Nano-scale zero-valent iron (nZVI) is highly-attractive material that is widely studied and used for pollution abatement, and thus it is one of the most abundant types of engineered nanoparticles introduced into the environment. Nevertheless, there is still a lack of information about the extent of nZVI migration and fate in real groundwater conditions and associated environmental impact and risks related to its introduction into the groundwater/soil. The present paper proposes a new analytical approach based on a multi-elemental signatures (ICP-MS analyses of trace elements in particular nZVI type and soil/groundwater samples) enabling easy tracing of nZVI and their transformation products, as well as their distinguishing from background colloids. A multi-elemental signatures approach was verified under laboratory conditions (in a large-scale sand-filled tank) and subsequently verified at three contaminated sites remediated with nZVI. Multivariate data analysis on 39 elements, such as principle component analysis (PCA), demonstrates that the method can be used to observe changes in signatures over time and it enabled us to confirm the presence of nZVI in monitoring wells. PCA analysis indicated that lanthanides are particularly suitable for tracing nZVI particles.