The state-run Korea Institute of Nuclear Safety (KINS) said it had found traces of radioactive iodine-131 in Seoul after analysing samples taken from the air in 12 places around South Korea, Yonhap news agency reported.
KINS said the amount of iodine was so small that there was no immediate risk to public health or the environment.
Japan's Fukushima Daiichi nuclear power plant was badly damaged by an earthquake and tsunami that hit the country on March 11 and radioactive material has leaked into the atmosphere.
Seawater near the plant has been found to contain radioactive iodine more than 1,850 times the legal limit, although it is not clear how the contamination spread to the Pacific Ocean.
The 9.0-magnitude quake and devastating tsunami that followed have left more than 28,000 people dead or missing.
Published 29 March 2011, 03:32 IST