Environmental health officials confirm a consistent - but very low level - of radioactive iodine in North Carolina. Gerald Speight of the state's Radiation Protection Section says the current concentration of Iodine-131 in the air is thousands of times below what would be considered a measurable dose in the body. "The levels we're seeing now are right at the limits of the detection capability of the most sophisticated instruments that we have out there," adds Speight. Iodine-131 has a half-life of eight days, meaning that it loses all radioactivity after about three months. Speight says Iodine-131 results from nuclear fission and does not occur naturally in the environment. The current levels are linked to events in Japan. Speight says state officials are now sampling the air daily to make sure the amount of radioactive iodine doesn't increase - or show up in plants or food sources.