Miniscule amounts of radioactive substances have been found in the air from 12 monitoring stations across the nation.

The Korea Institute of Nuclear Safety said on Monday that the highest figure recorded for radioactive iodine was 1.23 millibecquerels per cubic meter, while the figure for radioactive cesium was 0.253 millibecquerels per cubic meter.

The institute said that the levels are both negligible as the amount of radioactive iodine and cesium are about one-840th and one-760th, respectively, of the exposure of one X-ray.

The institute added that radiation levels checked by radiation monitors at 71 locations nationwide marked between 66 and 191 nanosievert per hour as of 9 a.m. Monday, all in the normal range.