The proceedings of Humic Substances Seminar III were published in the volume Understanding Humic Substances: Advanced Methods, Properties and Applications, E. A. Ghabbour and G. Davies (eds.), (ISBN 0-85404-799-9) by the Royal Society of Chemistry in November, 1999. Arrangements have been made for the proceedings of Seminar IV to be published by RSC in 2000.

Humic substances are ubiquitous and fascinating, and their study is important and multidisciplinary. The community of scholars seems to enjoy meeting on a regular basis at a convenient location to share the latest information on humic substances structures, properties and uses. The Seminars serve many useful functions, as indicated by the strong support for their continuation.

The Humic Substances Seminars encourage molecular descriptions of humic substances and practical applications of their remarkable properties. The Seminars now have a life of their own. Talented individuals determined to understand HSs come from all over the world to share information and advance the field. Young scientists learn from the masters, and the masters can catch up with the youngsters as they make their best contributions.

The desire to tackle HSs complexity seems to be increasing. A hint that HSs may be tractable is on the wind. Realization that the HSs mystery is too difficult for any individual or single research group to solve is driving collaboration and co-operation. Solving the HSs mystery is very important. Hopefully, the chronic lack of funding for fundamental work on HSs soon will come to an end, perhaps due in part to the quality and impact of these Seminars.

Humic Substances Seminar IV has many distinguished participants. We especially recognize Dr. Morris Schnitzer who (with Dr. Frank Stevenson, to whom Seminar IV is dedicated) was awarded the Wolf Prize for Agriculture by the State of Israel in 1996. 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 II in 1998.

Much of the progress in HSs research is due to the work of the International Humic Substances Society, which today is represented by its Immediate Past President (Dr. James Alberts, University of Georgia), President-Elect (Dr. Yona Chen, Hebrew University of Jerusalem), two Past Presidents (Dr. Michael Hayes, University of Limerick, and Dr. Nicola Senesi, University of Bari), a newly elected IHSS Board Member at Large (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).

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 production and environmental applications.

The program for Humic Substances Seminar IV follows the traditional sequence: Formation, Characterization, Separation, Solute Sorption, Metal Binding and HSs Applications. There are over 100 authors from 19 countries, which both are Seminar records. We have worked to achieve a seamless transition from one major area to another. We have interpolated two topics of very high current interest in the program: HSs aggregation and redox chemistry, as presented by leaders of these respective fields. And 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 IV program (from now to be totally oral). We thank all authors who contacted us, and had a difficult task in selecting the best papers for a balanced program.

As before, timely manuscripts based on new work presented at Humic Substances IV and received in Boston by May 31, 2000 will be promptly reviewed, considered for publication, edited and published by the Royal Society of Chemistry as the volume ‘Humic Substances: Versatile Components of Plants, Soil and Water'. The resulting volume will contain fine current work that relates humic substance structures to their properties and applications.

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

R. L. Wershaw

U.S. Geological Survey, Federal Center, Denver, Colorado 80225

No consistent paradigm exists for the study of non-living natural organic matter in soils and natural waters. This problem arises from the fact that different workers use different terminology to refer to the same group of compounds or the same terminology to refer to different suites of compounds. The inconsistency in terminology is illustrated by the usage of the term humic substance. Many workers are of the opinion that this term should be limited to compounds formed by secondary synthesis reactions. Other workers, however, have proposed that humic substances consist mainly of the partial degradation products of plant polymers. To compound the problem, it is often not clear which one of these two contradictory definitions is being used by a given author. I propose that a more fruitful approach is to study the degradation reactions that the chemical components of plant tissue undergo from senescence to natural organic matter. That is to say, to concern oneself with the humification process rather than with ill-defined intermediates in the continuum from well-characterized plant components to carbon dioxide.

The Structure of Humic Substances – Limits and Potential

Wolfgang Ziechmann¹ and Matthias Hüebner²

¹Kiefernweg 2, 37085 Göttingen, Germany
²Risø Forskningscenter, Afdeling Biogeokemi, DK-4000 Roskilde, Denmark

Humic substances (HSs) generally are considered to be a completely heterogeneous mixture of compounds lacking a defined common structure. However, they appear to exhibit recurring structural patterns and can be classified according to parameters resulting from their genesis. Knowledge about HSs genesis is comparatively poor. The formation of HS-like compounds arising from ubiquitous processes like baking bread, roasting coffee or brewing beer is at least basically understood. Yet, the proceedings in nature are appearently much more complex. Biosynthesis of organic material in living systems usually is subject to enzyme and compartment control. These conditions are hardly involved in the formation of natural HSs. In the past, attempts have been undertaken to simulate natural HSs formation in restricted systems. These experiments have largely contributed to what we know about HS genesis today. Among the first was Miller's experiment (1955) on chemical evolution, which has (besides the building blocks for life) produced HSs. In this paper, results from research on HSs genesis and characterization will be correlated with prospective applications.

M. Schnitzer,¹ H. Dinel, H -R. Schulten,² T. Paré and S. Lafond¹

¹ECORC, Agriculture and Agri-Food Canada, Ottawa, Ontario K1A 0C6, Canada
²University of Rostock, Rostock, Germany

Intensive poultry farming is a major, growing industry in Canada and world-wide. Composting, a widely used method for the recycling of manures and organic wastes, curtails environmental pollution and soil degradation, reduces landfilling and limits greenhouse gas emissions. During composting, carbonaceous and nitrogenous compounds are transformed through the activities of successive microbial populations into more stable organic structures that chemically and biologically resemble humic substances. We composted wood shavings, used as bedding materials for duck excreta, in an enclosed hall system for 29 days under controlled conditions of moisture and air-flow, and frequent mechanical mixing. Chemical changes occurring during composting were followed by chemical, ¹³C NMR and mass spectrometric methods. Holocellulose followed by lipids and lignins were the major components of the compost on day 0. After 29 days, the resulting compost consisted of holocelluloses, lignins, phenolic esters, and lipids, with sterols being prominent among the latter. By that time, the compost had lost 45.5% of its initial dry, ash-free weight. With increasing composting time, both Total Ion Intensity (TII) and Volatile Matter (VM) decreased while the C content changed relatively little. We interpret these findings as indicating greater molecular cross-linking and more inter- and intra-molecular associations in the composted organic matter.

References
1. Paré, T., H. Dinel and M.Schnitzer, Biol. Fert. Soils, 1999, 29, 31.
2. Schnitzer M. and H. -R. Schulten, Adv. Agron., 1995, 55, 167.

Solid-state ¹³C-NMR studies of composting of agricultural, industrial and municipal solid waste

Yona Chen, Benny Chefetz and Elad Amichai

The Hebrew University of Jerusalem, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, POB 12, Rehovot 76100, Israel

Composting is a controlled bio-oxidative process in which a heterogeneous solid organic substrate decomposes partially through a thermophilic phase leading to evolution of CO₂, H₂O, minerals and stabilized organic matter (OM). The stabilized and sanitized product of composting seems to be beneficial to plant growth and the term compost usually is used to describe this product. Compost maturity or stability reflects the degree of OM decomposition. Since natural OM stability is a relative term, defining it is not trivial. Definition requires a series of physical and chemical measurements. Among the methods applied, ¹³C-NMR and FTIR (or DRIFT) are especially helpful. This paper describes applications of these methods to composting research. Solid-state ¹³C-NMR spectroscopy is now the most helpful tool for examining the chemical structure of natural organic matter (NOM) and the chemical changes associated with OM decomposition. Changes can be measured on the bulk OM either fresh or composted, on humic substances (HSs) extracted from the compost or on dissolved organic matter (DOM). Changes measured on decomposing OM are less distinct in the following order of tested materials: DOM > Bulk OM > HSs > Core HSs. Humic acids (HAs) extracted from fresh and composted separated cattle manure (CSM) exhibited small changes during composting (increase in carboxyl and aromatic C and a decrease in alkyl C). During composting of municipal solid waste (MSW) aromatic C increased while aliphatic C decreased. Polysaccharides levels decreased with composting of MSW and other types of NOM. Carboxyl and carbonyl C increase with composting, thus reflecting the oxidation process. FTIR and DRIFT complement NMR measurements. Degradation of polysaccharides and an increase of carboxyl groups with composting has been reported, confirming the NMR observations. ¹³C-NMR analyses of unfractionated DOM extracted from composting MSW exhibit an increasing level of aromatic structures with composting time. The ¹³C-NMR spectra of the HoA fraction suggested a polyphenol-humic structure, whereas the HoN spectra exhibited strong aliphatic features. The spectra of the HiN fraction confirmed its polysaccharide nature and the hydrophilic bases fraction (NiB) contained mainly proteins and carbohydrate-amino complexes. ¹³C-NMR spectra of HoA and a soil fulvic acid (FA) were similar. The steady DOM concentration and the relative decrease of HiN as the HoA and HoN fractions increased indicates that DOM at the final stages of composting contained less bioavailable OM and more macromolecules related to HSs. The constant level of DOM observed during the curing and maturation stages represents a steady-state situation during which the chemical composition is continually changing. The differences in chemical structure of the HAs extracted from decomposing NOM led to a study that compared the HAs to "core-HA", which is an acid washed HA (the acid eliminates most of the polysaccharides). This ¹³C-NMR study showed that the structure of the core-HA did not change during the process (as opposed to non-treated HA). In summary, compost HSs that are "young" relative to soil HSs differ mostly in their high levels of aliphatic and polysaccharide components, which tend to decompose during composting. ¹³C-NMR is the most effective approach to structural studies of NOM.

Catalytic Effects of Hydroxy-Aluminum and Silicic Acid on Catechol Humification

C. Liu and P. M. Huang

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

Oxidative polymerization of phenols is an important pathway in the formation of humic substances.¹ Manganese(IV) and iron(III) oxides catalyze the polymerization of phenolic compounds, resulting in the formation of humic substances, since they can act as electron acceptors.^2,3 Although aluminum and silicon each have just one oxidation state, they are among the most abundant elements in the earth crust. Further, Al and Si are always present as impurities in the humic acids and fulvic acids extracted from soils. McBride et al. found that both soluble Al and colloidal Al hydroxide can increase the rate of oxidation of catechol by O₂, favoring the formation of highly colored solution products in the pH range 5 to 7.⁴ However, the precipitation of humification products catalyzed by hydroxy-Al was not observed. In the present study, the effects of aqueous hydroxy-Al ions and silicic acid at 10^-3 M on catechol humification for reaction periods ranging from 10 to 60 days under acidic conditions were investigated. The reaction products were compared with the International Humic Substances Society standard humic acid. The results show that hydroxy-Al ions greatly promoted the polymerization of catechol as indicated by the darkening of the supernatant and the formation of black precipitates, whereas the presence of silicic acid only slightly enhanced the darkening of the catechol solution compared with the pure catechol solution and no precipitates were formed. The nature of the solid phase reaction products formed in the hydroxy-Al-catechol system before and after purification was studied by atomic force microscopy (AFM) under ambient conditions (23.5 ± 0.5 °C), infrared absorption spectrometry (IR), X-ray diffractometry at a slow scanning speed, ¹³C CPMAS NMR and elemental analysis. The solution products in both systems were also investigated by UV-visible absorption spectrophotometry, AFM, IR and ¹³C NMR.

References
1. Stevenson, F. J., "Humus Chemistry. Genesis, Composition, Reactions", 2nd. ed., Wiley, New York, 1994.
2. Shindo, H. and P. M. Huang, Soil Sci. Soc. Am. J., 1984, 48, 927.
3. Huang, P. M., Abiotic catalysis. In: "Handbook of Soil Science", Sumner, M. E., Ed., CRC Press, Boca Raton, FL., 2000, p. B303.
4. McBride, M. B., F. J. Sikora and L. G. Wesselink, Soil Sci. Soc. Am. J., 1988, 52, 985.

Fast quantification and characterization of humic substances in sediment samples by DRIFT spectroscopy

L. Tremblay and J. -P. Gagné

Institut des sciences de la mer de Rimouski (ISMER), Université du Québec à Rimouski, Rimouski, Québec G5L-3A1, Canada

In order to understand the biogeochemistry of organic matter (OM), it is essential to know its diagenetic status. Characterization studies of marine sedimentary OM show that between 62 and 80% of this fraction cannot be characterized in terms of its chemical structure.^1,2 In spite of this lack of precision, it is known that humic substances (HSs) usually represent the main component of sedimentary organic material. However, the chemical composition and geochemical cycling of HSs remain ill-defined. The classical quantification of HSs in all natural environments and the majority of analytical techniques used for their study require the extraction of these compounds. The fractionation schemes have the disadvantages of requiring numerous time-consuming steps that can alter OM to a greater or lesser extent. The objective of this research was to develop a simple method using diffuse reflectance coupled with infrared Fourier transform spectroscopy (DRIFTS) for the quantification (fast screening) and the characterization of sedimentary OM and HSs in intact, dry samples. This technique is fast (5-20 mins/sample), simple to use, inexpensive, non-destructive, requires only few milligrams of solid, allows the analysis of opaque samples (soil, peat, etc.) and does not have the drawbacks encountered with the common KBr pellet method.^3,4 In this research, the influence of several parameters on the spectroscopic signal was studied. The number of scans, the resolution, the collected energy, the humidity, the mineral matrix and the size of the particles were all evaluated to optimize and normalize the method. To ensure reproducible quantitative analysis, it is especially important to control the particle size and the homogeneity of the powder mixtures through precise grinding and mixing procedures. The best calibration is obtained by using humic material representative of the studied area. Under optimized conditions, the quantification of HSs is possible with DRIFTS at a frequency of 2930 cm^-1 using whole dry sediment samples. The developed method accurately predicts the classical HSs content results obtained by extraction, but in a fraction of the time. Moreover, the distribution of total OM and of the three specific fractions of HSs can also be obtained. The potential of DRIFTS analysis for the discrimination of samples from different origins in a sediment core and for the determination of OM functional groups (including aliphaticity-aromaticity) is also evaluated. Fast screening of OM fractions in their natural matrix by DRIFTS provides quantitative and qualitative information that can be used in geochemical studies.

References
1. Wakeham, S. G. et al., Geochim. Cosmochim. Acta, 1997, 61, 5363.
2. Colombo, J. C., N. Silverberg, J. N. Gearing, Mar. Chem., 1996, 51, 295.
3. Griffiths, P. R. and M. P. Fuller, In: "Advances in Infrared and Raman Spectroscopy", Clark R. J. H. and R. E. Hester, Eds.; Heyden and Son: London, 1982, p. 63.
4. Swift, R. S., In: "Methods of Soil Analysis", SSSA Book Series #5, Madison, WI, 1996, 1011.

SPECTROSCOPIC CHARACTERISTICS OF HUMIC SUBSTANCES UNDER DIFFERENT COVER CROP SYSTEMS

Guangwei Ding,¹ Stephen Herbert,¹ Dula Amarasiriwardena,² Jeffrey Novak³ and Baoshan Xing¹

¹Department of Plant and Soil Sciences, University of Massachusetts, Amherst, MA 01003
²School of Natural Science, Hampshire College, Amherst, MA 01002
³USDA-ARS-Coastal Plains Soil, Water and Plant Research Center, Florence, SC 29501

Characterization of humic substances (HSs) is important for determining the overall quality of soils.^1,2 The purpose of this study was to examine the effect of cover crops on soil humic substances. We isolated humic substances from soils with following treatments: a) Vetch/Rye, b) Rye alone, and c) Check (no cover crops) with various nitrogen fertilizer rates. The results from Cross-Polarization and TOtal Sideband Suppression (CP-TOSS) ¹³C NMR indicate that humic acids (HAs) from Rye alone become more aromatic and less aliphatic than with the other two crop treatments, which also is confirmed by the high phenolic-C content (145-162 ppm) of the HAs extracted from the Rye system. The HAs from the Rye system are also relatively enriched in aromatic-C (110-145 ppm). Based on the diffuse reflectance Fourier transform infrared (DRIFT) spectra peak O/R ratios,³ the intensity of oxygen-containing functional groups to aliphatic and aromatic (referred to as recalcitrant) groups, the HAs from the Vetch/Rye system with nitrogen fertilizer have the highest ratio. The lowest ratio appears in the Vetch/Rye system without fertilizer treatment. The relatively high O/R ratios of HAs support the notion that soil organic matter in Vetch/Rye-fertilizer treatments is more biologically active. The O/R ratio of fulvic acids (FAs) is greater in the Vetch/Rye system without fertilizer than with fertilizer treatment, and the ratios from the Vetch/Rye treatments with or without fertilizer are higher than Rye treatments. These spectroscopic data show that cover crop systems have a significant influence on soil humic substance characteristics.

K. A. Thorn

U.S. Geological Survey, Denver Federal Center, Denver, CO 80225

Contamination of soils with 2,4,6-trinitrotoluene (TNT) is a worldwide problem. Approximately 2000 sites need to be remediated in the United States alone. Among biological treatments under investigation, composting has received the most attention. During composting, TNT is reduced to the monoamines 2ADNT (2-amino-4,6-dinitrotoluene) and 4ADNT (4-amino-2,6-dinitro toluene), the diamines 2,4DANT (2,4-diamino-6-nitrotoluene) and 2,6DANT (2,6-diamino-4-nitrotoluene) and, under strictly anaerobic conditions (Eh < -200mV), the triamine TAT (2,4,6-triaminotoluene). Once formed, the amines form covalent bonds with organic matter of the soil and compost. The efficacy of composting as a remediation strategy is based on no significant re-release of the toxic amines from the treated soils over the long term from microbial or abiotic hydrolysis and other degradative reactions. Understanding how amines from TNT form covalent bonds with organic matter and the environmental stability of the bonds is desirable. In the first part of this study, the reduced TNT amines, labeled with ¹⁵N in the amine positions, were reacted with the IHSS soil humic acid (HA) and model lignin and quinone compounds, then analyzed by liquid and solid state ¹⁵N NMR. The labeled amino groups underwent nucleophilic addition reactions with quinone and other carbonyl groups in humic acid to form both heterocyclic and nonheterocyclic condensation products. The order of reactivity followed the relative nucleophilicity of the amines: monoamines<diamines<triamine. 1,2-addition with quinones in the humic acid to form imines distinguished the reactivity of TAT and the diamines from the monoamines. The phenol oxidase enzyme horseradish peroxidase increased the total incorporation of all the amines into the soil HA and, in the case of TAT and the diamines, shifted heterocyclic condensation product formation toward imine formation. In the second part of the study, TNT labeled with ¹⁵N in the nitro groups was added to a soil of low organic carbon content and subjected to 20 day composting. In general, based on comparison with the spectra of the soil humic acid reacted with the individual amines, the solid state ¹⁵N NMR spectra of the whole compost confirmed reduction to and subsequent binding by the amines. The compost spectra suggest that covalent binding by diamines is significant in the transformation of TNT into bound residues. Studies of the chemical lability of the covalent bonds formed and analytical challenges in applying NMR to understand reactions involved in the biotransformation of TNT into soil organic matter bound residues will also be discussed.

¹³C NMR is a non-destructive quantitative technique that defines the different types of carbon in humic substances. The problem with most humic materials is that they are not or only partly soluble. In this case high resolution NMR cannot be used. Solid state NMR is a good alternative to overcome this problem because the complete sample is measured. Cross Polarization Magic Angle Spinning NMR (CP-MAS) is used to enhance the signal of the low abundance ¹³C nuclei. This is only a semi-quantitative technique because of the nature of cross polarization. For this reason, quantification of carbon types based on a single CP-MAS NMR spectrum is impossible. A technique to overcome this is a variable contact time experiment. By measuring signal intensities at different contact times, the quantification error can be reduced. The results of VCT experiments give a correction for the integration of a spectrum. However, even samples from the same area and/or origin can give different results and therefore give rise to altered signal intensities. So the correction factors must be determined for every single sample. Other problems occurring during CP-MAS NMR measurements are the influence of the high spinning rate of the sample and the impact of the high power radio frequency fields. We think that rearrangement of the material in the spinner (higher density of the material) gives another environment for the nuclei that changes the signal intensities. The presentation will illustrate some of the factors mentioned above and discuss the results of a pilot study on the quantification of the NMR spectra of soil and peat samples.

INVESTIGATION OF HUMIC ACID STRUCTURES USING 2D SOLID STATE NMR

Jingdong Mao,¹ Klaus Schmidt-Rohr² and Baoshan Xing¹

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

The structures of humic acids (HAs) play important roles in their reactivity with organic and inorganic contaminants. Although many functional groups have been identified in HAs, it is still not clear how different carbon units are connected. In this study, two-dimensional ¹H-¹³C heteronuclear correlation solid-state NMR (HETCOR) experiments^1-3 were conducted to investigate the carbon environments of functional groups. Amherst HA was extracted from a peat soil using a standard IHSS procedure. By employing different contact times and insertion of dipolar dephasing (40 µs) in HETCOR, carboxylic carbons were found to be predominantly in aliphatic environments, but a large fraction was also bonded to aromatic rings. Methyl groups were observed to be connected to both aromatic and aliphatic structural units. Both protonated and unprotonated anomeric carbons were detected. Other carbon structures were also examined. The new structural information identified in this study provides some constraints for the existing models of HAs.

References
1. Bielecki, A., D. P. Burum and D. M. Rice, F. E. Karasz, Macromolecules, 1991, 24, 4820.
2. Bronnimann, C. E., C. F. Ridenour, D. R. Kinney and G. E. Maciel, J. Magn. Reson., 1992, 97, 522.
3. Wilson, M. A., J. V. Hann, K. B. Anderson and R. E. Botto, Org. Geochem., 1993, 20, 985.

ADVANCES IN PROCEDURES FOR THE ISOLATION AND FRACTIONATION OF HUMIC SUBSTANCES

Michael H. B. Hayes¹ and Colin L. Graham²

¹Chemical and Environmental Sciences, University of Limerick, Ireland
²School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, England

Classical procedures for humic substances (HSs) isolation from soils use basic solutions and solutions of metal complexing agents, especially sodium pyrophosphate. Hayes has discussed the principles involved.¹ Soil humic acids (HAs) are precipitated at pH 1 from solution in base, while fulvic acids (FAs) are considered to be soluble at all pH values. The adaptation of XAD resin technology to soil HSs has allowed removal of saccharide and peptide components from the FA fraction.¹ More recently, XAD-8 resin [(poly)methylmethacrylate] technology has allowed the separation of saccharides and peptides not covalently linked to HAs.³ HSs are gross mixtures of components at various stages of transformation from parent materials to 'matured' products. Such mixtures need extensive fractionation before meaningful structural studies can be carried out. Effective fractionation processes make use of charge density, molecular size and polarity differences. Appropriate use can be made of exhaustive sequential extraction processes, culminating in applications of dipolar aprotic solvents (containing acid). There are some fundamental differences in concepts of the sizes (and shapes) of humic molecules (Soil Science, Vol 164, No. 11, 1999). It is accepted that HSs are polydisperse with respect to size, but there is disagreement about the boundaries of the polydispersity. Our recent research has focused on the possible influences of relatively hydrophobic non-humic components (such as fatty acids and waxes) interacting with humic molecules and thereby giving rise to associations that behave as pseudo high molecular weight (HMW) molecules. We have found that during filtration, non-polar components adhere to uncharged (0.2 μm) filtration membranes, and other hydrophobic components are not removed during back elutions of the HSs from XAD-8 resins. Preparative HPLC using eluent amendments to counter associations through hydrogen bonding and hydrophobic associations can decrease the MW polydispersity. There can be decreased charge polydispersity with gradient or stepwise (with respect to pH) back elution from XAD resins and fractionations based on charge density differences utilising various forms of electrophoresis. Our results show that different isolation and fractionation procedures can provide humic fractions that give meaningful compositional and structural data. With 2-D solution state NMR, we and our colleagues have resolved some of the fundamental HSs connectivities. There will be little point in attempting to obtain a detailed resolution of HSs structures, but it should be possible to get information about the components and connectivities of humic structures.

References
1. Hayes, M. H. B., In: "Humic Substances in Soil, Sediment, and Water", Aiken, G. R. et al., Eds., Wiley, New York, 1985, p. 329.
2. Aiken, G. R., In: "Humic Substances in Soil, Sediment, and Water", Aiken, G. R. et al., Eds., Wiley, New York, 1985, p. 363.
3. Hayes, M. H. B., In: "Humic Substances, Peats and Sludges: Health and Environmental Aspects", Hayes, M. H. B. and W. S. Wilson, Eds., Royal Society of Chemistry, Cambridge, 1997, p. 3.

MOLECULAR SIZE OF HUMIC SUBSTANCES. SUPRAMOLECULAR ASSOCIATIONS VERSUS MACROMOLECULAR POLYMERS

Alessandro Piccolo

Dipartimento di Scienze Chimico-Agrarie, Università di Napoli "Federico II", 80055 Portici, Italy

Recent experiments by size exclusion chromatography have cast considerable doubt on the traditional view that humic substances (HSs) from soils and other sources have a polymeric nature. The new conclusion is that the polydispersity of HSs is not due to random variations in high molecular weight values during an enzyme-assisted covalent polymerization of small molecules, but rather to the self-assembly of heterogeneous molecules into supramolecular structures held together by weak forces in only apparent high molecular dimensions. Results of High Performance Size Exclusion Chromatography (HPSEC) work have shown that dramatic changes in peak absorbances and elution volumes in humic chromatograms upon simple addition of small amounts of organic acids could have occurred only if HSs are supramolecular rather than polymeric. Moreover, isolation of humic fractions by preparative HPSEC either before or after addition of acetic acid and subsequent characterization of fractions by ¹H-NMR spectroscopy showed that, contrary to literature reports, the molecular composition of humic fractions of different molecular size was very different and the complexity of the spectra was significantly reduced after acetic acid treatment. This was attributed to the amphiphilic properties of acetic acid that, by disrupting the dispersive forces holding together humic superstructures, allowed a larger spread of humic sizes over the column matrix. Interactions of HSs with ¹³C-labelled 2-decanol before HPSEC separation indicated that the labelled alcohol became part of the humic supramolecular association and was distributed over the different humic size-fractions according to its chemical affinity for humic components. Humic supramolecular associations appear to be temporarily stabilized in aqueous solutions by weak interactions such as hydrogen bonds and dispersive forces (van der Waals, -, CH- bonds) depending on the solution pH and hydrophobic humic components, respectively. It is conceivable that the most polar components form associations that are sufficiently hydrated to remain stable and soluble in acidic aqueous solutions. These would represent the small-size fractions of the humic polydisperse system and well describe the fulvic acid components. Conversely, less polar components reduce the free energy of solvation by withdrawing from water and self-assembling into supramolecular associations of larger dimensions that are stabilized by relatively strong hydrophobic forces. These less hydrated fractions easily flocculate at low pH values. This type of high-molecular size association describes the humic acid fraction of HSs very well.

BACK TO THE FUTURE: critical analysis and PERSPECTIVES OF ELECTROPHORETIC TECHNIQUES APPLIED TO HUMIC SUBSTANCES at the beginning of the new millenium

M. De Nobili,¹ J. Niraneza,¹ E. A. Ghabbour² and G. Davies²

¹Dipartimento Produzione Vegetale e Tecnologie Agrarie, Università di Udine, via delle Scienze 208,33100 Udine, Italy.
²Northeastern University, Chemistry Department and the Barnett Institute, Boston, MA 02115

Electrophoretic techniques have been only sparingly applied to the study of humic substances (HSs). One of the reasons for this derives from the fact that, in most cases, HSs normally give either too much or too little separation, both of which are difficult to deal with. Traditional or capillary electrofocusing and isotachophoresis generate fingerprint patterns that would need long and careful experimental work for their interpretation. After the first enthusiasms caused by the visibly high resolution obtained, the results are often rejected as artefactual. This is actually true in most cases, but whenever reproducibility is satisfied this attitude leads to distrust of techniques that if interpreted correctly could bring a great amount of useful information. On the other hand, techniques based on sieving properties of chemical or physical gels do not allow the separation of more than a single broad band unless some spacing due to the presence of co-migrating substances or interactions with the gel matrix occurs. A broad, possibly symmetrical band is what one should expect from a complex mixture of randomly generated aliphatic-aromatic macromolecules with an undefined number of components, but many efforts are wasted looking for an improbable separation into bands. In spite of the apparent lack of separation, during gel electrophoresis HSs are actually fractionated on the bases of molecular size differences and many things can be learned from the study of their electrophoretic behaviour. Capillary electrophoresis of HSs in physical gels is a promising technique, but an insight into the mechanism of separation reveals its limits and shows that the radius of the gel-forming polymer actually limits the separation efficiency. The molecular weight distributions of HSs determined by capillary electrophoresis can be affected by differences in ionic strength between sample and buffer. As for other techniques of widespread use in biochemistry, the straightforward application to HSs of methods developed for proteins can lead to erroneous results. Notwithstanding, electrophoretic techniques and in particular the new capillary electrophoresis applications are certainly worth much more attention than they were given in the past.

CHARACTERIZATION OF FLUORESCENT FRACTIONS OF SOIL HUMIC ACIDS

M. Aoyama¹, A. Watanabe² and S. Nagao³

¹Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, 036-8561 Japan
²Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan
³Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki, 319-1195 Japan

Our previous study¹ showed that the major part of the fluorescent substances in soil humic acids (HAs) was different from the humic substances themselves. Furthermore, we succeeded in separating the fluorescent substances-rich fraction from soil HAs using Sephadex G-25 gel chromatography.² In the present study, we characterized this fraction by means of high performance size exclusion chromatography (HPSEC) with UV (280 nm) and fluorescence (excitation = 460 nm and emission = 520 nm) detection and spectroscopic methods (UV-visible, fluorescence and CP-MAS ¹³C-NMR). The HA samples used were prepared from two types of soils (Entisol and Andisol). HPSEC and CP-MAS ¹³C-NMR spectroscopy showed that the two HA samples differed largely in their molecular weight distribution and carbon chemistry. The Entisol HA was characterized by a larger molecular size and a higher content of aliphatic carbon, while the Andisol HA had a smaller molecular size and a higher content of aromatic carbon. The fluorescent substances-rich fraction, which is referred to as the fluorescent fraction in the present study, was separated from the HA samples by Sephadex G-25 gel chromatography. The percentage of carbon recovered in the fluorescent fraction was 2.8% for the Entisol HA and 18.1% for the Andisol HA. The HPSEC elution profiles of the fluorescent fraction of the two HA samples were similar to each other. The UV-visible, fluorescence and CP-MAS ¹³C-NMR spectra of the fluorescent fraction also showed similarities between the two HA samples. CP-MAS ¹³C-NMR spectroscopy revealed the predominance of aromatic carbon in the fluorescent fraction: aromatic carbon accounted for 74.1 and 76.4% of the total carbon in the Entisol and Andisol HAs, respectively. Thus, the fluorescent fraction of soil HAs consisted of highly aromatic components which were probably responsible for the fluorescence. The highly aromatic structure of the fluorescent fraction led us to the hypothesis that the fluorescent substances in the soil HAs originated from charcoals or charred plant residues. Strong support for this hypothesis was provided by the similarity of HPSEC elution profiles between soil- and charcoal-derived HAs.

References
1. M. Aoyama, Abstracts, 9th International Meeting of the International Humic Substances Society, Adelaide, 1998, p. 30.
2. M. Aoyama, in: "Understanding Humic Substances: Advanced Methods, Properties and Applications", E. A. Ghabbour and G. Davies, Eds., Royal Society of Chemistry, Cambridge, 1999, p. 179.

INVESTIGATIONS OF AGGREGATION IN HUMIC MATERIALS with SCATTERING TECHNIQUES

James A. Rice

Department of Chemistry and Biochemistry, South Dakota State University, Brookings, SD 57007-0896

G. Haberhauer, W. Bednar and M. H. Gerzabek

Department of Environmental Research, Austrian Research Centers, A-2444 Seibersdorf, Austria

The application of matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) to the characterization of fulvic acids was investigated. Sample preparation such as matrix optimization or sample concentration are shown to be crucial for examining such compounds. The use of conventional sample preparation techniques for MALDI-TOF MS failed in our experiments and resulted in spectra without significant peaks that could be assigned to fulvic acids. New sample preparation techniques were developed. The influence of matrices, of laser power and of other analytical parameters on the spectra were studied. Interferences of matrix molecules on the fulvic acid spectra were evaluated. The results will be compared with published mass spectra of fulvic acids, which were obtained by applying other soft ionization methods such as fast-atom bombardment or high-resolution Fourier transform ion cyclotron mass spectrometry. Analysis of MALDI-TOF mass spectra of fulvic acids of different origin will be discussed. Statistical cluster analyses were applied to identify and characterize fulvic acids and to examine if discrimination of fulvic acids from matrix spectra is possible. The mass distributions obtained from fulvic acid spectra are compared to results from size exclusion chromatography of the same fulvic acids. Such mass distributions can represent both cluster- and/or molecular ions. Discrimination of clusters from single molecules or identification of certain molecular ions is – due to the complexity of the analyzed material – not possible. Thus, in our experiments MALDI-TOF MS supplies no conclusive evidence regarding molecular weight distribution of fulvic acids.

Use of Concentrated Aqueous Humic Acids in Subsurface Remediation: Is Sorption a Limiting Factor?

Dale Van Stempvoort,¹ John Molson,² Suzanne Lesage¹ and Susan Brown¹

¹ National Water Research Institute, P.O. Box 5050, Burlington, Ontario L7R 4A6, Canada
² University of Waterloo, Waterloo, ON, Canada N2L 3G1, Canada

Commercial humic acids are being considered for potential use in subsurface remediation to mobilize and/or enhance the biodegradation of hydrophobic organic contaminants in soils and aquifers. Bench scale batch tests and a pilot scale study were used to investigate the sorption of aqueous concentrated Aldrich humic acid (HA) (100 mg/L to 2 g/L) by a coarse, carbonate-rich model aquifer material. For batch testing, a solids/solution ratio representative of aquifer conditions was selected. The series of batch data collected over 150 days indicated both fast (or practically instantaneous) and slow components of sorption, following Langmuir behavior. Sorption parameters derived from the batch tests provided a good prediction of the sorption of this HA to the same aquifer material at the pilot scale (5 m x 2 m x 1 m). The compatibility of the results at these two scales suggest that the bench scale batch tests are a useful tool for predicting the behavior of concentrated aqueous humic acids in aquifers. The sorption of HA to the test aquifer material reached an apparent saturation level of 0.4 mg/g, indicating that it would be feasible to use concentrated humic acid solutions for subsurface remediation of similar materials.

APPLICATION OF HUMIC ACIDS IN IN-SITU GROUNDWATER REMEDIATION

Juergen Poerschmann and Gerd Balcke

Center for Environmental Research Leipzig-Halle, 04318 Leipzig, Germany

Humic acids are known for their potential to interact with hydrophobic organics and heavy metals.¹ Our work has been focused on utilizing these sorbents for remediation purposes. The proposed process includes the following steps: (I) activation of aquifer materials (sands, clays) with iron or aluminum salts; (ii) immobilization of dissolved humic acids on activated aquifer material; and (iii) retardation of organic compounds onto the thin layer of humic acids anchored on the aquifer core. Special attention has to be focused on the stability of Fe(III)-salt coatings under anoxic conditions. To prepare humic acids with high functionality and hydrophobicity, the sorbents were subjected to sonication and hydrothermal treatment. The sorption capability of these activated humic materials was assessed with a cocktail of organic compounds covering a wide hydrophobicity range. Solid Phase Microextraction (SPME) and liquid-liquid extraction in combination with GC/MS and GC/AED was found to be a useful means to differentiate between the sorbate's state: freely dissolved, reversibly bound to humic acids or irreversibly bound to humic acids.² Results indicate a short-term activation of humic material as a result of these treatments. However, long-term activation is of minor importance. Obviously, activated humic acids return to their basis state. The humic acid coatings on activated aquifer materials are very useful for removing metalloids, including arsenic species.

References
1. 214th ACS National Meeting, Las Vegas, Sept. 7-11, 1997, Abstracts Vol. 37, No. 2.
2. J. Poerschmann, Zh. Zhang, F. D. Kopinke and J. Pawliszyn, Anal. Chem., 1997, 69, 597.

Humic Substances as Electron Acceptors and Electron Donors in Microbial Respiration

Derek R. Lovley

Department of Microbiology, University of Massachusetts, Amherst, MA 01003

Humic substances (HSs) are often considered to be biochemically inert, especially in the absence of molecular oxygen. However, recent studies in our laboratory have demonstrated that a wide phylogenetic diversity of Bacteria and Archaea are capable of using HSs as electron acceptors to support anaerobic respiration.^1-4 Microorganisms capable of transferring electrons to HSs and related organic compounds have been isolated from deep in the Earth's surface, hydrothermal vents, aquatic sediments, shallow aquifers, and agricultural soils. Microorganisms that can reduce humic substances can also reduce insoluble Fe(III) oxide, another microbial electron acceptor that can not enter the cell and must be reduced at or near the cell surface.^2,3,5 Microbial electron transfer to HSs is enzymatic and recent studies suggest that this electron transfer may be carried out by a membrane-bound hydrogenase. ESR studies indicate that quinone moieties are the primary electron-accepting groups in HSs that support microbial respiration.⁶ Microorganisms capable of reducing HSs can also reduce other extracellular quinones. Although microbial reduction of HSs may be important in a variety of anaerobic environments, it is can be especially significant in anaerobic subsurface environments that contain Fe(III) oxides. This is because microbially reduced HSs can abiotically transfer electrons to insoluble Fe(III) oxides.^2,3,7 Fe(III) is reduced and HSs are converted to oxidized forms that can again serve as an electron acceptor for microbial reduction. The electron shuttling between Fe(III)-reducing microorganisms and Fe(III) oxide via humic substances greatly accelerates the rate of Fe(III) reduction. In this manner, HSs significantly stimulate the anaerobic degradation of organic contaminants in subsurface sediments.^8,9 In addition to serving as electron acceptors in microbial respiration, microbially reduced HSs can also serve as reductants of more electropostive electron acceptors, most notably nitrate.¹⁰ HSs-dependent denitrification may influence N cycling in agricultural soils. The finding that many Archaea, (the organisms most closely related to the last common ancestor of extant life), have the ability to transfer electrons to HSs suggests that the ability to reduce extracellular quinones was a feature of early life.^4,11 These considerations demonstrate that, instead of being biochemically inert, HSs are dynamically involved in the carbon, nutrient, and electron flow of soils and sediments.

Jan Kochany and Wayne Smith

Conestoga-Rovers & Associates, Mississauga, Ontario L4Z 1P1, Canada

Interactions of humic substances (HSs) with environmental organic chemicals have long been reported.^1,2 It has been found that HSs can enhance biotic and abiotic degradation of phenols, polyaromatic hydrocarbons (PAHs) and pesticides in the aquatic environment. The catalytic effect of humic substances on degradation of organic chemicals in water and soil environment is particularly strong in photooxidation and biooxidation of large molecules like phthalates, fatty acids and PAHs. These properties make HSs attractive materials for bioremediation. Conestoga-Rovers & Associates (CRA) recently initiated biological studies on application of humates in bioremediation. The studies were conducted on humates supplied by U-Mate International using the N-CON respirometric system at the CRA laboratory in Waterloo, Ontario. The purpose of the studies was to determine the effect of humates on biological activities of activated sludge (RAS) from a wastewater treatment plant. Respirometric tests included humates without RAS, RAS with various amounts of humates and RAS with canola oil and humates. The experiments were supported by chemical analyses of respirometric reactor contents before and after the tests. Preliminary results of respirometric studies indicated that the effect of humates on biological processes depends on the humates/biomass ratio. It has been found that humates could support biological activities of RAS if no other food source is available. Humates also enhance biodegradation of canola oil but the extent of this phenomenon depends on the oil/humate and humate/RAS ratios. It has also been observed that the presence of humates increases solubility and bioavailiability of oil. This observation is particularly important since the presence of oils in wastewater substantially decreases the efficiency of wastewater treatment plants. In the next stage of biological studies we will investigate an application of humates in the removal of heavy metals and toxic organic substances. It is expected that the studies will provide a background for full-scale application of humates in environmental engineering.

References
1. Choudhry G. G., "Humic Substances. Structural, Photophysical, Photochemical and Free Radical Aspects and Interactions with Environmental Chemicals." Gordon and Breach, 1984, p. 185.
2. Kochany J., G. G. Choudhry and G. R. B. Webster, Sci. Total Environ., 1990, 92, 325.

The Interaction Between Esfenvalerate and Humic Substances of Different Origin

Lars Carlsen,¹ Marianne Thomsen,¹ Shima Dobel,¹ Pia Lassen,¹ Betty B. Mogensen¹ and Poul Erik Hansen²

¹National Environmental Research Institute, Department of Environmental Chemistry, DK-4000 Roskilde, Denmark
²Department of Chemistry, Roskilde University, DK-4000 Roskilde, Denmark

Pyrethroids have been used as agricultural insecticides for more than twenty years. This group of compounds is lipophilic and has shown to be highly toxic towards aquatic organisms. Sorption to dissolved organic matter (DOM) reduces of the bioavailability, and thus toxicity, of the pyrethroids. Sorption to DOM further affects the migration potential of these compounds. Several authors have investigated the binding of hydrophobic organic compounds to DOM and unambiguous interpretations of these investigations exist. Thus, the sorption of PAHs to DOM increases with an increase in the aromaticity of the DOM due to π-π interactions between the PAHs and the aromatic substructures within DOM. For the pyrethroids, however, no such clear relationship has been disclosed, possibly due to the structural complexity of the pyrethroids. To eludidate the possible mechanisms of interactions between pyrethroids and DOM, we have studied esfenvalerate as a representative for this class of compounds. We have estimated the partitioning (K_DOM) of this compound in humic substances of different origin. Humic substances constitute a major part of DOM. By use of ¹³C NMR spectra, elemental analysis and size exclusion chromatography of the different DOM´s as descriptors for the individual DOM properties, we have used multivariate analysis to explore the presence of any significant relationships between the DOM properties and the degree of sorption of esfenvalerate.

INTERACTION OF ENVIRONMENTAL ENDOCRINE DISRUPTORS WITH HUMIC ACIDS FROM SOILS AND SLUDGES

E. Loffredo, M. Pezzuto, G. Brunetti and N. Senesi

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

A wide range of xenobiotic molecules alter or disrupt the endocrine system in animals and humans directly by blocking or imitating natural hormones, or indirectly by interfering with the synthesis, storage, secretion, transport and catabolism of different endocrine molecules.¹ On the basis of their function, these molecules are called environmental "endocrine disruptors" (ED). In this study, adsorption and desorption interactions of two ED compounds, bisphenol A (BPA) and ethynil estradiol (EED), with six different humic acids (HAs) were investigated. The HA samples were extracted from two horizons of a Portuguese soil and a German soil (depths 0-30 cm, P30-HA and G30-HA, and 30-90 cm, P90-HA and G90-HA), and from a Portuguese (PS-HA) and a German sludge (GS-HA) used for soil amendments. Adsorption kinetics and adsorption/ desorption isotherms of BPA and EED interactions with each HA sample were determined with a batch equilibrium method and a HPLC technique with UV and fluorimeter detection for BPA and EED, respectively. Adsorption and desorption data were interpreted with Freundlich equation: x/m = KC^1/n in order to obtain adsorption (K_ads, 1/n_ads) and desorption (K_des, 1/n_des) parameters. The distribution coefficient K_d also was calculated. To investigate binding mechanisms, model interaction products of BPA and EED with HAs were prepared in the laboratory and characterized by FTIR, ESR and emission, excitation and synchronous scan fluorescence spectroscopy. Adsorption data obtained for BPA showed that both K_ads and K_d values of surface soil HAs were higher than those of deep soil HAs, and similar to those obtained for sludge HAs. The K_des values for BPA desorption were generally lower or much lower than the corresponding K_ads values, suggesting that adsorption of BPA onto HAs is reversible. In general, the values of 1/n_des were higher than those of 1/n_ads, which suggests fast desorption. The adsorption capacity of all HAs for EED was much higher than that for BPA, probably due to the lower water solubility and polarity of EED than for BPA. Similarly to BPA adsorption, for EED the adsorption capacities (K_ads and K_d) of surface soil HAs were twice those of deep soil HAs and similar to that of sludge HAs. The capacity and rate of EED desorption from all HAs was similar to the capacity and rate of adsorption on the basis of similar desorption and adsorption coefficients, thus indicating a reversible adsorption process. In general, the FTIR, fluorescence and ESR spectra of the interaction products of soil and sludge HAs with BPA and EED are similar to the spectra of the unreacted HAs, suggesting that BPA and EED are adsorbed on HAs by relatively weak chemical and physical binding mechanisms such as hydrogen bonding, Van der Waals forces and hydrophobic interactions.
This research was supported by EC Project Grant No. ENV4 CT 97/0473.

Cheryl Coolidge and David Ryan

Department of Chemistry, University of Massachusetts Lowell, Lowell, MA 01854

Several classes of organic nitrogen containing compounds may enter the environment as pollutants. Aniline is used as the starting material for azo dyes and other industrial products. Polynitroaromatics and their reduction products are found in munitions waste sites¹ and several widespread pesticides contain organic nitrogen.² Such compounds have been shown by a variety of techniques to interact strongly with humic substances (HSs). At pH < pK_a of ionizable nitrogen functional groups, these compounds should interact with humic carboxyl groups through electrostatic forces. At higher pH, the nitrogen lone pair has been shown to form nucleophilic addition products with the carbonyls of humic compounds.³ Aromatic amines may exhibit π–π interactions with aromatic groups of humic compounds. Fluorescence spectroscopy has been used extensively to study the interactions of HSs with a variety of metal ions, especially paramagnetic species, and polycylic aromatic hydrocarbons. In this study, the suitability of fluorescence spectroscopy for observing the interaction of a variety of organic nitrogen compounds with an isolated soil fulvic acid (SFA) was examined. Aniline was shown to quench the innate fluorescence of a 20 mg/liter sample of SFA over a concentration range of 2 – 200 mM aniline. This quenching was studied at pH 3.0, 4.0, 5.0, 6.5, and 8.0. Using the Stern Volmer model, the maximum association constant for the aniline fulvic acid interaction was determined to be 12.1 M^-1 at pH 5.0. The pK_a of aniline is 4.70. Thus at high pH, where the carboxyl functional groups of fulvic acid are largely negatively charged, the amino group is neutral. At lower pH where the amino group is significantly positive, the carboxyls begin to lose negative charge. The maximum association constant value at pH 5.0 indicates that the association is largely electrostatic and depends on the interplay of positive charge of the amino group with negative charge on the carboxyls of SFA. Binding of the toluidine isomers was also examined at pH 6.5. Results show diminished binding of the ortho isomer, possibly due to steric hindrance of the amino group. Paraquat, a cationic nitrogen herbicide, also quenched the fluorescence of SFA over a concentration range 2 – 4000 µM. The highest association constant for the paraquat SFA interaction examined in this experiment (270 M^-1) was observed at pH 6.5. This result is again consistent with an electrostatic attraction. Fluorescence spectroscopy shows promise as a tool for monitoring the interaction of organic nitrogen compounds with humic materials, and may shed light on the types and strengths of these interactions.
References
1. Li, A. Z., K. A. Marx, J. Walkerand and D. L. Kaplan, Environ. Sci. Technol., 1997, 31, 584.
2. Kolpin, D. W., J. E. Barbash and R. J., Gilliom, Environ. Sci. Technol., 1998, 32, 559.
3. Thorn, K. A., W. S. Goldenberg, , S. J. Younger and E. J. Weber, In: "Humic and Fulvic Acids: Isolation, Structure, and Environmental Role", Gaffney, J. S., N. A. Marley and S. B. Clark, eds., ACS Symposium Series 651, Washington D.C., 1996, 299.

Flow Field-Flow Fractionation-Inductively Coupled Plasma-Mass Spectrometry (Flow-FFF-ICP-MS): A New Approach for Characterization of Trace MetalS Complexed to Soil-Derived Humic Acids and Aqueous Humic Substances

Dula Amarasiriwardena,¹ Atitaya Siripinyanond² and Ramon M. Barnes²

¹School of Natural Science, Hampshire College, Amherst, MA 01002
²Department of Chemistry, University of Massachusetts, Amherst, MA 01003-4510

Humic acids (HAs) have strong affinity for both inorganic and organic contaminants. Analytical information about the physical and chemical characteristics of various molecular fractions of metal-HAs and metal-humic substances (HSs) are becoming increasingly important in characterizing their mobilization and transportation properties in soil and aqueous environments. Previously, high performance size exclusion chromatography (SEC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS) has been used to identify trace metal-bound HA molecular fractions in water¹ and in soil HAs². Flow Field-Flow Fractionation (Flow)-FFF offers particle size distribution in addition to molecular weight information. This separation approach also is relatively free from the charge-repulsion and solute adsorption effects observed in SEC.^3,4 The purpose of this investigation is to characterize the trace metals complexed to soil-derived HAs and to aqueous humic substances found in the municipal wastewater. A relatively new technique known as Flow-FFF-Inductively Coupled Plasma-Mass Spectrometry (Flow-FFF-ICP-MS) is valuable in accomplishing this objective. Trace metals (Al, Cu, Cd, Fe, Mn, Pb and Zn) bound to various soil, peat and compost-derived HA molecular fractions were identified by Flow-FFF-ICP-MS. Monomodal elemental fractograms with different polydispersities demonstrate that they are bound to a broad range of HA molecular sizes. Elemental fractograms were also obtained for aqueous colloidal organic matter (COM). Fractograms clearly show the removal of COM along the treatment process. Elemental fractograms also showed that some elements (Zn, Mn, and Mo) present in wastewater are not only associated with organic or inorganic colloidal matter, but they also are present as dissolved anionic complexes. Copper, Fe and Zn signals decrease as wastewater treatment proceeds. This demonstrates precipitation and subsequent removal of metal ions associated with the COM as sludge. Furthermore, halogens (Cl, Br, and I) associated with the COM and the aqueous phase of the influent were investigated after primary and secondary wastewater treatments. This information will provide further insight into the role of halogen-HS chemistry.

References
1. Rottmann, L and K.G. Heumann, Anal. Chem., 1994, 66, 3709
2. Ruiz-Haas, P., D. Amarasiriwardena and B. Xing, In: "Humic Substances: Structures, Properties and Uses", Davies, G. and E. A. Ghabbour, Eds., Royal Society of Chemistry, Cambridge, 1998, p. 147.
3. Beckett, R., J. Zhang and J. C. Giddings, Environ. Sci. Technol., 1987, 21, 289.
4. Hassellöv, M., B. Lyvén, C. Haraldsson, and W. Sirinawin., Anal. Chem., 1999, 71, 3497.

EXAFS studies and quantum-chemical simulations of interactions of metal ions with humic substances: effects of pH

Gregory V. Korshin,¹ Anatoly I. Frenkel² and A. M. Kuznetsov³

¹Department of Civil and Environmental Engineering, University of Washington, Seattle, WA 98195-2700
²Materials Research Laboratory, University of Illinois at Urbana-Champaign (mailing address: Building 510 E, Brookhaven National Laboratory, Upton, NY, 11973)
³Department of Inorganic Chemistry, Kazan State Technological University, Kazan, Tatar Republic, Russian Federation 420015

Interactions of metals with humic species (HS) constitute a very complex phenomenon. In this study, the structure-sensitive XAFS technique and theoretical simulations were used to further elucidate the identities of the functional groups participating in metal complexation as well as to explore the changes of the geometry and composition of the inner complexation shell over a wide range of pHs. The experiments were carried out using second- and third-generation synchrotron sources. The target element was copper. The range of pH was 4 to 12. The molar Cu/DOC ratios varied from <0.001 to >0.03. Experiments with model compounds (e.g., salicylic and sulfosalicylic acids) were also carried out. For the model systems, extensive quantum-chemical simulations of the geometry and distribution of charges in the complexes were performed. EXAFS and especially XANES experiments showed that pH changes are associated with significant effects in the local chemical environment around the copper(II) ions. At low pH, the XANES spectra of Cu-HS complexes were not dramatically different from those of copper complexes with the model compounds. At increased pH, the splitting of the first derivative of the XANES spectra for Cu-HS complexes becomes much more pronounced and dissimilar to that seen for the model systems. This appears to indicate an increase of the tetragonal distortion of the octahedron representing the inner shell in copper-HS complexes. Quantum-chemical studies of the model complexes indicated that the geometry of bonds even in relatively simple model systems may be complex. According to the simulations, the presence of organic ligands may cause the equatorial plane to be rhombically distorted, but transitions between different geometries may be relatively rapid due to low activation energy associated with the distortion. In Cu(II)-HS complexes, on the other hand, the energy of bonds between the central cation and the organic functional groups appears to exceed that in the model systems and the structure of the octahedron is more rigid. The experimental information will be further expanded to determine the exact number of ligands in the Cu²⁺ inner shell at different pH and directly compare different models explaining the copper-binding behavior of HS.

On Metal Ion Humate Complexation and the Charge Neutralization Process

G. Buckau

Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgungstechnik, D-76021 Karlsruhe, Germany

Some features of ion exchange and metal ion binding to polyelectrolytes and their application to humic acid are discussed. Emphasis is on ion exchange, the non-ideal charge distribution and the overall charge neutrality of polyelectrolytes in aqueous solution. The metal ion interaction with humic acid is discussed in view of these basic polyelectrolyte features. Due to co-inclusion of counterions, only a fraction of the proton exchanging functional groups of humic acid can be loaded with metal ions. This fraction, corresponding to the loading capacity, varies with the nature of the studied metal ion, the nature of the humic acid and physico-chemical conditions (pH and ionic strength). The strength of metal ion-humate complexation follows the same systematics as the loading capacity, i.e., the complexation strength and the counterion co-inclusion correlate. Possible reasons for this counterion co-inclusion are discussed.

Biogeochemical interactions of iron and humic substances in aquatic sediments

Diane McKnight

INSTAAR, University of Colorado, Boulder, CO 80309-0450

In aquatic environments, photochemical and microbial processes are important reactions involving dissolved iron species, iron oxides and dissolved humic substances. Because of the relative abundance of dissolved humic substances and dissolved iron in surface waters, iron-humic interactions influence photochemical and microbial processes involving iron. The complexation reaction involves formation of charge transfer complexes with carboxylic groups of humic molecules, and site specific ligand exchange reactions control humic sorption to iron oxides. One common aspect of iron oxides and humics is their lack of chemical definition and environmental variability, which makes it difficult to determine precise reaction coefficients that are generally applicable. The importance of this variability is illustrated for 1) humic-enhanced photochemical reductive dissolution of iron oxides in a mountain stream and 2) humic substances serving as electron acceptors, or electron shuttlers to iron oxides, in anoxic degradation of organic material in sediments. For both photochemical and microbial processes influencing iron-humic interactions, the reactivity of the humics varies with chemical characteristics, such as aromaticity, size and carboxylic acid content. Thus, quantitative models of iron-humic interactions in aquatic systems could be improved by using reactivity coefficients representative of the chemistry of the humics in the particular environment.

PRIMARY PHOTOCHEMICAL AND PHOTOPHYSICAL PROCESSES IN LAURENTIAN AND MOSSY POINT FULVIC ACID: LINKAGE TO OVERALL PHOTOCHEMISTRY AND PHOTOSENSITIZATION

Aldo Bruccoleri and Cooper H. Langford

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

The photobleaching of humic substances (HSs) in natural water is a well known phenomenon. It is also likely, although less easily quantified, that photodegradation of humic substances occurs to an important extent in the surface of soils. These photochemical processes are important for at least two reasons. First, the role of photoaccelerated oxidation of humics to CO₂ needs to be characterized in order to have a full accounting of the carbon cycle. Second, it is known that excited states of humics play a role in the sensitization of photodegradation of xenobiotic compounds in natural waters. Our research program started from the identification of the primary quantum yields for photophysical processes in two water soluble soil fulvic acid preparations that have a long history of analysis so that they can be described as well characterized. The processes initiated by near uv irradiation (350 nm) include intersystem crossing to triplets, prompt photoionization and fluorescence (in order of decreasing quantum yield). It has been suggested before that quinoid functionality is important to HSs spectroscopy and photochemistry. The small singlet-triplet splitting and large triplet quantum yields are consistent with the photochemistry of quinoids. Monitoring of the early stages of photooxidation by both difference spectroscopy and NMR provides strong support for the quinoid triplet interpretation. Low temperature fluorescence spectra and high resolution EPR show a close analogy between a fulvic acid and a benzoquinone-hydroquinone "semiquinone" complex. Molecular mechanics calculations reveal the response of "semiquinone" complex formation to substitution on the quinone moiety.

Development and application of EA-IRMS solutions to the measurement of Carbon, Nitrogen, Sulphur, Oxygen and Hydrogen isotopes in Earth Sciences

John Morrison

Micromass UK Ltd, Wythenshawe, Manchester M23 9LZ, UK

In the early 1980's, a standard elemental analyser was first interfaced to a stable isotope ratio mass spectrometer and almost immediately revolutionised the measurement of ¹⁵N isotopes in the field of soil science.¹ The method was based on Dumas combustion of the sample in a helium stream, part of which was diverted to the mass spectrometer for isotope analysis. The technique was quickly applied to the measurement of carbon isotopes and the application field expanded to include plant physiology, medicine, food adulteration and environmental sciences. In the early to mid 1990's, sulphur was added to the list of species addressable by the technique,² and led to adoption of the method by the geological sciences. 1997 saw the emergence of pyrolysis methodology involving the thermal decomposition of samples. Oxygen analysis by measurement of the product gas CO was the next isotope to be measured,^3,4 followed by hydrogen. Measurements of the hydrogen isotopes required changes in mass spectrometer design because of inevitable interference in the mass 3 measurement (HD) from the tail arising from the huge mass 4 helium peak. Today, virtually every area of scientific investigation involving stable isotope measurements can be served by the combination of elemental analyser and isotope ratio mass spectrometer, and as such the technique has proved itself one of the most important advances in the last 20 years. This presentation will cover the technical aspects of the EA-IRMS system and show examples of how it is useful in a variety of application areas.

References
1. Preston,T. and N. J. P. Owens, Analyst, 1983, 108, 971.
2. Giesemann, A., H. -J. Jager, A. -L. Norman, H. R. Krouse and W. A. Brand, Anal. Chem., 1994, 66, 2816.
3. Werner, R. A., B. E. Kornexl, A. Roßman and H. -L. Schmidt, Anal. Chim. Acta, 1997, 319, 159.
4. Koziet, J., J. Mass Spectrom., 1997, 32, 103.
5. Kornexl, B. E., M. Gehre, R. Hofling and R. A.Werner, Rapid Commun. Mass Spectrom., 1999, 13, 1685.

Main Conclusions of the EC-Humics Project: "Effects of Humic Substances on the Migration of Radionuclides: Complexation and Transport of Actinides"

G. Buckau,¹ P. Hooker,² V. Moulin,³ K. Schmeide,⁴ A. Maes,⁵ P. Warwick,⁶ Ch. Moulin,⁷ J. Pieri,⁸ N. Bryan,⁹ L. Carlsen,¹⁰ D. Klotz¹¹ and N. Trautmann¹²

¹ Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgungstechnik, D-76021 Karlsruhe, Germany; ² British Geological Survey, Keyworth, Nottingham NG12 5GG, UK; ³ CEA/Centre d’Etudes des Saclay, Fuel Cycle Division, DESD/SESD/LMGS, F-91191 Gif-sur-Yvette; ⁴ Forschungszentrum Rossendorf, Institut für Radiochemie, D-01314 Dresden, Germany; ⁵ Katholieke Univ. Leuven, Landbouwinst.-Lab. V. Colloidch., B-3001 Heverlee, Belgium; ⁶ Loughborough University. Department of Chemistry, Loughborough, Leicestershire LE11 3TU, UK; ⁷ CEA, Fuel Cycle Division, DCC/DPE/SPEA, F-91191 Gif-sur-Yvette Cedex, France; ⁸ Université de Nantes, Lab. Bio- et Radiochimie, F- 44322 Nantes, France; ⁹ University of Manchester, Department of Chemistry, Manchester M13 9PL, UK; ¹⁰ Nat. Environmental Res. Inst., Dept. of Environmental Chemistry, DK-4000 Roskilde, Denmark; ¹¹ GSF-National Research Center for Environment and Health, Institute of Hydrology, D-85764 Neuherberg, Germany; ¹² University of Mainz, Institute of Nuclear Chemistry, D-55128 Mainz, Germany

This paper reviews important findings of the title project. Conducted from January 1997 to December 1999, the project is partly funded by the European Commission. The influence of humic substances on the migration of actinide ions in the far field of radioactive waste repositories is investigated. Different systems are investigated and the results are compared. Designed laboratory systems (purified substances and controlled conditions (pH, ionic medium, temperature)) are investigated to establish data and adequate process understanding. This information is applied to/validated by investigations on near-natural systems in the laboratory (batch and column experiments with natural samples). Natural chemical analogues are investigated to validate/falsify the applicability of data and process understanding in real aquifer systems. Real aquifer system analysis is also used to collect data that cannot be obtained from laboratory investigations (e.g. origin and mobility of humic substances in natural aquifer systems). Data and process understanding are rationalized by models and implemented through codes. The outcome of the project is demonstrated by migration case studies on real sites. The most important findings are that (1) actinide humate interaction is subject to considerable kinetic influences; (2) metal humate complexes from laboratory investigations and analogous natural trace elements show different behavior; and (3) no indication is found for retention or decomposition of humic colloids in natural aquifer systems. Introduction of kinetics and implementation in transport models for the first time shows consistency between batch and column experiments on actinide ion transport. Laboratory investigations are restricted to kinetic processes that can be observed within such time-frames. However, actinide elements and their chemical analogues in natural humic colloids show a component that appears to remain basically irreversibly bound or at least is subject to very slow kinetics. The consequence of an irreversibly bound fraction is unhindered transport with groundwater flow. It remains unclear whether the kinetic data from actinide laboratory investigations or those from natural chemical analogues are the most appropriate for actinide far-field migration. For the purpose of a radioactive waste disposal safety assessment, however, unhindered actinide humic colloid transport must be assumed as long as no adequate evidence of the opposite case can be given.

Organoclays remove Humic Substances from Water

George R. Alther

Biomin, Inc., Ferndale, MI 48220

Organically modified clays, or organoclays, are finding use in the removal of humic acids from water. Good results have been achieved in Ireland, where the organoclays are replacing activated carbon for the cleanup of well water. In the U.S., some positive feedback has been received from Louisiana and Illinois. Organoclays are bentonite modified with quaternary amines. They can be modified to become resins of non-ionic, cationic or anionic character. A fair amount of laboratory work has been conducted to test the usefulness of organoclays with humics. This paper presents the results that we have received, including comparisons with activated carbon and commercial resins. The results are in the form of isotherms, jar tests and microcolumn studies.

Effect of Lake Acidification on Natural Organic Matter from a Norwegian Lake

James J. Alberts, Monika Takács and Mala Pattanayek

University of Georgia Marine Institute Sapelo Island, GA 31327

A dystrophic Norwegian lake was experimentally manipulated so that a section of the lake and its watershed were artificially acidified for a period of four (4) years, while the other section remained untreated.^1,2 Natural organic matter (NOM) isolated from this lake by reverse osmosis³ was analyzed for elemental composition, fluorescence spectral characteristics and proton and copper binding capacities. These parameters were evaluated relative to lake and watershed treatment scenarios and the changes observed in mercury and copper toxicity of the bacteria Vibrio fischeri in the presence of the RO isolates. Elemental analyses suggest that complex NOM loses small, highly oxygenated aromatic molecules as a result of lake and catchment acidification. Furthermore, organic matter from the acidified portion of the lake had higher ash contents and lower copper binding capacities (CuBC) than the material isolated from the control section. Fluorescence spectra of NOM from the lake were very similar to fulvic acid spectra reported in the literature. Subtle differences between the two treatments were observed in the excitation, synchronously scanned and total luminescence fluorescence spectra of the NOM. Little effect of lake and watershed treatment was observed on metal toxicity, but acidification of the NOM appeared to increase its toxicity relative to control NOM when the organisms were not challenged by metals.

References
1. Gjessing, E.T, Environ. Int. 1994, 20, 267.
2. Gjessing, E. T., J. J. Alberts, A. Bruchet, P. K. Egeberg, E. Lydersen, L. B. McGown, J. J. Mobed, U. Munster, J. Pemkowiak, E. M. Perdue, H. Ratnawerra, D. Rybacki, M. Takács and G. Abbt-Braun, Water. Res. 1998, 32, 3108.
3. Serkiz S. M. and E. M. Perdue, Water Res. 1990, 24, 911.

STUDY OF HALOGEN INCORPORATION INTO REACTIVE SITES IN HUMIC SPECIES BY A STOPPED-FLOW METHOD

Gregory V. Korshin,¹ Chao-Hong Wu,¹ Chi-Wang Li,² Mark M. Benjamin¹

¹Department of Civil and Environmental Engineering, University of Washington, Seattle, WA 98195-2700
²Department of Water Resources and Environmental Engineering, Tamkang University, Taipei, Taiwan

The objective of this work was to investigate rapid reactions between active chlorine and humic species or model compounds. The latter class of species was represented by resorcinol and 3,5-dihydroxybenzoic acid (DHBA). The behavior of humic species was probed using the hydrophobic fraction of Suwannee River natural organic mater (HPOA). The kinetic measurements were carried out with an Applied Photophysics X.18MV stopped-flow reaction analyzer, which was employed in either the direct or sequential mixing mode. The stopped-flow deadtime was 1.1 milliseconds. The mixture aging time was from 15 milliseconds to 500 seconds. The consumption of chlorine was measured by the DPD spectrophotometric method using an independent series of stopped-flow experiments run in the sequential mixing mode. The optical length of the reaction cell was either 2 or 10 mm. The spectra were recorded in the range of wavelengths 250 to 550 nm. Chlorination was carried out at pH 7 and 20ºC. The stopped flow experiments indicated that the incorporation of chlorine into the model compounds proceeds through a sequence of four or more steps whose rates decrease as the number of chlorine atoms incorporated into the aromatic rings increases. The absorbance of the reaction mixtures increased following the formation of halogenated products. The spectra of the intermediates so formed had similar features, especially at the later reaction steps, to those of mono- and polychlorinated phenols. However, the spectra of some transient species had features notably different from those of halogenated phenols and probably can be associated with charge-transfer complexes. The results of differential spectroscopy for HPOA and similar samples conducted in the conventional mode (that is, the reaction times was no less than a minute) had showed that interaction of chlorine with chromophores in humic species always caused the absorbance to decrease rather than to increase, although some indications of transient phenomena had been detected. The stopped-flow experiments with the same samples established the presence of intense transient spectral features located between 270 and 370 nm. In this range, the absorbance of HPOA increased following chlorination and then decreased below the original value. A quasi-isobestic point located at 305 nm was another conspicuous feature. The location and other parameters of the spectra signified that transient species hypothetically similar to polychlorinated phenols were formed but that they rapidly decayed. No evidence of the formation of compounds similar to charge-transfer complexes was detected. The kinetics of halogen incorporation in humic species appears to be much different from that of model compounds, while the stability of functional units similar to halogenated phenols and incorporated into the structural backbone of humic species appears to be much less than that in individual aromatic species. More work to establish the identity, concentration and kinetic behavior of the reactive sites in humic species is being carried out and will be discussed.

"Standard" coal derived humic acid, its analysis and characterization

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

¹Department of Analytical Chemistry, Faculty of Science, Masaryk University, 611 37 Brno, Czech Republic
²Chemapex s. r. o., 430 04 Chomutov, Czech Republic

So called "capucine" is a special form of oxidized bohemian brown coal from the western Bohemia region (Czech Republic), where coal is mined on a large scale from open-cast mines. Capucine raw material is a waste in coal production. It is used for large-scale industrial manufacture of alkali metal humates, which are applied for the production of new types of combined fertilizers, as additives in the concrete and ceramic industries and for other purposes.¹ It was found that these capucine materials are very rich in humic substances. Humic acid precipitated from raw humates was used as the starting material for the production of the so-called CHEMAPEX HA STANDARD.² The subject of this work is to analyze the HA Standard by elemental analysis, ash content, and to characterize it by capillary zone electrophoresis (CZE), matrix assisted laser desorption time of flight mass spectrometry (MALDI-TOF-MS), NMR and other methods.^3,4 The results of the analyses were compared with those of Aldrich and IHSS standard humic acids. It was found by MALDI-TOF-MS and CZE that many fractions of the CHEMAPEX standard are identical with those of humic materials from other producers and with IHSS humic acids (Peat HA standard, 1S103H, etc.). The conclusion is that the CHEMAPEX standard is a sufficiently pure, suitable and cheap humic acid standard for comparative studies.

References
1. CHEMAPEX s. r. o., http://www.nero.cz
2. Sákra, T., University of Pardubice, Nám. Čs. legií 565, 532 10 Pardubice, Czech Republic, unpublished results.
3. Remmler, M., A. Georgi and F. -D. Kopinke, Eur. Mass Spectrom., 1995, 1, 403.
4. Fetch, D., M. Hradilová, E. M. Peñ a Méndez and J. Havel, J. Chromatogr., 1998, A, 817, 313.

CHARACTERIZATION OF COAL-DERIVED HUMIC ACIDS PRODUCED FROM OXYHUMOLITE. A COMPARATIVE STUDY

L. Pokorná,¹ D. Gajdošová,¹ J. Havel¹ and A. Kotz²

¹Department of Analytical Chemistry, Faculty of Science, Masaryk University, 61137 Brno, Czech Republic
²TEHUM s.r.o., 415 01 Teplice, Czech Republic

Oxidized brown coal (oxyhumolite) formed by coal air-oxidation some 100 millions years ago is a very special source of humic acids located in western Bohemia (Czech Republic). From this extraordinary source humic acids are produced on an industrial scale by alkali leaching. The production process is aimed at obtaining quality products with the lowest ash content and the highest humic acids content. The product quality depends on the alkali used for the extraction and either sodium or potassium humate results. A unique drying process gives an appearance of flakes to the product. In this work oxyhumolite raw material and TEHUM’s Na(K) humates were analyzed and characterized by capillary zone electrophoresis and matrix assisted laser desorption time of flight mass spectrometry (MALDI-TOF-MS). The results were compared with those for humic acids of other producers. It was found that TEHUM´s humic acids obtained from oxidized brown coal are (like any other humic acids) mixtures of various compounds. It was demonstrated that several fractions are the same as those observed in natural (soil derived) and in other producers’ coal-derived humic acids. A comparison with IHSS humic acids standards, namely standard Peat HA and others was also made and it can be concluded that some parts of the electropherograms are similar. Thus, TEHUM´s oxyhumolite derived humic acid is similar to other products and some of the fractions appear to be the same as in naturally occurring HAs.

References
1. Pokorná L., D. Gajdošová and J. Havel, In: "Understanding Humic Substances: Advanced Methods, Properties and Applications", Ghabbour E. A. and G. Davies, Eds., Royal Society of Chemistry, Cambridge, 1999, p. 107.
2. TEHUM - http://www.tehum.cz

HUMASORB™ A Humic Acid-based Adsorbent to Remove Organic and Inorganic Contaminants

Amjad Fataftah, H.G. Sanjay, and Daman Walia

Arctech, Inc. Chantilly, Virginia 20151

HUMASORB™ is a cation exchange material developed by cross-linking and immobilizing a coal-derived humic acid. HUMASORB™ is a water insoluble adsorbent that is stable over a wide pH range. It exhibits all the properties of the original humic acid: high cation exchange, ability to chelate metals, and ability to sorb organics.¹ HUMASORB™ has been evaluated to remove single and mixtures of contaminants both in batch and column tests. The contaminants include metals, radionuclide surrogates, oxo-anions and organic compounds. The results demonstrate that HUMASORB™ can be used for removal of multiple types of contaminants in a single-step process. Willey et al. reported on the effect of various methods of drying on the humic acid surface area.² The effect on the HUMASORB™ surface area was evaluated by drying the wet beads by supercritical fluid CO₂ drying, freeze drying, air drying and vacuum oven drying. The total surface areas of the dried beads were 0.8-15.9 m²/gm. Supercritical fluid CO₂ drying resulted in the highest surface area and oven drying the lowest. However the capacity of the dried beads for metals and organics was similar. Earlier studies at Arctech had shown that the sorption capacity of HUMASORB™ is increased by reducing the particle size, which may indicate the increased effect of the external surface area on capacity. Humic acid is a cation exchange material that removes cationic species through the oxygen containing functional groups. HUMASORB™ has been modified by a proprietary method to remove metals that exist as oxyanions such as perrhenate. The modified HUMASORB™ has been selected by DOE to evaluate removal of radioactive technetium (present as TcO₄^-) and trichloroethylene (TCE) from contaminated water from the DOE site at Paducah, Kentucky. A general review of the method of development and properties HUMASORB™ and the results of HUMASORB™ evaluation for contaminant removal under simulated barrier conditions will be presented. The effect of drying and chemical modification on the capacity of HUMASORB™ will also be reviewed. Finally, the results of application of HUMASORB™ to treat Spent Decontamination Solution (SDS) and brines at Johnston Atoll will be discussed.

References:
1. Sanjay, H. G., D. Walia and K. Srivastava, "Adsorbent," US Patent number 5,906,960, 1999.
2. Willey, R. J., A. Radwan, M. E. Vozzella, A. Fataftah, G. Davies and E. A. Ghabbour, J. Non-crystalline Solids, 1998, 225, 30.

Kenneth Day

Kenneth Day Consulting, P.O. Box 5838, Fresno, CA 93755.

Humic acid (HA) products are being used increasingly on farms throughout the world. The major use of HA products is with phosphorus fertilizers to improve their efficacy. HAs can greatly improve phosphate uptake by crop plants and humic substances have been shown to improve phosphorus uptake by plants in most published studies. Several modes of action are proposed. At soil pH 7 or greater, complexation by HAs prevents calcium from forming polyphosphate precipitates. HAs also prevent phosphates tie up on iron or aluminum oxides. In acid soils, HAs complex dominant iron and aluminum cations and prevent precipitation of iron and aluminum phosphates. Amine functional groups of HAs may complex phosphate anions under acidic soil conditions, thereby rendering phosphorus more available to plants. Studies also show that HAs enhance the rate of respiration in roots and lead to substantially faster active uptake processes. Agronomists have utilized HA products derived from Leonardite (a soft brown coal) or peat. These products have been applied successfully in a dry form mixed with dry fertilizers. Liquid HA or FA extracts have been used with liquid phosphorus fertilizers. These products are applied with soil applied fertilizers. The products sometimes are applied with fertilizers through irrigation systems. An increasing number of published field trials are supporting the use of HA products in these applications.

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 R. R. Bloom, Eds., American Society of Agronomy, Madison, WI, 1990, p. 161.
2. Dixit, V. K. and N. Kishore, Ind. J. Sci. Ind. Sec., 1967, A1, 202.
3. Kazakova, V. N., Y. A. Vyatkin and E. G Polievktova, Khim. Sel’sk. Khoz., 1986, 8, 49.
4. Maggioni, A. et. al., Sci. Total Environ., 1987, 62, 355.
5. Nardi, S, G. Concheri and G. Dell’Agnola, In: "Humic substances in terrestial ecosystems", Piccolo, A., Ed., Elsevier, Amsterdam, 1996, p. 361.
6. Piccolo, A., In: "Humic substances in terrestial ecosystems", Piccolo, A., Ed., Elsevier, Amsterdam, 1996, p. 225.
7. Sladky, Z., Biol. Plant, 1959, 1, 142.
8. Thornton, M., M. Seyedbagheri and R. Thornton, Proceedings, Washington State Potato Conference and Trade Fair, 1993.
9. Vaughan, D. and R. E. Malcolm, Eds., "Soil organic matter and biological activity", Martinus Njihoff/Dr. Junk Publishers, Dordrecht, 1985.