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All the fish examined in the study showed elevated levels ofradioactive caesium - the isotopes 134 and 137. Caesium-137 is present in seawater anyway as a result of thefallout from atomic weapons testing, but the short, two-yearhalf-life of caesium-134 means the contamination can be tieddirectly to Fukushima. There is no other explanation for theisotope's presence. The measured concentrations were about 10 times the total caesiumradioactivity seen in tuna specimens taken from before theaccident. As a control, the team also examined Yellowfin tuna, which arelargely residential in the eastern Pacific. These animals showed no difference in their pre- or post-Fukushimaconcentrations. The research is likely to get attention because Bluefin tuna is aniconic species and a highly valuable fishery - thousands of tonnesare landed annually. But consumers should have no health concerns about eatingCalifornia-caught tuna from last year, the team says. The levels of radioactivity are well within permitted limits, andbelow those from other radioisotopes that occur naturally in theenvironment, such as potassium-40. "The potassium was about 30 times higher than the combinedradio-caesium levels. If you calculate how much additionalradioactivity there is in the Pacific Bluefin tuna caught inCalifornia relative to the natural background - it's about3%," said Prof Fisher. The scientists even calculated how much radioactivity might havebeen present in the fish before they swam across the Pacific (itwould have fallen over time) and figured it could have been 50%above background levels; but, again, this would still have met thelegal requirements for safe consumption. Tuna caught in the coming months will be subjected to new tests.These animals would have spent much longer in Japanese waters andso conceivably could have a very different pollution load. The team also believes the investigation should be extended toother migratory species that frequent Japanese waters. Fukushima pollution is potentially a very useful tool to trace theorigin and timing of animal movements. The ratio of caesium 134 to137 could be used like a clock to work out when and how long aparticular migration took. "This information might be useful in conservation efforts orin managing fisheries," said Prof Fisher. Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter. I am an expert from supuconnection.com, while we provides the quality product, such as China Ferrule Connection , Terminal Block Accessories, Screw Terminal Connector,and more.
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