SEOUL - Minuscule levels of plutonium have been detected in waters off the Korean peninsula, a state-run nuclear safety agency said Wednesday.

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Traces of plutonium, a man-made radioactive material hazardous to human health, was found in 12 of 23 spots examined from March 26 through April 9, but the amounts remain around the normal and will have no effects on human health, the Korea Institute of Nuclear Safety (KINS) said.

Minute levels of radioactive iodine and cesium were also found in the air, but the amounts remain tiny enough to pose no human health risks, the KINS added.

The state agency will run radiation checks on seawater and marine life once every month to better monitor levels of radioactive contamination in the aftermath of the devastating earthquake and tsunami that crippled nuclear reactors in neighboring Japan.

Such examinations were previously conducted only biannually.