Yellow dust blowing over South Korea every year from China is believed to contain radioactive materials presumed to have been leaked from nuclear power plants in the neighboring country, a state think tank said Sunday. 

Small amounts of cesium-137, a highly radioactive material, have been detected in the air and surface of South Korea between February and April, when the dust gets most serious, over the past 10 years, the Korea Institute of Nuclear Safety said in a report submitted to an opposition lawmaker.

The hazardous dust usually sweeps South Korea in spring every year.

Yellow dust -- fine sand blown from China and Mongolia every spring that sometimes includes toxic chemical smog emitted by Chinese factories -- can cause respiratory disorders.

The atmospheric concentration of cesium-137 reached up to 252 becquerels per cubic meters, especially when the yellow dust continued for up to 11 days, the institute said. The most recent figure was 89.6 becquerels per cubic meters, a relatively high amount, measured for three days in March last year.

On Saturday, South Korea was put under the first yellow dust advisory of the year.

Because the substance mostly is a product of artificial nuclear fission, it usually does not occur in nature to any significant degree until nuclear weapons testing begins.

A cesium concentration of more than 50,000 becquerels per cubic meters is considered harmful to the human body.

However, the lawmaker warned that the cesium level could increase in the future because China is building more nuclear power plants.

"We need to prepare for the potential danger, learning from the massive earthquake in Japan," said Rep. Byun Jae-il of the main opposition Democratic Party (DP).

The magnitude-9.0 earthquake that devastated Japan's northeastern region on March 11 triggered blasts in three nuclear reactors at the Fukushima plant, raising fears that radiation from the area could affect other parts of the world.

(Yonhap News)