'Don't worry about eating a little bit of tainted beef'

Tatsuya Kimura / Yomiuri Shimbun Staff Writer

The concentration of cesium remaining in the meat of cattle that were fed with highly radioactive straw is dramatically lower than the reading of the straw itself, according to a radioactivity expert.

The straw purchased as feed by a livestock farmer in Asakawamachi, southeastern Fukushima Prefecture, was found last week to have been contaminated with up to 97,000 becquerels of cesium per kilogram, according to prefectural authorities. That is 73 times higher than the government-set provisional regulatory limit for pasture plants.

However, the concentration of cesium in the meat from the farmer's cattle that was shipped to Tokyo via meat processors and wholesalers measured no more than 650 becquerels per kilogram.

Yoichiro Omomo, special advisor to the Institute for Environmental Sciences, has pointed out, "Since cattle eat many other foodstuffs in addition to straw, the cesium may have diluted substantially."

Beyond that, not all of the radioactive materials digested accumulate in the cattle, said Omomo, who specializes in how radioactive substances are taken up in cattle and farm produce.

"Radioactive cesium is highly soluble in water, so if ingested, it's gradually discharged from the body through urine and sweat," he noted.

Radioactive cesium in people is also discharged via urine and sweat, so whatever remains in the body is reduced by half every 80 to 120 days, according to Omomo.

Unlike radioactive iodine, which tends to accumulate in the thyroid gland, cesium does not accumulate in any specific organ, he said.

"Suppose a man eats 200 grams of beef containing 650 becquerels of radioactive cesium daily for a whole year," Omomo said.

"The internal radiation exposure reading in this example would be up to 0.6 millisievert," he added.

"That falls short of the government-set annual exposure limit of 1 millisievert, meaning there's no need to worry about eating cesium-tainted meat several times during a certain period," Omomo said.