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I watched an interesting documentary on the Japanese NHK TV last night. It was about an applied science research project on the radioactive caesium levels in fish following Fukushima Dai Ichi. Unfortunately, I cant remember all the figures and details.
In the 20 km exclusion zone, the marine levels were higher than anticipated. Initial estimations suggested that most of the radioactivity would be diluted and diffused. This has been proved wrong and high levels were found in the mud on the sea bed and in bottom-feeding fish there. It was believed that this may be because the fish fed on sandworms that burrowed in the mud but these critters had far lower levels than the fish themselves, a little inexplicable at this time.
Outside the exclusion zone, most fish (constantly monitored) are well under the acceptable limit and are OK for consumption. Just N of the Fukushima site, there is an estuary of a fairly major river. The Coriolis effect twists the fresh water current southwards, right past the plant, forming a strong coastal current which carries some of the caesium away. Monitoring of the mud over more than 200 km has generally shown a regression in distance. A few "hot spots" have nevertheless been found at more than 100 km away with levels much higher than can be easily explained.
One outstanding discovery was made ~100 km inland at a mountain lake at ~1000 m altitude. The fish, smelt and trout. had Cs levels exceeding those fit for consumption, yet the surrounding land was almost without contamination. The mud was radioactive down to 20 cm under the surface. The hypothesis is that numerous mountain streams each carried small amounts of fall-out and that the lake acted as an accumulation basin, the outlet river carrying practically nothing away.
We have not heard the end of this accident.
In the 20 km exclusion zone, the marine levels were higher than anticipated. Initial estimations suggested that most of the radioactivity would be diluted and diffused. This has been proved wrong and high levels were found in the mud on the sea bed and in bottom-feeding fish there. It was believed that this may be because the fish fed on sandworms that burrowed in the mud but these critters had far lower levels than the fish themselves, a little inexplicable at this time.
Outside the exclusion zone, most fish (constantly monitored) are well under the acceptable limit and are OK for consumption. Just N of the Fukushima site, there is an estuary of a fairly major river. The Coriolis effect twists the fresh water current southwards, right past the plant, forming a strong coastal current which carries some of the caesium away. Monitoring of the mud over more than 200 km has generally shown a regression in distance. A few "hot spots" have nevertheless been found at more than 100 km away with levels much higher than can be easily explained.
One outstanding discovery was made ~100 km inland at a mountain lake at ~1000 m altitude. The fish, smelt and trout. had Cs levels exceeding those fit for consumption, yet the surrounding land was almost without contamination. The mud was radioactive down to 20 cm under the surface. The hypothesis is that numerous mountain streams each carried small amounts of fall-out and that the lake acted as an accumulation basin, the outlet river carrying practically nothing away.
We have not heard the end of this accident.
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