Increasing concern and research on the subject of plastic pollution has engaged the community of scientists working on the environmental health and safety of nanomaterials. While many of the methods developed in nano environment, health and safety work have general applicability to the study of particulate plastics, the nanometric size range has important consequences for both the analytical challenges of studying nanoscale plastics and the environmental implications of these incidental nanomaterials. Related to their size, nanoplastics are distinguished from microplastics with respect to their transport properties, interactions with light and natural colloids, a high fraction of particle molecules on the surface, bioavailability and diffusion times for the release of plastic additives. Moreover, they are distinguished from engineered nanomaterials because of their high particle heterogeneity and their potential for rapid further fragmentation in the environment. These characteristics impact environmental fate, potential effects on biota and human health, sampling and analysis. Like microplastics, incidentally produced nanoplastics exhibit a diversity of compositions and morphologies and a heterogeneity that is typically absent from engineered nanomaterials. Therefore, nanoscale plastics must be considered as distinct from both microplastics and engineered nanomaterials.