Being reported by many sources, including:
[NYT] Japanese Parents Assail Government Over Radiation
[ABC (Australia)] Outrage as Japan lifts radiation limit for kids
At issue are updated government guidelines that allow schoolchildren to be exposed to radiation doses that are more than 20 times the previously permissible levels. That dose is equal to the international standard for adult nuclear power plant workers.
(I'd earlier blogged about the top radiation advisor who resigned in protest over this decision).
As ABC writes, the government position is one of perceived necessity: contamination is widespread enough that the old 1 mSv/year would demand an exodus.
The government says it had no choice but to raise the legal exposure limit, saying about three-quarters of the schools in Fukushima have radiation levels above the old safety level of one millisievert.
I'm not even aware of a map at this resolution: the ones available (like in my previous post) stop at 5 mSv/year external dose, which already covers a very wide area.
Like a sacrificial offering to an angry mob, an education ministry official was bundled outside to speak to the demonstrators, although he had very little to offer them at all.
The hapless official's words only seemed to anger the protesters further.
"The current radiation levels for schools in Fukushima pose no health risks to kids at all," the official said.
I find it bizarre that the government is claiming external doses of tens of mSv -- at the level of CT scans, or possibly several CT scans -- are absolutely risk-free. While there's little empirical data at this level, it's widlely believed that doses these high cause nonzero excess risk of cancer and cancer fatalities. See for instance an authoritative reference from a radiological professional society -- these for adult doses:
Radiation Exposure in X-ray and CT Examinations
This is a very messy situation. The high radiation levels in parts of Fukushima are, apparently, likely to cause cancer deaths. And this excess risk is relatively small compared to other risk factors. So how does one react to this? Should government apply ordinary risk-tolerance standards, doing nothing, and allow a few tens or perhaps hundreds of radiation deaths (epidemiologically undetectable)? Or should they mount a massively expensive and destructive evacuation effort over a large area (the 5 mSv/year external dose range currently encompasses about 1 million people), itself probably causing serious health hazards to the displaced? Or should it leave people to make their own risk judgements (whether rational or not), informing them of the situation accurately?
(One of the commenters on this blog suggested, correctly, that to evacuate at this risk level, one should equally evacuate most cities near fossil fuel plants, factories, major highways. Which is strictly accurate, if you weigh all risks equally without regards to source. But then it does not seem people choose to view radiation dangers in the same way as other dangers.)
What I think they should not be doing is denying the problem like the Japanese officials are at this point. This is either incompetent or unconscionable.
From some extrapolations of future dose (over more than one year), see the new ISRN report (pdf, in French). In my previous post I also made a graph charting the decay of dose rates from cesium. (Other isotopes are mostly decayed away at this point).
The average yearly dose of background radiation in the US is 3 microSieverts, considerably more in places like Denver, that are a mile high. Should we evacuate all the children of Denver, too, not to mention the more than half the children in the US who experience more than 1 microSievert per year?
ReplyDeleteWe have to think in terms of alternatives. Not letting people back to their homes is proven to cause psychological stress which also increases chances of bad health and even premature death. Chernobyl shows this easily exceeds the radiation effect. So yes if we were rational a much much higher threshold would be used. Possibly as high as 100 mSv/year external dose. That's the dose where cancer is statistically shown (with significance) to be correlated to dose.
ReplyDeleteThe people in Ramsar, Iran, are subjected to widely varying but always high doses of 2-260 mSv/year, most of which is from radionuclides in the ground (just like fallout - there are even lots of decay products such as radon and thoron which can be inhaled). It does not cause a higher cancer incidence, indeed the cancer incidence is somewhat lower than most of the rest of Iran.
I think we should wait until after the rain season and then allow people back to all areas <100 mSv/year on a voluntary basis. Remaining areas of >100 mSv/year should be cleaned up, IMHO.
Yes, there is an ugly tradeoff here. And not just psychological stress; what about the straight economic destruction of long-term evacuation? In other situations (like what I believe was yours, about industrial pollution), people don't abandon jobs, houses, property over a slightly-increased cancer death risk. Their cost/benefit calculus doesn't accept it, so why should mandatory evacuations enforce a more conservative risk tolerance than people themselves exhibit?
ReplyDeleteBut then there are middle grounds, e.g. measures like topsoil removal.
It does not cause a higher cancer incidence,
At that range epidemiological studies would not detect it, it would be masked by other variations and noise. As you say, statistical evidence stops below ~100 mSv.
@Anonymous -- check your numbers. m = milli, μ = micro. Natural radiation dose averages about 3 mSv/year, of which about 0.5 mSv is background radiation -- the rest is internal dose, mostly radon. I'm not advocating evacuations at a threshold of 1 mSv/year background, although given peoples' apparent risk tolerance for radiation, this may happen.
ReplyDeleteUvdiv, if you believe that external whole body gamma doses of 20 mSv/year have a low but negative health effect, then how do you explain the Taiwanese residents that lived in accidentally contaminated buildings (cobalt-60 in the construction steel)? This is also external whole body dose gamma. Very high dose rates - over 500 mSv/year for a large group.
ReplyDeletehttp://www.ecolo.org/documents/documents_in_english/low-dose-Cobalt-taiw-06.pdf
For sure, the lower age explains the lower cancer incidence at the beginning, but this does not explain the drastic drop in cancer incidence after that - to a tiny fraction of the national Taiwanese average. If you consider radiation hormesis then this makes sense. If you consider regulatory limits, then 500 mSv/year should be extremely deadly with a clear sign of increased cancer incidence - but we see the opposite.
It appears prolonged exposure to whole body external gamma dose is actually very good for you, even though the cumulative dose in in the multiple Sieverts range.
I would like to hear your take on radiation hormesis.
Another group with high radiation dose are astronauts. According to the report below, astronauts on the ISS receive between 80 and 160 mSv per six-month stay, depending on the solar activity cycle (page 2, second paragraph under "Measuring Radiation"). I have not seen reports of astronauts being diagnosed with cancer.
ReplyDeletehttp://spaceflight.nasa.gov/spacenews/factsheets/pdfs/radiation.pdf
I have not seen reports of astronauts being diagnosed with cancer.
ReplyDeleteAlan Shepard died of leukemia.
Given that 1 in 5 of the general population get cancer, it would be astonishing if astronauts didn't. A 100 mSv dose would, according to ICRP figures, increase this risk by 1 in 200: e.g. from 20% to 20.5% over a lifetime. This would be difficult to detect given all the confounding variables.
@Cyril R -- I think that is good evidence of radiation hormesis. Still, it's limited: they don't have information about how the affected population differs from the general population. As the authors put it, "more research is needed".
ReplyDelete"The findings of this study are such a departure from those expected by ICRP criteria that it is important that they are carefully reviewed by other, independent organizations and that population data not available to the authors be provided, so that a fully qualified epidemiologically valid analysis can be made. "
I don't have an opinion on low-dose hormesis: it looks credible, but it seems the science is still unresolved. As far as radiation safety, I imagine it only makes sense to take the conservative view.
Well, they are student houses and temporary housing mostly, so that explains why the cancer incidence was much lower at first. But that doesn't explain why cancer incidence went down over the years while cumulative dose only increased.
ReplyDeleteThe problem about the conservative view is that it's isolated. We can't consider the risk of ionising radiatiation in isolation from the rest of the world. A good example is continued use of fossil fuels because we've got bans on nuclear plants (many countries still have these bans). This results, according to the conservative linear no threshold model, in over 1 million premature deats per year (primarily from particulate from fossil combustion).
I could live with the conservative view if it was alternatives-based. It's not, so its just risk-delusional.
Of course I'm not arguing to replace nuclear plants with fossils! As you say, it's not really "risk averse" if you ignore the risks of the alternatives. But this isn't a decision about nuclear power; we have a NPP which already had a substantial radiological release, and we want to know what to do about it. Decisions like "should we spend money removing topsoil", "which buildings should be decontaminated", "who should leave and for how long", etc. These are the alternatives in consideration.
ReplyDelete"Well, they are student houses and temporary housing mostly, ...
ReplyDeleteNo, they weren't. Most of the residents of the apartments were permanent residents, who lived there from the time they were built until the government relocated them after the radioactive rebar was discovered. The "students" that you refer to were children, who were enrolled in schools, kindergarten, or daycare in buildings with the contaminated rebar. They originally were not going to be registered, but that changed after two children who had been in these contaminated classrooms died of leukemia.
Nevertheless, the students, because of their young age, represent a special case (higher risk for leukemia, less likely to die of solid cancers), which is why they are treated specially in the analysis.
Even a completely independent analysis than the paper cited above concluded that the rate of cancer in these residents was lower than the general population -- although a detailed analysis, breaking down the cancers by specific type, showed a statistically significant increase in a couple of cancers. Nevertheless, after looking at the table in the paper, I wondered whether this is a case of green jelly beans being linked to acne.
These units were not cheap housing. They were built during an economic boom in Taiwan, and the latter team of researchers mentioned above (the authors of the second study) even speculated that the affluence of the exposed population might explain the relatively low rates of cancer (i.e., a kind of "healthy resident" effect).
These data provide an interesting "experiment" in the effects of low-dose, low-dose rate radiation. I don't think that anyone looking objectively at the data can conclude anything other than something unexpected occurred. I'm not going to go so far as to say that the results provide convincing proof of radiation hormesis, but it is pretty clear that the standard LNT model failed spectacularly to predict the data.
Keep in mind, however, that this is only one type of radiation (gamma) and all of the exposure was external. What this says about more general radiation exposure is unclear.
Thanks for the extra info Brian.
ReplyDeleteThe principal cause of leukemia is chemical pollution such as benzene and other cyclic hydrocarbons, from e.g. refineries, gas stations, and oil storage terminals. Nuclear plants are often built in industrial regions because they need lots of cheap reliable baseload power. So yeah, there have been dishonest studies, especially the German studies, that tried to link leukemia to nuclear plants, and of course, the nuclear plants in question were all near heavy industrial areas, with lots of chemical emissions....
I'm not really sure if the 'healthy resident' effect is all that strong; for one thing wealthy people live longer so have more chances of cancer incidence (you actually see lower cancer rates in many poor countries that have low life expectancy due to other, non carginogenic causes, as they don't get live long enough to get lots of cancers).
I think the fact that its external whole body (gamma) dose, and the fact that cesium does not bioaccumulate, and has a gamma emitting daughter, makes the Taiwanese experiment very relevant to the Fukushima areas with high cesium depositions. If you look at the dose rates for the Taiwanese residents they are actually higher than what you'd get in the worst areas of the Fukushima fallout areas. And those people slept in the buildings whereas Fukushima residents don't sleep on the soil, contaminated or not.