Most of the radioactive iodine leaves your body in your urine in the first few days after treatment.

CNN: Thyroid cancer

One concern raised by such contaminants is that chemically, radioactive and non-radioactivie iodides are too similar for the body to tell apart, thus raising the risk that radioactive iodides can accumulate and lead to further health risks.

FORBES: Researchers Develop Material to Remove Radioactive Contaminants From Drinking Water