A Study on polonium-210 distribution and internal radiation dose to the fisherman due to consumption of koraiyar river food, tiruchirapalli – India

Man has been continuously exposed to natural radiation since his appearance on Earth. The radioactive substances occurring originally in the lithosphere or hydrosphere - some of the natural radionuclides ²³⁸U series (²²⁶Ra, ²¹⁰Pb) and those of the ²³²Th series are (²²⁸Ra) considered important either from the point of view of toxicology, or for their special accumulation behaviour in the environment. The natural alpha emitter ²¹⁰Po (T_1/2 = 138.4days) is of radio-ecological interest for a number of reasons, but mainly because of its large contribution (>90%) to natural radiation dose received by many species. It is toxic to living systems, and is accumulated strongly by organisms and transferred via food along a tropic chain. River water is used for irrigation, and for industrial and domestic uses. In the present work the distribution of naturally occurring alpha emitting radionuclides such as ²¹⁰Po in the environmental matrices of Koraiyar river (Tiruchirapalli, Tamilnadu) and its internal radiation dose due to the consumption of these river food to the fisherman was studied.

Koraiyar is a seasonal river and is 5 Km away from Tiruchirappalli. The river water is used for washing purpose, and hence is called the dhoby river. In the Koraiyar river, effluents of various industries and Tiruchirappalli's treated sewage water are mixed.

Samples of water, sediment, crabs, and fishes were collected and subjected to the analyses for ²¹⁰Po activity. The suspected ²¹⁰Po concentration in Koraiyar river water was 0.75 mBq/l and in sediment sample 3.1 Bq/Kg. ²¹⁰Po activity in crab muscle and exoskeleton was 43.92 Bq/Kg and 11.34 Bq/Kg, and in the 210Po activity in fishes ranged from 45.29 to 8.87 Bq/Kg in muscle and 25.09 to 4.76 Bq/Kg in bone.

The major route of radionuclide entry in organisms is through food or through ambient water. Further, the gill membranes may play a predominant role in the direct absorption of radionuclides from water. Among the fish Clarias batrachus showed higher activity. Fishes are potentially a significant pathway for transfer of radionuclides to humans. Lower concentration of ²¹⁰Po in muscle is important in humans who consume mostly the muscle of fish. Concentration factor of ²¹⁰Po in edible portion of fish from river water worked out to be 1.3 x 10³ to 6.0 x 10⁴. Radiation dose to the fisherman has been evaluated on the basic of dietary intake of fish from the Koraiyar river, and varied from 6.39 to 54.35 ìSv/y. In general, the radiation dose due to ²¹⁰Po received by the fisherman (Sum 0.16 mSv/y) is well below the maximum permissible dose of 5 mSv/y.