Abstract
On ecosystems, the radioactive material can have several consequences: the mechanisms of self-regulation of biocoenosis are affected; the interactions and composition of flora and fauna in biocoenosis are modified etc., and on humans, radioactive material presents a major risk through external exposure and internal exposure to radiation. On the other hand, floods and droughts, among others, can have the effect that they can act as a support for radionuclides. The existence of risks of radioactive and chemical pollution on the lower course of the Danube, in the Black Sea Danube spill area as well as in the Black Sea coastal area, where a number of complex processes occur, determined the study of the radiochemical processes taking place in these areas. The paper addresses the following issues: radiation risk and nuclear risk, general hydrological characteristics, radioactivity of the Lower Danube water and coastal zone of the Black Sea, radioactivity of the Lower Danube sediments and coastal zone of the Black Sea, modeling of radiochemical processes.