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Eating unchecked homegrown vegetables and wild game from radiation-tainted areas on a regular basis can lead to high levels of internal radiation exposure, according to the results of a study published Tuesday in the U.S. online science journal PLOS ONE.

However, levels of radioactive cesium detected in the bodies of the study’s participants declined once they stopped eating highly contaminated food, said the researchers, who called for renewed efforts to raise people’s awareness of risky foods at a time when public interest appears to be dwindling.

The study focused on Minamisoma, which stretches about 14 to 38 km north of the Fukushima No. 1 nuclear plant. Researchers followed nine people, who were the only ones out of 30,622 examinees from the city to have internal cesium-137 levels greater than 50 becquerels per kilogram in screenings between March 11, 2012, and March 10, 2013. That’s roughly equal to 0.1 to 0.2 millisieverts per year.

Cesium-137 levels among the nine participants ranged from 3,230 to 15,918 becquerels per body, which corresponds to between 0.07 to 0.53 millisieverts per year, the report said. The International Commission on Radiological Protection set a radiation exposure limit under normal situations of 1 millisievert per year and said cumulative exposure of 100 millisieverts would increase the chance of death by cancer by 0.5 percent.

The study said the participants, aged 60 to 74, consumed “homegrown produce without radiation inspection, and often collected mushrooms in the wild or cultivated them on bed-logs in their homes.”

The person with the highest levels regularly ate wild boar meat and river fish, the report said. Wild game, river fish and wild mushrooms are highly contaminated and banned from being shipped out of Fukushima Prefecture.

A few months after being screened, the participants were advised to consume mainly food from supermarkets and to refrain from eating potentially contaminated foods, such as mushrooms, mountain vegetables and wild game, without having it inspected first. The researchers found that the degree of contamination fell across the board. Most of the cesium-137 levels were halved in about three months and dropped to less than a third in six months.

The study was led by Masaharu Tsubokura, a physician at the University of Tokyo’s Institute of Medical Science. He said even though most of the Minamisoma residents’ internal radiation exposure level are nondetectable, it’s time to think about ways to support those who have little knowledge about, or interest in food contamination, as prolonged internal exposure may increase their risk of developing cancer.