How harmful is Japan's nuclear sewage entering the sea?

Japan officially launched the discharge of nuclear contaminated water into the sea on 24 August 2023 at 13:00 p.m. (12:00 a.m. Beijing time). Since the 2011 9.0 earthquake in Japan led to a nuclear leakage accident, Japan's Fukushima nuclear power plant has accumulated millions of tonnes of nuclear contaminated water. The Japanese government held a relevant cabinet meeting on 22 August and decided to start the Fukushima nuclear contaminated water discharge operation on the 24th despite strong opposition from both inside and outside Japan. Despite the opposition from many sides, Japan's nuclear sewage is insisting on discharging into the sea.

According to calculations by the German Institute for Marine Science and Research (GIMS), Japan's nuclear effluent will spread to most of the Pacific Ocean within 57 days, and the United States and Canada will be affected three years later, spreading to global waters within 10 years, with adverse impacts around the world. In 2021, Tsinghua University did experiments on the mechanism of nuclear effluent spreading in the Pacific Ocean regarding sewage discharge. Macro-simulation results show that nuclear sewage will reach China's coastal waters in 240 days after discharge, and will reach the North American coast and cover almost the entire North Pacific Ocean in 1,200 days.

How harmful is nuclear effluent and how long does it take for radioactive elements to be self-purified by the environment?

Radioactive substances in nuclear effluent may affect human, animal and plant health and increase the incidence of thyroid cancer. In addition, nuclear effluent may also contain harmful heavy metals, which may cause toxic effects on humans and affect health.

The 64 nuclides (including tritium, carbon 14, cobalt 60, strontium 90, caesium 137 and polonium 210) in nuclear effluent are characterised by generally long half-lives, such as tritium's half-life of 12.3 years, cobalt 60's half-life of 5.27 years, strontium 90's half-life of 28.79 years, caesium 137's half-life of 28.79 years, and carbon 14's half-life of 5,370 years. It can be seen that it takes quite a long time for these nuclides to be completely self-purified by the environment, which is unbearable to human beings.

Even if there is no direct contact with the sea, the dumping of nuclear effluent in the sea causes high radioactivity levels in a localised area and enrichment in the organisms of the sea creatures in that area, which can eventually reach the human body through the food chain, thus exposing the human body to the effects of internal irradiation.