Showing papers on "Humic acid published in 1993"

Interference of humic acids and DNA extracted directly from soil in detection and transformation of recombinant DNA from bacteria and a yeast

Abstract: A two-step protocol for the extraction and purification of total DNA from soil samples was developed. Crude DNA extracts (100 microliters from 5 g of soil) were contaminated with humic acids at concentrations of 0.7 to 3.3 micrograms/microliters, depending on the type of soil extracted. The coextracted humic acid fraction of a clay silt was similar to a commercially available standard humic acid mixture, as determined by electrophoretic mobility in agarose gels, UV fluorescence, and inhibition assays with DNA-transforming enzymes. Restriction endonucleases were inhibited at humic acid concentrations of 0.5 to 17.2 micrograms/ml for the commercial product and 0.8 to 51.7 micrograms/ml for the coextracted humic acids. DNase I was less susceptible (MIC of standard humic acids, 912 micrograms/ml), and RNase could not be inhibited at all (MIC, > 7.6 mg/ml). High inhibitory susceptibilities for humic acids were observed with Taq polymerase. For three Taq polymerases from different commercial sources, MICs were 0.08 to 0.64 micrograms of the standard humic acids per ml and 0.24 to 0.48 micrograms of the coextracted humic acids per ml. The addition of T4 gene 32 protein increased the MIC for one Taq polymerase to 5.12 micrograms/ml. Humic acids decreased nonradioactive detection in DNA-DNA slot blot hybridizations at amounts of 0.1 micrograms and inhibited transformation of competent Escherichia coli HB101 with a broad-host-range plasmid, pUN1, at concentrations of 100 micrograms/ml. Purification of crude DNA with ion-exchange chromatography resulted in removal of 97% of the initially coextracted humic acids.(ABSTRACT TRUNCATED AT 250 WORDS) Images

Evaluation of sequential extraction for speciation of trace metals in model soil containing natural minerals and humic acid

Abstract: A model soil synthesized with several natural minerals and humic acid is used to evaluate the sequential extraction for speciation analysis of trace elements in soil. Although the recommended sequential extractants are able to bring the individual geochemical phases into solution at the experimentally defined stage, none of the extractants is completely specific and efficient. Various proportions of metals released at exchangeable, carbonate-bound, Fe-Mn oxide-bound, organic-bound fractions are readsorbed onto the other solid geochemical phases during sequential extraction. However, it is difficult to quantify the extent of readsorption and/or redistribution for the individual element and for the individual geochemical phase.

Use of high-resolution carbon-13 NMR to examine the enzymatic covalent binding of carbon-13-labeled 2,4-dichlorophenol to humic substances

Abstract: A novel application of a standard NMR technique has been employed to characterize the enzymatic coupling of a pollutant (2,4-dichlorophenol, 2,4-DCP) to humic material. The application involves the use of 2,4-DCP labeled with 13 C at specific molecular sites in combination with broad-band decoupled 13 C NMR to determine the nature of bonding interactions with Minnesota peat humic acid. Any alteration in the chemical structure of the 2,4-DCP due to coupling with the humic acid results in changes in the 13 C chemical shifts of the labeled carbons which are indicative of the site and type of bonding interaction. These data provide direct evidence for the formation of covalent bonds between the pollutant and a humic acid via enzymatic coupling

Transport of humic matter-coated hematite in packed beds

Abstract: Column filtration experiments, using quartz grains as the bed media, were conducted to study the deposition kinetics of hematite particles in the presence of three wellcharacterized humic substances. Two pH conditions, 5.2 and 7.4, were selected such that the humic matter was adsorbed to an originally positive and negative hematite surface, respectively. Background NaCl concentrations ranged from 0.015 to 0.1 M. The particle deposition rates, expressed in terms of initial experimental attachment efficiencies (α exp ), depended on the magnitude of both electrostatic and steric repulsive interaction energies

Pyrene sorption by water-soluble organic carbon

Abstract: Natural dissolved organic matter (DOM) in soil solution has the potential to facilitate the transport of nonionic organic contaminants (NOC). The interactions between pyrene and ultrafiltration fractions of water-soluble organic carbon (WSOC), humic acid, and fulvic acid were quantified using fluorescence-quenching spectroscopy. Pyrene partition coefficients to the smaller WSOC fractions varied between 4.1 [times] 1.0[sup 3] and 6.8 [times] 10[sup 3] L kg[sup [minus]1], while partition coefficients for the largest fraction of WSOC, humic acid, and fulvic acid were 1.5 [times] 10[sup 4], 1.7 [times] 10[sup 5], and 1.1 [times] 10[sup 4] L kg[sup [minus]1], respectively. These results demonstrate that the use of the same [sup c]K[sub oc] value to describe NOC partitioning to both immobile organic matter and soil solution DOM will overestimate the ability of DOM to facilitate the transport of NOC. Conversely, pyrene partitioning data to the largest WSOC fraction suggest that the presence of colloidal organic matter suspended in the soil solution may have a large influence on NOC transport. 32 refs., 3 figs., 3 tabs.

Complexation of Trivalent Actinide Ions (Am3+, Cm3+) with Humic Acid: A Comparison of Different Experimental Methods

Abstract: The complexation of trivalent metal ions with humic acid has been studied at pH 4 and 5 in 0.1 Μ NaC104 by three different experimental methods, i.e. UV spectroscopy, time resolved laser fluorescence spectroscopy (TRLFS) and ultrafiltration. The direct speciation of the metal ion and its humate complex in the reaction process has been made by UV spectroscopy for Am(III) in the micromolar concentration range and by TRLFS for Cm(III) in the nanomolar concentration range. The ultrafiltration is used with the lowest pore size of filter (ca. 1 nm) to separate the uncomplexed metal ion from its complexed species. The concentrations of both metal ion and humic acid are varied in such a manner that the effective functional groups of the humic acid becomes loaded with metal ions from 1 % to nearly 100%. The loading capacity of the humic acid for the trivalent metal ion, determined separately at each pH, is introduced into the evaluation of complexation constants. The variation of the metal ion concentration from 6 χ 10\" 8 mol/1 to 4 χ 10\" mol/1 does not show any effect on the complexation reaction. The three different methods give rise to constants being comparable with one another. The average value of the constants thus determined is log β = 6.24 + 0.28 for the trivalent actinide ions.

Effects of fractions of coal-derived humic substances on seed germination and growth of seedlings (Lactuga sativa and Lycopersicum esculentum)

Abstract: Lettuce and tomato seeds were treated in Petri dishes with a humic acid derived from an oxidized coal and with fractions of the same humic acid obtained by ultrafiltration through membranes of known molecular cutoff and by extracting with buffers set at pH 4 and pH 5. The unfractionated humic acid was applied at 40, 100, 1000, and 5000 mg l-1 whereas the humic fractions were applied at 40, 100, and 200 mg l-1. Germination parameters such as the number of total germinated seeds, the velocity of seed germination, the fresh weight and dry weight of total seedlings were measured and related to the chemical and physicochemical properties of the humic material. No increase in the germination percentage or the germination rate was observed for either lettuce or tomato seeds. The fresh weight of total seedlings and per seedling increased in treatments with unfractionated humic acid with increasing concentrations for both lettuce and tomato plants without showing signs of growth inhibition up to 5000 mg l-1. This was attributed to cell elongation and more efficient water uptake. For the lettuce, the fresh weight both of total seedlings and per seedling was enhanced by treating the seeds with fractions of low molecular weight and high content of acidic functions, whereas the dry weight both of total seedlings and per seedling did not change with the humic fraction used. For the tomato seeds in contrast, the dry weight both of total seedlings and per seedling was increased by the use of unfractionated humic acid and by some of the humic fractions. An uptake of humic material by growing tomato seedlings was inferred.

Characterization by fluorescence of the dissolved organic matter in natural water. application to fractions obtained by tangential ultrafiltration and XAD resin isolation

Abstract: A tangential ultrafiltration procedure has been applied to separate the dissolved organic matter in the order of decreasing molecular weights of two water samples from a dam reservoir. Four fractions have been isolated and their fluorescence emission spectra, fluorescence excitation spectra and their fluorescence quantum efficiencies were compared with those of macroporous XAD8 and XAD4 extracts isolated from the same water samples. A clear one to one correspondence between the ultrafiltrated fractions and the resin extracts was observed which indicates that the two methods lead to isolate very similar type of organic material. The “apparent”; mean molecular weights deduced for humic, fulvic and hydrophilic acids appear consistent with previous values drawn from waters of various origins. Moreover, by using the fluorescence spectra characterizing each of these acids we have been able to estimate the contribution of their respective fluorescence to the total fluorescence spectra of the two studied...

Binding of a fluorescent hydrophobic organic probe by dissolved humic substances and organically-coated aluminum oxide surfaces

Abstract: The binding of perylene by Suwannee River humic substances in the presence and absence of colloidal-sized aluminum oxide particles was examined using a fluorescence quenching technique Our experiments show that binding is complete within 3 min and that the fluorescence of perylene associated with dissolved and adsorbed humic substances is fully quenched as evidenced by quantum yields which approached zero for all systems In the absence of alumina, both humic acid and fulvic acid were able to bind perylene, and the partition coefficients decreased with increasing pH and NaCl concentrations The presence of Ca^(2+) had little effect on the binding of perylene by either of the dissolved humic substances The adsorption of humic and fulvic acids onto alumina decreased their ability to bind perylene For all solution conditions examined, the association of perylene with adsorbed fulvic acid was never detected In NaCl solutions, partition coefficients for adsorbed humic acid at pH 4 were approximately half the values of those for dissolved humic acid; at pH 7 and 10, alumina-bound humic acid did not bind perylene in NaCl solutions In contrast to the results observed for dissolved humic acid, the presence of Ca^(2+) greatly enhanced the binding of perylene by adsorbed humic acid A major effect of solution chemistry is to alter the mechanisms by which humic substances adsorb to alumina, thereby determining how tightly the humic material is bound to the surface The ability of weakly-adsorbed humic acid to bind perylene approaches that of the dissolved species

High pH Treatments and the Alleviation of Soil Hydrophobicity on Golf Greens

Abstract: Hydrophobic soil associated with localized dry spots (LDS) on creeping bentgrass (Agrostis palustris Huds.) putting greens has been shown to be caused by a humic and/or fulvic acid coating of the sand particles. Under laboratory conditions, humic acid begins to solubilize at pH 7.0 and is completely soluble at pH 9.5 or greater. The purpose of this study was to determine the potential of high pH treatments for alleviating soil hydrophobicity of a creeping bentgrass golf green. Three separate studies were conducted on the University of Georgia Experimental Golf Green, Athens, GA, during the spring and summer of 1990 and spring of 1991. The creeping bentgrass green, constructed with an 85% sand and 15% peat root zone mixture, had a well documented history of LDS caused by hydrophobic soil [...]

Evidence for radionuclide transport and mobilization in a shallow, sandy aquifer

Abstract: Evidence is reported for the movement of plutonium, americium, thorium, and radium in a shallow, sandy aquifer after the forced injection of colloidal and macromolecular natural organic materials (humic and fulvic acids). Ultrafiltration was used to size-fractionate the materials smaller than 0.45 pm in the injection water. Characterization of these organic materials showed the most mobile to be primarily fulvic acids with a high carboxylate content. Fallout-derived plutonium and americium in the injected materials were transported in the aquifer with the smaller organic fractions. Americium was shown to move from the less mobile colloidal materials to the smaller more mobile fulvics during transport. Thorium, uranium, and radium levels all increased upon injection of the organics into the aquifer, demonstrating the ability of low molecular weight, high carboxylic content fulvic acids to dissolve and mobilize radionuclides from the aquifer's mineral matrices. This effect also increased with decreasing flow rate in the aquifer. The implications of these observations for the interactions of low-level radioactive waste with natural organics are discussed.

Fractal nature of humic materials

Abstract: Fractals are geometric representatives of strongly disordered systems whose structure is described by nonintegral dimensions. A fundamental tenet of fractal geometry is that disorder persists at any characterization scale-length used to describe the system. The nonintegral nature of these fractal dimensions is the result of the realization that a disordered system must possess more structural detail than an ordered system with classical dimensions of 1, 2, or 3 in order to accommodate this disorder within disorder.'' Thus from a fractal perspective, disorder is seen as an inherent characteristic of the system rather than as a perturbative phenomena forced upon it. Humic materials are organic substances that are formed by the profound alteration of organic matter in a natural environment. They can be operationally divided into 3 fractions; humic acid (soluble in base), fulvic acid (soluble in acid or base), and humin (insoluble in acid or base). Each of these fraction has been shown to be an extremely heterogeneous mixture. These mixtures have proven so intractable that they may represent the ultimate in molecular disorder. In fact, based on the characteristics that humic materials must possess in order to perform their functions in natural systems, it has been proposed that themore » fundamental chemical characteristic of a humic material is not a discrete chemical structure but a pronounced lack of order on a molecular level. If the fundamental chemical characteristic of a humic material is a strongly disordered nature, as has been proposed, then humic materials should be amenable to characterization by fractal geometry. The purpose of this paper is to test this hypothesis.« less

Desmutagenic activity of natural humic acids: inhibition of mitomycin C and maleic hydrazide mutagenicity

Abstract: Humic acids are natural components of organic matter widespread in the environment. In spite of the incomplete knowledge about their composition, increasing interest in humic acid activity is justified by their ubiquity. Four different humic acids have been tested in Chinese hamster ovary cells in vitro, both alone and in combination with two well-known mutagens (mitomycin C and maleic hydrazide). Data about sister-chromatid exchanges, mitotic and proliferation indices were collected. Our results, on the whole, indicate: (i) a slight mutagenicity and toxicity of tested humic acids, probably due to chlorination during sample preparation; (ii) a desmutagenic rather than antimutagenic activity of the tested humic acids.

Trace enrichment of polar pollutants from water and the influence of humic substances

Abstract: A practical liquid chromatographic early-warning system for polar pollutants in water ought to have detection limits at a level below a microgram per litre. Using ultraviolet absorbance detection this normally necessitates trace enrichment of the samples. In this study ten different sorbents have been tested with respect to their enrichment capacity. The hydrophobic polymeric PLRP-S material, in combination with a C-18 modified analytical column, proved to be the best choice. The influence of humic substances, present in surface water, was also studied. Lowering of the sample pH, resulted in a significant increase in the interferences due to the humic substances.

Complexation of Technetium with Humic Acid

Abstract: The complexation of technetium with well characterized humic acid, which was extracted from one of the Gorleben groundwaters in northem Germany, was studied. It was found that technetium humate was produced as a brownish-black precipitate by addition of Sn^^ as a reductant in a mixture Solution of pertechnetate and humic acid at pH 4 in 0.1 mol P ' NaC104. This precipitate could be distinguished from the TCO2 with respect to the dissolution behavior at higher pH. The produced amount of the formed technetium humate linearly increases with the added amount of Sn^ * with a slope of ca. 0.5, showing that the valence State of technetium is 3 + . With decrease of the concentration of humic acid in the Solution, the formation of TCO2 became prominent. The stock Solution was warmed after addition of H2O2 to guarantee complete oxidation to pertechnetate. The radioactivity measurements were carried out using a liquid scintillation counter (Aloka LC700). Proton exchange capacity, 5.38 meq g \" ' [5], of the humic acid (Gohy 573 HA) was used to indicate the HA concentration. 1. S p e c t r o p h o t o m e t r y The mixed Solution of pertechnetate (1.9x10\"\"^ m o l l \" ' ) and humic acid (1.5 x eq T i n 0.1 mol P ' NaC104 (at pH 4) was used to measure the absorption spectrum in the ultra-violet region. Introduction The radioactive nuclide, '®Tc {Tyi2 = 2.13 x 10^ y), is an important fission products, which has been introduced into the environment as a consequence of human uses of nuclear energy, i.e. from fallout of nuclear weapons tests or discharges from reprocessing plants. It easily migrates in an aerobic aquifer system in its chemical form of pertechnetate. However, it can be converted to hydrolyzed technetium dioxide under anaerobic conditions [1]. It is well known that naturally occurring organic substances such as humic acid (HA) or fulvic acid (FA) affect the migration behavior of metal ions [2]. As for technetium, a few reports have been concerned with interaction with humic acid. Belgian researchers [3, 4] studied the complexation of technetium and humic acid and found Tc—HA complex formation under a reduced condition. No stoichiometric study has been performed because of the complexity of the chemistry of technetium and the humic material. In this study, HA complexation of technetium was investigated by using purified and well characterized humic acid (Gohy 573 HA) [5] which was extracted from one of the Gorleben groundwaters in northern Germany, in order to get basic knowledge on the migration behavior of technetium. Experimental ®®Tc was purchased from the Radiochemical Centre, Amersham, as a Solution of ammonium pertechnetate. 2. R a d i o m e t r i e analysis Stannous chloride was used to reduce technetium in the absence and the presence of humic acid at pH 4 (0.1 M NaC104). Irrespective of the presence of humic acid, a dark colored precipitate was formed by addition of Sn^\"^. After pH adjustment, the Solution was centrifuged and a portion of the supernatant was submitted to radioactivity measurements. Gel chromatography (Sephadex G-15,1 cm 0 x 5 cm height) was carried out to separate chemical species in the Solution. Results and discussion (1) S p e c t r o p h o t o m e t r y A Solution of pertechnetate and humic acid at pH 4 (0.1 M NaC104) was submitted to UV absorption spectrum measurements, as shown in Fig. 1. The absorption peaks of pertechnetate (245 nm and 288 nm) are seen in this figure. Almost no significant change in the UV spectrum was observed for storage under aerobic conditions of up to 40 days, indicating that contact with humic acid did not influence technetium species under these conditions.

Effect of model organic compounds on potentiometric stripping analysis using a cellulose acetate membrane-covered electrode

Abstract: The effects of model surfactants (sodium dodecyl sulfate, Triton X-100), proteins (ovalbumin, gelatin), and carbohydrates (agar, starch) as well as D-camphor and humic acid on a cellulose acetate dialysis membrane-modified mercury film electrode (CM-MFE) in potentiometric stripping analysis (PSA) are described. The CM-MFE (1000 amu molecular weight cutoff) minimized interference by these compounds to the PSA measurement. The constant current stripping analysis (CCSA) mode was found to provide a more stable response than the used of Hg(II) as chemical oxidant with the CM-MFE