A major challenge in nanosafety research is the sensitve detection of nanoparticles at environmentally relevant concentration in the complex systems involved. It is said that many studies in the field of nanosafety research „do not offer any kind of clear statement on the safety of nanomaterials“, in part because of the unrealistically high concentrations used. The radiolabelling of nanoparticles can help overcoming this obstacle as it provides an easy way of reliably detecting nanoparticles in minute concentrations despite the complexity of the matrix. We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, CeO2, Silica and TiO2 nanoparticles. The labelling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labelling utilizing the recoil of a nuclear reaction to introduce a radiotracer into the nanoparticles, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag0, [124/125/131I]CNTs, [139Ce]CeO2, [48V]TiO2, [7Be]MWCNT, [7Be]SiO2, [44/45Ti]TiO2, etc.. All the particles were evaluated for radiolabel stability and alteration of the particle properties. Using the so-labelled nanoparticles we achieved to measure the release of nanoparticles from surface coatings, the transport of nanoparticles in porous media, the interaction of nanoparticles with complex media such as sewage sludge and the uptake of nanoparticles in plants. The easy quantification of nanoparticle fractions inside the various systems allows the extraction of crucial information in order to understand and evaluate the different processes involved.