The uniqueness of humic substances in each of soil,stream and marine environments

Definitive compositional differences are shown to exist for both fulvic acids and humic acids from soil, stream and marine environments by five different methods (¹H and ¹³C NMR spectroscopy, ¹⁴C age and δ¹³C isotopic analyses, amino acid analyses and pyrolysis-mass spectrometry). Definitive differences are also found between fulvic acids and humic acids within each environment. These differences among humic substances from various sources are more readily discerned because the method employed for the isolation of humic substances from all environments excludes most of the non-humic components and results in more purified humic isolates from water and soils. The major compositional aspects of fulvic acids and humic acids which determine the observed characteristic differences in each environment are the amounts and composition of saccharide, phenolic, methoxyl, aromatic, hydrocarbon, amino acids and nitrogen moieties.     

The inner filter effects and their correction in fluorescence spectra of salt marsh humic matter

The inner filter effects in synchronous fluorescence spectra (Δλ = 60 nm) of sedimentary humic substances from a salt marsh were studied. Accordingly to their type and the influence of plant colonization, these humic substances have different spectral features and the inner filter effects act in a different manner. The fluorescence spectra of the humic substances from sediments with colonizing plants have a protein like band (λ_exc = 280 nm) which is strongly affected by primary and secondary inner filter effects. These effects were also observed for the bands situated at longer wavelengths, i.e., at λ_exc = 350 nm and λ_ex = 454 nm for the fulvic acids (FA) and humic acids (HA), respectively. However, they are more important for the band at 280 nm, causing spectral distortions which can be clearly seen when the spectra of solutions 40 mg L⁻¹ of different samples (Dissolved Organic Carbon – DOC ∼ 20 mg L⁻¹) are compared with and without correction of the inner filter effects. The importance of the spectral distortions caused by inner filter effects has been demonstrated in solutions containing a mixture of model compounds which represent the fluorophores detected in the spectra of sedimentary humic samples. The effectiveness of the mathematical correction of the inner filter effects in the spectra of those solutions and of solutions of sedimentary humic substances was studied. It was observed that inner filter effects in the sedimentary humic substances spectra can be mathematically corrected, allowing to obtain a linear relationship between the fluorescence intensity and humic substances concentration and preventing distortions at concentrations as high as 50 mg L⁻¹ which otherwise would obscure the protein like band.     

Humic substances in surface waters of the Ukraine

The results of studies of humic substances in water bodies of different types (lakes, rivers, and reservoirs) are given. It is shown that concentration of these natural organic compounds varies in a wide range of values (from 1.2 to 126.5 mg L^?1) due to different sources of their formation. The highest concentrations of humic substances are characteristic for rivers of the Pripyat’ River basin flowing through the wetland. As we move from the north to the south, the content of humic substances is reduced. So, in the Kakhovka Reservoir, closing the Dnieper cascade of reservoirs, the concentration of humic substances is almost thrice as low as in the Kiev Reservoir, which is at the head of the cascade. Seasonal changes of humic substances concentration and the reasons for these changes are discussed. The prevailing fraction in the composition of humic substances is represented by fulvic acids, the content of which reaches 80.8–94.8% of the total. The results of studies of the molecular weight distribution of humic substances and the reasons for changes in the ratio of their individual fractions, depending on the detection method (spectrophotometric and fluorescence methods), are considered. The values of the number average (M _n) and weight average (M _w) molecular weight of humic substances and the degree of polydispersity are calculated. It is shown that M _w varies seasonally. In spring and summer it is lower, but significantly increased in autumn. The reason for this phenomenon is degradation of high-molecular fractions of humic substances under the influence of UV light of solar radiation and increased microbiological activity during the summer season. As a result of these processes high-molecular fractions of humic substances are transformed into fractions with lower molecular weight, which become predominant.     

Influence of the presence of surfactants and humic acid in waters on the indophenol-type reaction method for ammonium determination

This work has evaluated the influence of humic acid and/or surfactants in the quantification of ammonium in waters with the indophenol-type reaction method. Thymol has been employed with the colorimetric method for sample ammonium concentrations between 0.25 and 1 mg L⁻¹. In addition, SPE/diffuse reflectance method has been used for quantification of ammonium at low concentrations (between 0.025 and 0.25 mg L⁻¹). Matrix effect owing to humic substances were observed with the colorimetric method when the concentration was equal or higher than 25 mg L⁻¹. Lower concentrations of humic compounds produced matrix effects with the more sensitive SPE/diffuse reflectance method. Generalized H-point standard addition method (GHPSAM) was employed for evaluating the effect of humic acids and for eliminating the bias error produced by humic acids. Real water samples of different types were analyzed and accurate results for ammonium concentration were obtained with both procedures in presence or absence of humic acids. Cationic and anionic surfactants inhibited the derivatization reaction at percentages up to 0.001% and 0.5%, respectively, and non-ionic surfactants at percentages of 5.5%     

Determination of the phenolic-group capacities of humic substances by non-aqueous titration technique

The phenolic-group capacities of five humic substances, such as, the Aldrich humic acid, the humic and fulvic acids extracted from a soil, the humic and fulvic acids extracted from a peat have been precisely determined by the non-aqueous potentiometric titration technique. The titration by KOH in the mixed solvent of DMSO:2-propanol:water = 80:19.3:0.7 at [K⁺] = 0.02 M enabled to measure the potential change in a wide range of pOH (=−log [OH⁻]), and thus to determine the capacities of phenolic groups which could not be precisely determined in the aqueous titration. The results of the titration revealed that the mean protonation constants of the phenolic groups were nearly the same for all humic substances and close to that of phenol in the same medium, indicating that each phenolic-group in the humic substances is rather isolated and is not electronically affected by other affecting groups in the humic macromolecule.     

Flow Injection Determination of Humic Acid with Chemiluminescence Detection

Abstract

A very sensitive and fast flow injection chemiluminescence method, based on the oxidation of humic acid (HA) by 1,3‐dibromine‐5,5‐dimethylhydantion in the presence of glycine in alkaline medium, was developed for the determination of trace humic acids in water. A wide calibration range from 0.001 to 1.0 µg mL^?1 was obtained at the optimized conditions and the detection limit was as low as 0.5 ng mL^?1 of humic acids. Most of the foreign substances tested showed relatively high tolerance levels and the proposed method was successfully applied to the determination of humic acid in river water and tap water.     

Spectroscopic approaches to the study of the interaction of aluminum with humic substances

Aluminum ion (Al³⁺) in the ‘free’ (aquo) state is becoming increasingly prevalent in environmental waters, especially fresh waters, as a consequence of acid rain and other environmental processes. As Al³⁺ ion is known to affect markedly a wide range of biological systems, and since the presence of Al³⁺ in humans has been linked to a number of human diseases, it is important to understand the speciation of Al³⁺ ion in natural waters. Since some of the most important complexation agents for Al³⁺ in both fresh and sea waters are members of the complex humic substances group, it is important to understand the manner in which Al³⁺ interacts with this class of molecules, especially since binding of Al³⁺ to these molecules can effectively increase the bioavailability of this toxic metal ion to biological systems. The objective of this review is to present the current state of our understanding of aqueous aluminum complexation with the most acidic members (and therefore the most likely candidates for serving as Al³⁺ complexing agents) of the humic substances group, the fulvic acids. Much of the current knowledge has been revealed by comprehensive fluorescence titration analyses. Some additional information has come from other experimental approaches, including infrared spectroscopy, nuclear magnetic resonance spectroscopy, and a variety of electrochemical approaches. In this review, we also report on the results of our recent fluorescence and IR spectroscopy survey of the interaction of metals from of all three Nieboer and Richardson categories of environmental metals (Class A, Class B and Intermediate Class) with the fulvic acid sub-group of the humic substances. This has proven helpful in understanding some of the unique spectral behaviors of the Al³⁺-fulvic acid complex vis-a-vis fulvic acid complexes with many other metal ions. The results of our fluorescence and IR experiments with the model compounds, such as salicylic and phthalic acids, have allowed confirmation of the important roles played by both salicylic acid-like sites and phthalic acid-like sites in the unique complexation of Al³⁺ to humic substances, and help to explain some of the observed spectroscopic changes associated with Al³⁺ ion complexation to humic material. From the current work, it seems clear that major sources of the deviation in spectral properties between Al³⁺ and many other metal ions (across all three Nieboer and Richardson categories) are the unusually high value of its charge density and relatively low propensity for involvement in covalent bonding interactions (i.e. a very high ionic index combined with a relatively low covalent index in the Nieboer and Richardson classification of environmental metals), as well as affinity for certain functional groups.     

The application of 2,4,6-trinitrobenzene-1-sulphonic acid in the differential pulse polarographic determination of amines

The differential pulse polarographic behaviour of 2,4,6-trinitrophenyl (TNP) derivatives of several primary amines and amino acids was investigated in the presence of sulphite ion. All the derivatives produced a polarographic peak for their complexes with sulphite (1 × 10^?2 M) in pH 8.0 phosphate buffer (0.05 M)/0.1 M potassium chloride. The derivatives of proteins and peptides did not give such a peak. A 5-min reaction time at room temperature (or 50°C for lysine) and pH 10.5 using 1 × 10^?4 M 2,4,6-trinitrobenzene-1-sulphonic acid provides the optimal conditions for the determination of 5 × 10^?6?2.5 × 10^?5 M amines. The relative standard deviation for determining 1 × 10^?5 M glycine (n = 5) was 1%.     

Visible-light promoted photoprocesses on aqueous gallic acid in the presence of riboflavin. Kinetics and mechanism

Within the frame of possible precursory photoreactions in the generation of humic substances, the visible-light promoted interaction between riboflavin (Rf), a native photosensitizer in aqueous systems, and gallic acid (GA), a polyphenol naturally formed after lignin degradation, was investigated. A systematic kinetic and mechanistic study was conducted under aerobic conditions in aqueous media, through visible-light continuous photolysis, polarographic detection of oxygen uptake, stationary and time resolved fluorescence spectroscopy, time resolved near-IR phosphorescence detection and laser flash photolysis techniques. GA is degraded relatively fast in pH 7 aqueous solutions, where singlet molecular oxygen (O₂(¹Δ_g)), superoxide radical anion (O₂^?) and hydrogen peroxide (H₂O₂) – all three species photogenerated from triplet excited Rf – participate in the photoprocess. The general conclusion is that in natural waters GA can undergo spontaneous phototodegradation under environmental conditions. Radical species generated in the presence of Rf can participate in condensation or polymerization reactions promoting the natural synthesis of humic products.     

Fractionation analysis of trace metals in humic substances of soils irrigated with wastewater in Central Mexico by particle induced X-ray emission

The Mezquital Valley in Central Mexico has received wastewater from Mexico City for nearly 100 years. Wastewater brings in organic matter and nutrients but also trace metals. Humic substances, the main components of organic soil matter, are responsible for retaining and regulating the mobility of trace metals in soils. In this study, humic substances were extracted from the soil and separated into distinct fractions (humic acids, fulvic acids and humins). The particle induced X-ray emission (PIXE) technique was applied to determine the metal content in bulk soil as well as in humic acids and fulvic acids not soluble in H₃PO₄. In order to assess whether the long-term input of organic matter and metals modifies the metal association with these humic substances, parcels irrigated for three time periods (5, 47 and 89 years) were selected for this study. It was observed that metals such as Zn and Cu are mainly associated with the humic acids. Fulvic acids retain mainly Cr while Pb is distributed among humic and fulvic acids. It was also observed that in general, metal retention by humic substances increases with irrigation time. Depth also affects metal association with the humic substances.     

Hydrophilic interaction liquid chromatography method for measuring the composition of aquatic humic substances

A hydrophilic interaction liquid chromatography (HILIC) method was developed to measure the composition of humic substances from river, reservoir, and treated wastewater based on their physicochemical properties. The current method fractionates the humic substances into four well-defined groups based on parallel analyses with a neutral and a cationic HILIC column, using mobile phases of varied compositions and pH. The results indicate that: (i) the proportion of carboxylic acids in the humic substances from terrestrial origins is less than half of that from treated wastewater (Jeddah, KSA), (ii) a higher content of basic compounds was observed in the humic substances from treated wastewater and Ribou Reservoir (Cholet, France) than in the sample from Loire River (France), (iii) a higher percentage of hydrophobic macromolecules were found in the humic substances from Loire River than in the other samples, and (iv) humic substances of treated wastewater contained less ionic neutral compounds (i.e., pK_a 5–9) than the waters from terrestrial origins. The physicochemical property disparity amongst the compounds in each humic substances sample was also evaluated. The humic substances from the lightly humic Loire river displayed the highest disparity, whereas the highly humic Suwannee river (Georgia, USA) showed the most homogeneous humic substances.     

Differential-pulse polarography of amino acids in acetaldehyde-borax medium

A differential-pulse polarographic method for the determination of amino acids is reported, based on the formation of Schiff's base compounds in borax buffer solution (pH 10.10) containing acetaldehyde. The compounds are reduced at a mercury electrode with peak potentials of about ?1.5 V (vs. SCE) and well defined polarographic waves are obtained which can be used to determine amino acids in borax medium. The differential-pulse polarographic method was found to be the most sensitive and suitable for the determination of amino acids in the concentration range 1 × 10^?6–8 × 10^?4 M (lysine) and 2.8 × 10^?6–1 × 10^?3 M (arginine). The polarographic characteristics of these waves were studied by differential-pulse polarographic and cyclic voltammetric methods. The waves are ascribed to the reduction of the imido group in the Schiff's base compounds. The procedure was applied to the determination of lysine and arginine in foodstuffs and the total proteins in serum samples.     

Fire impact on forest soils evaluated using near-infrared spectroscopy and multivariate calibration

The assessment of physico-chemical properties in forest soils affected by fires was evaluated using near infrared reflectance (NIR) spectroscopy coupled with chemometric methods. In order to describe the soil properties, measurements were taken of the total organic carbon on solid phase, the total nitrogen content, the organic carbon and the specific absorbences at 254 and 280 nm of humic substances, organic carbon in humic and fulvic acids, concentrations of NH₄⁺, Ca²⁺, Mg²⁺, K⁺ and phosphorus in addition to NIR spectra. Then, a fire recurrence index was defined and calculated according to the different fires extents affecting soils. This calculation includes the occurrence of fires as well as the time elapsed since the last fire. This study shows that NIR spectroscopy could be considered as a tool for soil monitoring, particularly for the quantitative prediction of the total organic carbon, total nitrogen content, organic carbon in humic substances, concentrations of phosphorus, Mg²⁺, Ca²⁺ and NH₄⁺ and humic substances UVSA₂₅₄. Further validation in this field is necessary however, to try and make successful predictions of K⁺, organic carbon in humic and fulvic acids and the humic substances UVSA₂₈₀. Moreover, NIR coupled with PLS can also be useful to predict the fire recurrence index in order to determine the spatial variability. Also this method can be used to map more or less burned areas and possibly to apply adequate rehabilitation techniques, like soil litter reconstitution with organic enrichments (industrial composts) or reforestation. Finally, the proposed recurrence index can be considered representative of the state of the soils.     

Separation and determination of traces of heavy metals complexed with humic substances in fresh waters by sorption on diethylaminoethyl-sephadex a-25

Copper(II), lead and cadmium complexed with humic and fulvic acids in filtered 1-l samples of fresh water are sorbed on a column containing 0.5 ml of the macroreticular weak-base anion exchanger, diethylaminoethyl-Sephadex A-25 at a flow rate of 20 ml min^?1. Simple metal cations are not sorbed at all. The sorbed trace metals are quantitatively desorbed with 4 M nitric acid batchwise and determined by graphite-furnace atomic absorption spectrometry. For synthetic aqueous solutions containing traces of heavy metals and humic acid, the results are in conformity with those obtained by cationexchange separation. About 80% of the sorbed humic substances are eluted with 0.5 M sodium hydroxide solution from the A-25 column and its quantity is estimated spectrophotometrically at 400 nm.     

Detoxification of AM-241 solutions by humic substances: bioluminescent monitoring

The study addresses the effect of humic substances on marine luminous bacteria Photobacterium phosphoreum exposed to Am-241 (3,000 Bq L⁻¹, water solution). Luminescent intensity of the bacteria was applied as a marker of their physiological activity. Humic substances have been found to reduce the effect of Am-241 on luminescence, decrease damage to cells, and change distribution of Am-241 between bacterial cells and intercellular media. It was shown that water-soluble humic substances, being products of natural transformation of organic substances in soil and bottom sediments, can serve as protecting agents for water microorganisms exposed to alpha radionuclides.     

Polarographic determination of nitrate in concentrated sulphuric acid solutions

The possibility of the polarographic determination of nitrates in the presence of hydroquinone in 65–95% sulphuric acid solutions was investigated. It has been found that nitrates in 95% acid have one polarographic wave without inflection point the height of which is proportional to nitrate concentration. In 85% sulphuric acid and in other acids investigated with lower concentrations, nitrates are not polarographically active. If both nitrate and hydroquinone are present in H₂SO₄, two waves are observed on the polarogram. The more negative wave is completely defined. The height of this wave is proportional to nitrate concentration in the range 5×10^?5?5×10^?3M.     

Kinetics of the sulfate radical‐mediated photo‐oxidation of humic substances

The kinetics of the aqueous phase reaction of sulfate radicals with commercial humic acids and with organic matter extracted from vermicompost (VC) was studied by flash‐photolysis. The results can be interpreted by a mechanism that in a first step considers the reversible binding of the sulfate radicals by the humic substances. Both the bound and free sulfate radicals decay to oxidized products. From experiments performed with Aldrich humic acids in the temperature range from 283 to 303 K, the enthalpy change associated with the binding process was estimated to be ?(36 ± 11) kJ mol^?1. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40: 19–24, 2008     

Impact of environmental conditions on the sorption behavior of 60Co(II) on illite

In this work, a naturally occurring illite was characterized by using FT-IR and XRD technique to determine its surface functional groups and crystal structure. Sorption of ⁶⁰Co(II) on illite as a function of contact time, pH, ionic strength, foreign ions, humic substances and temperature was studied under ambient condition using batch technique. The results indicated that the sorption of ⁶⁰Co(II) on illite is strongly affected by pH values (2–9) and ionic strength. A positive effect of humic substances on ⁶⁰Co(II) sorption was found at pH < 7.0, whereas a negative effect was observed at pH > 7.0. At low pH, the sorption of ⁶⁰Co(II) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on illite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The Langmuir and Freundlich models were used to simulate the sorption isotherms of ⁶⁰Co(II) at three different temperatures of 298.15, 323.15 and 343.15 K. The thermodynamic parameters (ΔH ⁰, ΔS ⁰ and ΔG ⁰) calculated from the temperature dependent sorption isotherms indicated that the sorption process of ⁶⁰Co(II) on illite was endothermic and spontaneous.     

Polarographic determination of picolinaldehyde in the presence of some related compounds

A d.c. polarographic method is described for the determination of picolinaldehyde (1.5 × 10^?5–2.9 × 10^?4 M), based on the in situ formation of its Girard-P derivative in aqueous solution. A mechanism of reduction (E_1/2 = ?0.71 V at pH 3.5) is proposed. The applicability of this method is checked in synthetic samples containing pyridine, picoline and pyridine carboxylic acids.     

445 — Reaction of the purine and pyrimidine derivatives with the electrode mercury

The electrochemical behaviour of 30 purine and pyrimidine derivatives and of a further 12 derivatives containing sulphur or halogens was studied. It was demonstrated that most of these substances react with the electrode mercury and form sparingly soluble compounds; this phenomenon can be exploited for the determination of purine and pyrimidine derivatives at low concentrations. The relation between the structural formulae of the substances and their ability to yield anodic polarographic currents conditioned by formation of sparingly soluble compounds with mercury was found. The behaviour of adenine and 8-oxyadenine was studied in greater detail by means of differential (DPP) and normal pulse polarography (NPP), d.c. polarography and cathodic stripping voltammetry (CSV). Both substances can be determined with the aid of the CSV at concentrations of the order of magnitude of 10⁻⁹M, while DPP may be used at concentrations three to four orders of magnitude higher. Interactions of some purine and pyrimidine derivatives with Hg(II) ions in homogeneous aqueous solutions were investigated. On the one hand, a correlation was found between the ability of these substances to react with mercury in solution and form precipitates, and, on the other hand, to yield anodic polarographic currents.