Minuscule traces of radioactive silver were found in South Korean atmosphere for the first time Saturday since Japan's nuclear accident, the Korea Institute of Nuclear Safety said.

   The substance was detected in air samples taken from the central city of Daejeon and the southeastern city of Daegu, the agency said. Radioactive iodine and cesium had been found in South Korean air before, but it was the first detection of radioactive silver since the Japanese nuclear crisis.

   The agency said, however, that the detected amounts were too small that they pose little health risks to humans. The amounts are about one-3,700th of the dose of radiation emitted in a chest X-ray, it said.

   Traces of radioactive iodine were also found in 11 of the 12 checkpoints across the nation, but the amounts were about one-1,800th of the X-ray radiation dose, the agency said.

   Radioactive cesium was not found at all checkpoints, it said.

   South Korea has been keeping a close watch over radiation levels since the March 11 quake hit the nuclear power plant in the coastal Japanese city of Fukushima. (Yonhap News)