For many years the IAEA has published a set of documents aimed at assessing and limiting the radiation exposure of the population from various nuclear activities. The present publication is intended to support IAEA Technical Reports Series No.472 (TRS 472). It provides radioecological concepts, models, parameters and data for assessing site-specific past, present and potential future radiation exposures of humans and other biota in terrestrial and freshwater environments in various climate conditions. It can be used for radioecological assessment of both routine discharges of radionuclides to the environment and accidental releases. In addition, it will serve as useful background documentation for other relevant activities, such as training in radioecology and radiation protection.