Tokyo, Japan is the world’s most populous metropolitan area with over 12 million people in the metropolis of Tokyo. Tokyo is called a metropolis instead of a prefecture. The metropolis includes the wards formerly known as the city of Tokyo.
The distance from Fukushima Dai-ichi where the damaged nuclear power plant is located to Tokyo is 242 kilometers, approximately 150 miles, should send a message of how far this radioactive material travels. Obviously the question that must be asked is if and how much additional radioactive iodine is still entering the drinking water supply. An article titled “Tokyo Officials Say Radiation In Tap Water Twice Recommended Limit For Infants” describes the details.
Radioactive iodine is one of the more dangerous elements from nuclear contamination because it is something the body can’t distinguish from it nonradioactive version. The human body needs iodine for healthy functioning of the thyroid. The thyroid regulates growth in the human body. The thyroid will absorb iodine whether it is radioactive or not.
Radioactive iodine-131 is the reason potassium iodide is used to protect the thyroid from absorbing radioactive iodine. Potassium iodide is absorbed by the thyroid and since it will be full, the thyroid will not absorb the radioactive iodine. Infants and young children are particularly sensitive to radioactive iodine because they are still growing and their thyroids will respond to lower levels of radioactive iodine. High levels of radioactive iodine can cause thyroid cancer.