International Atomic Energy Agency chief Rafael Grossi has surveyed the site of the Fukushima Daiichi nuclear power plant and vouched for the safety of releasing treated radioactive water into the ocean.

In a major milestone for the decommissioning of the power plant, destroyed in a massive earthquake and tsunami in 2011, the agency said on Tuesday that a two-year review showed Japan’s plans for the water release would have a negligible impact on the environment.

Japanese fishing unions have long opposed the plan, saying it would undo work to repair reputational damage after several countries banned some Japanese food products for fear of radiation.

Japan regularly tests seafood from the Fukushima area and has found it to be safe.

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Mr Grossi said there were no pending issues, after surveying the wrecked power plant and feeding flounder raised in the treated radioactive water as proof of its harmlessness.

He also inaugurated an International Atomic Energy Agency (IAEA) office on site that will monitor the release of the water, which is expected to take 30 to 40 years.

“I don’t have a magic solution for the doubts and concerns that may exist, but we do have one thing … we are going to stay here with you for decades to come … until the last drop of the water has been safely discharged,” he said on Wednesday.

The Japanese government is looking to start releasing water as early as August, the Nikkei reported on Wednesday.

The plan still needs official approval from the national nuclear regulatory body, which is expected on Friday.

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Some neighbouring countries have also raised concerns over the threat to the environment, with Beijing emerging as the biggest critic.

Chinese foreign ministry spokesman Wang Wenbin on Wednesday criticised the move towards discharging the water and threatened action if the plan should move ahead.

“The relevant Chinese government departments will strengthen the monitoring of the ocean environment and inspection of marine products import, so as to ensure the health and food security of the public,” he said, but declined to give specific details on what sort of action the government would take.

To assuage international concerns, Grossi said he will follow up his visit to Japan with a tour of South Korea and the Pacific Islands to explain the water will have no negative impact on the environment.

Prime Minister Fumio Kishida said on Tuesday his country would aim to gain acceptance both domestically and internationally with the IAEA’s endorsement.

Mr Kishida may meet with South Korean President Yoon Suk Yeol to explain the water release, when attending the NATO summit meeting in Lithuania next week, the Mainichi newspaper said on Wednesday.

Japan’s foreign minister Yoshimasa Hayashi is also preparing to meet his Chinese and South Korean counterparts mid-July on the sidelines of a South-East Asia group summit, the Yomiuri newspaper reported on Wednesday.

Japan says the water has been filtered to remove most radioactive elements except for tritium, an isotope of hydrogen that is difficult to separate from water.

The treated water will be diluted to well below internationally approved levels of tritium before being released into the Pacific.

-Reuters