cr in sediments. In the transfer of Cd to consumer animals, inorganic particles and humic substances can act as a link (although not a highly efficient one) under oxidized conditions.

Comparison of the composition of humic and fulvic acids prepared by the IHSS method and NAGOYA method

Abstract: The composition of humic acids (HAs) and fulvic acids (FAs) prepared by the NAGOYA (Nagoya University) method and the IHSS (International Humic Substances Society) method was investigated using an an do soil and a brown forest soil. Extraction with a smaller volume of 0.1 N NaOH in the IHSS method yielded HAs containing larger amounts of 0, carboxyl groups, alcoholic hydroxyl groups, hexoses, and uronic acids than those prepared by the NAGOYA method. The contents of C, carbonyl groups, and amino acids were higher in the HAs obtained by the NAGOYA method. The relative content of aromatic C was higher in the HAs prepared by the NAGOYA method, especially in the ando soil. The FAs prepared by the IHSS method contained smaller amounts of H, N, alcoholic hydroxyl groups, saccharides, and amino acids than the F As obtained by the N AGOY A method, mainly due to the XAD-8 treatment in the IHSS method. The saccharide and amino acid contents in the XAD-8-adsorbed fractions obtained from the FAs prepared by ...

Cobalt, copper, and manganese adsorption by aluminium and iron oxides and humic acid

Abstract: Adsorption of cobalt (Co), copper (Cu), and manganese (Mn) by synthetic aluminium oxide, ferrihydrite, goethite, extracted humic acid, and a sandy soil sample were determined as a function of metals concentration (0–1.2 mM) and pH (3.8–8.2). For each pH and adsorbent, the Langmuir adsorption maximum (adsorption capacity) was calculated. The position of the adsorption curves for Co, Cu, and Mn as a function of pH has been shown to be related to the first hydrolysis constant of the cations in solution (pK1). The sequence of preference of the three metals to the studied adsorbents decreased in order Cu >> Co > Mn. The results obtained from this study showed that the Co, Cu, and Mn adsorption characteristics of soils are probably controlled to large extent by their organic matter and oxides contents.