News story

Date: 30-May-2012
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Ocean currents head from Japan to the West Coast of the U.S. Bluefin tuna, which spawn off Japan, with many migrating across the Pacific Ocean to the West Coast of USA, sometimes up to three times in 600 days, may well be exposed to radiation out in the ocean, and might then end up in U.S. waters.

It is not thought that there will be a significant risk within the next year. But as the plume of radioactivity from the Fukushima disaster spreads across the Pacific, and as bioaccumulation occurs (when small fish get eaten by bigger fish) testing of tuna catch needs to be carried out, and results may point to rising levels of contamination.

Reports say that in August 2011, five months after the meltdowns at Fukushima Daiichi Plant, 15 Bluefin tuna had tissue samples taken, all of which contained the reactor by-products cesium-134 and cesium-137, at levels that produced radiation about 3% higher than natural background sources.
Unlike some other compounds, radioactive Cesium does not quickly sink to the sea bottom but remains dispersed in the water column, from the surface to the ocean floor. Fish can swim through it, ingesting it through their gills, absorbing it in seawater, and absorbing it by eating organisms that are already contaminated.

If levels are low in these first samples, things are likely to get worse. The 15 fish that were tested were born about a year before the disaster, and it was anticipated that they would be unlikely to be affected by Cesium contamination, so it was a surprise to find they were contaminated. The results of samples taken from fish in future are going to be very interesting.

The situation will become clearer this summer, when researchers plan to test a much larger number of samples.  Bluefin tuna that migrated last year were exposed to radiation for about a month. Fish sampled in the new program will have been swimming in radioactive waters for a longer period and it is unknown how this will affect the concentrations of contaminants in their flesh.

The new fish targeted for sampling will start arriving in US West Coast waters very shortly, and will continue arriving in the coming months. They may well be carrying considerably more radioactivity and if that proves to be the case, they may possibly be determined as being a public health hazard.

Japanese and U.S. officials are reported as saying that the amount of radiation found in the Bluefin is safe.  However, the scientific consensus is that there is no safe level of radiation, and radiation eaten and thereby taken into the body is much more dangerous than background radiation.

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