Traces of radioactive particles were detected in air samples from seven out of 12 test areas throughout South Korea but they posed no immediate health risks to humans, a state agency on nuclear safety said Saturday.

Minuscule traces of iodine-131 were found in seven areas including Seoul, while traces of cesium-134 and cesium-137 were detected in five others, according to the Korea Institute of Nuclear Safety.

<YONHAP PHOTO-1029> 머리 쪽 방사선량은? (울산=연합뉴스) 김근주 기자 = 10일 울산동천체육관에서 열린 울산건강박람회에서 시민들이 동남권원자력의학원 직원에게 방사선량을 검사받고 있다. 2011.4.10 canto@yna.co.kr/2011-04-10 13:33:17/ <저작권자 ⓒ 1980-2011 ㈜연합뉴스. 무단 전재 재배포 금지.>
A woman receives a radioactivity check during a health fair in Ulsan on Sunday.   Yonhap News
<YONHAP PHOTO-1029> 머리 쪽 방사선량은? (울산=연합뉴스) 김근주 기자 = 10일 울산동천체육관에서 열린 울산건강박람회에서 시민들이 동남권원자력의학원 직원에게 방사선량을 검사받고 있다. 2011.4.10 canto@yna.co.kr/2011-04-10 13:33:17/ <저작권자 ⓒ 1980-2011 ㈜연합뉴스. 무단 전재 재배포 금지.> A woman receives a radioactivity check during a health fair in Ulsan on Sunday. Yonhap News

A woman receives a radioactivity check during a health fair in Ulsan on Sunday. (Yonhap News)

“The concentration levels of iodine went down compared to rain water collected the previous day,” a KINS official said.

Iodine and cesium are by-products of nuclear fission that apparently come from Japan’s troubled nuclear power plant in Fukushima where the March 11 earthquake and tsunami nearly destroyed the plant’s containment system.

The highest amount of radiation detected accounted for less than 0.01 percent of annual dose for humans or 1 millisievert, agency officials said.

(Yonhap News)