Green Swans countering chemical pollution.

If a problem has exponential features, its solution asks for counter-exponential approaches. Chemical pollution appears to be such a problem. Analyses of chemical hazards to human health, biodiversity, and ecosystem services and estimates of the cost of inaction suggest the potential for adverse impacts, and analyses of trends in the chemical economy appear exponential in kind. Here, we argue that we need and can develop an exponential and application-focused mindset in thinking about solutions

Tissue translocation, multigenerational and population effects of microplastics in Daphnia magna

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. ...Im Laufe des letzten Jahrhunderts hat Plastik in nahezu jeden Aspekt unseres täglichen Lebens Einzug gehalten. Chemisch betrachtet ist Plastik der Überbegriff für synthetische Polymere, bestehend aus Ketten von Untereinheiten (Monomeren). Die Eigenschaften des Monomers in Kombination mit zugesetzten chemischen Additiven erlaubt eine fast grenzenlose Vielfalt und Anwendbarkeit von Plastikmaterialien. Die Erfindung und Verbreitung von Plastikmaterialien wurde maßgeblich durch den zweiten Weltkrieg vorangetrieben und stellt eine gesellschaftliche Revolution dar. Plastik ist leicht, preisgünstig, robust, und endlos formbar. Viele alltägliche Plastikprodukte sind für den einmaligen Gebrauch bestimmt und gelangen danach absichtlich oder unabsichtlich in die Umwelt, wo sie Jahre bis Jahrhunderte benötigen, um abgebaut zu werden. Teil dieser Problematik ist das ubiquitäre Auftreten partikulären Plastiks, das größtenteils aus der Verwitterung größerer Plastikstücke entsteht und als Mikroplastik (gemeinhin Partikel < 1 mm Größe) bezeichnet wird. Verwitterungsmechanismen sind sowohl chemisch-physikalischer Natur wie z.B. die Einwirkung von (ultravioletter) Strahlung, mechanischer Abrieb, Salzgehalte und Sauer bzw. basische Milieus. Zusätzlich kommt es nach Eintrag in die Umwelt zur Sorption biologischer Makromoleküle und den Bewuchs mit Mikroorganismen. Auch Fragmentierung durch biologische Prozesse (Darmpassage von Tieren) wurde bereits beschrieben. Durch das breite Größenspektrum, in dem Mikroplastik auftritt, kann es Organismen aller biologischen Ebenen beeinflussen und ggf. von ihnen aufgenommen werden. Die Interaktion und Schadwirkungen von Mikroplastik auf verschiedene Organismen sind seit einigen Jahren Gegenstand vieler ökotoxikologischer Studien. Der wahrscheinlich meistuntersuchte Organismus ist hier der große Wasserfloh Daphnia magna, der als pelagischer Filtrierer Partikel bis zu einer Größe von 70-90 μm nicht-selektiv aus der Wasserphase aufnimmt. Die Untergrenze ist weniger klar definierbar, da hier weitere Prozesse über die Filtration hinaus zur Aufnahme von Partikeln führen können. Allgemein werden zwei Hauptmechanismen für eine Schadwirkung durch Mikroplastik diskutiert: I) die Reduktion der Nahrungsverfügbarkeit, beispielsweise durch Verdünnung von Nahrungspartikeln mit Mikroplastik oder der reduzierten Nahrungsaufnahme oder II) eine mechanische Schädigung des Organismus. Letzteres kann weiterhin unterschieden werden in interne und externe physische Schädigung. In einem Review-Artikel wurde die Aufnahme und der Transfer von Partikeln über Gewebegrenzen hinweg als Voraussetzung für das Auftreten von Entzündungsreaktionen und damit einhergehender Schadwirkung angenommen. Dieser Gewebetransfer von Mikroplastik wurde bereits in einer Vielzahl von Studien in aquatischen Invertebraten und Fischen untersucht. Im überwiegenden Teil dieser Studien wurden sphärische fluoreszenz-markierte Partikel genutzt, deren Gewebetransfer anhand eines Fluoreszenz-Signals im Zielgewebe nachgewiesen wurde. Biologisch betrachtet kommen drei Mechanismen in Frage, um einen Gewebetransfer zu bewirken, insgesamt ist der Transfer von für Partikel > 1 μm allerdings nicht plausibel. Da sie nur bedingt zwischen Futter- und nicht-Futter-Partikeln unterscheiden können, haben Daphnien mehrere Strategien und Adaptations-Mechanismen, um mit der Allgegenwärtigkeit nicht-verdaulicher Partikel umzugehen. Ihre Darminnenwand ist beispielsweise durch eine Chitin-basierte peritrophische Membran gegen mechanische Verletzungen geschützt, die gleichzeitig siebartig die Aufnahme größerer Partikel über den Darm verhindert. Unter anderem wegen der Existenz dieser Membran ist mindestens eine frühere Studie, die über Gewebetransfer von fluoreszierendem Mikroplastik in Daphnien aus dem Darm in Fettspeichergewebe berichtet hat, biologisch nicht plausibel. Diese Thesis besteht aus drei in Fachzeitschriften veröffentlichten Papern (Schür et al. (2019; 2020; 2021), Annex 1-3), sowie einer unveröffentlichten Studie (Annex 4). Die Studien beschäftigen sich mit verschiedenen Aspekten der Interaktion und Effekten von Mikroplastik auf den großen Wasserfloh Daphnia magna. Übergeordnet wurden dabei fünf Ziele verfolgt, die teils übergreifend in mehreren Studien behandelt wurden: (1) Gewebetransfer von sphärischem Mikroplastik. (2) Untersuchung der Toxizität von irregulär geformten Mikroplastikpartikeln. (3) Multigenerationale und Populations-Effekte von Mikroplastik. (4) Vergleich der Toxizität von Mikroplastik und natürlichen Partikeln. (5) Auswirkung von Partikel-Alterung auf die Mikroplastik-Toxizität. Die erste Publikation (Schür et al. (2019), Annex 1) befasst sich mit dem Gewebetransfer von Mikro- und Nanoplastik-Partikeln in Daphnia magna. Durch die Reproduzierung einer früheren Studie wurde im Detail untersucht wie es zu einem Transfer von Mikro- und Nanoplastik Partikeln in die Fettspeichergewebe von Daphnien kommen kann. Anfänglich konnten die Ergebnisse nicht reproduziert werden, weshalb eine zusätzliche Verfeinerung des Ansatzes durch Einbeziehung eines Probenbehandlungsprotokolls zur Verbesserung der Sichtbarkeit innerhalb der Tiere folgte. ..

Effects of microplastics mixed with natural particles on Daphnia magna populations

The toxicity of microplastics on Daphnia magna as a key model for freshwater zooplankton is well described. While several studies predict population-level effects based on short-term, individual-level responses, only very few have validated these predictions experimentally. Thus, we exposed D. magna populations to irregular polystyrene microplastics and diatomite as natural particle (both ≤ 63 μm) over 50 days. We used mixtures of both particle types at fixed particle concentrations (50,000 particles mL-1) and recorded the effects on overall population size and structure, the size of the individual animals, and resting egg production. Particle exposure adversely affected the population size and structure and induced resting egg production. The terminal population size was 28–42% lower in exposed compared to control populations. Interestingly, mixtures containing diatomite induced stronger effects than microplastics alone, highlighting that natural particles are not per se less toxic than microplastics. Our results demonstrate that an exposure to synthetic and natural particles has negative population-level effects on zooplankton. Understanding the mixture toxicity of microplastics and natural particles is important given that aquatic organisms will experience exposure to both. Just as for chemical pollutants, better knowledge of such joint effects is essential to fully understand the environmental impacts of complex particle mixtures. Environmental Implications While microplastics are commonly considered hazardous based on individual-level effects, there is a dearth of information on how they affect populations. Since the latter is key for understanding the environmental impacts of microplastics, we investigated how particle exposures affect the population size and structure of Daphnia magna. In addition, we used mixtures of microplastics and natural particles because neither occurs alone in nature and joint effects can be expected in an environmentally realistic scenario. We show that such mixtures adversely affect daphnid populations and highlight that population-level and mixture-toxicity designs are one important step towards more environmental realism in microplastics research

A benchmark dataset for machine learning in ecotoxicology

The use of machine learning for predicting ecotoxicological outcomes is promising, but underutilized. The curation of data with informative features requires both expertise in machine learning as well as a strong biological and ecotoxicological background, which we consider a barrier of entry for this kind of research. Additionally, model performances can only be compared across studies when the same dataset, cleaning, and splittings were used. Therefore, we provide ADORE, an extensive and well-described dataset on acute aquatic toxicity in three relevant taxonomic groups (fish, crustaceans, and algae). The core dataset describes ecotoxicological experiments and is expanded with phylogenetic and species-specific data on the species as well as chemical properties and molecular representations. Apart from challenging other researchers to try and achieve the best model performances across the whole dataset, we propose specific relevant challenges on subsets of the data and include datasets and splittings corresponding to each of these challenge as well as in-depth characterization and discussion of train-test splitting approaches.ISSN:2052-446

Exp_IV_gutevac

Gut evacuation data from Experiment IV

Exp_IV_aggregates

Data for evaluation of MP-aggregates in the gut of D. magna from experiment IV

The Effects of Natural and Anthropogenic Microparticles on Individual Fitness in <i>Daphnia magna</i>

<div><p>Concerns are being raised that microplastic pollution can have detrimental effects on the feeding of aquatic invertebrates, including zooplankton. Both small plastic fragments (microplastics, MPs) produced by degradation of larger plastic waste (secondary MPs; SMPs) and microscopic plastic spheres used in cosmetic products and industry (primary MPs; PMPs) are ubiquitously present in the environment. However, despite the fact that most environmental MPs consist of weathered plastic debris with irregular shape and broad size distribution, experimental studies of organism responses to MP exposure have largely used uniformly sized spherical PMPs. Therefore, effects observed for PMPs in such experiments may not be representative for MP-effects <i>in situ</i>. Moreover, invertebrate filter-feeders are generally well adapted to the presence of refractory material in seston, which questions the potential of MPs at environmentally relevant concentrations to measurably affect digestion in these organisms. Here, we compared responses to MPs (PMPs and SMPs) and naturally occurring particles (kaolin clay) using the cladoceran <i>Daphnia magna</i> as a model organism. We manipulated food levels (0.4 and 9 μg C mL^-1) and MP or kaolin contribution to the feeding suspension (<1 to 74%) and evaluated effects of MPs and kaolin on food uptake, growth, reproductive capacity of the daphnids, and maternal effects on offspring survival and feeding. Exposure to SMPs caused elevated mortality, increased inter-brood period and decreased reproduction albeit only at high MP levels in the feeding suspension (74% by particle count). No such effects were observed in either PMP or kaolin treatments. In daphnids exposed to any particle type at the low algal concentration, individual growth decreased by ~15%. By contrast, positive growth response to all particle types was observed at the high algal concentration with 17%, 54% and 40% increase for kaolin, PMP and SMP, respectively. When test particles comprised 22% in the feeding suspension, both MP types decreased food intake by 30%, while kaolin had no effect. Moreover, SMPs were found to homoaggregate in a concentration-dependent manner, which resulted in a 77% decrease of the ingested SMPs compared to PMPs. To better understand MP-processing in the gut, gut passage time (GPT) and evacuation rate of MPs were also assayed. SMPs and PMPs differed in their effects on daphnids; moreover, the particle effects were dependent on the MP: algae ratio in the suspension. When the MP contribution to the particle abundance in the medium changed from 1 to 4%, GPT for daphnids exposed to SMPs increased 2-fold. Our results suggest that MPs and, in particular, SMPs, have a greater capacity to negatively affect feeding in <i>D</i>. <i>magna</i> compared to naturally occurring mineral particles of similar size. Moreover, grazer responses observed in experiments with PMPs cannot be extrapolated to the field where SMPs dominate, because of the greater effects caused by the latter.</p></div

Exp_II_DW_comparison

Dry weights of daphnids used in statistical evaluation of experiment II

Exp_III_food_consumption

Data from experiment III on consumption of algae in the presence of inert particles (kaolin, primary or secondary microplastics)