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Tissue translocation, multigenerational and population effects of microplastics in Daphnia magna
(2021)
The last century saw the widespread adoption of plastic materials throughout nearly every aspect of our lives. Plastics are synthetic polymers that are made up of monomer chains. The properties of the monomer in conjunction with chemical additives allow plastics to have a sheer endless variety of features and use cases. They are cheap, lightweight, and extremely durable. Plastic materials are often engineered for single-use and in conjunction with high production volumes and insufficient waste management and recycling across the globe, this leads to a large number of plastics entering the environment. Marine ecosystems are considered sinks. However, freshwater ecosystems as entry pathways are highly affected by plastic waste as well. Throughout the past decade, the impact of plastic waste on human and environmental health has received a lot of attention from the ecotoxicological community as well as the public. Small plastic fragments (< 1 mm called microplastics) are a large part of this emerging field of research. Within this, the water flea Daphnia magna is probably the most common organism that is used to assess microplastics toxicity. As a filter-feeding organism, it indiscriminately ingests particles from the water column and is thus highly susceptible to microplastics. For this thesis, we identified some gaps in the available data on the ecotoxicity of microplastics to daphnids. To illuminate some of those gaps the present thesis was aimed at five main aspects:
(1) Tissue translocation of spherical microplastics in Daphnia magna
(2) Investigation of the toxicity of irregularly shaped microplastics
(3) Multigenerational and population effects of microplastics
(4) Comparison of the toxicity of microplastics and natural particles
(5) Effects of particle-aging on microplastics toxicity
The thesis is comprised of three peer-reviewed articles and one so-far unpublished study as “additional results”. The first study was aimed at understanding tissue translocation of spherical microplastics to lipid storage droplets of daphnids. The crossing of biological membranes is discussed as a prerequisite to eliciting tissue damage and an inflammatory response. Previously, researchers reported the translocation of fluorescently labeled spherical microplastics to lipid storage droplets of daphnids, even though no plausible biological mechanism to explain this occurrence. Therefore, in order to learn more about this process and potentially illuminate the mechanism we replicated the study. We were able to observe a fluorescence signal inside the lipid droplets only after increasing the exposure concentrations. Nonetheless, it appeared to be independent of particles. This led to the hypothesis, that the lipophilic fluorescent dye uncoupled from the particles and subsequently accumulated in lipid storage droplets. The hypothesis was further confirmed through an additional experiment with a silicone-based passive sampling device showing that the fluorescence occurred both independent of particles and digestive processes. Accordingly, we concluded that the reported findings were a microscopic artifact caused by the uncoupling of the dye from the particles. Therefore, a fluorescence signal alone is not a sufficient proxy to assume that particles have translocated. It needs to be coupled with additional methods to ensure that the observation is indeed caused by the translocation of particles.
It is still unclear whether the toxicity profile of microplastics is different from that of naturally occurring particles or if they are “just another particle”, as there are innumerable amounts in the natural environment surrounding an organism. The goal of the second study was to compare the toxicity of irregularly shaped polystyrene microplastics to that of the natural particle kaolin. The environment is full of natural non-food particles that daphnids ingest more or less indiscriminately and therefore are well adapted to deal with. Daphnids have a short generation time and usually experience food limitation in nature. Therefore, short-term studies only looking at acute toxicity with ad libitum food availability are not representative of the exposure scenario in nature. For a more realistic scenario, we, therefore, used a four-generation multigenerational design under food limitation to investigate how effects translate from one generation to the next. We observed concentration-dependent effects of microplastics but not of natural particles on mortality, reproduction, and growth. Some of the effects increased from generation to generation, leading to the extinction of two treatment groups. Here, microplastics were more toxic than natural particles. At least part of this difference can be explained by physical properties leading to the quick sedimentation of the kaolin, while microplastics remained in the water column. Nonetheless, buoyancy and sedimentation would also affect exposure in the environment and are likely different for most microplastics than for most naturally occurring particle types.
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COVID-19 brought about a shift in entrepreneurial opportunities and in the United States. In this paper, we proxy entrepreneurial processes by examining housing prices in different regions of the United States. Housing prices capture the movement in people, tax dynamics, and behavioral preferences for equity ownership in different regions and over time, all of which were drastically impacted by COVID-19. We examine all U.S. equity crowdfunding offerings starting with the very first offerings in 2016 Q2 until 2021 Q1 based on data from the Securities and Exchange Commission. The data indicate that regional housing prices post-COVID-19 are a strong predictor of the number of equity crowdfunding campaigns and the amount of capital raised. The impact of housing price changes on crowdfunding is more pronounced among more prosperous regions. The housing price effect is robust to numerous controls and consideration of outliers.
Leveraging data from a leading FinTech peer-to-peer lending platform in the United States, allowing us to capture both individuals’ successful and unsuccessful loan applications, we test the effect of FinTech loans on subsequent employment choice and future financial performance of serial borrowers, those repeatedly soliciting loans on the platform. An analysis of 198,984 loan requests made by 92,382 individuals shows that a failed loan application increases the probability of switching employment status. Self-employed individuals are 22% more likely to switch to becoming an employee following an unsuccessful loan application. This probability increases to 31% for those in the lowest income decile and decreases to 13% for those in the highest income decile. We document an improvement in monthly income and credit access following a successful loan application. However, this enhancement is asymmetric. Monthly income enhancement is 3.11 times larger for self-employed individuals in the lowest income decile relative to individuals in the highest income decile. Access to credit enhancement is 1.85 times larger for self-employed individuals in the lowest credit access decile relative to individuals in the second highest credit access decile.
We consider whether traders are more likely to commit securities violations when trading at home, a new form of working induced by the Covid pandemic. We examine data pre- and post-Covid, during which some traders were unexpectedly forced to work at home. The data indicate the presence of both a treatment and a selection effect, where work at home exhibits fewer misconduct cases. Work at home is associated with fewer cases of trading misconduct, although no difference in communications misconduct. The economic significance of working from home on trading misconduct is large for both the treatment and selection effects.
The nominee approach to equity crowdfunding pools all crowd investors into one (nominee) account where typically the platform acts as the legal owner but the crowd retains beneficial ownership. The platform plays an active digital corporate governance role that simultaneously enfranchises crowd investors with voting and ownership rights but removes the administrative burden on startups of having to deal with several hundred shareholders. Through an inter-platform and intra-platform analysis of a large sample of 1,018 initial equity crowdfunding campaigns, this paper assesses both the short-term and the long-term impact of nominee versus direct ownership. It finds that nominee initial campaigns are on average more successful than direct ownership campaigns in that they are more likely to succeed, raise more funds, attract overfunding and enjoy greater long run success in terms of successful seasoned equity crowdfunded offerings, numbers of such offerings, and probability of survival. These results hold inter-platform between the two main UK equity crowdfunding platforms (Seedrs and Crowdcube) as well as intra-platform, using the post-2015 quasi-natural experiment when the nominee approach became an option for startups raising capital on Crowdcube.
Non-standard errors
(2021)
In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in sample estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence-generating process (EGP). We claim that EGP variation across researchers adds uncertainty: non-standard errors. To study them, we let 164 teams test six hypotheses on the same sample. We find that non-standard errors are sizeable, on par with standard errors. Their size (i) co-varies only weakly with team merits, reproducibility, or peer rating, (ii) declines significantly after peer-feedback, and (iii) is underestimated by participants.
The importance of agile methods has increased in recent years, not only to manage software development processes but also to establish flexible and adaptive organisational structures, which are essential to deal with disruptive changes and build successful digital business strategies. This paper takes an industry-specific perspective by analysing the dissemination, objectives and relative popularity of agile frameworks in the German banking sector. The data provides insights into expectations and experiences associated with agile methods and indicates possible implementation hurdles and success factors. Our research provides the first comprehensive analysis of agile methods in the German banking sector. The comparison with a selected number of fintechs has revealed some differences between banks and fintechs. We found that almost all banks and fintechs apply agile methods in IT-related projects. However, fintechs have relatively more experience with agile methods than banks and use them more intensively. Scrum is the most relevant framework used in practice. Scaled agile frameworks are so far negligible in the German banking sector. Acceleration of projects is apparently the most important objective of deploying agile methods. In addition, agile methods can contribute to cost savings and lead to improved quality and innovation performance, though for banks it is evidently more challenging to reach their respective targets than for fintechs. Overall our findings suggest that German banks are still in a maturing process of becoming more agile and that there is room for an accelerated adoption of agile methods in general and scaled agile frameworks in particular.
We propose three governance mechanisms pertinent to equity crowdfunding and campaign success through mitigating pronounced information asymmetries and agency problems. First, unlike IPOs for which the effect of Delaware incorporation has declined or disappeared over time, we propose Delaware incorporation matters a great deal for success in the new setting of equity crowdfunding. Second, we propose that security design is a critical tool for equity crowdfunding success and even more important than the limited 2-year financial statement disclosure. Third, we propose that platforms as intermediaries between entrepreneurs and investors play an important role in mitigating and sometimes exacerbating information asymmetries and agency problems. The population of equity crowdfunding campaigns from market inception in May 2016 to Q2, 2021 in the United States provides strong support for these propositions.