Traces of radioactive iodine-131 have been found at all 12 radiation monitoring centers nationwide, following the radiation leak from the quake-stricken Fukushima nuclear power plant.

Head of the Korea Institute of Nuclear Safety (KINS) Yun Choul-ho told reporters Tuesday that an extremely small amount of radioactive iodine was found in the air samples taken from 12 regions across the nation, including Seoul and Daegu.

Up to 0.356 millibecquerels of iodine-131 were found per one cubic meter, a figure that amounts to one-30,000th of a human’s yearly allowance to radiation exposure.

Along with iodine, another radioactive substance cesium was also detected in Chuncheon, Gangwon Province—0.018 millibequerels of cesium-137 per one cubic meter and 0.015 millibequerels of cesium-134 per one cubic meter.

The detected amounts of iodine and cesium are so small that health experts say the substances will unlikely pose any immediate health risks to the human body.

The detection comes a day after the South Korean government confirmed that an extremely small amount of radioactive xenon-133 was found in Gangwon Province.