[转载][宫东风暑期班测测你的词汇量]2012年8月15日周三
原文地址:[宫东风暑期班测测你的词汇量]2012年8月15日周三作者:宫东风2012年8月15日周三 [宫东风暑期班测测你的词汇量] radioactive t na swim to us bl efin t na ca ght off the us coast have been fo nd to contain radioactive material from japan s q ake-str ck f k shima n clear plant, according to a new st dy. researchers fo nd "modestly elevated levels" of two radioactive isotopes in 15 bl efin t na ca ght off the coast of san diego, california in a g st 2011, according to the st dy p blished online monday by the proceedings of the national academy of sciences (pnas). the researchers said the elevated radioactivity posed no risk to p blic health as the observed levels were more than an order of magnit de lower than the japanese safety limit and were lower than other nat rally present isotopes. "we were q ite s rprised to find that bl efin carried both of these isotopes," co-a thor nicholas fisher, of new york s stony brook university, told cnn yesterday. the st dy fo nd slightly higher levels of radioactive cesi m-134 and cesi m-137 in the 15 t na, compared to bl efin t na ca ght in the same area before the f k shima n clear disaster and to yellowfin t na - which keep to the eastern pacific - ca ght before or after the accident. the st dy said the res lts provide " neq ivocal evidence" that the fish had carried f k shima-derived radioactive material across the ocean over the co rse of their easterly migration. "these findings indicate that pacific bl efin t na can rapidly transport radion clides from a point so rce in japan to distant ecoregions and demonstrate the importance of migratory animals as transport vectors," it said. the researchers emphasized that the level of cesi m isotopes detected wo ld not endanger p blic health, especially as they give off far less radiation than potassi m-40, a nat rally-present isotope fo nd in all the fish. "i personally wo ld not hesitate to eat the t na that were ca ght off the coast of california," fisher said. the massive 9.0-magnit de earthq ake and ts nami on march 11, 2011 killed tho sands of people and crippled the cooling systems at the f k shima plant, ca sing meltdowns in several of its reactors. radiation leaked into the air, soil and sea aro nd the plant, forcing tens of tho sands of people to evac ate their homes.