As countries throughout the European Union (EU) struggle to implement the requirements of the EU Water Framework Directive (WFD), the need for robust data sets on the sources, flux and fate of a wide range of xenobiotics (defined here as man-made organic compounds, heavy metals and metalloids) is frequently referred to by both researchers and practitioners. However, the EU WFD is not the only driver, with renewed interest in the use of stormwater and reuse of wastewater (in part a response to addressing challenges posed by climate change) further emphasising the need for an in-depth understanding of the impact of xenobiotics on both humans and the environment at a global level.

As a response to this need, leading researchers and practitioners from across Europe came together as part of COST Action 636 ‘Xenobiotics in the Urban Water Cycle’ with the twin aims of assessing the role of xenobiotics in the urban water cycle and developing strategies for minimising their impact on humans and ecosystems. COST Action 636 is focussed around the four key topics: Identification, sources and fluxes; Methods for treatment; Impact assessment and Analytical issues. The articles which appear in this special issue of Water Air and Soil Pollution FOCUS bring together selected papers and discussions which took place in association with the first of these themes, Identification, sources and fluxes, but also broadens its remit to include papers related to the implications of recent research findings as well as a consideration of possible mitigation strategies.

As co-editors of this volume, we are delighted to bring together papers from contributors working throughout Europe on a variety of aspects relating to xenobiotics, reflecting both a diversity of country-specific as well as more pan-European research concerns, priorities and findings. We would like to thank both authors and reviewers for their contributions to this special volume, and gratefully acknowledge the financial support of COST Action 636, of which this special volume is an output.