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Revista de la ciencia del suelo y nutrición vegetal

versión On-line ISSN 0718-2791

R.C. Suelo Nutr. Veg. v.8 n.especial Temuco  2008

http://dx.doi.org/10.4067/S0718-27912008000400019 

 

J. Soil Sci. Plant Nutr. v8 no especial 2008 (132-141)

ORAL ABSTRACTS   

                                             

Session 4. Dynamics and Transformations of Natural and Xenobiotic Compounds in Soil Environments

Pentachlorophenol Degradation in Two Biological Systems: Biobed and Fixed-Bed Column, Inoculated with the Fungus Anthracophyllum discolor

M.C. Diez1* and G.R. Tortella2

1Departamento de Ingeniería Química, 2Programa de Doctorado en Ciencias de Recursos Naturales. Universidad de La Frontera, Temuco, Chile. *E-mail: mcdiez@ufro.cl

Keywords: Pentachlorophenol degradation; biobed; Anthracophyllum discolor.

Anthracophyllum discolor, a white-rot fungus of southern Chile, produces ligninolytic enzymes specially manganese peroxidase (MnP), and has been studied for its potential use on bioremediation of contaminated soils with chlorophenols. The main purpose of this study was to evaluate the pentachlorophenol (PCP) degradation in two biological systems (biobed and fixed-bed column). Both systems used an Andisol and were inoculated with A. discolor immobilized in lignocellulosic material. The biobed system consisted of a mixture of straw (50% v/v), peat (25% v/v) and topsoil (Andisol) (25% v/v). The biobeds were contaminated with three successive application of 100 mg kg-1 of PCP each (0, 21 and 55 days). After the contamination, one biobed was inoculated with the fungus A. discolor immobilized on wheat straw, and the other was non-inoculated and was used as a control. During the incubation period (80 days at 25°C), C02 evolution, enzymatic activities (lacease and manganese peroxidase) and residual concentration of PCP were periodically evaluated. Fixed-bed columns (35 x 5 cm) packed with a mixture of 50% quartz sand and 50% of allophanic soil (Andisol) activated by acidification (pH 4.5) were used for PCP removal. Wheat grains colonized by A. discolor were put on the upper part of each column. The columns were operated in continuous and were fed with PCP (100 mg L-1) under a flow rate of 1.5 mL min" l, at room temperature during 29 days approximately. Samples were taken from the effluent of the columns at pre-determined time intervals and analyzed for the remaining concentration of PCP and for manganese peroxidase (MnP) and lacease enzymatic activity quantification. In biobed system, degradation of PCP occurred efficiently over the whole incubation period. However, it was significantly quicker in biobed amended with the fungi compared with non-inoculated biobed, mainly in the first 21 days. Over this time, no differences were found between inoculated and non-inoculated biobed on PCP degradation. A fraction of the initial PCP concentration was adsorbed (aprox. 40%) in each application by the biobed matrix. The MnP activity was the highest in inoculated biobeds, and the lacease activity was the highest in control biobeds. In fixed-bed column, PCP adsorption was high in the first 12 h and decreased suddenly up to 48 h. During the days 5 to 14, the PCP was efficiently degraded, and the concentration was stabilized in the range of 30 mg L-1 in the effluent. After that, PCP concentration increased and the column was saturated on day 16. The lowest values of PCP coincide with the production of MnP, showing that A. discolor increased degradation of PCP. In conclusion, the results of this study demonstrate that PCP was efficiently removed by the two biological systems, both by adsorption and by biodegradation processes.

Acknowledgements: Investigation financed by FONDECYT 1050614 and DIUFRO GAP-2007 projects.

Fate of Pentachlorophenol (PCP) and Dynamics of Chemical and Biological Properties in an Artificially PCP-contaminated Soil as Affected by Compost and Dissolved Organic Matter

R. Scelza, M.A. Rao* and L. Gianfreda

Dipartimento di Scienze del Suolo, delta Pianta, dell'Ambiente e delle Produzioni Animali, Universitá di Napoli Federico II, Portici, Italy. * E-mail: mariarao@unina.it

Keywords: Pentachlorophenol; compost; dissolved organic matter.

Pentachlorophenol is a highly chlorinated organic compound extensively used as a broad-spectrum biocide, particularly in the wood preservation industry. As with other xenobiotics, PCP can exist in soil in a strongly sorbed state and the size of this desorption-resistant fraction may increase with the length of time the chemical remains in the soil. Soil organic matter can enhance PCP adsorption and hinder it desorption whereas association with dissolved organic matter (DOM) in the soil solution can increase the water solubility and mobility of the chemical. Very limited information exists on the effect of pentachlorophenol on soil biological and biochemical properties which are highly sensitive to changes caused by management practices and environmental stress, and may provide an early warning of soil quality changes. The main goal of this study was to evaluate, in a long-term experiment (500 days) under laboratory conditions, the response of soil to PCP contamination and the relative effects and potential remediation capacities of compost and dissolved organic matter. Soil response was assessed by measuring the disappearance of PCP when added to a fresh, agricultural soil, with and without compost and dissolved organic matter, both added at two different rates and evaluating the dynamics of physical and chemical properties, microbial biomass, basal respiration and some enzymatic activities, related to carbon, nitrogen, phosphorus and sulfur cycling, in the contaminated soil amended or non-amended with the two compost or DOM doses. PCP concentrations declined progressively and significantly with time. This effect was most pronounced for the soils amended with the lower compost dose and with the two DOM amounts. The soil showed an endogenous microbial activity as indicated by basal respiration, microbial biomass and all the enzymatic activities tested (dehydrogenase, p-glucosidase, phosphatase, arylsulfatase, urease). Addition of the PCP severely depressed some of the tested biochemical properties suggesting an inhibitory effect on microbial activity. Conversely, higher basal respiration, and similar p-glucosidase and phosphatase activities were measured in comparison with the controls. No significant effects were observed following the addition of two doses of the compost or the DOM. Fungal colonies belonging to the taxonomic group of Ascomycetes and identified as Byssochlamys fulva developed with time in all the PCP-contaminated samples. Growth oí B.fulva in vitro in the presence of PCP showed that the isolate was tolerant to 12.5 and 25 mg -1 PCP and degraded 20% of its initial concentration in 8 d. Overall, the results indicate that many complex processes occurred in the contaminated soils and combinations of these determined the response to PCP contamination. The sorption of PCP to the soil matrix (which increased with time) and its degradation/transformation by indigenous soil microbial activity were likely involved. Both the processes appeared to be favored by the presence of dissolved organic matter.

 

Unraveling Plant-Soil-Microbe Interactions for Phytoremediation of Soil Organic Contamination: Limitations and Opportunities

J.Xu* and Y. He

Institute of Soil and Water Resources and Environmental Science, Zhejiang University, Hangzhou 310029, China. * E-mail: jmxu@zju.edu.cn

Keywords: Plant-soil-microbe interactions; phytoremediation; organic contamination.

 

Success in phytoremediation can be facilitated through the deep unravelment of plant-soil-microbe interactions under stress from organic contaminants (OCs). Due to the innovative methods, such as rhizosphere in situ sampling, mass separated detection and biomolecular techniques, we eagerly anticipate significant insights into plant-microbe interactions in a contaminated rhizosphere, providing a solid mechanistic understanding for phytoremediation. Several key aspects regarding the limitations and opportunities for research in the academic field mentioned above will be presented as follows:

Innovation of rhizosphere in situ sampling techniques. The rhizosphere is a heterogeneous system, and is difficult to physically sample and precisely manipulate. Some sensitivity of measurement is inevitably lost in an attempt to acquire a fixed quantity of root-free, homogenized rhizosphere soil, since the minute volumes of rhizosphere would be diluted by the bulk soil during sampling. It is challenging, but necessary to develop in-situ sampling techniques and protocols, which take into account the spatial and temporal variability of chemical and biological changes in the rhizosphere in response to OCs stress. Clarity for the adaptive regulation of plants under OCs stress. The lack of comprehensive knowledge of exúdate chemistry is a major barrier to unraveling the plant-soil-microbe interactions since the techniques used to collect the root exudates are often destructive, causing disturbance to the delicate interactions between the root and soil community. Given the exciting advances that have been achieved in the recent years in quantitative analytical approaches for measuring dissolved organic matter (DOM), we advance a new and alternative way to address this important scientific problem. A new approach to the direct and in situ study of rhizosphere C flow in the form of rhizosphere DOM will be presented. Application of novel techniques for rhizosphere microbial identification. Recent advances in molecular methods provide an exciting opportunity to link rhizosphere microbial structure and function with the role they play in rhizodegradation. One of the most powerful and innovative techniques is stable-isotope probing (SIP), which relies on the incorporation of isotope-labeled substrates, such as fatty acids, DNA and RNA, into the biomass of the active microorganisms. Following extraction of the labeled biomass, insight into the structure and identity of the active members of a microbial community can then be gained with unprecedented clarity and precision. Application of this technique is expected to disclose microbial phylogeny with function, providing detailed information on the main microbial taxa involved in rhizodegradation.

Despite the limitations in the scope of this paper, we hope our discussion will inspire exciting and promising avenues for further research in plant-soil-microbe interactions for phytoremediation of soil organic contamination.

 

Chlordecone Contamination of Root Vegetables in Long-term Polluted Soils in the FWI: Analysis of Levels of Pollution Provides a Decision Tool for Safe Production

M. Lesueur Jannoyer1*, R. Achard1 and Y.M. Cabidoche2

1PRAM CIRAD, Petit Morne, BP 214, 97285 LE LAMENTIN (FWI), Francia.

2INRA, UR 135 Agropédoclimatique de la Zone Caraibe, Domaine de Duelos, 97129 PETITBOURG

(FWI), Francia. * E-mail: jannoyer@cirad.fr

Chlordecone is an organochlorine pesticide whose use is now forbidden but which persists in soils. It was used as an insecticide against the banana weevil from the 1970s to the early 1990s in the French West Indies. Late contamination of root vegetables (RVs) was revealed in 2002. In our work, we studied the mode of transfer of chlordecone from different types of tropical soil (Andosol, Ferralsol and Nitisol) to different RVs (dasheen, yam, sweet potato, turnip and radish) to explore plant sensitivity to contamination. We conducted complementary experiments: surveys, field trials, and mesocosm trials to link soil chlordecone content with plant chlordecone contamination. In all those experiments, RVs contamination was heterogeneous as soil pollution was heterogeneous, but dispersion of the chlordecone molecule was the same for each crop. Due to this dispersion, the soil type did not significantly affect contamination. Average contamination values measured in harvested organs were positively correlated to chlordecone soil content. Belowground organs themselves were contaminated heterogeneously depending on where there was direct contact between the organ and contaminated soil. The cortex was more highly contaminated than the pulp (up to ten times more). These two results thus support the hypothesis that contamination by direct contact between the chlordecone molecule and the plant organ is the most important mode of transfer in RVs. This has already been demonstrated in the yam Discorea cayenensis, whose tubers were chlordecone free even when the root system explored contaminated soil. Chlordecone diffusion into the plant was very weak suggesting that it is a passive process in RVs. A common model, based on morphology and duration of the soil/organ contact, accounted for the RVs contamination. We calculated an envelope curve of the relationship between soil chlordecone content and RVs contamination and the maximum transfer ratio observed was 1/5. This envelope curve which represents zero risk of contamination was calculated for crops on both Andosol and Ferralsol. This relationship is thus a decision tool to determine whether or not there is a risk involved in cultivating roots and tubers based on the result of soil analysis. With this tool, the risk of contamination can be foreseen at planting which is preferable to analyzing the product at the harvest stage. Further studies are in progress to determine the sensitivity of other mainly horticultural crops and fruits, and to analyze the contamination of aboveground organs. Factors that govern the bioavailability of the chlordecone molecule in the soil for the plants, like water, organic matter content, type of clay, need to be analyzed in more detail to better understand chlordecone transfer to plants and thus improve pollution management. Keywords: Organochlorine pesticide; soil pollution; food safety.

 

Impact of Crop Residue Management on Sequestration of Soil Carbon, Transformation of Nitrogen and Irrigation Water use in Rice-Wheat Cropping System

N.S. Pasricha*

Potash Research Institute of India, Dundahera, Gurgaon, Haryana, India. *E-mail: nspasricha@sify. com

Keywords: Soil carbon sequestration; nitrogen; rice-wheat cropping system.

Rice-wheat is the most popular cropping system followed on around 13.5 million ha of land in the South Asia extending across the Indo-Gangetic alluvial plain. To vacate fields for the timely sowing of wheat, farmers often burn rice straw in the fields in India. To overcome this problem, Zero-Till Seed-cum-Fertilizer Drill (ZTP) has been tried for sowing of wheat without any pre-sowing irrigation in the standing straw of rice (after the combine harvesting of rice) in a field experiment conducted for quantification of saving in organic carbon and irrigation water, and transformation of N in rice-wheat rotation. Rice (Oryza sativa cv. Sugandha-2, fine quality fragrant Basmati rice) was grown in rotation with wheat (cv. WL-343) on sandy loam soil in Gurgaon, Haryana, India. Six, 15 by 10 m plots, were arranged in two blocks. Micro plots of 1.2 by 1.2 m were maintained in each plot for N-15 studies. At maturity, rice crop was simulated combine-harvested in one block of 3 plots, leaving the anchored rice-straw and stubbles in the field. In the other block of 3 plots, rice was harvested up to ground level and the straw was removed from the field. Wheat was sown with Zero Till (ZT) in the standing rice straw with residual moisture in one block of three plots (no pre-sowing irrigation for wheat). In the other block of 3 plots, pre-sowing irrigation was given and wheat sown when soil came to workable conditions by conventional tillage practice (CT) providing two hoeing followed by planking. Total crop residue of rice returned to the soil surface in rice-wheat rotation with ZT than with CT (to wheat) was 3.13 t ha-1 . Total amount of organic carbon added to the soil through the above ground straw of rice in the ZT plots was 1.25 t ha. On an average, 40% more of OC and around 45% more of N, P and K were returned with ZT as compared to CT practice. This practice of zero-tillage will prevent, on an average, 4.6 t ha-1 of C02 from emanating to the atmosphere. Zero-till wheat had lower N concentration than corresponding CT wheat indicating lower availability with zero tillage. Total N uptakes of N in wheat at harvest were lower in ZT (144.6 kg ha -1) as compared to CT plots (184.37 kg ha-1 ). However, percent N derived from fertilizer at 44.62 was almost 8% higher than CT treatment, which were only 36.05. Soil profile (0-1.2 m) N content after harvest of wheat at 2612 kg ha-1 in CT plots was higher by 200 kg-1than ZT plots at 2420 kg ha-1 . This could be ascribed to immobilization of the N, as residue decomposition is very slow in ZT plots due to lack of mixing. A mulched, non-plowed tillage system can potentially affect mineralization perhaps due to altered temperature and altered soil moisture content. Total amount of water needed to irrigate the wheat crop to full maturity was less by 1016.5 kg L ha-1 in ZT treatment and there was a net saving of 100 mm ha-1 water in wheat. Water use efficiency in terms of kg wheat grain ha-1 mm-1 was higher by 16% in ZT plots as compared to CT treatment. Post-harvest moisture content in the soil profile (0-1.2 m) in ZT treatment was 30 mm higher than in CT plots. Fewer evaporation losses due to mulching effect of rice-straw in wheat could be the reason for higher moisture content in 0-1.2 m-soil profile in ZT plots.

 

Enantioselective Degradation and Unidirectional Chiral Inversion of 2- Phenylbutyric Acid by Xanthobacter flavus PA1

J.D. Gu* and Y. Liu

Division of Microbiology, School of Biological Sciences, The University of Hong Kong, Hong Kong. *E-mail: jdgu@hkucc. hku. hk

Keywords: Enantioselective biodegradation; chiral inversion; Xanthobacter flavus

Linear alkylbenzenes, associated with detergents and chemical synthesis, are commonly detected in the environments. Microbial degradation of chiral 2-phenylbutyric acid, a carboxylic acid metabolite of linear alkylbenzene degradation, was investigated by using enantioselective high performance liquid chromatography (HPLC). A pure culture of bacteria, identified as Xanthobacter flavus strain PA1 based on 16S rRNA gene, was isolated from mangrove sediments of Hong Kong Mai Po Nature Reserve with ability to utilize the racemic 2-phenylbutyric acid as well as the single enantiomer as the sole carbon and energy source. Aerobic growth in batch experiments with the racemic compound showed that strain PA1 could degrade both enantiomers to completion and utilize them sequentially: the [S] enantiomer disappeared much faster than the [R] enantiomer. When the single pure enantiomer was used as the growth substrate, a unidirectional chiral inversion from [S] enantiomer to [R] enantiomer was observed. No difference was observed in the metabolites during the catabolism of individual enantiomers. The major two degradation intermediates were identified by liquid chromatography-mass spectrometry (LC-MS) and :H & 13C nuclear magnetic resonance (NMR) spectra as 3-hydroxy-2-phenylbutanoic acid and 4-methyl-3-phenyloxetan-2-one. These results provide evidence that the biochemical degradation pathway proceeds with an initial oxidation of the side chain before aromatic ring cleavage. This study reveals new evidence for enantiomeric inversion by pure culture of bacteria and shows the importance of examining the fate of both enantiomers of chiral pollutants in the environment.

Interactions of Bt CrylAa Toxin with Soil and Soil Components: Adsorption, Extraction and Persistence

N. Helassa, G. Daudin1, S. Noinville2, P. Déjardin3, J.M. Janot3, H. Quiquampoix1 and S. Staunton1*

1 INRA-Biogéochimie du Sol et de la Rhizosphére, place Viala, 34060 Montpellier, France. 2CNRS-LADIR, 2 rue Henri Dunant, 94320 Thiais, France. 3CNRS-Institut Européen des Membranes, 47 place Eugene Bataillon, 34095 Montpellier, France. * E-mail: staunton@montpellier.inra.fr

Keywords: Bt CrylAa Toxin; soil interactions; montmorillonite and kaolinite.

Genetically modified (GM) crops, which produce insecticidal Cry proteins from Bacillus thuringiensis (Bt), release the toxins into soils through root exudates and upon decomposition of residues. In contrast to the protoxin produced by the Bacillus, the protein produced in GM crops does not require activation in insect midguts and thereby potentially looses some of its species specificity. Although gene transfer and resistance emergence phenomena are well documented, the fate of these toxins in soil has not yet been clearly elucidated. Cry proteins, in common with other proteins, are adsorbed on soils and soil components. Adsorption on soil and the reversibility of this adsorption is an important aspect of the environmental behaviour of these toxins. The orientation of the molecule and conformational changes on surfaces may modify the toxicity and confer some protection against microbial degradation. Adsorption will have important consequences for both the risk of exposition of non target species and the acquisition of resistance by target species. We have adopted different approaches to investigate the fate of CrylAa in soils and model minerals. In each series of experiments we endeavored to maintain the protein in a monomeric form (pH above 6.5 and a high ionic strength imposed with 150 mM NaCl). The adsorption and the desorbability of the CrylAa Bt insecticidal protein were measured on two different homoionic clays: montmorillonite and kaolinite. Adsorption isotherms obtained followed a low affinity interaction for both clays and could be fitted using the Langmuir equation. Binding of the toxin decreased as the pH increased from 6.5 (close to the isoelectric point) to 9. Maximum adsorption was about 40 times greater on montmorillonite (1.71 g g) than on kaolinite (0.04 g g-1) in line with the contrasting respective specific surface areas of the minerals. Finally, some of the adsorbed toxin was desorbed by water and more, about 36%, by high pH buffers, indicating that it was not extremely tightly bound. Moreover, the toxin was easily and quasi-complete ly desorbed using zwiterrionic and non-ionic detergents. The evolution of the Amide I band measured by Fourier Transform Infrared Spectroscopy indicate pH-dependent changes in conformation of the protein when adsorbed on montmorillonite and silica. Adsorption on montmorillonite prevents oligomerisation. Adsorption was greater and caused a larger degree of conformational change when the silica was made hydrophobic. We have compared the persistence of CrylAa on various soils over several weeks varying microbial activity (inhibition or activation). We can thus distinguish between degradation of the protein and chemical fixation that leads to decreasing efficiency of extraction.

Carbon-13 NMR Spectroscopic Characterization of the HF-insoluble Organic Matter in some Palaeosols from the Loess Plateau, China

B.K.G. Theng1* and H. Knicker2

1bandeare Research, Private Bag 11 052, Palmerston North 4442, New Zealand. 2Lehrstuhlfiir Bodenkunde, Technische Universitat Miinchen, 85350 Fresing, Germany. * E-mail: ThengB@LandcareResearch. co. nz

Keywords: NMR spectroscopy; insoluble organic matter; Palaeosol

We have used solid-state 13C-nuclear magnetic resonance (NMR) spectroscopy to characterize the organic matter in five palaeosols and the topsoil from the Loess Plateau in north-central China that remained in the residue after extraction with HF. The Palaeosol samples were taken at different depths (10-76 m) along the 130 m thick loess-palaeosol type sequence near Luochuan, and ranged in age from 120 to 1070 kyr BP. The overlying surface soil was 10 kyr old. More than 60% of the initial C and N were lost during HF treatment, indicating that most of the organic matter was stabilized by interaction with the mineral constituents, notably CaC03. The 13C-NMR spectra of the organic residue (after HF-treatment) were divided into four chemical shift (δ) regions: (I) 5 = 160-220 ppm, due to carboxylic acids and amides, accounts for <18% of the total spectral intensity; (II) 5 = 110-160 ppm, identifiable with aromatic rings and olefinic (C=C) structures, makes up 28-36% of the total organic carbon; (III) 5 = 60-110 ppm, assigned to O-alkyl and anomeric carbon, accounts for 19-33% of the total carbon; and (IV) 5 = 0-60 ppm, due to aliphatic structures and amino acid side chains in proteins, makes up 26-31% of the total intensity. The abundance of 5-region (I) carbon tends to diminish with an increase in Palaeosol age. On the other hand, the contribution of 5-region (II) carbon increases with depth and time of soil burial. This would indicate a selective enrichment (with age) of aromatic constituents in humic material formed by biological processes. We also propose that these aromatic structures are partly associated with charred residues, formed during vegetation fires that seem likely to have occurred across the Loess Plateau. The long-term survival of 5-region (III) carbon, normally assigned to O-alkyl functional groups in carbohydrate structures, may be due to physical protection within micropores. Alternatively, these groups may be associated with polyhydroxy acids rather than carbohydrates. Carbon in 5-region (IV) may largely be assigned to polymethylene structures as indicated by the intense peak near 5 = 30 ppm. Since the ratio of region IV to region I carbon is < 4, the surviving polymethylene structures may partly represent polymers of short-chain aliphatic acids. Although their abundance tends to diminish with increasing palaeosol age, these recalcitrant structures still make up 26% of the total organic carbon in the oldest palaeosol investigated (1070 kyr BP). The similarity of the spectra of the older Palaeosol samples to those of charred residues and soils containing charred material, published in the literature, is indicative of the refractory character of charred residues and their important role in long-term carbon sequestration.

Molecular Interactions of Pesticides in Whole Soils using Modern NMR Spectroscopy

A.J. Simpson*. M.J. Simpson, A. Shirzadi, R. Kumar, A.J. Baer and Y. Xu

Department of Chemistry, University of Toronto, Scarborough College, 1265 Military Trail, Toronto, Ontario, M1C1A4, Canada. * E-mail: andre.simpson@utoronto.ca

Keywords: Pesticide; NMR spectroscopy; anthropogenic chemicals.

Pesticide sorption to soil organic matter (SOM) plays an important role in reducing pesticide bioavailability, and complicates bioremediation efforts. Elucidation of the mechanistic interactions of anthropogenic chemicals in whole soils as well as understanding the physical and chemical factors which influence their sorption is critical to understanding and eventually predicting their behavior in the environment. This presentation will introduce and explain a range of novel Nuclear Magnetic Resonance (NMR) approaches that can directly applied to whole soils to assess the molecular interaction of anthropogenic chemicals at the molecular level. Information garnered includes: 1) Identifying the binding mechanism of contaminants in whole soils, 2) Identifying the soil components responsible for binding, 3) Monitoring the real-time kinetic transfer of pesticides from the solution-phase, through the gel-phase and finally sequestration into solid phase. High Resolution Magic Angle Spinning NMR will be briefly introduced as well as the concepts of single (STD) and double difference (STDD) saturation transfer NMR.

Figure 1. The binding epitope of Acifluorfen in a whole peat soil. Percentage (%) indicates the relative strength of interaction for each proton with the soil surface.

 

 

Results will be provided showing how binding mechanisms can be easily extracted from these experiments for a range of pesticides. For example, the binding epitope of acifluorfen in whole soil (Figure 1) shows how NMR can be used to gain specific information as to the molecular binding of pesticides in whole soil. Results indicate that dipolar interactions, H-bonding, hydrophobic associations and potentially π-π interactions are the predominant sorption mechanisms for pesticides at the soil-aqueous interface. It is evident that soil physical and chemical characteristics are highly influential in determining the mechanisms of pesticide sorption, as they significantly affect soil conformation. In particular, different binding mechanisms were observed for 1-naphtol in soil swollen using buffer versus D20, indicating that the Koc alone may not be enough to accurately predict the behavior of a molecule in a real soil environment. Preliminary kinetic-based studies suggest that both the swelling solvent and soil moisture content significantly influence the sequestration of trifluralin. These studies demonstrate that HR-MAS and STDD NMR are powerful and versatile tools which can be applied to expand our knowledge of the mechanistic interactions of agrochemicals at the molecular level.

 

Coupled LTA - PAS FTIR Approach for Studies of Organic Matter Dynamics and Function at the Interface of Soil Aggregates

L.P. D'Acqui1*, A. Pucci1'2 and L. Calamai1

1istitutoper ¡o Studio degli Ecosistemi CNR - ISE, Via Madonna del Piano, 50019,- Sesto Fiorentino, Italy. 2Dipartimento di Scienze del Suolo e Nutrizione della Pianta, Universitá di Firenze. Piazzale delle Cascine 28, 50144-Firenze, Italy. * E-mail: dacqui@ise.cnr.it

Keywords: Organic matter; LTA - PAS FTIR spectroscopy; soil aggregates.

LTA-PAS FTIR approach can be considered as an original tool useful to study the dynamics, function and protection of soil organic matter (SOM). Studies on SOM are generally carried out mainly using chemical extraction methods that modify both organic substances and mineral phases resulting in possible artifact. Low-Temperature Ashing (LTA) by oxygen plasma allows a controlled removal at low temperature of SOM from the mineral matrix of soil aggregates with minimal disturbance and damage to the inorganic constituents. Photoacoustic (PAS) -FTIR spectroscopy allows to obtain IR spectra from the surface of irregular tri-dimensional specimens. When LTA is coupled with PAS-FTIR spectroscopy, it is possible, at each step, to obtain spectroscopic evidences of the residual OM layers and, by difference, the spectra of the removed SOM. Therefore, the coupled LTA-PAS-FTIR approach can provide insights on the nature of SOM as well as the surface interaction of organic substances in undisturbed soil aggregates or in other solid materials.

 

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