Humic Samples Research Articles

A comparison of water solubility enhancements of organic solutes by aquatic humic materials and commercial humic acids

Water solubility enhancements of 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (p,p'-DDT), 2,4,5,2',5'-pentachlorobiphenyl (2,4,5,2',5'-PCB), and 2,4,4'-trichlorobiphenyl (2,4,4'-PCB) by dissolved organic matter have been studied with the following samples: (1) acidic water samples from the Suwannee River, Georgia, and the Sopchoppy River, Florida; (2) a humic extract of a nearly neutral pH water from the Calcasieu River, Louisiana; (3) commercial humic acids from the Aldrich Chemical Co. and Fluka-Tridom Chemical Corp. The calculated partition coefficients on a dissolved organic carbon basis (K/sub doc/) for organic solutes with water samples and aquatic humic extracts from this and earlier studies indicate that the enhancement effect varies with the molecular composition of the aquatic humic materials, The K/sub doc/ values with water and aquatic humic samples are, however, far less than the observed K/sub doc/ values obtained with the two commercial samples, by factors of about 4-20. In view of this finding, one should be cautious in interpreting the effects of the dissolved organic matter on solubility enhancement of organic solutes on the basis of the use of commercial humic acids. 14 references, 3 figures, 2 tables.

An evaluation of the differences in the composition of humic acids in soils under oak and pine forest by GC-MS after mild degradation

Significant differences were found in the products released after eight samples of humic acids (HA’s) isolated from soils under mediterranean pine and oak forests underwent mild degradation. A number of compounds, including typical degradation products of lignins, were found exclusively in the HA’s from the soils under pine forests. The aliphatic constituents were more firmly retained in the HA’s under oak, which presented mean values for aromatic acids lower than the humic samples from pine forests. Different types of diterpene resin acids were also found amongst the mild degradation products of HA’s from the studied areas.

Studies on preconcentration methods for detecting the mutagenicity of organics in drinking water.

As a pretreatment in mutagenicity assays of non-volatile organic micropollutants in drinking water, the applicability of three methods of concentration (solvent extraction, XAD-2 column extraction and lyophilization) was investigated in conjunction with Ames Salmonella/microsome assays. Raw and tap water samples and ozonated and chlorinated humic samples used were assayed with strains TA 98, TA 100 and TA 104. When lyophilization was employed, the detection of the mutagenicity of organic micropollutants in tap water required at least 10000-fold concentration, and as a solvent of mutagenic materials in tap water, DMSO was more effective than distilled water. Of the three preconcentration methods, the acidic extracts in the ethyl ether extraction and the dichloromethane fractions in the XAD-2 column extraction were found to recover selectively mutagenic and non-volatile organic materials from all of raw water, tap water and chlorinated humic samples. In particular, the XAD-2-dichloromethane fraction was considered to recover quantitatively mutagenic products from chlorinated humic samples. These findings indicate that XAD-2 column extraction may be the most suitable preconcentration procedure for organic micropollutants in water.

Diborane reduction of humic substances

Changes in the composition and properties of humic substances following repeated treatments with diborane in tetrahydrofuran have been investigated. Solubility, ionic mobility, elementary composition and spectral characteristics of diborane-treated samples suggest that both humic and fulvic acids undergo a drastic chemical change-ypon reduction. The disappearance of the band at 1720 cm and the prominent absorption centred at 1010 cm in the IR spectra of the reduced samples are noticeable, and may be explained in terms of an efficient transformation of carboxyl groups into alcoholic OH. These modifications in the distribution of oxygen-containing functional groups, are probably responsible for the reported changes in the colloidal properties and the structural characteristics of the diborane-reduced humic samples.

Pyrolysis-mass spectrometry/pattern recognition on a well-characterized suite of humic samples

A suite of well-characterized humic and fulvic acids of freshwater, soil and plant origin was subjected to pyrolysis-mass spectrometry and the resulting data were analyzed by pattern recognition and factor analysis. A factor analysis plot of the data shows that the humic acids and fulvic acids can be segregated into two distinct classes. Carbohydrate and phenolic components are more pronounced in the pyrolysis products of the fulvic acids, and saturated and unsaturated hydrocarbons contribute more to the humic acid pyrolysis products. A second factor analysis plot shows a separation which appears to be based primarily on whether the samples are of aquatic or soil origin.

Extraction and neutron activation analysis of humic substances

Methods are described for the isolation of humaic substances from a soil samples. The produres and based on extractions with sodium hydroxide or sodium pyrophosphate. Four of the humic samples were dried and then analysed by thermal neutron activation analysis. The humic samples along with three standard rocks were irradiated for 15 hours in a flux of ∼1012 n·cm−2·s−1. Counting was carried out using both a large volume Ge(Li) detector and a high resolution LEP detertor. Quantitative analysis was based on the known element concentrations in the standard rocks. The elements determined were Sc, Cr, Fe, Co, As, Se, Br, Mo, Sb, La, Ce, Eu, Hf, Ta, Th, and U. concentrations ranged from 0.02 ppm (La) to 7900 ppm (Fe).

Analytical constraints on the structural features of humic substances

A rigorous calculation of the maximum fraction of aromatic carbon in humus or any other complex mixture of organic compounds is described. Input parameters include elemental composition, carboxyl content, carbonyl content, and an estimate of number-average molecular weight. The calculated upper limit constrains structural models that are based on interpretations of 13C-NMR spectra or on the products of degradation reactions and also directly limits the phenolic content of a sample. Another computational method is described that yields good estimates of the actual levels of aromatic (and aliphatic) carbon in a humus sample. Even though the method is capable of estimating only the most probable level of aromatic carbon, the predicted values are surprisingly close to the experimental values that have been determined by 13C-NMR spectroscopy.

Constantes de stabilité de complexes organo-minéraux. Interactions des ions plombeux avec les composés organiques hydrosolubles des eaux gravitaires de podzol

The complexation of lead(II) ions by water-soluble soil organic matter as ligand (recovered by percolating water through a A2 horizon of a podzolic soil) has been studied by potentiometric methods at 25°C in 0.1 M NaClO 4 medium. The total acidity of these solutions was resolved into strong, weak and very weak acidity. During the alkali titration, the dissociation of humic samples was characterized by an α coefficient that may be determined according to a procedure derived from Irving-Rossotti's method. The so-called Henderson-Hasselbalch equation was used to obtain pK A values for each of the two weak acidities ( pK A = 4.80 (COOH) and pK A = 8.85 (OH)). For the determination of stability constants of metal-humate complexes (HA) in the acidic range, three methods have been investigated: • —an approach using only pH measurements. • —direct estimation of the free metal ion concentrations from ISE determinations. • —application of Marinsky's method accounting for complications arising from the electric field at the surface of the polyelectrolyte which determines the effective concentration [A]. In these experiments typical values used for total lead(II) ion concentrations and total ligand concentrations are respectively in the range 4.10 −5 M to 4.10 −4 M and 0,33 to 0,57 meq·1 −1. All results agree with the existence of mono and bis-complexes PbA and PbA 2 with stability constants (protometric determinations): log K 1 = 4.2 and log K 2 = 3.7. The values obtained by direct estimation of free lead(II) concentration are slightly lower. An increase in stability constants was observed with increase in pH and also with decrease in total metal ion concentration (at constant pH). Ligand conformational properties are expected to be of great importance in the complexation phenomena.

New approach for the determination of stability constants of metal ions-soil organic matter

The binding of metal ions to organic materials in soil and water is an area of considerable interest. A better understanding of the equilibria that determine the behaviour of the chemical elements in the superficial environment is clearly essential for effective geochemical research. Naturally occurring organic compounds are an integral part of soils and aquatic systems. These substances play a major role in the retention and deactivation of anthropogenic organic and mineral chemicals and are involved in the geotransport of metals. Humic substances make up the bulk of organic matter and they probably control the abundance and distribution of trace metals in the environment by complexation or chelation processes through functional groups including carboxylic, phenolic, alcoholic and enolic OH, carbonyl and NH 2 sites at which binding may occur [1]. The determination of stability constants of metal-humic and fulvic acid complexes permits the prediction of the chemical speciation of many metals and the elucidation of their dispersion cycles. The present work deals with the interactions of lead(II), cadmium(II) and copper(II) ions with water soluble soil organic matter. Cu(II) like Zn(II), Mn(II)…, is a metal which is essential to plants while Cd(II) and Pb(II) are without known function in plants but are of considerable interest in view of their toxicity and accumulation in the environment. A variety of methods have been applied for determining stability constants of metalhumate complexes, as reviewed by Stevenson [1]. Considerable progress has been made, but agreement has not yet been reached as to how the data can best be analyzed and interpreted. One of the most popular methods is base titration, which uses the competition of metal ions and protons for complexing sites on the ligand. It is such a modified approach that has been developed in this work. Humic substance samples (in this context, this term will be used to designate a system of organic water soluble compounds including polymers) were recovered by percolating rain-water through a A2 horizon of a podzolic soil and purified by filtration, ultracentrifugation, and treatment by passage through ion exchange resins [2]. Stock solutions of metallic perchlorates were prepared from commercial products and standardized against EDTA. Samples containing constant quantities of humic substances and perchloric acid were titrated by sodium hydroxide in the absence and in the presence of metal ion. Protometric measurements were performed at 25 °C in 0.1 NaClO 4 medium under nitrogen atmosphere. An automatic titrator ‘Tacussel TT Processor’ fitted with extension glass and calomel electrodes was used for recording direct and differential titration curves; pH readings were combined with determinations of free metal ion concentrations by means of ion selective electrodes (ISE). Titration and Protonation Constants of Humic Samples For humic substances which contain COOH and OH groups of various acid strengths we shall define the ligand concentration in terms of titratable acidity. The total acidity content was resolved into a strong, weak and weak acidity by applying linear titration plots derived by McCallum and Midgley [3] in combination with Gran's plots as previously used by Takamatsu and Yoshida [4]. In order to obtain pK a values for each of the two weak acidities, the so-called extended Henderson-Hasselbalch equation was used pH = pK a + n log α/(1 − α) During the alkali titration, the dissociation of humic samples was characterized by a coefficient that may be determined from titration curves of perchloric acid alone and in the presence of humic substances, according to a procedure derived from Irving-Rossotti's method [5]. Figure 1 shows typical Henderson-Hasselbalch plots leading for instance to results such as: • strong acidity: 0.32 meq 1 −1 • weak acidity groups (COOH): 0.33 meq 1 −1; pK a = 4.54; n = 2.15. • very weak acidity groups (OH): 0.34 meq 1 −1; pK a = 9.33; n = 2.59. ▪ Stability Constants of MetalHumate Complexes (HA) Three different methods have been investigated in the acidic range: • an approach closely related to that of Gregor . [6] but the experimental values of [HA] and [A −] are determined using an original derivation of equations resulting from the application of Irving and Rossotti's concepts [5]. • direct estimation of the free metal ion concentrations from ISE measurements. • application of Marinsky's method [7] accounting for complications arising from the electric field at the surface of the polyelectrolyte which determines the effective concentration [A −]. Reasonable agreement is observed. The existence of mono-complexes MA is expected for the three metal ions, while bis-complexes MA 2 are detected with Pb(II) and Cu(II) ions. Stability of the complexes followed the order Cu > Pb 》Cd. An increase in stability constant was observed with increase in pH and also with decrease in total metal ion concentration (at constant pH), as exemplified by Fig. 2.

Analysis of the carbohydrates of fulvic and humic acids as their partially methylated alditol acetates

The carbohydrates of humic and fulvic acids were investigated using methylation analysis. The humic acid contains slightly more rhamnose and fucose than does fulvic acid and raw humus, the arabinose content of fulvic acid is less when compared to that of humic acid and raw humus. In addition to the common aldoses, the unmethylated humic samples contained small amounts of 2,3-di-O-methyl-rhamnose, 2,3-di-O-methyl-fucose, 2-O-methyl-rhamnose, 4-O-methyl-rhamnose, 3-O-methyl-rhamnose, 3-O-methyl-fucose and a 6-deoxy-hexose. The “average” polysaccharides of humic and fulvic acids are highly branched and extremely complex in composition. They contain at least 34 different aldose building units in addition to O-methyl-, di-O-methyl-, and amino-derivatives, ketoses and uronic acids. On average, the polysaccharides of fulvic acid are slightly less branched than those of humic acid, as indicated by a higher content of the chain unit 2,4,6-tri-O-methyl-glucose in the hydrolysate of methylated samples. In total, the polysaccharides of the different fractions are of great similarity. The common aldoses all participate as 1–2 different terminating units, 1–3 different chain units, and the hexoses as 2–4 different branching units. In methylated samples, only one 6-deoxy-hexose branching unit is found, 3-O-methyl-rhamnose, and no pentose unit. 3-O-methyl-rhamnose may also be a branching unit in unmethylated samples. The most important terminating units are 2,3,4,6-tetra-O-methyl-gluco- plus 2,3,4,6-tetra-O-methyl-manno- (15%), 2,3,4-tri-O-methyl-xylo- (6%) and 2,3,4-tri-O-methyl-fuco-pyranose (5%) units. Terminal 2,3,5-tri-O-methyl-xylo-, 2,3,5-tri-O-methyl-arabino- and 2,3,5,6-tetra-O-methyl-galacto-furanosidic units are also present (2.7-1.2%). The most important chain units are 2,4,6-tri-O-methyl-glucose (11–15%), 2,3-(or 3,4-) di-O-methylxylose (6.6%) and 3,4,6-tri-O-methyl-galactose (3.3%). The individual polysaccharides of the humic and fulvic acids are also of high complexity and most probably are present in a large number of varieties. All polysaccharides are strongly associated with the humic matrix, i.e., the aromatic and aliphatic polymeric structure composing the major part of the humic and fulvic acids.

Effect of pH on the filtration of aquatic humus using gels and membranes

The colour of aquatic humus increases with pH. The ‘molecular weight distribution’ of a concentrated humus sample has been studied at diffrent pH-levels and ionic strength by use of a molecular sieve (Sephadex G-25) and membrane dialysis. The fraction excluded from G-25 became greater, proportionally with increasing pH, and this was apparently not affected to any great extent by the ionic strength.

Alkaline nitrobenzene oxidation of plant lignins and soil humic colloids

Plant lignins and soil humic colloids were isolated using H2SO4, NaOH and 1,4-dioxane and their elemental composition, methoxyl contents and cation exchange capacities were determined. The isolated lignin and humic colloid samples were oxidized by the alkaline nitrobenzene technique and the degradation products characterized by the types and amounts of phenolic aldehydes produced.