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Accurate particle size distribution (PSD) measurements of suspended particulate matter composed of flocs and aggregates are important to improve understanding of ecological and geomorphological processes, and for environmental engineering applications. PSD can be measured in situ (in the field) using a submersible sensor, or ex situ (in the laboratory) using samples. The methodological choice is often guided by logistical factors, and the differences in PSDs acquired by in situ and ex situ measurements are not acknowledged. In this study, a laser-diffraction instrument (LISST-200X) was used to compare in situ and ex situ PSD measurements. Samples measured ex situ were stored for three consecutive weeks and measured each week in a laboratory using different stirrer speeds. We observed that ex situ measurements display a higher D50 (median particle size) than in situ measurements of the same sample (up to 613% larger, 112% on average). Our experiments show that the difference between in situ and ex situ measurements can be explained by flocculation of the riverine sediments during the first week of storage. During the subsequent ex situ measurements, the stirring results in a significantly lower D50. Ex situ measurements are therefore unsuitable for flocculated suspended particulate matter. This study provides recommendations for optimizing PSD measurements by calculating the measurement times required to obtain robust PSD measurements (exceeding three minutes per sample), which are larger for field samples with coarser particles and wider PSDs.

Because of the high production rates, low recycling rates, and poor waste management of plastics, an increasing amount of plastic is entering the aquatic environment, where it can provide new ecological niches for microbial communities and form a so-called plastisphere. Recent studies have focused on the one-way impact of plastic substrata or biofilm communities. However, our understanding of the two-way interactions between plastics and biofilms is still limited. This review first summarizes the formation process and the co-occurrence network analysis of the aquatic plastisphere to comprehensively illustrate the succession pattern of biofilm communities and the potential consistency between keystone taxa and specific environmental behavior of the plastisphere. Furthermore, this review sheds light on mutual interactions between plastics and biofilms. Plastic properties, environmental conditions, and colonization time affect biofilm development. Meanwhile, the biofilm communities, in turn, influence the environmental behaviors of plastics, including transport, contaminant accumulation, and especially the fragmentation and degradation of plastics. Based on a systematic literature review and cross-referencing from these disciplines, the current research focus, and future challenges in exploring aquatic plastisphere development and biofilm-plastic interactions are proposed. Refereed/Peer-reviewed

Microplastics are an unavoidable part of riverine systems, altering the natural composition of rivers and the associated processes. Within a riverine system, microplastics can be present throughout the water column or within bedload, implying different transport, deposition, and erosion mechanisms. Some recent models have been developed to predict and understand the depth distribution concentration of microplastics and macroplastics, primarily relying on the Rouse model for sediments. However, the great variety in microplastics shape and size accompanied by the dynamic nature of riverine systems (e.g., variety of flow conditions, sediment composition and bedforms) question how realistic and reliable models for plastic distribution along the water column and within sediments are. Present models are often analogous to suspended sediment models and assume diffusivity to be equal to turbulent viscosity, they often exclude the bedload, neglect the effect of turbulence and bed morphology, and come short in explaining the behaviour of mixtures of microplastics and sediments. Understanding these aspects is crucial to improve present models and to aid mitigation efforts and to optimize collection systems and policy. This project targets employing both physical and numerical modelling techniques to further develop depth concentration models of microplastics. We aim to further examine and quantify the influence of turbulence on microplastics transport and concentration distribution by establishing preliminary estimates for the eddy viscosity and diffusivity of microplastics and further examine a wider range of mixtures of microplastics and sediments with different shapes and sizes.

Our current era is often referred to as the 'age of data'. Increasing amounts of data and models are generated, often without being used sustainably - because they are not accessible, difficult to understand or difficult to transfer to other data sets. With https://envsci.fastresearch.io/, we aim to improve collaboration on data sets and analyses to make them usable and reproducible for everyone. With our innovative platform, we want to enable researchers to work together on data and data analysis by giving them a tool to collaborate and to make their data and analyses open access. On our platform, large amounts of data can be combined with extensive analyses and used either privately, partially publicly or completely publicly. With FastResearch.io, data and models will be easily accessible and usable even for non-specialists, as data are modularly exchangeable and users do not need to build their own environments to use the models. While a curated software environment is offered for R and Python, users can also use customized environments (docker images) due to the modular and containerized infrastructure, which allows coding in any programming language. The great advantage of FastResearch.io compared to other platform solutions is that data and analyses connected to these data are stored together within a working software environment, which ends consistency problems in collaborative projects forever.

Plastics accumulate in the environment due to inadequate waste management, and the durability of the material. A better understanding of fundamental plastic behaviour in the aquatic environment is essential to estimate transport and accumulation, which can be used for monitoring, prevention and reduction strategies. An important process for fate models is the vertical transport of particles, for which the rising and settling velocity are crucial variables. Several studies have described these for microplastics (0.5 cm) however, such data are scarce. In this study, the rising and settling behaviour of three polymer types (PET, PP, and PE) commonly found in the environment was investigated. The plastic particles were foils of different sizes and shapes. A new method for releasing rising plastics without interfering the flow and disturbing the column was used. Observational data were used to test the performance of four models, including one developed in this study, for estimating the settling and rising velocity based on the properties of the plastic particles. These models were validated using the data obtained in this study, as well as data from another study on plastic rising and settling rates. The newly introduced foil velocity model gave the best results (R² = 0.96 and 0.29 for both data sets, respectively). This model has the potential to estimate the rising and settling velocity of plastic foils, and should be further investigated using additional observational data. The results of our work can be used to further explore the vertical distribution of plastics in rivers, lakes and oceans, which is crucial for improving future efforts to monitor and reduce plastics.

Microplastics are detected in most environmental compartments and hence receive a great deal of attention, especially in aquatic environments where rivers act as pathways for microplastics. Currently, a particularly high input of microplastics through Asian rivers is assumed predominantly by modelling data, while field measurements are scanty.Three rivers in South India were considered for this purpose to focus on their microplastic loads. The emphasis was on the comparison of microplastic concentrations in urban and rural rivers to identify if the anthropogenic influence control the loads. While two rivers in the megacity Chennai (Tamil Nadu) were found to have an average microplastic concentration of 0.4 microplastic particles/L, a rural river near Munnar (Kerala) had an average concentration of 0.2 microplastic particles/L. The results show higher loads in the urban area with a high anthropogenic influence by wastewater discharges and waste disposal through high number of residents dumping directly by the river. Fibres were the predominant shape (64.13%), black was the predominant particle colour (44.80%) and polyethylene and polyprolyene were the predominant polymers (each 46.67%) detected within the identified particles of all samples.Rough estimates of annual microplastic discharge from the Adyar River (Chennai) into the Bay of Bengal are found to be as high as 11.6 trillion microplastic particles. This study, which is one of the first baseline studies for microplastic loads in South Indian streams, should be complemented with further environmental sampling during pre-monsoon, monsoon and post-monsoon seasons to get more detailed information on the storage and transportation of fluvial microplastics and to understand the seasonal effect on the river flow characteristics as well as the fate of microplastics.

Bedform occurrence and geometry in sand-bedded rivers is traditionally predicted with phase diagrams and empirical equations, in which regional river characteristic are used. Field observations supporting these equations are often made in regions where bedform fields are known to be present and are spatially uniform. However, bedforms occurrence and geometry can vary significantly at the scale of the river width, limiting the applicability of bedform diagrams and questioning the objectivity of field study area selection. To enable the prediction of dune geometry, its spatial variability needs to be better understood. In this study, we aim to relate spatial variations in dune characteristic to grain size characteristics, river geometry, and local flow variation governed by the sub-bedform topography. We hypothesize that curvature-induced bars and pools drive local hydrodynamics, which in turn determine local dune characteristics. To test this hypothesis, bathymetric field data and sediment samples were collected in the fluvial-to-tidal-transition zone of the Fraser river, a sand-bedded lowland river in British Columbia, Canada. A 2D hydrodynamic model was created to explore the impacts of spatial variation in hydraulic conditions. We find that the cross-sectional variability in dune geometry is larger than the longitudinal variability, and that the transition of one type of dune field into another is abrupt rather than gradual. Phase diagrams do not capture these observations accurately. Local hydraulic conditions are more important in determining spatial variability in dune geometry than regional scale changes in river geometry, grain size variation and tidal influence. Dune height has an ambiguous relationship with river depth: the spatial variation in dune height depends on local shear stresses governed by the sub-bedform topography characterized by pools and troughs.

Plastic accumulates in the environment because of insufficient waste handling and the materials' high durability. Better understanding of plastic behaviour in the aquatic environment is needed to estimate transport and accumulation, which can be used for monitoring strategies, prevention measures, and plastic clean-up activities. Plastic transport models benefit from accurate description of particle characteristics, such as rising and settling velocities. For macroplastics, these are however still scarce. In this research, the rising and settling behaviour of three different polymer types (PET, PP, and PE) was investigated, which are the most common in the environment. All of the plastic particles were foils of different surface areas. A new method for releasing rising plastics without interfering the flow and disturbing the column was used. Four models that estimate the velocity based on the characteristics of the plastics are discussed, of which three are from literature, and one is newly derived. These models are validated using the data generated in this research, and data from another study on rising and settling velocities of plastic. From the models that were discussed, the best results are from the newly introduced velocity model for foils (R^2 = 0.96 and 0.58, for both datasets). This model shows potential to estimate the rising and settling velocity of plastics, and should be examined further by using additional data. The results of our paper can be used to further explore the vertical distribution of plastics in rivers, lakes and oceans, which is crucial to optimize future monitoring and cleanup efforts.

Land-based plastic waste, carried to the sea through rivers, is considered a main source of marine plastic pollution. However, most plastics that leak into the environment never make it into the ocean. Only a small fraction of plastics that are found in the terrestrial and aquatic compartments of river systems are emitted, and the vast majority can be retained for years, decades, and potentially centuries. In this presentation we introduce the concept of river systems as plastic reservoirs. Under normal conditions, hydrometeorological variables (such as wind, runoff and river discharge) mobilize, transport and deposit plastics within different river compartments (e.g. riverbanks, floodplains, lakes, estuaries). The emptying of these plastic reservoirs primarily occurs under extreme hydrological conditions (e.g. storms, floods). We specifically focus on the retention mechanisms within different river compartments, and their effect on the fate of the plastics that are accumulated over various timescales. With this presentation, we aim to introduce the concept of rivers as (long-term) sinks for plastic pollution, and provide suggestions for future research directions.

Study region: The Santa Ana River middle reach, a small coastal urban catchment in Southern California, USA experiences a Mediterranean climate and lowflows dominated by wastewater effluent. Study focus: River macroplastic flux can inform watershed management of plastic pollution. However, continuous macroplastic monitoring is not possible, so concentrations must be predicted during unobserved periods. We monitored macroplastic concentration and aimed to improve macroplastic flux estimation using strategies commonly employed in estimating mineral sediment flux. New hydrological insights for the region: Floating macroplastic size distributions were statistically equivalent between lowflow and stormflow samples – evidence that channel processes controlled macroplastic size distribution or macroplastic size distributions outside the channel were the same as inside. Concentrations fell during the falling limb of one hydrograph and rose during the rising limb of another hydrograph. A generalized additive model (GAM) revealed that macroplastic concentration increased in response to small discharge increases but decreased for the largest discharges. Macroplasitc depletion (relative to discharge) occurs at high flow magnitudes or during the falling limb. The annual mass flux of floating macroplastic was 27.4 (2.8–84.8) tonnes1yr−1 or 18.2 (2.9–222.2) tonnes1yr−1 as predicted using mean concentration or the GAM, respectively. With little data, the mean concentration approach may be appropriate but likely underestimates uncertainty – which will require extensive monitoring to reduce.

Earth science reviews 228, 104021 (2022). doi:10.1016/j.earscirev.2022.104021, Published by Elsevier, Amsterdam [u.a.]

Microplastic (MP) has been detected in marine, limnic, terrestrial, and atmospheric environments. However, rivers are often only seen as transport paths for MPs from inland sources to the oceans, although transport rates in rivers can hardly be determined yet. MP in rivers can either be transported, or it settles to the bottom of the river and either remains there or is remobilized again at higher flow velocities. This remobilization, also known as erosion, depends on the critical shear stress of a particle and is influenced by the particle properties and the sediment bed. In this study, the critical shear stresses of 14 MP particles with different shapes, densities, and particle sizes on different sediment beds were experimentally determined and subsequently compared with the basic principles of erosion from sediment transport. Critical shear stresses of the MP particles were between 0.002 and 0.233 N/m2, depending on particle and sediment properties. Furthermore, the hiding-exposure effect was transferred to MPs and an equation was developed to determine the critical shear stress of different MP particles on natural sediment beds.

Water 13(12), 1648 (2021). doi:10.3390/w13121648 special issue: "Special Issue "Microplastics in Water Bodies and in the Environment" / Special Issue Editors: Dr. Hrissi K. Karapanagioti, Guest Editor; Dr. Ioannis K. Kalavrouziotis, Guest Editor", Published by MDPI, Basel

River flow is a major conveyance of microplastic (1-5000 μm) pollution from land to marine systems. However, the current approaches to monitoring and modeling fluvial transport of microplastic pollution have primarily relied on sampling the surface of flow and assumptions about microplastic concentration depth profiles to estimate the depth-averaged concentration. The Rouse profile was adapted to show that fluvial transport of microplastic pollution includes all traditional domains of transport (bed load, settling suspended load, and wash load), as well as additional domains specific to low-density materials with rising velocities in water (rising suspended load and surface load). The modified Rouse profile was applied to describe the positively buoyant particle concentration depth profiles and compared to field observations to showcase the utility of this approach. A procedure was developed for assessing the uncertainty and bias from using a surface sample to estimate the depth-averaged concentration while assuming either surface load or wash load concentration depth profiles. Both assumptions may introduce a large amount of uncertainty due to the range of suspended microplastic concentration depth profiles. Monitoring microplastic pollution and estimating the depth-averaged concentration of microplastics in fluvial systems would further benefit from broader adoption of depth-integrated sampling, characterization of particle concentration depth profiles, and estimation of uncertainties in depth-averaged concentration based on the sampling approach.

With the focus on microplastic in current research, macroplastic is often not further considered. Thus, this review paper is the first to analyse the entry paths, accumulation zones, and sinks of macroplastic in the aquatic, terrestrial, and atmospheric environment by presenting transport paths and concentrations in the environment as well as related risks. This is done by applying the Source–Pathway–Receptor model on macroplastic in the environment. Based on this model, the life cycle of macroplastic is structurally described, and knowledge gaps are identified. Hence, current research aspects on macroplastic as well as a sound delimitation between macro- and microplastic that can be applied to future research are indicated. The results can be used as basic information for further research and show a qualitative assessment of the impact of macroplastic that ends up in the environment and accumulates there. Furthermore, the applied model allows for the first time a quantitative and structured approach to macroplastic in the environment.

Microplastics in the environment is a highly relevant research topic. However, although more and more studies on environmental concentrations of microplastics are published, a profound risk assessment could not be carried out yet. This is mainly attributable to the fact that the current sampling and analysis methods do not provide a representative picture of the environmental pollution, as the fundamental knowledge about transport processes of microplastic is not present, and the ecotoxicological studies therefore cannot consider the relevant exposures of the organisms. To provide a methodological basis for further research and risk assessments, this paper applies the Source-Pathway-Receptor model to the context of microplastics, whereby the current state of knowledge can be compiled in a structured way and important knowledge gaps can be identified.

Microplastic (MP) has already been reported in terrestrial [1, 2], marine [3, 4] and limnic environments [5, 6] as well as in the atmosphere [7, 8], with the research focus recently shifting from marine to limnic compartments [9]. Although there are more and more studies on MP concentrations in rivers, the predominant transport mechanisms of MP have been investigated only sporadically [6, 10, 11, 12]. For this reason, it has not yet been possible to make reliable statements about hotspots, transport routes, sources and sinks of MPs in rivers [2, 13].

Microplastic is exposed to numerous weathering processes in the environment, which change particle properties and thus influence transport behaviors, including settling and rising velocities in aquatic environments. However, the extent to which particles in the environment differ from virgin particles in their transport behaviors has not yet been investigated. The settling and rising velocities of weathered fluvial microplastic and macroplastic particles collected from environmental samples are determined in this study and the transferability of theoretical approaches to predicting their transport behaviors is examined. The settling velocities of the environmental particles were between 0.16 and 3.52 cm/s and the rising velocities between 0.18 and 19.85 cm/s. Formulas were applied that were developed using experiments with virgin microplastic, but do not account for the effects of environmental impacts such as degradation, fragmentation and biofouling on the velocities. Accordingly, the transferability of the formulas to environmental particles must be verified. The formulas proved to be suitable for describing the settling and rising velocities of environmental microplastic particles in the shapes of pellets, fragments and foams, and were less suitable for describing the velocities of films and macroplastic particles. Further experiments will be necessary in the future to integrate effects from biofilm and particle deformation on the transport behaviors to adequately model the behavior of the highly diverse micro- and macroplastic particles in the aquatic environment.

In this study, the infiltration behavior of 21 microplastic particles with different densities, diameters, and shapes was investigated using columns of glass spheres with different grain diameters. The glass spheres were considered as an analogy for natural sediment and the results were afterward transferred to natural sediment and compared to fine sediment infiltration. The infiltration depth of the microplastic particles increased with decreasing diameter of the microplastic particles (dMP) and with increasing diameter of the glass spheres (dGS). At ratios of dMP/dGS > 0.32, hardly any infiltration could be observed. In regard to the particle shape, the data shows that spherical particles infiltrate deeper than fragments and fibers. In case of fibers, the fiber diameter, in particular, influences the depth of infiltration, with thinner fiber diameters leading to deeper infiltration depths. Fragments, such as tire abrasion, infiltrated less deeply than spherical particles, probably due to the entanglement of the angular particles in the pores. Finally, based on the experiments, this study provides initial indications of reasonable sampling depths in dependence of the grain sizes of the bottom sediment and the microplastic particles. According to this, microplastics in detectable particle sizes (>100 μm) are only found on the surface of sediment consisting of coarse silt and fine sand, while the particles might infiltrate up to 13 cm into sediment consisting of coarse sand, fine gravel, and medium gravel. A statement of depth-variable microplastic concentrations is therefore mainly useful for these sediment types. Accordingly, in future sediment samples, the grain size distribution of the sediment should always be indicated to better evaluate the detected microplastic concentrations.

Wie in den vorherigen Ausfuhrungen vermutlich deutlich geworden ist, steckt die Mikroplastikforschung noch in den Kinderschuhen. Beginnend bei einer allgemein anerkannten Definition der Mikroplastik-Partikel, uber vergleichbare Probenahmemethodiken und Konzentrationseinheiten bis hin zu den Folgen fur die aquatischen Lebewesen und uns Menschen mussen noch viele Fragen beantwortet werden. Dies gilt prinzipiell auch fur den Boden und die dort lebenden Organismen, auf die in dieser Schrift nicht eingegangen wurde.

Das Medieninteresse an Mikroplastik ist derzeit enorm und viele der popularwissenschaftlichen Artikel beschreiben grose Risiken fur Mensch und Tier. Aber was davon ist wissenschaftlich belegt? Eigentlich gibt es derzeit noch zu viele Wissenslucken, als dass ein klares Schadenspotenzial bestimmt werden kann. Hinzu kommt, dass viele okotoxikologische Studien mit Konzentrationen arbeiten, die deutlich hoher sind als die in der Natur vorkommenden, sodass ihre Aussagekraft derzeit noch relativ gering ist.

Die Vielzahl an Mikroplastikquellen und Eintragspfaden verdeutlicht, dass ein Eintrag in die aquatische Umwelt derzeit nicht verhindert werden kann. Daher wurde Mikroplastik bereits in allen beprobten Umweltbereichen nachgewiesen, einschlieslich abgelegener Orte wie Tiefsee, arktisches Eis und entlegene Bergseen.

Erste Studien gehen davon aus, dass sich praktisch alles jemals produzierte Plastik, welches nicht verbrannt wurde, noch auf dieser Erde befindet. Doch obwohl immer mehr Plastik produziert wird und damit auch in die Umwelt gelangen kann, scheinen die Konzentrationen in den beprobten Umweltbereichen entgegen aller Erwartungen nicht anzusteigen. Immer mehr Studien sprechen von dem „Missing Plastic“ und fragen sich, was mit dem Plastik im Laufe der Zeit geschieht.

Mikroplastik gelangt sowohl uber punktuelle, als auch uber diffuse Eintragspfade in die aquatische Umwelt. Eine umfangreiche Zusammenstellung der wichtigsten Quellen und Eintragspfade in die Binnengewasser und Ozeane gibt Abb. 3.1.

Microplastic (MP) contaminates terrestrial, aquatic, and atmospheric environments. Although the number of river sampling studies with regard to MP concentrations is increasing, comprehension of the predominant transport processes of MP in the watercourse is still very limited. In order to gain a better process understanding, around 500 physical experiments were conducted to shed more light on the effects of particle shape, size and density on the rise and settling velocities of MP. The determined velocities ranged between 0.39 cm/s for polyamide fibers (settling) and 31.4 cm/s for expanded polystyrene pellets (rise). Subsequently, the determined velocities were compared with formulas from sediment transport and, as there were large differences between theoretically and experimentally determined velocities, own formulas were developed to describe settling and rise velocities of MP particles with a large variety of shapes, sizes and densities. This study shows that MP differs significantly from sediment in its behavior and that a transfer of common sediment transport formulas should be treated with caution. Furthermore, the established formulas can now be used in numerical simulations to describe the settling and rising of MP more precisely.

Bei der Betrachtung des Themas Mikroplastik sollte zunachst auf den Wortteil des – plastiks naher eingegangen werden. Ursprung des Wortes ist das griechische plastikos, welches schon im 17. Jahrhundert Objekte beschrieb, die geformt werden konnten oder fur das Formen geeignet waren. Heute steht der Begriff fur eine Materialgruppe mit sehr variablen Eigenschaften und vielseitigen Anwendungen, die betrachtet werden sollten, um das Problem des Mikroplastiks besser zu verstehen. Im Folgenden werden daher zunachst die Historie der Kunststoffindustrie sowie die positiven und negativen Aspekte des Werkstoffs Kunststoff vorgestellt.