Anxiety and anger have been sparked by Japan’s controversial plan to dump treated waste water from Fukushima nuclear plant.

Over a million tonnes of treated waste water have accumulated at the plant since the 2011 tsunami. From 24 August, Japan will begin discharging it.

In Japan, local communities have expressed concerns about contamination despite the plan being endorsed by the UN nuclear watchdog, the International Atomic Energy Agency (IAEA).

The Japanese fishing industry and the wider region are also concerned about their livelihoods.

Japan has been accused by China of treating the ocean as its “private sewer”, and the IAEA has been accused of being one-sided. The South Korean government has said it has no objections to the plan, but many citizens oppose it.

Power plant company Tepco has been pumping water into the Fukushima nuclear reactors since the disaster. The plant produces contaminated water every day, which is stored in massive tanks.

Over 1,000 tanks have been filled, and Japan says it needs the land occupied by the tanks for new facilities to safely decommission the plant. Natural disasters could also cause the tanks to collapse.

Nuclear plants release treated waste water into the ocean as part of routine operations – although critics point out that the amount released from Fukushima is unprecedented, far greater than usual.

In addition to tritium and carbon-14, Tepco filters Fukushima water through its Advanced Liquid Processing System (ALPS).

Hydrogen and carbon-14 are radioactive forms of hydrogen and carbon, respectively, and are difficult to separate from water. As they are formed in the Earth’s atmosphere and can enter the water cycle, they are widely present in the natural environment, water, and even humans.

When consumed in large quantities, both emit very low levels of radiation.

To reduce the remaining substances’ concentrations, the filtered water is diluted with seawater before being released into the ocean via a 1km underground tunnel. At various stages as well as at the discharge site, Tepco will monitor the radioactivity of the processed water.

During a tsunami or earthquake, Tepco staff can manually shut down the discharge quickly by means of emergency valves, ensuring no undiluted waste water is accidentally released.

According to Japan’s government, the final level of tritium – about 1,500 becquerels per litre – is much lower than the level required by regulators for nuclear waste discharge, or by the World Health Organization for drinking water. According to Tepco, the carbon-14 level will also meet standards.

According to Tepco and the Japanese government, the discharged water poses little risk to humans and marine life.

The plan has also been supported by many scientists. The water released will be a drop in the ocean both in terms of volume and radioactivity. The extremely low levels of radioisotopes do not have a detrimental effect on health,” said Gerry Thomas, who advised the IAEA on Fukushima reports and worked with Japanese scientists on radiation research.a