Natural radionuclides in a tropical river subjected to pollution

The radionuclide concentrations in Periyar river at the industrial zone showed significant reduction, by factors ranging form 3 to 5 during the post-1980 period as compared to pre-1980 due to better effluent treatment practices adopted by industrial units situated on the river bank. The studies revealed that nearly 90% of Po-210 in the river environment was unsupported, showing atmospheric pathway of deposition by decay of Rn-222. The mass and activity (Ra-228) median diameters of sedimented particels of less than 63 µ were 15 ± 2.8 µm and 18 ± 2.5 µm. respectively. The particle size followed log-normal distribution. Depth distribution of Ra-228 in sediment was investigated for its concentration. This nuclide showed highest concentration at depths ranging from 10 to 30 cm. The studies have helped to identify that particles of less than 63 µm present in the sediment layer up to 30 cm were mainly responsible for transport of radionuclides in the river and its estuary.