Valeria D'Orazio

Humic acids in the first generation of EUROSOILS

Humic acids (HAs) were isolated from the first generation of the EUROSOILS, a reference set of five samples representing the most widespread soil units in the European Union (EU). The EUROSOIL (E)-HA were characterized for their compositional, structural, and functional properties by using chemical methods and spectroscopic techniques, including Fourier transform infrared (FT IR), nuclear magnetic resonance, fluorescence, and electron spin resonance. The E-HAs generally exhibit features typical of soil HAs of similar origin and nature, and differ in their composition, structure, and chemical properties on dependence on the parent soil type, vegetation cover, and land use. The E-HA from the Orthic Podzol under coniferous forest (E5-HA) exhibits the largest oxygen and acidic functional group contents, organic free radical concentration, aromatic polycondensation and humification degree, and the distinct presence of outer-sphere complexed Mn2+ ions. The E-HAs from the Dystric Cambisol under grassland/pasture (E3-HA) and the Orthic Luvisol cultivated for wheat (E4-HA) are generally characterized by a great content of nitrogen-containing and methoxyl groups and polysaccharide structures, small contents of acidic functional groups and free radicals, relatively small aromaticity and humification degree, and the presence of both inner-sphere complexed Cu2+ ions and outer-sphere complexed Mn2+ ions. The E-HAs from the Vertic Cambisol under grassland/meadow (E1-HA) and the Rendzina under broad-leaved tree cover (E2-HA) are characterized by properties that are generally intermediate between those of E5-HA and E3- and E4-HAs, being E1-HA more similar to E5-HA and E2-HA to E3- and E4-HAs. The differences in chemical and physicochemical properties of these E-HAs are expected to affect differently their reactivity toward soil organic and inorganic contaminants.

Characterization of solid and aqueous phases of a peat bog profile using molecular fluorescence spectroscopy, ESR and FT-IR, and comparison with physical properties

Abstract A peat core (10×10×100 cm) was removed from Etang de la Gruere, an ombrotrophic peat bog in the Jura Mountains of Switzerland. The core was sliced into 3 cm sections and the samples characterized with respect to ash content, bulk density, moisture content, and concentrations of C and H. Solid peat residues were freeze-dried, milled very finely and analyzed using Fourier transform infrared (FT-IR) and electron spin resonance (ESR) spectroscopy. Pore waters expressed from the peat slices were collected, filtered (0.2 μm membrane filters) and analyzed using fluorescence emission, excitation and synchronous-scan spectroscopy, in addition to pH. Taken together, the physical properties of the core and the ESR measurements of solid peats appear to record the variation in humification of refractory organic matter (peat). The fluorescence and FT-IR data, on the other hand, appear to characterize the extent of recent decomposition of labile organic matter. In fact, these data indicate the presence of two distinct zones in the bog: (i) the acrotelm, or zone of active decay, which may be oxygenated, depending on the season and the depth to the water table, and (ii) the catotelm which is always anoxic, and where organic matter decomposition rates are negligible.

Nature and origin of organic matter in carbonates from speleothems, marine cements and coral skeletons

Organic matter in speleothem calcite, marine carbonate cements and aragonitic coral skeletons was studied to determine its location, molecular structure, functionality and effect on mineral growth. SEM analyses showed that inorganically precipitated carbonates incorporate, during growth, adsorbed organic matter between submicroscopic subunits of the crystals whereas biologically secreted carbonates incorporate biogenic tissue between the crystals. Molecular fluorescence spectroscopy indicated that low molecular weight fulvic acids are the most important constituents of the organic matter. The fulvic acids are probably derived from soils (speleothem calcite), dissolved organic matter (marine carbonates) and biological decay products (aragonitic coral skeleton).

Characteristics of humic acids of some Venezuelan soils

Humic acids (HAs) extracted from the surface horizons of some Venezuelan soils were characterized by elemental and functional group analyses and visible, Fourier transform infrared (FT-IR), fluorescence and electron spin resonance (ESR) spectroscopies. The elementary composition of Venezuelan HAs was generally similar to that of HAs of temperate soils but carbon content was lower and oxygen content was higher. The HA from Entisol under natural palm savannah showed the highest acidity, whereas the lowest content of acidic functional groups was exhibited by the HA from Vertisol under flooded savannah. Both HAs from savannah soils were characterized by a pronounced aliphatic character and strong fluorescence intensity. The HAs originated from cultivated Inceptisol and Alfisol were characterized by fluorescence spectra indicating the presence of highly condensed, conjugated and substituted aromatic rings, and contained high concentration of free radicals. The ESR spectra also showed differences related to the vegetation cover of the soils. A high proportion of iron was present in the HA from the Amazonas Spodosol, which also showed a pronounced aliphaticity and low concentration of organic free radicals.

Adsorption mechanisms of s-triazine and bipyridylium herbicides on humic acids from hop field soils

Abstract Humic acids (HAs) have been isolated according to conventional extraction, fractionation and purification methods from soil samples collected in a hop field in Bavaria (Germany), under the plant rows (HAa), between the rows (HAb) and in an adjacent unexploited soil location (control, HAc). Interaction products between each HA sample and each of the herbicides atrazine, simazine, diquat and paraquat were laboratory prepared in aqueous medium and under ambient conditions, according to a previously tested procedure. Both the original, unreacted HAs and their herbicide interaction products were analyzed for elemental and functional group composition, and by Fourier-transform infrared (FT-IR), fluorescence and electron-spin resonance (ESR) spectroscopies. Minor differences are measured for properties of the three HAs studied, thus suggesting that the hop cultivation has affected only secondarily the compositional and functional chemical properties of HA in these soils. The three HAs also exhibit a similar behaviour in the interaction with each herbicide examined. The water-stable association between the N-rich herbicide molecules and HA is firstly supported by the N% increase measured in all the interaction products. FT-IR and ESR spectroscopic results suggest that multiple binding mechanisms may occur in the adsorption process with the formation of (a) ionic bonds between carboxylate groups of HA and protonated heterocyclic and amine N-atoms of the triazine or positively charged N-atoms of the bipyridylium compound; (b) charge-transfer (π-π) bonds between the electron-donor triazine ring or the electron-acceptor deactivated bipyridylium ring and complementary electron-donor or -acceptor structural moieties of HAs; (c) hydrogen bonds within suitable complementary groups of the HA and the triazine. Fluorescence data suggest that fluorophore groups may also be involved to various extent in the interaction mechanisms.

Fulvic acid–like organic compounds control nucleation of marine calcite under suboxic conditions

Intracrystalline organic compounds, enclosed within in situ–precipitated marine microcrystalline calcite (automicrite), might represent either an inclusion or the catalyst of such precipitation. We use evidence from a Lower Cretaceous deep-water carbonate mound to show (1) the original source, (2) the degree of condensation, (3) the redox conditions involved, and (4) the catalytic role of natural organic matter for the precipitation of automicrite. Fluorescence spectrometry of the intracrystalline organic fraction extracted from these carbonates identifies a marine fulvic acid–like organic compound with a low degree of polycondensation. This finding points to a temporal correlation of the initial stage of geopolymer formation with the precipitation of automicrite. Furthermore, the rare earth element (REE) distribution patterns in the mineral show a consistent positive Ce anomaly, suggesting an episode of reductive dissolution of iron-manganese oxyhydroxides during automicrite formation. In general, a relative enrichment of middle-weight REEs is observed, resulting in a convex distribution pattern typical for, e.g., phosphate concretions or humic acid material. By merging the results of spectrometry and REE geochemistry we thus conclude that the marine calcite precipitation was catalyzed by marine fulvic acid–like compounds during the early stages of humification under suboxic conditions. This indicates that humification, driven by the presence of a benthic biomass, is more important for calcite authigenesis than any site-specific microbial metabolism. The Neoproterozoic rise of carbonate mounds supports this hypothesis; there is molecular evidence for early metazoan divergence then, but not for a major evolutionary episode of microorganisms.

Chemical and Physicochemical Characterization Of Humic Acid-Like Materials From Composts

Humic acid (HA)-like materials were extracted from composts prepared from domestic organic wastes (HADu), sawdust (HASc), used coffee (HACf), and farmyard manure (HAFm). The HA-like fractions were characterized for elemental composition, E4/E6 ratio, and structural and functional properties by Fourier-transform infrared (FT IR), fluorescence and electron spin resonance (ESR) spectroscopies. Elemental composition and E4/E6 ratios were similar to those characteristic of young humic matter. Nitrogen content was related to that in the initial waste being high for HADu and HACf and low for HAFm and HASc. FTIR spectra of HADu and HACf were dominated by absorptions of N-containing groups (1650 and 1540 cm−1), whereas those of HASc and HAFm were dominated by bands of aromatic structures (1595, 1511, 1418 and 1125 cm−1). Data from ESR and fluorescence spectroscopy were similar for all the HA-like fractions analyzed. The low free radical concentrations and type of fluorescence patterns suggested simple structural components, low degree of aromatic polycondensation and low level of conjugated chromophores. In conclusion, HA-like substances obtained from composted materials exhibited an elemental composition related to the nature of the initial wastes and general characteristics close to those of soil fulvic acids rather than soil HAs.

Adsorption of chlordane onto humic acids from soils and pig slurry

Adsorption of trans- and cis-chlordane onto humic acids (HAs) isolated from soils and a pig slurry was measured using a batch equilibrium method followed by gas chromatographic analysis. Experimental data for adsorption of either chlordane isomers onto any HA examined were best fitted by a Langmuir-type isotherm. The adsorption capacity of pig slurry HA for chlordane was slightly lower than that of soil HAs. FT-IR, fluorescence and ESR spectroscopic data excluded the formation of strong chemical bonds between chlordane and HA, thus suggesting that chlordane can be adsorbed to HA only by physical (hydrophobic) mechanisms, involving to some extent fluorophore groups of the HAs.

Triallate adsorption onto humic acids of different origin and nature

Humic acids (HAs) isolated from two different soils sampled at two different depths and from a pig slurry used as soil amendment, and their interaction products with the herbicide triallate were characterized by elemental and functional group analyses and Fourier transform infrared (FT-IR), electron spin resonance (ESR) and fluorescence spectroscopy in the emission, excitation and synchronous scan modes. The pig slurry HA exhibited a greater aliphatic character, higher presence of proteinaceous and polysaccharide constituents, lower acidic functional group content, and lower aromatic polycondensation and humification degrees than soil HAs. Only small differences occurred between HAs from the two soil types and the two sampling depths of each soil. Adsorption of triallate onto HAs, measured using a slurry-type method combined with high-pressure liquid chromatography (HPLC), could be described in all cases by linear isotherms. The extent of adsorption of triallate onto pig slurry HA was between two and four orders of magnitude higher than that onto soil HAs. The types of binding mechanisms appeared to be related to the compositional, structural and functional properties of the HA. Hydrophobic bonds possibly prevailed in the interaction of triallate with pig slurry HA, whereas adsorption of triallate onto soil HAs possibly involved charge-transfer and ionic bonds, with the participation of fluorophore groups of the HA macromolecules.

Methylated arsenic species throughout a 4-m deep core from a free-floating peat island

Arsenic (As) occurs in soils mostly in inorganic forms, whereas the organic forms usually occur only in trace amounts. Peatlands are waterlogged, generally anoxic, organic soils representing the first step in coal formation; the contribution of organic vs. inorganic As species in this environment has received little research attention. Here, 57 peat samples collected throughout a 4-m deep, free-floating mire were analysed for total As and for its organic species, including dimethylarsinic acid (DMA), methylarsonic acid (MA), trimethylarsine oxide (TMAO) and arsenobetaine (AB), by HPLC-ICPMS. Aqueous trifluoroacetic acid was used as extractant, resulting in an average extraction efficiency of almost 80%. Total As concentration throughout the profile ranged between 0.2 and 9.8mg/kgpeat (mean: 1.4±1.2mg/kgpeat). Organic As species (DMA+MA+TMAO+AB) accounted, on average, for 28±10% of total As (range: 6-51%), and for 37±13% of the extracted As (range: 7-64%). The relative abundance of organoarsenicals generally followed the order DMA>TMAO~MA≫AB. A positive correlation (p<0.001) was found among all organic As compounds, whereas their concentrations were negatively correlated with total sulfur content. The submerged zone (bottom 300cm) showed average and maximum concentrations of organoarsenic compounds that were almost twice those found in the top 100cm. This study shows that significant proportions of methylated As species occur even in peat samples characterized by low total As concentration (mostly <2mg/kg). Finally, this work provides the first evidence of organoarsenic species in free-floating mires, i.e., a globally distributed but scarcely investigated ecosystem.