A worrying phenomenon has been discovered in Tokyo river eels that have been caught by local residents living near the Edogawa River – the eels that they have been catching, and may have eaten at one time or another, have very high cesium levels, in most cases higher than the safe levels required by the Japanese government.
Cesium-137 – normally called just “cesium” – is usually a byproduct of radioactive and nuclear processes, and is one of those isotopes that are easily spread in nature. The ingestion of high levels of cesium in the body would cause many negative effects to the health of humans. This is why the Japanese central government sets the safe limit in animals and the environment at 100 becquerels per kilogram.
The phenomenon at hand was officially noted starting with a 47-year-old self-employed woman who caught an eel from the Edogawa River in Tokyo’s Katsushika Ward n March 9. There have been reports of high cesium levels in fish from the river, so the woman sent the eel to Hideo Yamazaki, a professor of environmental analysis at Kinki University in Osaka Prefecture. Yamazaki then found that the eel had 147.5 becquerels of radioactive cesium per kilogram, higher than the central government standard of 100 becquerels. Professor Yamazaki passed on his findings to the Fisheries Agency in late March because he felt there was a need for an official investigation to back up his findings, and maybe look into other species as well. But the local governments of Tokyo and Chiba Prefecture refused to sanction official studies.
An official with the Tokyo’s fisheries division said, “Basically, only fish that enter the distribution network is subject to studies. The eel fishing season also does not start until summer.” The Chiba prefectural government was more downright blunt, saying, “No one in the prefecture catches eels for a living.” But eventually, the Japanese central government compelled both local units to sanction studies because eels were being consumed as food, which is a logical connection to make – not that it was logical enough for the two local government units.
Yamazaki conducted more studies on other eels caught by the same woman in April and May in the Edogawa river. The eels had cesium levels between 97.4 becquerels and 129.6 becquerels per kilogram, with three of the samples having cesium levels exceeding the government standard. Yukio Koibuchi, an associate professor of coastal environmental studies who has looked into the effects of cesium on marine life near the mouth of the Edogawa River, said the findings by Yamazaki may have been caused by various factors. He explained that other fish living in the river ingested cesium maybe at smaller amounts, and eels, being omnivorous, eat them in turn. “We have looked into other fish and shellfish from near the river mouth, but have yet to detect cesium,” Koibuchi said. “But, there is a need for further careful research.”
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