Exposure and Possible Risks of Engineered Nanomaterials in the Environment—Current Knowledge and Directions for the Future

The consequences that engineered nanomaterials (ENMs) may cause in the environment have been under investigation for more than 15 years. Hundreds of millions of euros/dollars have been invested into safety issues of ENMs, and much progress has been made in the understanding of their fate and effects in the environment. After an initial phase of “observing the effects,” research has shifted toward elucidating the mechanisms of fate and ecotoxicological effects. This also included a stronger focus on exposure issues and the development of analytical methods and computational models to predict exposure. First environmental risk assessments for ENM were performed, and much progress has been achieved on the way to nanospecific and material-specific assessments. The release of ENM from products and their transformation in technical and natural compartments profoundly affect the form in which the ENMs are present in the environment. A crucial aspect in all areas is if there are truly nanospecific issues of the novel-added functionalities of ENM that are different from dissolved metals, larger particles, or natural particles. This review outlines progress in understanding the environmental dimensions of ENMs and areas that merit further investigation: To what extent are ENMs different from their natural counterparts and how “long” do we need to track them in natural and technical systems? A major challenge will be in developing methods for studying particle-mediated processes and their effects on ecosystems and organisms in a more general sense, going beyond just ENM, for example, to natural nanoparticles, microplastics, and extracellular vesicles.