Miniscule amounts of radioactive substances have been found in rainwater across the nation.

The Korea Institute of Nuclear Safety said on Friday that it collected and tested Thursday's rainwater from monitoring stations nationwide except from one in Gangneung, which did not see much rain.

Radioactive iodine was found in all eleven regions, while radioactive cesium was detected in five regions, including Jeju Island and Gwangju.

Radioactive cesium was highest in rainwater from Jeju at 0.978 becquerels per cubic meter, while the levels of radioactive iodine detected in rainwater from southern provinces were generally higher.

The institute explained that if a person drinks two liters of the radioactive contaminated rain water for a year, it would amount up to one twentieth of the yearly human allowance to radiation.