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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    Impact of interspecific interactions on antimicrobial activity among soil bacteria
    Tyc, O. ; Berg, M. van den; Gerards, S. ; Veen, J.A. van; Raaijmakers, J.M. ; Boer, W. de; Garbeva, P. - \ 2014
    Frontiers in Microbiology 5 (2014). - ISSN 1664-302X
    community composition - bacillus-subtilis - gene-expression - antibiotics - diversity - rhizosphere - inhibition - environment - resistance - reveals
    Certain bacterial species produce antimicrobial compounds only in the presence of a competing species. However, little is known on the frequency of interaction-mediated induction of antibiotic compound production in natural communities of soil bacteria. Here we developed a high-throughput method to screen for the production of antimicrobial activity by monocultures and pair-wise combinations of 146 phylogenetically different bacteria isolated from similar soil habitats. Growth responses of two human pathogenic model organisms, Escherichia coli WA321 and Staphylococcus aureus 533R4, were used to monitor antimicrobial activity. From all isolates, 33% showed antimicrobial activity only in monoculture and 42% showed activity only when tested in interactions. More bacterial isolates were active against S. aureus than against E. coli. The frequency of interaction-mediated induction of antimicrobial activity was 6% (154 interactions out of 2798) indicating that only a limited set of species combinations showed such activity. The screening revealed also interaction-mediated suppression of antimicrobial activity for 22% of all combinations tested. Whereas all patterns of antimicrobial activity (non-induced production, induced production and suppression) were seen for various bacterial classes, interaction-mediated induction of antimicrobial activity was more frequent for combinations of Flavobacteria and alpha- Proteobacteria. The results of our study give a first indication on the frequency of interference competitive interactions in natural soil bacterial communities which may forms a basis for selection of bacterial groups that are promising for the discovery of novel, cryptic antibiotics.
    Biosynthetic genes and activity spectrum of antifungal polyynes from Collimonas fungivorans Ter331
    Fritsche, K. ; Berg, M. van den; Boer, W. de; Beek, T.A. van; Raaijmakers, J.M. ; Veen, J.A. van; Leveau, J.H.J. - \ 2014
    Environmental Microbiology 16 (2014)5. - ISSN 1462-2912 - p. 1334 - 1345.
    pseudomonas-fluorescens pf-5 - aspergillus-niger - sp nov. - identification - caryoynencins - antibiotics - mycophagy - bacteria
    The antifungal activity of bacteria from the genus Collimonas has been well documented, but the chemistry and gene functions that underlie this phenotype are still poorly understood. Screening of a random plasposon insertion library of Collimonas fungivorans Ter331 for loss-of-function mutants revealed the importance of gene cluster K, which is annotated to code for the biosynthesis of a secondary metabolite and which features genes for fatty acid desaturases and polyketide synthases. Mutants in gene cluster K had lost the ability to inhibit hyphal growth of the fungus Aspergillus niger and were no longer able to produce and secrete several metabolites that after extraction and partial purification from wildtype strain Ter331 were shown to share a putative ene-triyne moiety. Some but not all of these metabolites were able to inhibit growth of A.¿niger, indicating functional variation within this group of Collimonas-produced polyyne-like 'collimomycins'. Polymerase chain reaction analysis of isolates representing different Collimonas species indicated that the possession of cluster K genes correlated positively with antifungal ability, further strengthening the notion that this cluster is involved in collimomycin production. We discuss our findings in the context of other bacterially produced polyynes and the potential use of collimomycins for the control of harmful fungi.
    Assessing the impacts of livestock production on biodiversity in rangeland ecosystems
    Alkemade, R. ; Reid, R.S. ; Berg, M. van den; Leeuw, J. de; Jeuken, M. - \ 2013
    Proceedings of the National Academy of Sciences of the United States of America 110 (2013)52. - ISSN 0027-8424 - p. 20900 - 20905.
    land-use changes - south-africa - diversity - conservation - assemblages - grassland - management - scenarios - responses - savanna
    Biodiversity in rangelands is decreasing, due to intense utilization for livestock production and conversion of rangeland into cropland; yet the outlook of rangeland biodiversity has not been considered in view of future global demand for food. Here we assess the impact of future livestock production on the global rangelands area and their biodiversity. First we formalized existing knowledge about livestock grazing impacts on biodiversity, expressed in mean species abundance (MSA) of the original rangeland native species assemblages, through metaanalysis of peer-reviewed literature. MSA values, ranging from 1 in natural rangelands to 0.3 in man-made grasslands, were entered in the IMAGE-GLOBIO model. This model was used to assess the impact of change in food demand and livestock production on future rangeland biodiversity. The model revealed remarkable regional variation in impact on rangeland area and MSA between two agricultural production scenarios. The area of used rangelands slightly increases globally between 2000 and 2050 in the baseline scenario and reduces under a scenario of enhanced uptake of resource-efficient production technologies increasing production [high levels of agricultural knowledge, science, and technology (high-AKST)], particularly in Africa. Both scenarios suggest a global decrease in MSA for rangelands until 2050. The contribution of livestock grazing to MSA loss is, however, expected to diminish after 2030, in particular in Africa under the high-AKST scenario. Policies fostering agricultural intensification can reduce the overall pressure on rangeland biodiversity, but additional measures, addressing factors such as climate change and infrastructural development, are necessary to totally halt biodiversity loss.
    Observations of the Effect of Dry Soils on Air Temperatures
    Miralles, D.G. ; Teuling, A. ; Berg, M. van den; Jeu, R. de; Vilà-Guerau de Arellano, J. ; Heerwaarden, C. van - \ 2013
    A new approach is applied to satellite and in situ observations towards the characterization of regions of intense soil moisture-temperature coupling. We estimate two energy balances - one based on actual evaporation and one based on potential evaporation - and analyze their differential skill in explaining the dynamics of air temperature. The approach is applied to the study of climatological coupling hotspots as well as the anomalous role of soil moisture deficit during specific heatwaves in the past. Results using recently developed satellite-based evaporation (GLEAM) and temperature fields from reanalysis (ERA Interim) are validated using meteorological measurements and atmospheric profiles from sounding archives. We find strong soil moisture-temperature coupling during the 2003 and 2010 heatwave events in Western Europe and Russia, especially in the regions in which the peak of temperatures occurred. Much lower coupling is found in the 2006 heatwave in California, and soil moisture deficit is suggested to have played an insignificant role in the event. Our observational results of the importance of dry soils in the occurrence of heatwaves are complemented with results obtained from CLASS, a conceptual model that couples the surface properties to the diurnal atmospheric boundary layer dynamics. By combining all these methods, we expect to understand whether soil moisture deficit is a necessary condition for the occurrence of mega-heatwaves or whether similar temperatures can still happen due to large-scale synoptic conditions. Ultimately, our analyses aim to provide independent observational estimates of the effect of soil moisture on air temperature dynamics that can be used to benchmark climate models.
    Land tenure security and land investments in Northwest China
    Ma Xian lei, Xianlei ; Heerink, N. ; Ierland, E.C. van; Berg, M. van den; Shi, X. - \ 2013
    China Agricultural Economic Review 5 (2013)2. - ISSN 1756-137X - p. 281 - 307.
    property-rights - rural china - housing improvement - buenos-aires - insecurity - productivity - incentives - ethiopia - impact - policy
    Purpose - The purpose of this paper is to examine the effect of perceived land tenure security in China on farmers' decisions to invest in relatively long-term land quality improvement measures, taking into account the potential endogeneity of tenure security. Design/methodology/approach – Data from a survey held in 2008 and 2010 among 259 households in Minle County, Gansu province, covering the years 2007 and 2009, are used to estimate the factors affecting land levelling investments, irrigation canal investments and perceived land tenure security. The authors use the 2SCML technique and the IVLS method to estimate a selection model and a non-limited regression model, respectively, and use IVP methods to examine the robustness of the results. Findings - The authors' results indicate that perceived land tenure security significantly affects self-governed investments but does not affect individual investments in land quality improvements. In particular, the authors find that households that consider land certificates as important for protecting land rights invest significantly more in irrigation canals construction and maintenance. The authors' results further provide evidence that individual investments in land quality improvement contribute to higher perceived land tenure security. Originality/value - The paper contributes to the available literature on the relationship between land tenure security and land investments by examining the role of perceived (instead of formal) land tenure security and by making a distinction between individual household investments and self-governed land investments. The authors' results provide an explanation for the phenomenon that land readjustments still take place in some parts of China, but not in others
    Development of a tool to assess social influence on physical activity in low SES groups
    Wagemakers, A. ; Herens, M.C. ; Berg, M. van den; Ophem, J.A.C. van; Koelen, M. - \ 2012
    Assessing the impact of soil degradation on food production
    Bindraban, P.S. ; Velde, M. van der; Ye, L. ; Berg, M. van den; Materechera, S. ; Kiba, D.I. ; Tamene, L. ; Ragnarsdottir, K.V. ; Jongschaap, R.E.E. ; Hoogmoed, M. ; Hoogmoed, W.B. ; Beek, C.L. ; Lynden, G.W.J. van - \ 2012
    Current Opinion in Environmental Sustainability 4 (2012)5. - ISSN 1877-3435 - p. 478 - 488.
    conservation agriculture - carbon sequestration - land degradation - africa - erosion - yield - management - security - climate - trends
    Continuing soil degradation remains a serious threat to future food security. Yet, global soil degradation assessments are based on qualitative expert judgments or remotely sensed quantitative proxy values that suffice to raise awareness but are too coarse to identify appropriate sustainable land management interventions. Studies in China and Sub Saharan Africa illustrate the considerable impact of degradation on crop production but also point to the need for solutions dependent on location specific agro-ecological conditions and farming systems.The development of a comprehensive approach should be feasible to better assess both extent and impact of soil degradation interlinking various scales, based on production ecological approaches and remote sensing to allow disentangling natural and human induced causes of degradation. A shared common knowledge base cataloguing hard-won location-specific interventions is needed for successfully preventing or mitigating degradation
    Some OH-PCBs are more potent inhibitors of aromataseactivity and (anti-) glucocorticoids than non-dioxin like (NDL)-PCBs and MeSO2-PCBs
    Antunes Fernandes, E.C. ; Bovee, T.F.H. ; Daamen, F. ; Helsdingen, J.R. ; Berg, M. van den; Duursen, M. van - \ 2011
    Toxicology Letters 206 (2011)2. - ISSN 0378-4274 - p. 158 - 165.
    methyl sulfone metabolites - adrenocortical carcinoma-cells - brominated flame retardants - polychlorinated-biphenyls - hydroxylated metabolites - methylsulfonyl metabolites - placental-transfer - eastern slovakia - gene-expression - hormone levels
    Traditional risk assessment of potential endocrine-disruptive pollutants, including PCBs, focus mainly on the effects of parent compounds. Still, biotransformation results in systemic exposure to PCBs and their bioactive metabolites. In the present paper, the effects of twenty ultra-pure non-dioxin-like (NDL) PCBs and their environmentally relevant hydroxy- (OH-) and methylsulfonyl- (MeSO2-) metabolites on aromataseactivity and their glucocorticoid properties were investigated. Although most NDL-PCBs were inactive, PCB28 inhibited aromataseactivity in human placenta microsomes with an IC50 of 2.2 µM. Most of these NDL-PCBs were weak (ant-)agonist of the glucocorticoid receptor (GR). Interestingly, four OH-metabolites of the commonly found NDL-PCB180 were able to inhibit aromataseactivity (LOECs in the low µM range) and showed anti-glucocorticoid properties (LOECs in the low nM range), in a concentration-dependent manner. Further, four MeSO2-PCBs slightly inhibited aromataseactivity and showed anti-glucocorticoid properties. Although, these effects were also associated with cytotoxicity, they were dependent on the position of the MeSO2-group on the biphenyl ring. Our results are the first to show that OH-PCBs are both anti-glucocorticoids and aromataseinhibitors. Taken together, these results for PCBs again support the common idea that risk assessment of the endocrine disruptive potential of PCBs should also include their metabolites. --------------------------------------------------------------------------------
    Greenhouse gas emission profiles of European livestock sectors
    Lesschen, J.P. ; Berg, M. van den; Westhoek, H.J. ; Witzke, H.P. ; Oenema, O. - \ 2011
    Animal Feed Science and Technology 166-167 (2011). - ISSN 0377-8401 - p. 16 - 28.
    milk-production - dairy farms - management - nitrogen - deforestation - agriculture - strategies - losses - energy - meat
    There are increasing concerns about the ecological footprint of global animal production. Expanding livestock sectors worldwide contribute to expansion of agricultural land and associated deforestation, emissions of greenhouse gases (GHG), eutrophication of surface waters and nutrient imbalances. Farm based studies indicate that there are large differences among farms in animal productivity and environmental performance. Here, we report on regional variations in dairy, beef, pork, poultry and egg production, and related GHG emissions in the 27 Member States of the European Union (EU-27), based on 2003–2005 data. Analyses were made with the MITERRA-Europe model which calculates annual nutrient flows and GHG emissions from agriculture in the EU-27. Main input data were derived from CAPRI (i.e., crop areas, livestock distribution, feed inputs), GAINS (i.e., animal numbers, excretion factors, NH3 emission factors), FAO statistics (i.e., crop yields, fertilizer consumption, animal production) and IPCC (i.e., CH4, N2O, CO2 emission factors). Sources of GHG emissions included were enteric fermentation, manure management, direct and indirect N2O soil emissions, cultivation of organic soils, liming, fossil fuel use and fertilizer production. The dairy sector had the highest GHG emission in the EU-27, with annual emission of 195 Tg CO2-eq, followed by the beef sector with 192 Tg CO2-eq. Enteric fermentation was the main source of GHG emissions in the European livestock sector (36%) followed by N2O soil emissions (28%). On a per kg product basis, beef had by far the highest GHG emission with 22.6 kg CO2-eq/kg, milk had an emission of 1.3 kg CO2-eq/kg, pork 3.5 kg CO2-eq/kg, poultry 1.6 kg CO2-eq/kg, and eggs 1.7 kg CO2-eq/kg. However large variations in GHG emissions per unit product exist among EU countries, which are due to differences in animal production systems, feed types and nutrient use efficiencies. There are, however, substantial uncertainties in the base data and applied methodology such as assumptions surrounding allocation of feeds to livestock species. Our results provide insight into differences in GHG sources and emissions among animal production sectors for the various regions of Europe.
    The protein puzzle : the consumption and production of meat, dairy and fish in the European Union
    Westhoek, H. ; Rood, T. ; Berg, M. van den; Janse, J. ; Nijdam, D. ; Reudink, M. ; Stehfest, E. ; Lesschen, J.P. ; Oenema, O. ; Woltjer, G.B. - \ 2011
    The Hague : Netherlands Environmental Assessment Agency (PBL publication 500166001) - ISBN 9789078645610 - 218
    voedselconsumptie - eiwitbronnen - dierlijke eiwitten - milieueffect - voeding en gezondheid - duurzaamheid (sustainability) - vleesproductie - europese unie - dierlijke productie - dierenwelzijn - food consumption - protein sources - animal proteins - environmental impact - nutrition and health - sustainability - meat production - european union - animal production - animal welfare
    In het rapport 'The protein puzzle. The consumption and production of meat, dairy and fish in the European Union' brengen onderzoekers van het Planbureau voor de Leefomgeving (PBL) in kaart wat de gevolgen van de productie en consumptie van dierlijke eiwitten zijn voor milieu, natuur en gezondheid. Vervolgens schetst het PBL welke opties er in Europees verband zijn om de negatieve effecten te verminderen. Met deze studie verschaft het PBL relevante feiten en cijfers ten behoeve van het debat over eiwitconsumptie, inclusief een indicatie van de onzekerheden daarbij.
    PCB-47, PBDE-47, and 6-OH-PBDE-47 Differentially Modulate Human GABAA and a4b2 Nicotinic Acetylcholine Receptors
    Hendriks, H.S. ; Antunes Fernandes, E.C. ; Bergman, A. ; Berg, M. van den; Westerink, R.H.S. - \ 2010
    Toxicological sciences 118 (2010)2. - ISSN 1096-6080 - p. 635 - 642.
    polybrominated diphenyl ethers - brominated flame-retardant - neonatal brain-development - long-term potentiation - polychlorinated-biphenyls - adult mice - spontaneous behavior - perinatal exposure - hippocampus - metabolites
    Polychlorinated biphenyls (PCBs) and the structurally related polybrominated diphenyl ethers (PBDEs) are abundant persistent organic pollutants that exert several comparable neurotoxic effects. Importantly, hydroxylated metabolites of PCBs and PBDEs have an increased neurotoxic potency. Recently, we demonstrated that PCBs can act as (partial) agonist on GABAA neurotransmitter receptors, with PCB-47 being the most potent congener. It is, however, unknown whether PBDE-47 and its metabolite 6-OH-PBDE-47 exert similar effects and if these effects are limited to GABAA receptors only. We therefore investigated effects of PCB-47, PBDE-47, and 6-OH-PBDE-47 on the inhibitory GABAA and excitatory a4b2 nicotinic acetylcholine (nACh) receptor expressed in Xenopus oocytes using the twoelectrode voltage-clamp technique. Since human exposure is generally not limited to individual compounds, experiments with binary mixtures were also performed. The results demonstrate that PCB-47 and 6-OH-PBDE-47 act as full and partial agonist on the GABAA receptor. However, both congeners act as antagonist on the nACh receptor. PBDE-47 does not affect either type of receptor. Binary mixtures of PCB-47 and 6-OH-PBDE-47 induced an additive activation as well as potentiation of GABAA receptors, whereas this mixture resulted in an additive inhibition of nACh receptors. Binary mixtures of PBDE-47 and 6-OH-PBDE-47 yielded similar effects as 6-OH-PBDE-47 alone. These findings demonstrate that GABAA and nACh receptors are affected differently by PCB-47 and 6-OH-PBDE-47, with inhibitory GABAA-mediated signaling being potentiated and excitatory a4b2 nACh–mediated signaling being inhibited. Considering these opposite actions and the additive interaction of the congeners, these effects are likely to be augmented in vivo.
    Potentiation of the human GABA(A) receptor as a novel mode of action of lower-chlorinated non-dioxin-like PCBs
    Antunes Fernandes, E.C. ; Hendriks, H.S. ; Kleef, R.G.D.M. van; Berg, M. van den; Westerink, R.H.S. - \ 2010
    Environmental Science and Technology 44 (2010)8. - ISSN 0013-936X - p. 2864 - 2869.
    polychlorinated biphenyl congeners - cerebellar granule cells - developmental neurotoxicity - thyroid-hormone - ester binding - in-vitro - rat - brain - exposure - dopamine
    PCBs are still ubiquitous pollutants despite the ban on their industrial and commercial use. To date, risk characterization and assessment of non-dioxin-like PCBs (NDL-PCBs), especially with respect to neurotoxicity, is hampered by a lack of data. Therefore, the effects of six common NDL congeners (PCB28, 52, 101, 138, 153 and
    GHG emission profiles of the European livestock sectors
    Lesschen, J.P. ; Witzke, H.P. ; Berg, M. van den; Westhoek, H. ; Oenema, O. - \ 2010
    In: Listing of Abstracts to be presented at Greenhouse Gases and Animal Agriculture conference, 3-8 October 2010, Banff, Canada. - Bannff, Canada : Agriculture and Agri-Food Canada - p. 11 - 12.
    There are increasing concerns about the ecological footprint of global animal production. The expanding animal production sectors are implicated for their roles in the expansion of agricultural land and associated deforestation, the emissions of greenhouse gases (GHG), eutrophication of surface waters, and nutrient imbalances. Farm-based studies indicate that there are huge differences between farms in animal productivity and environmental performance. Comparisons at regional and country level have not been made yet. Here, we report on regional variations in dairy, beef, pork, poultry and egg production and related GHG emissions in the 27 Member States of the European Union (EU-27) for the year 2005. The analyses were made with the MITERRA-Europe model, which calculates nutrient flows and GHG emissions from agricultural sectors in EU-27 on annual basis. The main input data are derived from CAPRI (crop areas, livestock distribution and feed inputs), GAINS (animal numbers, excretion factors and NH3 emission factors), FAO statistics (crop yields, fertilizer consumption and animal products) and IPCC (CH4 and N2O emission factors). The following sources of GHG emissions were included: enteric fermentation, manure management, direct and indirect N2O soil emissions, cultivation of organic soils and fertilizer production. The beef sector had the highest GHG emission in the EU-27 with an annual emission of 160 Mton CO2-equivalents, followed by the dairy sector with 140 Mton CO2-equivalents. Enteric fermentation was the main source of GHG emissions in the European livestock sector (47%) followed by N2O soil emissions (32%). On a product basis beef had by far the highest GHG emissions (19 kg CO2-eq per kg product), followed by cheese (6.5 kg CO2-eq per kg product), pork (2.5 kg CO2-eq per kg product) and poultry (0.9 kg CO2-eq per kg product). Between countries a large variation in GHG emissions exists, which can be explained by differences in animal production systems, feed types, and nutrient efficiencies. The results of our study provide insight in the locations of stronger and weaker regions in Europe for animal production and form the basis for possible future development pathways towards more sustainable animal production
    Reverse breeding: a novel breeding approach based on engineered meiosis
    Dirks, R. ; Dun, K.P.M. van; Snoo, B. de; Berg, M. van den; Lelivelt, C.L.C. ; Voermans, W. ; Woudenberg, L. ; Wit, J.P.C. de; Reinink, K. ; Schut, J.W. ; Jong, J.H.S.G.M. de; Wijnker, T.G. - \ 2009
    Plant Biotechnology Journal 7 (2009)9. - ISSN 1467-7644 - p. 837 - 845.
    cytoplasmic male-sterility - meiotic prophase-i - chromosome segregation - arabidopsis-thaliana - gene - recombination - dmc1 - protein - plants - heterosis
    Reverse breeding (RB) is a novel plant breeding technique designed to directly produce parental lines for any heterozygous plant, one of the most sought after goals in plant breeding. RB generates perfectly complementing homozygous parental lines through engineered meiosis. The method is based on reducing genetic recombination in the selected heterozygote by eliminating meiotic crossing over. Male or female spores obtained from such plants contain combinations of non-recombinant parental chromosomes which can be cultured in vitro to generate homozygous doubled haploid plants (DHs). From these DHs, complementary parents can be selected and used to reconstitute the heterozygote in perpetuity. Since the fixation of unknown heterozygous genotypes is impossible in traditional plant breeding, RB could fundamentally change future plant breeding. In this review, we discuss various other applications of RB, including breeding per chromosome
    Het ontstaan van het Nederlandse landschap. Een canon in 12 thema's en 50 vensters
    Berg, M. van den; Beukenkamp, P. ; Brombacher, A. ; Burger, J.E. ; Dam, L. van; Dijkmans, J. ; Doorn, J. van; Erkens, G. ; Gans, W. de; Graaff, E. van der; Hendriks, M. ; Hijma, M. ; Hoek, W. ; Hoekstra, P. ; Kleijn, N. ; Klijn, J.A. ; Koomen, A.J.M. ; Lam, A. ; Meijering, J. ; Mourik, J. van; Oost, A. ; Peek, G.J.W.C. ; Rozemeijer, J. ; Sonneveld, M.P.W. ; Schouten, C. ; Visscher, H. - \ 2008
    [S.l.] : Werkgroep Canon - Geoheritage NL en Buro voor Explanation Design - ISBN 9789074980203
    landschap - landschapsecologie - geschiedenis - nederland - cultuurlandschap - natuurlandschap - landscape - landscape ecology - history - netherlands - cultural landscape - natural landscape
    De Canon van het Landschap vertelt over de ontstaansgeschiedenis van de Nederlandse landschappen (brede rivieren, meren, waterrijke veenpolders, blinkende duinen, stuwwallen, uitgestrekte wadden enz.).
    Subacute effects of hexabromocyclododecane (HBCD) on hepatic gene expression profiles in rats
    Canton, R.F. ; Peijnenburg, A.A.C.M. ; Hoogenboom, L.A.P. ; Piersma, A.H. ; Ven, L.T.M. van der; Berg, M. van den; Heneweer, M. - \ 2008
    Toxicology and Applied Pharmacology 231 (2008)2. - ISSN 0041-008X - p. 267 - 272.
    brominated flame retardants - polybrominated diphenyl ethers - tetrabromobisphenol-a - harbor porpoises - scheldt estuary - in-vitro - hypothyroidism - cells - river - dust
    Hexabromoyclododecane (HBCD), used as flame retardant (FR) mainly in textile industry and in polystyrene foam manufacture, has been identified as a contaminant at levels comparable to other brominated FRs (BFRs). HBCD levels in biota are increasing slowly and seem to reflect the local market demand. The toxicological database of HBCD is too limited to perform at present a solid risk assessment, combining data from exposure and effect studies. In order to fill in some gaps, a 28-day HBCD repeated dose study (OECD407) was done in Wistar rats. In the present work liver tissues from these animals were used for gene expression profile analysis. Results show clear gender specificity with females having a higher number of regulated genes and therefore being more sensitive to HBCD than males. Several specific pathways were found to be affected by HBCD exposure, like PPAR-mediated regulation of lipid metabolism, triacylglycerol metabolism, cholesterol biosynthesis, and phase I and II pathways. These results were corroborated with quantitative RT-PCR analysis. Cholesterol biosynthesis and lipid metabolism were especially down-regulated in females. Genes involved in phase I and II metabolism were up-regulated predominantly in males, which could explain the observed lower HBCD hepatic disposition in male rats in this 28-day study. These sex-specific differences in gene expression profiles could also underlie sex-specific differences in toxicity (e.g. decreased thyroid hormone or increased serum cholesterol levels). To our knowledge, this is the fist study that describes the changes in rat hepatic gene profiles caused by this commonly used flame retardant
    In Vitro antiandrogenicity of PBDEs, HBCD, TBP and hydroxylated and methoxylated PBDEs based on a yeast bioassay
    Canton, R.F. ; Bovee, T.F.H. ; Daamen, F. ; Duursen, M. van; Berg, M. van den - \ 2007
    Chemico-Biological Interactions 169 (2007)2. - ISSN 0009-2797 - p. 133 - 133.
    Brominated flame retardants (BFRs) are chemicals used in all kinds of materials for electronic and daily apparatuses to reduce fire risks. These compounds act in the gas phase of the fire by reacting with free radicals generated during combustion, thus terminating the reaction. From an environmental point of view, BFRs have become an increasingly important group of organohalogen compounds, which include among others polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) isomers. Global production of PBDEs alone was about 40,000 tons in 2001. PBDEs can be divided into three major commercial mixtures: Penta-, Octa- and Deca-BDEs. The first two have been recently banned, through voluntary actions by industry, in Europe and will be banned in the near future also in North America. PBDEs have been found in abiotic and biotic environments. They are generally lipophilic, persistent and thus have the potential to bioaccumulate and biomagnify. In the 1970s and 1980s, a substantial increase in PBDE concentrations for example in mother's milk was observed. However, a slight decrease in environmental samples during the last 5¿8 years in Northern Europe has been observed, probably due to the ban of the Penta- and Octa-BDE mixtures. PBDE metabolites, mainly tetrabromo- and pentabromo-methoxylated PBDEs (CH3O-PBDEs) and hydroxylated (OH-PBDEs), have also been detected in the blood and to a lesser extent in adipose and liver tissues of a limited number of fish, bird, and mammalian species. Some of these PBDE metabolites have also been detected in human blood. A number of OH-PBDEs have previously been isolated and structurally identified as natural compounds in marine sponges and in ascidians (tunicates). All naturally occuring OH-PBDEs in these marine organisms have a hydroxyl group at the ortho position relative to the ether bond, and are exemplified by 6-OH-BDE47 and 2¿-OH-BDE68. In vitro studies have shown how some of these OH-PBDEs can bind competitively to thyroid hormone transport proteins such as transthyretin (TTR). Further, some OH-PBDEs may cause estrogenic effects in vitro. Antiandrogenic effects have been shown previously in vitro for some of the BFRs, especially PBDEs, using the AR-CALUX reporter gene system. In some cases, the potency was higher than for natural ligands. Using the human adrenocortical carcinoma cell line (H295R), some of the PBDE derivatives were shown to significantly inhibit CYP19 (aromatase) and CYP17 activity, which are key enzymes in steroidogenesis. However, to some extent, these inhibitory effects were due to cytotoxicity. In order to establish and study the possible effects of BFRs and PBDE metabolites on the androgen receptor (AR), a new highly specific yeast androgen bioassay was used. Different controls and test compounds were tested on both their potential agonistic as well as their antagonistic potency.
    Nitrate in upper groundwater on farms under tillage as affected by fertilizer use, soil type and groundwater table
    Ruijter, F.J. de; Boumans, L.J.M. ; Smit, A.L. ; Berg, M. van den - \ 2007
    Nutrient Cycling in Agroecosystems 77 (2007)2. - ISSN 1385-1314 - p. 155 - 167.
    organic-carbon - surface-water - sandy regions - nitrogen use - netherlands - agriculture - denitrification - availability - management - balances
    Indicators are needed to check whether policies on protection of groundwater are effective and if regulations are complied with. We evaluated various indicators at different scales, both in space and in time, and at different degrees of complexity. Groundwater was sampled on 34 arable farms for 3 years. Nitrate concentration in upper groundwater was low on clay soil. On sandy soil, peat layers reduced the nitrate concentration with about 80 mg/l on average. Sandy soils with high groundwater tables had nitrate concentrations that were less than half of those at sandy soils with low groundwater tables. The relationship between different fertilization variables and nitrate in groundwater was investigated for sandy soils without peat layers. N surplus poorly correlated with nitrate concentrations in groundwater when individual sampling points were studied, but clearly increased when data were averaged at the farm level. Soil mineral nitrogen correlated best with nitrate concentrations in groundwater. The relationships show that especially on well drained soil drastic measures will be inevitable to reach good water quality.
    Determination of in vitro relative potency (REP) values for mono-ortho polychlorinated biphenyls after purification with active charcoal
    Peters, A.K. ; Leonards, P.E.G. ; Zhao, B. ; Bergman, A. ; Denison, M.S. ; Berg, M. van den - \ 2006
    Toxicology Letters 165 (2006)3. - ISSN 0378-4274 - p. 230 - 241.
    dioxin-like compounds - aryl-hydrocarbon receptor - toxic equivalency factors - dibenzo-p-dioxins - monkeys macaca-fascicularis - o-deethylase induction - ah receptor - risk-assessment - h4iie cells - dependent induction
    The TEF system for dioxin-like compounds has included assignment of TEF values for mono-ortho polychlorinated biphenyls (MO-PCBs). Small traces of aryl hydrocarbon receptor (AhR)-active impurities could result in artifactually higher relative potency (REP) values. MO-PCBs -105, -118, -156, and -167 were purified on an active charcoal column to remove AhR agonists that could be present as impurities. Activation or inhibition of AhR-dependent gene expression by purified MO-PCBs was studied in stably transfected cell lines (HlG1.1c3 mouse, H4G1.1c2 rat hepatoma), containing an AhR-responsive (AhR-EGFP) reporter gene. In addition, EROD activity was used as marker for CYP1A1 activity in these cell lines. MO-PCBs -105,-118,-156 induced AhR-EGFP expression in both rodent cell lines, with PCB-156 (10 mu M) being most effectively; inducing gene expression to similar to 27% of TCDD (mouse cells) and 62.5 +/- 3.4% (rat cells) of TCDD. This concurred with increased EROD activity in both cell lines to maxima of 20.5 +/- 1.5% and 68 +/- 3.2% of TCDD, respectively. No induction was observed for PCB-167. In the HIG1.1c3 mouse cells, PCB-105, -118 and -156 (10 mu M) significantly reduced TCDD-induced AbR-EGFP expression to 50.9 +/- 2.9%, 58.3 +/- 2.2% and 70.8 +/- 1.3% of TCDD. Reduced EROD activity was also observed, of 39.3 +/- 2.8%, 67 +/- 5% and 48.3 +/- 4% compared to TCDD. PCB-167 did not result in significant reduction. In rat cells, only PCB-156 resulted in significant decrease in TCDD-induced AhR-EGFP expression of 35%, suggesting species differences play a role. Our results suggest that purification of MO-PCBs is an essential step in determining accurate REP values, and could very likely lead to lower TEF values than those presently assigned by the WHO. (c) 2006 Elsevier Ireland Ltd. All rights reserved.
    Introduction of ethoxy-resorufin-o-deethylase activity by halogenated aromatic hydrocarbons and polycyclic aromatic hydrocarbons in primary hepatocytes of the green frog (Rana esculenta)
    Rouhani Rankouhi, T. ; Koomen, B. ; Sanderson, J.T. ; Bosveld, A.T.C. ; Seinen, W. ; Berg, M. van den - \ 2005
    Environmental Toxicology and Chemistry 24 (2005)6. - ISSN 0730-7268 - p. 1428 - 1435.
    polychlorinated-biphenyls pcbs - cell-line - in-vitro - cytochrome-p4501a induction - endocrine disruptors - population declines - xenopus-laevis - fish - cultures - liver
    In this study, we measured the ethoxy-resorufin-O-deethylase (EROD) activity in primary hepatocytes of the common green frog Rana esculenta as a biomarker for cytochrome P4501A induction. We exposed hepatocytes derived from male and female frogs to several halogenated aromatic hydrocarbons, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PCDF), polychlorinated biphenyls (PCB-126, PCB-118). and polycyclic aromatic hydrocarbons such as benzo[a]pyrene (BaP), chrysene, anthracene, and pyrene. Exposure to PCB-118, anthracene, and pyrene, up to 1 μ M, did not induce EROD activity, whereas TCDD and PCDF induced EROD activity maximally. In our primary frog hepatocytes, exposure to chrysene and BaP resulted in median effective concentration values (EC50) in the high nM range (82-1035 nM). Exposure to TCDD, PCDF and PCB-126 resulted in EC50 values of 0.4 to 8, 0.07 to 0.7, and 3 to 133 nM, respectively, which is in the same range as EC50 values found in primary hepatocytes of birds. Compared to our frog hepatocytes, primary rat hepatocytes seem to be more sensitive to TCDD, chrysene. and BaP.
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