I-131

Iodine-131 is produced in nuclear weapons testing and nuclear reactor accidents. It is one of the main short-lived radioactive contaminants. It poses a great radiation hazard for humans and animals due to its ability to accumulate in the body, replacing natural iodine. It is used in medicine for radioiodine therapy of the thyroid gland. That is why you may encounter a person who has undergone such therapy, for example, in the subway.