[en] During the atmospheric nuclear weapon tests during the periods 1945-1958 and 1961-1962 more radioactive contaminations were produced in the environment than any other human activities in total. The most important radionuclides produced by neutrons from the explosion are ^14C, tritium and ¹³⁷Cs. They will become part of the environment by fallout, in terrestrial waters and soils. These isotopes can and have been applied for radiocarbon dating, for tritium water age dating, and for the study of sedimentation processes in rivers and lakes. Some results in Hungary for the Lake Balaton are presented. (R.P.)