Sea change in ocean radiation after Fukushima

Sea change in ocean radiation after Fukushima

Five years after the meltdown at Japan's Fukishima nuclear power plant - one of the worst disasters in history - radiation levels across the Pacific Ocean are quickly returning to normal.

The huge magnitude 9 quake and subsequent tsunami which hit the northeast of the country did considerable damage including to the Fukushima Daiichi plant.

The destruction of the plant caused radiation levels off the coast of Japan to be tens of millions times higher than normal.

Now a study, published in the Annual Review of Marine Science, says in the last five years those levels have dissipated, though there is still radioactive material coming from the plant.

The study says the Fukushima disaster is the largest release of radioactive material into the ocean.

It looked at radioactive caesium levels in the ocean from Japan's coast to North America. Caesium is a by-product of nuclear power which is highly soluble in water, making it the best way to measure the release of the material into the ocean.

Professor of Environmental Radiochemistry Pere Masqué, who co-authored the report, says the data shows the level of radioactive material has dropped rapidly.

"Oceanic currents have dispersed the radioactive material across the Pacific Ocean as far away as North America," he says.

"Radiation levels across the ocean are likely to return to levels associated with background nuclear weapon testing over the next four to five years."

He says in 2011, around half of fish samples in the waters off the coast of Fukushima contained unsafe levels of radioactive material.

By 2015, that had dropped to less than 1 percent above the safe limit.

However, prof Masqué says there still needs to be continued monitoring, though there's been a lack of support to keep it going.

"The seafloor and harbour near the Fukushima plant are still highly contaminated and monitoring of radioactivity levels and sea life in that area must continue."

The international review was done as part of the Scientific Community of Oceanic Research.