Transport and Fate of Microplastics in Freshwater Sediments

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Microplastics (<5 mm in size) have become emerging pollutants and research has shown their detrimental effects to public health and the environment. While considerable research exists on microplastics in the marine environment, freshwater and freshwater sediments have not yet been studied with such detail. However, microplastics have been detected in freshwater bodies around the world. As primary particles or secondary products of macroplastics degradation they can cause toxicity directly, or by acting as vectors for sorbed contaminants. Recent studies suggest that microplastics can enter our food chain and that endocrine disrupting additives, such as Bisphenol A (BPA) and Nonylphenol (NP) can leach into freshwater resources during microplastics transport. Hereby, streambed sediments may represent potential hotspots for microplastics accumulation. The overall research aim of this project is to study the transport and accumulation of microplastics in freshwater and freshwater sediments.This project aims to answer the following two fundamental questions:(i) Which processes control the transport and accumulation of microplastics of different shapes, densities or composition and how do potential microplastics hotspots form at the freshwater-sediment interface?(ii): How can transport and accumulation of microplastics as well as the release of additives (such as BPA, NP) from microplastics be described and predicted under variable hydrodynamic, biogeochemical and sediment conditions?To answer these questions the following two work packages (WP) are proposed:WP1 will focus on uncovering the mechanisms of property (size, shape, composition, density buoyancy) dependent microplastics transport, to systematically study how and where different types of microplastics can accumulate at freshwater-sediment interfaces, with respect to varying hydrodynamic, streambed morphological and sediment conditions. For that, artificial river flume experiments will be conducted to simulate transport and accumulation of a representative range of primary and secondary microplastics for variable sediment, streambed morphological and hydrodynamic conditions. Flumes with representative streambed topographies will be used and additive release will be investigated during the experiments. Microplastics will be characterized using techniques such as single particle ICP-MS to determine the microplastics particle size or FT-IR to determine the type of microplastics polymer. During experiments, biogeochemical conditions in the flume sediments and biofilms as well as concentrations of BPA and NP in freshwater and pore water will be monitored to analyze the reactivity of formed accumulation hotspots.WP2 will focus on building and implementing a modeling tool to predict microplastics fate and transport and additive release at the freshwater-sediment interface. To overcome limitations of current models, the Lattice-Boltzmann method will be explored as a new modeling approach.