Sunday, December 27, 2009

Environmental pollution

Environmental pollution

  • Pathways of human exposure to radiation
  • Sources of pollution
  • How to Manage contaminated areas?
  • Total doses

We have seen in that natural radionuclides pervade our environment. This chapter deals with the artificial radionuclides that have been widely dispersed by events such as tests of nuclear weapons in the atmosphere and the Chemobyl acci­dent and by the deliberate discharge of radioactive wastes from nuclear and other installations. Such radionuclides find their way from air and water onto the ground and into foodstuffs and so deliver radiation doses in various ways to human beings.

The release of radionuclides to the environment can occur according to the following :

-Rain washing radioactive materials out of the air

-External radiation direct from cloud

-External dose direct from radioactive materials deposited on the ground

-Internal dose from eating and drinking radioactive materials in food

-Internal dose from water intake.

1) The Nuclear Fuel Cycle

2) Nuclear weapon tests

Nuclear Accidents

4) Radioactive discharges

5) Depleted uranium

6) Transport of radioactive materials

7) Radioactive Dispersal Devices

As we have seen (and will see from other examples in later chapters), areas in various parts of the world have become contaminated with radionuclides as a result of various human activities. In cases where the level of contamination is high, measures might be needed to ensure that the area is safe for people to live or use for other purposes. For small areas, it might be possible to do this by removing contaminated soil and other materials, but for large areas the amount of material would be too large.

Other ways of protecting people include restrictions on access to or use of areas, for example, preventing house building on areas affected by mining wastes that could produce high radon levels. Chemical treatments can also be used to reduce the amount of activity that gets from soil into food. Examples of this include giving 'Prussian blue' - a chemical that increases the rate at which caesium is excreted by the cow so that it does not get into milk and meat -to cows grazing on contaminated grass in the Chernobyl area and treating the soil on Bikini Island with potassium to stop the trees absorbing caesium.

With the exception of some military facilities and those mentioned above, no other facilities that discharge artificial radionuclides to the environment cause doses much above 0.02 mSv in a year to the most exposed people; nor do they make a significant contribution to collective dose. On average, therefore, the maximum effective dose from the discharge of artificial radionuclides, other than some military facilities, is about 0.14 mSv in a year and the collective effective dose about 5000 man Sv in a year or 0.001 mSv when averaged throughout the entire global population.

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