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  • AGRIS (United Nations, Food and Agriculture Organization)  (17)
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  • 1
    Language: English
    In: Journal of agricultural and food chemistry, 26 February 2014, Vol.62(8), pp.1912-8
    Description: Poultry manure (PM) chars were obtained at different temperatures and charring times. Chemical-physical characterization of the different PM chars was conducted by cross-polarization magic angle spinning (CPMAS) (13)C NMR spectroscopy and thermal analysis. CPMAS (13)C NMR spectra showed that the chemical composition of PM char is dependent on production temperature rather than on production duration. Aromatic and alkyl domains in the PM chars obtained at the lowest temperatures remained unchanged at all heating times applied for their production. The PM char obtained at the highest temperature consisted only of aromatic structures having chemical nature that also appeared invariant with heating time. Thermogravimetry revealed differences in the thermo-oxidative stability of the aromatic domains in the different PM chars. The PM char produced at the highest temperature appeared less stable than those produced at the lowest temperatures. This difference was explained by a protective effect of the alkyl groups, which are still present in chars formed at lower temperature. The analysis of the chemical and physicochemical character of poultry manure chars produced at different temperatures can increase understanding of the role of these materials in the properties and behavior of char-amended soils.
    Keywords: Charcoal -- Chemistry ; Manure -- Analysis
    ISSN: 00218561
    E-ISSN: 1520-5118
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  • 2
    Language: English
    In: Organic Geochemistry, 2011, Vol.42(8), pp.917-925
    Description: H wideline NMR spectra of soil samples offer the possibility to analyze soil material based on their proton mobility. Care has to be taken to remove unwanted signal contributions from the probe background. We demonstrate that unstructured wideline spectra can be analyzed quantitatively by a combination of a Gaussian line for rigid and a Lorentzian line for mobile protons. This is used to study effects of hydrogen-bonded water networks upon heat treatment for a series of different soil samples with varying water content as a contribution to study physical aging of soil organic matter (SOM). Results are combined with H projections from C 2D WISE (wideline separation) experiments representing solely the broad Gaussian line. Furthermore, for the first time applied to soils, H structural information from soil samples is obtained from 2D PMLG phase modulated Lee–Goldburg measurements under magic angle spinning (MAS). Low water contents improve the resolution of main functional groups significantly.
    Keywords: Geology
    ISSN: 0146-6380
    E-ISSN: 1873-5290
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  • 3
    Language: English
    In: Reviews in Environmental Science and Bio/Technology, 2013, Vol.12(3), pp.235-256
    Description: A main objective in the field of mixture toxicity is to determine how well combined effects are predictable based on the known effects of mixture constituents. Conducting toxicity tests for all conceivable combinations of chemicals, to understand all mechanisms in the combined toxicity of environmental pollutants, is virtually unfeasible due to cost- and time-consuming procedures. Therefore, predictive tools for mixture toxicity are required to be developed within the applicable range of predictive toxicology. The concept of concentration addition (CA) model is often considered a general method for estimating mixture toxicity at the regulatory level. In the long run, however, the possibility of toxicological synergism between mixture components actually occurs, especially from the no-effect level or non-toxic substances. This is ignored under the CA concept, and needs to be examined and integrated into existing addition models at a scientific level, this paper reviews existing integrated models for estimating the toxicity of complex mixtures in literature. Current approaches to assess mixture toxicity and the need for new research concepts to overcome challenges which recent studies have confronted are discussed, particularly those involved in computational approaches to predict mixture toxicity in an environment risk assessment based on mixture components.
    Keywords: Mixture toxicity ; Mixture risk assessment ; Prediction model ; Computational toxicology
    ISSN: 1569-1705
    E-ISSN: 1572-9826
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  • 4
    Language: English
    In: Colloids and surfaces, 2013, Vol.431, pp.150-160
    Description: The effect of grain water repellency on transport and deposition of hydrophilic colloids was studied by analyzing the breakthrough behavior of carboxylate-modified microspheres in water-saturated wettable and hydrophobic sand columns at different ionic strengths. Interaction free energies calculated from zeta (ζ)-potential and contact angle data were used to explain the specific colloid breakthrough behavior. Experimental breakthrough data could be well described with the finite-element code HYDRUS-1D using a one kinetic site model with attachment and detachment kinetics. Higher colloid deposition rates found for the hydrophobic sand could primarily be explained by its small electron-donor component of surface free energy (γₛ ⁻=1.6×10⁻²mJm⁻², compared to γₛ ⁻=64.1mJm⁻² for the wettable sand), leading to strongly attractive acid–base interactions at separation distances〈5nm. Increasing ionic strength reduced the repulsive electrostatic interactions and generally increased colloid deposition with the effect being more pronounced in the hydrophobic sand. It can be concluded that grain water repellency tends to increase the deposition of negatively charged hydrophilic colloids, which can be ascribed to specific acid–base interactions. However, our results further revealed that the calculated interaction free energy profiles should be considered only as an approximation showing general trends because surface chemical heterogeneity as detected by atomic forces microscopy impeded the determination of the actual interaction energy conditions, resulting in an overestimation of electrostatic repulsion. ; p. 150-160.
    Keywords: Models ; Sand ; Colloids ; Hydrophilicity ; Electrostatic Interactions ; Microscopy ; Hydrophobicity ; Energy ; Contact Angle ; Ionic Strength
    ISSN: 0927-7757
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 5
    Language: English
    In: Reviews in Environmental Science and Bio/Technology, 2012, Vol.11(1), pp.41-54
    Description: Interactions between cations and natural organic matter (NOM) are central for the stability of organic matter, formation of supramolecular NOM structure, formation of organo-mineral associations, soil aggregation and binding of organic contaminants. The effect of multivalent cations on environmental functionalities of NOM strongly depends on the relative importance between intramolecular complexation and intermolecular cross-linking, the degree of which will be determined by the spatial arrangement of the hydrophilic functional groups in NOM. This literature review seeks to evaluate the current state of the art regarding the relevance of intermolecular cross-links via bridges of multivalent cations. Cross-linking has been suggested to explain among others aggregate stability, retarded dissolved organic matter release, reduced organic matter (OM) solubility as well as increase in degree and nonlinearity of sorption or organic chemicals to NOM. Although the cross-linking mechanism has been suggested in numerous studies, it has not yet been verified directly. The dynamics of the intermolecular cross-links, their persistence as well as their interplay with OM and their influence on stability and bioavailability of organic chemicals is up to now unknown. The major challenge in this context is the development of a suitable combination of experimental and instrumental techniques and relating the results to molecular and physicochemical models on the basis of targeted combination of spectroscopic, molecular modelling and thermoanalytical methods.
    Keywords: Cations ; Natural organic matter ; Cross-linking ; Water molecule bridges ; Cation bridges ; NMR ; Thermal analysis
    ISSN: 1569-1705
    E-ISSN: 1572-9826
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  • 6
    Language: English
    In: Human and ecological risk assessment, 2014, Vol.20(1), pp.174-200
    Description: Concentration addition (CA) and independent action (IA) models are often applied to estimate the mixture toxicity of similarly and dissimilarly acting chemicals, respectively. An integrated addition model (IAM), called the “integrated CA with IA based on a multiple linear regression (ICIM) model” was recently proposed for predicting additive toxicity of non-interactive mixtures regardless of whether mixture components produce similar, dissimilar, or both similar and dissimilar modes of action. In the ICIM, the effective concentrations of mixtures experimentally tested were regarded as the response variable, and the results estimated by CA and IA were considered as the predictor variable. However, it can be highlighted that the multicollinearity problem (i.e. , a linear relationship between predictor variables), which may be caused in the existing ICIM model employing ordinary least squares regression. Therefore, the objectives of this study were to develop and evaluate a Partial Least Squares-based IAM (PLS-IAM) not only to overcome the multicollinearity problem, but also to combine the CA and IA into an IAM using the latent variable that accounts for most of the variation in the response. Through four test datasets, this study showed that the PLS-IAM overall outperformed the other reference models, including the CA, IA, and ICIM models. ; p. 174-200.
    Keywords: Data Collection ; Toxicity ; Prediction ; Least Squares ; Linear Models
    ISSN: 1549-7860
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 7
    Language: English
    In: Plant and Soil, 2005, Vol.275(1), pp.1-20
    Description: Variations of soil moisture conditions affect sorption properties of soil organic matter and the pore size distribution of the soils and thus are expected to have an impact on the availability of pollutants and nutrients in soils. At least two principal processes that occur when a soil-water contact is established, are involved. Wetting , which is the very first step, is governed by the interactions of water with the surface of soil organic matter (SOM). The wettability of the pore walls determines the pore accessibility for water. Only in wettable soils, water will occupy the smallest pores first. In the course of wetting, the wettability of the pore walls increases, leading to water redistribution. Swelling of SOM is accompanied by an increase of volume due to the water uptake of the solid SOM phase and will change the SOM polarity. Swelling will thus affect sorption processes in the bulk SOM phase and is expected to change the pore sizes. In this contribution, we investigated swelling and wetting kinetics of soil samples by H-NMR-Relaxometry. We found different effects of wetting and swelling on the development of relaxation time distribution and thus of the pore size distribution. Both swelling and wetting can be slow processes, lasting for up to some weeks. During this time, we found changes in the pore size distribution. For swelling phenomena, we observed a continuous change of the effective pore size, and for wetting phenomena, we found a change in water distribution in a probably rigid pore system. Thus, during swelling and wetting, neither pore size distribution nor sorbent properties of SOM nor hydraulic properties remain constant. Due to the slow kinetics, both processes play an important role in sorption, transport and accessibility for water in hydrophobic areas within a time scale of weeks after e.g. a rainfall event. This will affect the environmental availability and the transport of pollutants and nutrients in the field.
    Keywords: H-NMR-Relaxometry ; kinetics ; soil organic matter ; swelling ; water repellence ; wetting
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 8
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2014, Vol.177(2), pp.141-149
    Description: The objective of this study was to investigate the effects of mono‐ and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na, Ca, or Al and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca and Al decreased it. The H‐NMR relaxometry analyses showed that Al restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca or Na. According to contact‐angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt‐treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil.
    Keywords: Soil Organic Matter ; Sodium ; Calcium ; Aluminum ; Contact Angle ; Wettability ; Relaxation Time
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 9
    Language: English
    In: Plant and Soil, 2006, Vol.280(1), pp.209-222
    Description: 1 H NMR relaxometry is applied for the investigation of pore size distributions in geological substrates. The transfer to humous soil samples requires the knowledge of the interplay between soil organic matter, microorganisms and proton relaxation. The goal of this contribution is to give first insights in microbial effects in the 1 H NMR relaxation time distribution in the course of hydration of humous soil samples. We observed the development of the transverse relaxation time distribution of the water protons after addition of water to air dried soil samples. Selected samples were treated with cellobiose to enhance microbial activity. Besides the relaxation time distribution, the respiratory activity and the total cell counts were determined as function of hydration time. Microbial respiratory activities were 2–15 times higher in the treated samples and total cell counts increased in all samples from 1×10 to 5×10 cells g during hydration. The results of H NMR relaxometry showed tri-, bi- and mono-modal relaxation time distributions and shifts of peak relaxation times towards lower relaxation times of all investigated soil samples during hydration. Furthermore, we found lower relaxation times and merging of peaks in soil samples with higher microbial activity. Dissolution and hydration of cellobiose had no detectable effect on the relaxation time distributions during hydration. We attribute the observed shifts in relaxation time distributions to changes in pore size distribution and changes in spin relaxation mechanisms due to dissolution of organic and inorganic substances (e.g. Fe, Mn), swelling of soil organic matter (SOM), production and release of extracellular polymeric substances (EPS) and bacterial association within biofilms.
    Keywords: H NMR relaxometry ; extracellular polymeric substances (EPS) ; soil microorganisms ; soil organic matter (SOM)
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 10
    Language: English
    In: Organic geochemistry, 2012, Vol.47, pp.132-138
    Description: Cross-linking of humic substances with organic bridging groups is thought to contribute to the humification of soil organic matter. Model cross-linked humic substances were prepared by cross-linking Amherst soil humic acid by a diepoxide and a polycarboxylic acid, applying procedures established for cross-linking of polymers and textile fabrics. Products of the cross-linking reactions were analyzed by FTIR and ¹³C CPMAS NMR. Physicochemical properties of the products were determined by solubility experiments and thermal analysis. The incorporation of the cross-linker into the matrix of the humic acid by covalent linkages was confirmed by both the disappearance of bands of the reactive functional groups of the cross-linker in the FTIR spectrum and the increase of signals related to the incorporation of the cross-linker into the matrix of the humic acid in the FTIR and ¹³C CPMAS NMR spectra. The formation of covalent ester and ether linkages by the cross-linking reaction was indicated. Water solubilities at pH 6.2 of the cross-linked samples as determined by UV/Vis spectrometry were reduced compared to controls. Fewer water molecule bridges were formed in the cross-linked samples, which was attributed to a lower number of available functional groups and increased distances between humic acid strands caused by the cross-linking molecules. Reduced reactivities of humic acid strands in the cross-linked samples further indicated successful cross-linking. The reactions investigated in this study can be regarded as models for reactions occurring in natural soils to test the significance of cross-linking reactions in the humification process of soil organic matter and the physico-chemical properties and ecological function of organic matter in geosolids. ; p. 132-138.
    Keywords: Crosslinking ; Humic Acids ; Humification ; Solubility ; Models ; Thermal Analysis ; Fabrics ; Ecological Function ; Polymers ; Nuclear Magnetic Resonance Spectroscopy ; Ph ; Fourier Transform Infrared Spectroscopy ; Soil
    ISSN: 0146-6380
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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