About: Humic acid is a(n) research topic. Over the lifetime, 13030 publication(s) have been published within this topic receiving 330804 citation(s). The topic is also known as: humic acids & humin acids.
01 Oct 1994-Environmental Science & Technology
TL;DR: Data indicate that aquatic fulvic acids, a commercial humic acid, and unfractionated organic matter from four natural water samples are smaller and less polydisperse than previously believed.
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
28 Sep 1996-Nature
Abstract: HUMIC substances are heterogeneous high-molecular-weight organic materials which are ubiquitous in terrestrial and aquatic environments. They are resistant to microbial degradation1 and thus are not generally considered to be dynamically involved in microbial metabolism, especially in anoxic habitats. However, we show here that some microorganisms found in soils and sediments are able to use humic substances as an electron acceptor for the anaerobic oxidation of organic compounds and hydrogen. This electron transport yields energy to support growth. Microbial humic reduction also enhances the capacity for microorganisms to reduce other, less accessible electron acceptors, such as insoluble Fe(III) oxides, because humic substances can shuttle electrons between the humic-reducing microorganisms and the Fe(III) oxide. The finding that microorganisms can donate electrons to humic acids has important implications for the mechanisms by which microorganisms oxidize both natural and contaminant organics in anaerobic soils and sediments, and suggests a biological source of electrons for humics-mediated reduction of contaminant metals and organics.
03 Sep 1997-Journal of Membrane Science
Abstract: The role of chemical and physical interactions in natural organic matter (NOM) fouling of nanofiltration membranes is systematically investigated. Results of fouling experiments with three humic acids demonstrate that membrane fouling increases with increasing electrolyte (NaC1) concentration, decreasing solution pH, and addition of divalent cations (Ca2+). At fixed solution ionic strength, the presence of calcium ions, at concentrations typical of those found in natural waters, has a marked effect on membrane fouling. Divalent cations interact specifically with humic carboxyl functional groups and, thus, substantially reduce humic charge and the electrostatic repulsion between humic macromolecules. Reduced NOM interchain repulsion results in increased NOM deposition on the membrane surface and formation of a densely packed fouling layer. In addition to the aforementioned chemical effects, results show that NOM fouling rate increases substantially with increasing initial permeation rate. It is demonstrated that the rate of fouling is controlled by an interplay between permeation drag and electrostatic double layer repulsion; that is, NOM fouling of NF membranes involves interrelationship (coupling) between physical and chemical interactions. The addition of a strong chelating agent (EDTA) to feed water reduces NOM fouling significantly by removing free and NOM-complexed calcium ions. EDTA treatment of NOM-fouled membranes also improves the cleaning efficiency dramatically by disrupting the fouling layer structure through a ligand exchange reaction between EDTA and NOM-calcium complexes.
01 Mar 1977-Soil Science Society of America Journal
Abstract: The ratio of optical densities or absorbances of dilute, aqueous humic and fulvic acid solutions at 465 and 665 nm (E₄/E₆) is widely used by soil scientists for the characterization of these materials. While it has been suggested that the E₄/E₆ ratio is related to the degree of condensation of the aromatic carbon network, carbon content, and molecular weight of humic substances, little rigorous experimental evidence is available in the literature to confirm these hypotheses. The results of this investigation show that the E₄/E₆ ratio of humic and fulvic acid is: (i) mainly governed by the particle size (or particle or molecular weight); (ii) affected by pH; (iii) correlated with the free radical concentration, contents of O, C, CO₂H and total acidity in as far as these parameters are also functions of the particle size or particle or molecular weight; (iv) apparently not directly related to the relative concentration of condensed aromatic rings; (v) independent of humic acid and fulvic acid concentrations, at least in the 100–500 ppm range. Our data show, in agreement with M. M. Kononova (1966), that E₄/E₆ ratios for humic and fulvic acids should be determined between pH 7 and 8. This can best be done by dissolving the humic material in 0.05N NaHCO₃ solution at concentrations of 200–400 ppm.
01 May 1986-Environmental Science & Technology
TL;DR: Water solubility enhancements by dissolved humic and fulvic acids from soil and aquatic origins and by synthetic organic polymers have been determined for selected organic pollutants and pesticides.
Abstract: Water solubility enhancements by dissolved humic and fulvic acids from soil and aquatic origins and by synthetic organic polymers have been determined for selected organic pollutants and pesticides (p,p'-DDT,2,4,5,2',5'-PCB, 2,4,4'-PCB, 1,2,3,-trichlorobenzene, and lindane). Significant solubility enhancements of relatively water-insoluble solutes by dissolved organic matter (DOM) of soil and aquatic origins may be described in terms of a partition-like interaction of the solutes with the microscopic organic environment of the high-molecular-weight DOM species; the apparent solute solubilities increase linearly with DOM concentration and show no competitive effect between solutes. The K/sub dom/ values of solutes with soil-derived humic acid are approximately 4 times greater than with soil fulvic acid and 5-7 times greater than with aquatic humic and fulvic acids. The effectiveness of DOM in enhancing solute solubility appears to be largely controlled by the DOM molecular size and polarity. The relative inability of high-molecular-weight poly(acrylic acids) to enhance solute solubility is attributed to their high polarities and extended chain structures that do not permit the formation of a sizable intramolecular nonpolar environment. 41 references, 6 figures, 3 tables.