International Humic Substances Society Research Articles

Photodegradation of Ormetoprim in Aquaculture and Stream-Derived Dissolved Organic Matter

Ormetoprim (OMP) is an antibiotic approved for use in the United States to prevent the spread of disease in freshwater aquaculture. It has been shown in the previous literature to be photochemically stable to direct photolysis, but the role of photosensitization processes in the presence of dissolved organic matter (DOM) on the rate of degradation is not well understood. The present results show that water and DOM (specifically the fulvic acid fraction) isolated from a eutrophic aquaculture catfish pond and a nearby stream (Deer Creek) at the Mississippi State University Delta Research and Extension Center facility in Stoneville, MS, significantly increased the phototransformation of OMP relative to direct photolysis. Similar results were reported for reference fulvic acids obtained from the International Humic Substances Society. Results from a combination of scavenging experiments and experiments conducted under anoxic conditions indicate the indirect photodegradation pathway occurs by hydroxyl radical, singlet oxygen attack, and reaction with triplet excited-state DOM.

Detailed investigation of organic matter components in extracts and drainage waters from a soil under long term cultivation

Aqueous solutions of increasing pH (7.0, 10.6 and 12.6) were used to extract exhaustively the organic matter (OM) from a pelo-stagnogley (heavy clay) soil in long term cultivation. OM yield was 1.7 times greater when the extracts were processed using an XAD-8 and XAD-4 resin-in-tandem procedure than that from the procedure of the International Humic Substances Society (IHSS). The substantial difference can be attributed to the amount retained by the XAD-4 resin, which is lost in the IHSS process. Elemental, δ13C, δ15N, cation exchange capacity, neutral sugars, amino acids and solid state CPMAS 13C NMR analyses indicated significant, but rational similarities and differences between the various fractions isolated. There was strong NMR evidence for material derived from lignin in all the humic and fulvic acid isolates. The signals were attenuated in the more transformed/oxidized fractions isolated at lower pH. Novel humic acid fractions enriched in carbohydrate/peptide functionalities were isolated from the more hydrophobic extracts at pH 10.6 and 12.6. Isolates from XAD-4, of microbial origin, were enriched in neutral sugars but not in amino acids, and had minimal aromaticity. Components isolated from the cultivated soil were broadly similar to those from a comparable soil in long term grassland. The compositions of fractions isolated from the drainage water were similar to those extracted from the soil but had higher carboxyl content. The amount and composition of the various organic fractions in grassland and the continuously cropped soil are discussed in terms of their potential to contribute to carbon sequestration by soil under similar management regimes.

Trihalomethane formation potential of aquatic and terrestrial fulvic and humic acids: examining correlation between specific trihalomethane formation potential and specific ultraviolet absorbance

Environmental context When surface water is disinfected to produce potable drinking water, toxic by-products are generated by reaction with naturally occurring organic matter. The production of trihalomethane disinfection by-products was investigated for different types of well-characterised organic matter from various geographic locations. Increased understanding of the character of organic matter dissolved in water is needed for improving the ability to provide safe water and protect public health. Abstract Trihalomethanes (THMs) – a class of disinfection by-products (DBPs) including chloroform – are produced when natural water is chlorinated. Many THMs are believed to result from the reaction of chlorine with the aromatic structures in humic substances, which can be represented by ultraviolet absorbance at 254 nm (UVA). However, in the literature, plots of the specific, or carbon-normalised, UVA (SUVA) compared with the specific, or carbon-normalised, trihalomethane formation potential, THMFP (STHMFP) are poorly correlated. Therefore, well characterised samples of organic matter were obtained from the International Humic Substances Society (IHSS) to study the effect of type (fulvic acid, FA; humic acid, HA), origin (aquatic, terrestrial), geographical source (Nordic, Suwannee River, peat, soil) and pH (6, 9) on the formation of trihalomethanes. In this research, parameters expressed on a weight-average moles-of-humic substance basis were compared with those on a mass-of-carbon basis. Using factorial analysis, SUVA was statistically described by the main effect type (P = 0.0044), whereas STHMFP was statistically described by the main effects type (P = 0.0078) and origin (P = 0.0210). Separate relationships between SUVA and STHMFP normalised to moles of humic substance were defined for aquatic substances (R2 = 0.9948) and for terrestrial substances (R2 = 0.9512). The occurrence of aquatically derived fulvic-like humic acid (Suwannee River humic acid) and aquatically derived terrestrial-like humic acid (Nordic humic acid) were observed. Some aquatic substances were capable of generating levels of THMs per mole of humic substance that were greater than or equal to the most reactive terrestrial humic acid.

Multidimensional fluorescence studies of the phenolic content of dissolved organic carbon in humic substances

Indicators suggest that the amount of dissolved organic carbon (DOC) in natural waters may be increasing. Climate change has been proposed as a potential contributor to the trend, and under such a mechanism, the phenolic content of DOC may also be increasing. This study explores the assessment of the phenolic character of DOC using multidimensional fluorescence spectroscopy as a more convenient alternative to traditional wet chemistry methods. Parallel factor analysis (PARAFAC) is applied to fluorescence excitation emission matrices (EEMs) of humic samples to analyze inherent phenolic content. The PARAFAC results are correlated with phenol concentrations derived from the Folin-Ciocalteau reagent-based method. The reagent-based method reveals that the phenolic content of five International Humic Substance Society (IHSS) samples varies from approximately 5.2 to 22 ppm Tannic Acid Equivalents (TAE). A four-component PARAFAC fit is applied to the EEMs of the IHSS sample dataset and it is determined by PARAFAC score correlations with phenol concentrations from the reagent-based method that components C2, C3, and C4 have the highest probability of containing phenolic groups. The results show the potential for PARAFAC analysis of multidimensional fluorescence data for monitoring the phenolic content of DOC.

The role of the characteristics of humic substances in binding with benzo[h]quinoline

The binding constants (K(DOC)) of the mixture of benzo[h]quinoline and its protonated analog, benzo[h]quinolinium, to four types of humic substances obtained from the International Humic Substances Society were determined by the fluorescence quenching method. A simple mixing model was used to eliminate the fluorescent interference from the minor analog in the solution and to deduce K(mix), which represents the overall binding as the sum of that for the individual analogs. The characteristics of humic substances, especially their hydrophobicity and aromaticity, established by principal component analysis of structural and elemental compositions, were the main determinants of the binding affinity with both benzo[h]quinoline and benzo[h]quinolinium (K(BQ) and K (BQH+) across a range of pH values. The strongest overall affinity of benzo[h]quinoline for humic substances is observed near pH 4 and with more hydrophobic humic substances, which suggests possible choices in attempts at remediation of benzo[h]quinoline containing particles with humic substances.

Characterization of heterogeneities and domains in aquatic and sedimentary organic matter by 1H spin diffusion: Potential for elucidating the formation mechanisms

Although the information on domains and heterogeneities of natural organic matter (NOM) can provide insights into its formation mechanisms, the appropriate solid‐state NMR technique for measuring them is still lacking. The traditional technique requires mobility differences in NOM whereas NOM components are primarily rigid. We introduced a new 1H spin diffusion technique, 1H‐13C two‐dimensional heteronuclear correlation (2D HETCOR) NMR with 1H spin diffusion, for characterization of domains and heterogeneities in aquatic and sedimentary organic matter. It was achieved by collecting a series of 2D HETCOR spectra with a variable mixing time, tm, and monitoring the transfer of magnetization from one component to another. The rate of magnetization transfer provided the information on domains and heterogeneities because the magnetization of small domains or heterogeneities equilibrated faster than that of larger ones. Three samples, International Humic Substances Society (IHSS) Suwannee River NOM, IHSS Suwannee River humic acid (HA), and a sedimentary HA, were used. Two model polymers, a random copolymer poly(styrene‐n‐butyl methacrylate) with 0.6‐nm heterogeneity and a block copolymer polystyrene‐b‐poly(methyl methacrylate) with a domain size of 5 nm, were included for calibration. Within tm < 100 µs, half equilibration was reached for all three NOM samples and poly(styrene‐n‐butyl methacrylate), indicating that they were heterogeneous. In contrast, the spin diffusion of polystyrene‐b‐poly(methyl methacrylate) with 5‐nm domain was much slower. Unlike the traditional spin diffusion technique, this technique did not require the differential mobility in NOM and was suitable for investigating the domains and heterogeneities of NOM, which are mostly rigid.

A simple method for quantifying the humic content of commercial products

A method based on an analytical technique, initially developed for quantifying aquatic refractory organic matter (often called humics), has been applied to commercial samples claiming to contain humic-type substances. At present, no method exists for quantifying the humic content on this type of sample. The analytical method is based on measuring the peak current obtained by adsorptive stripping voltammetry of the complex formed by refractory organic matter in the presence of trace amounts of Mo(VI). The quantification procedure requires the response obtained for the unknown sample to be compared with the response obtained with International Humic Substance Society (IHSS) reference humic substances. A very simple procedure that enables the humic content of any sample to be expressed as IHSS standard equivalents is described in detail. The method is highly selective, reproducible and suitable for routine analysis.

Mechanism of the Removal of AuCl−4 Ions from Aqueous Solution by Means of Peat Soil Humin

Peat soil humin, obtained after the removal of fulvic and humic acid fractions according to the recommended procedure of the International Humic Substances Society (IHSS), has the ability to remove AuCl-4 ions from aqueous solution. The removal was greatest at medium acidity, which was equivalent to pH 2.0, and it was governed by two different processes, i.e. attachment onto un-ionized -COOH groups through hydrogen bonding and reduction to Au metal by the action of the -OH group. Purification of humin through repeated immersion and shaking in a mixed solution consisting of 0.1 M HCl and 0.05 M HF led to the abrupt increase in the -COOH contents from 386 mmol/kg to 2510 mmol/kg, while the content of total -OH functional groups remained relatively constant at values slightly higher than 3000 mmol/kg. The increase in -COOH content improved the removal of AuCl-4 ions from 23 mg/g to 27 mg/g, but it was unfortunately accompanied by a diminished reduction ability to Au metal. Hence, the role of the -COOH functi...

Caracterização estrutural das substâncias húmicas aquáticas extraídas dos rios itapanhaú e ribeira de iguape

The knowledge of the structure characteristic of the Organic Matter is important for the understanding of the natural process. In this context aquatic humic substances (principal fraction) were isolated from water sample collected from the two distinct rivers, using procedure recommended for International Humic Substances Society and characterized by elemental analysis, electron paramagnetic resonance and nuclear magnetic resonance (13C NMR). The results were interpreted using principal component analysis (PCA) and the statistical analyses showed different in the structural characteristics of the aquatic humic substances studied.

Sorption of Organic Chemicals to Soil Organic Matter: Influence of Soil Variability and pH Dependence

For modeling the sorption of organic compounds in soils it is typically assumed that the organic carbon/water partitioning coefficient (Koc) of neutral organic chemicals can be treated as a constant property that remains unaffected by the type of soil organic matter as well as pH in the soil solution. Here the validity of these assumptions is evaluated with a large and diverse experimental data set of our own and literature data. To this end sorption experiments with 3 different soils and one peat were carried out using a column method. Differences in log Koc at pH values of 4.5 and 7.2 were on average <0.06 log units for 60 chemicals on Pahokee Peat. This result indicates that protonation/deprotonation of carboxylic groups in humic matter has no significant influence on sorption. The soil-to-soil variability of Koc was within factor of 3 regardless of the type of chemicals. The Pahokee Peat standard from the International Humic Substances Society appears to represent Koc in solid soil organic matter from different origins with an accuracy of ±0.23 log units (root-mean-square error). The comparison of the sorption data in Pahokee Peat with literature sorption data from the air in hydrated humic and fulvic acids suggested that the thermodynamic cycle for converting sorption data between air and water is applicable provided that for small, highly polar chemicals an additional water phase in the hydrated organic matter is considered.

Potentiometric quantification and speciation of oxygenated groups in humic substances using BEST7 software

In this study the BEST7 software was employed to quantify different classes of functional groups and to model the proton titration behavior of humic substances. To illustrate the process, the Suwannee River fulvic acid of the IHSS (International Humic Substances Society) was used. Five categories – two classes of phenolic groups (phenol and cathecol), two classes of carboxylic groups (benzoic and phtalic) and the combination between them (salicylic) - of oxygenated groups were considered as being responsible for the potentiometric behavior of the sample and were quantitatively determined. The most and the least abundant groups were cathecol (3.300 0.010 mmol g-1) and phenol (1.225 0.070 mmol g-1), respectively. The estimated equilibrium constants were also determined and were in good agreement with the literature values for phenol and cathecol groups and for benzoic, phtalic and salicylic acids. Distribution diagrams of the species were generated with the software SPE and SPEPLOT.

An Experimental and Modelling Study of Cu2+ Binding on Humic Acids at Various Solution Conditions. Application of the NICA-Donnan Model

Humic substances are characterized by a strong binding capacity for both metals and organic pollutants, affecting their mobility and bioavailability. The understanding of the mechanisms of proton and metal binding to humic substances is of fundamental importance in geochemical modelling and prediction of cation speciation in the environment. This work reports results on copper binding on humic acids obtained through a thorough experimental and modelling approach. Two humic acids, a reference purified peat humic acid isolated by the International Humic Substances Society (IHSS) and a humic acid from a Greek soil, were experimentally studied at various pH values (4, 6 and 8), humic acid concentrations (ranging from 20 to 200 mg L−1) and ionic strength (0.1 and 0.01 M NaNO3). The binding of copper to humic acids was determined over wide ranges of copper ion concentrations using a copper ion selective electrode. The copper binding isotherms obtained at different conditions have shown that copper binding is dependent on the pH and ionic strength of the solution and on the concentration of both humic acids. Copper binding experimental data were fitted to non-ideal competitive adsorption NICA-Donnan model and the model parameter values were calculated. Both Cu2+ and CuOH+ species binding to humic acid with different binding affinities were considered. Two sets of the NICA-Donnan parameters have been calculated: one for humic acid concentrations of ≥100 mg L−1and one for humic acid concentration of 20 mg L−1. The meaning of the parameters values for each concentration level is also discussed.

Characterization of dissolved organic matter (DOM) extracted from soils by hot water percolation (HWP)

The Hot Water Percolation (HWP) technique for preparing soil extracts has several advantages: it is easily carried out, fast, and several parameters can be measured from the same solution. The object of this study was to examine the possible use of HWP extracts for the characterization of soil organic matter. The HPLC-SEC chromatograms, UV-VIS and fluorescence properties of the HWP extracts were studied and the results were compared with those of the International Humic Substances Society (IHSS) Soil Humic Acid (HA), IHSS Soil Fulvic Acid (FA) and IHSS Suwannee Natural Organic Matter (NOM) standards as well as their HA counterparts isolated by traditional extraction methods from the original soil samples. The DOM of the HWP solution is probably a mixture of organic materials, which have some characteristics similar to the Soil FA fractions and NOM. The HWP extracted organic material can be studied and characterized using simple techniques, like UV-VIS and fluorescence spectroscopy.

Characterization and grouping of aquatic fulvic acids isolated from clear-water rivers and lakes in Japan

Characteristics of aquatic fulvic acids (FAs) from 10 clear waters in Japan (around the temperate zone) were revealed by several analytical techniques—high performance size exclusion chromatography (HPSEC), elemental analysis, liquid-state 13C NMR spectroscopy, isotopic analyses (δ 13C and δ 15N), and compared with those of International Humic Substances Society (IHSS) standard samples including FAs from brown waters (Suwannee, Pony, and Nordic FAs). Generally clear-water FAs were different from brown-water FAs in chemical properties. Weight-average molecular weights (Mw) of the clear-water FAs were similar to each other, whereas their elemental compositions and carbon species distribution were different. The clear-water FAs all exhibited a high proportion of alkyl carbons, which may be attributed to microbial activity. δ 13C and δ 15N values of the FAs indicated that there would be a huge gap between origin and chemical structure of clear-water FA. Results of the chemical structural analyses described above were not always linked to those of the isotopic analyses (δ 13C and δ 15N). Multivariate statistical analysis, i.e. cluster and principal component analysis was applied to reveal differences or similarities in a more objective manner. The FAs were always classified into two clear-water groups and one brown-water group. Aryl-C and O-Alkyl-C contents were important for the grouping. We speculate that the grouping might depend on the differences of aquatic microbial activity caused by the differences of residence time of water.

The effect of humic acid and ash on enantiomeric fraction change of chiral pollutants

The aim of the study was to determine changes of enantiomeric fraction (EF) of chiral compounds interacting with components of soil and to describe the effect of amount of soil components on EF value. Soil components (humic acid and ash) were isolated from soil using method recommended by the International Humic Substance Society (IHSS). Dichloromethane was used as an extraction solvent for extraction of polychlorinated biphenyls (PCBs), mecoprop and its methyl ester enantiomers from humic acid (HA) and ash. The extracts were analyzed by a high performance liquid chromatography (HPLC). HPLC columns filled with silica gel modified by permethylated cyclodextrine acting as a chiral selector were used for analytical separation of enantiomers. The results confirm the stereoselective effect of soil components on extractable amount of individual enantiomers. Significant changes of EF of chiral pollutants were observed for investigated PCBs enantiomers (HA 0.49–0.45, ash 0.50–0.58) and for mecoprop-methyl ester (HA 0.55–0.59, ash 0.49–0.34), smaller changes of EF were observed for mecoprop (HA 0.52–0.50, ash 0.49–0.50). The changes of EF were dependent on an amount of humic acid and ash. Inverse trends of humic acid EF changes were obtained comparing to trends of EF changes of ash.

Effect of instrument‐specific response on the analysis of fulvic acid fluorescence spectra

Fluorescence spectroscopy has been extensively employed to characterize the source, age, and reactivity of aquatic dissolved organic matter (DOM). However, there is no consensus on the protocols for collecting and correcting DOM fluorescence spectra for the instrument‐specific response associated with each component on a fluorometer involved in the excitation of DOM and the resulting detection of DOM emission. The central objective of this study was to evaluate the removal of instrument‐specific response from DOM fluorescence spectra collected on three different fluorometers using manufacturer‐provided emission and excitation correction files. We evaluated criteria and protocols for comparison of removal of instrument response, using quinine sulfate, a well‐characterized fluorophore, as well as the International Humic Substance Society's microbially and terrestrially derived reference end‐member fulvic acids: Pony Lake and Suwannee River fulvic acids, respectively. Our results demonstrate that sample spectra collected on different fluorometers differed significantly before correction. Although the effectiveness of manufacturer‐provided correction factors in removal of instrument response from sample spectra varied by instrument, spectral overlap of the same sample on multiple instruments improved after correction. Our results suggest that conclusions based on analysis of trends within a dataset of DOM fluorescence spectra should be expected to be independent of the fluorometer employed.

Potentiometric quantification and speciation of oxygenated groups in humic substances using BEST7 software

In this study the BEST7 software was employed to quantify different classes of functional groups and to model the proton titration behavior of humic substances. To illustrate the process, the Suwannee River fulvic acid of the IHSS (International Humic Substances Society) was used. Five categories – two classes of phenolic groups (phenol and cathecol), two classes of carboxylic groups (benzoic and phtalic) and the combination between them (salicylic) - of oxygenated groups were considered as being responsible for the potentiometric behavior of the sample and were quantitatively determined. The most and the least abundant groups were cathecol (3.300 0.010 mmol g-1) and phenol (1.225 0.070 mmol g-1), respectively. The estimated equilibrium constants were also determined and were in good agreement with the literature values for phenol and cathecol groups and for benzoic, phtalic and salicylic acids. Distribution diagrams of the species were generated with the software SPE and SPEPLOT.

Selected pioneering works on humus in soils and sediments during the 20th century: A retrospective look from the International Humic Substances Society view

Organic matter in general, and humic substances (HS) in particular, are involved in many processes in soils, sediments, rocks and natural waters. These include rock weathering, plant nutrition, pH buffering, trace metal mobility and toxicity, bioavailability, degradation and transport of hydrophobic organic chemicals, formation of disinfection by-products during water treatment, heterotrophic production in blackwater ecosystems and, more generally, the global carbon cycle. Before the 1970s, natural organic matter of different ecosystem pools ( i.e., soils, sediments, and natural waters) was often studied in isolation, although many similarities exist between them. This is particularly so for HS. In this historical context, a need appeared at the international level for bringing together environmental chemists, soil scientists, hydrologists, and geologists who were interested in HS to provide a forum for the exchange of ideas, to standardize analytical procedures and agree on definitions of HS. The International Humic Substances Society (IHSS) was founded in Denver, Colorado (USA) in 1981 with several objectives among them “to bring together scientists in the coal, soil, and water sciences with interests in humic substances” (home page of the IHSS web site: http://ihss.gatech.edu/ihss2/index.html). This paper presents selected pioneering works on humus in soils and sediments during the 20th century with a special focus on the links between the studies of soil HS and the formation, during early diagenesis, of the precursors of kerogens. Temporal coverage includes key contributions preceding the founding of the IHSS, and a brief history of the organization is presented.

Adapted DAX‐8 fractionation method for dissolved organic matter (DOM) from soils: development, calibration with test components and application to contrasting soil solutions

SummaryMost methods to fractionate natural dissolved organic matter (DOM) rely on sorption of acidified DOM samples onto XAD‐8 or DAX‐8 resin. Procedural differences among methods are large and their interpretation is limited because there is a lack of calibration with DOM model molecules. An automated column‐based DOM fractionation method was set up for 10‐ml DOM samples, dividing DOM into hydrophilic (HPI), hydrophobic acid (HPOA) and hydrophobic neutral (HPON) fractions. Fifteen DOM model components were tested in isolation and in combination. Three reference DOM samples of the International Humic Substances Society were included to facilitate comparison with other methods. Aliphatic low‐molecular‐weight acids (LMWAs) and carbohydrates were classified as HPI DOM, but some LMWAs showed also a partial HPO character. Aromatic LMWAs and polyphenols partitioned in the HPOA fraction, menadione (quinone) and geraniol (terpenoid) in HPON DOM. Molecules with log Kow &gt; 0.5 had negligible HPI fractions. The HPO molecules except geraniol had specific UV absorbance (SUVA, measure for aromaticity) &gt;3 litres g−1 cm−1 while HPI molecules had SUVA values &lt;3 litres g−1 cm−1. Distributions of DOM from eight soils ranged from 31 to 72% HPI, 25 to 46% HPOA and 2 to 28% HPON of total dissolved organic carbon. The SUVA of the HPI DOM was consistently smaller compared with the HPOA DOM. The SUVA of the natural DOM samples was not explained statistically by fractionation and the variation coefficient of SUVA among samples was not reduced by fractionation. Hence, fractionation did not reduce the variability in this DOM property, which casts some doubts on the practical role of DOM fractionation in predicting DOM properties.

An experimental and modeling study of humic acid concentration effect on H + binding: Application of the NICA–Donnan model

Humic substances are the most abundant components of the colloidal and the dissolved fraction of natural organic matter (NOM) and they are characterized by a strong binding capacity for both metals and organic pollutants, affecting their mobility and bioavailability. The understanding of the humic acidic character is the first necessary step for the study of the mechanisms of binding of other positively charged soluble metal species by humic molecules. The present work, which constitutes part of the Ph.D. thesis of Roza Vidali, reports results on the influence of the concentration of humic acids on the binding of protons obtained through both an experimental and a modeling approach. A reference purified peat humic acid (PPHA) isolated by the International Humic Substances Society (IHSS) and a humic acid from a Greek soil (GHA) were experimentally studied at various humic acid concentrations, ranging from 20 to 200 mg L −1. The proton binding isotherms obtained at different humic acid concentrations have shown that proton binding is dependent on the concentration of both humic acids. Proton binding experimental data were fitted to the NICA–Donnan model and the model parameter values were calculated for humic acid concentrations of 20 and ⩾100 mg L −1. The results obtained for the NICA–Donnan parameters at humic acid concentrations ⩾100 mg L −1 are in excellent agreement with those reported in the literature. However, these model parameter values cannot be used for modeling and predicting cation binding in natural aquatic systems, where humic acid concentrations are much lower. Two sets of the NICA–Donnan parameters are reported: one for humic acid concentrations of ⩾100 mg L −1 and one for humic acid concentration of 20 mg L −1. The significance of the parameters values for each concentration level is also discussed.