Evaluation of permissible level of soluble 131I containing fission products for design of protective measures in livestock industry

Among soluble radioactive products of uranium nuclear fission entering a body iodine radioisotopes are the main radiation hazards. The impact of iodine radioisotopes selectively accumulated by the thyroid on a body depends on absorbed radiation dose to the gland, they can cause hypothyroidism or athyreosis. Athyreosis of non-radiation origin is characterized by metabolism decline, fatigue, bradycardia, cessation of hair growth, roughness of the skin, alopecia, reduced animal productivity with increased fat deposition and possible death of embryos in the initial stages of pregnancy. Therefore veterinary service has the opportunity and time to arrange the necessary activities in order to minimize adverse impact of the fission byproducts on dairy cattle in territories contaminated with radionuclides. Thyroid irradiation at a dose of 100 Gy does not cause impairment of cows reproductive traits. The animals can bring full-fledged offspring, their further use should be decided after the examination by veterinary service. Irradiation of the thyroid gland of heifers at a dose of 30 Gy resulted in phase changes in thyroid hormone levels. Subsequent studies of the animals hormonal status demonstrated a recovery trend. No changes in immunological reactivity and productivity were observed in animals. It was found that absorbed radiation dose to the thyroid below 30 Gy did not cause disturbance of hormonal status of animals. This thyroid dose of a cow was registered after the introduction of 333 MBq of 131I. This activity corresponds to the activity of 5,000 MBq/animal of the different radioisotopes accumulated during 10-hours of uranium nuclear fission. Similar safe doses were obtained in an experiment on lactating cows, received 6,475 MBq/animal. If the contribution of iodine radioisotopes to the total activity of soluble uranium fission products is known, it is possible to assess the appropriateness to start the dairy cattle grazing soon after the accident.