Fukushima across the Pacific
Let’s make it clear: the release of radioactive contamination from the Fukushima NPP to the environment — the air, the land, and the ocean — is a massive disaster. There’s no other way to describe it. Radiation in the air spread far and wide, and was even detectable, though barely, on other continents, while radiation in the ocean is spreading more slowly but inexorably. We know that some of the fish caught off Japan have been too contaminated to be sold for human consumption, and that wide expanses of farmland in Japan have been contaminated as well. But what effects can be expected overseas?
Lately there have been quite a few reports of die-offs, dangerously contaminated fish, and other horrors in the Pacific Northwest which have been ascribed to the effects of radioactive contamination in the Pacific ocean from Fukushima. Many people are worried and unsure, others are convinced that these reports are factual, and the stories have found a ready audience, mainly through online media. We’ve addressed and debunked a few of them already. Could it possibly be true that hazardous levels of Fukushima ocean radiation have reached North American Pacific shores? If this hasn’t happened yet, is it likely to happen in the future? The consensus among the many ocean scientists who have been monitoring the phenomenon is that Fukushima radiation is beginning to reach the Pacific coast, the levels will be so low they will only be measurable with extremely sensitive equipment, and that while the risks to people will not be zero, they will be “insignificant.”
Let’s try to understand why.
The ocean has been naturally radioactive since primordial times, and received quite a lot of fallout during the nuclear weapons testing era. Chernobyl added additional radioactive contamination to all of the world’s oceans, though considerably more to the North, Baltic, and Black Seas than to the Pacific. In addition, the Sellafield accident released quite a lot of contamination into the Irish Sea, and nuclear accidents in other locations have contributed as well. Ocean scientists have been measuring and tracking the radiation from all of these sources for decades, and have given us a very good idea of how the radiation found in different parts of the world’s oceans differs, where it came from, and how it moves through the environment.
This historical knowledge has been very useful for understanding the effects Fukushima has had and will continue to have on the Pacific. Many excellent researchers from Japan and abroad have been investigating this closely since March 2011, and anyone who is hoping to know more about what impact Fukushima radiation will have on the ocean far from Japan– in Hawaii, Alaska, or near California, for instance — should become familiar with what Fukushima ocean studies have shown. These researchers’ collaborations have been a model of cooperation among nations and institutions, and while the picture is not yet complete, the outlines — how much radiation is in the ocean, where it will go, and when it will get there — have been fairly well estimated.
These scientists conclude that the the Cs137 levels in the waterborne Fukushima radiation now reaching the North American Pacific coast will peak at between about 0.004 and 0.010 Bq/L, compared to about 0.001-0.002 Bq/L before the accident, will stay that way for a few years, and should start declining again around 2017. Percentage-wise this means 2 to 10 times existing Cs levels, which we could say is a lot, especially since the entire Pacific will be affected. But when one considers that the added radiation represents only about 1/1000 or less of the 7.4 Bq/L of Cs 137 the US EPA allows in drinking water (Japan and the WHO both allow 10 Bq/L), most people would probably conclude that it represents a minuscule health risk if any even if you drank it. The same appears to be true concerning the risks presented by the migratory Pacific bluefin tuna caught off California that had detectable levels of Cs137 as well: someone who ate 2 kg of it a week for a year would raise their risk of fatal cancer by only 0.00002%.
As always, the Devil is in the Details. As a recent press release from the Woods Hole Oceanographic Institute points out, “This is an evolving situation that demands careful, consistent monitoring to make sure predictions are true.” Detailed summaries of the research and the conclusions after the jump.
So who’s checking?
There have been quite a few very informative papers about the impact of Fukushima radiation on the ocean. Some of the most useful include:
Aoyama, et al: Fukushima derived radionuclides in the ocean
Buesseler, et al: Fukushima-derived radionuclides in the ocean and biota off Japan
Buesseler: Fishing for Answers off Fukushima
Dr. Ken Buesseler of The Woods Hole Oceanographic Institute (WHOI) has authored or co-authored several of the most informative studies of Fukushima ocean impacts. The illustration above is from one of his presentations, and shows how Fukushima radioactive releases to the world’s oceans compare to those from Chernobyl and weapons testing, as well as to natural radiation. As you can see, while Fukushima released quite a lot of Cs137 to the oceans, the amount appears to be somewhat less than that from Chernobyl, about 1/10 of that from global testing, and only a tiny fraction of the natural radiation (mainly Uranium 238 and Potassium 40) that has always been there. WHOI is reportedly in the process of testing water samples taken from the ocean offshore off northern California, and hopefully the results will not be long in forthcoming.
The WHOI has several excellent and readable online reports about Fukushima ocean impacts:
And this post at Deep Sea News covers the key points pretty well too:
The author, an ocean scientist, admits to getting a bit snarky, and we think his assessment of the risk to people is possibly not nuanced enough, but he does a good job of refuting some of the wilder speculation.
How do researchers know what will happen to the North American Pacific coast because of Fukushima, and how reliable are their estimates?
Some of the post-Fukushima Pacific Ocean studies are simulations that begin with estimates of how much radiation was released, where the wind and ocean currents is likely to have taken it, what resulting ocean contamination we can expect, and how that is likely to change over time. Other studies are primarily based on measurements of seawater at different depths, and of the seabed. These are used by researchers doing simulations to cross-check their assumptions and conclusions, and to refine their simulations. Because the methodologies and the aspects taken into consideration vary from study to study, different simulations result in slightly different estimates of the level of ocean contamination the Pacific will experience. But they all agree that while the increase in radioactivity in the ocean off Hawaii, Alaska, and California will be measurable, it will also be minute.
Some of the terminology can be confusing. The amount of radioactivity in a substance, like food, the ground, water, or in people’s bodies, is usually expressed in Becquerels (abbreviated as Bq). This actually refers to how many atomic disintegrations are happening each second (The older unit of Curies — Ci – is still sometimes found and can be easily converted to Bq). Radioactivity in food and other solids is usually expressed per unit of weight, such as Bq/kg, while liquids are give per unit of volume. For drinking water, milk, etc, it’s usually given as Bq/L, but because the concentration of radioactivity in seawater is usually so small, it is commonly expressed as Bq/m3, that is, per 1000 liters (264 gallons). Japanese and WHO guidelines currently allow up to 10 Bq/L of Cesium in drinking water, while the US stipulates a limit of 7.4 Bq/L. For easier comparison, I’ve tried to give both per liter and per cubic meter concentrations in the following discussion.
A team of Canadian ocean scientists has been measuring seawater samples gathered along a line which extends out to about 1500 km off of British Columbia since 2011, in order to track the approach of Fukushima radiation:
This is nicely summarized by MarineChemist at DailyKos, who has been providing very informed and readable summaries of findings from peer-reviewed literature:
The Canadian team’s conclusions are that so far, the radiation seems to be arriving at the the slightly faster pace Rossi’s simulation predicted, but at levels which fit more closely to the lower estimates given by the simulations of Behrens and Nakano. Only continued measurement will show for sure.
To summarize the findings from the papers linked above:
–The peak Cesium levels in the Pacific before the start of the Fukushima disaster were between 1-2 Bq/m3 (0.001-0.002 Bq/L, again, compared to 7.4 Bq/L allowed in drinking water by the EPA).
–As ocean currents slowly transport the contamination eastward, levels in the ocean near Hawaii and the Aleutians started to climb several months ago, and in Hawaii will peak between 4-30 Bq/m3 (0.004 – 0.030 Bq/L) over the next several years, and should start declining around 2017.
–Detectable Fukushima radiation has started to reach the North American coast, and will peak this year and the next at somewhat lower levels than Hawaii, somwewhere between 2-20 Bq/m3 (0.002 – 0.020 Bq/L). In June 2013, the Canadian team measured 0.3 Bq/m3 (0.0003 Bq/L) from Fukushima close to the coast of British Columbia.
— Again, while so far measurements have suggested that the lower estimates are accurate, we won’t know for sure for some time. Regardless, the levels are 10,000 to 100,000 times lower than in the ocean off Japan in 2011, and while one could calculate a statistical probability of radiation-induced illness to humans who might swim in or drink the seawater off the Pacific Coast of North America, it’s hard to describe it as anything but insignificantly small.
The ocean map above is from WHOI, and helps put the expected increases in the Pacific due to Fukushima in perspective. As the captions point out, in 1990 the Baltic had 125Bq/m3 of Cs137, and the Black Sea 52 Bq/m3; these were mainly due to Chernobyl. The 55Bq/m3 in the Irish Sea was mainly from Sellafield. The rest is mainly from nuclear testing. Several independent reports are due to be presented soon, but Japanese gov’t data indicates that similar levels have not been seen in the ocean 20km off Japan for over a year:
At this point, the overwhelming scientific consensus, with no credible dissenters, is that the consequences for humans in North America will be very small. The scientists themselves use words like “insignificant,” “inconsequential,” “minute,” “undetectable,” or “none.” But while the overall Pacific contamination levels are expected to be much less than seen in the Baltic, Black Sea, or Irish Sea in 1990, or even today, nearly the entire Pacific will be affected, a much bigger expanse of ocean than any of these seas. And, of course, however unlikely, nature could surprise us unpleasantly. We can’t say with absolute certainty that Fukushima Pacific radiation will never pose a danger to humans or the environment around the rest of the Pacific rim, and we should definitely continue to carefully monitor its spread.
What about the radioactive tuna?
Many people are concerned about radioactive cesium from Fukushima that has been detected in migratory Pacific bluefin tuna caught near California, which had approx. 4.0 Bq/kg of Cs 134 and 6.3 Bq/kg of Cs 137 (Japanese regs allow 100 Bq/kg, the EU allows 600 Bq/kg, while the US allows 1200 Bq/kg of Cs 137 and Cs134 combined.
The original study is here:
Madigan, et al: Pacific bluefin tuna transport Fukushima-derived radionuclides from Japan to California
One of the best sources of information on the risks this contamination poses can be found in this paper:
Fisher, et al: Evaluation of radiation doses and associated risk from the Fukushima nuclear accident to marine biota and human consumers of seafood
Among the important take-aways are:
–“…doses in all cases were dominated by the naturally occurring alpha-emitter 210Po and that Fukushima-derived doses were three to four orders of magnitude below 210Po-derived doses.”
–If a subsistence fisherman, who eats more fish than an average consumer, ate 124 kg of the contaminated tuna that was caught in 2011 over the course of a year, the additional committed effective (i.e. lifetime) dose they would get from the cesium in the fish, even taking the higher risk from internal emitters into account, would be 4.7 μSv (microsieverts). They would get more than 600 times this from the Po210 in the fish, and 2.8 mSv (millisieverts) from all the radiation in the fish, including K40. On the other hand, an average consumer who ate this tuna regularly for a year would receive about a 0.9 μSv lifetime dose.
–Pacific bluefin tuna caught off California in August, 2012 were found to have less than half the levels of Cs of those caught in August, 2011; doses to human consumers would be comparably smaller.
–It is often stated that any dose of radiation, no matter how small, carries a health risk; this can only be estimated statistically because it has been impossible to detect directly at very low doses. Assuming an excess relative risk of fatal cancer of about 5% per Sv of radiation dose, the doses to the fishermen from eating a lot of this fish “…can be estimated to result in two additional fatal cancer cases per 10,000,000 similarly exposed people.” That is, it would increase a person’s probability of fatal cancer by 0.00002%. Some scientists have proposed good reasons to adopt a higher risk coefficient, 10% per Sv instead of 5%, in which case the probability would be 0.00004% instead. Other potential health consequences from Cs would lie in a similar range of probability.
We try to avoid saying what is “safe” or “unsafe,” but this is a vanishingly small risk. These fish and other species need to be continually monitored, however, in the event the contamination increases for some reason. There are important gaps in our understanding of the foodchain interactions as fish cross the Pacific, but the evidence indicates that these tuna spent time in the ocean plume close to Japan in 2011 while it was still very dense and that’s why they ingested as much Cs as they did. Fukushima continues to release contamination to the ocean, but the amount per year as estimated by the scientists cited earlier is about 1/300 of what was released during the first few months after the disaster started in 2011 (about 0.1 Pbq now vs about 30 PBq in 2011).
This continuing release poses an ongoing threat to marine species and the environment off the coast of Japan, one that shows no sign of abating anytime soon. But from what we now know, and particularly taking into account the known rate of bioaccumulaton for fish — they accumulate 50-100 times of the Cs present in the water they swim through– its contribution to radiation in migratory species that reach the US is likely to be imperceptible.
In a later post we will talk about the radioactive contamination in the ocean off Japan itself, which presents a much more painful picture.