Plastic is the common name given to a wide range of synthetic or semi-synthetic organic polymers. These polymers are lightweight, durable, and cheap which explains a global production of 359 million tonnes in 2018 (PlasticsEurope 2019). However, due to several reasons plastic items can end up in the environment where its durability eventually can cause ecological, and socio-economic harm (Galgani et al. 2013, SAPEA 2019). Special attention by science, media and policy, has been given to plastic items smaller than 5 mm, so called microplastics (MP) which, to date, can be found in almost all natural habitats (Hurley et al. 2018). It has been estimated that about 80% of the environmental plastic is released by terrestrial sources (Andrady 2011, Rochman 2018), and that riverine transport plays an important role in distributing the plastic. Over the last years, numbers of studies on (micro)plastics have increased exponentially. Still, our knowledge on occurrences and types of MP in the freshwater environment remains fragmentary. Due to the even higher analytical challenges it is yet to be determined if, how and where even smaller plastics, so called nanoplastics (NP), occur and behave in the environment.
This thesis focussed on assessing the presence of MP in the urban water cycle which describes how humans get, use and re-use freshwater. Accurate data on MP types and concentrations are needed to assess their related risks, to trace back their emission sources, and to mitigate these sources. For this thesis three fields of interest were defined. After a general introduction (Chapter 1), we (i) addressed analytical requirements to accurately identify MP and NP (Chapter 2 and Chapter 3). Applying herein defined criteria, (ii) Chapter 4 and Chapter 5 contain the results of two field studies examining MP in and around the effluents of WWTPs. And (iii) in Chapter 6 the removal of NP during drinking water purification was assessed experimentally. Finally, Chapter 7 provides answers to the posed research questions, and ends with an outlook section discussing which research topics should (not) be studied in the future. This was done based on the findings of previous chapters, of which main conclusions are summarized below.