Japan’s government has to release more data from ocean radiation tests to accurately assess the contamination threat to seafood, according to a statement by the Oceanographic Society of Japan.
The government should release radiation readings in sea water that are below its minimum measurement level, because even at those low quantities the radioactive elements may pose a danger when concentrated in seafood, the group, which counts 1,860 marine scientists as its members, said yesterday.
“Depending on the species, fish have been known to accumulate as much as 100 times the amount of pollutants in the environment,” Jota Kanda, a professor at Tokyo University of Marine Science and Technology specializing in marine environment, said by phone yesterday.
Radiation threats to Japan’s food chain are multiplying as cesium emissions from the crippled Fukushima Dai-Ichi nuclear power plant spread. Aeon Co., Japan’s biggest supermarket chain, said yesterday 4,108 kilograms (9,056 pounds) of beef suspected of being contaminated by radiation was inadvertently put on sale at 174 stores across the country.
The government on July 19 banned cattle shipments from Fukushima prefecture, though not before some had been slaughtered and shipped. A ban on shiitake mushrooms was extended to another area of Fukushima on July 23 because of high cesium levels, the health ministry said.
Testing of seafood off the coast of Fukushima uncovered 68 cases of fish and marine life with radiation readings exceeding the government’s safety limit, according to a report by the Ministry of Health, Labour and Welfare.
Fukushima prefecture tested 505 seafood items to discover excessive radiation levels in 15 cases of sweetfish, seven cases of salmon, seven cases of greenling and six cases of sand lance, according the report. Ibaraki prefecture, south of Fukushima, reported 5 cases of excessive radiation levels after testing 265 samples.
Seafood tests by 15 other prefectures found no other cases of contamination, according to the report. Miyagi prefecture, north of Fukushima tested 44 samples, while Iwate, further north, tested two samples.
“The scope of testing needs to increase, especially in the neighboring prefectures of Miyagi and Iwate,” Kanda said. “In Chernobyl’s case, it took about six months to a year for cesium concentrations in fish to peak.”
That said, the concentrated release of radioactive material into Fukushima’s coastal waters is “unprecedented,” Kanda said.
Japan has no centralized system to check for radiation contamination of food. Prefectural authorities and local farmers run voluntary tests. Products including spinach, mushrooms, bamboo shoots, tea, milk, plums and fish have been found contaminated with cesium and iodine as far as 360 kilometers from Dai-Ichi.
Contaminated beef entered the food chain after eating hay contaminated with as much as 690,000 becquerels of radiation a kilogram, compared with a government safety standard of 300 becquerels.
Radiation in food is measured in becquerel, a gauge of the strength of radioactivity in materials such as Iodine-131 and Cesium-137. A becquerel represents one radioactive decay per second, which involves the release of atomic energy that can damage human cells and DNA, with prolonged exposure causing leukemia and other forms of cancer, according to the World Nuclear Association.
Levels of cesium-134 in seawater near the Fukushima plant’s No. 3 reactor rose to levels 30 times the allowed safety standards last week, according to tests performed by Tokyo Electric Power Co, national broadcaster NHK reported.
“The concern is that the contaminants will travel up the food chain reaching greater concentration in higher animals,” Eiji Tanaka, a professor at Tokyo University of Marine Science and Technology specializing in marine bioresources, said in an email yesterday. “The pollutants may spread to bluefin tuna and minke whales.”
Tests of sea water further off the coast of Fukushima, Miyagi and Ibaraki prefectures showed no traces of radioactive elements, according to a July 22 report by Japan’s Ministry of Education, Culture, Sports, Science and Technology.
The minimum detection limit is defined as 4 becquerels per liter for Iodine-131, 6 bq/l for Cesium-134 and 9 bq/l for Cesium-137, the report said.
“Which means that at 5 becquerels per liter the ministry will proclaim the water safe, but concentration in fish may exceed the 500 becquerel limit” per kilogram set by the government, Kanda said.
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