http://www.nature.com/news/2011/110412/full/472145a.htmlAs radioisotopes pour into the sea from the crippled Fukushima Daiichi nuclear plant, one reassuring message has been heard over and over again: the Pacific Ocean is a big place.
That the isotopes will be vastly diluted is not in question. Nevertheless, scientists are calling for a marine survey to begin as soon as possible to assess any damage to ecosystems in the area around Fukushima. Although the contamination is unlikely to cause immediate harm to marine organisms, long-lived isotopes are expected to accumulate in the food chain and may cause problems such as increased mortality in fish and marine-mammal populations.
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A team led by Dominique Boust, director of the French Institute of Radioprotection and Nuclear Safety (IRSN) in Cherbourg, is now predicting the level of contamination in marine organisms and sediments using estimates of the quantity of radioisotopes released from Fukushima, and the ratios of those isotopes calculated from available seawater measurements.
The team calculates that about 50 radio isotopes contribute to an overall concentration of roughly 10,000 becquerels per litre in the sea water within 300 metres of Fukushima. Before the accident, caesium-137 concentrations there were about 0.003 becquerels per litre, and iodine-131 was not detectable. On the basis of these figures, the IRSN researchers suggest that sediments in the region could now contain 10,000–10 million becquerels per kilogram; fish could carry 10,000–100,000?becquerels per kilogram; and algae, some of which are particularly susceptible to iodine uptake, could contain up to 100 million becquerels per kilogram. Japan has legal limits of radioactivity in fish for human consumption of 500 becquerels per kilogram for caesium-137, and 2,000 becquerels per kilogram for iodine-131.
"Doses will decrease very quickly with time and distance from the facility, if no further leaks occur, but there could remain a persistent low-dose component in the local marine environment for many years," says Thomas Hinton, deputy director of the IRSN's Laboratory of Radioecology, Ecotoxicology and Environmental Modelling in Cadarache, France. "The impacts are best addressed through an international long-term assessment."
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