The International Atomic Energy Agency has announced a "comprehensive and objective" review of Japan's decision to start pouring a million tonnes of contaminated wastewater from the stricken Fukushima nuclear plant into the sea. The water is currently held in about 1,000 steel tanks, and room is running out.
China and South Korea have reacted angrily - while many Japanese people have been protesting against the plan.
The government has made assurances that the water will be diluted to safe levels before being released. Some scientists agree - pointing out that the only radionuclide that will remain in the water in any quantity is tritium, which emits one of the lowest radiation doses.
But Dr Paul Dorfman, senior researcher at the Energy Institute of University College London, remains concerned.
"What we're talking about here is a million tonnes - it's an unprecedented amount... The ocean currents won't be removing this so they'll accumulate on the seabed in seas near Japan and what we'll see is a return to land and a return via the food web to humans."