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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Changes in body composition as a result of chemotherapy : Comparing women with and without breast cancer
Berg, Maaike M.G.A. van den - \ 2017
Wageningen University. Promotor(en): E. Kampman; M. Visser, co-promotor(en): R.M. Winkels; J.H.M. de Vries. - Wageningen : Wageningen University - ISBN 9789463436984 - 140
body composition - neoplasms - cancer - drug therapy - breast cancer - body weight - intake - diet - meta-analysis - toxicity - lichaamssamenstelling - neoplasma's - cancer - geneesmiddelenbehandeling - borstkanker - lichaamsgewicht - opname (intake) - dieet - meta-analyse - toxiciteit

Because of the improved survival rate, both short term and long term adverse effects of breast cancer treatment have become increasingly important. Body weight and body composition before, during, and after chemotherapy may influence side effects during treatment and survival. The aims of this thesis were to assess among stage I-IIIB breast cancer patients: 1) the association between pre-treatment body composition and dose-limiting toxicities during chemotherapy, 2) potential changes in body weight and body composition during and after chemotherapy compared to changes in age-matched women without cancer in the same time period, and 3) dietary intake during chemotherapy compared to age-matched women without cancer in the same time period.

Chapter 2 describes the association between pre-treatment body composition and dose-limiting toxicities during chemotherapy. Data from 172 breast cancer patients who participated in the COBRA-study were analysed. Body composition was measured using a total body Dual Energy X-ray Absorption (DEXA) scan. Information regarding dose-limiting toxicities was abstracted from medical records. A higher BMI (kg/m2) and a higher fat mass (kg and percentage) were associated with an increased risk of dose-limiting toxicity, while lean body mass (kg) was not associated with risk of toxicities.

Chapter 3 presents the findings of a meta-analysis on changes in body weight during chemotherapy in breast cancer patients. The meta-analysis showed an overall gain in body weight of 2.7 kg (95% CI: 2.0-3.3) during chemotherapy, with a high degree of heterogeneity (I2= 94.2%). Weight gain in breast cancer patients was more pronounced in papers published before 2000 and studies including cyclophosphamide, methotrexate and 5-fluorouracil as chemotherapy regime.

Chapter 4 describes changes in body weight and body composition during and after chemotherapy. Data from 145 patients and 121 women of an age-matched comparison group, participating in the COBRA-study were analysed. Body composition was measured using DEXA-scan at three time points during the study period. For the patient group, these tie points were: before start of chemotherapy, shortly after chemotherapy, and 6 months after chemotherapy. For the comparison group these measurements were conducted over a similar time frame: baseline, 6 months after baseline, and 12 months after baseline. In addition, we identified determinants of changes in body weight and body composition.

Shortly after chemotherapy, patients had a significantly higher body weight, BMI, and lean body mass than women in the comparison group, while fat mass was similar. Six months after chemotherapy no differences in body weight or body composition were observed between the patient and comparison group. A younger age, better appetite during chemotherapy, and an ER-receptor negative tumour were associated with greater changes in body weight over time. A younger age and better appetite during chemotherapy were associated with greater changes in fat mass over time, while the only determinant associated with greater changes in lean body mass over time was a better appetite during chemotherapy.

Chapter 5 describes the dietary intake and food groups before and during chemotherapy of breast cancer patients compared with women without cancer. In addition we assessed the association between symptoms and energy intake. Data from 117 breast cancer patients and 88 women without breast cancer who participated in the COBRA-study were used. Habitual dietary intake before chemotherapy was assessed using a food frequency questionnaire. Two 24-hr dietary recalls were used to assess actual dietary intake during chemotherapy for patients and within 6 months for the comparison group. Shortly after the 24-hr dietary recall, participants filled out questionnaires about symptoms. Before chemotherapy, dietary intake was similar for both groups. During chemotherapy, breast cancer patients reported significantly lower total energy, total fat, total protein, and alcohol intake than women without cancer, which could be explained by a lower intake of specific food groups.

Overall results from this thesis suggest that pre-treatment fat mass is associated with dose-limiting toxicities during chemotherapy. Weight gain during chemotherapy appeared to be more modest than we expected based on literature and changes in body composition during chemotherapy consist mainly of an increase in lean body mass, which is only temporary and returned to baseline within 6 months after chemotherapy. A higher appetite during chemotherapy was associated with changes in body weight and body composition. A younger age at diagnosis was associated with greater changes in body weight and fat mass, but not with changes in lean body mass. In addition, an ER-receptor negative tumour was associated with greater changes in body weight, but not with changes in fat mass or lean body mass. During chemotherapy women with breast cancer have a lower intake of energy, fat, protein and alcohol compared to age-matched women without cancer, which was expressed in a lower intake of specific food groups. The results of this thesis do not suggest that dietary intake is associated with weight gain during chemotherapy.

An economic approach to non-animal toxicity testing for skin sensitisation
Leontaridou, Maria - \ 2017
Wageningen University. Promotor(en): E.C. van Ierland, co-promotor(en): S.G.M. Gabbert; R. Landsiedel. - Wageningen : Wageningen University - ISBN 9789463431361 - 151
animal testing alternatives - toxicity - testing - sensitivity - sensitivity analysis - bayesian theory - alternatieven voor dierproeven - toxiciteit - testen - gevoeligheid - gevoeligheidsanalyse - bayesiaanse theorie

Chemicals applied in products, such as food products, pharmaceuticals or cosmetics, create great benefits in society while posing risks to human health and the quality of the environment. To control those risks, it is mandatory to perform risk assessments of chemicals which require information on their hazardous properties. To meet these information requirements without sacrificing large numbers of animal tests, many non-animal testing methods and strategies have become available. Given the increasing needs for assessing chemicals’ risks, toxicity testing has become costly in terms of testing costs, time and animal welfare.

Focusing on skin sensitisation as a case study, this thesis aims at introducing an economic approach towards the optimisation of toxicity testing strategies. Chapter 2 surveys the current status of non-animal toxicity testing strategies assessing skin sensitisation and compares criteria suggested in the toxicological literature with the conceptual and informational criteria introduced in this chapter for increasing resource-efficiency in the development of testing strategies. Chapter 3 extends to the development of a Bayesian Value-of-Information model for the optimisation of non-animal toxicity testing strategies. This optimisation model is applied to construct optimal non-animal toxicity testing strategies for the assessment of skin sensitisation potential.

Chapter 4 focuses on the precision of testing methods and the impact of limited precision on the evaluation of test results. The borderline range of testing methods is quantified and applied as an additional evaluation measure in the prediction models of testing methods to identify substances as positive and negative (for substances yielding clear-cut test results), or as discordant (for substances yielding test results within the borderline range). Chapter 5 addresses the uncertainties underlying the predictive accuracy metrics for non-animal testing methods due to their limited precision, the sample size and composition of the samples of chemicals used to estimate the predictive capacity of testing methods. Chapters 4 and 5 focus on non-animal testing methods for the assessment of skin sensitisation potential.

This thesis concludes that introducing the economic perspective into the construction of toxicity testing strategies is necessary to develop the means by which resource-efficiency in toxicity testing is achieved. Furthermore, the evaluation of testing methods should consider both predictivity and precision limitations such that decision makers can draw robust conclusions on the hazardous properties of chemicals.

Integrated strategy for the assessment of kidney toxicity : the case of aristolochic acids
Abdullah, Rozaini - \ 2017
Wageningen University. Promotor(en): Ivonne Rietjens, co-promotor(en): Ans Punt; Sebas Wesseling; Jochem Louisse. - Wageningen : Wageningen University - ISBN 9789463430807 - 207
animal testing alternatives - in vitro - toxicity - models - risk assessment - toxins - carboxylic acids - alternatieven voor dierproeven - in vitro - toxiciteit - modellen - risicoschatting - toxinen - carbonzuren

This PhD thesis aimed to provide additional evidence to demonstrate the potential of an integrated testing strategy using in vitro assays with physiologically based kinetic (PBK) modeling based-reverse dosimetry to predict in vivo toxicity without animal testing. Kidney toxicity was chosen as the toxicity endpoint and aristolochic acids (AAs) were selected as model chemicals. AAs are natural nephrotoxic, genotoxic and carcinogenic chemicals present in Aristolochia species. PBK models for rat, mouse and human were developed for aristolochic acid I (AAI) based on kinetic parameter values derived from in vitro incubations using relevant tissue fractions. Then, in vitro concentration-response curves for cytotoxicity of AAI were obtained in kidney cell lines and translated to in vivo dose-response curves for kidney toxicity using PBK modeling-based reverse dosimetry. The points of departure (PODs) obtained from these predicted in vivo dose-response curves generally fell within the range of PODs derived from in vivo literature data on kidney toxicity of AAI. The same PBK models were subsequently used to translate the in vitro concentration-response curves for AAI-DNA adduct formation to in vivo dose-response curves for kidney AAI-DNA adduct formation. The predicted in vivo AAI-DNA adduct formation in the rat, mouse and human kidney varied within an order of magnitude compared to the in vivo values reported in the literature. The PBK models were also used to predict the dose level that would be required in humans to obtain the level of DNA adducts in rats at the BMD10 (the benchmark dose causing a 10% extra risk above background level) value for AAI-induced tumor formation in the rat kidney. This analysis revealed that the dose level required to induce the level of DNA adduct formation that equals the DNA adduct level at the BMD10 were similar to AA doses estimated to be taken in Belgian patients that developed urinary tract cancer. Given that the exposure to AAI is often accompanied by the presence of AAII, in a next study the relative formation of DNA adducts by these two major AA congeners was investigated. The results revealed that the relative higher formation of AAI-DNA adducts as compared to AAII-DNA adducts observed in vitro was not reflected in vivo where the levels formed upon exposure to equal dose levels were relatively similar. PBK model based translation of the in vitro data to the in vivo situation revealed that PBK model based prediction of in vivo DNA adduct formation is feasible. However, predicted AAI-DNA adduct levels were higher than predicted AAII-DNA adduct levels, indicating that the difference between the in vitro and in vivo AAI-/AAII-DNA adduct ratios could only in part be explained by differences in in vivo kinetics of AAI compared to AAII. The discrepancy between the difference in DNA adduct formation of AAI and AAII in the in vitro and the in vivo situation is an issue that needs further investigation to also adequately predict the relative differences between the two AAs. In a final chapter this thesis aimed to investigate the possible risks associated with exposure to AAs based on AA levels measured in plant food supplements (PFS) and herbal products. This is of interest given the restrictions on the presence of AAs in food, installed in various countries including The Netherlands, after the incidences with induction of Aristolochic Acid Nephropathy upon use of herbal weight loss preparations that accidentally contained AAs. The risk assessment of PFS and herbal products containing AAs purchased via online markets revealed that consumers can still be exposed to AA-containing PFS and herbal products and that the corresponding levels of exposure raise concern especially for people who frequently use the products. Altogether, this thesis presented further support for the use of combined in vitro-PBK modeling based alternative tools for risk assessment and revealed the continued risks posed by AAs present in PFS and herbal products.

In vitro assays for hazard identification of nanoparticles
Kloet, Samantha K. - \ 2016
Wageningen University. Promotor(en): Ivonne Rietjens; Jochem Louisse; Nico van den Brink. - Wageningen : Wageningen University - ISBN 9789462579415 - 213
nanotechnology - particles - in vitro - models - hazards - toxicity - toxicokinetics - nanotechnologie - deeltjes - in vitro - modellen - gevaren - toxiciteit - toxicokinetiek

The production of nanoparticles (NPs) has increased in the last decades and the number of products in which NPs are being incorporated is still growing. The rapid increase of nanotechnology has several benefits for society, yet there is an increasing concern that exposure to NPs may result in significant adverse health effects. Since NPs are incorporated in a variety of consumer products, it is likely that the general population will be exposed to NPs. It would be desirable that the safety and risk assessment of NPs could be largely based on studies using in vitro models instead of in vivo models as this would reduce the use of test animals, costs and time required to test the large numbers of NPs. The aim of the present thesis was to investigate the potential of in vitro testing strategies to detect hazards of NPs, focusing on toxicokinetic as well as toxicodynamic endpoints. Toxicokinetic studies focused on translocation of NPs in in vitro models of the placental barrier, while toxicodynamic studies were directed at two endpoints that represent potential hazards of NPs that have not yet been well characterized including: developmental toxicity and immunotoxicity.

In the present thesis different types of NPs were used. Polystyrene nanoparticles (PS-NPs) were selected because of their commercial availability, with high quality and a wide variety of available physicochemical properties like surface charge, and fluorescent labeling enabling easy detection in toxicokinetic (translocation) studies. Several metal (oxide) NPs were selected as well, of which some are possible constituents of food additives like TiO2, Fe2O3, SiO2 and Ag. Other metal oxide NPs that were selected were Mn­2O3, CuO, Cr2O3, CoO and NiO to which we may be exposed via products like paints, catalysts, construction materials, coatings and batteries.

Placental translocation of NPs was studied as an important toxicokinetic aspect, since part of the toxicodynamic studies of the present thesis were directed at developmental toxicity testing of NPs. In order to obtain insight in toxicity and translocation of NPs across the placental barrier, cytotoxicity and translocation was studied for one positively and two negatively charged PS-NPs of 50 nm in an in vitro model of the placenta. In this study it appeared that in spite of similar size, surface charge and type of proteins in the protein corona, the differently charged NPs displayed a remarkable difference in cytotoxicity, with only the PS-NPs with an original positive charge inducing cytotoxicity. Translocation of PS-NPs appeared not to be related to PS-NP charge alone. A remarkable difference in translocation was found between the two 50 nm negatively charged PS-NPs that were obtained from different manufacturers. Since none of the characterized parameters, including size, surface charge and protein corona revealed remarkable differences between the two negatively charged NPs, the difference may originate from the chemical groups on the surface of the NPs generating the negative charge. The general conclusion from this study was that the in vitro BeWo b30 model can be used as a fast method to get an initial qualitative impression about the capacity of NPs to translocate across the placental barrier and to set priorities for further in vivo studies on translocation of NPs to the fetus.

The same PS-NPs as tested for placental translocation were investigated whether they are able to cause in vitro developmental toxicity in the ES-D3 cell differentiation assay of the embryonic stem cell test (EST) focusing also on the effect that charge may have. The study showed that the two negatively charged PS-NPs did not show any effect in the ES-D3 cell differentiation assay up to the highest concentration tested while the positively charged PS-NP showed a concentration-dependent inhibition of ES-D3 cell differentiation. However, effect concentrations in the ES-D3 cell differentiation assay were close to cytotoxic concentrations, which indicated that the inhibition of the ES-D3 cell differentiation may be due to cytotoxic effects of the positively charged PS-NPs. This indicated that the inhibition of the ES-D3 cell differentiation by the positively charged PS-NPs may be caused by non-specific effects. Although the experiments on placental translocation of the present thesis showed that positively charged PS-NPs are more toxic than negatively charged PS-NPs, it appeared that this may not be generalizable to other NPs. This follows from the fact that in SiO2, Ag and TiO2 NPs that were reported in other studies to inhibit ES-D3 cell differentiation were negatively charged, while the negatively charged PS-NPs of the present study did not affect ES-D3 cell differentiation. Although the limited data available indicate that charge, size and coating of NPs may be important characteristics that determine the developmental toxicity potential of NPs, more (systematic) studies are needed to assess how physicochemical characteristics of NPs relate to their developmental toxicity. This information may help to prioritize NPs for in vitro and in vivo developmental toxicity testing.

In addition, toxic effects of a series of metal (oxide) NPs were tested in macrophage RAW264.7 cells in order to obtain insight in effect of these NPs on cells of the innate immune response. In these macrophage RAW264.7 cells the effects of the metal (oxide) NPs were characterized on cell viability, TNF-α production and mitochondria-related parameters like production of reactive oxygen species (ROS), mitochondrial permeability transition pore (MPTP) opening, and intracellular ATP levels. Altogether, results obtained showed no or limited effects of the NP formulations of metal (oxide) food additives on cell viability, ROS production, MPTP opening, ATP levels and TNF-α production in RAW264.7 macrophages. Effects were only observed at high concentrations that may not be physiologically relevant, indicating that related adverse effects upon exposure to the respective NPs in vivo may be limited.

Taken together, the present thesis provided further evidence of the influence of physicochemical properties of NPs in driving toxicity in in vitro models. However, the determination of the fate and toxicity of NPs using in vitro or in vivo models is a challenge that needs further evaluation. A combination of several factors likely play a role in determining the outcome of exposure including factors like NP core material and presence and type of coating agents resulting in various physicochemical properties (size, charge, etc.). This appears to hamper conclusive evaluation of the role of physicochemical characteristics of NPs in their potential hazards and risks so far. The results obtained do show however that in vitro assays can detect differences in potential hazards posed by NPs. Therefore it is concluded that the results of the work presented in this thesis will contribute to the further development and use of non-animal based testing strategies for safety testing of NPs providing insight into selected potential hazards of the tested NPs.

An in vitro – in vivo integrated approach for hazard and risk assessment of silver nanoparticles for soil organisms
Makama, S.I. - \ 2016
Wageningen University. Promotor(en): Ivonne Rietjens, co-promotor(en): Nico van den Brink. - Wageningen : Wageningen University - ISBN 9789462578432 - 190
particles - nanotechnology - toxicity - earthworms - gene expression - soil - coatings - deeltjes - nanotechnologie - toxiciteit - aardwormen - genexpressie - bodem - afdeklagen

Owing to their small sizes, nanoparticles (NPs) exhibit completely different and novel characteristics compared to their bulk counterparts of the same chemical composition. These novel properties include increased reactivity due to large specific surface area, fluorescence and colour changes, increased biological barrier crossings and increased material strengthening combined with light-weight. Virtually all fields of human endeavours are exploiting nanotechnology to combat different challenges. This has led to an increase in the production and potential release of NPs into the environment. The novel properties of these NPs however, mean an enhanced potential for interactions with biological systems that are different from the interactions of known conventional chemicals, thus raising environmental and public health/safety concerns. Available literature has reported NP uptake in different organisms along with associated hazards. Therefore, to safeguard human and environmental health and safety, regulatory measures are necessary. Such measures must be based on sound scientific evidence and be risk-based rather than hazard-based. As such, the need to understand the fate of NPs after environmental release and their potential to pose hazards and risks to the environment is critical for a proper risk assessment and further development of policy strategies on the future regulation of the use of NPs.

Some studies have demonstrated different and sometimes conflicting effects of NP properties on their uptake in different organisms. Given that exposure determines whether hazards will turn into risks, there is a critical need for further systematic evaluation of the physico-chemical properties of engineered or manufactured NPs that influence uptake in terrestrial organisms, and also of how soil properties may affect these processes. The objective of this project was to determine the influence of size and surface coating (charge), two important physico-chemical properties of NPs, on their bioavailability, uptake and toxicity. The red earthworm Lumbricus rubellus, common in most parts of Europe, was used as a model soil organism. Silver nanoparticles (AgNPs) have been identified as one of the most commonly used NPs in many products, and their production is expected to continue to increase. Therefore, we selected AgNPs as our model NPs. For our investigations, we applied an integrated in vitro - in vivo approach, utilising high throughput in vitro methods as well as well-established in vivo toxicity end-points in the earthworm. A systematic experimental approach was developed for which AgNPs were synthesized in three sizes: 20, 35 and 50 nm. Surface-coating with bovine serum albumin (AgNP_BSA), chitosan (AgNP_Chit), or polyvinylpyrrolidone (AgNP_PVP) resulted in negative, positive and neutral particles respectively.

Firstly, macrophage cells (RAW 264.7) were exposed to AgNPs at 0 – 200 µg/mL (nominal concentrations) and uptake dynamics, cell viability, as well as induction of tumour necrosis factor (TNF)-α and reactive oxygen species (ROS) were assessed (Chapter 2). Generally, the adverse effects of exposure to the tested AgNPs resulted in reduced overall viability of the cells, which was similar for all AgNPs tested. On adenosine triphosphate (ATP) production and specific mechanisms of toxicity (TNF-α and ROS production) however, we observed that the AgNPs differed significantly, with the negatively charged AgNP_BSA being the most toxic. Significant ROS induction was only observed after exposure to the 20 nm positively charged AgNP_Chit. Effect of size was less prominent than that of surface coating, showing mostly limited differences that were not statistically significant under our experimental conditions. Live confocal imaging of exposed cells allowed the monitoring of the uptake dynamics and subcellular cytoplasmic accumulation of AgNPs. We observed fast uptake of AgNPs within 2.5 hours which is essential in case of exposure durations of 6 and 24 hours, as applied in our experiments. However, similar uptake did not always result in similar effects.

With the insights obtained from the in vitro assessments, we investigated the effects of size and surface coating (charge) of AgNPs on the bioaccumulation in, and toxicity (survival, growth, cocoon production) to the earthworm L. rubellus. Currently, metal engineered NPs in tissues are generally quantified based on total metal concentrations after acid destruction of samples. Such destructive methods are limited in providing information on the speciation and the forms of NPs which is essential for characterising the fate of NPs. In the present thesis, we developed a method using a combination of enzymatic tissue processing and single particle inductively coupled plasma–mass spectrometry (sp-ICP-MS) to characterise and quantify AgNPs in tissues of earthworms (Chapter 3). Subcellular fractionation of tissues was also applied to investigate potential association of AgNPs with the cellular metallothionein (MT) containing fraction of the earthworm tissues. This study provided, to the best of our knowledge, the first estimates of tissue Ag concentrations in both particulate and ionic forms in earthworms exposed in vivo to AgNPs via soil. The results obtained showed fairly low uptake of AgNPs, with earthworms exposed to a commercially obtained PVP-coated AgNP showing approximately 34% of their total Ag tissue burden being in particulate form. This indicates that although AgNPs accumulated in tissues of earthworms in their primary form, the dissolution of Ag in the soil, organism, or both played an important role in determining the ultimate fate of the AgNPs. Although the biological uptake of AgNPs was generally low, the method described in Chapter 3 was still capable of extracting NPs in quantities sufficient for identification, quantification and characterisation. It should be noted however, that the lower size detection threshold for the ICP-MS instrument used for these analyses is approximately 30 nm. Consequently, information on NPs smaller than 30 nm was not available. With the increasing optimisation of analytical systems that combine sp-ICP-MS, or other detection methods with, for example, asymmetric flow field-flow fractionation (AF4) which pre-sort different particle sizes, the potential for application of methods described in this thesis will be even greater.

Having developed a method for extracting Ag from tissues, we exposed earthworms to all nine synthesized AgNPs as well as to AgNO3 at two concentrations below known EC50s to control for ionic effects of Ag in a 28-day sub-chronic reproduction toxicity test in soil in Chapter 4. Uptake was observed to be generally highest for the negatively charged AgNP_BSA especially at the lower exposure concentration ranges. Total Ag concentrations in earthworm tissues reached a plateau level of about 80 mg Ag/kg dry weight (DW) for exposure concentrations between 15 – 100 mg Ag/kg soil DW. Reproduction was impaired at high nominal soil concentrations of all AgNPs tested, with AgNP_BSA particles being the most toxic. Size had an influence on uptake of the AgNP_PVP, showing both uptake and effect on reproduction of the 20 nm sized group to be significantly more than those of the 35 and 50 nm AgNP_PVP. This size effect however, did not hold for AgNP_BSA nor AgNP_Chit. Higher uptake from the soil may consequently lead to a higher potential for toxicity in organisms. Interestingly, internal total Ag tissue concentrations measured after 72 hour exposure were better at predicting the effect on reproduction than tissue concentrations after 28 days exposure. It is likely therefore, that reproduction was affected already in the 72 hour exposure window.

In order to further elucidate the likely mechanisms by which these AgNPs were exerting their effects, we conducted a toxicogenomic study in Chapter 5. Although AgNPs have been increasingly investigated, information regarding their effect on the gene expression profile of especially soil organisms is yet inadequate. Using RNAseq, we investigated the transcriptome and gene expression profiles of the earthworm L. rubellus, following exposure to the nine AgNPs. Overall, exposure to medium sized AgNPs at a concentration close to the EC50 for effects on cocoon production caused most pronounced responses at the transcriptional level. There was a correlation however, between the numbers of differentially expressed genes (DEGs) and internal Ag concentrations in the earthworms. Within the medium size AgNPs, AgNP_BSA caused extensive transcriptional responses, with 684 genes affected. In contrast ionic silver (AgNO3) did not affect gene expression at low as well as higher exposure levels. Only one gene was regulated by all AgNP and Ag+ treatments, indicating that there was hardly any functional overlap between the responses of the organisms to AgNPs with different coatings. Remarkably, this gene was metallothionein, a cysteine-rich peptide known to strongly bind free metal ions for chelation and detoxification, which was strongly up-regulated. Gene ontology enrichment analysis for 35 nm AgNP_BSA exposures revealed a total of 33 significantly enriched gene ontology terms related to biological processes. These included responses to pH, proton transport, cell differentiation, microtubule organisation, and and MT induction. Surface coating (BSA) was important in triggering the AgNP-induced differential gene expression profiles in earthworms. The importance of physicochemical properties of NPs in influencing their fate and toxicity is thus elucidated in the current study.

The studies reported in the current thesis showed that within the range of 20 to 50 nm, effects of the size of AgNPs on toxicokinetics and toxicodynamics are limited. However, effects of surface coating were consistent over the different levels of biological integration. Generally, the negatively charged AgNP_BSA accumulated to a higher extent in the earthworms, especially at lower concentrations. The in vitro uptake was fast for all NPs, but also showed the highest uptake of AgNP_BSA. The negatively charged AgNPs were also the most toxic, likely related to their increased uptake. This was evident at all levels: gene expression, cellular, and individual (population dynamic parameters) levels. At the in vitro level, this applied mostly to effects on specific modes of action (TNF-α induction, ROS production). For more general cytotoxic effects, the effects of surface coatings were less evident. Except in cells exposed to AgNP_Chit 20 nm, where there was a slight increase in ROS production, this set of AgNPs under the experimental conditions applied, did not appear to induce the production of ROS. This was supported by the lack of expression of any ROS-related gene in the gene expression profile analyses.

Based on the results of the current research, it can be concluded that the physico-chemical properties of NPs do influence their environmental fate and toxicity. It should be noted however that general predictions on the outcome of exposure to NPs are difficult to make, and NPs should be evaluated on a case by case basis. Our research supports the use of in vitro models to limit and prioritize further in vivo studies. Studies investigating the fate and effects of NPs for soil organisms are vital for a holistic approach towards a comprehensive and adequate environmental risk assessment (ERA). The studies described in this thesis contribute to this knowledge, thereby improving our understanding of the hazards and risks due to exposure to AgNPs, thus enabling their adequate and comprehensive ERA.

Replacing animal experiments in developmental toxicity testing of phenols by combining in vitro assays with physiologically based kinetic (PBK) modelling
Strikwold, Marije - \ 2016
Wageningen University. Promotor(en): Ivonne Rietjens; Ruud Woutersen, co-promotor(en): Ans Punt. - Wageningen : Wageningen University - ISBN 9789462576926 - 169
animal experiments - animal testing alternatives - toxicity - testing - phenols - in vitro - embryonic stem cells - tissues - cells - dosage - toxicology - animal health - dierproeven - alternatieven voor dierproeven - toxiciteit - testen - fenolen - in vitro - embryonale stamcellen - weefsels - cellen - dosering - toxicologie - diergezondheid
Alternative testing strategies for predicting developmental toxicity of antifungal compound
Li, H. - \ 2016
Wageningen University. Promotor(en): Ivonne Rietjens; Bennard van Ravenzwaay, co-promotor(en): Jochem Louisse. - Wageningen : Wageningen University - ISBN 9789462576780 - 197
toxicity - fetal development - transfer - infant development - adolescent development - child development - pregnancy - in vivo experimentation - modeling - placenta - in vitro - risk assessment - tebuconazole - conazole fungicides - antifungal agents - alternative methods - toxiciteit - foetale ontwikkeling - overdracht - zuigelingenontwikkeling - adolescentenontwikkeling - kinderontwikkeling - zwangerschap - in vivo experimenten - modelleren - placenta - in vitro - risicoschatting - tebuconazool - conazoolfungiciden - antimycotica - alternatieve methoden

Determination of safe human exposure levels of chemicals in toxicological risk assessments largely relies on animal toxicity data. In these toxicity studies, the highest number of animals are used for reproductive and developmental toxicity testing. Because of economic and ethical reasons, there is large interest in the development of in vitro and/or in silico test systems as alternatives for the animal studies. The aim of the present thesis was to evaluate the applicability of combined in vitro approaches taking toxicokinetic and toxicodynamic aspects into account, as well as of an integrated in vitro and in silico approach for prediction of developmental toxicity using a series of antifungal compounds as the model compounds.

Transplacental transfer of compounds is highly likely to play an important role in developmental toxicity, so we developed and validated an in vitro placental barrier model using BeWo b30 cells to predict placental transfer. Then we investigated the applicability of the ES-D3 cell differentiation assay combined with the in vitro BeWo transport model to predict the relative in vivo developmental toxicity potencies of two sets of selected antifungal compounds. The data obtained show that the combined in vitro approach provided a correct prediction for the relative in vivo developmental toxicity, whereas the ES-D3 cell differentiation assay as stand-alone did not. In order to detect specific structural alterations induced by chemicals, we investigated the applicability of the ex ovo assay of chicken embryos to predict the specific alterations induced by the antifungal compounds. Data revealed that the ex ovo assay of chicken embryos is able to assess the teratogenic potential of antifungal compounds, and, when combined with the in vitro BeWo transport model, is able to better predict relative in vivo prenatal developmental toxicity potencies.

Subsequently, we translated in vitro concentration–response data of the antifungal compound tebuconazole, obtained in the ES-D3 cell differentiation assay and the ex ovo assay of chicken embryos, into predicted in vivo dose–response data using physiologically based kinetic (PBK) modelling-facilitated reverse dosimetry. The results show that the BMD10 values from predicted dose–response data from both assays are in concordance with BMD10 values derived from in vivo data (within 5-fold difference). This revealed that PBK modeling is a promising tool to predict in vivo dose-response curves based on the results of in vitro toxicity assays, and may therefore be used to set a point of departure for deriving safe exposure limits in risk assessment.

It is concluded the combined in vitro approaches and the integrated in vitro-in silico approaches appear to be promising for the screening and prioritization of chemicals and to provide reference values, such as BMD10 values, without using animals, therefore contributing to the 3R principle of animal testing.

Assessing the effects of chemicals on aquatic microbial ecosystems
Rocha Dimitrov, M. - \ 2016
Wageningen University. Promotor(en): Hauke Smidt; Paul van den Brink. - Wageningen : Wageningen University - ISBN 9789462576667 - 264
aquatic ecosystems - microorganisms - macroinvertebrates - microbial ecology - aquatic fungi - chemicals - tebuconazole - fungicide residues - pesticides - marine sediments - toxicity - enrofloxacin - fluoroquinolones - zooplankton - phytoplankton - antibiotic resistance - periphyton - bacteria - ecological risk assessment - aquatische ecosystemen - micro-organismen - macroinvertebraten - microbiële ecologie - waterschimmels - chemicaliën - tebuconazool - fungicidenresiduen - pesticiden - mariene sedimenten - toxiciteit - enrofloxacine - fluoroquinolonen - zoöplankton - fytoplankton - antibioticaresistentie - perifyton - bacteriën - ecologische risicoschatting
Driftblootstelling van omstanders en omwonenden door boomgaard bespuitingen
Zande, J.C. van de; Wenneker, M. - \ 2015
Wageningen : Plant Research International, Business Unit Agrosystems (Rapport / Plant Research International 609) - 67 p.
fruitteelt - pesticiden - boomgaarden - boomgaardspuiten - spuiten - toxiciteit - drift - veldproeven - gemeenten - fruit growing - pesticides - orchards - orchard sprayers - spraying - toxicity - field tests - municipalities
Spray drift can be limited through the use of drift- reducing nozzles and spray techniques; and is obligatory when applying Plant Protection Products (PPP) alongside waterways in the Netherlands. The spray drift reducing measures implemented to protect the surface water also protect spray drift exposure of bystanders and residents in the neighbourhood of sprayed orchards.Spray drift is estimated at different distances from a sprayed orchard based on earlier performed spray drift field experiments. A differentiation is made to measured spray drift deposition at ground level and estimated airborne spray drift up to 50 m distance from the treated field. Airborne spray drift curves are based on measured airborne spray drift at 7,5 m distance from the last tree row. Airborne spray drift is further divided in exposure in the 0-3 m high air layer and the 3-6 m high air layer. Both for the dormant (before May 1st) and the full leaf situation (after May 1st) analyses have been performed based on spray drift data related to dermal and inhalation exposure of bystanders and residents of some often used plant protection products in the Netherlands. It is shown that spray drift reducing technology (DRT) is important in reducing the exposure risk of bystanders and residents too. Also the effects of filter crops, like wind breaks, hedgerows etc., grown on the edge of the field on exposure of bystanders and residents is shown.
Bio-induced solid selenium for recovery from water
Hageman, S.P.W. - \ 2015
Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): Renata van der Weijden; Fons Stams. - Wageningen : Wageningen University - ISBN 9789462575103 - 156
selenium - waste water - waste water treatment - recovery - toxicity - bioreactors - selenium - afvalwater - afvalwaterbehandeling - terugwinning - toxiciteit - bioreactoren

Selenium in the form of selenate or selenite in wastewater needs to be removed due to its potential toxicity in the environment. Also, selenium is a valuable element that is used in several industries and current selenium resources are likely to be exhausted in less than 50 years. Waste streams containing selenium can therefore be used as a source of selenium. This requires conversion of the selenium in wastewater into a form that can be recovered. Biologically induced selenate reduction to recoverable selenium has the advantage that it uses the selective reduction capacities of biomass and a renewable electron donor.

To improve the recoverability of selenium the conversion of selenate to selenite was seen as an interesting opportunity. Selenite is more reactive than selenate and can be removed in a second step. As described in Chapter 2, it proved possible to convert selenate to mainly selenite at a low electron donor concentration.

Another method which is reviewed in this thesis is direct biological reduction of selenate to elemental selenium. After reduction the solids can be removed by a liquid solid separation process. Previously amorphous selenium particles were produced, which hampered recovery. In this research it is demonstrated that at a higher temperature, around 40 - 50°C, and at a higher pH, around pH 8 - 9, a more hexagonal selenium structure can be produced (Chapter 3). Crystalline acicular selenium particles of different sizes were thus obtained. This implies that selenium particles formation can be controlled and that selenium particles can grow. Large selenium particles make the separation process economic.

To grow larger selenium particles, a long-term experiment was performed at 50°C (Chapter 4). The reduction rate was poor, but selenium acicular particles were produced. These particles were also detected as clusters. These clusters open up new recovery opportunities. With Eerbeek sludge the optimal conditions for selenate conversion are around pH=7 and 30°C. To enlarge the selenium particles it is strongly recommended to use a different sludge since the optimal conditions with Eerbeek sludge do not match the conditions needed for acicular particle formation.

When selenate is converted to selenite, the selenite can be precipitated by sulphide to form selenium sulphide. Emmtec sludge was used to reduce the sulphur compounds to sulphide, leaving selenium as the sole remaining element. This process was performed at T=30°C and a pH between 6 and 7. The selenium thus recovered had a crystalline hexagonal structure (revealed by x-ray diffraction) and the particles were as large as 125µm3.

Future research on the two routes that are explored in this thesis can give insights into selenium reduction mechanisms and the formation of large selenium particles. The recoverability of biological selenium particles has also been improved (as discussed in this thesis). In conclusion, this thesis has resulted in a new, bio-selective, renewable selenium recovery method via selenium sulphide.

Sediment toxicity testing and prospective risk assessment of organic chemicals
Diepens, N.J. - \ 2015
Wageningen University. Promotor(en): Bart Koelmans, co-promotor(en): Paul van den Brink. - Wageningen : Wageningen University - ISBN 9789462574991 - 346
sediment - toxiciteit - testen - sedimenttest - verontreinigde sedimenten - chemicaliën - risicoschatting - ecotoxicologie - sediment - toxicity - testing - sediment test - contaminated sediments - chemicals - risk assessment - ecotoxicology

While providing an option for development in coastal areas, shrimp farming is usually associated with high environmental cost due to the loss of mangrove forest and high social cost as farmers suffer heavy financial losses due to disease outbreaks. Planning shrimp farming requires to integrate risk as well as social and environmental cost. This thesis, using the Mekong Delta as a case, presents an approach to investigate, with local stakeholders, options to plan a resilient and sustainable shrimp farming sector. First, Olivier Joffre analyzed the different shrimp production systems from economic point of view before analyzing farmer’s strategies and providing insights on drivers that will push or, at the opposite, constraint farmers to choose integrated mangrove shrimp systems. This knowledge was integrated in an Agent Based Model (ABM) that was calibrated using Role Playing Games (RPG).

The effect of future scenarios and different policies on the farmers’ decisions was tested using a combination of RPG and ABM. For one coastal district of the Mekong Delta, the results showed that promotion of intensification of shrimp production has a high social cost and decreases the total production in the study area after 10 years. Policies for supporting the spread of integrated mangrove-shrimp systems, such as Payment for Ecosystem Services, or access to an organic value chain, are not strong enough to influence farmers’ decision toward adopting these systems. Without any adaptation to climate change a sharp decrease of the production is expected. The approach brought local farmers’ knowledge to the attention of decision makers.

Role of anti-competitor toxins in the origin and maintenance of diversity in Saccharomyces yeast microbial populations
Pieczynska, M.D. - \ 2015
Wageningen University. Promotor(en): Bas Zwaan, co-promotor(en): Arjan de Visser. - Wageningen : Wageningen University - ISBN 9789462573093 - 123
gisten - rna-virussen - toxinen - symbiose - toxiciteit - co-evolutie - fenotypen - fermentatie - yeasts - rna viruses - toxins - symbiosis - toxicity - coevolution - phenotypes - fermentation

Abstract

Saccharomyces cells occasionally carry cytoplasmic ds-RNA “killer” viruses coding for low-mass proteins, which upon secretion to the environment can kill related cells that do not carry the viral particles. Such killer viruses are not infectious, and can spread only through cell division and during mating. Three principal classes of Saccharomyces viruses (ScV-M1, ScV-M2 and ScV-M28) belonging to the Totiviridae family have been characterised, each capable of forming a specific anti-competitor toxin and corresponding antidote. Presumably, toxic killing provides competitive benefits to the yeast host. However, the ecological and evolutionary significance of toxin production remains poorly understood. For example, it is unknown where yeast killers occur and at what frequency, how evolvable killing ability is, whether it is constrained by possible trade-offs with resource competitive ability and how it is shaped by interactions with toxin-sensitive competitors. Also unknown is how stable yeast-virus symbioses are, and how coevolution between host and virus may affect this stability and the killing phenotype itself. It is believed that killer yeasts are common based on the fact that they have been found among yeasts isolated from different sources over several decades. In chapter 2, we assay two large yeast collections from diverse habitats, including nature and man-made habitats (in total 136 strains with known genome sequences), for killer phenotype and toxin resistance. We find that ~10.3% carry a killer virus, while about 25% are resistant to at least one of the three known killer toxins (12.5% to different combinations of two and ~9% to all three), most likely due to chromosomal mutations. Analyses of their evolutionary relationship indicate that host-virus associations are relatively short lived, whereas the relatively high frequency of resistance suggests that toxins have a substantial impact on yeast evolution.

In order to understand the ecological and evolutionary role of toxin production, it is essential to reliably assess the killing rate of toxin producers by measuring how many toxin-sensitive individuals are killed by a single toxin producer during a given time interval. To identify a convenient method with high sensitivity and reproducibility, in chapter 3 we perform a systematic comparative analysis of four methods, including the conventional “Halo method” and three more quantitative liquid assays. We apply these methods to a set of three known yeast killer strains (K1, K2 and K28) and find that the easy applicable Halo method provides the most sensitive and reproducible killing rate estimates (with best discrimination between killer strains).

Understanding the evolution of the yeast-virus association is crucial for a full understanding of the ecological and evolutionary role of killer strains. In chapter 4, we present experimental tests of the strength of the dependence of yeast host strains on their killer viruses. We cross-infect several viruses among killer strains of the genus Saccharomyces – all expressing the K1-type toxin, and test native and new combinations for the strength of host-virus co-adaptation. We find explicit host-virus co-adaptation, because native yeasts hosts display the highest toxicity and highest stability of killer viruses relative to hosts carrying non-native viruses. Even stronger, we find that curing these wild killer yeasts from their virus reduces their competitive fitness, despite initial fitness costs of viral carriage reported for constructed killer strains. These results demonstrate co-adaptation of host and virus in the natural killer strains resulting in their dependence on the killer virus. To explore the evolutionary costs and benefits of virus carriage and toxin production, and understand whether they are shaped by the coevolution between host and virus and the presence of toxin-sensitive competitors in the environment, we conduct a series of laboratory experiments where we manipulate the opportunity for coevolution (chapter 5). Analyses of killing ability, toxin sensitivity and fitness (i.e. resource competitive ability), show rapid reciprocal changes in killer and sensitive strain when coevolution is allowed, modulated by the rapid invasion of toxin-resistant mutants and subsequent reduction of killing ability. Remarkably, we find that the rapid invasion of toxin-resistant mutants involves two mutational steps, the first being a mutation showing a meiotic drive phenotype as well as a strong fitness benefit in heterozygotes, the second the resistance mutation. Shifts in the competitive fitness of evolved killer isolates with increased killing ability show a clear trade-off between killing rate and resource competitive ability, indicating that resource and interference competitive ability are alternative competitive strategies. Moreover, by cross-infecting the killer virus between the ancestral and an evolved strain, we are able to demonstrate the rapid co-adaptation between host and killer virus, supporting our previous findings of co-adaptive responses in wild yeast killers (chapter 4).

Our analyses are based on screens of natural isolates, laboratory evolution experiments and phenotypic analyses, complemented by classical genetics. To more fully understand the reciprocal nature and molecular mechanisms of adaptive responses, genome analyses are required. The motivation for such analyses and other follow-up studies are proposed in chapter 6. My studies show the usefulness of the killer yeast system to address questions related to interference competition and coevolution, which may proof valuable also given potential applications of killer yeasts in the fermentation industry.

Effects of silver nanoparticles and ions and interactions with first line of defense
Georgantzopoulou, A. - \ 2015
Wageningen University. Promotor(en): Tinka Murk, co-promotor(en): A.C. Gutleb. - Wageningen : Wageningen University - ISBN 9789462572492
waterorganismen - toxiciteit - zilver - deeltjes - ionen - nadelige gevolgen - darmen - aquatic organisms - toxicity - silver - particles - ions - adverse effects - intestines

Summary

Silver nanoparticles (Ag NPs) are among the most promising groups of NPs (particles with all dimensions below 100 nm) for application in numerous consumer products due to their broad spectrum antimicrobial activities. Examples are incorporation in textiles and plastics, personal care products, water filters, food supplements etc. The extensive application and use together with the not yet fully understood properties of Ag NPs as well as the toxicity of Ag itself has raised concerns on potential impact of Ag NPs on human and environmental health.

The research conducted within this thesis aimed at the evaluation of potential hazards of Ag NPs and identification of some key factors that determine the toxicity of Ag NPs. A tiered approach was employed using a battery of standard bioassays with model aquatic organisms, followed by the determination of sub-lethal concentrations for mechanistic endpoints, the identification of target tissues and organisms for Ag NP exposure and uptake and the integration of a proteomic tool to identify subtle changes. One of the main uptake routes for Ag NPs is through ingestion making the gastrointestinal epithelium one of the first ports of potential NP uptake and cell-particle interactions. An in vitro co-culture model incorporating a mucus layer mimicking the gastrointestinal epithelium was established for a more realistic evaluation of Ag NP potential toxicity than using intestinal epithelial cells alone. Indeed, the absence of mucus resulted in an overestimation of Ag NP toxicity. To be able to elucidate subtle changes in cellular functions and identification of particle specific effects and NP modes of action, a proteomic approach was employed. Differences and commonalities were observed between the cellular responses induced Ag NPs of different sizes and AgNO3 as a source of free Ag ions.

As the Ag NPs are expected to reach the aquatic environment, a combination of adapted standard ecotoxicity assays with organisms of different trophic levels were used to evaluate the toxic effects Ag NPs. Synthetically produced Ag NPs of different sizes (Ag 20 and 200 nm) as well as Ag NPs synthesized by a biological method (using plant leaf extracts of Ocinum sanctum and Azadirachta indica, Ag 23 and 27 nm, respectively) were used as model particles in order to elucidate the relation between size, synthesis method, NP surface properties, ion dissolution and toxicity. Based on earlier indications of interference of another type of NPs with the multi xenobiotic resistance mechanism (MXR), a first line of defense against xenobiotics, the effects of Ag NPs on the MXR mechanism were studied as well. The MXR mechanism is present in all animals, including humans and aquatic organisms. MXR can be compromised by chemical agents that are structurally and chemically unrelated, and interference with MXR could be the basis for enhanced toxicity by contaminant mixtures. A fast in vitro cellular efflux pump inhibition assay (CEPIA) was established evaluating first the effects of contaminants commonly found in the environment. Next, an in vivo CEPIA assay was established using the juvenile D. magna model aquatic organism and the potential of the MXR modulation by Ag NPs and ionic Ag was quantified in vitro and in vivo.

This integrated approach revealed that the size and the synthesis method are the factors affecting most the uptake and toxicity in both cells in vitro as well as in vivo in freshwater crustaceans (daphnids) and dissolution in the different media with the biologically synthesized Ag NPs being more potent compared to the conventional Ag NPs. The gastrointestinal tract is expected to be a target site for Ag NPs exposure and a co-culture of Caco-2-TC7 and HT29-MTX cells optimized and employed in the current study represents a more realistic model compared to Caco-2 monocultures. The mucus layer provides an additional protective barrier and its absence can lead to overestimation of effects in in vitro studies. Ag was detected both in the cells in co-culture, in the gut of daphnids’ as well as specific areas, seemingly developing oocytes, indicating a potential translocation of Ag NPs that could have consequences for fecundity. MXR efflux transporters were found to be modulated by Ag at low concentrations (0.18 µg/L), that are slightly lower compared to the predicted environmental concentrations.

The extent to which the Ag ions contribute to the effects of Ag NPs depends on the size and surface properties of the Ag NPs. For the conventional, uncoated Ag NPs, the Ag release is minimal and the size is the determining factor while for biologically synthesized particles the biomolecules present due to the synthesis method and Ag release affect most the uptake and effects. The simultaneous presence of Ag ions and NPs releasing ions can lead to an exacerbation of the effects.

The proteomic approach was successfully applied and it proved to be a useful technique in discerning subtle cellular changes in response to Ag NP exposure that would otherwise be unnoticed. Ag NPs 20 nm regulated different sets of proteins with a distinct pattern of cellular responses compared to Ag 200 nm and AgNO3, suggesting a different mode of action with effects being particle- and size-dependent.

These results obtained during this thesis are promising for future toxicity testing of new materials using invertebrate organisms and more realistic in vitro models leading to more meaningful results and more accurate assessment of Ag NP hazards.

The Isolated Chicken Eye test to replace the Draize test in rabbits : from development to implementation: “The long and winding road”
Prinsen, M.K. - \ 2014
Wageningen University. Promotor(en): Ruud Woutersen; C.F.M. Hendriksen, co-promotor(en): C.A.M. Krul. - Wageningen : Wageningen University - ISBN 9789462570030 - 184
ogen - konijnen - kippen - laboratoriumdieren - alternatieven voor dierproeven - dierproeven - toxiciteit - toxicologie - histopathologie - dierenwelzijn - eyes - rabbits - fowls - laboratory animals - animal testing alternatives - animal experiments - toxicity - toxicology - histopathology - animal welfare
Dit proefschrift beschrijft de ontwikkeling, optimalisatie, validatie (binnen TNO) en toepassing van een alternatieve test met geïsoleerde ogen van kippen (de Isolated Chicken Eye, kortweg de ICE test) en in bredere zin de internationale validatie en acceptatie van de ICE test door overheidsinstanties.
Matrix modulation of the toxicity of alkenylbenzenes, studied by an integrated approach using in vitro, in vivo, and physiologically based biokinetic models
Al-Husainy, W.A.A.M. - \ 2013
Wageningen University. Promotor(en): Ivonne Rietjens; Peter van Bladeren, co-promotor(en): Ans Punt. - Wageningen : Wageningen UR - ISBN 9789461738066 - 199
methyleugenol - toxiciteit - keukenkruiden - flavonoïden - methyl eugenol - toxicity - culinary herbs - flavonoids

Alkenylbenzenes such as estragole and methyleugenol are common components of spices and herbs such as tarragon, basil, fennel, mace, allspice, star anise and anise and their essential oils (Smithet al., 2002). There is an interest in the safety evaluation of alkenylbenzenes because these compounds can induce hepatic tumours in rodents when dosed orally at high dose levels (Milleret al., 1983; NTP, 2000). Based on the rodent studies with estragole, methyleugenoland structurally related alkenylbenzenes like safrole the hepatocarcinogenicity of alkenylbenzenes is ascribed to their bioactivation by cytochrome P450 enzymes leading to the formation of the proximate carcinogenen, the 1′-hydroxy metabolite, which is further bioactivated to the ultimate carcinogenen, the 1′-sulfooxy metabolite (Milleret al., 1983; Phillipset al., 1984; Randerathet al., 1984; Smithet al., 2010). The 1′-sulfooxy metabolite is unstable and binds via a presumed reactive carbocation intermediate covalently to different endogenous nucleophiles including DNA (Phillipset al., 1981; Boberget al., 1983; Milleret al., 1983; Phillipset al., 1984; Randerathet al., 1984; Fennellet al., 1985; Wisemanet al., 1987; Smithet al., 2002).

Because of their genotoxicity and carcinogenicity, the addition of estragole and methyleugenolas pure substances to foodstuffs has been prohibited within the European Union since September 2008 (European Commission, 2008). In 2008, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) re-evaluated the safety of alkenylbenzenes and indicated that although evidence of carcinogenicity to rodents given high doses of alkenylbenzenes exists, further research is needed to assess the potential risk to human health at relevant dietary exposure levels (JECFA, 2008).

A significant difficulty in evaluating the toxicological data for alkenylbenzenes is that human exposure to these substances results from exposure to a complex mixture of food, spice, and spice oil constituents which may influence the biochemical fate and toxicological risk of the alkenylbenzenes. In this regard, it was shown that a methanolic extract of basil inhibited the formation of estragole DNA adducts in human HepG2 cells exposed to the proximate carcinogen 1′-hydroxyestragole (Jeurissenet al., 2008). This inhibition occurred at the level of sulfotransferase (SULT)-mediated bioactivation of 1′-hydroxyestragole into 1′-sulfooxyestragole (Jeurissenet al., 2008).

The objective of this PhD research was to study the inhibitory action of components in alkenylbenzene-containing herbs and spices on SULT-mediated alkenylbenzene DNA adduct formation and the consequences of this combination effect for risk assessment using estragole and methyleugenol as the model alkenylbenzenes. To achieve this objective, an integrated approach of in vitro, in vivo and physiologically based biokinetic (PBBK) models was applied to investigate how the SULT inhibition influences the bioactivation and thus potentially also the toxicity and risk assessment of estragole and methyleugenol.

Chapter 1of the thesis presents an introduction to the bioactivation, detoxification, genotoxicity and carcinogenicity of the alkenylbenzenes estragole and methyleugenol as well as a short introduction to PBBK modeling and the state-of-the-art knowledge on risk assessment strategies and regulatory status for alkenylbenzenes.

Chapter 2of the thesis identifies nevadensin as a basil constituent able to inhibit SULT-mediated DNA adduct formation in rat hepatocytes exposed to the proximate carcinogen 1′-hydroxyestragole and nevadensin. The type of inhibition by nevadensin was shown to be non-competitive with an inhibition constant (Ki) of 4 nM. Furthermore, nevadensin up to 20 μM did not inhibit 1′-hydroxyestragole detoxification by glucuronidation and oxidation. The inhibition of SULT by nevadensin was incorporated into the PBBK models describing bioactivation and detoxification of estragole in male rat and human. The models thus obtained predict that co-administration of estragole at a level inducing hepatic tumours in vivo (50 mg/kg bw) with nevadensin at a molar ratio to estragole representing the molar ratio of their occurrence in basil, results in more than 83% inhibition of the formation of the carcinogenic metabolite, 1ʹ-sulfooxyestragole, inthe liver of male rat and human even at 1% uptake of nevadensin.

To extend the work to other alkenylbenzene-containing herbs and spices than basil chapter 3 presents data showing that methanolic extracts from different alkenylbenzene-containing herbs and spices such as nutmeg, mace, anise and others are able to inhibit the SULT enzyme activity. Flavonoids including nevadensin, quercetin, kaempferol, myricetin, luteolin and apigenin were the major constituents responsible for this inhibition of SULT activity with Kivalues in the nano to sub-micromolar range. Also, the various flavonoids individually or in mixtures were able to inhibit estragole DNA adduct formation in human HepG2 cells exposed to the proximate carcinogen 1ʹ-hydroxyestragole, and to shift metabolism in favour of detoxification (e.g. glucuronidation) at the cost of bioactivation (e.g. sulfonation).

In a next step, the kinetics for SULT inhibition were incorporated in PBBK models for estragole in rat and human to predict the effect of co-exposure to estragole and (mixtures of) the different flavonoids on the bioactivation in vivo. The PBBK-model-based predictions indicate that the reduction of estragole bioactivation in rat and human by co-administration of the flavonoids is dependent on whether the intracellular liver concentrations of the flavonoids can reach their Ki values. Finally, we concluded that it is expected that this is most easily achieved for nevadensin which has a Kivalue in the nanomolar range and is, due to its methylation, more metabolically stable and bioavailable than the other flavonoids.

Chapter 4of the thesis investigates whether the previous observation that nevadensin is able to inhibit SULT-mediated estragole DNA adduct formation in primary rat hepatocytes could be validated in vivo. Moreover, the previously developed PBBK models to study this inhibition in rat and in human liver was refined by including a sub-model describing nevadensin kinetics. Nevadensin resulted in a significant reduction in the levels of estragole DNA adducts formed in the liver of Sprague–Dawley rats orally dosed with estragole and nevadensin simultaneously at a ratio reflecting their presence in basil. Moreover, the refined PBBK model predicted the formation of estragole DNA adducts in the liver of rat with less than 2-fold difference compared to in vivo data and suggests more potent inhibition in the liver of human compared to rat due to less efficient metabolism of nevadensin in human liver and intestine.

Also, an updated risk assessment for estragole was presented taking into account the matrix effect and this revealed that the BMDL10 and the resulting MOE for estragole increase substantially when they would be derived from rodent bioassays in which the animals would be exposed to estragole in the presence of nevadensin instead of to pure estragole.

To extend the work to other alkenylbenzenes than estragole chapter 5 of the thesis investigates the potential of nevadensin to inhibit the SULT-mediated bioactivation and subsequent DNA adduct formation of methyleugenolusing human HepG2 cells as an in vitro model. Nevadensin was able to inhibit SULT-mediated DNA adduct formation in HepG2 cells exposed to the proximate carcinogen 1′-hydroxymethyleugenol in the presence of nevadensin.To investigate possible in vivo implications for SULT inhibition by nevadensin on methyleugenolbioactivation, the rat PBBK model developed in our previous work to describe the dose-dependent bioactivation and detoxification of methyleugenolin male rat was combined with the recently developed PBBK model describing the dose-dependent kinetics of nevadensin in male rat. Similar to what was presented for estragole in chapter 4, chapter 5 presents an updated risk assessment for methyleugenoltaking the matrix effect into account. This revealed that the BMDL10 and the resulting MOE for methyleugenolincrease substantially when they would be derived from rodent bioassays in which the animals would be exposed to methyleugenolin the presence of nevadensin instead of to pure methyleugenol.

In a next step, we aimed at moving one step forward towards endpoints that are closer to initiation of carcinogenesis than DNA adduct formation, namely, formation of hepatocellular altered foci (HAF). Chapter 6 presents data showing that the potent in vivo inhibitory activity of nevadensin on SULT enzyme activity and on alkenylbenzene DNA adduct formation is accompanied by a potent in vivo reduction in early markers of carcinogenesis such as HAF. This also suggests that a reduction in the incidence of hepatocarcinogenicity is expected in liver of rodents when alkenylbenzenes would be dosed simultaneously with nevadensin.

Chapter 7presents a discussion on the in vitro and in vivo activity of dietary SULT inhibitors and their potential in reducing the cancer risk associated with alkenylbenzene consumption. This chapter also presents some future perspectives based on the major issues raised by our research.

Altogether, the results of the present thesis indicate that the likelihood of bioactivation and subsequent adverse effects may be lower when alkenylbenzenes are consumed in a matrix containing SULT inhibitors such as nevadensincompared to experiments using pure alkenylbenzenes as single compounds. Also,the consequences of the in vivo matrix effect were shown to be significant when estragole or methyleugenolwas tested in rodent bioassays in the presence of nevadensin at ratios detected in basil, thereby likely increasing BMDL10 and resulting MOE values substantially in a subsequent risk assessment. However, the results also indicate that matrix effects may be lower at daily human dietary exposure levels of estragole or methyleugenoland nevadensin resulting from basil consumption. Also, matrix effects seem to be limited in the presence of other SULT inhibiting dietary flavonoids even at high exposure levels of these flavonoids coming from supplements. This indicates that the importance of a matrix effect for risk assessment of individual compounds requires analysis of dose dependent effects on the interactions detected, an objective that can be achieved by using PBBK modeling.

Overall, the present study provides an example of an approach that can be used to characterise dose- species- and inter-individual differences as well as matrix effects in the risk assessment of food-borne toxicants present (e.g. alkenylbenzenes). In this approach the most important toxicokinetic interactions are addressed using an integrated strategy of in vitro, in vivo and PBBK modeling approaches.

Managing technological aspects of Lupinus mutabilis from a food sovereignty perspective in Ecuador
Carvajal Larenas, F.E. - \ 2013
Wageningen University. Promotor(en): Tiny van Boekel, co-promotor(en): Anita Linnemann; Rob Nout. - S.l. : s.n. - ISBN 9789461736789 - 222
lupinus mutabilis - bitterheid - voedselverwerking - voedselgewassen - ecuador - toxiciteit - voedselsoevereiniteit - lupinus mutabilis - bitterness - food processing - food crops - ecuador - toxicity - food sovereignty

The present thesis deals with the technological aspects of the debittering process of lupin in a food sovereignty framework. Of all investigated lupin species,Lupinus mutabilishas the best nutritional composition, which is similar to that of soya bean (Glycine max). Lupins can be used to fortify the protein content of many products. In addition, specific lupin protein concentrates or isolates display functional properties of industrial interest (as emulsifier, gelling and foaming agent). On the other hand, lupins contain bitter alkaloids that have to be removed prior consumption because are toxic (the fatal acute dose of lupin alkaloids was reported as 10 mg kg-1 body weight (bw) for infants and children, and 25 mg kg-1 bw for adults). However, alkaloids also have medical uses for their hypocholesterolemic, anti-arrhythmic and immunosuppressive activity. Bitter lupins have been detoxified by biological, chemical or aqueous processes. However, our research concentrated on the aqueousprocessing because this is the only way to produce debittered lupin for human consumption in an environment-friendly manner.The process investigated involved soaking, cooking, and washing of the raw seeds. This process showed to be inefficient because it took 5.7 ±1.0 days, used water at almost 62 times the weight of the raw dry and bitter lupine, and caused a 22% loss of total solids, principally fat, minerals, and carbohydrates. In addition, the microbiological quality deteriorated during this debittering process. Mathematical modeling based on Fickian diffusion suggested that the diffusion coefficient of alkaloids would be expected to vary between 10-10 and 10-11 m2s-1 because the process is carried out in unsteady conditions. In this scenario, it was clear that a new technology for debittering lupins is needed. For this purpose ahydro-agitator was designed, built and used to test the effect of different washing conditions on alkaloids content, solids in the product, final weight, processing time and water and energy consumption. Results were modeled and optimal processing conditions were inferred from a technological point of view; the optimum solution comprised 18h of soaking, 1h cooking, 3 changes of water/day and 22h of agitation/day. For estimating the washing time a mathematic function was inferred (∂c / ∂t = kc;k= -0.188- 4.973-3*Agitation – 0.0043 * Changes - 1.681-3 Agitation*Changes). Then, the products obtained from different processing conditions were evaluated by consumers on the basis of their willingness to pay in relation to their appreciation scores and product price. Results were modeled. Treatments with more processing increased the product price and diminished liking level. However, the willingness to pay is the combined effect of both variables. For example, people would accept an increase in price of 0.3$/kg if the liking level increases from “like slightly” to “like moderately”. The new developed technology could be used to optimize processes such as hydration and/or removal of undesired materials of legumes and other seeds. The approach used in this study also seems suitable to estimate relationships between processing conditions, liking, price and willingness to pay in other products. The generated information can be helpful in decision making, such as selection of consumers´ preferred process and liking in relation to pricing.

Towards a realistic risk characterization of complex mixtures using in vitro bioassays
Montano Garces, M. - \ 2013
Wageningen University. Promotor(en): Tinka Murk, co-promotor(en): A.C. Gutleb. - [S.l.] : s.n. - ISBN 9789461736598
risicoschatting - persistente organische verontreinigende stoffen - verontreinigde sedimenten - mengsels - biotesten - in vitro - toxiciteit - schildklierhormonen - risk assessment - persistent organic pollutants - contaminated sediments - mixtures - bioassays - in vitro - toxicity - thyroid hormones

This thesis aims to better understand and further improve the relevance and reliabilityof in vitro bioassaysfor a biobased risk characterisation of complex mixtures, with special focus on persistent organic pollutants (POPs) in sediments.

In Chapter 1 the importance of complex mixture characterization in modern society is introduced. The methods available, their current advantages and their disadvantages for complex mixture testing are described. With the shift from policy oriented chemical testing towards the inclusion of in vitro bioanalysis, important challenges have to be overcome to ensure a relevant and reliable quantification of the toxic potency of complex mixtures. These challenges are explained in the introduction, including the status of development and validation of those aspects for reliable testing. One of the main advantages that in vitro bioanalysis has to offer is the possibility to quantify the toxic potency of compounds for which chemical analytical methods have not or hardly been developed, for example because standards do not yet exist. Hydroxylated metabolites of POPs are an example of a toxicologically relevant group of compounds that can exert endocrine disrupting effects, but they cannot yet be routinely analysed. A selection of yet unsolved issues are further studied and discussed in this thesis, as outlined in the “approach and structure of the thesis”.

In Chapter 2 a meta-analysis is performed to study the occurrence and relevance of hydroxylated (OH) compounds in humans and wildlife. Reported body burdens of halogenated phenolic contaminants (HPCs), including OH-POP in different tissues from humans and wildlife species, are reviewed in relation to the concentration of their putative parent compounds to be able to reveal relevant exposure routes and sub-populations at risk. Highest OH-POP levels were found in blood plasma, and highly perfused and fetal tissues. Plasma concentrations of analysed known HPCs ranged from 0.1-100 nM in humans and up to 240, 454, 800 and 7650 nM for birds, fish, cetaceans and other mammals, respectively. Reported metabolite blood plasma levels also are compared with relevant toxicological threshold concentrations from toxicological studies, and appeared to fully fall within the in vitro (0.05–10000 nM) and in vivo (3-940 nM) effect concentrations reported for OH-POPs. Given the sensitivity of early developmental stages, and information lacking about the general population, it is advisable to determine HPC background blood levels in children and fetal tissue .

Given the toxicological relevance of the OH-POPs, Chapter 3 aims at providing solutions to the long standing problem of the in vitro production and analysis of OH-POP metabolite thyroid hormone disrupting (THD) potency via binding to plasma thyroid hormone binding proteins (THBPs). In sediments and for example seafood, the POPs occur as parent compounds that would only become THD after metabolisation (hydroxylation). Several methods have shown the competitive thyroxine (T4) T4 displacement potency of pure metabolites. However, in vitro metabolization of, among others, polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers(PBDEs) followed by in vitro quantification of their potency has encountered drawbacks related to the co-extraction of compounds disturbing the T4-TTR competitive binding assay. The present study identifies and quantifies the major co-extractants, cholesterol and saturated and non-saturated fatty acids (SFA and NSFA), at levels above 20 μM (20 nmol per mg protein in the incubation mixture) following various extraction methods. A new method is presented to in vitro metabolise parent compounds into OH-metabolites followed by selective extraction of metabolites while four-fold reducing co-extraction of the disturbing compounds. In addition a microplate-format non-radioactive fluorescence displacement assay was developed to quantify the TTR binding potency of the metabolites formed. The effectiveness of the in vitro metabolism and extraction of the OH-metabolites of the model compounds CB 77 and BDE 47 was chemically quantified with a newly developed chromatographic method analyzing silylated derivatives of the OH-metabolites and co-extractants. Due to the mentioned improvements, it is now possible to make a dose-response curve up to 50% inhibition with OH-metabolites extracted from bioactivated CB 77 and BDE 47. Without taking the toxic potencies of bio-activated POPs into account with bioanalysis, the hazard and risk posed by POPs will be seriously underestimated.

The chapters 4 and 5 are committed to tackle the issues of supramaximal (SPMX) responses and sample extract concentration which are crucial to reliably quantify of the toxic potencies of complex mixtures with in vitro bioassays.

A SPMX effect is the phenomenon that compounds induce a maximum response in an assay that is significantly higher than that of the positive control. As the positive control is used to quantify the toxic potency of a sample, this could result in over-estimation of its toxic potency. As this has been most elaborately reported for in vitro estrogenicity assays, a meta-analysis was performed of such assays, compounds and conditions in which the effect is observed (Chapter 4a).For the 21 natural and industrial chemicals that could be identified as SPMX inducers, the culture and exposure conditions varied greatly among and between the assays. Relevant information on assay characteristics, however, sometimes lacked. Diethylstilbestrol (DES), genistein (GEN) and bisphenol A (BPA) were selected to build a database. The meta-analysis revealed that the occurrence of SPMX effects, could be related to a number of specific assay characteristics: 1) the type and concentration of the serum used to supplement the exposure medium; 2) the endpoint used to quantify the estrogenic potency (endogenous or transfected reporter gene), 3) the number of EREs (estrogen responsive elements) used before the reporter gene, and 4) the nature of the promoter’s. There were no indications that solvent concentration in culture, exposure period or cell model influenced the occurrence of SPMX. It is important to understand the mechanism behind this phenomenon because in vitro assays for estrogenicity are used extensively to characterize and quantify the estrogenic potency of compounds, mixtures and environmental extracts.

Several SPMX inducers also have been reported to block cellular efflux pumps in vivo and in vitro (Anselmo et al. 2012; Georgantzopoulou et al. 2013). Therefore it was hypothesized that efflux pump blockers present in environmental matrices could increase the internal concentration of bioassay agonists and thus cause the SPMX. In Chapter 4b this hypothesis was tested by adapting a 96-well plate cellular efflux pump inhibition assay (CEPIA) to the H4IIE rat hepatoma cell line used for the DR.Luc reporter gene assay for dioxin-like compounds. The influence of various environmentally relevant efflux pump inhibitors on the 2,3,7,8-tetrachlorodibenzo-p-dioxine (TCDD) response was tested. Under the DR.Luc assay conditions there was no evidence that P-gp efflux pump inhibitors modified or potentiated the activity of TCDD. Neither genistein nor quercetin, two potent SPMX inducers on ER-mediated assays, induced any signal on the DR.Luc assay, nor influenced the luciferase induction by TCDD. Future work should be focused on testing the consequences of efflux pump inhibition with an AhR-agonist which is a P-gp substrate, as this could result in intracellular accumulation of this AhR-agonist.

It is standard practice to use a high single stock concentration of extracts to further dilute test concentrations from and perform the analysis. However, a high contaminant load in an extract may oversaturate the solubility of the extracted compounds in carrier solvents and overload the clean-up columns which may reduce the efficiency of polyaromatic hydrocarbons (PAHs) elimination from the extract. These problems may cause respectively under- or over-estimation of the quantified dioxin-like toxic potency. Therefore Chapter 5 focuses on the effects of initial stock concentrations, including sonication assisted dissolution and exposure time, on the quantified dioxin-like potency of cleaned nonpolar sediment extracts. Indeed, more than 20 g sediment equivalents (SEQ)/mL DMSO) as initial stock concentrations resulted in underestimation of bio-TEQ levels in the sediments as observed for cleaned nonpolar sediment extracts from various locations in Luxembourg. An overload of extract on clean-up columns caused an over-estimation of the dioxin-like potency at 24 hours of exposure, probably due to limited removal of PAHs that can induce false positive responses in the in vitro assays. Sonication assisted dissolution of the stock before serial dilution strongly reduced the standard variation of the outcomes. Taking into account the aspects revealed in this study, in addition to already described important issues for quality control, the in vitro bioassays based bio-TEQs can be applied in a comprehensive monitoring program to determine whether sediments comply with health and safety standards for humans and the environment. For the generally applied sediment quality criteria, advices are given about maximum initial stock concentrations to achieve reliable bioassay outcomes.

The methods and concepts developed for metabolic activation of compounds in non-polar sediment extracts and in in vitro analysis of the TTR-competitive binding are applied in Chapter 6 to extracts from highly or less contaminated sediments collected in Luxembourg. Nonpolar fractions of sediment extracts were incubated with S9 rat microsomes, and the metabolites were extracted with a newly developed method that excludes most of the lipids to avoid interference in the non-radioactive 96-well plate transthyretin (TTR) competitive binding assay. Metabolic activation increased the TTR binding potency of nonpolar fractions of POP-polluted sediments up to 100 times, resulting in potencies up to 240 nmol T4 equivalents/g sediment equivalent (nmol T4-Eq/g SEQ). Without bioactivation, medium polar and polar fractions also contained potent TTR-binding compounds with potencies from 1.6 to 17 nmol T4-Eq/g SEQ. This demonstrates that a more realistic in vitro sediment THD risk characterization should also include testing ofboth polar and medium polar sediment extracts for THD, as well as bioactivated nonpolar sediment fractions. Without bioactivation THD potency is not observed in nonpolar sediment extracts, although in in vivo experiments PCBs and PBDEs, and not with dioxins or PAHs, have shown to be thyroid hormone disrupting (THD), demonstrating this bio-activation is toxicologically relevant and therefore required for sediment hazard characterisation.

Chapter 7 discusses the implications of our results to improve the relevance and reliability of in vitro bioassay applied for risk characterisation of complex mixtures from sediments and other matrices. The evidence obtained to support the relevance of POP bio-activation is considered both from the exposure perspective as well as the toxicity perspective. Various features of the newly developed methods and knowledge acquired within this PhD project are discussed in relation to in vitro bioassay risk characterization of sediments towards a realistic in vitro bioassay-based risk characterization of complex mixtures. Some important aspects for the inclusion of metabolizing systems within in vitro bioassay are discussed. In addition, alternatives to deal with the SPMX effect and the definition of suitable sample amounts to improve in vitro bioassay reliability are offered. The suitability of the developed approach application is considered for the risk characterization of sediments. Furthermore, an analysis is made to decide whether this thesis have made in vitro bioassays more reliable and relevant for risk characterization of complex mixtures. Finally, it provides some concluding remarks and aspects for further applications and research.

Hoe giftig is nitraat voor Afrikaanse meerval?
Schram, E. ; Roques, J.A.C. ; Abbink, W. ; Vries, P. de; Bierman, S.M. ; Vis, J.W. van de - \ 2012
Aquacultuur 27 (2012)6. - ISSN 1382-2764 - p. 6 - 11.
clarias gariepinus - clarias - recirculatie aquacultuur systemen - recirculatiesystemen - aquacultuur - nitraat - nitraatstikstof - voeropname - toxiciteit - clarias gariepinus - clarias - recirculating aquaculture systems - recirculating systems - aquaculture - nitrate - nitrate nitrogen - feed intake - toxicity
In een recirculatiesysteem kan de nitraatconcentratie hoog oplopen. Hoe hoog mag de nitraatconcentratie worden zonder dat dit negatieve effecten heeft op de vissen? IMARES onderzocht dit in samenwerking met de Radbaoud Universiteit Nijmegen voor Afrikaanse meerval. Conclusie: nitraat is niet ongevaarlijk. Tot 140 mg nitraatstikstof per liter lijken meervallen weinig hinder te ondervinden. Wordt de concentratie hoger dan daalt de voeropname en groei behoorlijk.
'Doorbreek de stilte rond nanotechnologie in voedsel'
Kampers, F.W.H. - \ 2012
Kennis Online 9 (2012)december. - p. 4 - 5.
nanotechnologie - voedseltechnologie - voedselveiligheid - organische scheikunde - toxiciteit - bionanotechnologie - houding van consumenten - nanotechnology - food technology - food safety - organic chemistry - toxicity - bionanotechnology - consumer attitudes
Levensmiddelenbedrijven vertellen liever niet dat hun eten uit de fabriek komt. Gevaarlijk, zegt Frans Kampers van de Agrotechnolgy & Food Sciences Group. Want als er iets misgaat, zal een ongeïnformeerde consument helemaal in paniek raken.
The impact of metal transport processes on bioavailability of free and complex metal ions in methanogenic granular sludge
Bartacek, J. ; Fermoso, F.G. ; Vergeldt, F. ; Gerkema, E. ; Maca, J. ; As, H. van; Lens, P.N.L. - \ 2012
Water Science and Technology 65 (2012)10. - ISSN 0273-1223 - p. 1875 - 1881.
afvalwaterbehandeling - bioreactoren - anaërobe omstandigheden - korrelslib - biologische beschikbaarheid - metalen - toxiciteit - kernspintomografie - waste water treatment - bioreactors - anaerobic conditions - granular sludge - bioavailability - metals - toxicity - magnetic resonance imaging - magnetic-resonance - dynamics - immobilization - biofilm - nickel
Bioavailability of metals in anaerobic granular sludge has been extensively studied, because it can have a major effect on metal limitation and metal toxicity to microorganisms present in the sludge. Bioavailability of metals can be manipulated by bonding to complexing molecules such as ethylenediaminetetraacetate (EDTA) or diethylenetriaminepentaacetate (DTPA). It has been shown that although the stimulating effect of the complexed metal species (e.g. [CoEDTA]2-) is very fast, it is not sustainable when applied to metal-limited continuously operated reactors. The present paper describes transport phenomena taking place inside single methanogenic granules when the granules are exposed to various metal species. This was done using magnetic resonance imaging (MRI). The MRI results were subsequently related to technological observations such as changes in methanogenic activity upon cobalt injection into cobalt-limited up-flow anaerobic sludge blanket (UASB) reactors. It was shown that transport of complexed metal species is fast (minutes to tens of minutes) and complexed metal can therefore quickly reach the entire volume of the granule. Free metal species tend to interact with the granular matrix resulting in slower transport (tens of minutes to hours) but higher final metal concentrations.
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