What caused 1,200 tons of fish to wash up on Japan’s shores?

In 2011, a 9.0 magnitude earthquake caused damage to the Fukushima Daiichi nuclear power plant.

Around 1.17 million cubic tons of water surrounding the plant became contaminated. It was later stored in tanks fitted with a purification system that removes radionuclides. According to officials, the purification process has been effective in removing most of the radioactive material from the water.

However, the removal did not include tritium, a radioactive isotope of hydrogen.

This summer, the government decided to release the purified water back into the ocean, as the tanks were reaching full capacity. Precautions were taken to minimise the levels of tritium content, such as diluting the water with seawater.

While it is considered a low-energy radiation emitter and relatively harmless in small quantities, high levels of exposure can pose health risks to the surrounding environment, including disruption to the food chain, biodiversity loss, or throwing off the overall ecological balance.

Over 17 days in October, around 7,800 cubic metres (275,454 cubic feet) of purified water was discharged into the Pacific Ocean.

Despite continued assurance from the Japanese government that the process would be safe, the first release of purified water in late in August triggered China, Hong Kong, and Macau to ban seafood imports from Japan.

The washing up of mackerel and sardines came four months after the plant began its first release of the water.

Before proper tests are conducted, it’s impossible to know whether the mass death of fish was caused by the discharging of nuclear-purified water.  For now, the authorities in Japan are rebuking any claims that the two events are connected.

Clean up is expected to continue until the end of the year, given the sheer amount of fish covering the shorelines.