Japan is planning on releasing treated radioactive water from the Fukushima nuclear accident into the ocean. They claim this will be completely safe, but there are protests going on in both Japan and South Korea, and China has just placed a ban on seafood from Japan. In a perfect world we would just have a calm and transparent discussion about the relevant scientific facts, make a reasonable decision, and go forward without any drama. But of course that is not the world we live in. But let’s pretend it is – what are the relevant facts?

In 2011 a tsunami (and poor safety decisions) caused several reactors at the Fukushima Daichi nuclear power plant to melt down. These reactors were flooded with water to cool them, but heat from continued radioactive decay means they need to be continuously cooled. The water used has become contaminated with 64 different radioactive isotopes. In the past 12 years 350 million gallons of contaminated water has been stored in over 1,000 tanks on site, but they are simply running out of room, which is why there is urgency to do something with the stored contaminated water. How unsafe is this water?

Over the last 12 years the short half-life isotopes have lost most of their radioactivity, but there are still some long half-life isotopes. This is good because the shorter the half-life the more intense the radioactivity per mass, by definition. Really long half-life isotopes, like carbon-14 (half-life 5,000 years), have much lower intensity. Also, the contaminated water as been treated with several processes, such as filtration and sedimentation. Most of the remaining radioactive isotopes have been removed (to levels below acceptable limits) by this process, although carbon-14 and tritium remain.  How much radioactivity is left in this contaminated but treated water? That is the key question.

The limit for tritium in the Fukushima water is 1,500 becquerel per liter (a standard measure of radioactivity equal to 1 radioactive decay per second). The international standard for tritium is 7,000 Bq/L – that’s for drinking water. So the treated Fukushima water is less than the accepted standard for drinking water. However, I did find this article in which the Ontario Drinking Water Advisory Council (ODWAC) recommends lowering that limit to 20 Bq/L. But this is under the principle of keep exposure “as low as possible”, not just below safety levels. In any case, 7,000 Bq/L remains the international standard.

What about the Carbon-14? The Tokyo Electric Power Company (TEPCO) claims that the levels of Carbon-14 in the treated water is at 2% of the upper limit of acceptability for water to be released into the environment. Another way to look at the levels of radioactivity is that, once the water is dumped into the Pacific, after several kilometers of diffusion the radioactivity will be at background levels. So if we just consider the physics, it seems that the radioactivity is negligible and will rapidly be diluted to the point that it is indistinguishable from the background. According to this Nature article on the topic:

Jim Smith, an environmental scientist at the University of Portsmouth, UK, says the risk this poses to nations around the Pacific Ocean will probably be negligible. “I always hesitate to say zero, but close to zero,” he says. “The nearest Pacific island is about 2,000 kilometres away.” He argues that a greater risk is posed by keeping the treated water on-site. “The risk of another earthquake or a typhoon causing a leak of a tank is higher, and they’re running out of space.”

That seems reasonable – but, some critics say we can’t just consider physics, we also have to consider biology. What if living organisms in the region of the water release concentrate these radioisotopes in their tissues? This concentrated radioactivity can then spread through the web of ocean life, causing harm. That is a reasonable question. Here is where I think the final line of disagreement is. A panel of Pacific nations who might be affected by the release say that more study is necessary. However, TEPCO reports that:

“…the company has been conducting tests in which marine organisms are raised in seawater containing ALPS-treated water. “We have confirmed that the tritium concentrations in the bodies of marine organisms reach equilibrium after a certain period of time and do not exceed the concentrations in the living environment,” the spokesperson said. The tritium concentrations then decrease over time once the organism is returned to untreated seawater.”

They also claim that there is little fishing done in the 3 km radius of the planned water release (which has already started). Essentially they are counting on the dilution effect which will not provide time for any significant bioaccumulation, which goes away once fish swim in normal seawater anyway.

My take on all of this is that the remaining levels of radioactivity in the treated water seem to be very low, and will quickly dilute to background levels once released into the ocean. It doesn’t seem plausible that there will be any significant or lasting bioaccumulation from this. More scientific research is always better, but at some point you have to make a decision. As Jim Smith pointed out in the quote above – not releasing the water is also a decision that carries its own risks, that of a local release of the water due to another weather event or accident. They are also simply running out of room so something has to be done with the water. All of the water will not be released at once, so there is time to monitor environmental effects as the water is slowly released into the Pacific. Also, there is a plan to further dilute the water before release. This doesn’t reduce the total amount of radioactive isotopes, but is just pre-dilutes the treated water so the radioactivity goes down to background levels more quickly after release.