Aquatic Pollution and Coastal Management

Unit 10 : Radioactive pollution

10.4.1.Natural Radionuclides
More than 60 radionuclides occur naturally on earth which are derived from various sources.

Solid Earth Radionuclides
These are created during the formation of the earth. Since then, radioactivity decay processes have lead to the formation of daughter products some of which are U238, Th232 and K40. About 32 radioisotopes are known to be derived from these sources. The radioisotopes formed in this fashion are transported to the ocean during the normal weathering process.

Radionuclides from Cosmic Rays
High energy subatomic particles entering the earth atmosphere from space interacts with atoms in the air. For example the nuclei of nitrogen and oxygen react with cosmic rays and produce radionuclides such as C14 and tritium. The radioisotopes formed in this way can be in gaseous form and they enter the environment through rain.

Background Radioactivity in the Sea
Seawater is naturally radioactive largely due to K40, but also contains decay products of thorium and receives continuous input of tritium through the radioactivity of about 12.6 Bq/l. Marine sands have a radioactivity of 200-4000 Bq/kg and marine sediments have a radioactivity of 700-1000 Bq/kg. In parts of the world there are instances of marine sand having high levels radioactivity. The best known examples are Kerala in southwest coast of India and Rio-de-jeniero in Brazil. At one popular bathing beach at Guarapari, near Rio-de-jeniero, the visitors are exposed to a dose rate of 20µGy/hr.