Radioactive and biochemical researches prove that after big reactor breakdowns nuclear explosions pastures and vegetation get polluted with radioactive iodine 131. High level of radioactive contamination has been established lucerne and other grasses, which required the prohibition of feeding farm animals with green fodder from the first slope. Milk is the most affected by the radioactive contamination of food of animal origin. Caught up in the human body radionuclides distributed in various organs, tissues and systems, they have complex kinetics, which depends on the nature of the metabolic processes. The distribution in the body depends on the manner of introduction of the radionuclide.