Staff Publications

Staff Publications

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    '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.

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    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.


    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.


    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.


    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.


    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.


    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.


    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.

    Water holding of protein gels
    Urbonaite, V. - \ 2015
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Laurice Pouvreau; H.H.J. de Jongh. - Wageningen : Wageningen University - ISBN 9789462574229 - 206
    sojaeiwit - ovalbumine - wei-eiwit - waterbergend vermogen - gelering - structuur - morfologie - reologie - permeabiliteit - centrifugeren - soya protein - ovalbumin - whey protein - water holding capacity - gelation - structure - morphology - rheology - permeability - centrifugation


    Food products are typically multicomponent systems, where often the spatial volume is set by a protein continuous network. The ability of protein-based food products to entrap water and to prevent its exudation upon mechanical deformation is important for the texture and thus sensory perception of food products. Understanding of structural origins that determine gel water holding is therefore essential, and would allow designing foods with controlled sensory perception. Water removal from the gel (quantity, kinetics and mechanism) is related to the coarseness and deformation of the network. An understanding of the interplay between the effect of coarseness and stiffness on WH in fine and coarse gels allows one to take a better control and tune juiciness and the release of tastants from food products.

    Naar een database van bodemhydraulische karakteristieken voor Nederland
    Verzandvoort, S.J.E. ; Vroon, H.R.J. ; Wesseling, J.G. ; Bakker, G. ; Oostindie, K. ; Stoffelsen, G.H. ; Heidema, A.H. ; Heuvelink, G.B.M. - \ 2012
    Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2238) - 148
    bodemfysica - bodemwater - permeabiliteit - fysische bodemeigenschappen - databanken - soil physics - soil water - permeability - soil physical properties - databases
    Bodemhydraulische karakteristieken zijn relaties van vochtgehalte (θ) en doorlatendheid (K) met de capillaire drukhoogte (h) in de onverzadigde zone van de bodem. Deze karakteristieken worden gebruikt voor modelsimulaties van het transport van water en opgeloste stoffen in de onverzadigde zone van de bodem. Doel van deze studie is de bij Alterra beschikbare basisgegevens voor bodemhydraulische karakteristieken te controleren, aan te vullen en beschikbaar te stellen voor het Bodemkundig Informatie Systeem (BIS) van Alterra. Hiervoor werden meetgegevens, afgeleide gegevens en beschrijvende gegevens van grondmonsters in de bestaande database Priapus gecorrigeerd en aangevuld. De variatie door metingen, functiebeschrijvingen en ruimtelijke variatie werd inzichtelijk gemaakt. Voor een betere bepaling van afgeleide gegevens uit de meetgegevens werd een nieuwe functiebeschrijving voor bodemhydraulische karakteristieken ontwikkeld in de vorm van cubical splines. Om de selectie van bodemhydraulische karakteristieken meer flexibel te maken voor gebruikers werd een nieuwe indeling van Nederlandse gronden ontwikkeld met als criteria: afzettingsmilieu, textuur en organische stofgehalte.
    Kwaliteitsdocumentatie voor de verkrijging van Status A voor de gegevens van de Staringreeks zoals opgenomen in het gegevensbestand Priapus
    Stolte, J. ; Wesseling, J.G. ; Verzandvoort, S.J.E. - \ 2007
    Wageningen : Alterra (Alterra-rapport 1522) - 84
    bodemwater - hydrologie - fysische bodemeigenschappen - bodemporiënsysteem - permeabiliteit - meetsystemen - soil water - hydrology - soil physical properties - soil pore system - permeability - measurement systems
    De Staringreeks is een presentatie van gemeten bodemhydraulische karakteristieken. De reeks bevat gemiddelde waterretentie- en doorlatendheidskarakteristieken voor 36 onderscheiden boven¬gronden (18) en ondergronden (18). Deze karakteristieken vormen essentiële invoergegevens in simulatiemodellen waarbij de opslag en het transport van water en opgeloste stoffen in de onverzadigde zone van de bodem worden berekend. Dit rapport is een kwaliteitsdocumentatie van de meetgegevens die ten grondslag liggen aan de Staringreeks, en die zijn opgenomen in het nieuwe gegevensbestand Priapus.
    Onderbouwing kwaliteitsborging HYDROSTAB : aanvullend veld-, laboratoirum- en modelonderzoek
    Boels, D. ; Bril, J. - \ 2006
    Wageningen : Alterra (Alterra-rapport 1374) - 85
    afvalstortplaatsen - stortterreinen - kwel - lekkage - bekledingen - permeabiliteit - silicagel - materialen - kwaliteit - waste disposal sites - landfills - seepage - leakage - linings - permeability - silica gel - materials - quality
    Hydrostab bestaat uit reststoffen en waterglas voor de afdichting van stortplaatsen. Vrije CaO uit bijgemengde vliegassen reageren met puzzolane stoffen tot CSH-gel. Hydrostab gaat minstens 100 jaar mee als initieel minstens 20 g CSH per kg ds ontstaat. Simpele methoden zijn ontwikkeld voor vaststelling van geschiktheid van vlieg-assen en het CSH-gehalte. Hydrostab tast HDPE niet aan en is zelf ongevoelig voor de chemische samenstelling van aangrenzende lagen. De gerealiseerde kwaliteit van Hydrostab te Nuenen, Schijndel en Antwerpen blijkt gelijk aan die op het (oud) proefveld te Hengelo. Aanvullende eisen t.a.v. grondstoffen en mengsels zijn geformuleerd. Een levensduur van 100 jaar onder een systeem van sluitende kwaliteitsborging blijkt mogelijk.
    Nutritional strategy affects gut wall integrity in weaned piglets
    Verdonk, J.M.A.J. - \ 2006
    Wageningen University. Promotor(en): Martin Verstegen, co-promotor(en): J. Huisman. - [S.l. ] : S.n. - ISBN 9789085043461 - 153
    biggen - spenen - melk - dunne darm - fysiologische functies - voeropname - maag - spijsvertering - morfologie - permeabiliteit - diervoeding - piglets - weaning - milk - small intestine - physiological functions - feed intake - stomach - digestion - morphology - permeability - animal nutrition
    Weaning is a stressful event for pigs and induces changes in the gut integrity of pigs. Feed intake is a very important determinant for gut integrity. In this thesis the effect of nutritional strategies (with regard to feed intake level and physical structure of the feed) on changes in gut morphology, barrier function and inflammatory response were investigated. In the experiments individually housed piglets were fed diets at different intake levels with different physical forms and compositions during 4 to 14 days post weaning. The working hypotheses were that high feed intake minimizes the degeneration of the gut integrity and stimulates the regeneration of a compromised integrity.

    Weaning induced changes in gut integrity. Overall, feed intake level modulated parameters related to gut integrity like morphology, in vitro barrier function and inflammatory response. The effects found depended on sampling site in the gut and sampling day post weaning.

    Only the supply of reconstituted milk resulted in voluntary feed intake level sufficiently high to maintain gut integrity. In vitro paracellular permeability for small molecules was transiently increased after weaning, while permeability for large molecules was decreased. High intake feed (milk) resulted in lower permeability values compared to a low intake level.

    Changes in gut morphology and permeability were related to feed intake level. In most experiments, individual feed intake was also correlated with body weight gain and in some experiments with inflammatory response parameters. At a low feed intake level, gut barrier function was already affected at day 1 post weaning, followed by changes in gut morphology.

    Variation in parameters related to gut integrity between piglets within trials and between experiments was high making it very difficult to compare data of different experiments.
    Durability of Hydrostab; a field investigation and prognosis
    Boels, D. ; Bril, J. ; Hummelink, E.W.J. ; Boersma, O.H. - \ 2005
    Wageningen : Alterra (Alterra-rapport 1218) - 54
    afvalverwijdering - afvalstortplaatsen - stortterreinen - kwel - lekkage - controle - technologie - verzegelen - methodologie - permeabiliteit - silicagel - personeelsbeoordeling - waste disposal - waste disposal sites - landfills - seepage - leakage - control - technology - sealing - methodology - permeability - silica gel - performance appraisals
    Eight years after installation on a test site, the enclosing properties of Hydrostab are undiminished and satisfy the requirements of the Dutch Decree on Soil Protection for Disposal to Landfill (“Stortbesluit” 1993). Also no change was found in the moisture content. Analysis of the processes and components that determine the characteristics of Hydrostab shows that C-S-H- and C-A-H-gels form from fly ash which subsequently fall apart and produce silica gels. In this process the capillary pore space initially decreases. Only after transformation of all C-S-H and C-A-H into silica-gel the amount of gel in the soil pores decreases slowly, producing the final end product quartz. In this process the capillary pore space increases. When the value of the capillary pore space increases above 0.18, the sealing properties of Hydrostab decrease. This moment in time can therefore be marked as the end of the functional lifetime of the Hydrostab. Dependent on model parameterization this moment is 180 - 500 years in the future
    De doorlatendheid van de bodem voor infiltratiedoeleinden; een gebiedsdekkende inventarisatie voor het Waterschap Peel en Maasvallei
    Massop, H.T.L. ; Gaast, J.W.J. van der; Kiestra, E. - \ 2005
    Wageningen : Alterra (Alterra-rapport 1212) - 95
    permeabiliteit - infiltratie - hydraulisch geleidingsvermogen - kwel - watervoerende lagen - grondwaterstroming - fysische bodemeigenschappen - grondwater - geohydrologie - limburg - permeability - infiltration - hydraulic conductivity - groundwater - mapping - seepage - aquifers - groundwater flow - geohydrology - limburg
    In opdracht van waterschap Peel en Maasvallei is een onderzoek uitgevoerd naar de geohydrologische eigenschappen van het topsysteem. Het waterschap gebruikt deze informatie bij de beoordeling en advisering ten behoeve van infiltratievoorzieningen. Voor de beoordeling van deze voorziening zijn de doorlatendheid en de dikte van de deklaag van belang alsook het doorlaatvermogen van het onderliggende watervoerende pakket. Voor het gebiedsdekkend vaststellen van de eigenschappen is het gebied geschematiseerd in 60 eenheden op basis van bodemeigenschappen en opbouw diepere ondergrond. Aan deze eenheden is een k-waardetabel gekoppeld. Deze tabel is gebaseerd op beschikbare metingen en schattingen en aangevuld met metingen die in het kader van dit onderzoek zijn uitgevoerd. Naast k-waarden is een diktekaart van de deklaag vervaardigd op basis van bruikbare boringen. Het doorlaatvermogen van het eerste watervoerend pakket is afgeleid uit verschillende bronnen, waaronder pompproeven. Een belangrijk punt bij gebruik van de geïnventariseerde gegevens is de anisotropie van de deklaag als gevolg van het voorkomen van klei, leem of veenlagen
    Porosity-permeability properties generated with a new 2-parameter 3D hydraulic pore-network model for consolidated and unconsolidated porous media
    Acharya, R.C. ; Zee, S.E.A.T.M. van der; Leijnse, A. - \ 2004
    Advances in Water Resources 27 (2004)7. - ISSN 0309-1708 - p. 707 - 723.
    poreus medium - porositeit - permeabiliteit - poriëngrootte - transportprocessen - toepassingen - modellen - bodemporiënsysteem - grondwaterstroming - porous media - porosity - permeability - pore size - transport processes - applications - models - soil pore system - groundwater flow - diffusion-coefficients - residual saturations - transport-properties - mercury porosimetry - capillary-pressure - tomographic-images - size distribution - multiphase flow - packed-beds - prediction
    A new method is presented to construct a simple and general site bond correlated 3D HYdraulic POre Network model (HYPON) of hydraulic behavior of porous media for a wide range of permeability and porosity. Pore scale microstructure in this model is captured through simple power functions of Beti’s influence lines that fix both the location and the size of throat (the narrowest section of bond) by relating the important elements of microstructure such as coordination number, porebody sizes and pore wall curvature
    A new method is presented to construct a simple and general site bond correlated 3D HYdraulic Pore Network model (HYPON) of hydraulic behavior of porous media for a wide range of permeability and porosity. Pore scale microstructure in this model is captured through simple power functions of Beti's influence lines that fix both the location and the size of throat (the narrowest section of bond) by relating the important elements of microstructure such as coordination number, porebody sizes and pore wall curvature. The new element in pore-network architecture is thus, the location of throat, which is important for smooth hydraulic transitions during steady state flow conditions. Despite the reduced number of parameters in comparison with other pore-network models, the morphological characteristics of HYPON compare well to those of the process-based predictive models in literature, and these characteristics are sensitise to the variance of porebody sizes rather than to the used type of the porebody size distributions. Processes such as diagenesis and dissolution are captured implicitly through the pore wall curvature parameter. Different combinations of porosity and permeability relations are obtained if the bond curvature and porebody sizes are varied. These relations reveal that effects of diagenesis and dissolution on the permeability may be ignored as they are secondary to effects on porosity. (C) 2004 Elsevier Ltd. All rights reserved.
    Optimale watergift na het vullen
    Amsing, J.G.M. - \ 2003
    Paddestoelen : onafhankelijk vakblad voor Nederland en België 2003 (2003)5. - ISSN 1380-359X - p. 6 - 7.
    paddestoelen - compost - groeimedia - bodemwatergehalte - permeabiliteit - fysische bodemeigenschappen - bodemdichtheid - mushrooms - composts - growing media - soil water content - permeability - soil physical properties - soil density
    Verslag van onderzoek naar de oorzaken van het ontstaan van een verstoorde laag boven in de compost na het vullen van de champignoncel. Gegevens in bijgaande figuren: 1) Invloed van het vochtgehalte van doorgroeide compost op bulkdichtheid en veerkracht; 2) Sproeipatronen waarmee water op de dekaarde is aangebracht
    Are TRISOPLAST barriers sustainable? An evaluation of old barriers in landfill caps
    Boels, D. ; Melchior, S. ; Steinert, B. - \ 2003
    Wageningen : Alterra (Alterra-report 541) - 163
    bodemverontreiniging - barrières - ondergrondse barrières - bentoniet - permeabiliteit - verdroging - penetratie - infiltratie - veiligheid - nederland - soil pollution - barriers - subsurface barriers - bentonite - permeability - desiccation - penetration - infiltration - safety - netherlands
    Trisoplast is a mineral barrier material composed of sand, bentonite (> 10.7%) and a non-biodegradable polymer. Its permeability is less than 3 x 10 -11 m/s , which in general is not seriously affected by external physico-chemical influences. Trisoplast barriers, installed in 1995-1996 were excavated to check the occurrence and potential effects of ageing phenomena in situ. Incidentally root penetration in Trisoplast was observed, which obviously had not caused visible desiccation and crack formation. The actual permeability had not changed significantly since the installation. The safety factor of the barriers according to the regulations in the Netherlands actually varies from 2.1 to 10.2 and it is expected that due to possible future worst-case conditions the variation can drop to 2.2-6.4. As this is still above the required value of 1, Trisoplast is sustainable at these sites. The average infiltration rate derived from water and salt-balances of the barriers without a geomembrane, ranges from 1to 2 mm annually and only amounts to 5-10% of the permitted maximum rate of 20 mm annually.
    Investigation of the functional lifetime of TRISOPLASTr in relation to chemical compositions of pore water solutions in barriers
    Boels, D. ; Beest, H. te; Zweers, H. ; Groeneveld, P. - \ 2003
    Wageningen : Alterra (Alterra-rapport 528) - 49
    barrières - chemische samenstelling - permeabiliteit - bodemwaterbeweging - poriën - kationenwisseling - stortterreinen - bodembescherming - membraanpermeabiliteit - membranen - barriers - chemical composition - permeability - soil water movement - pores - cation exchange - landfills - soil conservation - membrane permeability - membranes
    Trisoplastr is a mixture of sand, bentonite and a polymer, used amongst others as landfill cover as well as barriers. Its permeability is generally lower than 1-2 x 10-11 m/s. Trisoplast keeps its functionality even in contact with different kinds of liquids, is not susceptible to cyclic drying and rewetting, and the permeability hardly depends on its dry bulk density. Tests with 10¿iaxial strain show only a slight increase in permeability. The functional lifetime of Trisoplast is governed by exchange of adsorbed sodium ions against dissolved calcium ions. This process depends on the composition of the pore water solution in the soil layers directly in contact with Trisoplast and the displacement rate of dissolved calcium ions either by convectiveor diffusive transport phenomena. The functional lifetime of Trisoplast even under relatively extreme conditions is at least 100 years and scores clearly better than the reference sand-bentonite barrier.
    Percolation Thresholds in 2-Dimensional Prefractal Models of Porous Media
    Sukop, M.C. ; Dijk, G.J. van; Perfect, E. ; Loon, W.K.P. van - \ 2002
    Transport in Porous Media 48 (2002). - ISSN 0169-3913 - p. 187 - 208.
    percolatie - bodemwaterbeweging - permeabiliteit - poreus medium - modellen - fractal meetkunde - porous media - percolation - soil water movement - permeability - models - fractal geometry
    Considerable effort has been directed towards the application of percolation theory and fractal modeling to porous media. We combine these areas of research to investigate percolation in prefractal porous media. We estimated percolation thresholds in the pore space of homogeneous random 2-dimensional prefractals as a function of the fractal scale invariance ratio b and iteration level i. The percolation thresholds for these simulations were found to increase beyond the 0.5927... porosity expected in Bernoulli (uncorrelated) percolation networks. Percolation in prefractals occurs through large pores connected by small pores. The thresholds increase with both b (a finite size effect) and i. The results allow the prediction of the onset of percolation in models of prefractal porous media and can be used to bound modeling efforts. More fundamental applications are also possible. Only a limited range of parameters has been explored empirically but extrapolations allow the critical fractal dimension to be estimated for a large combination of b and i values. Extrapolation to infinite iterations suggests that there may be a critical fractal dimension of the solid at which the pore space percolates. The extrapolated value is close to 1.89 - the well-known fractal dimension of percolation clusters in 2-dimensional Bernoulli networks.
    The influence of water percolation on flow of light non aqueous phase liquids in soil
    Marsman, A. - \ 2002
    Wageningen University. Promotor(en): S.E.A.T.M. van der Zee. - S.l. : S.n. - ISBN 9789058087348 - 141
    waterstroming - horizontale stroming - modellen - percolatie - bodemoplossing - permeabiliteit - bodemwater - technieken - water flow - horizontal flow - models - percolation - soil solution - permeability - soil water - techniques

    Keywords ,: multi-phase flow, entrapment, numerical modeling, similarity solution, horizontal migration, percolation theory, relative permeability.

    In this thesis the physical behavior of Light Non-Aqueous Phase Liquids (LNAPL) at the capillary fringe, is studied with multiphase flow models. Phenomena like a fluctuating water table or percolation of (infiltration) water have a large impact on this behavior. Both the geometry and the mobility of the LNAPL lens are affected. These two physical phenomena mentioned imply downwards and upwards water flow through the LNAPL lens. Different techniques were used in this investigation. Numerical calculations show that fluctuations of the phreatic groundwater level result in retardation of the horizontal migration of the LNAPL lens over the groundwater level. An expression is derived which quantifies the part of the simulated time during which the LNAPL can actually flow. This expression is implemented in an existing analytical solution that describes horizontal LNAPL migration, to enable that the effect of a fluctuating water level can be calculated analytically. Laboratory experiments are performed which verify these results. The effect of water flow through an LNAPL lens also affects the mobility of LNAPL. Numerical results show that both for upwards and for downwards water invasion of a lens, the mobility of the LNAPL has increased significantly. To obtain more qualitative insight on the pore scale, percolation theory is used. Percolation theory is applied to this problem and the appropriate series of drainage and imbibition processes are calculated to simulate the water percolation. The accompanying relative permeabilities show that the mobility increases after water percolation. Qualitative insight on the pore scale shows that the LNAPL is displaced to a larger amount of pore radii which advances the mobility of the LNAPL. This observation is in agreement with the numerical results.

    SATEM 2002: software for aquifer test evaluation
    Boonstra, J. ; Kselik, R.A.L. - \ 2001
    Wageningen : ILRI (ILRI publication 57) - ISBN 9789070754549 - 148
    watervoerende lagen - grondwaterstroming - permeabiliteit - modellen - pompproeven - bodemfysica - grondwater - hydrologie - software - aquifers - groundwater flow - permeability - models - pumping tests - software
    Beoordeling van vloeistofdichtheid
    Braam, C.R. - \ 1999
    Agrabeton 9 (1999)2. - ISSN 0167-3246 - p. 20 - 21.
    beton - landbouw - bouwconstructie - structuren - permeabiliteit - concrete - agriculture - building construction - structures - permeability
    In de praktijk zijn er veel vloerconstructies die dateren voor de totstandkoming van het Plan Bodembeschermende Voorzieningen (PVB). In dit artikel wordt in het kort besproken hoe deze constructies worden beoordeeld
    Permeability and modulation of the intestinal epithelial barrier in vitro
    Duizer, E. - \ 1999
    Agricultural University. Promotor(en): J.H. Koeman; P.J. van Bladeren; J.P. Groten. - S.l. : Duizer - ISBN 9789058080677 - 152
    darmslijmvlies - epitheel - permeabiliteit - in vitro - karteldarm - intestinal mucosa - epithelium - permeability - in vitro - colon

    The bioavailability of all ingested compounds is to a great extend determined by the ability of these compounds to pass the intestinal epithelium. A high bioavailability is guaranteed for most nutrients and electrolytes since they are actively absorbed by the epithelium. The same epithelium, however, renders the entrance of non-nutrient (potentially harmful) hydrophilic (macro-) molecules, viruses and bacteria into the systemic circulation very low by presenting an almost impermeable barrier to these agent. The functional and structural properties of the single cell layer forming the intestinal epithelium determine the transepithelial permeability, which is an important factor in determining the bioavailability of all ingested compounds. Thus, insight in this transepithelial permeability is of considerable interest. However, the complexity of the gastrointestinal tract, and of the pre-and post-absorptive kinetics hampered the collection of accurate data. Therefore, a simple, accurate, reproducible, and cheap in vitro model was needed to screen the vast amount of newly developed, or discovered compounds for their intestinal transepithelial permeation.

    One very popular model consists of the human colonic carcinoma cell line Caco-2 grown in a two-compartment system. Transport experiments with this Caco-2 system yielded in vitro permeation rates which allowed prediction of the oral bioavailability in humans for many different compounds. However, it is generally assumed that the Caco-2 cells restrict the paracellular permeation (extracellular passage along the cells) of hydrophilic compounds such as intact peptides to a greater extent than the small intestinal epithelium in vivo . Thus especially for the modeling of hydrophilic macromolecular permeation, an additional model would be of great value. We posed the question whether the small intestinal epithelium derived cell line IEC-18 could be that model. We found that whereas the Caco-2 cells presented a good model for a general screen on intestinal permeation for a wide variety of compounds, the IEC-18 cells did allow for a better discrimination between the hydrophilic compounds on the basis of their molecular weight. Consequently, experiments with the filter grown IEC-18 cells yielded discriminative permeation rates for the paracellular permeation of hydrophilic compounds with differing bioavailabilities. Thus, data presented in this thesis suggest that the filter grown IEC-18 cells could be valuable as model for paracellular permeability in the small intestine.

    However, the cell morphology and brush border enzyme activities of IEC-18 cells cultured under standard conditions showed that the cells obtained only a low status of differentiation, while addition of dexamethasone to the culture medium triggered the cells to acquire a more enterocyte-like phenotype. Concomitant with the morphological changes, a tightening of the paracellular barrier was found which suggests that IEC-18 cells might present a model to study the effects of intestinal epithelial cell differentiation on paracellular permeability development along the intestinal crypt-villus axis.

    Additionally, since it has been recognized that the intestinal epithelial barrier can be compromised by compounds such as drug absorption enhancers or ingested toxins, we studied the effects of a proposed drug absorption enhancer (palmitoyl carnitine) and the bio-active heavy metal cadmium, on structural and functional features of the two intestinal cell lines. We concluded that for studies to modulation of intestinal epithelial barrier function, the Caco-2 is a more convenient model than the IEC-18 cells due to the high basal barrier function for hydrophilic molecules of the Caco-2 cells relative to the low barrier function of IEC-18 cells. The occurrence of increased hydrophilic macromolecular permeability concomitant with membrane damage but without concurrent alterations in the expression of the tight junctional protein ZO-1, as was found after palmitoyl carnitine exposure, strongly suggests the enhancement of transcellular permeability. On the other hand, increased hydrophilic macromolecular permeability and a decreased transepithelial electrical resistance, concomitant with alterations in junctional ZO-1 expression, but without concurrent membrane damage, as was found after cadmium exposure, strongly suggests the enhancement of the paracellular pathway.

    In conclusion, the two intestinal cell lines Caco-2 and IEC-18, together, offer the possibility to obtain in vitro permeation rates, enabling bioavailability modeling for virtually all classes of compounds. Furthermore, the in vitro systems and research strategies presented in this thesis might help to elucidate modes of action of newly developed compounds on the barrier function of the intestinal mucosa and might thus help to assess the effectivity and safety of absorption enhancers, and to indicate mucosal toxicity of orally ingested compounds such as drugs or food related products.

    Efeda-Spain and Hapex-Sahel: a further analysis of data.
    Soet, M. ; Stricker, J.N.M. ; Droogers, P. ; Esenbrink, J. - \ 1998
    Wageningen : LUW (Rapport / Landbouwuniversiteit Wageningen, Afdeling Waterhuishouding 79) - 72
    bodem - permeabiliteit - wijnbouw - wijngaarden - plantenfysiologie - plantenontwikkeling - wortels - spanje - niger - soil - permeability - viticulture - vineyards - plant physiology - plant development - roots - spain - niger
    Geohydrologisch veldonderzoek in het Purmerbos : uitwerkingen en interpretatie van doorlatendheidsmetingen en pompproeven
    Gaast, J.W.J. van der; Peerboom, J.M.P.M. - \ 1996
    Wageningen : DLO-Staring Centrum (Rapport / DLO-Staring Centrum 437) - 65
    watervoerende lagen - conservering - milieubescherming - bosbouw - bossen - permeabiliteit - gesteenten - nederland - noord-holland - pompproeven - aquifers - conservation - environmental protection - forestry - forests - permeability - rocks - netherlands - noord-holland - pumping tests
    Hydrologie en waterhuishouding van bosgebieden in Nederland; fase 2: meetopzet en eerste resultaten
    Elbers, J.A. ; Dolman, A.J. ; Moors, E.J. ; Snijders, W. - \ 1996
    Wageningen : SC-DLO (Rapport / DLO-Staring Centrum 333.2) - 65
    bosbouw - bodemwater - permeabiliteit - absorptie - hygroscopiciteit - bodembescherming - waterbescherming - erosie - hydrologie - beheer van waterbekkens - nederland - forestry - soil water - permeability - absorption - hygroscopicity - soil conservation - water conservation - erosion - hydrology - watershed management - netherlands
    Verdampings-, voelbarewarmte- en impulsflux, bodemvochtgehalte, weervariabelen en doorval zijn op vier boslocaties (populier, lariks, grove den, gemengd naald- en loofbos) in 1995 nagenoeg continu gemeten. In de zomer nam het interceptieverlies als percentage van de brutoneerslag af in de volgorde lariks (32,2%), populier (26,7%) en grove den (21,5%). De transpiratie nam af in de volgorde populier (422 mm), lariks (375 mm) en grove den (283 mm). Dit is een eerste schatting uit de metingen van de totale verdamping en interceptie voor het groeiseizoen van dag 120 tot en met dag 275. Het totale waterverbruik van populier (655 mm) en lariks (651 mm) is vrijwel gelijk, en hoger dan dat van grove den (539 mm).
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