Application of approach to equilibrium analytical ultracentrifugation (Archibald method) to the determination of molecular weights of humic substances.
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Benzopyrans↗
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Determination of the carboxyl content in humic substances by methylation.
The carboxyl content of different fulvic acids was estimated by means of a methylation technique. The procedure involved methylation by diazomethane followed by base catalyzed hydrolysis, esterification with propionyl chloride and gas chromatographic analysis of the methyl ester formed. After optimization of each step, the whole sequence of reactions was performed using only a few milligrams of starting material. The method was applied to two fulvic acid samples of different origin (surface water and groundwater, respectively). The carboxylic content was estimated to about 3.5 meq/g material for the surface water fulvic acid and about 4.5 meq/g material for the groundwater fulvic acid. This estimates approximately 80% of the total content of acidic groups obtained for the same materials by using potentiometric titration.
Benzopyrans↗
Bioavailability of aluminium in the presence of humic substances at low and moderate pH.
Fish kills have been observed in lakes with low pH and high Al content. The monomeric inorganic Al seems to be the most acute toxic fraction. Humic lake waters, situated in acidified areas, often have high values of aluminium. However, the fraction of Al bound to humus is regarded as a relatively nontoxic form of Al. As pH is decreasing, the physical and chemical properties of humus change. The molecular size, electronegativity and colour decrease. An important question in this matter is the potential change in bioavailability of "Al-humus" as pH decreases. The bioavailability of the Al-humus complex was studied; in relation to surface water acidification and in relation to drinking water and human health. The work is based on the octanol/water partition coefficient (Khow), estimated by measuring the UV absorption at 254 nm. Al concentration is determined in the water phase and in the octanol phase. The results show that the amount of organic material soluble in the octanol phase relative to the amount in the aqueous phase increases with decreasing pH, while no Al is detected in the octanol phase. It is concluded that Al is only weakly bound to humus and consequently Al complexed with humus is of minor concern in bioaccumulation.
Aluminum↗
Effect of an addition of sodium sulfite on the mutagenicity of chlorinated solutions of aquatic humic substances.
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Chlorine↗
A study of inactivation reactions of N-acetylcysteine with mucochloric acid, a mutagenic product of the chlorination of humic substances in water.
The Salmonella typhimurium (TA100) mutagenic compound, mucochloric acid [3,4-dichloro-5-hydroxy-2(5H)-furanone (MCA)], was inactivated by in vitro N-acetylcysteine (NAC). The reaction of MCA with NAC at pH7 was second order and gave products 4, 5, and 6a that resulted from the displacement of chlorine from C-3 or C-4 of MCA. The sodium borohydride treatment of product 4 gave the same product (7) as was obtained by treating 3,4-dichloro-2(5H)-furanone with NAC. The treatment of MCA with (R)-(+)-cysteine gave the bicyclic product 9a, in which the two chlorine atoms of MCA were still present. This product was slightly more mutagenic than MCA, whereas product 5 was less mutagenic than MCA and product 4 was nonmutagenic in the Salmonella typhimurium (TA100) assay.
Acetylcysteine↗
[A long-term experiment on the complex influence of cultivating, fertilizing, and crop rotation measures on humic substances in soil and development of yield (author's transl)].
In a 10-year field experiment, the influence of fertilizing, cultivating, and crop rotation measures on the C-content of the soil, humus quality of the organic soil substance, and the yield was investigated. With cultivation of fodder plants only, the C-content of the soil can be improved by increased mineral and increased organo-mineral fertilization at any depth of cultivation. When in the same location there was a turn between cereals and green crops, a decrease of C-rate can only be prevented by increased organo-mineral fertilization. Continuous cultivation of root crops resulted in a decrease of the C-content. Deeper tillage of the soil generally decreased C-content. Within the years, a variability of the pure humin substances could be detected, depending on the rotation of crops and C-content. The composition of the fulvic acids is differentiated in dependence on the factors "time" and "cultivation". The effect of fertilization variants on the yield was different. Fertilization in that location with manure only, compared with mineral fertilization, caused in most cases depression in yield. Decrease on yield by deeper ploughing had the least influence with root crops.
Agriculture↗
Humic-like substances of bacterial origin. II. Fractionation of the bacterial humic-like substances by gel filtration on sephadex gels.
Humic-like substances obtained from cells of Pseudomonas acidovorans were separated on Sephadex G-25 into two groups of substances of different molecular weight. The substances of the molecular weight greater than 5000 were successively separated on Sephadex gels G-50, G-75, G-100. Five fractions of different molecular weight were obtained, the percentage of which varied depending on the media used and time of incubation of the bacteria. Most (38%--46%) of the compounds contained in the bacterial humic acids were of approximate molecular weight of 40 000--50 000. The distribution of the fractions in the bacterial "humic-acids" was compared with those of the humic acid made by Fluka A. G. The synthetic humic acid contained most (approximately 40%) of the compounds of approximate molecular weight of 8000--10 000. In the bacterial and synthetic material the content of the compounds with the molecular weight above 100 000 was very similar (8%--12%).
Chromatography, Gel↗
Humic-like substances of bacterial origin. III. Production of humic-like substances by Pseudomonas acidovorans in media containing certain benzene derivatives.
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Aniline Compounds↗
Humic-like substances of bacterial origin. I. Some aspects of the formation and nature of humic-like substances produced by Pseudomonas.
Two bacterial strains Pseudomonas acidovorans No 26 and Pseudomonas sp. No 4 grown in Conn and yeast extract-glucose media, or in the media enriched with tyrosine, were found to produce dark brown pigment. It was shown that in the bacterial cultures numerous phenolic and quinone-type compounds were formed and transformed to humic-like polymers. Formation of humic-like substances started in the bacterial cells and was accompanied by the presence of phenyloxidases in the bacterial cultures. The bacterial "humic acids" were obtained from the supernatants in amounts varing from 0.05 to 0.865 mg/1 mg of dry weight of cells and from the cells in amounts of 0.02 to 0.165 mg/1 mg of dry weight of cells, depending on the medium used and time of incubation. The IR spectra of the bacterial "humic acids" appeared to be very similar to IR spectrum of the synthetic humic acids (Fluka A.G.) and contained the same chemical groups as the soil humic acids. The culture medium after growth of the strain No 26 was fractionated into "fulvic, hymatomelanic and humic acid" fractions. The hydrolysates from the obtained fractions contained amino acids and uronic acids. The amino acid composition appeared to be very similar to that of soil humic acids.
Humic Substances↗
Biological and chemical interactions of pesticides with soil organic matter.
There is little doubt that organic matter plays a major role in the binding of pesticides in soil, and that this phenomenon is usually the most important cause for interaction of pesticides in the soil environment. Fulvic or humic acids are the chemicals most commonly involved in the binding interactions. Binding can occur with the original pesticide or a transformation product, the reaction being caused by abiotic agents or biotic agents (microbial or plant enzymes). The reactions or processes involved appear to be the same as those responsible for the formation of humic substances, i.e. for the humification process. Binding of pesticides to organic matter can occur by sorption (Van der Waal's forces, hydrogen bonding, hydrophobic bonding), electrostatic interactions (charge transfer, ion exchange or ligand exchange), covalent bonding or combinations of these reactions. Our investigation focused primarily on the binding of substituted phenols and aromatic amines to humus monomers and humic substances. In model reactions, we demonstrated the formation of covalent linkages between pesticides and humus constituents and fulvic or humic acids in the presence of phenol oxidases or clay minerals. With chlorinated phenols and carboxylic acids, it was possible to isolate and identify cross-coupling products and to elucidate the site and type of binding. The binding of chlorinated phenols to humic substances was determined by using 14C-labelled chemicals and by measuring the uptake of radioactivity by the humic material. These experiments provide a base for explaining the formation of bound residues in certain cases and for assuming the toxic potential of the immobilized pollutants.
Adsorption↗
Humate-induced activation of human granulocytes.
Naturally occurring humic substances are particular chemical compounds which are found in humus. They bind to carbohydrates, amino acids and steroids by means of hydrogen bonds, covalent bonds and epsilon donor-acceptor complexes. Three specimens of low-molecular humic substances were tested (two naturally occurring humates and one synthetically prepared humate). They were all capable of stimulating certain functions of human neutrophils (PMN), such as the respiratory burst which results in the production of toxic oxygen compounds. This PMN stimulation can be demonstrated with the help of chemiluminescence, as well as by cytochemistry and with the electron microscope. The main product of the humate-induced PMN response is H2O2. There was no activation of neutrophilic chemokinesis or chemotaxis. It is suggested that the low-molecular humic substances originating from decaying organic material contain chemical structures which can act as signals to change dormant PMN into activated cells.
Acridines↗
Anion exchange as a potential method for removal of humus in drinking water treatment.
Removal of humus by anionic exchange is a potential process for small waterworks in Norway. The interaction between humic substances and a strong base anion exchange resin has been studied and the results are used for characterization of the humic substances. Thirty per cent of the organic matter were removed from the water during the first six seconds of contact with the resin. This fraction had a higher negative charge and lower molecular weight than the average for the water sample. With increasing contact time, fractions with a decreasing charge density and increasing colour and molecular weight were removed. The unabsorbed DOC fraction had a net positive charge. The anion exchange process results in a reduction in pH, and dissolved iron and aluminium are transformed from organic complexes to inorganic species. This may represent an obstacle for the practical use of the process.
Chromatography, Ion Exchange↗
SED88: a Pascal program for the analysis of sedimentation equilibrium data.
Analytical ultracentrifugation is commonly used for the determination of molecular weights (sedimentation equilibrium) and sedimentation coefficients (sedimentation rate) of biological macromolecules in solution. A Turbo Pascal program for the analysis of sedimentation equilibrium centrifugation data produced by absorbance optical systems is described. The user may enter data from a scan of absorbance versus distance from the centre of rotation, via a graphics tablet (or ASCII file). This is subsequently manipulated to yield an apparent weight average molecular weight for the given sample. Plots of ln (absorbance) versus (radius2) may also be produced. The method described uses readily available computational equipment requiring only a graphics tablet in addition to an IBM PC compatible computer. This technique and the software developed have been used to investigate the molecular weight range of two International Humic Substances Society (IHSS) reference samples from the Suwannee River.
Absorption↗
Some natural products from two soft coals. Their removal, metal-binding and enzyme inhibitory activity.
The chemical constituents of coal have not been fully characterized in relation to the incidence of coal workers' pneumoconiosis (CWP). In this study two soft coals obtained from mines in which workers had high and low incidences of CWP were leached with aqueous base and acid to remove their acidic and basic components. The results suggest that humic substances similar to those found in soil are present in the coal samples. Further, differences in the quantity of material removed ant its metal-binding and enzyme inhibitory activity are related to disease incidence.
Alcohol Oxidoreductases↗
Trihalomethane levels in Madras public drinking water supply system and its impact on public health.
It is known that trihalomethanes (THM) are formed during chlorination of drinking water for disinfection. Heightened concern about these substances is due to the fact that THMs are now characterized as potential mutagen, carcinogen and teratogen. Thus, it is a risk factor in human beings. In the present study, a total number of 13 stations located in different drinking water trunk mains of the city of Madras were analysed for THM using the Gas Liquid Chromatographic method. It is reported that THM are formed after treatment of raw water with chlorine at the levels required for disinfection. The THM level in drinking water increased towards the dead-end of the water trunk mains. A relationship between the distance travelled by the potable water and the level of THM was established. At certain stations, the total trihalomethanes level (TTHM) was found to exceed the EPA's maximum contaminant level. Further, an intermittent addition of the precursors for the formation of THM through the seepage of polluted River Cooum water into the pipe lines has been demonstrated. An experiment on the trihalomethane formation potential (THMFP) clearly revealed the occurrence of higher magnitude of humic substances in source water. Therefore, it is suggested that if suitable steps are not taken, various environmental factors may trigger the THM kinetics. Hence, it is obvious that pretreatment regulations proposed by developed countries are essential if safe drinking water is to be supplied to the people of Madras.
Chloroform↗
Plant-derived and microbial biostimulants in sustainable agriculture: mechanisms, applications, and challenges.
Plant biostimulants have emerged as transformative and sustainable tools for improving crop productivity, resource-use efficiency, and resilience under rapidly intensifying environmental stresses. Unlike conventional agrochemicals, biostimulants function by activating physiological, biochemical, and molecular processes that optimize plant performance without directly supplying nutrients or exerting pesticidal effects. This review comprehensively examines the integrated roles of plant-derived and microbial biostimulants in sustainable agriculture, with particular emphasis on microbial-mediated mechanisms underlying plant stress adaptation and rhizosphere functioning. Plant-derived biostimulants, including seaweed extracts, humic substances, protein hydrolysates, amino acids, and chitosan, enhance nutrient acquisition, root architecture, hormonal regulation, and antioxidant defense systems. More importantly, microbial biostimulants, such as plant growth-promoting rhizobacteria (PGPR), endophytic microorganisms, mycorrhizal fungi, actinomycetes, yeasts, and cyanobacteria, exert multifunctional effects through biological nitrogen fixation, mineral solubilization, phytohormone biosynthesis, volatile signaling, osmolyte accumulation, pathogen suppression, and modulation of stress-responsive genes. These beneficial microorganisms reshape rhizosphere microbial communities, improve nutrient cycling, and enhance plant tolerance to drought, salinity, heat, and heavy metal toxicity. Emerging evidence from genomics, transcriptomics, metabolomics, and microbiome-based investigations has further revealed the molecular networks and signaling pathways governing biostimulant-induced resilience and plant-microbe interactions. Despite their substantial promise, inconsistent field performance, formulation instability, regulatory limitations, and inadequate mechanistic understanding continue to restrict their large-scale adoption. This review highlights recent advances in microbial and plant-derived biostimulants while identifying critical knowledge gaps and future opportunities for precision biostimulant engineering, microbiome manipulation, and climate-resilient crop management. The integration of next generation biostimulant technologies into sustainable agricultural systems may significantly reduce dependence on agrochemicals while improving crop productivity, environmental sustainability, and global food security.
Agriculture↗
Mutagenicity of ozonation and chlorination products from p-hydroxybenzaldehyde.
p-Hydroxybenzaldehyde, a component of soil humic substances, was ozonated and chlorinated. The ether extract and the residue were subjected to the Ames assay; mutagenic activities were identified. The non-ionic resin CSP800 and the anion exchange resin CHPA25 were used for separation of mutagenic compounds. The compounds in the water layer were not adsorbed on CSP800 or CHPA25 and exhibited strong mutagenic activity. Mutagenic activity was reduced as the added chlorine was increased. Ether extracts were analyzed by gas chromatography-mass spectrometry (GC-MS) and chloral, 1,3-dichloro-2-propanone, 1,2,3-trichloro-1-propene, tetrachloroethylene and 1,1,1,3,3-pentachloro-2-propanone were identified as mutagenic compounds.
Animals↗
Chemical topology and ecotoxicology.
The experimental determination of environmental parameters (e.g. soil sorption, bioconcentration, biodegradation and biotransformation, toxic effects, etc.) of commercial chemicals is a costly and time-consuming process. Since there is a large number of chemicals currently in common use (approximately 100,000) and new chemicals are registered at a very high rate (1000/year) it is obvious that our human and material resources are insufficient to obtain experimentally even basic information on environmental fate and effects for all those chemicals. Thus, it is necessary to develop quantitative models that will accurately and rapidly predict environmental behaviour for large sets of chemicals. Thus far, molecular connectivity indices have been shown to be the most successful structural property for describing and predicting soil sorption coefficients, association with dissolved humic substances, Henry's law constants, bioconcentration factors in aquatic organisms and vegetation, biodegradation, and acute toxicity. We describe and discuss the most recent results on modelling environmental fate of organic pollutants by the application of molecular connectivity indices. Two sections describe the usefulness of environmental QSAR models based on n-octanol/water coefficients and the systematics and possible physical interpretation of molecular connectivity indices. Some practical and theoretical weaknesses and pitfalls are discussed concerning the use of n-octanol/water partition coefficients in environmental QSAR research.
Biodegradation, Environmental↗