Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

    We have a manual that explains all the features 

    Current refinement(s):

    Records 1 - 20 / 181

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    Dermal absorption and toxicological risk assessment : pitfalls and promises
    Buist, H. - \ 2016
    Wageningen University. Promotor(en): Ruud Woutersen; Ivonne Rietjens, co-promotor(en): J.J.M. van de Sandt. - Wageningen : Wageningen University - ISBN 9789462577275 - 200
    skin - absorption - permeability - in vitro - experiments - exposure assessment - risk assessment - toxicology - biocides - rodenticides - preservatives - disinfection - huid - absorptie - permeabiliteit - in vitro - experimenten - blootstellingsbepaling - risicoschatting - toxicologie - biociden - rodenticiden - conserveermiddelen - desinfectie

    Absorption of toxic substances via the skin is an important phenomenon in the assessment of the risk of exposure to these substances. People are exposed to a variety of substances and products via the skin, either directly or indirectly, while at work, at home or in public space. Pesticides, organic solvents and metalworking fluids are seen to be important contributors to adverse health effects due to occupational exposure via the skin. In daily life, cosmetics, clothing and household products are the most relevant commodities with respect to exposure via the skin.

    Given the importance of skin exposure in the assessment of the risk of toxic substances, the objective of this thesis was to further develop, evaluate and improve methods for including skin absorption data this assessment.

    In this thesis, four factors influencing dermal absorption, namely dermal loading (chapters 3 and 6), irritative/corrosive potential (chapters 3 and 4), frequency of exposure (chapters 3, 4 and 5) and the vehicle used (chapter 5), were investigated in more detail. Furthermore, a model to extrapolate infinite dose absorption data to finite dose conditions, baptized Dermal Absorption Model for Extrapolation (DAME), was developed and tested.

    I

    n chapter 2 of this thesis, the relationship between relative dermal absorption and dermal loading was investigated. Hundred-and-thirty-eight dermal publicly available absorption experiments with 98 substances were evaluated. The results obtained revealed that dermal loading ranged mostly between 0.001 and 10 mg/cm2. In 87 experiments (63%), an inverse relationship was observed between relative dermal absorption and dermal loading. On average, relative absorption at high dermal loading was 33 times lower than at low dermal loading. Known skin irritating and volatile substances less frequently showed an inverse relationship between dermal loading and relative absorption. It was concluded that when using relative dermal absorption in regulatory risk assessment, its value should be determined at or extrapolated to dermal loadings relevant for the exposure conditions being evaluated.

    I

    n chapter 3 of this thesis, a literature search was presented with the aim to investigate whether neglecting the effects of repeated exposure may lead to an incorrect estimate of dermal absorption. The results demonstrated that the effect of repeated versus single exposure does not demonstrate a unique trend. Nevertheless, an increase in daily absorption was frequently observed upon repeated daily exposure. The little information available mostly concerned pharmaceuticals. However, consumers and workers may be repeatedly exposed to other types of chemicals, like disinfectants and cleaning products, which often contain biocidal active substances that may decrease the barrier function of the skin, especially after repeated exposure. These biocidal products, therefore, may present a safety risk that is not covered by the current risk assessment practice since absorption data are usually obtained by single exposure experiments. Consequently, it was decided to investigate the importance of this issue for biocide safety evaluation. As the literature search revealed that hardly any data on absorption upon repeated dermal exposure to biocides are available, it was concluded that data need to be generated by testing.

    To cover the entire range of biocidal products in such testing, a representative series of biocidal substances should be tested, making in vitro testing of dermal absorption the preferred choice over in vivo testing. Based on an inventory made, it appeared that the 16 product types represented among the biocidal products authorised in the Netherlands could be clustered into 6 more or less homogeneous categories based on similarity in active substances. This result could facilitate experimental testing by providing a basis for selection of a limited number of representative compounds to be evaluated.

    I

    n chapter 4 of this thesis, the importance of the effect of repeated dermal exposure on skin permeability for biocide safety evaluation was investigated, using a selection of nine representative biocides from the inventory made in chapter 3. The in vitro dermal penetration of tritiated water and [14C]propoxur was chosen as a measure of the permeability and integrity of human abdominal skin after single and repeated exposure. The results indicated that single and repeated exposure to specific biocidal products (e.g. the quaternary ammonium chlorides DDAC and ADBAC) may significantly increase skin permeability, especially when the compounds are applied at high concentrations, while a substance like formaldehyde may reduce skin permeability under specific conditions.

    I

    n chapter 5 of this thesis, the in vitro dermal absorption kinetics of the quaternary ammonium compound didecyldimethylammonium chloride (DDAC) during single and repeated exposure was studied in more detail. In addition, the influence of biocidal formulations on the absorption of DDAC was investigated, because it was expected that formulation characteristics may be another factor influencing its dermal absorption. The analysis of biocidal products on the Dutch market, reported in chapter 3, indicated that DDAC is often used in combination with other active ingredients. DDAC was most frequently combined with formaldehyde, glutaraldehyde and/or alkyldimethylbenzyl­ammo­nium chloride (ADBAC). Consequently, commercial formulations containing one or more of these additional active ingredients were selected, in addition to one formulation containing only DDAC as an active ingredient. The selected commercial formulations tended to reduce skin penetration of DDAC. This was most pronounced with the formulation containing the highest concentration of formaldehyde (196 mg/mL) and glutaraldehyde (106 mg/mL), which reduced the flux of DDAC across the skin by 95%. The reduction caused by the only tested formulation containing no other active ingredients than DDAC, and thus incorporating no aldehydes, was smallest, and did not reach statistical significance.

    I

    n chapter 6 of this thesis, a simple in silico model to predict finite dose dermal absorption from infinite dose data (kp and lag time) and the stratum corneum/water partition coefficient (KSC,W) was developed. This model was tentatively called Dermal Absorption Model for Extrapolation (DAME). As dermal exposure may occur under a large variety of conditions leading to quite different rates of absorption, such a predictive model using simple experimental or physicochemical inputs provides a cost-effective means to estimate dermal absorption under different conditions.

    To evaluate the DAME, a series of in vitro dermal absorption experiments was performed under both infinite and finite dose conditions using a variety of different substances. The kp’s and lag times determined in the infinite dose experiments were entered into DAME to predict relative dermal absorption value under finite dose conditions. For six substances, the predicted relative dermal absorption under finite dose conditions was not statistically different from the measured value. For all other substances, measured absorption was overpredicted by DAME, but most of the overpredicted values were still lower than 100%, the European default absorption value for the tested compounds.

    In conclusion, our finite dose prediction model (DAME) provides a useful and cost-effective estimate of in vitro dermal absorption, to be used in risk assessment for non-volatile substances dissolved in water at non-irritating concentrations.

    I

    n chapter 7 of this thesis, the results of the research reported in chapters 2 to 6 were put into perspective, the pitfalls and promises emanating from them discussed and general conclusions drawn. The possible influence of vehicles on absorption and the possible impact of irritative or corrosive vehicles or chemicals on the skin barrier have been demonstrated in this thesis. An in silico predictive model tentatively called DAME was developed, which enables the user to evaluate a variety of dermal exposure scenarios with limited experimental data (kp and lag time) and easy to obtain physicochemical properties (MW and log KOW). The predictions of our experiments reported in chapter 6 were compared to those of the Finite Dose Skin Permeation (FDSP) model published on the internet by the US Centers for Disease Control and Prevention (CDC). DAME outperformed FDSP (R2 of the correlation predicted/measured potential absorption 0.64 and 0.12, respectively). At present, the applicability domain of DAME is limited to non-volatile substances dissolved in aqueous solvents. However, in future the model will be adapted to include volatile substances as well.

    Altogether, it is concluded that dermal exposure can be an important factor in risks posed by chemicals and should be taken into account in risk assessment. The methods to actually do this are still open for further improvement to better account for the various factors influencing skin penetration and to develop adequate combinations of in vitro and in silico models that can accurately predict human dermal absorption.

    Interacties tussen ijzerchelaten en andere spoorelementen vaak onderschat : analysecijfers tonen niet altijd wat beschikbaar is voor plant
    Staalduinen, J. van; Voogt, W. - \ 2015
    Onder Glas 12 (2015)5. - p. 10 - 11.
    glastuinbouw - voedingsstoffen - bemesting - ijzerhoudende meststoffen - plantenvoeding - ijzerabsorptie - chelaten - meststoffen met sporenelementen - absorptie - zuurgraad - substraten - recirculatiesystemen - irrigatiewater - greenhouse horticulture - nutrients - fertilizer application - iron fertilizers - plant nutrition - iron absorption - chelates - trace element fertilizers - absorption - acidity - substrates - recirculating systems - irrigation water
    IJzer is onder normale wortelcondities vaak moeilijk opneembaar voor planten. Dat geldt ook en misschien wel juist voor substraatteelten. IJzerchelaten – organische moleculen die ijzerionen adsorberen en afstaan aan of in plantenwortels – bieden uitkomst. Bij de keuze van het juiste chelaat dient men niet alleen oog te hebben voor de pH van de voedingsoplossing of in de mat. Zij kunnen ook verbindingen aangaan met andere spoorelementen, waardoor drainwateranalyse soms een vertekend beeld geeft van wat er werkelijk beschikbaar is.
    Osmose houdt cellen op spanning : de drijvende kracht achter openen en sluiten van huidmondjes
    Heuvelink, E. ; Kierkels, T. - \ 2009
    Onder Glas 6 (2009)11. - p. 24 - 25.
    tuinbouwbedrijven - kassen - teelt onder bescherming - planten - osmose - absorberend vermogen - waterbalans - opname (uptake) - beweging van huidmondjes - sluitcellen - absorptie - glastuinbouw - market gardens - greenhouses - protected cultivation - plants - osmosis - absorptivity - water balance - uptake - stomatal movement - guard cells - absorption - greenhouse horticulture
    Osmose houdt cellen op spanning. Het is ook de druivende kracht achter openen en sluiten van huidmondjes. Bij de opname van water door de wortels, is osmose juist een tegenwerkende kracht, vooral bij een hogere EC. Aandacht voor watervoorziening, EC kalium- en calciumvoorziening is nodig om de zaken goed te laten verlopen
    Energy efficient multistage zeolite drying for heat sensitive products
    Djaeni, M. - \ 2008
    Wageningen University. Promotor(en): Gerrit van Straten; Johan Sanders, co-promotor(en): Ton van Boxtel; Paul Bartels. - [S.l.] : S.n. - ISBN 9789085852094 - 162
    drogers - drogen - droogmethoden - absorptie - adsorptie - adsorberende middelen - energiegebruik - ontvochtiging - drogende lucht - energiebesparing - computationele vloeistofdynamica - driers - drying - drying methods - absorption - adsorption - adsorbents - energy consumption - dehumidification - drying air - energy saving - computational fluid dynamics
    Although drying takes a significant part of the total energy usage in industry, currently available drying technology is often not efficient in terms of energy consumption. Generally, the energy efficiency for drying processes ranges between 20-60% depending on the dryer type and product to be dried. This research focuses on the development of single and multistage zeolite drying combined with heat recovery unit to enhance the energy efficiency. The evaluation using steady state and two dimensional model showed that for single stage system the energy efficiency can reach 70-75% and it increases corresponding to the stage number. For 2-3 stages, the energy efficiency 80-90% can be achieved. The experimental work using single stage zeolite dryer also showed that the energy efficiency is close to conceptual approach. Based on the impressive results, a number of potential options have been formulated to construct the zeolite dryer in continuous operating systems for industrial application.
    Trees : relief for the city
    Hiemstra, J.A. ; Schoenmaker-van der Bijl, E. ; Tonneijck, A.E.G. ; Hoffman, M.H.A. - \ 2008
    Boskoop : Plant Publicity Holland - 33
    bomen - luchtkwaliteit - luchtverontreiniging - stedelijke gebieden - steden - stof - ozon - stikstofoxiden - windschermen - absorptie - nederland - fijn stof - trees - air quality - air pollution - urban areas - towns - dust - ozone - nitrogen oxides - windbreaks - absorption - netherlands - particulate matter
    This brochure describes the underlying principles that form a basis for better-informed choices with regards to the management of trees and shrubs in cities and the design of functional planting schemes.
    Modelling volatile fatty acid dynamics and rumen function in lactating cows
    Bannink, A. - \ 2007
    Wageningen University. Promotor(en): Seerp Tamminga; J. France, co-promotor(en): Jan Dijkstra. - [S.l.] : S.n. - ISBN 9789085047858 - 251
    koeien - lactatie - vluchtige vetzuren - dynamische modellen - pensfermentatie - absorptie - pensepitheel - voedingsfysiologie - celmetabolisme - cows - lactation - volatile fatty acids - dynamic models - rumen fermentation - absorption - rumen epithelium - nutrition physiology - cell metabolism
    Mathematical models are developed to quantity and integrate the various processes involved with rumen fermentation. Three extant mechanistic models of rumen fermentation were studied (Baldwin et al., Danfær and Dijkstra et al.), each with a truly dynamic representation but different conceptual approach. The models were compared on mathematical representation of individual processes and their prediction accuracy was evaluated. Although the models predicted similar rates of substrate degradation and rumen outflow of organic matter, total crude protein and microbial protein, they differed substantially in representation of the underlying microbial mechanisms. The model of Baldwin et al. performed best in prediction of the combination of rumen pool sizes and duodenal flows, whereas the model of Dijkstra et al. was evaluated to deliver the most realistic outflow of rapidly fermentable carbohydrates. Further, it was identified that all models needed improvement with respect to the prediction of amounts and type of volatile fatty acids (VFA) produced. In a subsequent evaluation is was investigated to what extent individual model elements, of a selection of five, could be responsible for inaccurate VFA predictions. The results suggested that inaccuracy of stoichiometric coefficients of VFA yield from fermented substrate (VFA coefficients) and incorrect representations of VFA absorption kinetics are the most likely causes. New values of VFA coefficients were derived by regression of a stoichiometric model of VFA yield against data of VFA molar proportions observed in vivo in rumen fluid of lactating cows. Inputs to the model were observed rates of rumen substrate degradation. Regression against simulated data sets including random error indicated that the accuracy of this method to estimate VFA coefficients is acceptable. Estimates from regressions against in vivo data delivered new sets of VFA coefficients for roughage-rich and concentrate-rich diets. In a follow-up study the representation of stoichiometry was made pH-dependent. With regression of this model against in vivo data a profound effect of rumen pH on the type of VFA formed from rapidly fermentable carbohydrates was established. Besides VFA production, the rumen concentrations and the amount and profile of VFA available for the cow are also affected by absorption and metabolism of VFA by epithelial tissues in the rumen wall. A mechanistic model was constructed that represents the dynamics of these processes, including the effects of changes in VFA concentration differences between different compartments, the effect of competitive inhibition between VFA and the effect of changes in surface area and epithelial mass. Although some essential characteristics of VFA transport and intra-epithelial metabolism could be reproduced by the model, it was concluded that there is a definite need for more experimental data. It is concluded that various levels of functioning need to be included when representing whole rumen function. Besides intrinsic degadation characteristics and passage of ingested substrates, environmental conditions in the rumen and the functionality of the rumen wall need to addressed.
    Vooronderzoek absorptie grondgeluid Polderbaan Schiphol
    Akker, J.J.H. van den; Kekem, A.J. van - \ 2006
    Wageningen : Alterra (Alterra-rapport 1358) - 80
    geluidshinder - lawaaibestrijding - absorptie - bodem - grondverbeteraars - nederland - bodemfysica - luchthavens - grondbewerking - noord-holland - airports - noise pollution - noise abatement - soil physics - tillage - absorption - soil - soil amendments - netherlands - noord-holland
    Het geluid van startende vliegtuigen vanaf de Polderbaan veroorzaakt overlast in Hoofddorp-Noord, vooral bij noordoostelijke wind in de winter. Dit grondgeluid zou ten dele door poreuze gronden geabsorbeerd kunnen worden. Dit onderzoek gaat na wat de bodemkundige mogelijk¬heden zijn voor het aanleggen van stabiele ploegruggen of grondruggen. Ook worden de land¬bouwkundige en landbouweconomische aspecten behandeld. Daarnaast zijn diverse stakeholders benaderd. In een vervolgonderzoek zullen de effecten van ploegen en grondruggen op geluidsabsorptie nader onderzocht worden
    Effects of flavour absorption on foods and their packaging materials
    Willige, R.W.G. van - \ 2002
    Wageningen University. Promotor(en): A.G.J. Voragen; J.P.H. Linssen. - S.l. : S.n. - ISBN 9789058086402 - 140
    geurstoffen en smaakstoffen - absorptie - verpakkingsmaterialen - voedselverpakking - eiwitten - koolhydraten - vetten - membraanpermeabiliteit - smaakpanels - modellen - flavour compounds - absorption - packaging materials - food packaging - proteins - carbohydrates - fats - membrane permeability - taste panels - models

    Keywords: flavour absorption, scalping, packaging, food matrix, lldpe, ldpe, pp, pc, pet, pen,b-lactoglobulin, casein, pectin, cmc, lactose, saccharose, oil, modelling, storage, oxygen permeability, taste perception, sensory quality.

    Absorption of flavour compounds by linear low-density polyethylene (LLDPE) was studied in model systems representing differences in composition of the food matrix. Proteins,b-lactoglobuline and casein, were able to bind flavours, resulting in suppression of absorption of flavour compounds. Polysaccharides, pectin and carboxymethylcellulose, increased viscosity, and consequently decreased absorption. Disaccharides, lactose and saccharose, increased absorption, probably caused by a "salting out" effect of less apolar flavour compounds. The presence of a relative small amount of oil (50 g/l) decreased absorption substantially. Combined oily model systems, oil/casein and oil/pectin, showed a similar effect. The extent of absorption of flavour compounds by LLDPE was influenced by food components in the order: oil or fat >> polysaccharides and proteins > disaccharides. A model based on the effect of the polarity (log P) of flavour compounds and on their partitioning coefficients between food(matrix) and packaging material was developed. The model is able to predict absorption of flavour compounds from foods into LLDPE when lipids in the food matrix are the determining factor in flavour absorption. Results show that the model fits nicely with experimental data of real foods skim and whole milk.

    LLDPE, polypropylene (PP), polycarbonate (PC), polyethylene terephthalate (PET film and PET bottle) and polyethylene naphthalate (PEN) were immersed in a model flavour solution at different temperatures up to 14 days. The absorption rate and/or total amount of absorbed compounds increased considerably with increasing temperature. Depending on temperature, the total absorption of flavour compounds by the polyolefins (LLDPE and PP) was up to 2400 times higher than by the polyesters (PC, PET and PEN).

    The effect of absorbed flavour compounds on the oxygen permeability of low-density polyethylene (LDPE), PP, PC and PET was studied. Due to swelling of the polymers as a result of absorption of flavour compounds, LDPE and PP showed a significant increase of oxygen permeability of 21% and 130%. The oxygen permeability of PC showed a significant decrease of 11% due to occupation or blockage of the "micro-cavities" by the absorbed flavour compounds. Flavour absorption by PET did not affect the oxygen permeability significantly.

    The influence of flavour absorption LDPE, PC and PET on the taste perception of a flavour model solution and orange juice stored in glass bottles was studied with and without pieces of the respective plastic films. Although the content of flavour compounds between controls and polymer treated samples decreased substantially due to absorption, no significant effect on the taste perception of the model solution and orange juice were observed by triangular taste panel tests.

    Landschapselementen ter verbetering van de luchtkwaliteit rond de Ruit van Rotterdam. Een haalbaarheidsstudie.
    Tonneijck, A.E.G. ; Blom-Zandstra, M. - \ 2002
    Wageningen : Plant Research International - 26
    steden - stedelijke gebieden - luchtverontreiniging - verkeer - planten - groene zones - absorptie - stikstofoxiden - luchtkwaliteit - milieuwetenschappen - fijn stof - towns - urban areas - air pollution - traffic - plants - green belts - absorption - nitrogen oxides - air quality - environmental sciences - particulate matter
    Haalbaarheidsstudie naar het gebruik van landschapselementen als zuiveraars van lucht rond de Ruit van Rotterdam (ringweg die bestaat uit de A20, A15, A16 en de A4). Waarbij gelet op de soms extreme groeiomstandigheden in de restruimten. De aandacht is speciaal gericht op stikstofdioxiden (NO2) en fijn stof.
    Effects of fermented soya bean on digestion, absorption and diarrhoea
    Kiers, J.L. - \ 2001
    Wageningen University. Promotor(en): F.M. Rombouts; M.J.R. Nout; M.J.A. Nabuurs. - S.l. : S.n. - ISBN 9789058084729 - 110
    gefermenteerde voedingsmiddelen - tempé - natto - sojaproducten - metabolisme - voedingsfysiologie - spijsvertering - absorptie - diarree - darmmicro-organismen - fermented foods - tempeh - natto - soyabean products - metabolism - nutrition physiology - digestion - absorption - diarrhoea - intestinal microorganisms

    For many centuries Asian people have consumed soya beans in various forms of traditional fermented soya bean foods. Major desirable aspects of fermented soya bean foods are their attractive flavour and texture, certain nutritional properties, and possible health promoting effects. This study describes effects of fermented soya beans on gastrointestinal physiology and addresses digestion, absorption and diarrhoea.

    Using an in vitro digestion model it appeared that fermentation increased solubility and absorbability to a large extent as a result of protein and carbohydrate degradation. The level of water-soluble dry matter increased during fermentation with Rhizopus sp. (tempe) from an initial 7 up to 27%, and during fermentation with Bacillus sp. from an initial 22 up to 65%. In vitro digestibility was only slightly higher for the fermented soya beans. Soya beans are more or less pre-digested by the action of the micro-organisms and can therefore serve as a source of easily available nutrients.

    Tempe extracts did not inhibit the growth of Escherichia coli. Enterotoxigenic E. coli (ETEC) induced haemagglutination of red blood cells was strongly inhibited by tempe extracts, and in vitro adhesion of ETEC to brush border membranes isolated from the small intestine of piglets was inhibited up to 95% by several tempe extracts.

    Perfusion of small intestinal segments of anaesthetised piglets showed an inverse relationship between osmolality and net fluid absorption (linear correlation). ETEC infection of small intestinal segments prior to perfusion resulted in an osmolality independent reduction of net fluid absorption of approximately 400μl/cm 2. Both cooked soya bean and tempe were able to minimise this reduction in net fluid absorption induced by ETEC. However, sodium losses as a result of ETEC infection were lower and dry matter and total solute absorption were higher for tempe when compared to cooked soya bean. A fraction containing high-molecular-weight components (> 5kDa) was shown to be mainly responsible for the observed protective effect of tempe. Several possible mechanisms of action are outlined and discussed.

    Soya beans fermented with Rhizopus microsporus showed better protection against ETEC-induced diarrhoea compared to cooked and especially toasted (commercial) soya beans in weaned piglets in vivo . Furthermore, fermentation of cooked soya beans, especially with Bacillus subtilis , resulted in increased feed efficiency probably as a result of increased digestibility. These characteristics imply the potential of using fermented soya beans in individuals suffering from diarrhoea and malnutrition.

    Bioavailability of the fungicides carbendazim and iprodione in soil, alone and in mixtures
    Matser, A.M. ; Leistra, M. - \ 2000
    Wageningen : Alterra (Alterra-rapport 156) - 60
    bodemverontreiniging - pesticiden - fungiciden - absorptie - biologische beschikbaarheid - soil pollution - pesticides - fungicides - absorption - bioavailability
    Measures to protect soil ecosystems require research data on the effects of toxic chemicals on soil organisms. In the co-operative MIXTOX project, the effect of mixtures of toxic chemicals on some animal species in soil is studied. Mutual interactionsin the behaviour of toxic chemicals in soil may be expected to affect the exposure of the organisms to the mixtures. The fungicides carbendazim and iprodione compete in the adsorption on soils, which increases their bio-availability in mixtures. The transformation of the fungicides is slowed down in mixtures, which also increases their bio-availability. The exposure of soil animals to the fungicides in soil solution is much higher in the mixtures than when a fungicide alone is present in soil. The inclusion of copper in the mixture has little additional effect on the bio-availability of the fungicides in pore water. Chemical analyses in the framework of the dose-response experiments of the research partners serve as a check on the dose and on unexpected losses of the fungicides.
    Vochtverbruik en droogtegevoeligheid van voedergewassen : experimenteel onderzoek 1994 - 1996
    Smid, H.G. ; Grashoff, C. ; Aarts, H.F.M. - \ 1998
    Wageningen : AB-DLO (Rapport / Dienst Landbouwkundig Onderzoek, Instituut voor Agrobiologisch en Bodemvruchtbaarheidsonderzoek 91)
    voedergewassen - oogsttoename - oogstverliezen - opbrengsten - groei - gewassen - oogstschade - beschadigingen door droogte - waterbehoefte - vloeistoffen (liquids) - absorptie - emissie - omloop - bodemwatergehalte - fodder crops - yield increases - yield losses - yields - growth - crops - crop damage - drought injury - water requirements - liquids - absorption - emission - circulation - soil water content
    Kinetic Freundlich equation applied to soils with a high residual phosphorus content
    Chardon, W.J. ; Blaauw, D. - \ 1998
    Soil Science 163 (1998)1. - ISSN 0038-075X - p. 30 - 35.
    bodem - fosfor - absorptie - adsorptie - soil - phosphorus - absorption - adsorption
    Modelling water and nutrient uptake of crops grown in protected cultivation
    Willigen, P. de; Heinen, M. - \ 1998
    Acta Horticulturae 456 (1998). - ISSN 0567-7572 - p. 227 - 236.
    bodem - elektrische eigenschappen - elektrische geleiding - magnetische eigenschappen - vloeistoffen (liquids) - absorptie - modellen - onderzoek - computersimulatie - simulatie - simulatiemodellen - glastuinbouw - soil - electrical properties - electrical conductance - magnetic properties - liquids - absorption - models - research - computer simulation - simulation - simulation models - greenhouse horticulture
    This paper presents results of model calculations on uptake of water and nutrients by a lettuce crop grown in a sand bed. Emphasis is on the effect of salt concentration (osmotic head) on water uptake. This effect was studied using a two-dimensional model of water and nutrient transport in and uptake from a rooting medium. The main conclusion is that under normal conditions as found in Dutch horticulture, osmotic effect on water uptake is not important, but that it depends on the distribution of salts with respect to that of the roots.
    Theory of radiative transfer models applied in optical remote sensing of vegetation canopies
    Verhoef, W. - \ 1998
    Agricultural University. Promotor(en): M. Molenaar; N.J.J. Bunnik. - S.l. : S.n. - ISBN 9789054858041 - 310
    remote sensing - absorptie - reflectie - plantengemeenschappen - vegetatie - onderzoek - toepassingen - modellen - remote sensing - absorption - reflection - plant communities - vegetation - research - applications - models

    In this thesis the work of the author on the modelling of radiative transfer in vegetation canopies and the terrestrial atmosphere is summarized. The activities span a period of more than fifteen years of research in this field carried out at the National Aerospace Laboratory NLR.

    For the interpretation of optical remote sensing observations of vegetation canopies from satellites or aircraft the use of simulation models can be an important tool, as these models give insight in the relations between vegetation properties and observed remote sensing data.

    The models discussed here are first presented from a theoretical point of view. An attempt has been made to construct a framework in which all the discussed models, for vegetation as well as for the atmosphere, can be represented. After an introduction on basic radiometric quantities and relations (chapter 2), and a classification of radiative transfer models and solution methods (chapter 3), examples of existing models are discussed in chapter 4.

    In chapter 5 a new generalized theory of radiative transfer models for azimuthally isotropic media is presented, namely the (N+2)-stream theory. This theory describes radiative transfer in vegetation canopies or atmospheres to any desired numerical accuracy. In the formulation of the analytical solution of this model, which is based on eigenvector decomposition, much attention has been paid to possible numerical problems. Symmetry relations are exploited in order to reduce memory requirements and computation time, and expressions have been found for which the so-called reciprocity relations are automatically fulfilled. The numerical capabilities of this model for simulation of atmospheric radiative transfer are demonstrated in chapter 6.

    The theory of the vegetation canopy bidirectional reflectance models SAIL and SAILH are discussed in chapters 7 and 8. Both are four-stream models. In SAILH the so-called hot spot effect, which is related with the finite leaf size, is incorporated. After these more theoretic chapters, practical aspects of the radiative transfer models are discussed in the following chapters.

    In chapter 9 the application of a four-stream atmosphere model to the correction and calibration of Landsat Thematic Mapper images is demonstrated. This atmosphere model has been coupled with the SAILH model into an overall four-stream model of optical remote sensing observations from any altitude. This model is called OSCAR (optical soil-canopyatmosphere radiance) and is presented in chapter 10.

    Applications of radiative transfer modelling to optical remote sensing problems are illustrated in chapter 11, and chapter 12, summarizes the conclusions of this thesis.

    De 'beschikbaarheid' van zware metalen voor planten.
    Lexmond, T.M. ; Castilho, P. del - \ 1998
    Bodem 8 (1998). - ISSN 0925-1650 - p. 14 - 16.
    bodem - zware metalen - vloeistoffen (liquids) - absorptie - wortels - soil - heavy metals - liquids - absorption - roots
    The role of macromolecular stability in desiccation tolerance
    Wolkers, W.F. - \ 1998
    Agricultural University. Promotor(en): L.H.W. van der Plas; F.A. Hoekstra. - S.l. : Wolkers - ISBN 9789054858805 - 244
    vloeistoffen (liquids) - absorptie - emissie - omloop - veroudering - abcissie - degeneratie - necrose - verouderen - verwelking - biochemie - metabolisme - polymeren - moleculaire biologie - biofysica - eiwitten - enzymen - nucleïnezuren - celfysiologie - liquids - absorption - emission - circulation - senescence - abscission - degeneration - necrosis - aging - wilting - biochemistry - metabolism - polymers - molecular biology - biophysics - proteins - enzymes - nucleic acids - cell physiology

    The work presented in this thesis concerns a study on the molecular interactions that play a role in the macromolecular stability of desiccation-tolerant higher plant organs. Fourier transform infrared microspectroscopy was used as the main experimental technique to assess macromolecular structures within their native environment.

    Protein secondary structure and membrane phase behavior of Typha latifolia pollen were studied in the course of accelerated aging. The overall protein secondary structure of fresh pollen highly resembled that of aged pollen, which indicates that endogenous proteins in these pollen are very stable, at least with respect to their conformation. In contrast, large changes in membrane phase behavior were detected between fresh and aged pollen. Membranes isolated from fresh pollen occurred mainly in the liquid crystalline phase at room temperature, whereas the membranes of aged pollen were at least partly in the gel phase (Chapter 2).

    The in situ heat stability of the proteins in this pollen was studied as a function of the water content of the pollen. Temperature-induced denaturation of proteins was accompanied by the formation of intermolecular extendedbeta-sheet structures. Below 0.16 g H 2 O g -1dry weight (DW), the temperature at which the proteins began to denature increased rapidly and the extent of protein structural rearrangements due to heating decreased (Chapter 3).

    Inspection of the overall protein secondary structure of thin slices of embryo axes of onion, white cabbage and radish seeds did not show signs of protein aggregation and denaturation after long-term dry storage. It was concluded that, despite the loss of viability and the long postmortem storage period, secondary structure of proteins in desiccation-tolerant dry seed is very stable and conserved during at least several decades of open storage (Chapter 4).

    Adaptations in overall protein secondary structure in association with the acquisition of desiccation tolerance were studied using isolated immature maize embryos. Isolated immature maize ( Zea mays ) embryos acquire tolerance to rapid drying between 22 and 25 days after pollination (DAP) and to slow drying from 18-DAP onwards. In fresh, viable 20- and 25-DAP embryo axes, the overall protein secondary structure was identical, and this was maintained after flash drying. On rapid drying, 20-DAP axes showed signs of protein breakdown and lost viability. Rapidly dried 25-DAP embryos germinated and had a protein profile similar to the fresh control. On slow drying, thealpha-helical contribution in both the 20- and 25-DAP embryo axes increased when compared with that in the fresh controls, and survival of desiccation was high. The protein profile in dry mature axes resembled that after slow drying of the immature axes. Rapid drying resulted in an almost complete loss of membrane integrity in 20-DAP embryo axes and much less so in 25-DAP axes. After slow drying, membrane integrity was retained in both the 20- and 25-DAP axes. It was concluded that slow drying of excised immature embryos leads to an increased proportion ofalpha-helical protein structures in their axes, which coincides with additional tolerance of desiccation stress (Chapter 5).

    A novel FTIR method was used to study glasses of pure carbohydrates and glasses in the cytoplasm of desiccation-tolerant plant organs. The method is based on a temperature study of the position of the OH-stretching vibration band (vOH). The glass transition temperatures ( Tg s) of several dry carbohydrate glasses determined by this FTIR method resembled those of produced by other methods. FTIR analysis gives additional information on the molecular properties of glassy structures. The shift ofvOH with temperature - the wavenumber-temperature coefficient (WTC) - is indicative of the average strength of hydrogen bonding in glasses. The WTC was found to be higher in sugar glasses having higher Tg . This suggests that carbohydrate glasses are more loosely packed when they have higher Tg . For Typha latifolia pollen and dried Craterostigma plantagineum leaves similarvOH vs temperature plots were obtained as for pure carbohydrate glasses, indicating that a glass transition was observed. The data suggested that the carbohydrates that are present in the cytoplasm of these plant organs are the primary components contributing to the glassy state (Chapter 6).

    In order to find a relation between desiccation tolerance and physical stability, the heat stability of proteins and the properties of the glassy matrix in several dry maturation-defective mutant seeds of Arabidopsis thaliana were studied. Proteins in dried wild-type seeds did not denature up to 150°C. In dried desiccation-sensitive lec1-1 , lec1-3 and abi3-5 seeds, protein denaturation occurs at temperatures below 100°C. In desiccation-tolerant abi3-7 and abi3-1 seeds, protein denaturation commenced above 120 and 135°C, respectively. The maximal rate of change ofvH with temperature was much higher in abi3-5 , lec1-1 and lec1-3 mutant seeds than in wild-type, abi3-1 , and abi3-7 seeds. This was interpreted as a higher molecular packing density in dried desiccation-tolerant than in dried desiccation-sensitive seeds, which is associated with a higher, respectively lower protein denaturation temperature. The generally lower physical stability of the desiccation-sensitive mutant seeds coincides with a lack of biochemical adaptations that normally occur in the later stages of seed development (Chapter 7).

    The relation between physical stability and desiccation tolerance was also studied in slowly dried (desiccation-tolerant) and rapidly dried (desiccation-sensitive) carrot somatic embryos. Although protein denaturation temperatures were similar in the embryos after slow or rapid drying, the extent of protein denaturation was higher in the rapidly dried embryos. Slowly dried embryos are in a glassy state at room temperature, whereas no clearly defined glass transition temperature was observed in the rapidly dried embryos. Moreover, the molecular packing density of the cytoplasmic glassy matrix was higher in the slowly dried embryos. While sucrose is the major soluble carbohydrate after rapid drying, on slow drying, the trisaccharide umbelliferose accumulates at the expense of sucrose. Dry umbelliferose and sucrose glasses have almost similar Tg s. Both umbelliferose and sucrose depressed the transition temperature of dry liposomal membranes equally well; prevented leakage from dry liposomes after rehydration, and preserved the secondary structure of dried proteins. The similar protecting properties in model systems and the apparent interchangeability of both sugars in viable dry somatic embryos suggest no special role for umbelliferose in the improved physical stability of the slowly dried somatic embryos. It was suggested that LEA proteins, which are synthesized during slow drying together with the sugars, are responsible for the increased stability of the slowly dried embryos (Chapter 8).

    The dehydration-sensitive polypeptide, poly-L-lysine was used as a model to study dehydration-induced conformational transitions of this polypeptide as influenced by drying rate and carbohydrates. In solution poly-L-lysine adopts a random coil conformation. Upon slow drying of small droplets of the polypeptide solution over a period of several hours, the polypeptide adopts an extendedbeta-sheet conformation. Upon fast air-drying within 2-3 minutes, the aqueous polypeptide structure is preserved. Slow air-drying in the presence of sugars also preserves the aqueous conformation and results in the formation of a glassy state having a higher Tg than that of sugar alone. The importance of direct sugar - polypeptide interaction in stabilization during slow air-drying was studied by drying the polypeptide in the presence of glucose, sucrose or dextran. Compared to dextran (and sucrose to a lesser extent), glucose gives superior protection, while having the lowest Tg and the best interacting properties. It was suggested that during slow drying, a protectant with sufficient interaction is required for preservation of the aqueous protein structure (Chapter 9).

    The structure of a D-7 LEA (late embryogenesis abundant)-like protein protein isolated from Typha latifolia pollen was studied using FTIR. In solution, the protein adopts a random coil conformation. Fast air-drying (5 minutes) leads to the formation ofalpha-helical structure, whereas slow drying (few hours) leads to bothalpha-helical and intermolecular extendedbeta-sheet structures. When dried in the presence of sucrose, the protein adopts predominantlyalpha-helical conformation, irrespective of drying rate. Drying of a mixture of LEA protein and sucrose results in the formation of a glassy state having higher Tg and a higher average strength of hydrogen bonding than a pure sucrose glass. It was suggested that LEA proteins might be involved in the formation of a tight molecular network in the dehydrating cytoplasm of anhydrobiotic organisms, which may contribute to desiccation tolerance (Chapter 10).

    Taken together, in situ FTIR studies can give additional information on the molecular organization in desiccation-tolerant cells. The added value of this approach is that molecular structures and inter-molecular interactions can be studied in intact biological systems (Chapter 11).

    Opname en afvoer van stikstof, fosfaat, kali en magnesium bij spruitkool
    Everaarts, A. - \ 1997
    PAV-bulletin. Vollegrondsgroenteteelt / Praktijkonderzoek voor de Akkerbouw en de Vollegrondsgroenteteelt 1997 (1997)2. - ISSN 1385-5298 - p. 8 - 10.
    brassica oleracea var. gemmifera - spruitjes - vloeistoffen (liquids) - absorptie - emissie - omloop - groei - ontwikkeling - ontogenie - stikstof - fosfor - kalium - magnesium - trofische graden - voedingsstoffen - hydrobiologie - zaaitijd - planttijd - rijenafstanden - plantdichtheid - oogsttoename - oogstverliezen - opbrengsten - brassica oleracea var. gemmifera - brussels sprouts - liquids - absorption - emission - circulation - growth - development - ontogeny - nitrogen - phosphorus - potassium - magnesium - trophic levels - nutrients - hydrobiology - sowing date - planting date - row spacing - plant density - yield increases - yield losses - yields
    Theory of SWAP version 2.0; simulation of water flow, solute transport and plant growth in the soil-water-atmosphere-plant environment
    Dam, J.C. van; Huygen, J. ; Wesseling, J.G. ; Feddes, R.A. ; Kabat, P. ; Walsum, P.E.V. van; Groenendijk, P. ; Diepen, C.A. van - \ 1997
    Wageningen : DLO Winand Staring Centre (Report / Wageningen Agricultural University, Department Water Resources 71) - 167
    bodemwater - vloeistoffen (liquids) - absorptie - wortels - oogsttoename - oogstverliezen - opbrengsten - waterbalans - methodologie - modellen - onderzoek - soil water - liquids - absorption - roots - yield increases - yield losses - yields - water balance - methodology - models - research
    Inversion techniques in radar remote sensing of agricultural field : case studies on sugar beet and winter wheat
    Rijckenberg, G.J. - \ 1997
    Agricultural University. Promotor(en): R.A. Feddes; G.P. de Loor. - S.l. : Rijckenberg - ISBN 9789090101460 - 207
    bodemwatergehalte - vloeistoffen (liquids) - absorptie - emissie - omloop - remote sensing - in de grond doordringende radar - scannen - triticum aestivum - tarwe - hexaploïdie - beta vulgaris - suikerbieten - microgolfstraling - soil water content - liquids - absorption - emission - circulation - remote sensing - ground-penetrating radar - scanning - triticum aestivum - wheat - hexaploidy - beta vulgaris - sugarbeet - microwave radiation

    This thesis is an attempt to gain insight in the retrieval of the soil moisture content and the vegetation water content from the radar backscatter of agricultural fields. Two crops have been selected: sugar beet and winter wheat. For a retrieval of the two agricultural parameters two approaches have been adopted.

    The first approach is based on an inversion of existing models, which describe the electromagnetic interaction with a vegetated surface on basis of the radiative transfer theory. A solution to this inversion problem is suggested involving the inversion of the simple Cloud model, which is connected to the complex MIMICS model.

    In the second approach a semi-empirical algorithm is developed, which decomposes the covariance matrix of polarimetric radar data into a vegetation, soil, and vegetation-soil covariance matrix. It is shown how centrical symmetry and the Brewster angle effect can be used in this decomposition technique. The procedure for an assessment of the three covariance matrices has resulted in two solutions for the algorithm. A choice between these solutions can be made by means of three polarimetric tools. A sensitivity analysis reveals that decomposition results at C- and L-band are not always sensitive enough to changes in the agricultural parameters.

    The validity of the two radiative transfer models is examined using backscatter measurements and accompanying ground data. Because of the complex structure of winter wheat the Cloud model has been applied to sugar beet data only. The backscatter of sugar beet and winter wheat at C- and L-band is predicted with MIMICS.

    The performance of the Cloud model could not be tested properly because of two reasons. Firstly the temporal resolution in most of the data sets is too low and secondly a systematic decrease occurred in practically all backscatter data, which complicates the use of the Cloud model.

    The inversion scheme with MIMICS could not be applied to the examined data, because there are disagreements between model predictions and measurements. In particular the predicted extinctions with MIMICS are too low compared with the experimental observations. Polarimetric backscatter is investigated with the three tools. Sugar beet backscatter at C- and L-band exhibits centrical symmetry. A significant Polarimetric Phase Difference ( PPD ) is found in the backscatter of winter wheat at L-band. This PPD can be explained by means of simulations with a radiative transfer model.

    The semi-empirical algorithm has been applied to sugar beet and winter wheat polarimetric backscatter at C- and L-band. The decomposition results so obtained are then considered in relation to trends in the agricultural parameters. The analysis yields promising results since the predicted trends are in agreement with the few available ground data. It appears that the calibration accuracy of the measurements is a limiting factor for the sensitivity of the results for the two agricultural parameters, and for soil moisture content in particular. Of the two frequencies considered the L-band gives the best information.

    The available radar backscatter data could be applied in a vegetation study because of the synergy with optical data. In spite of the large amount of investigated data, there is still a need for detailed experiments, e.g. tower-based measurements. With such experiments the validity of backscatter models can be further evaluated and a better interpretation of phenomena occurring in the polarimetric backscatter becomes possible.

    Check title to add to marked list
    << previous | next >>

    Show 20 50 100 records per page

     
    Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.