Just how radioactive is the Pacific?

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Anyone that heard the news that the Fukushima Daiichi nuclear plant was releasing contaminated water probably felt a pang of concern. However reassurances that the Pacific Ocean is a big place and that any radioactivity will be diluted may have been misplaced.

Scientists are now calling for a marine survey to begin as soon as possible to assess any damage to the surrounding ecosystems.

The past few weeks have seen extremely high concentrations of radioactive iodine-131 and caesium-137 – the latter of which has a half-life of 30 years – in the seawater around the Fukushima reactors and up to 30km offshore.

By the end of March, levels of radioactivity in the water were tens of thousands of times higher than before the accident and it is thought that discharges – both accidental and deliberate - are on-going.

It is thought that while contamination is unlikely to cause any damage in the short term to marine organisms, that long-lived radioactive isotypes may accumulate in the food chain and cause problems for marine life.

Globally, scientists are now working on studies to assess the present and future damage. Researchers from Japan are aiming to monitor the accumulation of radionuclides in the muscles, organs, eggs and bones of marine organisms.

While a team from the French Institute of Radioprotection and Nuclear Safety (IRSN), is now predicting the level of contamination in marine organisms and sediments using estimates of the quantity of radioisotopes released from Fukushima.

The team have calculated that sediments in the region could now contain 10,000–10 million becquerels per kilogram of radioisotopes where previously amounts were undetectable; 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.

Although radioisotope concentrations in fish, shellfish and seaweed could exceed limits for human consumption for weeks, scientists believe that it is unlikely that there will be any genetic effects on marine life as affected creatures would probably disperse into the Pacific, or die more quickly.