Japan Is Releasing Wastewater Into the Pacific: What to Know About Radioactivity and Seafood

Early afternoon local time on Thursday, after years of questions and criticisms directed at the plan, Japan has begun the controversial release into the Pacific Ocean of water previously used to cool the reactors at the defunct Fukushima Daiichi Nuclear Power plant after they were damaged in 2011 by a massive earthquake and tsunami.

The 1.3 million metric tons of treated wastewater—enough to fill more than 500 Olympic-size swimming pools—are currently stored in more than 1,000 tanks at the site of the power plant, and it is expected to take up to four decades to finish emptying all of it into the sea.

The plant manager Tokyo Electric Power Company (TEPCO), the Japanese government, and international agencies have conducted multiple assessments of the filtering process to decontaminate the water, and they have declared the plan to be safe according to scientific standards, but some neighboring nations, environmental advocates, and those involved in the seafood industry have starkly opposed the plan, claiming that the data is neither sufficient nor conclusive to ensure the water will be harmless.

The governments of China and Hong Kong have already taken measures to ban fish, sea salt, and seaweed imports from Japan, and South Koreans, despite assurances from their own government, have begun shunning seafood from Japan amid concerns about radioactivity risks.

The situation—with strong feelings expressed on either side—has left many consumers around the globe anxious and confused. Just how toxic will the tuna from the waters off the coast of Japan be? Will your next plate of sushi be safe to eat? TIME spoke to four scientists for their insights. Here’s what they had to say.

You can’t completely avoid radioactivity

Radioactive material can kill you. Scientists agree on that. Simply put, radioactivity refers to the disintegration of atoms. But at the same time, everyone, everywhere, is exposed to radioactivity every day, according to the International Atomic Energy Agency (IAEA). Radiation, more broadly, is present in sunlight and soil, in the air we breathe and the food we eat. It’s also in the technology we use, from X-rays to microwaves. But not all radiation is harmful to humans, and what’s most important is the amount of radioactive exposure.

The oceans already have a fair share of radioactivity, long before Japan started releasing its treated wastewater into the Pacific. Most of the radioactivity is from naturally-occurring elements, but it’s also been introduced by nuclear submarines, past nuclear weapons tests, and previous discharges from power plants across the world.

Among the commonly found radioactive isotopes in the ocean is tritium. It’s also the isotope that can’t be removed from Fukushima’s wastewater, despite repeated treatment. TEPCO’s advanced liquid processing system reduces 62 of 64 radioactive elements to acceptable thresholds under international safety standards, save for tritium and carbon-14. The treated wastewater is then diluted to a concentration of 1,500 becquerels (units of radiation released) per liter, which is around a seventh of the radioactivity level of drinking water under the World Health Organization’s guidelines. According to the Canadian Nuclear Service Commission, a person would need to take in billions of becquerels of tritium before seeing a health effect.

Jim Smith, a professor of environmental science at the University of Portsmouth, who has extensively studied the impact of radioactive pollutants on the environment, tells TIME fish and seafood from Japan would still be safe to eat and farm.

“If you eat a fish that has tritium, most of the tritium passes through as water, like water through our bodies,” Smith says. “As the fish grows, it accumulates in the muscle, and then you're eating an organically bound form. It does increase the rate of what we call the radiotoxicity factor… but it's still incredibly low.”

The average person’s exposure to radiation from natural sources, according to the IAEA, is 2.4 milliSievert (mSv, a unit of absorbed radiation) per year, and the International Commission on Radiological Protection recommends a maximum annual dose of 1 mSv of non-natural radiation exposure from things like X-rays or air travel (a chest scan, for example, is estimated to give a dose of 0.1 mSv, while an East Coast to West Coast flight is estimated to expose travelers to 0.035 mSv). A dose of 100 mSv is believed to increase the risk of developing cancer by 5%. TEPCO’s assessment of its water treatment process shows the radiation of the treated water, if a human were to be exposed to it, has an exposure dose of at most 0.0003 mSv annually. 

The risks are very, very low—but not zero

Rudolf Wu, a professor of environmental science at the Education University of Hong Kong, tells TIME the risk of radiotoxic effects depends both on exposure concentration and duration of exposure. “We all know that smoking is no good, that smoking can cause lung cancer. But this does not mean that [if] you just smoke once [in] a while, [it] will cause cancer,” he says. He cautioned, however, that continuous exposure to low concentrations does pose a risk.

Ken Buesseler, a marine geochemist from Woods Hole Oceanographic Institution in Massachusetts, similarly tells TIME he’s not concerned about the safety of seafood from Fukushima because of the rigorous testing processes that have been implemented to ensure radioactivity levels remain low.

“They have extensive testing programs in Japan,” he says. “I know they test their fish more thoroughly than any other country.”

Japan plans to test flounder and other seafood daily for tritium and any radiation-caused abnormalities in surrounding areas of the plant. (Fish in the area where the water is directly released—through an underground tunnel ending about one kilometer away from the shore—won’t typically be consumed anyway: fishers are voluntarily avoiding making their catch within 10 km. of the plant, according to Nikkei Asia.)

Still, not every scientist is convinced of the precautions being taken. “When we see radionuclides going into the ocean, [it’s] very unlikely they will kill anything,” says Bob Richmond, research professor at the University of Hawaii at Manoa and the director of Kewalo Marine Laboratory. But, he adds, “death is a rather crude estimator of stress. You don't wait for something to die before you intervene.”

Richmond is a scientific adviser to Pacific Island states that have opposed the Fukushima discharge plan. He tells TIME that Japan’s extensive monitoring plans do not actually mitigate health risks posed by dumping the wastewater into the ocean.

“It’s the same thing as saying, ‘I'm going to smoke three packs of cigarettes a day, but I'm not worried because I'm gonna get a chest X-ray every year. That's my monitoring programme.’ One year you get a lesion on your lung, and you don't say, ‘OK, I'm done smoking, I see the lesion. I'm going to quit.’ You've got cancer.”

(For what it’s worth, smoking one pack of cigarettes a day is estimated to amount to 0.36 mSv per year.)