Toxicity and teratogenesis in zebrafish embryos (Danio rerio)

The present thesis gives an overview about the potentials zebrafish embryos can be used for in the area of ecotoxicology. The first chapter summarizes the outcome of the ZFET (Zebrafish Embryo Toxicity Test) OECD validation study, an international attempt for the standardization and development of an embryo toxicity test as an (animal) alternative test to the acute (adult) fish test which is a mandatory component of chemical registration worldwide. The overall reproducibility of the ZFET within all participating laboratories was acceptable and the comparison of the fish embryo LC50 data calculated in the validation study with available acute adult fish LC50 data revealed good correlation. Hence, the fish embryo test is a reliable alternative method which is able to replace conventional acute (adult) fish toxicity testing. The following chapters deal with more specific questions on toxicity and teratogenicity. Recently, zebrafish embryos have been shown to be a useful model for the detection of direct acting teratogens. Therefore, chapter II investigated the capability of zebrafish embryos for bioactivation (via CYP P450) of various proteratogenic substances. Apart from one substance, which mainly produced lethal effects, all proteratogens were teratogenic in zebrafish embryos. The test compounds revealed characteristic patterns of fingerprint endpoints. Chapter III investigated detailed both toxic and teratogenic effects of coumarin and warfarin, which are intensively metabolized in animals and humans. Both chemicals produced teratogenic and lethal effects in zebrafish embryos. The comparison of the ratios between the embryo effect concentrations and human therapeutic plasma concentrations revealed a distinct teratogenic potential of warfarin, as well as the equivocal status of coumarin. Since zebrafish embryos are able to (bio)activate proteratogens and also show a promising correlation to humans, in chapter IV very specific teratogenic endpoints were assessed. A dithiocarbamate pesticide (disulfiram) and a hydrazide (acetic acid hydrazide) were selected for the assessment of cartilage and bone teratogenesis in the head of six day old zebrafish larvae. Cartilages of the neurocranium proved to be more stable than cartilages of the pharyngeal skeleton, whereas bones proved more susceptible than cartilages. In chapter V, cartilage and bone malformations after exposure to additional hydrazides and hydrazines were investigated. Despite of the different order of acute toxicity, the dose-dependent malformation of cartilages and decrease of ossification were comparable between all test substances. Chapter VI deals with oxygen consumption of sediments and embryos. The zebrafish embryo test is a widely used bioassay for the testing of effluents and sediments, e.g. in Germany it is now mandatory for effluent testing. In this context, oxygen depletion of sediments and effluents is very important and may be a confounding factor in the interpretation of apparent toxicity. Zebrafish embryos can withstand a broad range of oxygen concentrations, but concentrations lower than 0.88 mg/L are 100 % lethal. In the sediment contact test with zebrafish embryos, native sediments rapidly developed strongly hypoxic oxygen conditions. Chapter VII then summarizes embryotoxic and teratogenic effects of a sediment contact assay with specific sediments from locations in the Tietê River Basin (Brazil), providing a comprehensive and realistic insight into the bioavailable hazard potential of these sediments. High embryo toxicity could be found in samples in the vicinity of the megacity São Paulo, but also downstream. Results confirm that most toxicity is due to the discharges of the metropolitan area of São Paulo. Along all findings, the overall results indicate that zebrafish embryos are a useful alternative method for traditional toxicity and teratogenicity testing. Regarding chemical testing, the OECD validation study and further work proved that embryos tests are neither better nor worse than conventional testing with adult fish, the correlation including all data available at this time being excellent (r² > 0.9). Furthermore, zebrafish embryos proved to be a suitable model for the determination of teratogenic effects and a potential alternative method for traditional teratogenicity testing including mammalian species

Adverse effects in the fish embryo acute toxicity (FET) test : a catalogue of unspecific morphological changes versus more specific effects in zebrafish (Danio rerio) embryos

Funding Open Access funding enabled and organized by Projekt DEAL. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grand agreement No 681102.Publisher PD

OECD validation study to assess intra- and inter-laboratory reproducibility of the zebrafish embryo toxicity test for acute aquatic toxicity testing

The OECD validation study of the zebrafish embryo acute toxicity test (ZFET) for acute aquatic toxicity testing evaluated the ZFET reproducibility by testing 20 chemicals at 5 different concentrations in 3 independent runs in at least 3 laboratories. Stock solutions and test concentrations were analytically confirmed for 11 chemicals. Newly fertilised zebrafish eggs (20/concentration and control) were exposed for 96 h to chemicals. Four apical endpoints were recorded daily as indicators of acute lethality: coagulation of the embryo, lack of somite formation, non-detachment of the tail bud from the yolk sac and lack of heartbeat. Results (LC50 values for 48/96 h exposure) show that the ZFET is a robust method with a good intra- and inter-laboratory reproducibility (CV 30%) for some very toxic or volatile chemicals, and chemicals tested close to their limit of solubility. The ZFET is now available as OECD Test Guideline 236. Considering the high predictive capacity of the ZFET demonstrated by Belanger et al. (2013) in their retrospective analysis of acute fish toxicity and fish embryo acute toxicity data, the ZFET is ready to be considered for acute fish toxicity for regulatory purposes

Satın alım, çevrim içi derin indirim sonrası yeniden satın alım ve kulaktan kulağa pazarlama ile ilgili tüketici çalışmaları

Thesis (M.A.)--Özyeğin University, Graduate School of Business, Department of Business, June 2015.Daily deal sites are e-commerce businesses that offer deep discounts (e.g., 50%, 90%) for products and services to consumers through local service providers. These sites increase consumer's buying power and attract more customers for local service providers. The fact that most deal sites keep half of the revenue from each consumer makes this model unprofitable for service providers. To increase the viability of this business model, after purchasing from deal sites, consumers would need to repurchase at full and/or different discount rates from service providers and generate positive Word of Mouth (WOM). For that aim, three studies were conducted. The first study is a survey conducted in Turkey, which examines the consumer motivations based on McClelland Need Theory. The results revealed that need for achievement affects deal purchases while need for group affiliation drives the intention to repurchase at full price and need for power increases the generation of WOM. The second study addresses consumer motivations through a multi-method approach, combining in-depth interviews with an experimental study. The results revealed that price discount and distance are key action variables that managers can control in order to give fewer discounts and make higher profits. Moreover, consumers with a high need for achievement are more likely to generate WOM, while those with a high need for affiliation create more electronic WOM (eWOM). The third study is an experimental study, which reveals that satisfaction is a primary driver for repurchase and WOM. Furthermore, consumer characteristics as coupon proneness and price quality schema are key characteristics for both deal sites and service providers.Fırsat siteleri, tüketicilere yerel servis sağlayıcılar aracılığıyla çeşitli ürün ve hizmetleri, derin indirimlerle (örneğin,% 50,% 90) sunan e-ticaret işletmeleridir. Bu siteler hem tüketicinin alım gücünü artırmakta hem de yerel hizmet sağlayıcıları için daha fazla yeni müşteri çekmektedir. Fırsat sitelerinin tüketicinin servis sağlayıcıya verdiği gelirin yarısını almaları, servis sağlayıcılar için bu modeli kârsız hale getirmektedir. Bu iş modelinin devam edebilmesi için tüketicilerin fırsat sitelerinden satın aldıktan sonra, tam fiyatından ve/veya farklı indirim oranları ile servis sağlayıcılardan yeniden servis satın alması ve kulaktan kulağa pozitif pazarlama üretmeleri gerekmektedir. Bu amaçla, üç çalışma yapmıştır. İlk çalışma Türkiye de uygulanan, McClelland'ın İhtiyaçlar Teorisine dayalı olarak tüketici motivasyonlarını inceleyen bir anket çalışmasıdır. Başarı ihtiyacının fırsat sitelerinden indirimli satın almayı, bağlanma ihtiyacının ise indirimsiz yani tam fiyatından servis sağlayıcılardan geri satın almayı etkilediği ve güç ihtiyacının kulaktan kulağa pazarlamayı arttırdığını ortaya koymuştur. İkinci çalışmada derinlemesine görüşme tekniği ve deneysel bir çalışma birleştirilerek, çoklu yöntem yaklaşımı ile tüketici motivasyonları incelenmiştir. İndirim oranı ve servis sağlayıcının tüketiciye olan mesafesi, yöneticilerin daha az indirim vererek daha yüksek kar yapabilecekleri kilit eylem değişkenleri olarak bulunmuştur. Ayrıca başarı ihtiyacı yüksek kişilerin her tür kulaktan kulağa pazarlama ve bağlanma ihtiyacı yüksek kişilerin ise elektronik kulaktan kulağa pazarlama (çevrimiçi) ürettikleri görülmüştür. Üçüncü çalışma, memnuniyet değişkeninin yeniden satın alım ve kulaktan kulağa pazarlama için birincil sürücü olduğunu ortaya koyan deneysel bir çalışmadır. Ayrıca, kupon yatkınlığının ve fiyat kalite şeması adlı tüketici özelliklerinin hem fırsat siteleri ve hem de servis sağlayıcılar için anahtar özellikler olduğu bulunmuştur

Sediment-contact fish embryo toxicity assay with Danio rerio to assess particle-bound pollutants in the Tiete River Basin (Sao Paulo, Brazil)

The Tiete River and its tributary Pinheiros River receive a highly complex organic and inorganic pollutants load from sanitary sewage and industrial sources, as well as agricultural and agroindustrial activities. The aim of the present study was to evaluate the embryotoxic and teratogenic effects of sediments from selected locations in the Tiete River Basin by means of the sediment contact embryo toxicity assay with Danio rerio, in order to provide a comprehensive and realistic insight into the bioavailable hazard potential of these sediment samples. Lethal and sub-lethal effects were recorded, and high embryo toxicity could be found in the samples not only in the vicinity of the megacity Sao Paulo (Billings reservoir and Pinheiros River samples), but also downstream (in the reservoirs Barra Bonita, Promissao and Tres Irmaos). Results confirm that most toxicity is due to the discharges of the metropolitan area of Sao Paulo. However, they also indicate additional sources of pollutants along the river course, probably from industrial, agricultural and agroindustrial residues, which contribute to the degradation of each area. The sediment contact fish embryo test showed to be powerful tool to detect embryo toxicity in sediments, not only by being a sensitive method, but also for taking into account bioavailability. This test provides an ecological highly realistic and relevant exposure scenario, and should therefore be added in ecotoxicological sediment quality assessments. (C) 2011 Elsevier Inc. All rights reserved.Baden-Wurttemberg (Germany)[AZ 34.9184.90-2

Mountain Lakes: Eyes on Global Environmental Change

Mountain lakes are often situated in protected natural areas, a feature that leads to their role as sentinels of global environmental change. Despite variations in latitude, mountain lakes share many features, including their location in catchments with steep topographic gradients, cold temperatures, high incident solar and ultraviolet radiation (UVR), and prolonged ice and snow cover. These characteristics, in turn, affect mountain lake ecosystem structure, diversity, and productivity. The lakes themselves are mostly small and shallow, and up until recently, have been characterized as oligotrophic. This paper provides a review and update of the growing body of research that shows that sediments in remote mountain lakes archive regional and global environmental changes, including those linked to climate change, altered biogeochemical cycles, and changes in dust composition and deposition, atmospheric fertilization, and biological manipulations. These archives provide an important record of global environmental change that pre-dates typical monitoring windows. Paleolimnological research at strategically selected lakes has increased our knowledge of interactions among multiple stressors and their synergistic effects on lake systems. Lakes from transects across steep climate (i.e., temperature and effective moisture) gradients in mountain regions show how environmental change alters lakes in close proximity, but at differing climate starting points. Such research in particular highlights the impacts of melting glaciers on mountain lakes. The addition of new proxies, including DNAbased techniques and novel stable isotopic analyses, provides a gateway to addressing novel research questions about global environmental change. Recent advances in remote sensing and continuous, high-frequency, limnological measurements will improve spatial and temporal resolution and help to add records to spatial gaps including tropical and southern latitudes