Update: (Posted August 30, 2013 0646) There is a companion post in response to comments and additional information developed in the period since the original publication. End Update.

I’ll start with the bottom line first: despite all word to the contrary, there is no reason for anyone to be concerned that “contaminated” water from the damaged Fukushima Dai-ichi nuclear power station is going to cause them any physical harm, now or in the future. The only way my bottom line statement could possibly be wrong is if some really nutty activists decide to occupy the site and drink directly from the water tanks that have been assumed to be leaking. Those nutty activists would have to be very patient people, because they would have to drink that water for many years before any negative effects might show up.

Fish swimming in the harbor have nothing to worry about; people who eat fish that swam in the harbor have nothing to worry about; people who decide to swim in the harbor would have nothing to worry about. A basic tenet of radiation protection is that the farther from the source you are, the less you have to worry about, but I am not sure how I can state that you have less than nothing to worry about.

Nearly all of the fear mongering stories I have read about the water leaking from the large number of tanks on the site of the Fukushima Dai-ichi nuclear power station contain few, if any facts that allow an accurate risk assessment. A long time ago, I learned that there were several ways to respond to a report of “contaminated” water. The most effective way was to make a fairly quick determination of the level of contamination so the appropriate resources could be applied to the problem.

Radioactive contamination is not a “go; no go” question, there is an infinite spectrum of possible concentrations and total sizes; the top end of that spectrum should generate a flight response, the bottom end of the spectrum should generate a yawn. A quantity of radioactive material that is small enough to generate a yawn should not rise on the scale just because more clean water is added to the mix to make the problem seem larger.



Unlike biological pathogens, radioactive material does not reproduce. A fixed quantity never grows; it decays and gradually gets less and less dangerous. In fact, a perfectly rational, but long ago discouraged response mantra is “the answer to pollution is dilution.”

Aside: I will remain focused on the topic at hand and not discuss why that useful mantra has been actively discredited and discouraged. End Aside.

I probably should have written more about this a long time ago, but I have never understood why there were so many tanks being built at the Fukushima Dai-ichi power station to hold treated water. From everything I have read, water that is used to cool the damaged reactors is contaminated to a level that might be of concern, but then it is run through treatment systems that remove essentially all of the isotopes that would harm to the heath of any living creature. The very best place to put that treated water is the same place where most treated sewage ends up – into the vast ocean where it will never again be a source of worry or harm to anyone.

An effective, low cost solution to alleviate any concerns of local fishermen would be bringing an occasional tanker to the site. The contents of a limited number of holding tanks could be put on the tanker, which could then take the water a few miles out to sea. At that point, the treated water could be diluted into an enormously large ocean.

Warning: From here out, there is going to be a little math and some units that you might need to look up.

According to the scary stories I have read, the reason we are all supposed to be concerned is that bone-seeking strontium-90 has been detected in the contaminated water. The level has been reported as “thirty times” the drinking water standard.

Unfortunately, most “news” sources these days have a very low opinion of their readers and seem to think that using internationally accepted scientific units will confuse them. In my opinion, attempting to avoid using standard units is what confuses people.

Here is my attempt at helping you understand why I yawn when someone thinks we should all be frightened by the news that 300 tons of water contaminated with Sr-90 at 30 times the drinking water standard might have leaked out of a storage tank and might soon reach the Pacific Ocean.

According to Chapter 9 (Radiological Aspects) of the World Health Organization’s document titled “Guidelines for Drinking-Water Quality”, radiation standards for drinking water are set with some extremely conservative assumptions.

The levels are established so that a person drinking two liters of water at the limit every day for an entire year (a total of 730 liters) will receive a “committed effective dose” of just 0.1 mSv.

Note: The calculation of the “committed effective dose” value recognizes that the dose will occur over a period long after the drinking has stopped due to internal accumulation and biological half life of the isotope of concern. Because the dose is in Sieverts, it takes into account the biological damage caused by ingesting Sr-90, which emits a high energy beta particle. End note.

A dose of 0.1 mSv is 10% of the maximum allowed additional dose (1 mSv) to a member of the general public. The average background dose rate from all sources of radiation has been calculated to be 2.4 mSv/year.

For strontium-90, the drinking water standard is 10 Bq/l. The water of concern is contaminated to 30 times that standard and there are 300 tons of it. There are one thousand liters in a metric ton of water. Determining the amount of Sr-90 that might flow into the Pacific Ocean is a simple multiplication problem.

10 Bq/l x 30 x 300 tons x 1000 l/ton = 90,000,000 Bq

Written in scientific notation on a blog where I dislike making the effort to use exponents, that can also be written as 9E+7 or 9 x 10^7.

That might sound like a lot of material, but each gram of Sr-90 contains approximately 5,000,000,000,000 Bq. That can also be written as 5E+12 or 5 TBq (terabecquerels)

If someone drank two liters per day of the water that we are supposed to be afraid of for an entire year, their committed effective dose would be just 3 mSv; it would slightly more than double their annual background dose. If the entire amount of that water entered the Pacific Ocean, it would contain less than 0.00002 grams (0.02 milligrams) of strontium-90.

Now can you see why I am not worried and why I think you need to stop worrying? Of course, I expect that most of the people who have made it this far were never worried in the first place, but you might have family, friends or acquaintances who have been losing sleep in fear of the Blob – in the form of water leaking from Fukushima – coming to get them.

One more thing – the most recent stories have included concerns that additional groundwater is flowing onto the power station site an might become contaminated on its normal path to the ocean. Remember what I wrote earlier; a limited amount of radioactive material does not get any larger just because more clean water is added.

Recommended reading

Fukushima Commentary August 24 Japan’s Disastrous Flirtation with Worst-Case Scenarios

The Register – Oh noes! New ‘CRISIS DISASTER’ at Fukushima! Oh wait, it’s nothing. Again: But hey, let’s soil ourselves repeatedly anyway

New Scientist – Should Fukushima’s radioactive water be dumped at sea?

Atoms in Japan – METI Panel Clarifies Approach to Stop Contaminated Water from Leaking at Fukushima Daiichi