Gennaro Brunetti

CHARACTERIZATION, DIFFERENTIATION, AND CLASSIFICATION OF HUMIC SUBSTANCES BY FLUORESCENCE SPECTROSCOPY

Fifty samples of humic acids and fulvic acids isolated from various soils and soil-related materials (including paleosols, peat, leonardite, composted and earth-worm-composted organic materials, sewage sludges, and materials synthesized by soil fungi) have been investigated by fluorescence spectroscopy in the emission, excitation, and synchronous-scan excitation modes. Emission spectra are generally characterized by a unique broad band showing a maximum wavelength and relative fluorescence intensity that depend mainly on the nature and origin of the humic material. Excitation and synchronous-scan excitation spectra generally exhibit a number of peaks and shoulders of relative intensity at wavelengths that also vary according to the type and source of the humic material. The observed, distinct fluorescence properties of humic substances provide useful diagnostic criteria for distinguishing between humic and fulvic acids from the same source and between humic or fulvic acids from various sources. As a consequence, a classification of humic substances is proposed on the basis of their fluorescence behavior. Hypotheses on the chemical nature of relevant fluorescing structures in the various humic materials are suggested by comparing experimental data with corresponding fluorescence data available for defined simple molecules. The long wavelengths and low intensities measured for the major fluorescence peaks of paleosol, soil, peat, and leonardite humic acid are mainly ascribed to the presence of linearly-condensed aromatic ring and other unsaturated bond systems, capable of a high degree of conjugation and bearing electron-withdrawing substituents such as carbonyl and carboxyl groups, and to their high molecular weight units. The short wavelengths and high intensities generally measured for main fluorescence peaks of compost and earth-worm-composted humic acid and soil and peak fulvic acid are associated with the presence of simple structural components of low molecular weight, low degree of aromatic polycondensation, low levels of conjugated chromophores, and bearing of electron-donating substituents such as hydroxyls, methoxyls, and amino-groups. In the Conclusions, emphasis is given to the utility of further investigations on fluorescence behavior of humic substances.

Spectroscopic and compositional comparative characterization of I.H.S.S. reference and standard fulvic and humic acids of various origin

Abstract Eleven standard and reference fulvic acids (FA) and humic acids (HA) of aquatic and terrestrial origin from the collection of the International Humic Substances Society have been studied by chemical and spectroscopic methods. Aquatic HA appear richer in O and lower in C than terrestrial HA, while the opposite is generally true for the corresponding FA. The N content of aquatic samples is always much lower, and C/N ratio and E 4 /E 6 ratio much higher than those of terrestrial samples. The infrared spectra of all samples but soil HA are qualitatively similar one to another, but they differ mainly in the relative intensity of carboxyl, aromatic and aliphatic group bands. Fluorescence of terrestrial HA occurs at higher wavelengths than terrestrial FA and aquatic HA and FA in both emission and excitation modes, while synchronous-scan spectra appear more resolved and informative. ESR spectra are featured by resonances consistent with conjugated semiquinone free radicals and Fe(III) ions, the latter resonance being generally more intense for terrestrial than for aquatic samples.

Chapter 14 – Humic-like Substances in Organic Amendments and Effects on Native Soil Humic Substances

Publisher Summary This chapter reviews the chemical and physicochemical data available for the evaluation on a molecular scale of the humic substances (HS) like components in organic amendments of various origins and nature, and the effects of added HS-like materials on the composition, structure, and chemical reactivity of native soil HS. The organic amendments are discussed based on four classes: sewage sludge; municipal solid wastes; animal manures; and plant, wood, and food industry residues. Soil application of mature, stabilized, and partially humified organic wastes of any nature and origin affects the composition, structure, and chemistry of native soil HS. These modifications are more extensive and lasting in the fulvic acid (FA) fraction than in the humic acid (HA) fraction of an amended soil. The proteinaceous, S-containing, lignin, and aliphatic structures contained in HS of organic amendments are extensively incorporated into native soil HS in forms relatively resistant to further decomposition. The chapter also summarizes the scope of the treatment processes of organic wastes intended to produce soil amendments with beneficial properties for agriculture.

Determination of heavy metals in soils by Laser Induced Breakdown Spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) is a recent analytical technique that is based upon the measurement of emission lines generated by atomic species close to the surface of the sample, thus allowing their chemical identification. In this work, the LIBS technique has been applied to the determination of total contents of heavy metals in a number of reference soil samples. In order to validate the technique, LIBS data were compared with data obtained on the same soil samples by application of conventional Inductively Coupled Plasma (ICP) spectroscopy. The partial agreement obtained between the two sets of data suggested the potential applicability of the LIBS technique to the measurement of heavy metals in soils.

Chemical and spectroscopic characterization of humic acids isolated from different Slovak soil types

Abstract Humic acids isolated from six different Slovak soils have been characterized comparatively by using chemical methods and spectroscopic techniques including ultraviolet-visible (UV-VIS), 13C nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR), fluorescence, and electron spin resonance (ESR). Results from elemental and functional group analyses and spectroscopic data are generally well correlated. Humic acids from the Calcaro-Calcic Chernozem and Gleyic Phaeozem are characterized by a high degree of aromaticity, high content of carboxylic groups and polycondensed aromatic and conjugated structures, low fluorescence intensity with main peaks in the long-wavelength spectral region, and very high organic free-radical concentrations. Differently, HAs from the Dystric Planosol, Eutric Cambisol, Orthic Luvisol, and Stagno-Gleyic Cambisol exhibit low aromaticity and high aliphatic character, low degree of polycondensation, low content of carboxylic groups and organic free radicals, fluorescence in the intermediate- and low-wavelength regions, and the distinct presence of amide groups and polysaccharidic structures. These differences in chemical structure and functionalities suggest a higher degree of humification and higher chemical reactivity for the first two humic acids, with respect to the other four samples. The agronomic functions and environmental implications of the two groups of humic acids examined are, therefore, expected to be markedly different.

Chemical and Physico-Chemical Parameters for Quality Evaluation of Humic Substances Produced during Composting

The principal scope of the compo sting process is to transform organic wastes of various origins and nature into a stable, mature, humus-like material suitable for use as soil amendment. The knowledge of the quality of humic acid-like and fulvic acid-like fractions formed during the composting process is of primary importance for the evaluation of the economic value, agronomic efficacy and environmental safety of the final product, the compost, which will be applied to soil. In this review paper, the chemical and physico-chemical analytical properties and data available for the evaluation on a molecular scale of the humic acid-like and fulvic acid-like constituents in composts are summarized and discussed in comparison with indigenous soil humic acids and fulvic acids. Discussed data include elemental and functional group composition, E4/E6 ratio, molecular weight distribution, isoelectrofocusing patterns, pyrolysis-gas chromatography-mass spectra, and infrared and Fourier transform infrared, nuclear magnetic resonance, electron spin resonance and fluorescence spectra. With respect to native soil humic and fulvic acids, humic and fulvic acid-like fractions in composted sewage sludges, municipal solid wastes, animal manures and plant wastes are generally characterized by (i) higher molecular heterogeneity; (ii) lower degree of aromaticity and structural polycondensation; (iii) higher aliphatic character; (iv) marked presence of incorporated proteinaceous materials, partially modified lignin moieties and polysaccharide-like structures; and (v) lower amounts of oxygen containing and acidic. especially carboxylic, functional groups. With composting, however, a loss of Ncontaining groups, alkyl chains and carbohydrates, and an increase in oxygenation, carboxyl groups and aromaticity generally occur in fulvic acids and. especially, humic acids. This is an important result which supports the validity of the compo sting process for organic wastes in approaching the quality of humuslike components to native soil humic substances.

ORGANIC MATTER IN DOUBLE-CROPPED LOWLAND RICE SOILS: CHEMICAL AND SPECTROSCOPIC PROPERTIES

Limited studies have been conducted to characterize soil organic matter (SOM) in intensively cropped lowland rice soils that support multiple annual rice crops. Previous nuclear magnetic resonance spectroscopy analysis suggested that increased frequency of soil submergence in long-term field experim

Tolerance and accumulation of heavy metals by wild plant species grown in contaminated soils in Apulia region, Southern Italy

Many sites inside a protected area in Apulia region (Italy) have been contaminated with heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) because an inadequate disposal of a variety of wastes with different sources of origin. As first measure in-situ phytoremediation techniques were evaluated using only the natural plants that grew wildly on the contaminated soils, in order to minimize the environmental impact on this fragile ecosystem. Total contents of metals in soils generally exceeded the maximum levels indicated in Italian and European regulations, specially Cr and Zn. Although the extractable fraction was element-dependent, the metal immobilization was enhanced by the components of soils. Maximum mobilizable fractions (%DTPA of total content) were 30% Cd, 0.01% Cr, 11.5% Cu, 4.1% Ni, 13.3% Pb and 13.8% Zn. The general trend of metal accumulation in plants was Zn > Cu > Cr > Pb > Ni > Cd and statically accumulation differences were found to largely depend on plant species. Thus different metal uptake and translocation strategies were suggested in the studied species: exclusion for Stipa austroitalica and Dasypyrum villosum, whereas tolerance mechanisms for Carduus pycnocephalus, Silybum marianum and Sinapis arvensis. The metal contents in above ground parts of these species were within the values of normal in plants and below phytotoxic levels, thus faraway from phytoextraction applicability. These species can be considered as metal excluder or tolerant plants with ability of growing in soils with a wide range of heavy metal concentrations, mainly immobilized by soil conditions. Thus they accomplished the criteria to be considered for phytostabilization technique in these contaminated sites.

ADSORPTION OF ALACHLOR BY HUMIC ACIDS FROM SEWAGE SLUDGE AND AMENDED AND NON-AMENDED SOILS

Organic matter content is ascertained to be the major factor for alachlor adsorption in soils. Limited knowledge exists, however, as to the effects of structural and chemical properties of soil organic matter on the mechanisms and extent of alachlor adsorption. The binding mechanisms and adsorption isotherms for alachlor have been measured onto three humic acids (HA) originating from a municipal sewage sludge, a sludge-amended soil, and a control soil. Spectroscopic techniques, including Fourier-transform infrared, fluorescence and electron spin resonance analyses, and high-pressure liquid chromatography have been used. The magnitude of alachlor adsorption and the type of binding mechanism involved depended on the nature and chemical properties of the HA. Soil HA exhibited linear isotherms and higher alachlor adsorption at low concentration, whereas sludge humic acid featured an S-shaped isotherm and increasing adsorption at higher alachlor concentration. Multifunctional hydrogen bonds and charge-transfer bonds were preferentially involved in the adsorption of alachlor at low concentration, especially onto well humidified, highly aromatic soil humic acids rich in O-containing groups. Hydrophobic bonding appeared to predominate at higher alachlor concentration, especially onto low-humified, highly aliphatic sludge HA. A reliable quantitative evaluation of the extent of adsorption of alachlor to HA in the experimental range of concentration used could be provided by the use of both the Freundlich K-values and the distribution coefficients, Kd.

Comparative chemical and spectroscopic characterization of humic acids from sewage sludges and sludge-amended soils

The main objectives of the present work were to evaluate the compositional and functional differences between a sewage sludge humic acid (HA) and nonamended soil HA and to determine the effects of various sewage sludge amendments on the composition, structure, and chemical properties of HAs from uncultivated and cultivated soils. For this purpose, the HA fraction was isolated by conventional methods from a sewage sludge used as soil amendment, the nonamended soil, and soils amended with two rates of dewatered and liquid sludges, either in the presence or absence of barley. The HAs isolated were characterized comparatively for their compositional, structural, and chemical properties by use of elemental analysis and by Fourier Transform infrared (FT IR), fluorescence, and electron spin resonance spectroscopies. The sludge HA was predominantly aliphatic and, therefore, markedly different from the nonamended soil HA and was characterized by a low oxygenated functional group content, high contents of S- and N-containing groups and polysaccharide components, very low free radical concentration, high molecular heterogeneity, low ring polycondensation and polymerization, and low humification degree. The application of the dewatered sludge induced only limited modifications in the structural and chemical properties of HAs from amended soils, which were only partially affected by the amendment rate used. However, marked modifications of HAs did occur in soils amended with liquid sludge, especially at high rates. The absence or presence of barley cultivation did not show any measurable effect on the composition and properties of sludge-amended soil HAs.