The current lack of commonly used protocols for dispersion, characterization, and aquatic toxicity testing of nanomaterials (NMs) has resulted in inconsistent results, which make meaningful comparisons difficult. The need for standardized sample preparation procedures that allow the reproducible generation of relevant test conditions remains a key challenge for studies of the environmental fate and aquatic toxicity of NMs. Together with the further development of optimized and cost-effective analytical techniques for physicochemical characterization that depend on reproducible sample preparation, such methods have the potential to overcome the current uncertainties with regard to NM dispersion properties, effective dose, and particle dissolution. In this review, recent data available on the challenges are summarized, especially those associated with preparing and quantifying NM dispersions, determining NM uptake and accumulation in aquatic organisms, and the transformation of organic and inorganic NM in aquatic species. Additional limitations and challenges that are specific to certain types of NMs are highlighted. The release of highly persistent carbon nanotubes (CNTs) from nanocomposites is determined to be a potential source of environmental contamination. Furthermore, the role of NM dissolution and the contribution of ions versus particles to NM toxicity are discussed. A phenomenon of particular relevance for the environment is photoactivation of NMs. This is elucidated with regard to its consequences in complex aquatic ecosystems. Widespread implementation of standardized protocols alongside the consideration of phenomena associated with different life cycle stages of industrial products is crucial to the future establishment of NM environmental risk assessment.

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Published in Environmental Science: Nano, v. 5, issue 1, p. 48-63.

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The authors acknowledge support from the EU FP7 project ‘NANoREG’ (Grant Agreement number 310584). The authors wish to thank this project for financial support of their research and for periodic teleconferences and meetings. Acknowledgements (A. M. Booth): Supported by Polish-Norwegian Research Programme (Project Contract No. Pol-Nor/237761/98/2014) and the Research Council of Norway (Contract No. 239199/O70). Acknowledgements (C. Cerrillo): Gemma Mendoza, Olatz Areitioaurtena, Amaya Igartua, Gotzone Barandika, and the ZABALDUZ Program for financing her contract with UPV/EHU in collaboration with IK4-TEKNIKER. The project was supported by the Swiss National Science Foundation (SNF, grant no. 200020_134750/1).