Monday, August 22, 2011

"Ecological Half Life" of Cesium-137 May Be 180 to 320 Years?

A Wired Magazine article dated December 15, 2009 cites a poster session presentation of the research of the Chernobyl exclusion zone at the American Geophysical Union conference in 2009, and says radioactive cesium may be remaining in the soil far longer than what the half life (30 years) suggests.

To note: it was a poster session presentation, and I'm looking to see if it has been formally published in a scientific paper since then.

From Wired Magazine (12/15/2009):

SAN FRANCISCO — Chernobyl, the worst nuclear accident in history, created an inadvertent laboratory to study the impacts of radiation — and more than twenty years later, the site still holds surprises.

Reinhabiting the large exclusion zone around the accident site may have to wait longer than expected. Radioactive cesium isn’t disappearing from the environment as quickly as predicted, according to new research presented here Monday at the meeting of the American Geophysical Union. Cesium 137’s half-life — the time it takes for half of a given amount of material to decay — is 30 years. In addition to that, cesium-137’s total ecological half-life — the time for half the cesium to disappear from the local environment through processes such as migration, weathering, and removal by organisms is also typically 30 years or less, but the amount of cesium in soil near Chernobyl isn’t decreasing nearly that fast. And scientists don’t know why.

It stands to reason that at some point the Ukrainian government would like to be able to use that land again, but the scientists have calculated that what they call cesium’s “ecological half-life” — the time for half the cesium to disappear from the local environment — is between 180 and 320 years.

“Normally you’d say that every 30 years, it’s half as bad as it was. But it’s not,” said Tim Jannik, nuclear scientist at Savannah River National Laboratory and a collaborator on the work. “It’s going to be longer before they repopulate the area.”

In 1986, after the Chernobyl accident, a series of test sites was established along paths that scientists expected the fallout to take. Soil samples were taken at different depths to gauge how the radioactive isotopes of strontium, cesium and plutonium migrated in the ground. They’ve been taking these measurements for more than 20 years, providing a unique experiment in the long-term environmental repercussions of a near worst-case nuclear accident.

In some ways, Chernobyl is easier to understand than DOE sites like Hanford, which have been contaminated by long-term processes. With Chernobyl, said Boris Faybishenko, a nuclear remediation expert at Lawrence Berkeley National Laboratory, we have a definite date at which the contamination began and a series of measurements carried out from that time to today.

“I have been involved in Chernobyl studies for many years and this particular study could be of great importance to many [Department of Energy] researchers,” said Faybishenko.

The results of this study came as a surprise. Scientists expected the ecological half-lives of radioactive isotopes to be shorter than their physical half-life as natural dispersion helped reduce the amount of material in any given soil sample. For strontium, that idea has held up. But for cesium the the opposite appears to be true.

The physical properties of cesium haven’t changed, so scientists think there must be an environmental explanation. It could be that new cesium is blowing over the soil sites from closer to the Chernobyl site. Or perhaps cesium is migrating up through the soil from deeper in the ground. Jannik hopes more research will uncover the truth.

“There are a lot of unknowns that are probably causing this phenomenon,” he said.

Beyond the societal impacts of the study, the work also emphasizes the uncertainties associated with radioactive contamination. Thankfully, Chernobyl-scale accidents have been rare, but that also means there is a paucity of places to study how radioactive contamination really behaves in the wild.

“The data from Chernobyl can be used for validating models,” said Faybishenko. “This is the most value that we can gain from it.”

Update 12/28: The second paragraph of this story was updated after discussion with Tim Jannik to more accurately reflect the idea of ecological half-life.

Image: flickr/StuckinCustoms

Citation: “Long-Term Dynamics of Radionuclides Vertical Migration in Soils of the Chernobyl Nuclear Power Plant Exclusion Zone” by Yu.A. Ivanov, V.A. Kashparov, S.E. Levchuk, Yu.V. Khomutinin, M.D. Bondarkov, A.M. Maximenko, E.B. Farfan, G.T. Jannik, and J.C. Marra. AGU 2009 poster session.


Anonymous said...

Wasn't there a powerpoint presentation on here yesterday showing neptunium at Fukushima? I was looking for it and I can't find it anymore.

Anonymous said...

The half life of a radioactive isotope refers to the time it takes for said isotope to become half as radioactive as it was when it first became unstable. It usually takes 10 half lifes for an isotope to become "stable." With a half life of 30 years Cesium-137 will be dangerous for 300 years. A good thumbnail estimate for an isotope to be dangerous is to multiply the half life by a factor of 10. I don't know why anyone would think Cesium-137 would be stable and "safe" after only 30 years.

Anonymous said...

No, the half life refers to the time it takes for half of the atoms to decay into other products. So in 30 years, half of the cesium from Chernobyl should have disappeared (or, more precisely, decayed into other products - Barium137 I think). In 10 half lives, the isotope should have decayed to a point to where the amount is insignificant compared to the original amount. Of course, if you start with a massive amount of a dangerous isotope, then even after 10 half lives you may still have a dangerous amount. In the case of cesium, if you have land that is contaminated with 1000 bq/meter, half of that cesium will decay in 30 years, and your land will then be contaminated with 500 bq/meter. (Gradual decay of course, not all of a sudden).

arevamirpal::laprimavera said...

@anon at 1:42PM, I took it down temporarily after receiving a correspondence that accused me of:

- destroying the career of a young scientist whose paper that include this data is being peer-reviewed
- that I don't care about the plight of Iitate-villagers, unlike the correspondent
- posting the article only to increase traffic to my blog

among many others. All I did was to post what's already been on the net for over a month, on this researcher's website, no less. Anyone can access it.

It was a rather rude correspondence, so much so that caused me to pull the article for the fear that whatever else this correspondent may do.

You can probably still see/download it on his site, even though I warned this correspondent that if they are so concerned that should be the first thing they remove, before badmouthing me for posting the public information.

If the researcher handed out the data to people who attended the public seminar as well as posted it on his public website and that data was supposed to be secret until the peer review is over, I don't know what to say to him or to my correspondent other than "???"

Viola said...

Faybishenko was one of the panelists at NRC: RIC 2011 Agenda, International Panel Discussion on Radionuclide Sources and Migration in the Subsurface
Ironically, the date was March 10, 2011...

He has written a lot; for sure it's somwhere out. Maybe here?
Faybishenko, Boris, Young, Alvin L., Baryakhtar, Victor G., Taboas, Anibal L. and Habegger, Loren. 2003. Reflections on the Chernobyl Accident and the Future of Nuclear Power. Environmental Science and Pollution Research(Special Issue 1), LBNL-54152.

Anonymous said...

The pen could be mightier than the sword,but even an army of paid propagandists cannot really have much impact on the relative permanence of unstable elements.

Of course the words that could have helped,'Not Approved' would never come from the enablers pen.

netudiant said...

Cesium is pretty tightly bound to soil, afaik.
So barring some way of mobilizing and removing it, perhaps by growing crops on the land and then disposing of them, it is difficult to see why the environmental half life should be as low as a few decades.
If nothing else, this practical insight should guide the decisions about the future of Fukushima's surroundings.
Something akin to a memorial forest might be the best that can be done. Resettlement of the former residents is clearly essential.

Viola said...

Here we go:

Long-Term Monitoring of Radionuclides in Soils and Groundwater:
Lessons Learned from Chernobyl
Boris Faybishenko
Lawrence Berkeley National Laboratory

arevamirpal::laprimavera said...

Many Fukushima Farmers insist on farming in Fukushima, same for cattle farmers. They blame consumers in big cities for "baseless rumors" that "hurt" their produce, and are determined to have them eat their produce by launching a governmment-sponsored PR campaign with fancy website.

Reminds me of the Fed and Treasury assuring people that the big Wall Street banks are safe and solvent.

Anonymous said...

"Wasn't there a powerpoint presentation on here yesterday showing neptunium at Fukushima? I was looking for it and I can't find it anymore."

"@anon at 1:42PM, I took it down temporarily after receiving a correspondence .."

Perhaps they didn't like this article,

Iitatemura's cattle industry in disarray

"The purpose of my life is to raise breeding cattle. The cows' bloodlines cross more than a dozen generations." the 60-year-old farmer said.

So because of those 12 generations of cattle the people should poison themselves to keep the hapless farmer in business?


"Many Fukushima Farmers insist on farming in Fukushima, same for cattle farmers. They blame consumers in big cities for "baseless rumors" that "hurt" their produce, and are determined to have them eat their produce .."

Read this article,

Their attitudes are in fact belligerent. Time to gain a new purpose in life, 60-year old.

Anonymous said...

@ Anon 4.37pm
Time to bloody 'retire' the 60 year-old git if you ask me.

arevamirpal::laprimavera said...

@viola, vielen Dank.

Anonymous said...

It's not the farmers fault, FFS!! They simply haven't had the true situation explained to them by the government because...the truth is simply too harsh and damaging to tell.

'your land is unihabitable and your food and produce is inedible and will be for at least 300 years...what is more is that we can't afford to compensate you, for if we admit what we all actually know, there is no way to compensate all the affected people from Tohoku and as far south as Shizuoka, west to Niigata, north to Aomori and the fishermen who ply the Pacific Ocean for the restaurants in Tokyo.'

It's a hard one to swallow. Japan has been cut in half really and we're only going to find out real nice and slowly over the years.Either that of have a very nasty shocker now which could destroy what is left of this economy and country as we know it, millions of refugees, mass movement of the younger generations, families split up, old left to die etc...For a politician, unpalatable scenes for the TV. And the end of worldwide nuclear energy, period.

Maybe Iitate mura beef can survive though. They just have to make sure that nobody under the age of 60 eats it. Come to think of it, all the radioactive food could be eaten by the old folk. Thata's not being malicious, rather a method of survival for the younger generation-who in this instance are far more important I'm afraid, and a way to keep farming the rice and vegetables etc so that people dont lose their livelihoods.
It's a grim thought though. And puts a new face on the 'stoicism' of the Japanese...

Anonymous said...


Chernobyl is essential vitamin: just send in the japanese experts, makedo "interviews" with MSNBC mas0ns...

While Sahara winds can lift sand, cause sandstorms in Florida, luckily cant do that from Chernobyl neither from Japan soil. Just ask the ex perts.

Anonymous said...

i can only say, that i'm not suprised.

it is allway "funny" to see how something that had been tested under laboratory conditions enters the real world. hahaha

what we learn through the data that comes from the soil around chernobyl is that even atoms don't live in there one little universe. an atom is not an island. yay

Anonymous said...


correction: their own little...

Anonymous said...

From an article in WIRED (2009):

“I have been involved in Chernobyl studies for many years and this particular study could be of great importance to many [Department of Energy] researchers,” said Faybishenko.

The results of this study came as a surprise. Scientists expected the ecological half-lives of radioactive isotopes to be shorter than their physical half-life as natural dispersion helped reduce the amount of material in any given soil sample. For strontium, that idea has held up. But for cesium the the opposite appears to be true.

Anonymous said...

So, how cheap is "clean" nuclear power now?
See, playing with a piece of the Sun is very bad....idiots!

Anonymous said...

I'm still lost on the concept of the ecological half-life. Even if a cesium atom is bound to soil, wouldn't it decay as other cesium atoms do? If the cesium supply is being replenished by cesium from deeper underground or by aerial contamination, then the concept of the cesium ecological half-life would be subject to regional variations. A bit confusing, but I think a very important topic that merits some more detail if you can spare the time.

Anonymous said...

".. the government is considering using areas around the nuclear plant as temporary storage sites for radioactive waste, including debris and sludge left after treating contaminated water at the plant.

The government will further discuss this plan after examining the ministry's radiation survey, the sources said."

"If this situation continues, we'll go out of business," one livestock farmer said. Another commented, "Consumers will think, 'More trouble in Fukushima.'" [long lasting trouble, Fukushima]

"Chiba worried about buyers criticizing such things as the color and texture of the meat. It also is uncertain how his cows' beef will be priced after being checked for contamination with radioactive materials."

"Unless they're shipped at usual prices, I don't know if I can make a living," Chiba said. "I want the government to promote exports of domestically produced beef to revitalize the beef market."

Toshitaka Ogura, a 59-year-old livestock farmer in Minami-Soma, Fukushima Prefecture, said angrily: "Is the government waiting for livestock farmers to go bankrupt?"

"Life Corp., which operates the Life supermarket chain, plans to sell beef raised in Miyagi Prefecture. The company's public relations division said sales of domestically raised beef in its stores fell by 20 percent after it was learned that beef cows had been fed with rice straw contaminated with radioactive cesium."

"SENDAI--A rice farmer in Miyagi Prefecture plans to ship newly harvested rice after a private institute he approached found it free of radioactive substances and fit for human consumption.

.. The central and prefectural governments are clearly disconcerted by the farmer's plan as other farmers in the prefecture have been asked to refrain from shipping rice due to the crisis .."

"Some golf courses in Fukushima Prefecture are suffering from radioactive contamination ..

Radiation-measuring instruments dotted around the golf course constantly issue alarms indicating radiation levels of 0.3 microsieverts per hour or above; in some areas, levels have reached over 3 microsieverts per hour."

"A group of about 50 lawyers will be assigned to mediate between TEPCO and victims of damage caused by the nuclear accident .."


Anonymous said...

I think the "unexpectedly" long half-lives are actually due to the fact that the amount of radionuclides introduced into the environment is officially under reported at every major nuclear accident. The sad fact is release and dispersion models are only best guesses and they are only as good as the data set they are fed. This is just "extend and pretend" coming back to bite the liars and minimizes in their backside. Now they will spend years trying to come up with a bogus but plausible explanation, anything other than they lied about the initial level of contamination.

Atomfritz said...

This really made me think much.

I think the explanation is very simple.

Look, as most areas of the world are low in phosphates, plants try to grab all phosphates they can and transfer them to above surface. Remember, phosphates are necessary for reproduction (blossoms need them to develop).

So the phosphate-similar cesium also gets always pulled up to surface.
Plants grab all cesium available to their roots, including the cesium salts that already made being washed out to deeper soil.

Conclusion: Plants keep cesium away from ground water, instead concentrating it in top soil, which consists of disintegrating organic stuff (previous years plants).

Dunno if that's good or bad.
At least it keeps my groundwater well somewhat cesium-free.

jmdesp said...

There's actually a very simple explanation to all of that, when you read the original study (and a link to it has already been posted above !!) :

"changes in the exposure dose resulting from the soil deposited 137Cs now depend only on its radioactive decay" as "It was found that the 137Cs absolute T1/2 ecol values are 3–7 times higher than its radioactive decay half life value."

So the searcher just found that the biologic half-life did not really result in an acceleration of the effective half-life, from the radiologic value of 30 years.

And here we have everyone not even reading the abstract of the paper, mixing the biological half-life with the radiologic one, and thinking an half-life of 200 years was measured !! Sic.

Using the numbers of the paper, what they really measured was around 26 years of effective half-life, meaning that the contribution of the biologic dispersion is very minor.

Cyril R said...

What the previous commenter said is correct. The "real" half life is obtained by substracting the ecological half life from the physical half life. Since the ecological half life is usually a lot less than infinite, the "real" environmental half life is always shorter than the physical half life.

I'm currently doing an exercise of comparing risks in light of evacuations. The linear no threshold theory, which is dubious for low dose rates (ie atomic bomb survivor statistics aren't very useful), states that a 1% excess cancer mortality risk arises for each 100 mSv or radiation. So a 500 mSv/year dose, roughly the highest measured in the surrounding Fukushima area, would mean a 5% excess cancer lethality risk.

Interestingly, the excess cancer lethality risk from living in a polluted city, such as Tokyo, is over 10% in most areas of the city.

How come we're not evacuating Tokyo?

Shockingly, I concluded that the nuclear evacuation criterion is not based on societal risk assessment. This is unfortunate since evacuating people kills (it is a massive phychological blow to people, losing their entire livelihoods, causing suicide and increased morbidity etc.). Part of societal risk assessment is to make sure the cure isn't worse than the disease. It appears in Fukushima, the cure is worse than the disease, even using the flawed linear no threshold model that gets exaggerated results...

Anonymous said...

Where did you get that the linear model yields exaggerated results?
I thought it was suspected of *underestimating* the risk.

Anonymous said...

At least plants aren't affected much by radioactivity. I love the idea of planting forests that we can only use in 100 years or so, hopefully just for recreation. Chernobyl area could be a huge old growth forest. It might become that even without planting it. Turning disaster into an asset for future generations, and a warning as well.

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