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In order to investigate the long-term fate of the herbicide chloridazon and its polar metabolites desphenyl-chloridazon and methyl-desphenyl-chloridazon, a lysimeter experiment was conducted. The plant protection product Pyramin WG, which contains chloridazon, was applied to a weighable, monolithic lysimeter and a backfilled, gravitation lysimeter. Leachate, soil and maize samples were analyzed, and the data from the monolithic lysimeter was used to simulate the transport through the soil profile with the pesticide leaching model Pesticide Emission Assessment at Regional and Local scales (PEARL). Chloridazon rapidly degraded to desphenyl-chloridazon and methyl-desphenyl-chloridazon. In leachate, chloridazon was therefore detected at concentrations up to 3.5 μg L−1, whereas the metabolites desphenyl-chloridazon and methyl-desphenyl-chloridazon were present for more than 2 years at higher concentrations up to 24 and 6.1 μg L−1. The concentrations of chloridazon in soil decreased significantly with depth and time, whereas both metabolites increased up to 370 and 16 μg kg−1. The high concentrations, even 916 days after the application, clearly indicate a continuous downward migration and degradation in soil. In maize, chloridazon and purely the metabolite desphenyl-chloridazon were detected in leaves and stems. Desphenyl-chloridazon was additionally found in grains. It was noted that the design and setup of the two lysimeters lead to significant variations in terms of transformation rate, soil retention time and accumulation by plants. A comparison of the simulated results and the leaching rates measured from the monolithic lysimeter yielded adequate results for the metabolites, but rather poor correlation for chloridazon. The results obtained suggest persistence and high dispersion of chloridazon, and especially its metabolites, in leachate and soil. In maize, the migration in leaves and stems and the accumulation by grains might be relevant in terms of food security.

An overview of the variety of processes induced by the aluminum cation interacting with carboxyl and carboxylate groups is given by means of quantum chemical density functional theory (DFT) calculations. Different hydration states of Al3 + ranging from the hexaaquo complex down to the unhydrated cation and direct/indirect bonding with the polar groups are considered. The calculations reflect the amphoteric character of the hydrated aluminum complex showing in most cases its acidic character via proton transfer from the water molecules of the hydration shell to the carboxylate group, but in some cases also deprotonation of the carboxyl group. Several additional processes are observed such as interconversion of bidentate and monodentate bonding by the carboxyl/carboxylate groups and strong hydrogen bonding between proton transfer partners. Comparison with analogous previous investigations on cation bridges induced by calcium and sodium shows the pronounced activity of the triply charged aluminum cation. The importance of the strong polarizing and bridging power of the aluminum cation for soil organic matter with low exchange capacities and a low concentration of charged groups is discussed.

A simple and inexpensive liquid chromatography-tandem mass spectrometric method for the determination of anthelmintics in alfalfa plants (Medicago sativa L.) was developed and validated. Anthelmintics in plant leaves and stems (green chops) were extracted with methanol/acetonitrile (7:3, v/v) followed by a concentration and clean-up step using solid-phase extraction (Strata-X, 500 mg, 6 ml cartridge). After drying with nitrogen gas, the adsorbed analytes were eluted with methanol/acetonitrile (50:50, v/v) mixture followed by 100% acetonitrile. Chromatographic separation was achieved on an Atlantis T-3 (2.1 × 100 mm × 3 µm) analytical column with a Phenomenex guard cartridge (C8, 4 × 3 mm) attached to a Waters triple quadrupole mass spectrometer operated in positive electrospray ionisation mode with selected reaction monitoring. Samples were analysed using gradient elution at a flow rate of 0.35 ml min⁻¹. The mobile phase consisted of a 10 mM ammonium formate solution in (A) water/acetonitrile (90:10, v/v) and (B) methanol/acetonitrile (50:50, v/v). The method was validated for levamisole, fenbendazole, fenbendazole sulphoxide and fenbendazole sulphone at 10, 20 and 40 µg kg⁻¹ and for eprinomectin at 20, 40 and 80 µg kg⁻¹. Limits of quantification (LOQ) were 10 µg kg⁻¹ for all analytes except eprinomectin, which had an LOQ of 20 µg kg⁻¹. The overall mean recovery in green plants was between 74.2% and 81.4% with repeatabilities ranging from 2.2% to 19.1% and reproducibilities in the range 3.8-8.7%. The validated method was applied to plant samples in a study on the behaviour of anthelmintic drugs in a soil, plant and water system.

Knowledge about the stabilization of organic matter input to soil is essential for understanding the influence of different agricultural practices on turnover characteristics in agricultural soil systems. In this study, soil samples from a long-term field experiment were separated into silt- and clay-sized particles. In 1967, 14C labeled farmyard manure was applied to three different cropping systems: crop rotation, monoculture and permanent bare fallow. Humic acids (HAs) were extracted from silt- and clay-sized fractions and characterized using photometry, mid-infrared and fluorescence spectroscopy. Remaining 14C was determined in size fractions as well as in their extracted HAs. Yields of carbon and remaining 14C in HAs from silt-sized particles and Corg in clay-sized particles decreased significantly in the order: crop rotation > monoculture ≫ bare fallow. Thus, crop rotation not only had the largest overall C-pool in the experiment, but it also best stabilized the added manure. Mid-infrared spectroscopy could distinguish between HAs from different particle size soil fractions. With spectroscopic methods significant differences between the cropping systems were detectable in fewer cases compared to quantitative results of HAs (yields, 14C, Corg and Nt). The trends, however, pointed towards increased humification of HAs from bare fallow systems compared to crop rotation and monoculture as well as of HAs from clay-sized particles compared to silt-sized particles. Our study clearly shows that the largest differences were observed between bare fallow on one hand and monoculture and crop rotation on the other., Highlights ► All cropping systems significantly influenced the Corg stocks in bulk soils. ► There were differences between the turnover of Corg pools in the cropping systems. ► More humified HAs were found in bare fallow vs. monoculture and crop rotation. ► Carbon stabilization was: crop rotation > monoculture ≫ bare fallow. ► Crop rotation had the largest C-pool and stabilized the farmyard manure best.

Molecular dynamics simulations have been performed by means of density functional theory with tight binding (DFTB) in order to describe the structure and the energetic stability of water bridges in humic substances (HS) model. This model is constructed from two parallel aliphatic chains geometrically restrained on one end and terminated with a carboxyl group on the other to supply the structural pattern for supramolecular contact of two HS chains through hydrogen bonds. Molecular dynamics simulations were used to analyze the interactions of the carboxylic groups with a variable number of water molecules up to 14 representing domains of micro hydration states of polar centers in humic acids. For the present geometrical arrangements of the model five water molecules form a stable bridge between the two carboxylic groups located at each aliphatic chain. The effect of environment through three solvents of different polarities (n-hexane, acetonitrile and water) was investigated. Distribution profiles of oxygen atoms of carboxyl and chain water molecules show that the environmental effect of the solvent with moderate polarity (acetonitrile) is most pronounced in exerting an ordering effect on the water bridge. Energy profiles for incremental addition of water molecules and hydrogen bond analysis demonstrate the remarkable stability of the five water complex as compared to all other models investigated in both gas phase and in acetonitrile. These findings correlate nicely with experimentally observed antiplasticizing effects of water bridges in organic matrices.

The stabilizing effect of water molecule bridges on polar regions in humic substances (HSs) has been investigated by means of molecular dynamics (MD) simulations. The purpose of these investigations was to show the effect of water molecular bridges (WAMB) for cross-linking distant locations of hydrophilic groups. For this purpose, a tetramer of undecanoid fatty acids connected to a network of water molecules has been constructed, which serve as a model for spatially fixed aliphatic chains in HSs terminated by a polar (carboxyl) group. The effect of environmental polarity has been investigated by using solvents of low and medium polarity in force-field MD. A nonpolar environment simulated by n-hexane was chosen to mimic the stability of WAMB in a hydrophilic hotspot surrounded by a nonpolar environment, while the more polar acetonitrile environment was chosen to simulate a more even distribution of polarity around the carboxylic groups and the water molecules. The dynamics simulations show that the rigidity of the oligomer chains is significantly enhanced as soon as the water cluster is large enough to comprise all four carboxyl groups. Increasing the temperature leads to evaporization processes which destabilize the rigidity of the tetramer-water cluster. Embedding it into the nonpolar environment introduces a pronounced cage effect which significantly impedes removal of water molecules from the cluster region. On the other hand, a polar environment facilitates their diffusion from the polar region. One important consequence of these simulations is that although the local water network is the stabilizing factor for the organic matter matrix, the degree of stabilization is additionally affected by the presence of nonpolar surroundings.

Structural and energetic properties of cation bridges in soil supramolecular aggregates were studied by means of a model system in which two carboxylate groups connected to aliphatic oligomer chains were bound by Ca 2þ and Na þ , respectively. Wetting/drying conditions in soils because of environmental changes were modeled by different content of water molecules forming the solvation shell of the cations. Density functional theory calculations were performed for unpolar (isolated structures) and polar (water as continuum polarization model) environment. Direct and indirect complexes of the cations with the carboxylate groups were found to have different stability. Formation of indirect complexes was computed by means of potential energy curves for the approach of bare (reference set) and solvated cations to the dimer chain containing the carboxylate groups. Characteristic difference on drying (stepwise reduction of water molecules) between Ca 2þ and Na þ complexes were observed affecting the predicted mobility of monovalent and divalent cations in soils. V C 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 1531-1542, 2011

Prediction of the sorption behavior of environmental pollutants is of utmost importance within the framework of risk assessments. In this work two approaches are presented with the aim to describe sorption of aromatic substances to geosorbents. First, analytical solutions of kinetic models were fitted to experimental data of batch sorption experiments with aniline and 1-naphthylamine onto animal manure-treated soil and the soil mineral montmorillonite. The models, accounting for equilibrium and nonequilibrium sorption coupled to transformation and/or irreversible sorption processes, could well reproduce the concentration course of the sorbates. Results suggest that the amounts transformed/degraded and irreversibly bound were higher for the soil than for the clay mineral. In the second part, quantum chemical calculations were performed on aniline and 1-naphthylamine interacting with acetic acid, acetamide, imidazole, and phenol as models of functional groups present in humic substances. Molecular modeling showed that formation of hydrogen bonds is the dominating binding mechanism in all modeled complexes, which are energetically very similar between aniline and 1-naphthylamine.

Molecular simulations using density functional theory (DFT/PBE and DFT/tight-binding (DFTB)) have been performed to study wetting processes of model nanopore segments in humic substances (HS). A complex of two poly(acrylic acid) trimers (trimer complex, TC) arranged in parallel alignment was used to provide the structural example for supramolecular contact of two HS chains by means of hydrogen bonds. Their interaction with a local network of water molecules represented the influence of wet spots. Displaced TC structures were constructed by horizontal motion of the chains relative to each other in order to study the capacity of the water cluster to hold the two chains together even though their distance is too far for direct hydrogen bonding between the carboxyl groups. Geometry optimizations and molecular dynamics simulations were used to investigate the hydrogen-bonded structures formed and to compute their energetic stabilities. At shorter distances between the two oligomer chains an outer solvation was...

Density functional theory is used to compute the effect of protonation, deprotonation, and dehydroxylation of different reactive sites of a goethite surface modeled as a cluster containing six iron atoms constructed from a slab model of the (1 1 0) goethite surface. Solvent effects were treated at two different levels: (i) by inclusion of up to six water molecules explicitly into the quantum chemical calculation and (ii) by using additionally a continuum solvation model for the long-range interactions. Systematic studies were made in order to test the limit of the fully hydrated cluster surfaces by a monomolecular water layer. The main finding is that from the three different types of surface hydroxyl groups (hydroxo, μ-hydroxo, and μ3-hydroxo), the hydroxo group is most active for protonation whereas μ- and μ3-hydroxo sites undergo deprotonation more easily. Proton affinity constants (pKa values) were computed from appropriate protonation/deprotonation reactions for all sites investigated and compared to results obtained from the multisite complexation model (MUSIC). The approach used was validated for the consecutive deprotonation reactions of the [Fe(H2O)6]3+ complex in solution and good agreement between calculated and experimental pKa values was found. The computed pKa for all sites of the modeled goethite surface were used in the prediction of the pristine point of zero charge, pHPPZN. The obtained value of 9.1 fits well with published experimental values of 7.0–9.5.

Hydrogen bonded and cation bridged complexation of poly(acrylic acid) oligomers, representing a model compound for humic acids, with acetic acid and the herbicide (4-chloro-2-methylphenoxy) acetic acid (MCPA) have been studied by means of density functional theory. Solvation effects were computed by means of a combination of microsolvation (explicit insertion of water molecules) and global solvation (polarizable continuum approach). The stability of hydrogen bonded complexes in solution is characterized by a strong competition between solute and solvent molecules. The cation bridged complexes of the negatively charged (deprotonated) ligands were found to be strongly favored explaining the capability of humic acids to fixate anionic species from soil solutions and the ability to form cross-linking structures within the humic acid macromolecules.

A 13 C natural abundance experiment including GC-c-IRMS analysis of phospholipid fatty acids (PLFAs) was conducted to assess the temporal dynamics of the soil microbial community and carbon incorporation during the mineralization of plant residues under the impact of heavy metals and acid rain. Maize straw was incorporated into (i) control soil, (ii) soil irrigated with acid rain, (iii) soil amended with heavy metal-polluted filter dust and (iv) soil with both, heavy metal and acid rain treatment, over a period of 74 weeks. The mineralization of maize straw carbon was significantly reduced by heavy metal impact. Reduced mineralization rate of the added carbon likely resulted from a reduction of the microbial biomass due to heavy metal stress, while the efficiency of 13 C incorporation into microbial PLFAs was hardly affected. Since acid rain did not significantly change soil pH, little impact on soil microorganisms and mineralization rate was found. Temporal dynamics of labelling of microbial PLFAs were different between bacterial and fungal PLFA biomarkers. Utilization of maize straw by bacterial PLFAs peaked immediately after the application (2 weeks), while labelling of the fungal biomarker 18:2 ω 6,9 was most pronounced 5 weeks after the application. In general, 13 C labelling of microbial PLFAs was closely linked to the amounts of maize carbon present in the soil. The distinct higher labelling of microbial PLFAs in the heavy metal-polluted soils 74 weeks after application indicated a large fraction of available maize straw carbon still present in the soil.

Concentrations of the stable isotope oxygen-18 in precipitation samples have been modeled by geographical and meteorological features of the sampling stations. Precipitation samples are from 30 locations in Austria; oxygen-18 concentrations have been determined by isotope ratio mass spectrometry; each location has been characterized by three geographical features (longitude, latitude and elevation), and five meteorological features (relative humidity, fresh snow, wind speed, precipitation, and air temperature). All data are monthly means for the summer period April to September computed as long term averages for a time period of typically 20 years. The basic feature set has been augmented by 49 nonlinear transformations of the original features giving a data set with 57 features. The number of objects was 180 corresponding to the 30 sampling stations times six months. Different methods of feature selection (correlation coefficient, backward elimination, all subsets regression, and genetic algorithm) have been applied, and for the 20 best feature subsets the prediction errors of PLS models have been estimated from test sets. The final best model for a prediction of oxygen-18 concentrations contains ten features selected by a genetic algorithm. This model has been applied to the computation of a geographical oxygen-18 distribution map from Austria based on computed oxygen-18 values for 200 locations, and experimental values of 30 locations.

Summary The present study investigated the impact of long-term soil management on the metal retention capacity of soil. We examined the sorption behaviour of Cu, Cd and Zn in soils and in the various particle-size fractions of these soils, which had been amended with farmyard manure, mineral fertilizers or were fallow for 38 years in a long-term field experiment. The soils investigated contained different amounts and origins of organic matter and differed in soil pH, but the mineral phase showed less response to the different soil managements. Batch adsorption and desorption experiments as well as a sequential fractionation schema, which defines seven geochemical fractions, were used to investigate the retention properties of soil. Sequential extraction was conducted with original as well as with metal-spiked soils. Results showed that amounts of Cu, Cd and Zn retained differed by a factor of more than 3 among the treatments in the longterm field experiment, when a massive concentration of metal was added to soil. An increased sorption on

Summary This study provides insight into the relevance of the chemical functional groups of soil organic matter (aromatic, paraffinic, O-alkyl, carboxyl and carbonyl carbon), as determined by CPMAS 13C NMR, on adsorption processes. Batch adsorption experiments with eight naphthalene derivatives were conducted with soils from a long-term field experiment and model sorbents. Although the adsorption of some derivatives was mainly affected by the paraffinic organic carbon content in soil, the relation between the C-distribution and adsorption was complex. This casts doubt on the use of such NMR data to estimate sorption behaviour. Additionally, sorption experiments were performed with six model sorbents representing typical soil components. Considerable adsorption of naphthalene derivatives was observed for montmorillonite and lignin; the smallest values were for kaolinite and cellulose. A quantum chemical approach was used to calculate a local polarity parameter as a molecular property of the naphthalene derivatives. This parameter was correlated with the logarithm of the adsorption coefficients, logKd. Here, clear trends were observed for three of the model sorbents (kaolinite, montmorillonite and lignin).

Summary The determination of the structure of humic substances from soils and natural waters is an intriguing problem in soil science. Humic substances consist of molecules covering a broad distribution of molecular size and involving different functional groups. Taking this into account, we have chosen smaller model systems with functional groups typically present in humic substances. We investigated theoretically, by quantum chemical calculations, the environmental effects on the complexes formed from the interaction of 2,4-dichlorophenoxyacetic acid and its anion with acetaldehyde, methanol, methylamine, protonated methylamine, acetic acid and water. The important case of a cation bridge mechanism, with Ca2+ as the bridging cation, is also included into the set of model reactions. It is found that this cation bridge belongs to one of the most stable mechanisms of fixation of organic compounds in soils. According to our calculations the hydroxyl group forms the most stable complexes with 2,4-D in a polar solvent environment.

Aim of our study was the development of the methodological basis for the characterization of humic fractions of a long-term field experiment. Humic acids (HAs) were extracted from three layers of a nontilled soil using three different extractants (1 M NaOH, 0.1 M Na4P2O7, 1 M Na2CO3), and the humin fraction was enriched. NaOH as extractant for FTIR analysis of humic substances yields higher resolved IR spectra, especially in the important regions of stretching vibrations including aromatic and aliphatic groups and in the fingerprint area including amides, aliphats, and aromats than the other extractants. The NaOH extraction has lower extraction yields as compared to Na4P2O7 and Na2CO3 and represents a different part of the soil organic matter (SOM). This is reflected by lower C : N ratios and higher E4 : E6 and fulvic acid–to–humic acid ratios as compared to the other extractants. The FTIR band areas of HA fraction obtained by NaOH showed an increase of the aromatic and carbonyl groups and a decrease of amide groups with increasing soil depth. Aliphatic groups showed contradicting results: The bands of the stretching vibrations increased, and the band of the bending vibrations decreased. We assume that band interactions in the bending vibrations were responsible for that phenomenon under the assumption of an increase of aliphatic groups with increasing soil depth. The IR bands of the enriched humin fraction showed a decreasing trend in case of both aliphatic bands deriving from stretching vibrations and an increase of aromatic characteristics with depth. Our study led to the conclusion that HA fractions obtained by 1 M NaOH represent a small and dynamic fraction indicated by the measured yields in combination with values of Nt, C : N, E4 : E6 ratios, and ratios of fulvic acids (FA) to HA. The humin fraction has a high contribution to the total organic C and represents a more stabilized fraction of SOM which still shows changes in its aromatic and aliphatic characteristics with soil depth.

Summary Sorption of the anionic form of the pesticide 2,4–D (2,4–dichlorophenoxyacetic acid) on the surface of the clay mineral montmorillonite was investigated using a short-time ab initio molecular dynamics (MD) simulation at room temperature. Three different situations were modelled: sorption on a dry surface, on a hydrated surface and an intercalation between montmorillonite layers. In all three cases, the calcium cation compensates the excess negative charge of the montmorillonite layer and the negative charge of the 2,4–D anion. It was found that in all models with direct contact of the Ca 2þ cation with the montmorillonite layer, the most stable position of Ca 2þ is above the ditrigonal hole of the mineral layer. While in the case of a dry surface very stable bidentate binding is created between the 2,4–D anion and the Ca 2þ cation, the formation of the monodentate complexes is preferred in all models that include water molecules. Hydrogen bonds formed between water molecules and the 2,4–D anion make a considerable contribution to the formation of the monodentate complexes. Tetrahedral substitutions in the montmorillonite layer have a significant effect on the formation of the complexes of any type. However, the MD simulations did not support the role of Ca 2þ as a cation bridge in the adsorption mechanism. Calculations showed that hydrated 2,4–D��� Ca 2þ complexes are thermodynamically more stable than complexes in which the Ca 2þ cation acts as a bridge to the surface. On the other hand, it is possible that phyllosilicates with a greater concentration of isomorphic substitutions (e.g. mica) will be able to form stable surface complexes with a cation bridge mechanism.

An ab initio theoretical approach has been used to calculate optimized geometries and the relative energies of various compositional arrangements in structures of dioctahedral smectites based on models consisting of two unit-cells. These calculations indicate that the energy differences between structures having vacancies in sites with cis- or trans-OH coordination are small and that their relative energies vary with the chemical nature of the substitutions. For example, a cis-OH coordination for the vacancy was the most stable when the interlayer charge originated from substitution of Al for Si in the tetrahedral sheet, whereas the trans-coordination was the more stable for most cases of substitution in the octahedral sheet, an exception being Fe(II) for Al where the cis-OH coordination was favored. It seems likely, therefore, that long-range structural disorder will be a common phenomenon in natural phyllosilicate specimens.

Summary The present work investigates the impact of site management on the retention of organic compounds in soil in a long-term field experiment and focuses on the role of particle size fractions. Specifically, we studied the influence of long-term farming practices on the soil’s ability to adsorb five hydrophobic organic compounds (HOCs), specifically naphthalene derivatives (naphthalene, 1-naphthol, 1-naphthylamine, 1-hydroxy-2-naphthoic acid, 1,4-naphthoquinone). We examined the sorption on soil and its particle-size fractions with varying amounts and origins of organic matter in soil amended with farmyard manure and mineral fertilizers over more than 40 years. The soil organic matter had no significant impact on the sorption behaviour of the HOCs. Adsorption on the clay and silt fraction provided a deeper insight into the mechanisms and indicates a strong affinity with adsorption sites of the mineral phase. Naphthalene derivatives with hydrogen atoms in their functional groups adsorbed more strongly than other compounds on to soils containing smaller amounts of organic carbon. Desorption experiments with five organic extractants showed partitioning models for HOCs between extractant and soil surface. Only in experiments with the most polar extractant, formamide, did we observe an influence of the compound’s functional groups on the desorption mechanisms. Column experiments with a HPLC-system and on-line UV-detection proved to be a satisfactory alternative to batch experiments. This approach should enable investigations of adsorption with larger numbers of compounds and soils at the same time.

In the last decades, the 18O/16O signature of meteoric water became a key tracer intensively used both in hydrology and in paleoclimatology, based primarily on the correlation of the 18O/16O ratio in precipitation with temperature. This correlation with temperature is generally well understood as a result of Rayleigh processes of atmospheric vapour during the formation of precipitation. The resulting isotopic signals in precipitation are also transferred into the groundwater body since the isotopic composition of groundwater is determined by the precipitation infiltrating into the ground. However, the whole variability of the 18O/16O ratio especially in temporal data series of precipitation and groundwater can not be explained with temperature alone. Here we show that certain interactions between different climate induced changes in local parameters prevailing during precipitation events are able to explain a significant part of the observed deviation. These effects are superimposed by an overall isotopic pattern representing the large scale climate input primarily based on temperature. The intense variability of isotopes due to the particular topography of Austria recorded over a time period of 40 years provides an unique possibility to uncover this hidden information contributed by relative humidity and type of precipitation. Since there is a growing need to predict the variation of climate together with its associated potential hazards like floods and dry periods the results of this work are contributing to a better overall understanding of the complex interaction of climate with the corresponding water cycle.

Humic substances are ubiquitous in the environment and have manifold functions. While their composition is well known, information on the chemical structure and three-dimensional conformation is scarce. Here we describe the Vienna Soil-Organic-Matter Modeler, which is an online tool to generate condensed phase computer models of humic substances (http://somm.boku.ac.at). Many different models can be created that reflect the diversity in composition and conformations of the constituting molecules. To exemplify the modeler, 18 different models are generated based on two experimentally determined compositions, to explicitly study the effect of varying e.g. the amount of water molecules in the models or the pH. Molecular dynamics simulations were performed on the models, which were subsequently analyzed in terms of structure, interactions and dynamics, linking macroscopic observables to the microscopic composition of the systems. We are convinced that this new tool opens the way for a wide range of in silico studies on soil organic matter.

The interaction between the (110) goethite surface and water, acetic acid, acetate, 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4-dichlorophenoxyacetate (2,4-D-), and benzene was studied by means of quantum mechanical calculations based on density functional theory (DFT) using the B3LYP approach. Furthermore, Moller−Plesset calculations to second order using the resolution-of-identity approach (RI-MP2) were also performed for the goethite/benzene interaction. Structural and energetic features of the surface complexes were evaluated using cluster models for the goethite surface derived from a periodic slab surface. Our investigations showed that the (110) goethite surface formed by three types of the hydroxyl groups offers a variety of possibilities for hydrogen bond formation with appropriate polar adsorbents. Calculated interaction energies for the water molecule on different sites are on the order of ca. −20 kcal/mol, a number that is in line with the number and type of hydrogen bonds formed. Comparison o...

Sorption of heavy metals to organic matter and mineral soil constituents can hardly be separated experimentally. Here we studied the retention capacity of organic matter and minerals from soils in a long-term field experiment in which the organic carbon content had been altered, but the mineral phase had remained constant over time. The sorption of Cu, Cd and Zn showed a non-additive contribution of soil organic matter and minerals to the sorption capacity of soil. Sorption on organic matter exceeded mineral sorption from 6 to 13 times. This is the first time that sorption to soil organic matter is quantified in bulk soils.

We thank the Austrian Science Fund (Fonds zur FOrderung der wissenschaftlichen Forschung) for funding this bilateral project.

This study investigated the effect of different farming practices over long time periods on the sorption-desorption behavior of Cu, Cd, and Zn in soils. Various amendments in a long-term field experiment over 44 y altered the chemical and physical properties of the soil. Adsorption isotherms obtained from batch sorption experiments with Cu, Cd, and Zn were well described by Freundlich equations for adsorption and desorption. The data showed that Cu was adsorbed in high amounts, followed by Zn and Cd. In most treatments, Cd ions were more weakly sorbed than Cu or Zn. Generally, adsorption coefficients K F increased among the investigated farming practices in the following order: sewage sludge ≤ fallow < inorganic fertilizer without N ≈ green manure < peat < Ca(NO 3 ) 2 < animal manure < grassland/extensive pasture. The impact of different soil management on the sorption properties of agricultural soils for trace metals was quantified. Results demonstrated that the soil pH was the main factor controlling the behavior of heavy metals in soil altered through management. Furthermore, the constants K F and n of isotherms obtained from the experiments significantly correlated with the amount of solid and water-soluble organic carbon (WSOC) in the soils. Higher soil pH and higher contents of soil organic carbon led to higher adsorption. Carboxyl and carbonyl groups as well as WSOC significantly influenced the sorption behavior of heavy metals in soils with similar mineral soil constituents.

The present study evaluated the effect of fertilizer amendments (organic manure and mineral fertilizers), management practices (fallow and untilled vs. cropped and tilled) on changes of N in bulk soil and N associated with different particle-size fractions. The long-term field experiment was conducted since 1962 in Gumpenstein, Austria, on a Dystric Cambisol. The N content of the topsoils changed distinctively during 28 and 38 yr of treatments under both fallow and cropped management practices. Highest increase in total N content was found in animal-manure (liquid)-treated plots. The remaining ranking was: animal manure (solid) > cattle slurry > half cattle slurry + straw = PK = NPK. Quite short N-half-life values of around 2 yr were found for the cattle-slurry application, while animal manure exhibited longer N-half-lives of around 8 yr. Crop removal of N and mineralization losses in cropped plots obviously were higher than N losses from the bare soil plots lacking a plant cover to keep N in the system. This was confirmed by a consistent shift in the natural 15N abundances. Comparing the mean N contribution of particle-size fractions to the total N amounts revealed the following ranking after 28 and 38 yr of different treatments: silt > clay > fine sand > coarse sand, with small exceptions. Particle-size separates showed more significant responses to changes in the N dynamics of the system due to the various treatments than the bulk soil and can be regarded as the better indicators in this respect.

A long-term field experiment, conducted since 1962 in Gumpenstein (Austria) on a Dystric Cambisol, was used for the present investigation. We combined a physical fractionation procedure with the determination of natural abundance of 13C and FT-IR spectroscopy to study the influence of fertilizer amendments (organic manure and mineral fertilizers) and management practices (fallow vs. cropped) on changes in organic carbon (OC) associated with different particle-size fractions. The OC content in bulk soil decreased or was not affected by slurry+straw, PK, and NPK treatments in both fallow and cropped plots after 28 and 38 yr of treatment. However, OC in plots receiving organic manures increased depending on the quality of the organic manures applied. The ranking among the different treatments under both fallow and cropped plots was: animal manure (liquid) > animal manure (solid) > cattle slurry = slurry+straw = PK = NPK. Results showed that the two types of management practices, fallow (non-tilled) vs. cropped (tilled) had effects on OC concentrations. Comparing the OC contribution of particle-size fractions to the total OC amount revealed the following ranking: silt > clay > fine sand > coarse sand except in the plots receiving solid or liquid animal manure. Size fractions within treatments showed larger variations of 13C abundances than bulk samples between treatments. The natural abundances of 13C increased especially in cropped (and tilled) plots. It was shown by cluster analysis that FT-IR spectra differentiated between the different treatments originating from different land management practices. The present study revealed that below-ground C deposition by agricultural plants can hardly compensate the C losses due to tillage. Langzeiteffekte von Brache auf die organische Bodensubstanz im Vergleich zu Fruchtfolge und Dungerausbringung I. Organischer Kohlenstoff Ein Langzeitversuch, der in Gumpenstein (Steiermark, Osterreich) 1962 auf einer Braunerde angelegt wurde, wurde fur die vorliegende Untersuchung herangezogen. Wir kombinierten eine physikalische Fraktionierung mit der Bestimmung von C-Gehalten, der naturlichen Variation von 13C und einer FT-IR-spektroskopischen Charakterisierung, um den Einfluss der Dungung und der Bodennutzung allgemein auf C-Pools in Partikelgrosenfraktionen zu untersuchen. Gehalte an organischem Kohlenstoff (OC) nahmen nach 28 bzw. 38 Versuchsjahren etwas ab oder wurden nicht verandert durch Rindergulle + Stroh, PK- oder NPK-Dungung und zwar sowohl in bepflanzten (und bearbeiteten) Plots als auch in den Bracheplots (ohne Bodenbearbeitung). Jene Plots, die Stallmist erhielten, zeigten eine Zunahme der OC-Gehalte. Die Reihung der OC-Gehalte war: Stallmist (flussig) > Stallmist (fest) > Rindergulle = Rindergulle mit Stroh = PK = NPK. Die Bodenbearbeitung (bepflanzte Varianten) fuhrte zu einer klaren Abnahme der OC-Gehalte. Die C-Verteilung in den Partikelgrosenfraktionen nahm von Schluff uber Ton, Feinsand zu Grobsand ab. Die 13C-Haufigkeiten variierten zwischen den Korngrosenfraktionen starker als zwischen den Behandlungen, wobei die Bodenbearbeitung zu einer deutlichen Verschiebung zu starker positiven δ13C-Werten fuhrte. FT-IR-Spektren konnten die Unterschiede zwischen den Behandlungen zeigen. Unsere Untersuchung verdeutlichte, dass der C-Input durch Pflanzenreste die C-Verluste durch die Bodenbearbeitung nicht kompensieren kann.

Nitrogen dynamics in semi-natural environments is crucial for the development and ecological stability of these systems. The present paper shows the results of the reinvestigation of a 15N-tracer experiment, which was established in the Grossglockner massif in Austria at 2300 m a.s.l. in 1974/1975. We show that large quantities of nitrogen introduced by a single pulse labelling (amounting to approximately 1.7% of the nitrogen in the system) into an alpine grassland remain in the soil–plant system, with only 55% being lost during 27–28 years. In the first 10 cm of the four investigated soil profiles 40% of 15N was recovered, being mainly bound in organic forms. A simple site specific model was established on the basis of the results considering a biological, residual and labile N-pool, the latter being the source for N-losses. By the model a long mean residence time close to 100 years was derived for the remaining 15N.

Twenty Emmental cheeses from six European regions (Allgau (D), Bretagne (F), Finland, Savoie (F), Switzerland and Vorarlberg (A)) were analysed for stable isotope ratios such as 13C/12C, 15N/14N, 18O/16O, D/H and 87Sr/86Sr, as well as major (Ca, Mg, Na, K), trace (Cu, Mn, Mo, I) and radioactive elements (90Sr, 234U, 238U). The discriminating potential of these parameters was evaluated using difference tests of mean values and principal component analysis (PCA). “Finland”, “Bretagne” and “Savoie” cheeses were well separated using δ13C-, δ15N-, δ2H- and δ87Sr-values. Concentrations of molybdenum and sodium allowed the groups “Switzerland”, “Vorarlberg” and “Allgau” to be separated. 90Sr activity was highly correlated with the altitude of the production zone. Using this parameter, “Finland” and “Bretagne” were separated from “Vorarlberg” cheese. The results of the current screening test will help selecting the best tracers of origin for the remainder of the project.

We studied the effect of humified organic matter (OM) on the mineralization of a representative labile organic compound in soil. In an incubation experiment, a 13 C-labeled 2-decanol was added to soil either alone (2-dec p ) or in mixture with two humic acids from compost (HAC p ) and lignite (HAL p ) which had different hydrophobic properties. Isotopic dilution (d 13 C) showed that after 3 months of incubation about 58, 40 and 28% of the added 13 C was retained in the whole soil treated with HAL p , HAC p and 2-dec p , respectively. The higher the hydrophobicity of the employed humic material, the larger was the sequestration of organic carbon in soil. Fractionation of incubated samples revealed that the labeled carbon progressively accumulated in the finest particle-size fractions. However, the high hydrophobicity of the lignite HA favored accumulation of 13 C also in the sand-sized fraction. The NMR spectra of humic extracts showed that the 13 C-methyl group in the original 2-decanol had been oxidized to a 13 C-carboxyl group during incubation for all treatments. This indicated that despite its hydrophilicity, the resulting carboxyl carbon was sequestered into the hydrophobic domains of the humic pool in soil. In fact, the residual 13 C was larger in humic than in fulvic extracts for the control sample (2-dec p ) and even more so in extracts from soil treated with both exogenous humic acids. Our results suggest that labile organic compounds may be effectively protected in soil by humified OM and their microbial mineralization substantially reduced. Innovative soil management practices employing hydrophobic humic substances may increase the biological stability of soil OM and thus contribute to significantly mitigate CO2 emissions from agricultural soils. q 2002 Elsevier Science Ltd. All rights reserved.

Ab initio molecular dynamics room-temperature simulations and full relaxation of atomic positions are performed in the study of adsorption sites on the octahedral and tetrahedral surfaces (parallel to the (001) plane) of the kaolinite group of clay minerals. Interactions of water and acetic acid molecules with both surfaces are investigated. Simulations showed that both polar molecules are strongly bound to the octahedral surface forming several simultaneous hydrogen bonds. Surface hydroxyl groups located at the octahedral surface act as proton donors as well as proton acceptors demonstrating their amphoteric character. Moreover, proton jumps between the carboxyl group of acetic acid and one surface hydroxyl group were observed in the molecular dynamics simulations. On the other hand, both molecules interact only very weakly with the tetrahedral side of the kaolinite layer showing the hydrophobicity of this surface. The octahedral surface is hydrophilic.

Hydrogen-bonded interactions in the acetic acid dimer and in complexes formed by acetic acid with acetaldehyde, acetamide, ammonia, methanol, and phenol and in corresponding complexes between the acetate anion and the same ligands as before were studied in the gas phase and in solution by means of quantum chemical DFT/BLYP calculations. Three solvents (heptane, DMSO, and water) of largely varying polarity were chosen. The polarized continuum model was used for the description of the solvent. Optimized geometries, reaction energies, and Gibbs free energies of complex formation were computed. In the neutral complexes an opening of the weaker of the two hydrogen bonds formed in the complex is observed with increasing polarity of the solvent. This opening is interpreted by the creation of optimal conditions for separate solvation of the subsystems of the hydrogen bond in competition with the geometrical requirements for the formation of this bond. Even though almost all reaction energies are found to be negative, only the strongly bound complexes, acetic acid dimer, and acetic acid-acetamide are stable according to Gibbs free energy results. The main factors for this finding are the entropy loss on the formation of the bimolecular complex and the changes of the free energy of solvation. Solvation effects are interpreted in terms of dipole moments, solvent-accessible surfaces, and cavity volumes of the separate molecules and of the complexes.

In a study on the behaviour of pesticides in a soil–plant–water system, the quick, easy, cheap, effective, rugged and safe (QuEChERS) method for analysing pesticide or metabolite residues in soil and maize (leaves, roots and kernels) was optimized and validated. The pesticides bentazone, chloridazon and terbuthylazine and their metabolites bentazone-methyl, chloridazon-desphenyl, chloridazon-methyl-desphenyl, terbuthylazine-desethyl and terbuthylazine-2-hydroxy were selected in this study. The QuEChERS extracts obtained from soil and maize matrices and the collected leachate were analysed by liquid chromatography–electrospray ionization–tandem mass spectrometry (LC–ESI–MS/MS) using a high-performance liquid chromatography and an ultra-high-performance liquid chromatography (UHPLC) analytical column. As expected, shorter run times and higher sensitivity were achieved with the UHPLC column. Validation studies focused on recovery, repeatability, matrix effects, limits of detection and quantification. Recoveries (and repeatability relative standard deviation (RSD)) of the spiked samples were in the range of 55 to 98 % (7.4–18) in soil, 23 to 101 % (1.7–20) in maize and 82 to 105 % (4.4–25) in leachate. Quantification limits were lower than 3.0 μg kg−1 in soil, 7.3 μg kg−1 in maize and 0.080 μg l−1 in leachate.

Quantum chemical calculations within the framework of a two-layered ONIOM approach using the B3LYP density-functional method were carried out for the study of adsorption sites on regular (001) surfaces of the kaolinite group of clay minerals. A molecular cluster of an appropriate size (about 80 atoms including H atoms saturating dangling bonds) was cut from a structure of a single kaolinite layer. This cluster contains two types of interaction sitesone at the tetrahedral side and one at the octahedral side of the layer. Interactions of water and acetic acid molecules with the tetrahedral side and of water molecule and acetate anion with the octahedral side were investigated. Geometry optimizations were carried out, and interaction energies between the clay surfaces and the molecular species were computed. Hydrogen bridges between the hydroxyl groups of the octahedral surface and the water molecule were observed with total adsorption energy about −8 kcal/mol. The carboxylate group of the acetate anion bind...

A chromatographic method has been developed for enrichment of methionine-bound sulfur in casein, for stable-isotope analysis. Casein is precipitated from milk samples and cleaved by acid hydrolysis in 6m hydrochloric acid at 95 °C. The amino acids released are converted into theirN-acetyl derivatives by addition of acetic acid anhydride. After lyophilization,N-acetylmethionine is separated from the accompanying components on octadecylsilica by use of a gradient prepared from 0.02m formic acid and methanol. The fractions containingN-acetylmethionine are pooled and freeze dried. Procedures for hydrolysis and derivatization were optimized to furnish the highest yields. The influence of the abundance ratio on the chromatographic separation is shown and discussed. From 1.0 g casein 16.5 mgN-acetylmethionine were isolated.

Summary Changes in farming practices over long times can affect the sorption behaviour of MCPA ((4-chloro-2-methylphenoxy)acetic acid). We studied the adsorption–desorption mechanisms of MCPA on soil with varied amounts and origins of soil organic matter obtained from a long-term field experiment with various organic amendments. The origin of the soil organic matter seems to be crucial for the sorption behaviour of MCPA. Samples of soil amended with sewage sludge sorbed MCPA more strongly than the soil under any other treatment. Peat-amended soil was second followed by soil receiving animal manure, green manure, mineral fertilizer without N and the fallowed soil. Both the carbon content and the origin of the organic matter are important for the sorption. A decrease of carbon content of a soil does not necessarily imply a reduction of sorption capacity for polar organic acids such as MCPA. Nevertheless, our adsorption–desorption experiments suggest that with decreasing carbon content the role of mineral sorption mechanisms could become more pronounced. Our results showed that interactions of soil organic matter and soil minerals distinctly influence adsorption properties for MCPA.

Diffuse Reflectance Infrared Fourier Transform DRIFT technique was used to investigate decomposition of maize straw residues in particle-size fractions of three European soils in a 1-year incubation experiment that simulated both incorporation and mulching practices. The aliphatic bands in the 2920-2860 cm y1 regions were used to derive decomposition curves and mineraliza- tion rates of maize residues. Evaluation of soil organic matter changes by DRIFT in particle-size fractions depended on soil texture and soil aggregate stability. Decomposition could be followed over the full incubation period only in three size-fractions of the silty German soil because of its intermediate aggregate stability. DRIFT spectra were not useful in the least stable sandy Danish soil and in the most stable clayey Italian soil. Decomposition rates derived from DRIFT results were similar to those obtained by isotopic techniques. DRIFT spectroscopy may represent a rapid and accurate method to follow fresh organic matter degradation directly in soil matrix or particle-size fractions in some soils provided that adequate soil dispersion is obtained. q 2001 Elsevier Science B.V. All rights reserved.

Density-functional calculations have been performed on tridentate, hydrated aluminium–citrate complexes using fully (quadruply) and triply deprotonated citric acid ligands. Water molecules in the inner solvation sphere have been included explicitly in the quantum-chemical calculation, whereas the remaining solvent effects have been computed using the polarized continuum model (PCM). As is to be expected, solvation effects play an important role for the calculation of formation energies of the complexes. Optimized geometries are in good agreement with X-ray data. Reaction enthalpies and Gibbs reaction energies have been computed for the substitution of water molecules of the aluminium–hexaaquo complex by citrate molecules. Formation of the tridentate complexes is strongly favored by entropy effects in analogy to previous findings for bidentate acetate and oxalate complexes. Comparison of the stability of acetate, oxalate and citrate complexes shows a pronounced preference for the latter.

The dynamics of incorporation of fresh organic residues into the various fractions of soil organic matter have yet to be clarified in terms of chemical structures and mechanisms involved. We studied by 13 C-dilution analysis and CPMAS- 13 C-NMR spectroscopy the distribution of organic carbon from mixed or mulched maize residues into specific defined fractions such as carbohydrates and humic fractions isolated by selective extractants in a year-long incubation of three European soils. The contents of carbohydrates in soil particle size fractions and relative δ 13 C values showed no retention of carbohydrates from maize but rather decomposition of those from native organic matter in the soil. By contrast, CPMAS- 13 C-NMR spectra of humic (HA) and fulvic acids (FA) extracted by alkaline solution generally indicated the transfer of maize C (mostly carbohydrates and peptides) into humic materials, whereas spectra of organic matter extracted with an acetone solution (HE) indicated solubilization of an aliphatic-rich, hydrophobic fraction that seemed not to contain any C from maize. The abundance of 13 C showed that all humic fractions behaved as a sink for C from maize residues but the FA fraction was related to the turnover of fresh organic matter more than the HA. Removal of hydrophobic components from incubated soils by acetone solution allowed a subsequent extraction of HA and, especially, FA still containing much C from maize. The combination of isotopic measurements and NMR spectra indicated that while hydrophilic compounds from maize were retained in HA and FA, hydrophobic components in the HE fraction had chemical features similar to those of humin. Our results show that the organic compounds released in soils by mineralization of fresh plant residues are stored mainly in the hydrophilic fraction of humic substances which are, in turn, stabilized against microbial degradation by the most hydrophobic humic matter. Our findings suggest that native soil humic substances contribute to the accumulation of new organic matter in soils.

The sorption and desorption behaviors of four phenoxyalkanoic acid herbicides and their metabolites on four agricultural soils and soil particle size fractions were examined. Generally, there was a trend of increasing adsorption and decreasing desorption in the order mecoprop < MCPA < dichlorprop < 2,4-D. The significant increase in adsorption of the phenolic metabolites can be explained by their lower polarity and enhanced partition in the organic soil matrix. Estimation of sorption distribution coefficients from particle size fraction adsorption data was possible for a sandy soil and a silty Cambisol soil only. It is suggested that increasing steric demand, for example, molecular volume, and slight changes in the polarity of the compounds affect their adsorption properties. Comparison of adsorption and desorption data of structurally similar compounds obtained from a variety of soils allows investigation of structure-induced differences in sorption strength.

Density-functional theory (DFT) methods were used for investigations on the aluminum−hexaaquo complex and on aqueous aluminum−acetate complexes. Solvent effects were computed by means of the polarized continuum model (PCM). Extensive basis set studies and comparison of several functionals lead to efficient and accurate procedures which were applied to the computation of aluminum−acetate complexes. A variety of structural arrangements such as monodentate or bidentate with respect to the bonding of the carboxylate group or cis/trans with respect to the relative position of two acetate molecules were considered. ΔH and ΔG values were calculated for the substitution reaction of water molecules in the aluminum−hexaaquo complex by acetate anions. Characteristic differences in ΔS were found depending on the number of water molecules released per acetate. Overall, we find that monodentate structures are only slightly preferred over bidentate ones and that we expect a relatively complicated system of chemical equi...

Regional origin assignment of highly valuable milk products such as butter, is of considerable importance for legal, fiscal and trade controls within the European Union (EU). It is also of value for ensuring fair competition and as a means of protecting consumers against fraud due to mislabelling. Conventional chemical methods of analysis are not able to determine the regional provenance of butter unambiguously. Therefore, stable isotope ratio determinations of the light elements (C,N,O,S; bioelements) and the heavy element, Sr (a trace element), have been used for this purpose. Stable isotope ratios of these elements in natural cycles, their variations due to climate and geology, the abiotic and biological fractionation of isotopes and, finally, the reasons for regional differences in multielement stable isotope ratios of butter are discussed. Results are given for butter from several European countries and from outside the EU. The results indicate that stable isotope ratios and subsequent discriminant analysis based on data for samples of certified origin can enable the reliable detection of the regional provenance of butter.

This article describes a series of transmission Fourier transform infrared (FT-IR) spectroscopy measurements of soil layers, especially organic soil layers, originating from a tropical forest and from a pasture, which was developed after deforestation of the tropical soil in 1987. Spectral information obtained from forest and pasture soil layers from central Rondônia, Brazil, was analyzed and compared. A variety of bands characteristic of molecular structures and functional groups have been identified for these complex samples. Cluster analysis revealed that such land use change affects the spectroscopic behavior of the organic soil layers. A significantly closer relationship between the pasture soil layers in comparison to the forest soil layers was obtained. This result indicates a higher homogeneity of the intoduced litter from pasture vegetation compared to forest. The application of regression models enabled the estimation of soil parameters, such as organic carbon and nitrogen; the identification and differentiation of organic forest soil horizons; and the determination of the decomposition status of soil organic matter in distinct layers. On the basis of the data presented in this study, it may be concluded that FT-IR spectroscopy is a powerful tool for the investigation of decomposition dynamics and litter quality in tropical soils.