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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    Effects and moderators of coping skills training on symptoms of depression and anxiety in patients with cancer : Aggregate data and individual patient data meta-analyses
    Buffart, L.M. ; Schreurs, M.A.C. ; Abrahams, H.J.G. ; Kalter, J. ; Aaronson, N.K. ; Jacobsen, P.B. ; Newton, R.U. ; Courneya, K.S. ; Armes, J. ; Arving, C. ; Braamse, A.M. ; Brandberg, Y. ; Dekker, J. ; Ferguson, R.J. ; Gielissen, M.F. ; Glimelius, B. ; Goedendorp, M.M. ; Graves, K.D. ; Heiney, S.P. ; Horne, R. ; Hunter, M.S. ; Johansson, B. ; Northouse, L.L. ; Oldenburg, H.S. ; Prins, J.B. ; Savard, J. ; Beurden, M. van; Berg, S.W. van den; Brug, J. ; Knoop, H. ; Verdonck-de Leeuw, I.M. - \ 2020
    Clinical Psychology Review 80 (2020). - ISSN 0272-7358
    (individual patient data) meta-analysis - Anxiety - Coping skills training - Depression - Neoplasm - Psychosocial care

    Purpose: This study evaluated the effects of coping skills training (CST) on symptoms of depression and anxiety in cancer patients, and investigated moderators of the effects. Methods: Overall effects and intervention-related moderators were studied in meta-analyses of pooled aggregate data from 38 randomized controlled trials (RCTs). Patient-related moderators were examined using linear mixed-effect models with interaction tests on pooled individual patient data (n = 1953) from 15 of the RCTs. Results: CST had a statistically significant but small effect on depression (g = −0.31,95% confidence interval (CI) = −0.40;-0.22) and anxiety (g = −0.32,95%CI = -0.41;-0.24) symptoms. Effects on depression symptoms were significantly larger for interventions delivered face-to-face (p =.003), led by a psychologist (p =.02) and targeted to patients with psychological distress (p =.002). Significantly larger reductions in anxiety symptoms were found in younger patients (pinteraction < 0.025), with the largest reductions in patients <50 years (β = −0.31,95%CI = -0.44;-0.18) and no significant effects in patients ≥70 years. Effects of CST on depression (β = −0.16,95%CI = -0.25;-0.07) and anxiety (β = −0.24,95%CI = -0.33;-0.14) symptoms were significant in patients who received chemotherapy but not in patients who did not (pinteraction < 0.05). Conclusions: CST significantly reduced symptoms of depression and anxiety in cancer patients, and particularly when delivered face-to-face, provided by a psychologist, targeted to patients with psychological distress, and given to patients who were younger and received chemotherapy.

    Transition pathways - analyzing transitions in food systems : A synthesis of seven case studies
    Dengerink, Just ; Roo, Nina de; Dijkshoorn-Dekker, Marijke ; Bos, Bram ; Hetterscheid, Bas ; Kraan, Marloes ; Bonnand, Johann ; Haas, Wim de; Linderhof, Vincent - \ 2020
    Wageningen : Stichting Wageningen Research, Wageningen Plant Research, Business Unit Field Crops (Report / Stichting Wageningen Research, Wageningen Plant Research, Business Unit FieldCrops WPR-838) - 55
    From Rationalities to Practices : Understanding Unintended Consequences of CBNRM
    Dekker, Lideweij A.G. ; Arts, Koen ; Turnhout, Esther - \ 2020
    Conservation and Society 18 (2020)2. - ISSN 0972-4923 - p. 137 - 147.
    Community-based natural resource management - Enduimet Wildlife Management Area - Human-wildlife conflict - Maasai - Nature conservation - Overgrazing - Participation - Tanzania

    Community-Based Natural Resource Management (CBNRM) aims to resolve issues of legitimacy and social justice but in practice this aim is not always met. In this article, we contribute to the understanding of the outcomes of CBNRM by drawing on the concepts of governmentality, practice, and rationalities. We apply this conceptual approach to a CBNRM project in northern Tanzania: Enduimet Wildlife Management Area (WMA). Here a conflict emerged about proposed new livestock herding regulations which were intended to address a grass shortage affecting both wildlife and the Maasai community living in the WMA. Although these regulations were designed as part of the CBNRM process, they were resisted by community members. Our analysis highlights the role of conflicting rationalities between the WMA board and community members about the causes of and solutions to the grass shortage in the ensuing conflict. Specifically, we demonstrate how these conflicting rationalities can be understood as unintended outcomes of dynamic interactions between assumptions and intentions of involved actors, formal processes related to CBNRM, and the communication and participatory strategies employed around the introduction of the new livestock herding regulations. As such, our article illustrates the value of explicitly considering the role of practice in analysing unintended consequences of conservation interventions.

    Transition pathways - contours of an analytical framework
    Elzen, Boelie ; Haas, Wim de; Wigboldus, Seerp ; Bos, Bram ; Dijkshoorn-Dekker, Marijke - \ 2020
    Wageningen : Stichting Wageningen Research, Wageningen Plant Research, Business Unit Field Crops (Report WPR 839) - 30
    Food Secure Metropolitan Areas: The Transition Support System Approach
    Dijkshoorn-Dekker, M.W.C. ; Linderhof, Vincent ; Mattijssen, T.J.M. ; Polman, N.B.P. - \ 2020
    Sustainability 12 (2020)13. - ISSN 2071-1050
    Metropolitan areas are highly complex systems where a transition towards food security encompasses a systematic change in the whole food chain. Existing decision support tools that have been developed to inform policy-makers are mostly data-driven but hardly consider the activities and preferences of different stakeholders in the food system. The aim of this article is to contribute to urban food security by combining stakeholder participation with model-driven decision support. For this purpose, we developed and tested the Transition Support System (TSS) approach. In this TSS approach, decision support tools and participatory processes are mutually employed to promote urban food security in an ongoing, stakeholder-inclusive and reflexive process of governance. Our application of the TSS approach in two contrasting case studies highlights how this can contribute towards the development of new perspectives on urban food security, building a joint agenda towards the future and better (mutual) understanding of the issues at stake. We conclude that promoting a transition in the urban food system demands joint learning and reflexive evaluation in order to adapt governance, requiring researchers to play a supporting role in a broader process of change.
    Gold and silver dichroic nanocomposite in the quest for 3D printing the Lycurgus cup
    Kool, Lars ; Dekker, Floris ; Bunschoten, Anton ; Smales, Glen J. ; Pauw, Brian R. ; Velders, Aldrik H. ; Saggiomo, Vittorio - \ 2020
    Beilstein Journal of Nanotechnology 11 (2020). - ISSN 2190-4286 - p. 16 - 23.
    3D printing - Dichroism - Lycurgus cup - Nanocomposite

    The Lycurgus cup is an ancient glass artefact that shows dichroism as it looks green when a white light is reflected on it and a red colouring appears when a white light is transmitted through it. This peculiar dichroic effect is due to silver and gold nanoparticles present in the glass. In this research we show the synthesis of dichroic silver nanoparticles and their embedding in a 3D printable nanocomposite. The addition of gold nanoparticles to the silver nanoparticle composite, gave a 3D printable nanocomposite with the same dichroism effect of the Lycurgus cup.

    Mogelijkheden voor monitoring van CO2-vastlegging en afbraak van organische stof in de bodem op melkveebedrijven
    Lesschen, Jan Peter ; Vellinga, Theun ; Dekker, Sanne ; Linden, Annelotte van der; Schils, Rene - \ 2020
    Wageningen : Wageningen Environmental Research (Wageningen Environmental Research rapport 2993) - 63
    Emissies en vastlegging van koolstof in de bodem worden nog niet meegerekend in de carbon footprint van melkveebedrijven. Het doel van deze studie is om een betrouwbaar en transparant monitorings- en berekeningssysteem voor de vastlegging en emissie van koolstof in de bodem op melkveebedrijven te ontwikkelen. Er is gewerkt met studiegroepen met melkveehouders, data-analyse en modelontwikkeling. Een monitoringssysteem gebaseerd op metingen van OS-gehaltes in bestaande bodemanalyses biedt op dit moment onvoldoende houvast voor een betrouwbare bepaling van de vastlegging van C in de bodem. Een monitoringssysteem in de vorm van een combinatie van metingen, registratie van activiteiten en berekeningen van de veranderingen in hoeveelheden C in de bodem is technisch wel uitvoerbaar. De onzekerheid in de berekeningen is echter op dit moment nog te groot om hier op bedrijfsniveau een betrouwbare afrekening of beloning aan te koppelen.
    Verrijken, benutten en sparen : Bewegen richting natuurinclusieve landbouw
    Smits, M.J.W. ; Dawson, A.W. ; Dijkshoorn-Dekker, M.W.C. ; Ferwerda-van Zonneveld, R.T. ; Michels, R. ; Migchels, G. ; Polman, N.B.P. ; Schrijver, R.A.M. ; Sukkel, W. - \ 2020
    Wageningen Economic Research - 11 p.
    Van A naar Biodiversiteit : Op weg naar een natuurinclusieve landbouw
    Smits, Marie-José ; Dawson, Andrew ; Dijkshoorn-Dekker, Marijke ; Ferwerda-van Zonneveld, Reina ; Michels, Rolf ; Migchels, Gerard ; Polman, Nico ; Schrijver, Raymond ; Sukkel, Wijnand ; Vogelzang, Theo ; Kistenkas, Fred - \ 2020
    Wageningen : Wageningen Economic Research (Rapport / Wageningen Economic Research 2020-043) - ISBN 9789463953955 - 67
    This report explores first of all literature on transition management. The knowledge gained is taken into account to develop a route planner, which can be used to stimulate nature-inclusive agriculture at a regional level. This route planner is intended for stakeholders who want to promote nature-inclusive agriculture in their own region. We then ask ourselves what nature-inclusive agriculture means, and how it relates to circular agriculture and ecosystem services. An important focus in the route planner is the development of a vision. For this reason, concrete measures are described for arable farming and livestock farming that fit into such a nature-inclusive vision.
    Dataset Nasonia strains
    Liefting, Maartje ; Verwoerd, Lisa ; Dekker, Myrthe ; Hoedjes, Katja ; Ellers, Jacintha - \ 2020
    associative conditioning - memory retention - Nasonia vitripennis - Nassonia girauli - performance index
    De transitie naar een natuurinclusieve stad : Breng de vastgoedsector in beweging
    Dijkshoorn-Dekker, M.W.C. ; Kortstee, H.J.M. ; Mattijssen, T.J.M. ; Haaster-de Winter, M.A. van; Polman, N.B.P. ; Rooij, S.A.M. van; Steingröver, E.G. - \ 2020
    Wageningen University & Research - 19 p.
    green infrastructure - towns - house building - nature - public space - climate
    De bijdrage van de vastgoedsector aan een natuurinclusieve leefomgeving : Achtergrondrapport
    Dijkshoorn-Dekker, Marijke ; Mattijssen, Thomas ; Haaster-de Winter, Mariët van; Kortstee, Harry ; Polman, Nico - \ 2020
    Wageningen : Wageningen Economic Research (Rapport / Wageningen Economic Research 2020-01) - ISBN 9789463954006 - 37
    The real estate industry can play a key role in a wider transition to a nature-inclusive living environment that offers social, economic and ecological resilience. In this research, we look explicitly for a pro-active green contribution from the industry to the liveability and resilience of urban areas. To set such practices in motion, we are looking for points of departure in the considerations being made by different actors in the real estate industry. We do this by developing a transition approach for nature-inclusive enterprise. This approach looks at the real estate industry more widely, including landowners, investors, architects, property owners and project developers.
    pH-Controlled Coacervate-Membrane Interactions within Liposomes
    Last, Mart G.F. ; Deshpande, Siddharth ; Dekker, Cees - \ 2020
    ACS Nano 14 (2020)4. - ISSN 1936-0851 - p. 4487 - 4498.
    coacervates - liposomes - liquid−liquid phase separation - membranes - microfluidics

    Membraneless organelles formed by liquid-liquid phase separation are dynamic structures that are employed by cells to spatiotemporally regulate their interior. Indeed, complex coacervation-based phase separation is involved in a multitude of biological tasks ranging from photosynthesis to cell division to chromatin organization, and more. Here, we use an on-chip microfluidic method to control and study the formation of membraneless organelles within liposomes, using pH as the main control parameter. We show that a transmembrane proton flux that is created by a stepwise change in the external pH can readily bring about the coacervation of encapsulated components in a controlled manner. We employ this strategy to induce and study electrostatic as well as hydrophobic interactions between the coacervate and the lipid membrane. Electrostatic interactions using charged lipids efficiently recruit coacervates to the membrane and restrict their movement along the inner leaflet. Hydrophobic interactions via cholesterol-tagged RNA molecules provide even stronger interactions, causing coacervates to wet the membrane and affect the local lipid-membrane structure, reminiscent of coacervate-membrane interactions in cells. The presented technique of pH-triggered coacervation within cell-sized liposomes may find applications in synthetic cells and in studying biologically relevant phase separation reactions in a bottom-up manner.

    Consumer and technological insights for improving the quality of osmo-dehydrated mango
    Sulistyawati, Ita - \ 2020
    Wageningen University. Promotor(en): V. Fogliano, co-promotor(en): M. Dekker; R. Verkerk. - Wageningen : Wageningen University - ISBN 9789463953368 - 212

    Processing of mango can alter consumers’ perception of the final dried mango quality. To optimize the dried mango quality by product and process design, consumer’s insights on perceived product quality should be taken into account. The insights, which can consist of both product and process characteristics, should be transformed into useful input for designing food products. Previous consumer perception studies were focused on sensory, convenience and health aspects, and their interrelation with consumer perception, but less on that of process, particularly processing technology. No studies taking into account various drying technologies and the pre-treatments which can differently affect the intrinsic characteristics of dried mango and thus consumer perception. This thesis aimed at exploring insights from consumers and connecting them to technological optimization of the product quality during product and process design of dried mango.

    Exploration of consumers’ health perception across cultures and demonstration of its relevance for product and process design in the early stages of new product development was studied using dried mango as a case. A focus group approach was used with participants from three countries (The Netherlands, China, and Indonesia). Themes relating to health perception emerged, namely nutrition, naturalness, taste, and wellbeing, which were all expressed on different levels of abstractness. Participants’ health perception of dried mango varied and is related to the product category with which it is compared, e.g. candy or fresh fruit; and the eating context, e.g. position in the diet either as a snack or a meal. Additionally, it was shown that consumer insights in the health perception of a product not only relate to product characteristics but also processing and its characteristics. These insights were applied to product and process design through iterative interdisciplinary interactions between consumer scientists and food technologists. The transformation of consumers’ perception into technical product and process specifications was demonstrated through an illustrative example of two product concepts of natural dried mango. This result suggests that iterative interactions are necessary to obtain relevant product and process characteristics in the simultaneous design of the technical product and process specifications based on consumer perceptions.

    The perception of key intrinsic quality attributes and preferences of dried mango between consumers with different familiarity and health consciousness was further studied using an Adaptive Choice-Based Conjoint Analysis. This study involved respondents from three countries (The Netherlands, China, and Indonesia). Texture, taste and colour preferences of dried mango attributes differed between the three countries studied. The most important attribute for the Dutch and Chinese respondents was ‘free from extra ingredients’ as they preferred a “more pure” mango product. While Indonesians considered texture as the most important attribute preferring a crispier dried mango product. Familiarity with dried mango and health consciousness do not influence consumer preference of intrinsic attributes of dried mango. Different preferences of intrinsic attributes of dried mango between the studied respondent groups are related to cultural differences.

    Effects of pretreatments with vacuum impregnation (VI) and high pressure (HP) and adding pectin methylesterase (PME) with calcium on the quality of osmo-dehydrated mango (Mangifera indica var. Kent) of different ripeness were studied. The use of unripe mango in OD showed two to five-fold higher soluble solid gain (SSG) compared to ripe mango for all treatments. Unripe mango pretreated with OD-VI showed the lowest water loss (WL) and the highest SSG. The OD-HP treatment had a similar but less pronounced effect as OD-VI on the parameters WL and SSG. The addition of the cell wall modifying enzyme PME increased OD efficiency for the treatments high pressure as well as vacuum impregnation, but only for ripe mango. Colour is an important quality attribute for dried mango. Overall, the applied settings for OD treatments appeared to be suitable for the preservation of the colour quality of mango. The hue (h*) values were generally preserved and colour intensity (C*) was maintained or only slightly increased in both ripeness in all treatments. Lightness (L*) was greatly reduced in unripe mango but stable in ripe mango. In general, adding PME increases a bit more effect on texture in terms of firmness and work of shear. This study thus demonstrates that using different ripeness of mango resulted in different quality of osmo-dehydrated mango upon pretreatments with calcium.

    As a follow-up study, the effects of vacuum impregnation (VI) pretreatment and PME addition on the kinetics of mass transfer and vitamin C loss was studied during osmotic dehydration of mango. The water loss (WL) and weight reduction (WR) were modelled by the Weibull’s model, while soluble solid gain (SSG) was better described by Peleg’s model. VI increases soluble solid gain (SSG) indicated by a 55% lower value of the equilibrium constant (k2) in the Peleg model. Vitamin C loss was described by a multiresponse model incorporating both degradation and leaching processes into the osmotic solution (OS). Degradation was found to be the most important mechanism during osmo-dehydration of mango. The pretreatments have no significant effect on degradation and leaching rate constants of vitamin C. The combined modelling of the mass transfer and vitamin C retention was shown to be valuable in optimizing the OD process design to improve the health-promoting value of OD mango (e.g. sugar content, vitamin C) and reduce the processing time.

    Furthermore, the results of this research highlight that taking into account both the consumer and technological insights is useful to optimize product and process design of dried mango with the desired quality.

    Maternal allergy and the presence of nonhuman proteinaceous molecules in human milk
    Dekker, Pieter M. ; Boeren, Sjef ; Wijga, Alet H. ; Koppelman, Gerard H. ; Vervoort, Jacques J.M. ; Hettinga, Kasper A. - \ 2020
    Nutrients 12 (2020)4. - ISSN 2072-6643
    Allergen transfer - Human milk - Maternal allergy - Nonhuman proteins - β-lactoglobulin

    Human milk contains proteins and/or protein fragments that originate from nonhuman organisms. These proteinaceous molecules, of which the secretion might be related to the mother’s allergy status, could be involved in the development of the immune system of the infant. This may lead, for example, to sensitization or the induction of allergen-specific tolerance. The aim of this study was to investigate the relation between maternal allergy and the levels of nonhuman proteinaceous molecules in their milk. In this study, we analysed trypsin-digested human milk serum proteins of 10 allergic mothers and 10 nonallergic mothers. A search was carried out to identify peptide sequences originating from bovine or other allergenic proteins. Several methods were applied to confirm the identification of these sequences, and the differences between both groups were investigated. Out of the 78 identified nonhuman peptide sequences, 62 sequences matched Bos taurus proteins. Eight peptide sequences of bovine β-lactoglobulin had significantly higher levels in milk from allergic mothers than in milk from nonallergic mothers. Dietary bovine β-lactoglobulin may be absorbed through the intestinal barrier and secreted into human milk. This seems to be significantly higher in allergic mothers and might have consequences for the development of the immune system of their breastfed infant.

    Volatile antimicrobial absorption in food gel depends on the food matrix characteristics
    Wang, Li ; Fogliano, Vincenzo ; Heising, Jenneke ; Meulenbroeks, Erik ; Dekker, Matthijs - \ 2020
    Food Hydrocolloids 107 (2020). - ISSN 0268-005X
    Antimicrobial packaging design - Antimicrobials absorption in gel - Carrageenan - Carvacrol - Microstructure of gel - Whey protein isolate

    The aim of this study was to investigate the influence of the food microstructure on the release, absorption and partitioning of the volatile antimicrobials from antimicrobial packaging film. Carvacrol loaded polylactic acid (PLA) film was prepared and tested on a food gel model simulating products like jellies, jams and dressings. Whey protein isolate/carrageenan gels with different microstructures were prepared by varying the NaCl concentration (50–250 mM): the higher the salt concentration the lower the gel consistency. Results showed carvacrol partitioning in the gel increase at higher concentration of NaCl. A 41% increase of carvacrol absorption after 7 days was found in gels prepared with 250 mM of NaCl, compared with the gels at 50 mM NaCl. The results can be explained by the differences in gel microstructures: gels with higher NaCl concentrations showed the small WPI-containing aggregates and large pores from confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) images, in turn facilitating carvacrol absorption by proteins in the gels. The physical properties of gels revealed that gels with higher NaCl concentrations showed lower strength and water holding capacity, pointing to a more loose structure of the gel. The results demonstrate that the microstructure of gels have a clear effect on carvacrol absorption and this factor should be taken into account for designing antimicrobial packaging for the preservation of the gel-like foods.

    Op Pad met... : Henk Baas in IJdoorn
    Dekker, Jos ; Sluis, T. van der - \ 2020
    Landschap : tijdschrift voor landschapsecologie en milieukunde 37 (2020)1. - ISSN 0169-6300 - p. 28 - 33.
    Carvacrol release from PLA to a model food emulsion : Impact of oil droplet size
    Wang, Li ; Dekker, Matthijs ; Heising, Jenneke ; Fogliano, Vincenzo ; Berton-Carabin, Claire C. - \ 2020
    Food Control 114 (2020). - ISSN 0956-7135
    Antimicrobial packaging - Carvacrol - Emulsion - Oil droplet size - Partitioning

    The effect of food structure on the release of a volatile antimicrobial from an active packaging (AP) was investigated by measuring the migration of carvacrol from a polylactic acid (PLA) film to a model food system, namely, an oil-in-water (O/W) emulsion. We aimed to understand the influence of the oil droplet size on the kinetics of carvacrol migration from the PLA film to the emulsions, on its final partitioning and antimicrobial activity. Five model systems were prepared: they had the same composition, i.e., an oil fraction of 20 wt% and an aqueous phase containing 1.5 wt % whey protein isolate, but different structures. Emulsions with the smallest oil droplets (d3,2 = 0.27 μm) absorbed a higher amount of carvacrol than emulsions with large oil droplets (d3,2 = 0.34 μm and d3,2 = 0.51 μm). Despite the higher overall carvacrol concentration, inhibition of bacterial growth was less effective in emulsions with the smallest droplet (d3,2 = 0.27 μm). This can be explained by the highest log K of carvacrol in this emulsion indicating that carvacrol partitioned more into the oil droplet phase than in the continuous phase. The current study suggests that the spatial distribution of carvacrol in the emulsion determines its actual antimicrobial effect. The combined findings of antimicrobial distribution and activity highlight the need for tailoring active packaging systems based on the physical characteristics of multiphase food matrices.

    Predation risk shapes the degree of placentation in natural populations of live-bearing fish
    Hagmayer, Andres ; Furness, Andrew I. ; Reznick, David N. ; Dekker, Myrthe L. ; Pollux, Bart J.A. - \ 2020
    Ecology Letters 23 (2020)5. - ISSN 1461-023X - p. 831 - 840.
    Life-history - live-bearing - matrotrophy - placenta - placentotrophy - Poeciliidae - predation - superfetation - Trexler–DeAngelis - viviparity

    The placenta is a complex life-history trait that is ubiquitous across the tree of life. Theory proposes that the placenta evolves in response to high performance-demanding conditions by shifting maternal investment from pre- to post-fertilisation, thereby reducing a female’s reproductive burden during pregnancy. We test this hypothesis by studying populations of the fish species Poeciliopsis retropinna in Costa Rica. We found substantial variation in the degree of placentation among natural populations associated with predation risk: females from high predation populations had significantly higher degrees of placentation compared to low predation females, while number, size and quality of offspring at birth remained unaffected. Moreover, a higher degree of placentation correlated with a lower reproductive burden and hence likely an improved swimming performance during pregnancy. Our study advances an adaptive explanation for why the placenta evolves by arguing that an increased degree of placentation offers a selective advantage in high predation environments.

    A systems approach to understand microplastic occurrence and variability in Dutch riverine surface waters
    Mintenig, Svenja ; Kooi, M. ; Erich, M.W. ; Primpke, S. ; Redondo Hasselerharm, P.E. ; Dekker, S.C. ; Koelmans, A.A. - \ 2020
    Water Research 176 (2020). - ISSN 0043-1354
    Assessment methods on data quality and environmental variability are lacking for microplastics (MP). Here we assess occurrence and variability of MP number concentrations in two Dutch rivers. Strict QA/QC procedures were applied to identify MP using Fourier-transform infrared (FTIR) microscopy followed by state of the art automated image analysis. For a series of randomly selected, yet ever smaller subareas of filters, we assessed how accurately MP numbers and polymer types are represented during partial filter analysis. Levels of uncertainty were acceptable when analysing 50% of a filter during chemical mapping, and when identifying at least a subset of 50 individual particles with attenuated total reflection (ATR)-FTIR. Applying these guidelines, MP number concentrations between 67 and 11532 MP m−3 were detected in Dutch riverine surface waters. Spatial differences caused MP number concentrations to vary by two orders of magnitude. Temporal differences were lower and induced a maximum variation of one order of magnitude. In total, 26 polymer types were identified, the most common were polyethylene (23%), polypropylene (19.7%) and ethylene propylene diene monomer rubber (18.3%). The highest diversity of polymer types was found for small MPs, whereas MP larger than 1 mm was scarce and almost exclusively made of polyethylene or polypropylene. Virtually all sampling locations revealed MP number concentrations that are considerably below known effect thresholds for anticipated adverse ecological effects.
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