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Nicholas D. Bryan - One of the best experts on this subject based on the ideXlab platform.
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The effects of Humic Substances on radioactivity in the environment.
2002Co-Authors: Rose E. Keepax, Dominic M. Jones, Sarah E. Pepper, Nicholas D. BryanAbstract:In a review the effect of Humic Substances on the environmental radioactivity are outlined. The definition and classification of Humic Substances are given, as well as their origin and colloidal properties. Further topics were the binding of metals to Humic Substances, with specific considerations to radionuclide binding kinetics, and the modeling of the mobility of radionuclides in an environment contg. Humic Substances. [on SciFinder (R)]
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colloidal properties of Humic Substances
Advances in Colloid and Interface Science, 1998Co-Authors: Malcolm N. Jones, Nicholas D. BryanAbstract:Abstract Humic Substances are structurally complex large to macromolecules which occur in soils and natural waters as a consequence of the breakdown of plant and animal residues by microbial activity. A major portion (approx. 50%) of the earth's carbon is in the form of Humic materials (fulvic and Humic acids). The characterisation of Humic Substances is a major problem due to their heterogeneity both in terms of structure and size and to their tendency to associate in solutions as their concentration increases. Methods of characterisation of Humic materials are reviewed and their interactions with Substances such as clay particles, herbicides, pesticides and metallic ions which occur in the natural environment considered. The experimental methods of investigating the binding of metallic ions are also reviewed. There have been several approaches to the molecular modelling of metal ion binding based on the representation of Humic molecules as colloidal particles with an associated electrical double layer. The various theoretical models have been described and the relative merits of the approaches compared.
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Selectivity in the complexation of actinides by Humic Substances.
Environmental Pollution, 1997Co-Authors: Yingjie Zhang, Nicholas D. Bryan, Francis R. Livens, Malcolm N. JonesAbstract: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.
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Complexing of metal ions by Humic Substances
1995Co-Authors: Nicholas D. Bryan, Yingjie Zhang, Malcolm N. JonesAbstract:The interaction of metal ions with Humic Substances is being studied using two different techniques. UV-scanning ultracentrifugation is being used to determine molecular weights and to investigate changes in aggregation brought about by metal ion complexation. The relationship between cation charge and conformation of the Humic ligands is also being investigated. The complexation of actinide elements (U, Np, Pu, Am) by Humic Substances from soils contaminated by both natural processes and by low-level effluent releases is also being studied. Gel permeation chromatography has been used to show both that different fractions of Humic Substances vary greatly in their effectiveness as ligands and that different actinide elements associate with different fractions. These studies have also shown that uranium desorption is kinetically controlled by Humic Substances.
Malcolm N. Jones - One of the best experts on this subject based on the ideXlab platform.
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colloidal properties of Humic Substances
Advances in Colloid and Interface Science, 1998Co-Authors: Malcolm N. Jones, Nicholas D. BryanAbstract:Abstract Humic Substances are structurally complex large to macromolecules which occur in soils and natural waters as a consequence of the breakdown of plant and animal residues by microbial activity. A major portion (approx. 50%) of the earth's carbon is in the form of Humic materials (fulvic and Humic acids). The characterisation of Humic Substances is a major problem due to their heterogeneity both in terms of structure and size and to their tendency to associate in solutions as their concentration increases. Methods of characterisation of Humic materials are reviewed and their interactions with Substances such as clay particles, herbicides, pesticides and metallic ions which occur in the natural environment considered. The experimental methods of investigating the binding of metallic ions are also reviewed. There have been several approaches to the molecular modelling of metal ion binding based on the representation of Humic molecules as colloidal particles with an associated electrical double layer. The various theoretical models have been described and the relative merits of the approaches compared.
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Selectivity in the complexation of actinides by Humic Substances.
Environmental Pollution, 1997Co-Authors: Yingjie Zhang, Nicholas D. Bryan, Francis R. Livens, Malcolm N. JonesAbstract: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.
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Complexing of metal ions by Humic Substances
1995Co-Authors: Nicholas D. Bryan, Yingjie Zhang, Malcolm N. JonesAbstract:The interaction of metal ions with Humic Substances is being studied using two different techniques. UV-scanning ultracentrifugation is being used to determine molecular weights and to investigate changes in aggregation brought about by metal ion complexation. The relationship between cation charge and conformation of the Humic ligands is also being investigated. The complexation of actinide elements (U, Np, Pu, Am) by Humic Substances from soils contaminated by both natural processes and by low-level effluent releases is also being studied. Gel permeation chromatography has been used to show both that different fractions of Humic Substances vary greatly in their effectiveness as ligands and that different actinide elements associate with different fractions. These studies have also shown that uranium desorption is kinetically controlled by Humic Substances.
Nigel Graham - One of the best experts on this subject based on the ideXlab platform.
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degradation of atrazine by manganese catalysed ozonation influence of Humic Substances
Water Research, 1999Co-Authors: Nigel GrahamAbstract:A bench-scale, laboratory study has been undertaken on the ozonation of atrazine in the presence of manganese using a conventional gas bubble-contacting column. Manganese was present in solution either as Mn(II) or as in situ formed Mn(IV). The experimental results indicate that the presence of Humic Substances has a substantial influence on the Mn-catalysed ozonation of atrazine. In the presence of a small amount of Humic Substances (e.g. 1 mg/l as DOC), the Mn-catalysed ozonation is obviously enhanced. However, with the further increase of Humic substance concentration, a negative effect of Humic Substances on the catalytic oxidation of atrazine is observed for both the cases of Mn(II) and Mn(IV). It is proposed that Mn-catalysed ozonation of atrazine follows a radical-type mechanism. At low concentrations of Humic Substances, both the manganese species and the Humic Substances may initiate and promote the formation of hydroxyl radicals during ozonation which enhance the destruction of atrazine. However, at higher concentrations, Humic Substances may scavenge these highly reactive hydroxyl radicals, thus decreasing the oxidation efficiency of atrazine.
Nadezhda Kudryasheva - One of the best experts on this subject based on the ideXlab platform.
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Detoxification of AM-241 solutions by Humic Substances: bioluminescent monitoring
Analytical and Bioanalytical Chemistry, 2011Co-Authors: Tatiana Rozhko, Lidia Bondareva, Olga Mogilnaya, Galina Vydryakova, Alexander Bolsunovsky, Devard Stom, Nadezhda KudryashevaAbstract: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.
G.mathumathi - One of the best experts on this subject based on the ideXlab platform.
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Characterization, transformation and application of Humic Substances ÃÂÃÂÃÂÃÂ Review
Research and reviews in biosciences, 2012Co-Authors: J.arunkumar, G.mathumathiAbstract:Humic Substances are derived from Soil Organic Matter (SOM) which is playing a major role in agriculture. Quality, maturity, nativity assessment and activity of humus are determined by hydrophobic and hydrophilic (HB/HI) index, which is based on chemical composition of core structure of Humic Substances. Because till now there is no exact chemical formula or structure for HA and it is vary depend on source material, microbial populations, physical and chemical environment for Humic Substances formation, but in general it is composed ofC,H,OandN. Important functions of Humic Substances in environment are, it aids in nutrient solubilization fromdrought and compacted soils, nutrient uptake by plants, heavymetals immobilization, controlling soil erosion, improvedmultiplication of essential microorganisms (EM) for agriculture. This review introduces the basic properties, composition, chemical reactivity and characterization of HS with highlighting the need of innovative research for better fundamental understanding of the mechanisms, formation transformations and application of Humic Substances.
