Engineered nanoparticles in soils and waters.

Over the last decade, the variety and number of products and techniques based on the use or the addition of engineered nanoparticles has increased dramatically. This includes among others the use of e.g. silver, titanium dioxide, or other nanoparticles in amultitude of personal care products, clothing, colors, and other consumer products (Schaumann et al., 2015-in this issue), and their direct application in the environment, e.g., for site remediation (Fajardo et al., 2015-in this issue; Schöftner et al., 2015-in this issue) or drinking water treatment (Simeonidis et al., 2015-in this issue). It is widely accepted that such nanoparticles can enter aquatic and terrestrial ecosystems and may impact biotic and abiotic processes in those environments (Schaumannet al., 2015-in this issue). The environmental relevance was recognized longer than a decade ago, and in contrast to the situation for other innovativematerials and compounds, the research on potential environmental impacts of engineered nanoparticles has actually started before first negative environmental effects were reported. The pioneer researchers were challenged by limited analytical access to the nanoparticles and demanding experiments arising from the distinctive features of these emerging materials. Not only the chemical composition, but also specific particle characteristics determine their mobility, chemical affinity and biological effects. Even today, it is still highly challenging to detect nanoparticles in environmental matrices and distinguish them from an omnipresent natural colloidal background. The presentations and discussions on the International Workshop Nanoparticles in Soils and Waters: Fate, Transport and Effects, held 11th–13th March, 2014 in Landau in der Pfalz, Germany, with 81 participants from 15 countries, 32 oral and 29 poster presentations (Schaumann, 2014), led to a common agreement that it is reasonable and required to summarize and critically discuss current approaches and research activities in a special issue on engineered nanoparticles in soils and waters. This special issue is a collection of 18 publications, part of which is based on presentations during the workshop in Landau. The publications cover awide spectrumof relevant issues related to engineered nanoparticles in the environment: they (i) stand for the current state of knowledge, (ii) demonstrate actual approaches to experimentally investigate fate and biological effects of six representatives of engineered nanoparticles: Ag, AgCl, TiO2, zerovalent iron, magnetite and copper oxide and (iii) present new approaches for characterizing and modeling fate, effects and the life cycle of nanoparticles. As a large part of engineered nanoparticles enter the environment via wastewater, they will pass waste water treatment systems, which then serve as hotspots for their transformation determining the colloidal speciation and the chemical status of the nanoparticles released from the wastewater treatment plants. This is central for silver (Kaegi et al., 2015-in this issue), but also for other oxidic and metallic nanoparticles (Schaumann et al., 2015-in this issue). Also use activities for products containing