Cesium contamination in food appears to be on wane

It's been 18 months since the Fukushima nuclear disaster contaminated much of the prefecture and beyond, and reports are still coming in about radiation in food exceeding the government limit.

Vote of support: Octopus caught off the coast of Fukushima Prefecture are displayed in a supermarket in the Ueno district in Tokyo on Aug. 2. The sign hanging from the shelf voices support for Fukushima produce and includes a test result indicating the seafood on display has no detectable radioactive cesium. KYODO

In late August, Tokyo Electric Power Co. announced that heavily contaminated "ainame" (greenlings) had been caught in the Pacific within 20 km of the crippled Fukushima No. 1 power plant. Earlier this month, sweet chestnuts from Tochigi Prefecture were found tainted with cesium beyond the government's limit of 100 becquerels per kilogram. Is it too early to stop being concerned about eating fish, meat and vegetables grown by Fukushima and neighboring areas?

Here is the latest update on food safety regarding the meltdowns in Fukushima:

Have any changes been observed in contamination levels? Overall, the data indicate food contamination has dropped over the past year. Health ministry data show that radiation from cesium has not been detectable in most vegetables declared unsafe last year. This trend is the same with beef. This is good news because last year excessive cesium levels were found in beef that had already been sold. The radiation is believed to have come from tainted rice straw fed to the cattle.

The agriculture ministry meanwhile says local governments are checking all beef before it goes to market. Only three out of the 58,460 beef samples tested have exceeded the government ceiling since April, when stricter limits for radioactive cesium were imposed on food, officials said. The crisis has been kinder to pork and chicken, with only one pork sample from Fukushima exceeding the limit since the crisis started, the agriculture ministry says.

Between April 1 and Sept. 19, local governments checked 105,913 food items, including beef and vegetables, according to the health ministry. Of those samples, 1,360 items, or 12 percent of the total, exceeded the limit for cesium. About half of the tainted samples originated in Fukushima Prefecture. When produce is found to exceed the government limit, all of the same kind of produce grown in areas surrounding the source is banned from shipment until the radiation drops to within norms.

What types of food are showing excessive contamination?

Mainly food sourced from forests, rivers and lakes in the Tohoku and northern Kanto regions and from the Pacific Ocean. This includes mushrooms, mountain vegetables, wild game, freshwater fish and bottom fish. Samples of Japanese tea and tea made from "yacon" leaves also shot through the ceiling this year. Experts say radiation tends to be higher in the forests, where tainted leaves fall and contaminate the soil, tainting plants and any animals that feed on them.

Why is cesium still high in bottom fish?

This is hard to determine. Unlike the situation on land, where experts say they have a good idea how radioactive material goes through the food chain, its movement in marine produce is not yet understood. For the most part, contamination of fish that live near the surface and at medium depths, like "konago" (sand lance), "mekajiki" (swordfish) and "masaba" (chub mackerel), has declined along with the dropping levels of cesium in the waters they inhabit, according to Fisheries Agency data. But bottom fish, such as "hirame" (flounder) caught off Fukushima, Ibaraki, Iwate and Miyagi prefectures, have been found with too much cesium. The same with "madara" (cod) caught off Aomori Prefecture — some 400 km north of the crippled power plant.

"Suzuki," or sea bass, has also been found above the government limit. Takashi Ishimaru, a professor of ocean sciences at Tokyo University of Marine Science and Technology, said bottom fish are apparently being contaminated by benthos, the tiny organism they eat. When waste and plankton carcasses tainted with radiation sink to the seabed, they are eaten by the bottom-feeding organisms, which in turn are eaten by bottom fish, he said.

Keeping a close watch: Officials on Sept. 12 check bags of rice for radiation in the town of Aizubange, Fukushima Prefecture. The circle on the screen indicates that no radioactive materials were detected. KYODO

Ishimaru said it will take "much, much more time" before all fish near the coast of Fukushima are free of contamination. Commercial fishing near Fukushima Prefecture has been voluntarily banned since March, but it resumed in June with two types of octopus and one kind of shellfish. Seven more species followed in September. They are "kegani" (hairy crab), "kichiji" (marbled rockfish), three types of shellfish — "chijimiezobora," "ezoboramodoki" and "nagabai" — and two types of squid named "surumeika" and "yariika." Cesium accumulates far less in these mollusks, experts say.

What about rice? Is there any risk of tainted rice slipping through the tests like last year in Fukushima? Learning its lesson from last year, when tainted rice was found in Fukushima Prefecture after Gov. Yuhei Sato declared its grain safe, the Fukushima Prefectural Government is checking all rice harvested this year before distribution. About 360,000 tons of it is expected to be harvested in Fukushima this year. As of last Thursday, the prefecture had checked 31,354 standard 30-kg bags of rice and found all within the radiation limit. Tested rice is tagged with an "inspected" mark bearing a QR, or quick response, code so consumers can check its cesium level.

Is the central government taking any measures to double-check food safety?

Yes. The health ministry, without notifying vendors, is purchasing food from supermarkets and over the Internet to run spot checks. The ministry says it checked 699 items between April 1 and Aug. 31, and found a package of mulberry leaf tea from Fukushima over the radiation limit.

Can we believe government data? Are there any other data that indicate contamination of food we are eating is low? Co-op Fukushima has been examining cesium levels in meals cooked by Fukushima Prefecture residents and the results are showing a similar trend. Any cesium detected is usually very low, the consumer group says. The co-op has performed the tests two times, with each round covering 100 households. The families prepare an additional setting for every meal over the course of two days for testing by the co-op. About 90 percent of the participating households used produce from Fukushima Prefecture in their meals.

Among the 100 households tested between November and March, radioactive cesium was detected in 10 meals. But the highest detected amount was 11.7 becquerels per kilogram, far below the government limit of 100 becquerels per kilogram. Cesium levels in the second set of testing between June and August showed a similar trend. Of the 100 tested households, cesium was detected in meals from just two of the 82 households the co-op has been able to confirm data from so far.

The highest amount was a mere 3.2 becquerels per kilogram, it said. If the family that made this meal ate the exact same one each day for a year, their total exposure to radioactive cesium would be 0.037 millisieverts, according to the co-op. By comparison, when someone is exposed to a cumulative dose of 100 millisieverts, the risk of dying from cancer goes up by 0.5 percent, according to many scientists. Co-op Fukushima said it will continue to perform the tests and keep track of the contamination levels.

Japan Times

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