Radioactive iodine in milk is absorbed through the bowel wall, and migrates in the blood to the thyroid gland in the neck where it may produce thyroid cancer. Strontium 90 is also absorbed through the bowel after being ingested in contaminated milk and is incorporated in bone because it chemically resembles calcium. This element may cause osteogenic sarcoma - a highly malignant, lethal bone tumor, or leukaemia, a cancer of the white blood cells. The blood cells are formed in the bone marrow, and are therefore subjected to the affects of radiation from strontium 90 in the adjacent bone. Caesium 137 is deposited in muscles of the body where it can produce malignant changes.
Plutonium is one of the most carcinogenic substances known.
It is not absorbed through the bowel wall, except in infants in the first four weeks of life when it is ingested in milk. As previously described, infants are extremely sensitive to the toxic effects of radiation. The route of entry of plutonium is by inhalation of contaminated air into the lungs. Small particles of plutonium are deposited deep in the respiratory passages, where they remain for years. It is accepted that one millionth of I gram of plutonium is sufficient to produce lung cancer 151050 years after initial inhalation of the element.