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PubMed2001

Interaction of cadmium toxicity in embryos and larvae of zebrafish (Danio rerio) with calcium and humic substances.

The influence of humic substances (HS) and calcium (Ca) on cadmium (Cd) toxicity was determined using zebrafish (Danio rerio). Embryo and larvae of the zebrafish were exposed to various Cd concentrations (1.8; 2.8; 4.2; 6.2; 9.3 mg/l Cd) for 144 h. Combinations of low (0.2 mmol/l) and high (2 mmol/l) Ca, +HS (5 mg/l C) or -HS were used during Cd exposure. The toxicity of Cd was affected by (1) exposure concentration; (2) exposure time; (3) presence of HS; and (4) the Ca concentration. The results show that Ca and HS protect against Cd toxicity in zebrafish embryos. The best protection was in the high Ca-HS group, followed by high Ca+HS group and low Ca+HS group. The survival in the low Ca-HS group was the worse. Survival in the high Ca-HS group and the high Ca+HS group was similar with the exception of the highest Cd concentration (9.3 mg/l) where the survival of the high Ca+HS group was less than in the high Ca-HS group. The exposure system was modelled using a chemical equilibrium program (MINEQL+) to determine if the likely mechanism causing the anomalous result in the highest Cd concentration. The equilibrium model cannot explain these results, which suggests that this effect has a kinetic basis, such as time needed for Cd to displace Ca already bound by HS.

Animals↗

PubMed2002

Ozonation of Han River humic substances.

This study investigated the characteristics of extracted humic substances (HS) which are ubiquitous in river waters and affect the treatment of the water. HS were extracted from the Han River and the samples obtained were analyzed before/after oxidation with the following analytical methods: DOC, THMFP, UV-abs, chemical composition, molecular weight distribution, IR. Ozonation experiments were conducted in batch-type reactors. Ozone dose was 1 mg/L and contact time was varied from 0 to 20 minutes. The fraction of hydrophobic matter was 56.0% of total organic carbon in the Han River and the ratio of humic/fulvic acids was 22.4/77.6, showing high fractions of aromatic and/or double carbon bond functional groups and high fractions of saturated aliphatic carbons. Oxygen fraction of Han HS was relatively high compared with other humic substances (Suwannee River humic and fulvic acids), which are consistent with the results of IR spectra. The IR spectra showed the increase in aliphatic groups by ozonation of the Han HS. Humic substances could not completely be oxidized to CO2, H2O etc., but were partly oxidized to low molecular weight matter (aliphatics, aldehydes, carboxylics, polysaccharides etc.), so low removal efficiencies in terms of DOC (31-35% with 5 minute contact) were observed. For UV254, 5 minute or shorter contact showed more than 80% removal efficiencies.

Benzopyrans↗

PubMed2004

Characterization of humic substances: implications for trihalomethane formation.

Humic substances are precursors of carcinogenic trihalomethanes (THMs) formed during disinfection by chlorination in water treatment processes. In an effort to understand the relationship between trihalomethane formation potential (THMFP) and physicochemical properties of humic substances, UV-visible absorbance, fluorescence in emission and synchronous scan modes, and NMR spectra were measured for several aquatic fulvic and humic acids. For comparison, a soil fulvic acid was also examined using these methods. The feasibility of the gradient modified spin-echo (GOSE) NMR experiment to selectively measure singlet resonances arising from isolated protons was examined. In addition, diffusion coefficients were measured for DMSO solutions of the fulvic acids using BPPLED and GOSE-edited pulse sequences. Although none of the methods tested produced results that correlated with THMFP, the GOSE intensities determined for different regions of the NMR spectra did reflect the relative abundance of different types of functional groups produced by lignin oxidation. In addition, the GOSE-edited diffusion results suggest that the isolated protons, those most reactive to chlorination, are more likely contained in the larger molecular weight fractions of fulvic acids.

Journal Article↗

PubMed2005

Immobilized humic substances as sorbents.

A new method was developed for the immobilization of humic substances. Humic acids (HA) immobilized onto different carriers were studied as sorbents for organic and inorganic substances. The sorption isotherms of 4-aminoazobenzene, Crystal Violet, Methylene Green, and flavine mononucleotide on immobilized HA show that pH and salt concentration have a significant effect on the sorption process, largely depending on the properties of polymeric matrix. Humic acids from different sources showed differing sorption capacity for the studied groups of substances.

Adsorption↗

PubMed2004

Determinations of humic substances and other dissolved organic matter and their effects on the increase of COD in Lake Biwa.

Humic substances and other dissolved organic matter (DOM) in Lake Biwa and the surrounding rivers were investigated to elucidate their origins and behavior. An annual increase in chemical oxygen demand (COD) has been observed in the northern basin of Lake Biwa since 1985. The concentrations of dissolved organic carbon (DOC) in the northern and southern basins of Lake Biwa were 1.7-2.4 mgC/l and 1.9-2.6 mgC/l, respectively. The DOC concentrations tended to be high in summer and low in winter, and the seasonal changes in the concentrations of humic substances were small. The humic substances content of DOM was considered to be comparatively small because the ratio of the concentration of humic substances to DOC was in the range of 0.14-0.32. From the results of the fractionation of DOM in lake waters, it was estimated that hydrophobic acids, such as humic substances and hydrophilic acids, were about 25% and 45%, respectively. The main origin of hydrophobic acids in Lake Biwa may be humic substances from soils around the rivers that flow into Lake Biwa, while hydrophilic acids may be due to the inner production by phytoplankton. Therefore, the increase of COD in the northern basin of Lake Biwa may be attributed to the contributions of not only humic substances but also hydrophilic acids.

Journal Article↗

PubMed2006

Reactions of compost-derived humic substances with lead, copper, cadmium, and zinc.

Thermodynamic stability constants of the formation of complexes from the reactions of humic substances with various metals are usually used as parameters to judge the reactivities of both humic substances and metals. However, in calculating the thermodynamic stability constants, complicated processes for the acquisition of activities of components in reactions are absolutely inevitable. In this study, we investigated the average conditional concentration quotients of the complexes formed from the reaction of metals with humic substances and the relations of these quotients to thermodynamic stability constants. The characterized humic substances including HA (MW>1,000), FA (MW>1,000), and FA (MW<1,000) extracted from a swine compost were prepared to react with Pb, Cu, Cd, and Zn at 25 degrees C and at pH 4.00 and 6.50. Reactions of HA (MW>1,000), FA (MW>1,000), and FA (MW<1,000) with the four metals were carried out at 1:0.1, 1:0.5, 1:1, 1:5, and 1:10 ligand:metal stoichiometry. The concentrations of the free ions of Pb, Cu, Cd, and Zn in the reaction systems of metal-HA suspensions and metal-FA solutions were measured by anodic stripping voltammetry (ASV). The sequence of the average conditional concentration quotients of the formed complexes from the reaction of humic substances with metals was FA(MW<1,000)>FA(MW>1,000)>HA(MW>1,000), showing the relative reactivities of the fractions of swine compost-derived humic substances. The sequence of reacting metals with humic substances was Pb>Cu>Cd>Zn, which is in good agreement with the sequence reported by judging the thermodynamic stability constants. The average conditional concentration quotients of the formed complexes from the reaction of humic substances with metals were thus useful parameters that can be directly related to thermodynamic stability constants and other parameters.

Cadmium↗

PubMed1996

Micelle-like conformation of humic substances as revealed by size exclusion chromatography.

To gain further insight into the macromolecular behaviour of humic substances we treated a humic material with simple organic compounds and followed the change in molecular size distribution. Monocarboxylic, dicarboxylic, and tricarboxylic acids shifted the humic absorbance from high to low molecular sizes in size exclusion chromatograms. Mineral acids, phenol, alcohols, were not able to produce the same shift and gave total absorbance at the column void volume as in the case of humic substances alone. Our results are evidence of the micellar behaviour of humic substances in solution and of the importance of hydrophobic bondings in holding humic molecules together. The organic acids enter in the interior of the humic micelle and alter its stereochemical hydrophobic arrangement. In alkaline conditions, the developed negative charges disrupt the apparent high molecular size configuration and disperse the humic material into small-size micelles. This macromolecular property, that we report for the first time, may be of great importance in understanding the biological activity and the overall environmental behaviour of humic substances.

Acids↗

PubMed1990

Arsenic as a promoter in the effect of humic substances on plasma prothrombin time in vitro.

Protocatechuic acid can be oxidized and polymerized to from humic substances (humic acid and fulvic acid). Should AS2O3 occur in the process of oxidative polymerization, humic acid output can increase by 1.5 - 2.3 times and, in the case of fulvic acid, at least 10 times. After protocatechuic acid is oxidized and polymerized, the resultant humic and fulvic acids both exhibit the ability to shorten the prothrombin time of human pool plasma in vitro. This ability becomes more apparent when AS2O3 serves as a promoter in the course of oxidative polymerization as described above. However, AS2O3 or protocatechuic acid alone is unable to shorten the prothrombin time of human pool plasma.

Arsenic↗

PubMed1997

Selectivity in the complexation of actinides by humic substances.

The interactions of a range of actinide elements (Th, U, Np, Pu, Am) with humic substances from the Needle's Eye natural analogue site were studied by gel permeation chromatography. Bulk humic substances were isolated by ammonia extraction, followed by dialysis against distilled water and freeze-drying. The gel permeation results suggest that Needle's Eye humic substances can be fractionated into three incompletely resolved fractions with average molecular weights determined by analytical ultracentrifugation around 49 000 for Fraction 1, around 14 700 for Fraction 2 and around 8000 for Fraction 3. Although there are significant differences between the organic matter elution patterns in individual gel permeation experiments, presumably due to differences in column packing, these are much smaller than the differences between metal ions. The uranium that is naturally present in these humic substances is largely bound in the late-eluting fraction. Spikes of the early actinides, including Np and Pu in controlled valency states, have been added to the humic substances, and gel permeation of the spiked humic substances shows that the three humic fractions vary greatly in their effectiveness and selectivity as ligands for early actinides.

Journal Article↗

PubMed2001

Effects of humic substances on fluorometric DNA quantification and DNA hybridization.

DNA extracts from sediment and water samples are often contaminated with coextracted humic-like impurities. Estuarine humic substances and vascular plant extract were used to evaluate the effect of the presence of such impurities on DNA hybridization and quantification. The presence of humic substances and vascular plant extract interfered with the fluorometric measurement of DNA concentration using Hoechst dye H33258 and PicoGreen reagent. Quantification of DNA amended with humic substances (20-80 ng/microl) using the Hoechst dye assay was more reliable than with PicoGreen reagent. A simple procedure was developed to improve the accuracy for determining the DNA concentration in the presence of humic substances. In samples containing up to 80 ng/microl of humic acids, the fluorescence of the samples were measured twice: first without Hoechst dye to ascertain any fluorescence from impurities in the DNA sample, followed with Hoechst dye addition to obtain the total sample fluorescence. The fluorescence of the Hoechst dye-DNA complex was calculated by subtracting the fluorescence of the impurities from the fluorescence of the sample. Vascular plant extract and humic substances reduced the binding of DNA onto the nylon membrane. Low amounts (<2.0 microg) of humic substances derived from estuarine waters did not affect the binding of 100 ng of target DNA to nylon membranes. DNA samples containing 1.0 microg of humic substances performed well in DNA hybridizations with DIG-labeled oliogonucleotide and chromosomal probes. Therefore, we suggest that DNA samples containing low concentrations of humic substances (<20 ng/microl) could be used in quantitative membrane hybridization without further purification.

Bisbenzimidazole↗

PubMed2003

The effects of humic substances on the intake of micro-organic pollutants into the aquatic biota.

Humic substances, naturally occurring highly polymerized organic compounds, exist widely in the water and soil environments. It has been known that the humic substances affect the fate of micro-organic pollutants (e.g. intake, accumulation, movement, degradation, toxicity, etc.). Of these, the effect of humic substances on the intake into biota (i.e. living cell) is one of the most important. In this research, the effects of co-existing humic substances on the intake of micro-organic pollutants into aquatic biota were experimentally evaluated. The humic acid filtrate using a 3,000 Da ultra-filtration membrane was used. Two PAHs (i.e. pyrene and phenanthrene) were used as micro-organic pollutants. Liposome for simulating living cell membrane was synthesized in the laboratory, and used for investigating the intake of micro-organic pollutants into aquatic biota precisely. The batch experiment results (PAHs onto humic acid, humic acid into liposome, and PAHs into liposome (K(lipw))) led to the fact that the sorption of PAHs into liposome is suppressed apparently by binding with humic acid in the aqueous phase. This suggests that the accumulation and/or toxicity of micro-organic pollutants is retarded by humic substances in the actual aqueous environment. Moreover, the experimental results indicated that the sorption into liposome (i.e. liposome/water partition coefficient (K(lipw))) could be a better parameter for estimating the intake of micro-organic pollutants into aquatic biota than n-octanol/water partition coefficient (K(ow)) in the aqueous environment.

Filtration↗

PubMed2000

Investigation of metal ions binding of humic substances using fluorescence emission and synchronous-scan spectroscopy.

The binding site interactions of IHSS humic substances, Suwannee River Humic Acid, Suwannee River Fulvic Acid, Nordic Fulvic Acid, and Aldrich Humic Acid with various metals ions and a herbicide, methyl viologen were investigated using fluorescence emission and synchronous-scan spectroscopy. The metal ions used were, Fe(III), Cr(III), Cr(VI), Pb(II), Cu(II) and Ni(II). Stern-Volmer constants, Ksv for these quenchers were determined at pH 4 and 8 using an ionic strength of 0.1 M. For all four humic substances, and at both pH studied, Fe(III) was found to be the most efficient quencher. Quenching efficiency was found to be 3-10 times higher at pH 8. The bimolecular quenching rate constants were found to exceed the maximum considered for diffusion controlled interactions, and indicate that the fluorophore and quencher are in close physical association. Synchronous-scan spectra were found to change with pH and provided useful information on binding site interactions between humic substances and these quenchers.

Benzopyrans↗

PubMed2004

Effects of humic substances on the decomposition of 2,4-dichlorophenol by ozone after extraction from water into acetic acid through activated carbon.

The objectives of this study are to clarify the behavior of humic substances throughout the processes of 2,4-dichlorophenol (2,4-DCP) adsorption on granular activated carbon (GAC) from water and extraction into acetic acid, and the influence of the extracted humic substances on the decomposition of 2,4-DCP by ozone in the acetic acid. The adsorption capacity of GAC for 2,4-DCP was not influenced by the humic substances preloaded to have equilibrium concentration of 24.9mg Cl(-1) (14.5mg Cg(-1)). The adsorption capacity of GAC for 2,4-DCP decreased to one tenth of new GAC after the first adsorption-extraction step because of only 16% desorption in the first step. However, 2,4-DCP adsorbed on GAC was completely extracted after the second step suggesting that GAC can be used as adsorbent to transfer 2,4-DCP from water to acetic acid. The concentration ratio of 2,4-DCP from water into acetic acid was around 2x10(5), whereas the concentration ratio of humic substances was about 3.5, indicating that 2,4-DCP was selectively adsorbed and extracted by this system. The first order degradation rate constant for 2,4-DCP by ozone in acetic acid increased with the addition of humic substances. The rate constant with 16mg Cl(-1) of humic substances was 2.6 times as high as that without humic substances. Humic substances behaved as a promoter for the degradation of 2,4-DCP by ozone.

Acetic Acid↗

PubMedDate not supplied

Phenanthrene adsorption by soils treated with humic substances under different pH and temperature conditions.

The mobility of phenanthrene (PHE) in soils depends on its sorption and is influenced by either the existing soil humus or exogenous humic substances. Exogenous humic acids (HAs) were added to soil to enhance the amount of soil organic carbon (SOC) by 2.5, 5.0, and 10.0 g kg(-1). PHE desorption of the treated soils was determined at two pH levels (3.0 and 6.0) and temperatures (15 and 25 degrees C). Soil PHE adsorption was related to pH and the type and quantity of added HAs. Humic acid (HA) and fulvic acid (FA) derived from peat had different effects on adsorption of PHE. Adsorption increased at first and then decreased with increasing quantity of exogenous FA. When the soil solution pH (in 0.005 M CaCl(2)) was 4.5 or 3.0, the turning points were 2.5 g FA kg(-1) at pH 3.0 and 5 g FA kg(-1) at pH 4.5. When soil solution pH was 6, the amount of adsorbed PHE was enhanced with increasing exogenous HAs (HA or FA) and amount of adsorption by soil treated with FA was higher than with HA. Adsorption of PHE in the FA treatment at 10.0 g kg(-1) was lower than the controls (untreated soil or treatment with HAs at 0 g kg(-1)) when the soil solution pH was 3.0. This suggests that FA adsorbed by soil was desorbed at low pH and would then increase PHE solubility, and PHE then combined with FA. PHE adsorption was usually higher under lower pH and/or lower temperature conditions. PHE sorption fitted the Freundlich isotherm, indicating that exogenous humic substances influenced adsorption of phenanthrene, which in turn was affected by environmental conditions such as pH and temperature. Thus, exogenous humic substances can be used to control the mobility of soil PAHs under appropriate conditions to decrease PAH contamination.

Adsorption↗

PubMed2003

On-the-fly fluorescence lifetime detection of humic substances in capillary electrophoresis.

On-the-fly fluorescence lifetime detection was investigated as a tool for studying humic substances in capillary zone electrophoresis (CZE). Humic substances are complex, heterogeneous mixtures of natural products that tend to migrate in a single, broad CZE peak. The intrinsic fluorescence lifetime of five humic substances from the International Humic Substances Society (IHSS) was monitored using excitation at 488 or 364 nm to produce intensity-lifetime electropherograms for each of the substances. Each frequency-domain lifetime measurement, collected at subsecond intervals during the CZE run, contains the equivalent of a complete decay profile. Lifetime analysis of each decay profile was used to construct a lifetime-resolved electropherogram for each lifetime component, from which the variation in relative intensity contributions of each lifetime across the broad CZE peak could be determined. Absorption spectra, fluorescence excitation-emission spectra, and lifetime profiles of batch solutions of the samples were determined as well. It was found that, whereas absorption and fluorescence spectral characteristics tended to discriminate between humic acids and fulvic acids, the batch solution lifetime profiles discriminated instead between samples from different sources, regardless of fraction. On-the-fly lifetime detection provided a more detailed view of the fluorescence decay of the samples, including greater resolution of lifetimes for two of the fulvic acids and greater discrimination among samples based on lifetime profiles across the CZE peaks.

Benzopyrans↗

PubMed2004

Physiological interactions of silver and humic substances in Daphnia magna: effects on reproduction and silver accumulation following an acute silver challenge.

Silver (Ag) in aquatic environments mediates its toxic actions by inhibiting sodium influx. Humic substances protect against silver toxicity by complexing the toxic, ionic form of the metal, but may also directly stimulate sodium influx in aquatic organisms. This study investigated the effects of silver and humic substances on the water flea Daphnia magna. Acute silver challenge (24 h; 1 microg L(-1)) and the chronic exposure to humic substances (Aldrich humic acid; 7 mg C L(-1)) had considerable influence on daphnid physiology and reproduction. In particular silver exposure in the absence of humic substances stimulated reproduction, resulted in enhanced adult mass, and altered both the response of the animal to subsequent silver exposure and a physiological surrogate measure of silver toxicity (whole body sodium concentration). The presence of humic substances countered the effects on adult mass and reproduction, returning these parameters to control levels. Humic substances also lowered silver body burden, but with significantly improved whole body sodium status than previously silver-exposed animals. These changes may distort the correlation between silver body burden and indicators of toxic action, an important tenet of site-specific risk assessment tools such as the biotic ligand model.

Animals↗

PubMed2005

Infrared spectroscopic evidence supporting heterogeneous site binding models for humic substances.

Infrared spectroscopy was used to corroborate predictions made by newly developed heterogeneous site binding models for humic substances. Experimental conditions to acquire the spectra of soil humic substances (humic and fulvic acid and a polysaccharide fraction) in an aqueous state using horizontal attenuated total reflectance Fourier transform infrared spectroscopy (HATR-FTIR) were established. Elimination of the water spectrum from that of the sample was achieved by spectral subtraction of the water peak at 2020 cm(-1). A KSCN internal standard with an absorption band at 2067 cm(-1) was used to verify the efficacy of the subtraction procedure. Spectral artifacts produced by the water spectrum subtraction and from contaminants within the humic materials have been identified. Three fulvic and one humic acid solution were examined in solutions of varying pH. Results show that the observed proportion of ionized carboxylate in relation to pH is consistent with models that assume electrostatic effects and a continuous distribution of proton association constants (log KH). The spectroscopic data were in accordance with calculations made using the generic humic and fulvic acid NICA-Donnan model parameters.

Adsorption↗

PubMed1991

Mutagenicity of the components of ozonated humic substance.

Eight components of humic substances were ozonated. Mutagenic activity was found with TA100 with and without S9 mix for all ozonated components. Ozonated products of p-hydroxybenzaldehyde were separated into five fractions by silica gel chromatography and each fraction subjected to mutagenicity assay. Mutagenic activity was found in the chloroform and chloroform-acetone (1:1) fractions. The compounds in these fractions were identified, and aldehydes such as formaldehyde, acetaldehyde, glyoxal, glyoxylic acid and methyl glyoxal were found to be mutagenic. Mutagenic compounds are present in the polar fraction.

Aldehydes↗