[en] Nuclides of the natural radioactive decay series are well suited for investigations of environmental and geochemical processes. Examples of applications of these nuclides will be outlined: (i) A ²¹¹Pb (i.e., epiphaniometer) is used as continuous monitor for environmental aerosol at very low concentrations. (ii) Radioactive disequilibria in the uranium decay series give insight into geochemical processes. (iii) Dated (²¹⁰Pb) lake sediments and glacier ice cores allow, together with the analysis of cations and anions, a reconstruction of past environmental conditions. In the context of the 100th anniversary, the geochemical behaviour of radium in the water column and in sediments of Lake Zurich will be discussed. (author)