ABSTRACT
Different kinds of water cover more than two thirds of the Earth’s surface. Water is a medium for the transport and interaction of radionuclides with and within different compartments of the troposphere: soils, sediments, crustal rocks, biota, and even air are continuously exchanging their radioactive contents with water. This chapter presents an overview of radioactivity in the oceans. The first and last routes are the most important ones explaining the presence of natural radionuclides in rivers and lakes, while the second and third routes, together with direct discharges from nuclear facilities, are the main ways artificial radionuclides are deposited in aquatic ecosystems. Ocean waters are continuously interacting with different substrates, which act either as sources or sinks for radionuclides. Artificial radionuclides are present in the ocean as a result of different anthropogenic activities. The chapter analyzes the behavior of several natural radionuclides in groundwater.
