Humic Substances Seminar V
Wednesday March 21 to Friday March 23, 2001

 

INTRODUCTION

Humic substances are fascinating, and their study is multidisciplinary. Humic Substances Seminar participants continue to meet on a regular basis to share information on humic substances structures, properties and uses. The Seminars encourage molecular descriptions of humic substances and practical applications of their remarkable properties. Talented individuals come from all over the world to advance the field. Young scientists learn from the masters, and the masters can follow the progress of the youngsters.

The HSs mystery is too difficult for any individual or single research group to solve. The desire for new knowledge is driving collaboration and co-operation. Chronic lack of funding for fundamental work on HSs hopefully soon will end, helped we hope by the impact of the Seminars.

Humic Substances Seminar V has many distinguished participants. We especially recognize Drs. Morris Schnitzer and Patrick MacCarthy (to whom Seminar V is dedicated). Also with us as a most welcome participant is Dr. Robert Wershaw (USGS, Denver), through whom the Seminars originated and who served as Honorary Chair of Seminar I in 1997.

Much of the progress in HSs research is due to the work of the International Humic Substances Society, which today is represented by its President (Dr. Fritz Frimmel, University of Karlsruhe), its Immediate Past President (Dr. James Alberts, University of Georgia), President-Elect (Dr. Yona Chen, Hebrew University of Jerusalem), two Past Presidents (Dr. Russell Christman, University of North Carolina, Dr. Michael Hayes, University of Limerick, and Dr. Nicola Senesi, University of Bari), its Treasurer (Dr. Edward Clapp, USDA-ARS & University of Minnesota), its Immediate Past Treasurer (Dr. Patrick MacCarthy, Colorado School of Mines), an IHSS Board Member (Dr. Maria De Nobili, University of Udine) and the Co-ordinators of Canada (P. M. Huang), Egypt (E. A. Ghabbour), Ireland (M. H. B. Hayes), Israel (Y. Chen), Italy (N. Senesi) and the United States (J. A. Rice).

We are honored by the presence of Dr. Donald L. Sparks (University of Delaware), the Immediate Past President of the Soil Science Society of America.

Interest in the Seminars from industry, sparked initially by Arctech, Inc. and its President Dr. Daman Walia, has grown steadily and we now have a full day devoted to commercial HS production and environmental applications.

The program for Humic Substances Seminar V follows the traditional sequence: Formation, Characterization, Separation, Solute Sorption, Metal Binding and HSs Production and Applications. There is a new focus on principles and the modeling of HS structure and function. We run the gamut from aqueous systems to coal derived humic acids while keeping our sights on a molecular picture of properties and behavior.

The Humic Substances Seminars would not be possible without new research and the support of authors and reviewers. We were blessed with more submissions than we could fit into the Seminar V program. We thank all authors who contacted us and have selected the best papers for an outstanding program.

As before, timely manuscripts based on new work presented at Humic Substances V and received in Boston by May 31, 2001 will be promptly reviewed, considered for publication, edited and published by the Royal Society of Chemistry as the volume with proposed title ‘Humic Substances: Structures, Models and Functions.’ The resulting volume will contain fine current work that relates humic substance structures to their properties and applications.

Welcome to Humic Substances Seminar V, which we hope you will find helpful and memorable!

C. Edward Clapp        Geoffrey Davies         Elham A. Ghabbour
Honorary Chair            Chair                         Co-Chair
March, 2001

 

 

ABSTRACTS

The Principles of Humic Substances

Patrick MacCarthy

Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401

Two basic principles define humic substances and describe their fundamental essence from both a chemical and an ecological point of view. The principles incorporate fundamental developments that have occurred throughout the history of humic studies. They provide a simple rationale for the occurrence in the soil environment of a medium having the particular combination of properties exhibited by humic substances. These principles also offer a conceptual framework for evaluating the applicability and limitations of various experimental methods and for assessing the interpretability of data from those methods that are applicable. The nature of the extreme molecular complexity in humic substances is analyzed and it is proposed that humic substances be classified as a unique category of natural product that requires an alternative intellectual approach for its investigation and understanding. New definitions of humic substances that offer greater insight into the molecular nature of these materials arise from the principles. The use and limitations of hypothetical quasi-structures to help visualize humic molecules and account for their properties is discussed. Some of the unique problems associated with the chemical and instrumental analysis of humic substances are addressed. The concepts presented have broad implications in many fields, including chemistry, geochemistry, environmental and soil sciences, and ecology.

References

1. MacCarthy, P. and J. A. Rice, In ‘Scientists on Gaia,’ Schneider, S. H. and P. J. Boston, Eds., MIT Press, Cambridge, 1991, pp. 339-345.
2. Stevenson, F. J., ‘Humus Chemistry,’ Wiley, New York, 1982.
3. Rice, J. A. and P. MacCarthy, Org. Geochem., 1991, 17, 635-648.
4. Gjessing, E. T., ‘Characterization of Aquatic Humus,’ Ann Arbor Science, Ann Arbor, MI, 1976.
5. Schnitzer, M. and S. U. Khan, ‘Humic Substances in the Environment,’ Dekker, New York, 1972.

 

AN ORGANIC MATTER TRAIL: POLYSACCHARIDES TO WASTE MATERIALS TO HUMIC SUBSTANCES

C. Edward Clapp

USDA-ARS and University of Minnesota, St. Paul, MN 55108

A farm boy from Princeton, MA went to the University of Massachusetts to study chemistry and learn how to make dynamite. After 4 years with a chemistry major and agronomy minor he went off to Cornell University to become a soil biochemist. Jeff Dawson became the mentor who started the way along the ‘Organic Matter Trail.’ Fractionation of a water-soluble peat extract and isolation of a ‘pure’ polysaccharide using paper-curtain and column electrophoresis was the first step. The USDA-ARS Soils Laboratory at Beltsville, MD under Hub Allaway in 1956 provided the first chance to study the ‘effects of organic matter on soil structure.’ Rhizobial polysaccharides and aggregate stabilization were main topics. A transfer to the University of Minnesota in 1961 to continue the organic matter/soil structure work led to a one-year cooperative and rewarding venture with Bill Emerson, CSIRO soil physicist, looking at soil crumbs and clay-polysaccharide complexes. Al Olness joined me as a grad student and we carried on the polysaccharide-clay interaction studies. The ‘Organic Matter Trail’ continued when Bill Larson came to St. Paul as Leader of the ARS Soils Unit. By 1972 a call was issued for more practical and field oriented research, leading to waste management experiments involving application of municipal sewage sludges and wastewaters to agricultural land. Ten years (and many publications) later, a series of field and laboratory experiments were initiated involving nitrogen-tillage-residue management (NTRM) including 15N and later 13C isotope studies. Art Edwards was the guiding inspiration for the 15N work; Dave Clay (grad student) and Jean Molina (Professor) provided experimental and modeling expertise. Other members of the ARS Soil and Water Management Research Unit were involved in research and publication activities. During the early to mid-1980s, the ‘Organic Matter Trail’ was side-tracked, but later developed into a super highway! Humic substances were re-introduced to me by Michael H. B. Hayes, an old Cornell lab-mate and friend, who reappeared from the University of Birmingham. Along with other IHSS associates and friends — especially Ron Malcolm, Pat MacCarthy, Yona Chen, Nicola Senesi, Roger Swift, Frank Stevenson, Morris Schnitzer, Jack Bremner, Geoff Davies, Elham Ghabbour, et al. – we have set out on a combination of research projects, society programs, publication endeavors (some controversial) and other fun activities. Cooperating humic scientists are looking at new isolation and characterization techniques, sizes and shapes of humic ‘macro’-molecules, organic contaminant studies, metal-HS interactions, water treatment and humic-plant stimulation, among other topics. We have not solved all of the problems still out there, but in my own case, after some 45 years on the ‘Organic Matter Trail’, we trust that you ‘younger and wiser’ scientists will carry on for the next generations to come.

References

1. Clapp, C. E., and W. W. Emerson, Soil Sci. Soc. Amer. Proc., 1965, 29,127-130; 130-134.
2. Olness, A. E. and C. E. Clapp, Soil Biol. Biochem., 1975, 7, 113-118.
3. Stark, S. A. and C. E. Clapp, J. Environ. Qual., 1980, 9, 505-512.
4. Clapp, C. E. and M. H. B. Hayes, Soil Sci., 1999, 164, 899-913.
5. Clapp, C. E., R. R. Allmaras, M. F. Layese, D. R. Linden and R. H. Dowdy, Soil Tillage Res., 2000, 55, 127-142.

NMR characterization of the mobile components in intact green and senescent leaves as a means of studying the humification process

R. L. Wershaw1 and Igor Goljer2

1 U.S. Geological Survey, Denver, CO 80225

2 Varian NMR Systems, Columbia, MD 21045

Humification is the process whereby living plant tissue is converted into natural organic matter (NOM). We have chosen to study the humification of leaf tissue because leaf fall from deciduous trees is a major source of NOM in forest soils. The molecular species of living leaf tissue can, in general, be divided into two categories: rigid and mobile components. The molecules of some leaf components, such as lignin and cellulose, normally exist in rigid networks in which they can undergo only very limited molecular motion. The molecules of the mobile species, such as the relatively low molecular weight molecules dissolved in cellular fluids, higher molecular weight components that are strongly hydrated, cell membrane components that exist in dynamically-ordered bilayer structures or molecules in waxy coatings can move much more freely. These mobile components are much more susceptible to chemical reaction than the non-mobile components. As long as a leaf is alive, the chemical reactions that take place in the leaf must be very tightly controlled in order to maintain the physiological processes upon which the life of the organism depends. Much of this control is achieved by spatial segregation of the mobile components into specialized organelles of the leaf cells. However, during senescence the cell walls rupture and the component molecules from one organelle mix with molecules from other organelles. The reactions that take place during this mixing process constitute the first step in the humification process. We have been able to measure the high resolution NMR spectra of the mobile components of leaf tissue before and after senescence using a new type of magic-angle-spinning probe. These spectra therefore provide insight into the first reactions that the mobile components undergo during humification.

 

Some details of the structure and mechanism of formation of humic acid

Alexandr A. Shapovalov,1 Yury Gr. Putsykin1 and Vladislav A. Leonov2

1 Research Institute of Plant Protection Chemicals, Moscow, Russia
2 Independent University, Lote9-1800-255, Lisbon, Portugal

The idea that humic acids (HAs) are polymers with structure determined by statistical conformities does not agree with their key role in the processes of forming and functioning of soil as a highly stable system. In this work, HAs in the form of water solutions of Na salts were isolated from coals from deposits in Russia and Portugal by extraction with alkali. The solutions were used to prepare water systems containing HA at two concentrations with different pH. Average molecular weight and fractional composition of HA were determined by ultra-centrifugation of the solution (centrifuge with analytical rotor of An-G type, 6 cells v=0.45 mL each and a scanning optical system that allows study of the dynamics of sedimentation in water). The determination was made at room temperature, at 48000 rpm and 330-410 nm. The dependence of molecular weight of HA on pH is shown in Figures 1 and 2. At 2 mg/L in neutral medium, a considerable part of HA transformed into low molecular monomers (about 1000 Da). In alkali media this transformation was quantitative. During long experiments with the use of turf-podzol soil after applying additional HA, the formation of montmorillonite was fixed (IR spectroscopy). At the same time the process of humification of organic vegetable remainders accelerated. On the basis of all these results it is possible to make some suppositions. In soil, monomers interact with clay minerals (montmorrilonite) and then they polymerize. In this case the mineral content plays the role of a matrix, gives a relative regularity of structure of soil HAs and hence the stability of their characteristics. HAs formed in such a way can play the role of matrix in the process of forming of mineral and organic contents of soil. Monomers of HA connect through acetal bonds, which are easily broken and formed again in water (Scheme 1).

 

The Structure of Humic Substances - a Mirage?

J. Burdon

School of Chemistry, The University, Birmingham, B15 2TT, UK

Many structures have been proposed for humic substances (HSs): Maillard products, "aromatic core and periphery" models, hydrogen-bonded assembles and aromatic units linked by short and long aliphatic chains, with some that include heterocyclic moieties. Polysaccharides and peptides commonly are attached to these basic structures. This contribution proposes that all these suggestions are wrong, not because of wrong formulas, but because HSs of the types mentioned above do not exist. Instead there are just mixtures of substances with pure plant compounds at one extreme and pure microbial compounds at the other. With lignin as the origin, there are compounds of intermediate structure as well. There is nothing of major significance other than these materials, certainly not a complex structure of the types alluded to in the first paragraph. These HSs mixtures are further resolved in time and space (that is down the soil profile), depending on such factors as solubility and climate, so that any sample of HSs will be the complex result of the interaction of many factors. Carbohydrates provide the simplest example. Plants contain cellulose and hemicelluloses (consisting mainly of pentoses) that are broken down by soil microorganisms into monosaccharides and in turn are mainly mineralized. A minor portion is degraded to smaller molecules that enter the general metabolic pool of the microorganisms from which new carbohydrates, amino acids and fatty acids are synthesised by well-known routes. Another portion of the monosaccharides is converted into other monosaccharides and all can be incorporated into microbial polysaccharides, which are distinguished from plant polysaccharides mainly by their low pentose content and the presence of chitin. As far as carbohydrates are concerned, HSs simply are mixtures of plant and microbial polysaccharides, as accepted by some workers in the field. Proteins and peptides essentially behave in the same way. The plant materials are broken down into their component amino acids, which then are mineralized, taken into the general metabolic pool, or utilized by microorganisms to make their own proteins. In this case, however, there are no obvious distinctions between the amino acid contents of plant and microbial materials. Heterocyclic compounds must be abandoned as major constituents of HSs, as 15N NMR shows that N occurs overwhelmingly as amide. Lignin is different because there is no microorganism lignin, so lignin just gets broken down into simpler species and then either is mineralized or added to the general metabolic pool. On the way, lignin forms a significant component of HSs. Breakdown comprises oxidation of the 3-C side-chain (most commonly at C-1), demethylation of OMe groups and depolymerization and cleavage of aromatic rings. This gives a very complex mixture of products and chemical degradations of HSs may be dominated by them. Although microorganisms do not make lignin, they do make aromatics, but usually by the polyketide route, which leads to compounds that clearly are not of lignin origin: e.g. 3-hydroxybenzoic acid. Lipids, melanins, chars, cutins, suberins and other materials may also be mentioned. But what is the evidence for the complex structures mentioned in the first paragraph? This presentation will argue that the evidence does not stand up to close scrutiny. Chemical degradation gives aliphatic acids and various aromatic species, almost all of which are single substituted benzene rings, and there is very little justification in linking them all together. Pyrolytic methods can produce artifacts (naphthalene and phenanthrene rings) and long-chain alkylated benzene rings could be artifacts of pyrolysis. Many other factors need to be considered and unsolved problems solved in the HS field - the influence of plant cover, soil nature, climate, season, the role of microfauna, unknown N, degradation-resistant compounds and many others - but to search for a complex structural type, unique to HS, is to search for a mirage.

 

Is C1s NEXAFS spectroscopy a useful way to determine the functional group chemistry of natural organic matter?

Andreas C. Scheinost,1 Ruben Kretzschmar,1 Iso Christl1 and Chris Jacobsen2

1 Department of Environmental Sciences, ETH Zurich, CH-8952 Schlieren, Switzerland
2 Department of Physics and Astronomy, SUNY Stony Brook, Stony Brook, NY 11794

Near-edge X-ray absorption fine-structure spectroscopy (NEXAFS) at the C1s-edge can be applied to characterize the bonding environment of C in solids, gels and dissolved species, which makes it a useful tool for in situ studies of natural organic matter (NOM). Furthermore, the scanning transmission X-ray microscope at beamline X-1A at the National Synchrotron Light Source, Brookhaven National Laboratory allows combination of NEXAFS and imaging to investigate the spatial heterogeneity of NOM with high resolution (>30 nm).1,2 In spite of these promising features, the NEXAFS spectra of NOM have been interpreted only qualitatively and a quantitative approach is still missing. Specifically, the sensitivity of NEXAFS spectra to variations in the functional group composition of NOM is unknown. To fill in this gap, we measured the NEXAFS spectra of a range of humic and fulvic acids and NOM standards and of size fractions of a humic acid. Absorption bands of aromatic, phenolic, carbonyl and carboxyl groups were determined by a Gaussian deconvolution method. We have compared the functional group chemistry of the samples as determined by NEXAFS with that determined by independent methods like NMR, FTIR and UV spectroscopies, and by acid-base titrations.

References

1. Rothe, J., M. A. Denecke and K. Dardenne, J. Colloid & Interface Sci., 2000, 231, 91-97.
2. Scheinost, A. C., S. Abend, E. J. Elzinga, M. Nachtegaal, C. Jacobsen and D. L. Sparks, In-situ carbon speciation of soil organic matter - Application of x-ray absorption spectromicroscopy, Environ. Sci. Technol., submitted, 2001.

 

Some aspects on measurement of hydrodynamic size and molecular mass of humic and fulvic acids

M. Wolf,1 G. Buckau,2 A. Piccolo,3 H. Geckeis,1 Ngo Manh Thang,1 E. Hoque,1 W. Szymczak4 and J. I. Kim2

1 GSF-National Research Center for Environment and Health, Institute of Hydrology, D-85758 Neuherberg, Germany
2 Research Center Karlsruhe, Institute for Nuclear Waste Management, D-76021 Karlsruhe, Germany
3 University of Naples "Federico II", Department of Chemical Agriculture, 80055 Portici, Italy
4 GSF-National Research Center for Environment and Health, Institute of Radiation Protection, D-85758 Neuherberg, Germany

The measurement of size and mass distribution of humic and fulvic acids has received considerable attention throughout the past decades. A variety of experimental methods have been used and applications of new ones are under development. Interpretation of results requires a clear understanding of the actual information obtained with the different methods and their respective limitations. Another issue that needs to be considered is whether primary units or associates/agglomerates/micelles are detected. Finally, one should be aware of the possible differences in humic material studied, such as aquatic humic and fulvic acids, humic and fulvic acids isolated from solid sources and humics embedded in a soil matrix. This paper discusses the general information obtained by application of different experimental methods, with emphasis on the difference between size and mass, likely limitations of these methods and the possible influence of association/agglomeration/micelle generation. The overall conclusion is that the hydrodynamic size of isolated humic and fulvic acids varies considerably with pH, ionic strength and the degree of metal ion complexation. Within the analytical limitations, the molecular mass distribution maximum of observed primary units falls in the region around or below 1000 Da.

 

Chemical heterogeneity of soil humic acid in relation to molecular size

Iso Christl and Ruben Kretzschmar

Institute of Terrestrial Ecology, Swiss Federal Institute of Technology, CH-8952 Schlieren, Switzerland

In recent decades, major progress has been made in understanding the chemical nature of humic acids in soils and aquatic environments. However, the chemical heterogeneity within the humic acid fractions extracted from soils and its effects on proton and metal cation binding are not well understood. In this study we investigated the chemical composition of molecular size fractions of a soil humic acid in relation to the binding of protons and metal cations (Cu2+ and Pb2+). Soil humic and fulvic acids were extracted from a Humic Gleysol in northern Switzerland. The purified humic acid was separated into four molecular size fractions using a cross-flow hollow fibre ultrafiltration technique with nominal molecular weight cut-offs 10, 30, 100, and 300 kD. All fulvic and humic acid fractions were characterized by elemental analysis (C, H, N, S, O), size exclusion chromatography, UV-VIS absorption and fluorescence spectroscopies, FT-IR spectroscopy and CP-MAS 13C NMR spectroscopy. Smaller size fractions of the humic acid contained more chargeable functional groups and a larger percentage of aromatic carbon than the larger size fractions. The percentage of aliphatic carbon increased with increasing apparent molecular weight. The smallest humic acid fraction contained much more aromatic carbon and less aliphatic carbon than the fulvic acid fraction.1 The pH and ionic strength dependent protonation behavior of the fulvic and humic acid fractions was studied by potentiometric acid–base titrations.2 The binding of Cu2+ and Pb2+ to the fulvic acid and the humic acid size fractions was measured at constant ionic strength (0.1 M NaNO3) and constant pH values (pH 4, 6 and 8) using ion selective electrodes (ISE).3 The data were modeled using the consistent NICA-Donnan model. The acid-base titration behavior of the humic acid size fractions was closely related to differences in the carboxylic and phenolic carbon contents measured by 13C NMR spectroscopy. However, the metal binding isotherms were similar for all humic acid size fractions, indicating that the chemical differences between the size fractions do not strongly affect metal cation binding at low concentration levels. The use of chemical characterization results, such as obtained from 13C NMR spectroscopy, for parameter estimation in the NICA-Donnan model will be discussed.

References

1. Christl, I., H. Knicker, I. Koegel-Knabner and R. Kretzschmar, Europ. J. Soil Sci., 2000, 51, 617-626.
2. Christl, I. and R. Kretzschmar, Relating ion binding by fulvic and humic acids to chemical composition and molecular size: I. Proton binding, submitted, 2001.
3. Christl, I., C. J. Milne, D. Kinniburgh and R. Kretzschmar, Relating ion binding by fulvic and humic acids to chemical composition and molecular size: II. Metal binding, submitted, 2001.

 

COMPUTATIONAL MODELING OF HUMIC STRUCTURES: A View from the Edge of the cliff

Aldo G. Bruccoleri, Bradley Sorensen, and Cooper H. Langford

Department of Chemistry, University of Calgary, Calgary, Alberta, Canada T2N 1N4

Computational modeling of humic substances presents unique problems. Most molecular modeling proceeds from known molecular "learning sets" against which the inevitable approximations can be calibrated. A first question with humics is choice of hypothetical building blocks that can calibrate procedures in the face of uncertainties about the details of interactions in humic mixtures. This fundamental problem will not be resolved easily or soon. However, we can comment on useful tactics to minimize the danger of being misled and on alternative approaches to test computations against experiment. Until now, published computational models have used molecular mechanics geometrical optimization. The energy of a structure is calculated as a function of steric and non-bonded interactions. The force fields exploited have distinct limitations that arise from the learning sets on which they were calibrated. Careful review of the literature on these tools is required if they are to be exploited well. Specifically, for example, the Sybyl and MM+ force fields are intended for small mono-functional organics without polarizable groups. They are known to lead to unacceptable errors if used outside their range. Of particular significance in humic modeling, MM2 and MM+ have major problems dealing with "aromatic stacking." Overestimation of aromatic face-to-face interactions is well documented. An alternative that has not so far received attention in computational models of humics is semi-empirical quantum mechanical calculations as opposed to molecular mechanics. Semi-empirical methods treat electrons explicitly and parameters for elements are independent of the chemical environment. As an illustration, we have computed the minimum geometry of two "representative" fulvic acid type structures using the PM3 semi-empirical quantum chemistry approximations. Where Sybyl and MM+ molecular mechanics give emphasis to aromatic stacking in these structures and, as an extension, a helical geometry for polymers, PM3 calculations (Spartan 4.1.1 run on an IBM RS6000) give a more open quasi-hemispherical structure that resembles a half tennis ball. Two of the half tennis balls join under weak forces to give a "tennis ball" dimer rather than a helical polymer. The dimer can serve as a cage to capture a model of a contaminant, fluorobenzoic acid. Similar results were obtained for a different structure chosen to represent a partial model of our Laurentian fulvic acid. We are intrigued by the fact that the half tennis ball and the tennis ball structures often have been found in the literature on self-assembly under weak force interactions. Perhaps the literature of self-assembly has a contribution to make to humic chemistry.

References

1. Sein, L., Jr., J. Varnum and S. Jansen, Environ. Sci. and Technol., 1999, 33, 546-552.
2. Rebek, J., Accts. Chem. Res., 1999, 32, 278-286.

 

ARE THERE HUMIC ACIDS IN ANTARCTICA?

D. Gajdošová,1 L. Pokorná,1 P. Prošek,2 K. Láska2 and J. Havel1

1 Department of Analytical Chemistry, Faculty of Science, Masaryk University, 611 37 Brno, Czech Republic
2 Department of Geography, Faculty of Science, Masaryk University, 611 37 Brno, Czech Republic

Scientists and chemists are interested in antarctic soil.1 Antarctica, covered by a gigantic ice shield, is the last vast wilderness on this planet. Plant species in Antarctica are relatively numerous. There are about 1000 species of algae, 350 species of lichen, 100 species of moss, two species of vascular plants, and so on. The aim of this work was to monitor the occurrence and content of humic acids (HAs) in antarctic soil in different stratigraphic positions (distances from the coast) in west Antarctica (South Shetland Islands, King George Island). Organic matter from antarctic soil samples was processed using several extraction procedures. Extraction with sodium hydroxide solution was the most efficient. Capillary zone electrophoresis (CZE), Matrix Assisted Laser Desorption/Ionization Time-of-Flight mass spectrometry (MALDI TOF MS) and UV-VIS spectrophotometry methods were used to study the organic matter extracted from the soil. Results of analyses were compared to analyses of IHSS standards and other HAs of various origin. It was found, in agreement with ref. 1, that the content of organic matter is low and part of the organic matter can be considered to be humic acids. It was proved both by MALDI TOF MS and CZE that Antarctic humic acids show some similarities to HAs of different origin from other continents.2

References

1. Beyer, L., H. -P. Blume, C. Sorge, H. -R. Schulten, H. Erlenkeuser and D. Schneider, Arctic and Alpine Research, 1997, 29, p. 358-365.
2. E. A. Ghabbour and G. Davies, Eds., ‘Humic Substances: Versatile Components of Plants, Soils and Water’, RSC, Cambridge, 2000.

 

NMR Evidence for Multiple Domains in Soil Humic Substances

Amrith S. Gunasekara,1 L. Charles Dickinson2 and Baoshan Xing1

1 Plant and Soil Sciences Department, University of Massachusetts, Amherst, MA 01003
2 Polymer Science and Engineering Department, University of Massachusetts, Amherst, MA 01003

Soil organic matter (SOM) is a dominant sorbent for organic contaminants in soil and it has been modeled as a dual-mode sorbent that has both flexible, rubber-like and rigid, glassy domains.1 Spectroscopic evidence for these domains is lacking. This study uses solid-state proton (1H) nuclear magnetic resonance spectroscopy (NMR) to identify and quantify domains of soil humic substances based on the understanding that NMR free induction decay (FID) profiles are composed of slow relaxing components (Lorentzian exponential decay) and fast relaxing components (Gaussian exponential decay).2 Samples of humic substances used in this study include humic acids, fulvic acids and humins. In all humic samples used, two distinctly different relaxation times (T2, spin-spin proton relaxation) were observed, indicating the presence of multiple domains. A rigid, immobile domain is supported by the fast relaxing Gaussian component and T2 ranged from 4 to 6 µs. The slow relaxing Lorentzian component, indicative of a relatively mobile domain, had T2 values ranging from 19 to 50 µs. There were large variations in relative proportions of the rigid and flexible domains for humic samples from different locations. We also observed that water can significantly change the domain distribution of humic samples. Results from temperature and solvent studies also will be presented.

References

1. Xing, B. and J. J. Pignatello, Environ. Sci. Technol., 1997, 31, 792.
2. Adducji, D. J., P. A. Hornung and D. R. Torgeson, Rev. Sci. Instrum., 1976, 47, 1503.

 

Nanometer-scale compositional heterogeneities in humic substances detected by solid-state NMR

Jingdong Mao and Klaus Schmidt-Rohr

Department of Chemistry, Iowa State University, Ames, IA 50010

We have studied the size and chemical structure of compositional heterogeneities in humic substances using two-dimensional exchange NMR and chemical-shift filter experiments with 1H spin diffusion. In a peat humic acid, we have detected significant nanometer-size aliphatic domains of low oxygen content. By contrast, aromatic and oxygen-rich aliphatic groups are intimately mixed. This result excludes the presence of significant amounts of polysaccharide regions. The chemical composition of the low-oxygen aliphatic domains can be characterized by 1H chemical-shift filter experiments with 13C detection. The relationship with lignin-derived heterogeneities and poly(methylene) domains found previously will be discussed.

 

A 1D, 2D and Multinuclear Liquid State NMR Investigation of Laurentian Fulvic Acid

Robert L. Cook,1 Deane D. McIntyre,1 Hans J. Vogel1 and Cooper H. Langford2

1 Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4
2 Department of Chemistry, University of Calgary, Calgary, Alberta, Canada T2N 1N4

This paper discusses the interrogation of Laurentian fulvic acid (LFA) by a series of NMR techniques (1D techniques; 13C spectra with APT and INEPT, 2D techniques TOCSY, HSQC, HSQC-TOCSY, NOESY, ROESY, and multinuclear 1H, 13C, 14N, 15N, 19F, 31P). Why these techniques were chosen for the study of LFA is explained and the discussion is extended to the study of biogeopolymers as a whole. The experimental results are discussed in terms of the chemical make-up of LFA and its primary and tertiary structures (in DMSO). Evidence for small molecules or highly mobile moieties are presented and no evidence of amino acids is found. The new results are compared to previous studies of LFA in an effort to develop a more detailed meso-structural model for LFA.

 

Characterization of Humic Acid Using 1D and 2D Solution NMR Techniques

Kaijun Wang,1 L. Charles Dickinson,2 Elham A. Ghabbour,3 Geoffrey Davies,3 and Baoshan Xing1

1 Plant and Soil Sciences Department; University of Massachusetts, Amherst, MA 01003
2 Polymer Science and Engineering Department; University of Massachusetts, Amherst, MA 01003
3 Department of Chemistry and the Barnett Institute, Northeastern University, Boston MA 02115

Many studies have been conducted on the conformation of humic acids. Several structural models have been proposed in these studies but humic acid structure and its configuration are still poorly understood. We applied 1-D and 2-D solution NMR techniques to evaluate the changes in humic acid configuration caused by concentration and solvent effects. Two humic acids from Massachusetts and New Hampshire were used to measure the spin-lattice relaxation times (T1) of the protons on different functional groups. Although the T1 values were on the order of seconds, they were different for each functional group. In 0.5 M sodium deuteroxide (NaOD) solution, T1 values of aliphatic groups were shorter than those of the aromatic groups. The T1 values in dimethylsulphoxide (DMSO) were much shorter than in NaOD. The large T1 differences of humic acids in the two solvents reflect changes in humic acid configuration. High concentrations of humic acid in DMSO resulted in decreased T1 values for all the functional groups. The results suggest that the mobility of aromatic components of humic acid in solution is greater than for unsubstituted aliphatic and oxygen-substituted aliphatic counterparts. Results from 2-D techniques will also be discussed in terms of functional group connectivity and dipolar-dipolar interactions.

References

1. Friebolin, H., ‘Basic One- and Two-Dimensional NMR Spectroscopy,’ Wiley-VCH, Weinheim, 1998, p. 161-177.
2. Chien, Y. and W. F. Bleam, Environ. Sci. Technol., 1998, 32, 3653-3658.
3. Nanny, M. A., J. M. Bortiantynski and P. G. Hatcher, Environ. Sci. Technol., 1997, 31, 530-534.

 

Variation of free radical concentration of peat HA by methylations

T. Shinozuka, Y. Enomoto, H. Hayashi, H. Andoh and T. Yamaguchi

Chiba Institute of Technology, Narashino, Chiba 275-0016, Japan

It has been reported that humic acids contain high concentrations of free radicals. It is widely understood that the free radical is of the semiquinone type in FAs, which have larger COOH contents than soil HA.1 In this study ESR parameters of a variety of peat HAs were investigated. The relationship between carboxyl groups content and free radical concentration is discussed on the basis of methylation of the carboxyl and hydroxyl groups by certain methods. A powdered sample of humic acid was extracted in this laboratory from a tropical woody peat (Kalimantan, Indonesia) by a method based on the IHSS standard. Permethylation by the Hakomori method, methoxylation with diazomethane and methylesterification with methanol were carried out. ESR measurements were performed with a JES-FE2XG spectrometer (X-band 9 GHz). Experimental conditions were as follows; spectrometer modulation 100kHz; modulation amplitude 6.3G, microwave power 1.0mW, gain range 3350±500G. The relative concentration of ESR signals was obtained by an approximation based on the absolute signals for free radicals using DPPH (1,1-diphenyl-2-picrylhydrazyl; MW 394.24; 3.1×1020 spin/g). Carboxyl and hydroxyl groups of HA were eliminated by permethylation with the Hakomori method. The free radical concentration of HA decreased with the carboxyl and hydroxyl groups content. However, when HA was methoxylated with diazomethane, the free radical concentration was not changed. Therefore, this showed that the free radical concentration of peat HA is related to its carboxyl group content. In the case of methylesterification with methanol + H+ in suspension, the free radical concentration was not changed. The methyl esterification is limited to the surface carboxyl groups. From this result it seems that free radicals are stabilized by trapping with carboxyl groups existing in the inside of peat HA molecules.

Reference

1. Senesi, N. and M. Schnizer, Soil Sci., 1977, 123, 224-234.

 

Studies of the structureS of humic substances by electrospray ionization coupled to a Quadrupole-Time of Flight (Qq-TOF) mass spectrometer

Patrick G. Hatcher, Elizabeth B. Kujawinski, Xu Zang, Kari B. Green-Church, R. Benjamin Jones and Michael A. Freitas

Department of Chemistry, The Ohio State University, Columbus, OH 43210

The mass spectra of well-studied humic substances (HSs) measured by electrospray ionization coupled to a Qq-TOF mass spectrometer are significantly different. The HSs include HA and FA fractions of the Armadale soil1,2 and HAs from a diluvial soil in Iwata, Japan.1,3 Solid-state 13C ramp-CPMAS NMR data4 indicate that Armadale HSs are rich in aliphatic structures (intense signals between 0 and 110 ppm). The fulvic acid is more aromatic and shows higher intensity from carboxyl (160-180 ppm) and carbonyl carbon (180-220ppm). By contrast, the diluvial HAs are mainly carbon-linked benzenepolycarboxylic acids.3 The FAs and HAs have nearly identical mass spectra with clusters of peaks in the 80-200, 300-400 and 550-800 m/z ranges. Sharp peaks extend from a background of peaks from low mass to 3000 amu. The sharp peaks are due to specific molecular contaminants.5 Fatty acids are easily discernable from their high mass discrimination and separation from the clustered masses. Their M+1 ion also shows high mass discrimination. The sharp signals are only minor contributors to the summed intensity over the range of interest. Furthermore, the mass clusters occur at every nominal mass with little or no signals at fractional masses in between. Thus, the ions are singly charged and may be sodium adducts, as observed in spectra from a Mt. Rainier HA. The exact mass for each cluster is notable, especially for the diluvial HAs. Clustered masses with insignificant mass discrimination usually centered at 0.1 to 0.2 amu above the nominal mass indicate generally hydrogen poor structures compared to structures containing long-alkyl substituents. Ions centered at 0.1 to 0.2 amu above the nominal mass suggest significant amounts of hydrogen atoms on the aromatic rings, with substantial amounts of carboxyl functional groups present as suggested by the NMR data.3 Thus, condensed ring aromatics are not likely structures for the ion clusters, and carbon-linked carboxylated aromatic units of one or possibly two fused rings are more likely. Much more information can be gleaned from the spectra, but the data are only qualitative at present because little is known of the ionization efficiencies and relative detectabilities of various HSs structures. At the very least, the Qq-TOF technique is a rapid way of examining qualitative differences among HSs. This allows samples to be screened for more detailed studies by electrospray-FTICR-MS, where exact formula weights can be measured.

References

1. Matsuda, K. and M. Schnitzer, Soil Sci., 1972, 114, 185-193
2. Ogner, G. and M. Schnitzer, Can. J. Chem. 1971, 49, 1053-1063.
3. Hatcher, P. G., M. Schnitzer, A. M. Vassallo and M. A. Wilson, Geochim. Cosmochim. Acta, 1989, 53, 125-130.
4. Dria, K., M. S. Thesis, The Ohio State University, 2000.
5. Schnitzer, M. and J. A. Neyroud, Fuel, 1975, 54, 17-19.

 

Analysis of humic substances using ESI and APCI mass spectrometry

Michael Spiteller and Thomas Pfeifer

Institute of Environmental Research (INFU), University of Dortmund, D-44227 Dortmund, Germany

A detailed characterisation of humic substances by chromatographic and spectroscopic methods has always been hampered by the chemical heterogeneity of this class of substances. Mass spectrometry is a powerful technique and offers the possibility of improving the characterisation of humic substances. Mass spectra of various humic substances and dissolved organic matter were obtained in positive and negative ionisation mode using electrospray ionisation and atmospheric pressure chemical ionisation (APCI) as ionisation techniques. Using APCI, average masses are reduced 5 fold compared to ESI. High resolution time-of-flight mass spectrometry revealed the formation of multiply charged molecules in the electrospray ionisation mode. Moreover, it is possible to obtain daughter ion mass spectra of humic substances by nanospray tandem mass spectrometry. The size exclusion chromatography elution profile of humic substances is highly influenced by the pH of the analyte solution. However the pH had no significant influence on the observed mass spectra of humic substances.

References

1. Brown, T. L. and J. A. Rice, Anal. Chem., 2000, 72, 384.
2. Perminova, I. V., Soil Sci., 1999, 164, 834.
3. Piccolo, A., S. Nardi and G. Concheri, European J. Soil Sci., 1996, 47, 319.
4. Klaus, U., T. Pfeifer and M. Spiteller, Environ. Sci. Technol., 2000, 34, 3514.
5. Zwiener, C., M. U. Kumke, G. Abbt-Braun and F. H. Frimmel, Acta Hydrochim. Hydrobiol., 1999, 27, 208.

 

A Comparative Evaluation of Known liquid Humic Acid Analysis Methods

Amjad Fataftah, Daman Walia and Benny Gaines

ARCTECH, Inc. Chantilly, Virginia 20151

Manufacturers all over the world are making earnest efforts to promote the use of humic acid products in agriculture. These products not only are gaining acceptance by the agriculture community, but also many government institutions are including these products as part of their import specifications that designate humic acid content, as is the practice in the U.A.E. and Turkey. In the United States, all the states require registration of products specifying guaranteed analysis to comply with U.S. weights and measures laws. However, due to there being no standard method, the humic acid content of the products is labeled based on arbitrary humic acid analysis methods. For example, three methods utilized by the commercial testing facilities are: the acid precipitation method, the barium chloride precipitation method, and the optical density method. In this paper a comparative evaluation of these three methods was conducted on several commercial liquid humic acid products. The results show that the measurements based on barium chloride lead to the highest humic acid content. This anomaly also was observed for products that contain NPK and micronutrients.

 

STABILITY OF HUMIC ACIDS IN ALKALINE MEDIA

L. Pokorná,1 D. Gajdošová,1 S. Mikeska2 and J. Havel1

1 Department of Analytical Chemistry, Faculty of Science, Masaryk University, 611 37 Brno, Czech Republic
2 CHEMAPEX s.r.o., 430 03 Chomutov, Czech Republic

Humic acids (HAs) play an important role in nature and therefore they are intensively studied. Recently, it was confirmed that HAs represent a complex mixture of many compounds of low molecular weight.1-3 It is known2,3 that humic acids are soluble in alkaline solution. However, they might undergo degradation, radical reactions, hydrolysis and other processes in alkaline media. The aim of this work was to study in detail the stability and/or possible degradation of humic acids in alkaline media. The influence of different hydroxides, complexing and reducing agents was investigated. As a model compound for this study, a coal derived humic acid Chemapex HA Standard4 was chosen. Chemapex HA Standard is similar and in some ways equivalent to IHSS HA standards. This new humic acid standard prepared from Bohemian brown coal3 was analyzed in detail and characterized using capillary zone electrophoresis (CZE), Matrix Assisted Laser Desorption/Ionization Time-of-Flight mass spectrometry (MALDI TOF MS) and UV-VIS spectrophotometry methods. The stability study of Chemapex HA Standard was completed with a comparison of this product behavior with those of HAs of different origin. Conclusions of the reactions of HAs in alkaline media were drawn and some mechanisms proposed.

References

1. Wershaw, R. L., K. A. Thorn, D. J. Pinckney, P. MacCarthy, J. A. Rice and H. F. Hemond, in ‘Peat and Water-Aspects of Water Retention and Dewatering in Peat’, C. H. Fuchsman, Ed., Elsevier, London, 1986, p. 133.
2. Ghabbour, E. A. and G. Davies, Eds., ‘Understanding Humic Substances: Advanced Methods, Properties and Applications’, Royal Society of Chemistry, Cambridge, 1999.
3. Ghabbour, E. A. and G. Davies, Eds., ‘Humic Substances: Versatile Components of Plants, Soils and Water’, Royal Society of Chemistry, Cambridge, 2000.
4. CHEMAPEX s.r.o., http://www.CHEMAPEX.cz

 

THEORY AND APPLICATIONS OF DIFFERENTIAL SPECTROSCOPY IN STUDIES OF the INTRINSIC CHEMISTRY AND TRANSFORMATIONS OF HUMIC SPECIES

Gregory V. Korshin, Wells Wu and Mark M. Benjamin

Department of Civil and Environmental Engineering, University of Washington, Seattle, WA 98195-2700

This presentation will examine the utility and potential of differential spectroscopy in the elucidation of the intrinsic chemistry of humic species (HSs). This technique utilizes the concept of probing complex systems through controlled modulation of their state and examination of the corresponding spectral response. This approach was first summarized by Manuel Cardona and applied to studies of the electronic structures of solids.1 In the studies of HSs, the modulation can be achieved by changing the temperature, pressure, oxidation conditions, pH, etc. In this work, the modulation of the physico-chemical state of HSs was achieved by chlorination, changes of temperature and pH, or a combination of these controls. In the case of chlorination, the differential spectra of HS have two major features described in detail in our preceding publications.2,3 These features include a broad intense band with a maximum at 260 to 275 nm (band P) and relatively weak transient features located at ca. 280-290 and 340-380 nm, respectively. The transient features have been suggested to correspond to the formation of halogenated aromatic units incorporated into the backbone of HSs. The elucidation of the chemical nature of the intense band P remains a challenge. As will be outlined in the presentation, the contributing mechanisms include but are not necessarily limited to the destruction of aromatic units or other chromophores and breakdown of the HS molecules into smaller fragments. Differential spectroscopy of unaltered or chlorinated HS subjected to temperature and pH modulation has yielded unexpected results. For unaltered HS, the temperature modulation affects the organic molecules quasi-reversibly. The corresponding differential spectra contain relatively weak bands located at 270 and 325 nm. For chlorinated samples, the intensity of these bands increases several-fold. Simultaneous measurements of the fluorescence indicated a breakdown of the chlorinated HS molecules that is absent for unaltered HS. The unusual aspect of the changes initiated by the thermal treatment is that apparently it is accompanied by the formation rather than elimination of aromatic chromophores. The nature of the involved chemical processes and their relevance to the generation and fate of HSs in the environment will be discussed.

References

1. Cardona, M., ‘Modulation Spectroscopy’, Academic Press, New York, 1969.
2. Korshin, G. V., M. M. Benjamin and H. -B. Xiao, Interactions of Chlorine with Natural Organic Matter and Formation of Intermediates: Evidence by Differential Spectroscopy. Submitted to Acta Hydrochimica et Hydrobiologica, 2000.
3. Korshin, G. V., C. -W., Li and M. M. Benjamin, Water Sci. Technol., 1999, 40, 9-16.

 

Characterization of dissolved organic matter (DOM) in biological wastewater treatment by size-exclusion chromatography

Sebastian Hesse and Fritz H. Frimmel

Engler-Bunte-Institut, Water Chemistry, Universität Karlsruhe (TH), Germany

Effluents from biological wastewater treatment plants contain a variety of dissolved organic substances (DOM), including poorly biodegradable and refractory substrates. These complex organic compounds result from condensation reactions of influent organics with both intermediate and final degradation products and they contain soluble microbial products.1 Because of its complexity, the dissolved organic matter in wastewater is rather poorly defined. For the characterization of organic matter, size-exclusion chromatography (SEC) in combination with continuous high sensitivity detection of dissolved organic carbon (DOC), UV absorbance and dissolved nitrogen (DN) has been shown to be a very useful analytical tool.2 With this analytical tool, information on molecular size and hydrophobicity of dissolved organic substances can be obtained as they pass through the different physical, chemical, and biological steps of wastewater treatment. Besides the classical characterization of DOM based on fractionation by resins or ultrafiltration, the dissolved organic matter can be described by the content of bonded carbohydrates and low molecular weight acids determined chromatogra-phically after application of specific hydrolysis methods. The pattern of the hydrolysis products gives important indications on the origin and maturity of DOM in waters (biomarker). In addition, continuously fed miniaturized biofilm column reactors have been shown to be very useful for quantifying the biological degradation potential of organic matter in wastewater. The results allow the assessment of the refractory properties of DOM and soluble microbial products in biological wastewater treatment and the prediction of the effect of the influent wastewater quality on the performance of the treatment plant and the resulting effluent. In combination, the biological test system (biofilm reactor) and the analytical DOM characterization (SEC) are well suited to study the anthropogenic and humic fractions in aquatic systems.

References

1. Barker, J. D. and D. C. Stuckey, Wat. Res., 1999, 33, 3063-3082.
2. Hesse, S., and F. H. Frimmel, Acta hydrochim. hydrobiol., 1999, 27, 94-97.

 

Apparent Size Distribution and Properties of Natural Organic Matter Isolated from Six Rivers in Southeastern Georgia, USA

Monika Takács and James J. Alberts

The University of Georgia Marine Institute, Sapelo Island, GA 31327

Five major rivers draining 89,500 km2 of forested and agricultural watersheds bring on average 35 km3/yr of freshwater to approximately 150,000 hectares of salt marsh habitat1 along a 170 km Georgia coastline.2,3 These rivers vary in dissolved organic carbon (DOC) content from approximately 5 to 30 mg C L-1.4 Seventy five percent of the DOC is believed to be humic substances5 and 55-95% of the DOC occurs in relatively large molecular size fractions.6 In addition, the nitrogen associated with the DOC represents between 50-90% of the total dissolved nitrogen in the rivers.7 These estimates are based on monitoring databases, which provide total concentration values over a 20-year period, while the size fraction data reflect summer conditions for two distinct years. In this study, the rivers were sampled in low flow (June) and high flow (February) conditions and the DOC was fractionated by ultrafiltration to give insight into seasonal variations in size distribution and elemental content, as well as to examine the ultraviolet and fluorescence characteristics of the DOC and its fractions. Data for samples taken in 2000 indicate that 17-45% of the DOC occurred in relatively large fractions during high flow conditions, while only 6-28% of the DOC occurred in these fractions during low flow. Atomic C/N ratios for the fractions ranged from 17 to 54, with the smaller size fractions always having larger C/N ratios, indicating a relative depletion of N relative to C in those fractions. Specific UV absorbances for the whole waters ranged from 0.03 to 0.05 for all rivers and for both seasons, with the largest molecular size organic matter exhibiting the greatest specific absorbances. Relative fluorescence intensities for the whole waters ranged from 30 to 37 during high flow conditions and 19 to 48 during low flow conditions, with no apparent seasonal trend. However, unlike the ultraviolet size trends, the smallest sized organic matter had the largest relative fluorescence intensities. These findings are pertinent to the nutrient quality of the dissolved organic matter and the ability to remotely sense DOC concentrations using spectroscopic methods.

References

1. Alexander, C. E., M. A. Broutman and D. W. Field, ‘An Inventory of Coastal Wetlands of the USA,’ - NOAA, U.S. Department of Commerce, Washington, DC, 1986, 25 pp.
2. NOAA, ‘National Estuarine Inventory Data Atlas,’ U.S. Department of Commerce, Washington, DC, 1985.
3. Alberts, J. J. and Z. Filip, Trends in Chem. Geol., 1994, 1, 143-162.
4. Stokes, III, W. R., R. D. McFarlane and G. R. Buell, Water Resources Data Georgia Water Years 1974 to 1996, U. S. Geol. Surv., Atlanta, GA, 1974-1996.
5. Beck, K. C., J. H. Reuter and E. M. Perdue, Geochim. Cosmochim. Acta, 1974, 38, 361-364.
6. Alberts, J. J. and C. Griffin, Arch. Hydrobiol. Spec. Issues Advanc. Limnol., 1996, 47, 401-409.
7. Alberts, J. J. and M. Takács, Org. Geochem., 1999, 30, 385-395.

 

Molecular Structures and Associations of Humic Substances in the Terrestrial Environment

André J. Simpson,1 Patrick Hatcher,1 William L. Kingery,2 Michael H. B. Hayes,3 Manfred Spraul,4 Eberhard Humpfer,4 Peter Dvortsak,4 Rainer Kerssebaus,4 Markus Godejohann4 and Martin Hofmann4

1 Department of Chemistry, The Ohio State University, Columbus, OH 43210
2 Department of Plant and Soil Sciences, Mississippi State University, MS 39762
3 Department of Chemical and Environmental Sciences, University of Limerick, Ireland
4 Bruker Analytik GmbH, Silberstreifen, D-76287 Rheinstetten, Germany

We show evidence of the primary molecular structures in humic substances (HS), the most abundant naturally occurring organic molecules on Earth, and their associations as mixtures in terrestrial systems. Multi-dimensional NMR experiments allowed us to identify the major molecular structural components in HSs as being aliphatic acids, ethers, esters and alcohols, polysaccharides, polypeptides and aromatic lignin derived fragments. Using Diffusion Ordered Spectroscopy, distinct diffusion coefficients consistent with relatively low molecular weight molecules were observed for all the components in the mixtures and 3- to 8-unit sugar chains were determined to be the largest compounds present. Liquid Chromatography-NMR confirmed that HSs components can be easily separated and NOE enhancements support the findings that the components are of relatively low molecular weight <~2000 Da. The widely known properties of HSs that is, characteristics indicative of cross-linked, macromolecular networks, can now be explained as the aggregation of mixtures, most likely instigated by complexation with metal cations.

 

BINDING OF HUMIC ACIDS TO PROTEINS: PRELIMINARY INVESTIGATION OF THE EFFECT OF pH

Maria De Nobili,1 G. Bragato2 and L. Leita2

1 Dipartimento di Produzione Vegetale e Tecnologie Agrarie, University of Udine, 33100 Udine, Italy
2 Istituto Sperimentale per la Nutrizione delle Piante, sezione di Gorizia, 34170 Gorizia, Italy

Binding of humic acids to proteins is one of the mechanisms by which enzymes are made resistant to microbial degradation in soil. Although this protection results in partial deactivation of the enzyme, it allows persistence and accumulation of catalytic activities that are not directly connected with the biological activity of living organisms. In recent years, the large scale cultivation of transgenic plants, some of which contain truncated genes that code for the synthesis of active toxins, could, in principle, by the same mechanism lead to the accumulation of toxins in the soil. This points to the need for systematic investigations of binding of humic acids to proteins in order to gain information on both structural characteristics or soil conditions that minimise or increase environmental risks. The interaction of humic acids with different enzymes has been investigated by means of a two dimensional electrophoretic technique and by size exclusion chromatography. Humic acids have a strong polyanionic character and migrate towards the anode at any pH (unless they precipitate). Sawannee River reference HA (SW-R) precipitates in the application pocket below pH 5.2 and shows a diffuse migration zone up to pH 5.5. Above this pH the mobility of SW-R is quite high and is not affected by any further increase in pH. American standard soil humic acids (AM-S) and humic acids extracted from peat (IB-P) show traces of precipitation up to pH 7, with a wide and diffuse migration zone whose anodic limit increases from pH 4 to pH 7.5. Above this pH the mobility of AM-S and IB-P becomes similar to that of SW-R. Interactions of humic acids with bovine serum albumin, catalase, protease, alkaline phosphatase and ribonuclease modify the electrophoretic behavior of HA and cause the complete precipitation of the proteins at pH values below their isoelectric point up to a 8:1 protein:humic acids ratio. From about pH 4.7 to pH 6 there is an increase in mobility of the proteins towards the anode that testifies to interactions with HA. For proteins such as BSA that can combine into oligomers, the interaction affects the larger molecular weights more than the monomeric protein. Tests also were carried out in 6M urea but this had only secondary effects on the binding and differences were only observed when urea modified the electrophoretic behavior of the protein. The binding of HA to proteins evidently is electrostatic for the most part, but once established it is not destroyed by changes in pH. Hydrophobic interactions must therefore contribute to the stabilisation of the HA-protein adduct. From our results it follows that binding of humic acids to proteins is more likely to occur in acid soils, whenever the pH of the soil is below or near to the isoelectric point of the protein. Interactions in alkaline soil are much more unlikely and could occur only at acidic microsites.

 

Glomalin as a Constituent of Humic Substances

K. A. Nichols,1,2 S. F. Wright,1 W. F. Schmidt1 and E. K. Dzantor2

1 USDA-ARS, Beltsville, MD 20705
2 University of Maryland, College Park, MD 20742

Humic acids (HAs), fulvic acids (FAs) and humin are operationally defined by the extraction method and solubility. Dissolved HAs and FAs are heterogeneous mixtures of biopolymers, polysaccharides, proteins and metals that have been further purified by chemical fractionation techniques. A novel extraction method (citrate, pH 8.0, at 121oC for 1 h) has been used on soil samples to remove a glycoprotein produced by hyphae of arbuscular mycorrhizal fungi. This ubiquitous and recalcitrant glycoprotein, glomalin, accumulates in soils throughout the US and the world (typically 2-14 mg g-1). Two approaches were taken to define glomalin as a constituent of humic substances: (1) citrate extraction followed by alkaline extraction, and (2) alkaline extraction followed by citrate extraction. When the first approach is used, glomalin is removed by citrate and HAs and FAs are alkaline extractable from the residual soil. Likewise, the second approach yields citrate extractable glomalin from residual soil after HAs and FAs have been removed. If glomalin is not extracted first, it is present in small amounts in the HA fraction as a proteinaceous contaminant. This indicates that a specific extraction procedure and sequence should be used to obtain relatively pure HAs or FAs. For glomalin, the extreme conditions used in the citrate extraction limit contaminants. Weight, C and N content, total protein analysis and 1H NMR spectra all show that glomalin, HAs and FAs are distinct constituents. Since glomalin may be further extracted from the soil after alkaline extraction and requires extreme conditions for solubilization, we propose that glomalin is part of 'insoluble' humin in soils.

References

1. Hayes, M. H. B. and C. L. Graham, In ‘Humic Substances: Versatile Components of Plants, Soils and Water’, Ghabbour, E. A. and G. Davies, Eds., Royal Society of Chemistry, Cambridge, 2000, pp. 91-109.
2. Swift, R. S., In ‘Methods of soil analysis. Part 3. Chemical methods,’ Sparks, D. L. et al., Eds., SSSA Book Series, no. 5, Madison, WI, 1996, pp. 1018-1022.
3. Wright, S. F., M. Franke-Snyder, J. B. Morton and A. Upadhyaya, Plant and Soil, 1996, 181, 193-203.

 

Binding of Organic Solutes to Dissolved Organic Matter: A Predictive Approach Based on Computer Assisted Structure Elucidation, Atomistic Simulations and Flory-Huggins Solution Theory

Mamadou S. Diallo,1, 2 William A. Goddard III1 and James H. Johnson, Jr.3

1 Materials and Process Simulation Center, Beckman Institute, California Institute of Technology, Pasadena, CA 91125
2 Departments of Civil Engineering and Chemistry, Howard University, Washington, DC 20059
3 Department of Civil Engineering, Howard University, Washington, DC 20059

The interactions of organic solutes with dissolved organic matter (DOM) determine to a large extent their fate and transport in aquatic systems. Fulvic acids (FAs) and humic acis (HAs) typically constitute 30 to 50% of DOM. Because they are operationally defined as "solubility" classes of compound, accurate and reliable structural models that capture the relevant chemistry for FAs and HAs from a given source have not yet been achieved. This lack of reliable structural models is the primary reason behind the current proliferation of phenomenological models with adjustable parameters of organic solute uptake by FAs and HAs in aqueous solutions. Phenomenological models of organic solute uptake by FAs and HAs include the partitioning model of Chiou et al.1 and the dual reactive domain model (DRDM) of Weber and co-workers.2 Although some of these models have been shown to provide adequate fits of experimental data through the use of adjustable parameters, their predictive capability remains to be established. In this paper we describe a hierarchical approach for predicting the binding of organic solutes to dissolved FAs and HAs. This novel approach combines computer assisted structure elucidation (CASE) with atomistic simulations and Flory-Huggins solution theory to estimate the binding constants of organic solutes to dissolved FAs and HAs without the use of any adjustable parameter.

References

1. Chiou, C. T. et al., Environ. Sci. Technol., 1983, 17, 227.
2. Weber, W. J. and co-workers, Environ. Sci. Technol., 1997, 31, 697.

 

Modeling of molecular Interactions of soil components with organic compounds

G. Haberhauer,1 A. Aquino,1 D. Tunega,1,2 M. H. Gerzabek1 and Hans Lischka2

1 Department of Environmental Research, Austrian Research Centers, A-2444 Seibersdorf, Austria
2 Institute for Theoretical Chemistry and Structural Biology, University of Vienna, A-1090 Vienna, Austria

Understanding soil processes at a molecular level is crucial for a systematic interpretation of the vast manifold of information available from experiments. The molecular processes are very complex and much effort is being spent to understand them in detail using physical and chemical methods. Molecular modeling is a very powerful tool to get direct insight into molecular processes by means of computer simulations. This technique has been in use in chemistry and molecular biology for a long time. The objectives of this work were to examine the possibility and investigate the limitations in studying the interactions of pesticides with soil constituents by means of molecular modeling techniques. Modeling the whole soil system in full complexity on a molecular level is practically impossible. Thus, one has to introduce several idealizations and simplifications for the construction of appropriate models. We have focused on several particular problems. Density functional theory (DFT) methods were used for the calculations. Aluminum complexes with citrate ligands in water solution were found to be most stable in a calculation comparing the aluminum-hexaaquo complex and various aluminum-acetate,1 aluminum-oxalate2 and aluminum-citrate3 complexes. Based on these studies, interactions of a model pesticide with regular 001 surfaces of the kaolinite group of clay minerals were investigated. On the basis of our results we can conclude that the octahedral site is more attractive for polar species and adsorption energies will be higher than for the tetrahedral site. The inclusion of a model for humic substances adds another level of complexity. Due to the highly polymeric and complex structure of HSs, their molecular structures are still unknown. Thus, it was necessary to restrict ourselves to models of better defined nature. We focused on the specific interaction of a model pesticide with functional groups that are known to be present in humic substances. This certainly is a crude simplification but it should at least be a reasonable starting point based on experimental evidence. A set of possible molecular interactions of a model pesticide with organic matter was selected. In real situations in soil solution, these subsystems will be surrounded by different kinds of environments, ranging from polar to nonpolar character. Therefore, our main interest was directed towards the investigation of the dependence of interaction energies on the character of the environment (as described, for example, by the dielectric constant  ) into which these clusters were embedded. First results of these calculations will be presented and limitations of possible free energy calculation studies will be discussed.

References

1. Tunega, D., G. Haberhauer, M. Gerzabek and H. Lischka, J. Phys. Chem. A, 2000, 104, 6824.
2. Aquino, A. J. A., D. Tunega, G. Haberhauer, M. Gerzabek and H. Lischka, Phys. Chem. Chem. Phys. 2000, 2, 2845.
3. Aquino, A. J. A., D. Tunega, G. Haberhauer, M. Gerzabek and H. Lischka, Phys. Chem. Chem. Phys. – accepted.

 

Metal-Humics Speciation by Capillary Electrophoresis ICP-MS

Jeroen E. Sonke and Vincent J. M. Salters

Geochemistry Division, National High Magnetic Field Laboratory and Florida State University, Tallahassee, FL 32306

We report on capabilities for metal-humic speciation studies of the coupling of capillary electrophoresis to a Magnetic Sector Inductively Coupled Plasma Mass Spectrometer (CE-ICP-MS). The superior multielement detection capability of ICP-MS and the separation potential of CE provide the basis for determining elemental speciation in aqueous solutions. Full control of the electrolyte flow in the CE capillary allows for optimal tuning of a specific separation experiment. At the cost of resolution, rapid analyses times (3 min) make possible kinetic studies of complexation reactions. Longer analyses times (30 min) may facilitate the high resolution necessary for metal-humic separations. We studied equilibrium speciation and kinetics of Cu-ligand binding involving both ligand (EDTA, humics) and metal (Cu, Zn) competition at micro molar levels. Similar experiments were performed by perturbing an equilibrium speciation of Nd(III) and Ce(IV)-humics at pH 8.1 by adding EDTA to solution. After EDTA addition, Nd and Ce rapidly convert from CO3 complexes to the EDTA complex. However, Nd and Ce release from the humic complexes is slow due to stronger binding. Equilibrium and kinetic studies of REE speciation may give insight into actinide behavior under similar conditions. Conditional binding constants for Cu-fulvic acid complexes were investigated through direct and competition speciation experiments. Results are comparible with published values. We expect a promising role for ICP-MS in metal-humic binding studies for a range of biogeochemically interesting metals.

References

1. Hering, J. G. and F. M. M. Morel, Geochim. Cosmochim. Acta, 1988, 53, 611-618.
2. Kinzer, J. A., J. W. Olesik and S. V. Olesik, Anal. Chem., 1996, 68, 3250-3257.

 

Aluminum sorption to humic substances: can it be measured with capillary electrophoresis?

Frank J. von Willert and R. C. Stehouwer

Department of Agronomy, The Pennsylvania State University, University Park, PA 16802

Humic substances, especially dissolved organic matter (DOM), play an important role in the solution chemistry of aluminum in soils at low pH. The complexation of Al by humic substances can influence the degree of Al toxicity in low pH soils and also plays a major role in the podzolization process.1 Up to now, all analytical techniques for measuring Al binding to humic substances have relied on indirect methods such as reaction with chelating agents, exchange resins, monitoring of F- concentration with an F- selective electrode or spectroscopic methods that are time consuming and complicated. Often, these indirect methods will analyze an operationally defined Al form. Accordingly, the database for binding of Al to humic substances is rather small and the accuracy of some of the data is questionable. Recently, it has been pointed out that capillary electrophoresis can be used to measure Al3+ concentration in aqueous solutions2,3 because separation is based on electrophoretic mobility. Organic Al complexes that are present in the solution will not migrate at all or not at the same speed as Al3+. The "true" Al3+ concentration can be measured without affecting the speciation of the sample. Detection of peaks in capillary electrophoresis is by UV absorption. Because Al3+ does not absorb UV light, a highly UV absorbing background electrolyte (4-methylaminophenolsulfate) is used and cations are detected as negative peaks. While previous reports indicated a linear range of the detector response for Al concentrations between 0.1 and 2 mg L-1,2 we found that with slight modifications of the original method the linear range can be extended from 0.1 to over 50 mg/L. It was shown that measured Al3+ concentrations in Al–oxalate solutions closely match theoretical values. Initial experiments also show that Al binding by compost derived DOM can be quantified. Data will be presented on Al3+ sorption by compost derived DOM and a fraction that is soluble at low pH and at high Al3+ concentrations. Because different cation concentrations can be measured at the same time using capillary electrophoresis, competitive sorption experiments can be conducted. The potential and limitations of capillary electrophoresis for competitive metal sorption experiments will be discussed.

References

1. Sposito, G., Ed., ‘The Environmental Chemistry of Aluminum,’ Lewis Publishers, Boca Raton, FL, 1996.
2. Göttlein, A., Europ. J. Soil Sci., 1998, 49, 107-112.
3. Wu, N., W. J. Horvath, P. Sun and C. W. Huie, J. Chromatog., 1993, 635, 307-312.

 

The influence of pH and metal species on the precipitation of dissolved organic matter (DOM)-metal complexes

Klaas G. J. Nierop, Boris Jansen and Jacobus M. Verstraten

Centre for Geo-ecological Research (ICG), Institute for Biodiversity and Ecosystem Dynamics (IBED), Department of Physical Geography and Soil Science, Faculty of Science, University of Amsterdam, 1018 WV Amsterdam, The Netherlands

Although dissolved organic matter (DOM) comprises only a small part of the total amount of soil organic matter in the soil environment, it is a very important fraction due to its high mobility. DOM is able to interact with common soil constituents (SOM, plant remains, mineral particles), and also with pesticides, polyaromatic hydrocarbons (PAHs) and heavy metals. We focused on the interaction of DOM with metals occurring naturally in the soil (Al and Fe) and compared them with Cu, a metal with strong complexation properties. When a given DOM ‘molecule’ meets a metal ion, three possible situations may occur: i) the formation of a DOM-metal complex that remains soluble, ii) the formation of a DOM-metal complex that precipitates, and iii) no interaction. The distribution of these fractions is determined by the type of metal, the composition of DOM in terms of functional groups that are able to bind with the metal and the ratio of metal/DOM concentration. We studied the parameters that determine precipitation using DOM extracted from a humified (H) horizon containing 40 mg C/L, a common concentration in soil solutions. Increasing quantities of metals (Al, Fe(II), Fe(III) and Cu, separately and combined to study competition) were added to the DOM solutions at three pH values: 3.5, 4.0 and 4.5. During these titration experiments the strongest complexes are likely to be formed first, and, consequently, the metals bind to DOM with decreasing strength. It appeared that Al caused the highest degree of DOM precipitation and Cu the lowest. The amount of DOM precipitation was highest at pH 4.5 for both Al and Cu, while less effect of pH was found for both Fe(II) and Fe(III). Crossing a metal specific threshold (metal/DOM ratio) value in the DOM solutions increased the amounts of precipitated DOM. After a second critical point the amounts of precipitated DOM leveled off and only little DOM precipitated with increasing metal addition. As a consequence, precipitated DOM versus metal addition resulted in an ‘S-curve’. The various parts of this curve may imply different types and strengths of DOM-metal complexes. In a subsequent study, the precipitated DOM will be characterized by e.g. pyrolysis and thermally assisted hydrolysis and methylation (THM) to find out to what extent DOM composition determines differences in amounts, types of bonding and their strengths of precipitated DOM-metal complexes as a function of metal and pH.

 

Spectroscopic and Flow-Field Flow Fractionation-Inductively Coupled Plasma-Mass Spectrometry (Flow-FFF-ICP-MS) Study of Humic Acids Isolated from Organic and Conventional Agricultural Soils, and Vermin Compost

Tom Anderson,1 Dula Amarasiriwardena,1 Baoshan Xing,2 Atitaya Siripinyanond3 and Ramon Barnes3,4

1 School of Natural Science, Hampshire College, Amherst, MA 01002
2 Department of Plant and Soil Sciences
3 Department of Chemistry, University of Massachusetts, Amherst, MA 01003
4 University Research Institute for Analytical Chemistry, Amherst, MA 01002

Humic acids (HAs), an important component of soil organic matter, are highly functionalized and therefore they complex extensively and ion exchange with cations. Complexation and ion exchange with trace metals and sorption of organic contaminants makes HAs central to agricultural processes such as nutrients mobilization and pesticide retention.1 Flow-field flow fractionation (Flow-FFF) has been used for the determination of molecular weight and polydispersity2 and to investigate trace metals complexed to HA molecular fractions.3 The purpose of this study is to explore metal complexation and colloidal characteristics of several HA samples derived from conventional (i.e., with nitrogen fertilizer inputs) and organic agriculture soils, and the HA isolated from vermin compost using spectroscopic and flow-FFF coupled to inductively coupled plasma-mass spectrometry (Flow-FFF-ICP-MS). HAs for this investigation were extracted from a conventional agricultural soil, the soil from an organic farm in Western Massachusetts and a vermin compost sample from Solis Valley, Mexico. HAs functionality was characterized by diffuse reflectance infrared spectroscopy (DRIFTS), NMR and UV-visible spectroscopy. The maturity of the HAs was compared from the intensity ratio of oxygen containing functional groups (O) to aliphatic and aromatic groups (recalcitrant groups-R) using DRIFTS measurements (O/R).4 The fractograms of trace metals complexed to HA molecular weight fractions were determined by Flow-FFF-ICP-MS. The molecular weights, polydispersity, hydrodynamic diameter and diffusion coefficients of the isolated humic samples will be presented. Elemental fractograms of soils and vermin compost-derived HAs are used to compare the role of HAs in the mobilization of nutritionally important trace metals such as Zn, Cu and Mn in high nitrogen fertilizer input soils to soils amended with organic farming practices. Results from this study will be useful for evaluating the effect of agricultural management on humic substances and carbon cycling.

References

1. Stevenson, F. J., ‘Humus Chemistry,’ 2nd Edn., Wiley, New York, 1994.
2. Beckett, R., J. Zhang and J. C. Giddings, Environ. Sci. Technol., 1987, 21, 289.
3. Amarasiriwardena, D., A. Siripinyanond and R. M. Barnes, In ‘Humic Substances: Versatile Components of Plants, Soil and Water,’ Ghabbour, E. A. and G. Davies (Eds.), Royal Society of Chemistry, Cambridge, 2000, p. 215-226.
4. Wander, M. M. and S. J. Traina, Soil Sci. Soc. Am. J., 1996, 60,1087.

 

Trace Metal Speciation and Colloidal Properties of Soil Humic Acids Isolated from Three Different Soils: A Flow-Field Flow Fractionation-Inductively Coupled Plasma-Mass Spectrometry (Flow-FFF-ICP-MS) Study

Laura Shifley,1 Dula Amarasiriwardena,1 Baoshan Xing,2 Atitaya Siripinyanond3 and Ramon Barnes3,4

1 School of Natural Science, Hampshire College, Amherst, MA 01002
2 Department of Plant and Soil Sciences, University of Massachusetts, Amherst, MA 01003
3 Department of Chemistry, University of Massachusetts, Amherst, MA 01003
4 University Research Institute for Analytical Chemistry, Amherst, MA 01002

Humic acids (HAs) in the soil and aquatic environments are known to form stable complexes with trace metals through omnipresent functional groups having ligand sites. The complexation mechanism of trace metals at these sites either is a metal-ligand interaction or proton displacement via ion exchange.1 Consequently, the physical nature of the HA colloids and chemical interaction with trace elements and colloidal matter is important to characterize HA bound toxic trace elements such as As, Pb, and Cd and nutritionally important elements like Cu, Zn and Mn. Field flow fractionation (FFF) is an analytical approach that can accurately estimate the hydrodynamic colloidal particle diameter, molecular weight and diffusion parameters, which are increasingly important in investigation of environmental behavior of trace elements in soil environments.2,3 The purpose of this study is to investigate the metal complexation properties and colloidal characteristics of several HA samples derived from various sources using flow field flow fractionation (flow-FFF) coupled to inductively coupled plasma-mass spectrometry (Flow-FFF-ICP-MS). HAs were extracted from a sub-topical agricultural soil in Mexico and a temperate soil from the Western Massachusetts, and from contaminated sediments of the Blackstone River Valley, Massachusetts. The HAs functionality was characterized by diffuse reflectance infrared spectroscopy (DRIFTS), NMR, and UV-visible spectroscopy. Fractograms of trace metals (Pb, Cu, Zn, As, Mn and Fe) complexed to HA molecular weight fractions and the polydispersitivity, particle sizes and diffusion coefficients of humics determined by Flow-FFF-ICP-MS will be presented. This study provides valuable information on relative contributions of different molecular fractions of humic acids to metal binding.

References

1. Stevenson, F. J., ‘Humus Chemistry,’ 2nd Edn., Wiley, New York, 1994.
2. Beckett, R., J. Zhang and J. C. Giddings, Environ. Sci. Technol., 1987, 21, 289.
3. Amarasiriwardena, D., A. Siripinyanond and R. M. Barnes, In ‘Humic Substances: Versatile Components of Plants, Soil and Water,’ Ghabbour, E. A. and G. Davies, Eds., Royal Society of Chemistry, Cambridge, 2000, p. 215-226.

 

interaction of dissolved organic matter with Al, Cu, Fe(II) and Fe(III) in soil solutions

Boris Jansen, Klaas G. J. Nierop and Jacobus M. Verstraten

Center for Geo-ecological Research, Institute for Biodiversity and Ecosystem Dynamics (IBED), Department of Physical Geography and Soil Science, Universitey of Amsterdam, NL-1018WV Amsterdam, The Netherlands

Dissolved Organic Matter (DOM) in soil solutions plays a crucial role in substance transport through forest soils. It can act as a carrier for components ranging from nutrients and trace elements to toxics such as pesticides.1 The mobility of DOM and substances bound to it is mainly regulated by precipitation and sorption of DOM on the solid soil matrix.2 Polyvalent metal cations such as Al, Cu, Fe(II) and Fe(III) can strongly bind to DOM.3,4 At low metal concentrations where no precipitation is expected, the formation of strong soluble metal-DOM complexes can influence DOM mobility and its ability to bind and transport other substances.1,5,6 Binding of metals to DOM could enhance DOM mobility by occupation of functional groups of DOM involved in sorption to clay minerals. Or DOM mobility may be impeded when DOM is immobilized on clay minerals through cation bridging by metals. Understanding complexation in soil solutions is necessary to assess the importance of the formation of strong, soluble metal-DOM complexes on DOM mobility in soils. An improved understanding of the dependence of complexation on pH and the presence competing metals is essential. However, for many metals direct estimation of the amount of strong soluble metal-DOM complexation suffers from problems of distinguishing free metal and dissolved labile complexes on the one hand and dissolved strong organic complexes on the other.3,7 After successful tests of the technique of Diffusion Gradients in Thin films (DGT),8 we used it to assess strong complexation of Al, Cu, Fe(II) and Fe(III) as a function of the metal/organic C ratio at different pH in artificial forest soil solutions. Furthermore, we studied the influence of competition effects between the four metals. Our preliminary results indicate that at lower metal/organic C ratios and ample functional groups availability, > 70 % of the total metal mass in solution was present as strong organic complexes. The extent of complexation increased with increasing pH as more acidic functional groups dissociate and become available for bonding. At higher metal/organic C ratios the degree of complexation in solution decreased and a shift in the differences in complexation at different pH values was observed. Such differences also were observed between Fe(II) and Fe(III), indicating that the soil redox potential could indirectly influence DOM mobility by determining the redox state of dissolved metals.

References

1. Fox, T. R., In ‘Carbon Forms and Functions in Forest Soils’, McFee, W. W. and J. M. Kelly, Eds., SSSA, Madison, WI, 1995; 1, pp 43-62.
2. Guggenberger, G. and W. Zech, Geoderma, 1993, 59, 109-129.
3. Stevenson, F. J., ‘Humus chemistry,’ 2nd Edn.; Wiley, New York, 1994.
4. Tam, S. C. and J. G. McColl, J. Environ. Quality, 1990, 19, 514-520.
5. Kaiser, K., Org. Geochem., 1998, 28, 849-854.
6. Lores, E. M., R. A. Snyder and J. R. Pennock, Chemosphere, 1999, 38, 293-310.
7. Saar, R. A. and J. H. Weber, Environ. Sci. Technol., 1982, 16, 510A-517A.
8. Zhang, H. and W. Davison, Anal. Chem., 1995, 67, 3391-3400.

 

The Influence of Catechol Humification on Surface Properties of Metal Oxides

C. Liu and P. M. Huang

Department of Soil Science, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada

Organic and inorganic components are closely associated in soil.1 Metal oxides such as manganese(IV) and iron(III) oxides catalyze the polymerization of phenolic compounds and the subsequent formation of humic substances.2,3 However, the surface chemistry of the resultant metal oxide-humic complexes remains obscure. The surface of metal oxide-humic complexes is the region of their interaction with heavy metals and organic pollutants. Therefore, the surface characteristics of the complexes can greatly affect the transformation and transport of inorganic and organic pollutants in soils and associated environments. In the present study, the surface properties, including the specific surface, surface charge, Point of Zero Salt Effect (PZSE) and fine-scale surface features of synthetic Mn, Fe, and Al oxides before and after reaction with catechol and the residence time effect of the interaction were investigated. The nature of the metal oxides and their humic complexes was investigated by X-ray diffraction and Fourier transform infrared spectroscopy (FTIR). The solution products of the metal oxide-catechol systems were studied by UV-visible absorption spectrophotometry, FTIR and elemental analysis. The synthetic Mn, Fe, and Al oxides were, respectively, birnessite, short-range ordered Fe oxide and mixtures of gibbsite and bayerite. Black solid products were formed in all the metal oxide-catechol systems and the rate of formation of black products was in the order Mn oxide > Fe oxide > Al oxide. Catechol humification significantly altered the birnessite structure even after just a 1-d reaction period. However, the structure of Al oxides was not significantly modified by catechol humification even after a 20-d reaction period. The surface properties of the metal oxides were substantially modified by catechol humification. The specific surface areas of the Al, Fe, and Mn oxide-humic complexes formed at the end of a 20-d reaction period were, respectively, decreased by 49%, 93%, and 66%. This is attributed to an increase in aggregation of the metal oxide-humic complexes. Catechol humification substantially decreased the PZSE of Al and Fe oxides and increased that of birnessite, apparently through two mechanisms: (1) replacement of some of the bound H2O from M-OH20.5+ and/or the bound OH from M-OH0.5- groups on the oxide surfaces by the humic substances and (2) dissociation of protons from the functional groups of the humic substances. Compared with the respective metal oxides, the Al and Fe oxide-humic complexes had higher net negative charges and birnessite-humic complexes had lower net negative charges at the same pH.

References

1. Schnitzer, M., In ‘Environmental Impact of Soil Component Interactions,’ Huang, P. M., J. Berthelin, J. -M. Bollag, W. B. McGill and A. L. Page, Eds., Vol. 1, Natural and Anthropogenic Organics. CRC, Lewis Publishers, Boca Raton, FL, 1995, p. 3-19.
2. Shindo, H. and P. M. Huang, Soil Sci. Soc. Am. J., 1984, 48, 927-934.
3. Huang, P. M., In ‘Handbook of Soil Science’, Sumner, M. E., Ed., CRC Press, Boca Raton, FL, 2000, p. B303-B332.

 

Atomic Force Microscopy (AFM) study of the adsorption of IHSS Standard Soil HA and Standard Soil FA at the mica-water interface

A. -M. Tugulea, D. R. Oliver, D. J. Thompson and F. Hawthorne

Department of Geological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada

The adsorption of humic molecules on clay minerals improves their geochemical stability and provides an active surface for cation exchange and sorption of organic compounds. The importance of clay-humic complexes in contaminant binding and transport has been demonstrated. Experimental data suggest that the interaction between humic substances and clay particles influences the conformation of the humic molecules, and consequently their sorptive properties. Atomic Force Microscopy (AFM) is a relatively new imaging technique used in the study of humic and fulvic acid morphology. Compared with electron microscopy, AFM provides three-dimensional images and, in most cases, better image resolution. A diversity of humic materials have been studied by AFM using different materials as atomically-flat solid supports: polished graphite, glass and mica. In the present study, IHSS Standard Soil Humic/Fulvic Acid and freshly cleaved muscovite mica were used in an attempt to model adsorption of a natural humic/fulvic acid fraction to clay minerals. Freshly cleaved mica provides an atomically smooth surface (flatness better than 3 Ĺ over areas of tens of square microns) that is similar in properties to many of the particulate mineral materials in natural environments. Adsorption was performed with the mica plate immersed vertically in the humic solution (in order to avoid deposition of humic aggregates by sedimentation) for 24 hours. The mica plate was then removed, excess water drained and the sample air-dried. Adsorption experiments were done at different pH, ionic strength and humic material concentrations. Contact-mode AFM was used for the imaging of the mica surface after adsorption. The three-dimensional images can be used to derive information about humic particle shape, dimensions, degree of aggregation and mica surface coverage under different conditions.

References

1. Liu, C. and P. M. Huang, In ‘Understanding Humic Substances,’ Ghabbour, E. A. and G. Davies, Eds., Royal Society of Chemistry, Cambridge, 1999, pp. 87-100.
2. Plaschke, M., J. Romer, R. Klenze and J. I. Kim, Colloids and Surfaces A, 1999, 160, 269-279.
3. Shevchenko, S. M., Y. S. Yu, L. G. Akim and G. W. Bailey, Holzforschung, 1998, 52, 149.

 

Ni SPECIATION IN A HUMIC ACID-KAOLINITE SYSTEM

Maarten Nachtegaal,1 Elham A. Ghabbour,2 Geoffrey Davies2 and Donald L. Sparks1

1 Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19717-1303
2 Barnett Institute and Chemistry Department, Northeastern University, Boston, MA 02115-5000

Partitioning reactions at the solid-water interface control the fate, bioavailability and mobility of trace metals in soils. Whereas much is known about metal sorption mechanisms on individual soil components (i.e. clay minerals, oxides and SOM), very few studies have been conducted on metal sorption to clay mineral-oxide-humus associations.1 Recent time-resolved extended x-ray absorption fine structure spectroscopy (EXAFS) studies have shown that surface precipitation is an important sorption mechanism for some of the first row transition metals like Ni, Co or Zn on clay minerals and Al oxides under ambient soil conditions.2 These surface precipitates show a dramatic stabilization over time in the model systems studied and thus may lead to an important long-term removal of the metal from solution. The objective of this work was to study the competing effects of SOM on metal surface precipitation processes. We performed kinetic sorption and desorption experiments of Ni to a kaolinite-humic acid complex (containing both 1 and 5 wt% HA). Selected samples were retained for EXAFS and diffuse reflectance spectroscopy (DRS) analyses to monitor sorption mechanisms at the mineral surface. Synchrotron based microspectroscopy3 and x-ray absorption near edge structure spectroscopy (XANES) studies will be used to describe interactions of humic acids with kaolinite and Ni. Ni sorption by kaolinite was found to be enhanced with increasing presence of HA. EXAFS and DRS studies indicate the formation of surface precipitates on the kaolinite surface, even in the presence of 5 wt% HA. More work to establish the identity of the reactive sites involved with metal/mineral binding using micro-XANES is being carried out and will be discussed.

References

1. Hayes, M. H. B. and F. L. Himes, In ‘Interactions of Soil Minerals with Natural Organics and Microbes’, Huang, P. M. and M. Schnitzer, Eds., Soil Science Society of America, Madison, WI, 1986, p. 133.
2. Scheidegger, A. M., G. M. Lamble and D. L. Sparks, J. Colloid Interf. Sci, 1997, 186, 118.
3. Scheinost, A. C., S. Abend, E. J. Elzinga, M. Nachtegaal, C. Jacobsen and D. L. Sparks, Environ. Sci. Technol., submitted.

 

Humic Substances, polysaccharides and pH effects on the dispersion, flocculation and rheology of clay suspensions

Yona Chen and Jorge Tarchitzky

Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel

Humic substances (HSs) and polysaccharides are important factors in soil particle associations. However, little is known about the mechanisms of clay–HS interactions and their effects on aggregation at different pH levels have not been studied adequately. Studies on flocculation and dispersion characteristics of homoionic montmorillonite were performed as a function of exchangeable cation, humic acid (HA), fulvic acid (FA), polygalacturonic acid (PGA) and dextran (three different MWs) concentration and pH. A matrix of experimental conditions was employed and the corresponding flocculation values (FV) were measured. Edge-face (E-F) and edge-edge (E-E) interactions at various pH levels, as well as heteroflocculation and its response to pH and concentration of the organic molecules will be discussed. In general, the negatively charged molecules increased the stability in suspension of the clay particles (reflected in increased FVs). This effect was pH dependent due to changes in the edge charge of the clay and the increase in the dissociation of functional groups of the organic molecules with increased pH. The Na-montmorillonite suspension exhibited a non-Newtonian rheology. The addition of both HS and PGA into a clay suspension changed the flow behavior from non-Newtonian to Newtonian as the organic material concentration increased. This change is a result of the disruption of E-E and E-F bonds by the adsorption of the negative macromolecules at the positive edges of the clay. The mechanisms involved in the interactions between Na-montmorillonite and the HSs and with the anionic polysaccharide (PGA) are the edge charge reversal and mutual flocculation (heteroflocculation). Some differences were recorded, apparently as a result of the differences of structure and characteristics of the organic molecules. In contrast to the charged organic molecules (HA, FA and PGA), the low molecular weight dextran (T-40, 40000 Da) did not cause any significant change in the flocculation of Na-montmorillonite, whereas the other two neutral polysaccharides (T-500, 5x105 Da; and T-2000, 2x106 Da) enhanced clay flocculation and consequently a sharp decrease in the FV was recorded. The observed mechanisms and effects are important to soil properties that can be influenced by the presence of these (or similar) components and by polysaccharides biosynthesized by microorganisms.

 

Effects of forest clear-cutting on the structure and chemistry of humic substances of the Hubbard Brook Experimental Forest, New Hampshire, USA

David A. Ussiri and Chris E. Johnson

Department of Civil and Environmental Engineering, Syracuse University, Syracuse, NY 13244

Organic matter influences many biogeochemical processes in terrestrial ecosystems. Forest clear-cutting alters the organic matter cycle by changing decomposition rates and also by changing litter inputs. We studied the effects of forest management on the chemistry and structural properties of humic substances (HSs) at Hubbard Brook Experimental Forest in New Hampshire. Humic substances were extracted and isolated chromatographically into humic acid, fulvic acid and polysaccharide fractions from soils collected prior to clear-cutting and 3, 8 and 15 years after. Also, aquatic humic substances from soil solutions and streams draining clear-cut and unmanaged watersheds were isolated and fractionated into hydrophobic and hydrophilic solutes. Wet chemical methods and spectroscopic analyses were used to study the properties of the isolated fractions. The percentage of organic matter extracted as humic substances increased with soil depth (horizon Oa < E < Bh < Bs1 < Bs2). Humic acid in the Oa horizon decreased from nearly 40% of the extracted organic matter before clear-cutting to 24% three years after clear-cut and did not return to the pre-harvest concentrations 15 years after clear-cut. Fulvic acid increased in the Bh and Bs1 horizons from about 21% of the extracted HS to 33% nine years after harvest. Increased polysaccharide content in Bh and Bs2 horizons was detected 15 years after harvest. Total acidity of humic acid ranged from 138 to 618 cmolckg-1 (mean = 356.5 cmolckg-1), of which carboxylic acid acidity was about 70%. Fulvic acid acidity ranged from 531 to 975 cmolckg-1 (mean = 716 cmolckg-1) of which carboxylic acid acidity accounted for about 82%. Solid-state 13C nuclear magnetic resonance (NMR) analysis revealed that alkyl C was the largest C fraction in both humic acid and fulvic acid, while in polysaccharides carbohydrate was more than 65%. Carboxyl content was twice as much in fulvic acid relative to humic acid. This supports the above finding that fulvic acid had more carboxyl acidity and is generally more acidic than humic acid. The proportion of C assigned to carboxyl (chemical shift = 160-185 ppm) followed this order: soil fulvic acid (16%) > aquatic fulvic acid (12%) > soil humic acid (8%) > polysaccharide (2%).

References

1. Aiken, G. R., D. McKnight, R. L. Wershaw and P. MacCarthy, ‘Humic Substances In Soil, Sediment, and Water: Geochemistry, Isolation and Characterization,’ Wiley-Interscience, New York, 1985.
2. Dai, K'o. H., M. B. David and G. F. Vance, Biogeochem., 1996, 35, 339-365.
3. Hayes, M. B., P. MacCarthy, R. L. Malcolm and R. S. Swift, ‘Humic Substances II: In Search of Structure,’ Wiley-Interscience, Chichester, 1989.
4. Stevenson, F. J., ‘Humus Chemistry,’ 2nd Edn., Wiley, New York, 1994.

 

Spectroscopic Evaluation of Humin Changes in Response to Soil Managements

Guangwei Ding,1 Jingdong Mao,1 Stephen Herbert,1 Dula Amarasiriwardena,2 and Baoshan Xing1

1 Department of Plant and Soil Sciences, University of Massachusetts, Amherst, MA 01003
2 School of Natural Science, Hampshire College, Amherst, MA 01002

Understanding the nature and dynamics of soil organic matter (SOM) has considerable potential to improve soil management technologies for sustainable crop production.1,2 Although characterization of humic substances is important for determining the overall quality of soils, the application of 13C nuclear magnetic resonance (NMR) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) to study the humin fraction (HU) is limited because low C and high magnetic particle contents reduce spectral quality.1 We isolated the humin fraction from soils with following treatments: a) Vetch/Rye, b) Rye Alone and c) Check (no cover crops) with varying nitrogen fertilizer rates. Organic-carbon-enriched HU was prepared using 1.0 M HF accompanied by a magnetic stir bar to minimize the content of ferromagnetic materials.3 Preliminary solid-state CP-TOSS (cross polarization-total sideband suppression) 13C NMR results indicate that the HU fraction has a very strong signal at about 30 ppm for all 6 HU samples, which is assigned to carbons in long -CH2- chains. The aromaticity [(108-162 ppm)/(0-162 ppm)] of HU is higher in Rye Alone plots with or without nitrogen fertilizer than the other two systems. Another main feature of the intensity distribution for HU is that fertilizer application is associated with a slight increase of relative intensity for the O-alkyl region (60-96 ppm). This O-alkyl C increase may simply reflect large plant residue inputs with nitrogen fertilizers. All 6 HU DRIFTS spectra were assigned to organic functional groups and several mineral peaks. Based on the DRIFTS spectra, the O/R (reactive groups/recalcitrant groups) ratio of HU in Rye Alone is lower than that from Vetch/Rye systems with or without nitrogen fertilizers. These data suggest that agricultural practices affect the compositions of HU, a large fraction of SOM.

References

1. Preston, C. M., M. Schnitzer, and J. A. Ripmeester, Soil. Sci. Soc. Am. J., 1989, 53,1442-1447.
2. Stevenson, F. J., ‘Humus Chemistry,’ Wiley, New York, 1994.
3. Preston, C. M. and R. H. Newman, Geoderma, 1995, 68, 229-241

 

Significance of burning vegetation in the formation of black humic acids in Japanese volcanic ash soils

Haruo Shindo1 and Hiromi Honma2

1 Faculty of Agriculture, Yamaguchi University, Yamaguchi, Japan
2 Forensic Science Laboratory, Yamaguchi Prefectural Police Headquarters, Yamaguchi, Japan

Volcanic ash soils, which are characterized by the accumulation of large amounts of black humus, are widely distributed in Japan and the black color is due to the presence of Type A humic acids with a high degree of darkening.1 Several hypotheses referred to as lignin, polyphenol and sugar-amine condensation theories have been proposed for the mechanisms of formation of humic substances.2 On the other hand, in the case of Japanese volcanic ash soils it has been assumed that grassland plants are the major source responsible for the abundance of humus and that burning is necessary to maintain a grassland for a long time, since forest is the climax vegetation under the meteorological conditions prevailing in Japan.3 Furthermore, burning vegetation not only has been often practised by man (including shifting cultivation) since ancient times, but also occurred by wild fires.4 The objective of the present study was, therefore, to evaluate the role of burning vegetation in the formation of black humic acids by investigating the distribution of charred plant fragments in volcanic ash soils in Japan and comparing the physicochemical and spectroscopic properties of the humic acids obtained from charred plant residues after the prescribed burning of a grassland and from volcanic ash soils. We report here that charred plant fragments commonly are distributed in Japanese volcanic ash soils containing Type A humic acids,1 the light fraction (less than s. g. 1.6 Mg m-3) of the soils mainly is composed of charred plant fragments and that the organic carbon content of the fraction is correlated (r=0.619) with that of the whole soil. Furthermore, the physicochemical and spectroscopic characteristics (degree of darkening, elementary composition, UV, Visible, and IR spectra, 13C-NMR, and x-ray diffraction pattern) of the humic acids isolated from the charred plant residues, which were collected after prescribed burning of a grassland and then oxidatively degraded with dil. HNO3, were similar to those of humic acids in volcanic ash soils. The findings indicate that burning vegetation merits close attention as one of the mechanisms for the formation of black humic acids in Japanese volcanic ash soils.

References

1. Arai, S., T. Honna and Y. Oba, In ‘Humus Characteristics in Ando Soils in Japan’ Wada, K., Ed., Kyushu University Press, Fukuoka, 1986, p. 57-68.
2. Stevenson, F. J., ‘Humus Chemistry,’ Wiley, New York, 1982, p. 443.
3. Ministry of Agriculture and Forestry, Japanese Government, Volcanic Ash Soils in Japan, Sakurai-Koseido, Tokyo, 1964, p. 211.
4.Pyne, J. S., P. L. Andrews and R. D. Laven, ‘Introduction to Wildland Fire,’ 2nd Ed., Wiley, New York, 1996, p. 769.

 

The long-term effect of a mono-culture (hops) on the relatively available humus fractions

Ádám Zsolnay

Institut für Bodenökologie, GSF, D-85764 Neuherberg, Germany

In 1958, an agricultural field was sub-divided and a portion of it was dedicated to hops cultivation. In 1988, hop cultivation ceased and the entire field was again cultivated as a unit with rotational cultivation. Superficially, the two sections can no longer be differentiated. The goal of this research was to determine if an agricultural practice can have long term effects on the relatively available humus (water extractable organic matter, WEOM and the so called fulvic acids, FA). A detailed explanation of the parameters used in this study is given in ref 1. The dimensionless humification index, the ratio of the fluorescence emission in the red region of the spectrum divided by that in the blue region, is an indicator of fluorophore complexity.1

Table 1

Absorptivity

Relative Fluorescence

Humification Index, HIX

(L mg-1 m-1)

(AU L mg-1)

WEOM

1.64

351

5.65

FA

1.15

1 102

32.16

Figure 1. The percent change in parameter values between the control and the ex-hop field areas. The open bars are the data of the WEOM, the solid bars of the FA.

Figure 2. The distribution of total copper across the investigated field. The positive distances are into the ex-hop field area.

The results show that 1) the WEOM differed drastically from the FA (Table 1). WEOM contained far fewer fluorophores per carbon atom and contained molecules that have a simpler structure than those of the FA. This confirms that WEOM is not dominated by FA and that FAs are not the truly mobile fraction of the soil’s humus; 2) the effects of hop cultivation are still strongly evident after 10 yr. of non-hop cultivation. Interestingly, the effects differ between the WEOM and the FA (Figure 1); 3) the ex-hop field is relatively heavily impacted with copper (Figure 2), but separate studies with freshly added CuSO4 could not explain the effects shown in Figure 1.

References

1. Zsolnay, A., E. Baigar, M. Jimenez, B. Steinweg and F. Saccomandi, Chemosphere, 1999, 38, 45-50.

 

HUMIC ACIDS and HUMATES BASED PRODUCTS FROM "CAPUCCINES"–RICH SOURCEs OF HUMIC ACIDS from WESTERN BOHEMIA

S. Mikeska,1 J. Honzák,1 M. Krajča,1 S. Siňár1 and J. Havel2

1 CHEMAPEX s r.o., 430 03 Chomutov, Czech Republic
2
Department of Analytical Chemistry, Faculty of Science, Masaryk University, 611 37 Brno, Czech Republic

Brown coal is mined in the Czech Republic (western Bohemia region) on a large industrial scale. Some millions of years ago a considerable part of the coal was transformed by air-oxidation to so called "oxihumolites" or "cappuccines" that are rich (~ 70-80 %) in humic acids and represent an equivalent to American Leonardite. This oxihumolite rich in humics raw material is used by Chemapex Co. for industrial production of a series of products like humic acid, humates (Na, K, Fe, Ca, etc.), sorbents, water or soil remediators, fertilizers, and so on. Recently, a so called "CHEMAPEX Standard" of the coal-derived humic acid was introduced and characterized in detail.1 All products were analyzed, characterized and their use in agriculture, for soil remediation, water purification, waste water treatment, ceramics manufacturing, the paper industry and the military will be reviewed.

References

1. Pokorná, L., D. Gajdošová, S. Mikeska and J. Havel, In ‘Humic Substances: Versatile Components of Plants, Soils and Water’, Ghabbour, E. A. and G. Davies, Eds., Royal Society of Chemistry, Cambridge, 2000.
2. www.chemapex.cz.

 

LEONARDITE AND HUMIFIED ORGANIC MATTER

D. M. Ozdoba,1 J. C. Blyth,1 R. F. Engler,1 H. Dinel2 and M. Schnitzer2

1 Luscar Ltd., Edmonton, Alberta, Canada
2 Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Ottawa, ON, Canada K1A 0C6.

Humified organic matter has been studied for many years and has been used in numerous applications around the world. Depending on the rank of coal deposit, the humified organic matter has been referred to as lignite, leonardite or humolite. Several of these ore deposits exist throughout North America with many similar, but somewhat different physical, chemical and biological characteristics due to geological factors. Opportunities exist to utilize high quality humified organic matter products that are rich in humic and fulvic acids for improving agronomic production and reclamation practices. The geological and geographic distribution of a number of organic ores in different regions of North America will be discussed.

 

SOME CHEMICAL AND SPECTROSCOPIC CHARACTERISTICS OF SIX ORGANIC ORES

M. Schnitzer,1 H. Dinel,1 T. Paré,1 H. -R. Schulten2 and D. Ozdoba3

1 Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Ottawa, Ontario K1A 0C6, Canada
2 University of Rostock, Rostock, Germany
3 Luscar Ltd, Edmonton, Alberta

Six organic ore samples from different locations in North America (North Dakota, Utah, Wyoming, New Mexico, and Alberta) were characterized by chemical, spectrophotometric, and spectroscopic methods. Except for one sample, which contained close to 85 % ash, elemental analyses of the five remaining samples averaged 63.67 + 1.23% C, 3.97 + 0.09% H, 1.32 + 0.13% N, 1.52 + 1.23% S and 29.49 + 1.58% O. Atomic H/C ratios ranged from 0.73 to 0.78, and atomic O/C ratios from 0.31 to 0.37. Carboxyl groups in the ores varied from 1.9 to 3.6 mmol g-1, and phenolic OH groups from 5.8 to 7.5 mmol g-1. Major peaks in FTIR spectra occurred near 1600 cm-1 (COO-) and shoulders at 1720 cm-1 (COOH). 13C NMR spectra of the ores showed two prominent resonances: (a) near 32 ppm, due to (CH2)n in long paraffinic chains, which appeared to be the dominant structures in these materials, and (b) at 130 ppm due to aromatic C not substituted by N or O. As estimated from the 13C NMR spectra, aromaticities of the ores ranged from 27.3 to 42.8 %. Curie-point Pyrolysis-Gas Chromatography/Mass spectrometry of the ores showed two dominant groups of components: aliphatics and aromatics. The major aliphatic components identified were C6 to C29 n-alkanes, C5 to C23 alkenes and a number of branched alkanes and alkenes. Major aromatic components identified were benzene, methyl-, dimethyl-, trimethyl- and ethyl-methyl-benzenes, styrene, benzofuran, methyl- and dimethyl-benzofurans, methyl-indene and coumaranone. Other aromatics identified were phenol, methyl- and dimethyl-phenols, naphthalene, methyl-, dimethyl- and trimethyl-naphthalenes and the S-compound thiophene. On the basis of the data obtained, the organic ores can be classified as lignites, which are organic materials in an early stage in the coalification process.

Reference

1. Kobe, W. R., H. H. Schobert, S. A. Benson and F. R. Karner, In ‘The Chemistry of Low Rank Coals’, H. H. Schobert, Ed., American Chemical Society, Washington, D.C., 1984, p. 39.

 

Principal-component analysis (PCA) as a tool for the analysis of complex pyrolysis-mass spectra from lignite-like ores

H. Dinel,1 M. Schnitzer,1 T. Paré,1 H. -R. Schulten,2 D. Ozdoba3 and T. Marche4

1 Eastern Cereals and Oilseed Research Centre, Ottawa, Ontario, Canada K1A 0C6
2 University of Rostock, Rostock, Germany
3 Luscar Ltd, Edmonton, Alberta, Canada
4 Department of Civil and Environmental Engineering, Carleton University, Ottawa, Ontario, Canada

Seven lignite-like ores and an Armadale humic acid were analysed by Pyrolysis-Field Ionization Mass Spectrometry (Py-FIMS) to yield the distribution of molecular fragments between m/z 20 to 900. The Py-FIMSc data were analyzed by PCA to differentiate the ores on the basis of their humification characteristics. The Py-FIMS data revealed that the ores and the humic acid contained relatively high concentrations of n-fatty acids (n-C16 to n-C33), unsaturated fatty acids (C16-C23), n-alkanes (n-C18 to n-C25), alkenes (C18-C25), lignin dimers, alkyl aromatics and n-alkyl diesters. Two-step PCA analysis showed that two mass regions between m/z 290 to 359 and m/z 600 and 619 explained 98.1 % of the total variation and allowed discrimination of the ores on the basis of Py-FIMS analysis. The ranking of the ores derived from the Py-FIMs spectra and PCA is in good agreement with spectroscopic and chemical characterizations by 13C NMR, FTIR and chemical methods. The analysis and interpretation of the very complex Py-FIM spectra of lignite-like ores to assess potential uses of the ores as sources of chemicals can be simplified by using the two mentioned mass regions and PCA.

References

1. Schnitzer, M., H. Dinel, T. Paré, H. -R. Schulten and D. Ozdoba, Some chemical and spectroscopic characteristics of six organic ores. In this volume, 2001.
2. Dinel, H., C. M. Monreal and M. Schnitzer, Geoderma, 1998, 86:279-293

 

EFFECTS OF HUMIC ACIDS AND NITROGEN MINERALIZATION ON CROP PRODUCTION IN FIELD TRIALS

Mir-M. Seyedbagheri and James M. Torell

University of Idaho, Moscow, ID 83647

Growers have both realistic and unrealistic expectations with regard to humic acid based products. The objectives of this study were (a) to use different application rates of humates and evaluate the impacts on potato yield and quality; and (b) to evaluate nitrogen mineralization rates from soil organic matter in sugar beet and potato fields. Replicated potato field trials were conducted from 1994 to 2000 in conjunction with cooperating farmers, using their normal cultural practices and adequate mineral nutrition. Field bag tests and laboratory incubation studies were conducted to evaluate the amount of mineralized nitrogen from soil organic matter in the sugar beet and potato fields. The humic acid data indicate that, at the rate recommended by most commercial suppliers, yield responses are minimal and inconsistent. On the other hand, for a few high quality commercial products, yield increased with increased application rate up to a maximum yield increase of about 14 percent, corresponding to an application rate of about 75 liters/hectare. At the highest rates, yield decreased. Humic acid applications greatly increased root growth (root length and number of secondary roots) and moderately increased shoot growth. Using water mark sensors, we measured a greater water holding capacity in the soils to which humic acid had been applied than in the controls. Nitrogen mineralization from organic matter in 20 fields varied from 39.2 to 224 kilograms/hectare. This plays a pronounced role in crop nitrogen management and its environmental ramifications.

References

1. Chen, Y. and T. Aviad, In ‘Humic Substances in Soil and Crop Sciences: Selected Readings’, MacCarthy, P., C. E. Clapp, R. L. Malcolm and P. R. Bloom, Eds., Soil Science Society of America, Madison, WI, 1990, p. 161-186.
2. Seyedbagheri, Mir-M., In ‘Eleventh Annual Nonpoint Source Water Quality Monitoring Results Abstracts,’ Idaho Department of Environmental Quality, Boise, ID, 2001, p. 16.
3. Sklodowski, P. and A. Maciejewska, In ‘Humic Substances and Organic Matter in Soil and Water Environments’, Clapp, C. E., M. H. B. Hayes, N. Senesi and S. M. Griffith, Eds., Proc. 7th Int. Conf. IHSS, Univ. of Minnesota, St. Paul, 1996, pp. 113-118.

 

ANTICLASTOGENIC ACTIVITY OF humic substances IN plantS

Giuseppe Ferrara, Elisabetta Loffredo and Nicola Senesi

Dipartimento di Biologia e Chimica Agroforestale ed Ambientale, Universitŕ di Bari, 70126 Bari, Italy

The possible genetic action of humic substances (HSs) on living organisms scarcely has been investigated. Although a mutagenic action of HSs is referred to in the literature, few data are available on the possible antimutagenic activity of HSs, including their potential to inhibit clastogenic events in plant organisms. Clastogenic events consist of structural damages, such as breakage of chromosomes and formation of micronuclei, which may be produced by various agents. Anticlastogenic agents are able to suppress or limit these events by acting either inside or outside the cell depending on their properties and characteristics. In this study, two different soil humic acids (HAs), a leonardite HA, a peat HA, an aquatic HA, a soil fulvic acid (FA) and two aquatic FAs from the Standard and Reference Collection of HAs and FAs of the International Humic Substances Society (IHSS) were tested at concentrations ranging from 20 to 500 mg L-1, either alone or in the presence of 10 mg L-1 of the known mutagen maleic hydrazide (MH), on germinated seeds of the plants Vicia faba, Pisum sativum and Allium cepa. All experiments were conducted in triplicate. Root tips were collected after seed germination and prepared for observation in the microscope. Fifteen root tips (5 x 3 replicates) and 30,000 cells (2,000 cells per root tip) were observed for each treatment. The evaluation of clastogenic activity was achieved by considering the frequency of two genetic aberrations, i.e., the micronuclei (MN) and the aberrant anatelophases (AAT) in root tip cells. Regular anatelophases (RAT) were also counted as an index of cell division. Data obtained were analyzed statistically by one-way analysis of variance (ANOVA), and the mean values were separated by using the least significance difference test (LSD). The two genetic aberrations MN and AAT were detected in all treatments including the control (H2O). For all species the frequencies of the two anomalies were very low in the control treatment and the presence of any HS at any concentration did not cause a variation of these frequencies statistically different from the control. As expected, the treatment with MH produced high frequencies of both cytogenetic anomalies. A marked anticlastogenic activity was measured when any HS was used in combination with MH, which was statistically significant (99% and 95%) in almost all treatments. Leonardite and peat HAs appeared to exert the most intense anticlastogenic activity in V. faba, with a reduction of about 65% of both MN and AAT in the case of leonardite HA, and of 56% MN and 66% AAT in the case of peat HA. No difference of anticlastogenic behavior was generally observed between HAs and FAs of the same origin. However, the genetic action of FAs appeared more effective at higher doses, whereas for HAs the effect of concentration did not show any clear trend, and varied with the different plant species examined. Although every plant used has shown to be appropriate as a test species for the evaluation of anticlastogenic effects of HS, the highest decrease of MN and AAT frequencies by MH were observed in V. faba experiments.

 

RESPONSE OF ALFALFA TO CALCIUM LIGNITE FERTILIZER

T. Paré,1 M. Saharinen,1 M. J. Tudoret,1 H. Dinel,1 M. Schnitzer1 and D. Ozdoba2

1 Eastern Cereal and Oilseeds Research Centre, Ottawa, Ontario K1A 0C6, Canada
2 Luscar Ltd, Edmonton, Alberta, Canada

A greenhouse experiment was conducted to evaluate the agronomic potential of first generation of Ca fertilizer derived from chemical modifications of a lignite ore and to develop appropriate agronomic practices. Alfalfa (Medicago sativa L., cv. Nitro) was grown and fertilized by spraying or by substrate application with four rates of Ca in lignite, in chemical (CaCl2) or as a chelated form (EDTA-Ca). After twelve weeks of growth, plants were harvested and roots and shoots were separately collected. Applied by spraying or on substrate, Ca lignite and CaCl2 produced similar dry masses of roots, shoots and total plants and there was no significant differences between Ca levels applied. Applied as a spray or on substrate, EDTA-Ca decreased root, shoot and total plant dry masses proportionally to Ca levels applied. Ca lignite produced 117 to 502% more root masses and 58 to 77% more shoot masses than did EDTA-Ca when sprayed. When applied on substrate, Ca lignite produced 80 to 592% more root masses and 45.8 to 82% more shoot masses than did EDTA-Ca. Calcium and other nutrients concentrations and uptake will be discussed. Preliminary data indicate that Ca lignite fertilizer did as well as CaCl2 as a source of Ca for plants, but much better than the commercially available chelated form of Ca (EDTA-Ca).

References

1. Schnitzer, M., H. Dinel, T. Paré, H. -R. Schulten and D. Ozdoba, Some chemical and spectroscopic characteristics of six organic ores. In this volume, 2001.
2. Dinel, H., M. Schnitzer, T. Paré, H. -R. Schulten, D. Ozdoba and T. Marche, Principal-component analysis (PCA) as a tool to analyse complex pyrolysis-mass spectra from lignite-like ores. In this volume, 2001.