Micropollutants in water and wastewater represent one of the central challenges in contemporary water and environmental protection. Advances in analytical chemistry in recent years have made it possible to detect an ever-increasing number of anthropogenic substances in surface water, groundwater and wastewater, often at concentrations below 1 µg/L. However, numerous studies demonstrate that, despite their low concentrations, many of these substances exert ecological effects due to their persistence, bioaccumulation and toxicological properties, and potentially also pose risks to human health and the environment (Bertling et al., 2018; Bajer et al., 2023). Against this background, risk-based assessment approaches are becoming increasingly important for distinguishing ecologically relevant pollution loads from negligible concentrations (Fuhrmann et al., 2021).
The key groups of substances include microplastics other organic trace substances. Microplastics comprise plastic particles and fibres smaller than five millimetres, for which a size-based classification into macro-, meso-, micro- and nanoplastics has become established in the scientific literature (Thompson et al., 2004). Depending on the type of polymer, density, shape and surface properties, these particles can float in water, remain suspended or settle, which significantly influences their transport and ecological impact. Furthermore, microplastics act as a carrier medium, as organic pollutants and heavy metals can be adsorbed onto the particle surface. A distinction is made between primary and secondary microplastics based on their origin. Primary microplastics of type A are specifically produced during the manufacturing process (e.g. pellets or microbeads in cosmetics and cleaning products). Primary microplastics of type B are released during use through abrasion (particularly from tyre wear). Secondary microplastics are produced by physical, chemical and biological degradation processes of larger plastic parts in the environment. Tyre abrasion is considered the dominant source of microplastic emissions, releasing over 100,000 tonnes of microplastics annually in Germany alone (Miklos et al., 2016; Bertling et al., 2018; Venghaus et al., 2021).
Micropollutants constitute a heterogeneous group of predominantly dissolved or nanoscale substances. These include active pharmaceutical ingredients, plant protection products, industrial chemicals, endocrine disruptors, and per- and polyfluoroalkyl substances (PFAS). PFAS are of particular concern due to their extremely stable carbon-fluorine bonds, as they are practically non-degradable and accumulate in the environment and organisms over the long term. As so-called ‘forever chemicals’, they are now detectable in almost all environmental compartments (Buck et al., 2011; Glüge et al., 2020). The overarching term ‘micropollutants” encompasses anthropogenic organic substances occurring at very low concentrations; within this group, priority substances and priority hazardous substances occupy a special position, as they are subject to binding environmental quality standards under the Water Framework Directive. However, the lack of harmonised definitions for microplastics and other trace substances hinders both scientific comparability and effective regulatory governance (UBA, 2015; Ramboll, 2025).
From a regulatory perspective, the management of trace substances is primarily governed by the European Water Framework Directive (WFD) (2000/60/EC), which requires water bodies to achieve good chemical status. This is assessed on the basis of environmental quality standards. In addition to this, the amended Urban Waste Water Treatment Directive (UWWTD) (EU 2024/3019) mandates the expansion of a fourth treatment stage for larger wastewater treatment plants by 2045 and, for the first time, introduces extended producer responsibility for certain product groups, whereby producers of products associated with pollutant emissions – such as those from the pharmaceutical or chemical industries – are required to contribute financially to wastewater treatment measures, even though these sectors are not the primary contributors to overall pollutant loads (Ramboll, 2025; DHI 2025). Further regulatory instruments include the Microplastics Regulation (EU 2023/2055), which restricts intentionally added microplastics in products, and the REACH Regulation (EC 1907/2006) on the risk assessment of substances.
At national level in Germany, the Water Resources Act (WHG) forms the central legal framework for water protection, whilst the Surface Water Ordinance (OGewV) and the Groundwater Ordinance (GrwV) establish environmental quality standards (EQS) and watch lists for emerging pollutants. Despite this extensive regulatory framework, only around 29% of European surface waters currently achieve good chemical status (EEA, 2024).
The pathways by which microplastics and micropollutants enter the aquatic environment are diverse and complex. Municipal wastewater treatment plants represent a central node within this system, as they collect wastewater from households, industry, the medical sector and agriculture. It is estimated that around 92% of micropollutants inputs originate from municipal wastewater streams, as many persistent substances are not completely removed in conventional treatment stages (Golovko et al., 2021; Ofrydopoulou et al., 2022). Whilst mechanical and biological processes can retain a large proportion of particulate microplastics, this leads to an accumulation of particles in sewage sludge, which is frequently used in agriculture and thus creates additional pathways for the transfer of contaminants into soils and food chains (Schuhen & Sturm, 2020).
Against this backdrop, the use of advanced wastewater treatment processes is becoming increasingly important. Advanced treatment processes associated with the fourth treatment stage such as ozonation, activated carbon filtration or membrane technologies achieve removal rates of over 90%, but are associated with higher energy consumption and additional costs. Innovative hybrid processes that combine physical, chemical and biological processes are therefore increasingly discussed as promising complementary approaches (UBA, 2015; Bodzek & Pohl, 2022). In parallel, risk-based assessment approaches are playing an increasingly important role in regulatory decision-making. Environmental quality standards, PNEC (Predicted No Effect Concentration) and NOEC (No Observed Effect Concentration) values form the basis for this, but reach their limits particularly in the case of mixtures of substances and cumulative effects (SCHEER, 2022).
Overall, the management of micropollutants in water and wastewater is increasingly characterised by the integration of analytical monitoring, risk assessment, regulatory frameworks and treatment technologies. In addition to technical measures in wastewater treatment, source-oriented approaches, harmonised definitions and a consistent focus on the actual risk to humans and the environment are becoming increasingly important. Sustainable water protection requires integrated strategies and close cross-sectoral cooperation.
