For frequently used engineered nanomaterials (ENMs) CeO 2 -, SiO 2 -, and Ag, past, current, and future use and environmental release are investigated. Considering an extended period (1950 to 2050), we assess ENMs released through commercial activity as well as found in natural and technical settings. Temporal dynamics, including shifts in release due to ENM product application, stock (delayed use), and subsequent end-of-life product treatment were taken into account. We distinguish predicted concentrations originating in ENM use phase and those originating from end-of-life release. Owing to unique qualities and manifold variation possibilities of engineered nanomaterials (ENMs), numerous products and processes involving ENMs have been developed during the past decades 1-4 . Medium-term forecasts predict a constant growth of ENM production 5 . Without much doubt, the volume and variety of ENMs released into the environment during manufacture, transport, use, and disposal will increase accordingly 6 . This trend demands a comprehensive analysis of present and future toxin exposure in order to prepare for potential preventive measures 1 . Recent indications on the toxicity of already established ENMs reveal that widespread use of a substance should not be mistaken for evidence that the substance does no harm 7 . As producers engage in abrasion, burning, cleaning, or degradation of matrices containing ENMs, all environmental compartments are likely to be exposed to ENMs. To date, the investigation of toxicological and, in particular, ecotoxicological effects of ENMs has lagged behind the study of their technical qualities and the development of new applications 8 . Synthetic amorphous silicas (SiO 2 -ENMs) have been used since the middle of the last century and are produced in large amounts 9 . In recent years, leading producers of SiO 2 -ENMs have increased their production capacities, in particular for mass applications such as tires 10,11 . Nanosilver (Ag-ENM) has been used for medical purposes since the beginning of the last century 12 . Similar to SiO 2 -ENMs, Ag-ENM is quite versatile in its applications. It has antimicrobial properties and is a component of many consumer products 13 . Unlike SiO 2 -ENMs, however, Ag-ENM has been studied broadly 14,15 . Turning to CeO 2 -ENM, a large percentage is used for chemical-mechanical planarization (CMP), and CeO 2 -ENM has also been used in automotive catalytic

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As a fuel additive, cerium oxide nanoparticles may become widely dispersed throughout the environment. Commercial information from the United Kingdom (UK) on the use of cerium oxide nanoparticles was used to perform a modeling and risk assessment exercise. Discharge from exhausts took into account the likely removal by filters fitted to these vehicles. For predicting current soil exposure, scenarios were examined, ranging from dispersion occurring across the entire UK landmass to only within the urban area to only 20 m on either side of road networks. For soils, the highest predicted contamination level was 0.016 mg/kg within 20 m of a road following seven years of continuous deposition. This value would represent 0.027% of reported natural background cerium. If usage were to double for five more years, levels would not be expected to exceed 0.04 mg/kg. River water contamination considered direct aerial deposition and indirect contamination via runoff in the water and entrained soil sediment, with the highest level of 0.02 ng/L predicted. The highest predicted water concentration of 300 ng/L was associated with water draining from a road surface, assuming a restricted deposition spread. These predictions are well below most toxicological levels of concern.

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