MIT Study: Prolonged Low-level Radiation Exposure Poses Little Risk 142
JSBiff sends this quote from MITnews:
"A new study from MIT scientists suggests that the guidelines governments use to determine when to evacuate people following a nuclear accident may be too conservative. The study (abstract), led by Bevin Engelward and Jacquelyn Yanch and published in the journal Environmental Health Perspectives, found that when mice were exposed to radiation doses about 400 times greater than background levels for five weeks, no DNA damage could be detected. Current U.S. regulations require that residents of any area that reaches radiation levels eight times higher than background should be evacuated. However, the financial and emotional cost of such relocation may not be worthwhile, the researchers say."
Re:5 weeks = long term? (Score:4, Informative)
They also said 400x normal, rather than 8x normal.
Re:5 weeks = long term? (Score:5, Informative)
once radioactive material gets inside them it will be there for the rest of their lives.
Wrong. Many radioactive isotopes aren't absorbed by the body and are flushed out rapidly, and some of the most damaging particles (alpha emitters in particular) are at their worst when airborne, only staying 'in' your body for the length of a breath. There are some isotopes that are absorbed easily (namely Iodine), but they are the minority. There is not a single "Radiation", there are a staggering number of different radioactive elements, and for each one, the chemistry matters far more than the half-life.
Re:Magical DNA damage testing? (Score:5, Informative)
If you follow the links to the abstract, it actually explains what they measured. Apparently, certain types of DNA damage leave easily measured chemical signatures. They also dosed them with the same radiation total over a short period of time and observed damage.
This is akin to turning your thermostat up 10 degrees for a few weeks as opposed to heating your house up to 500 degrees for a minute.
I'm not saying I want to invest in cheap Fukushima real estate. I'm just saying that maybe this science isn't as junky as some Slashdotters think.
Background level (Score:5, Informative)
Btw, 100x background for 5 weeks is still less than the maximum year-long dose. Check the should-now-be-iconic xkcd radiation chart [xkcd.com].
Re:As opposed to... (Score:5, Informative)
Are you talking about chemical poisoning, or magical evil pixie dust. 125I decays emitting low-energy gamma radiation (the type that gets adsorbed adversely by living things). Eating this will have no different an affect than living right under it, as an object like a person, or mouse, is not a relevant shield for gamma radiation.
Now, if we were talking about inhaling dusted alpha emitters, then you'd have a point. However, those are either heavy metals, oxidize and drop out of the air, or decay rapidly to long-term emitters. The dust will be much more poisonous than dangerous as a radioisotope.
Damnit, I fed the troll.
Re:5 weeks = long term? (Score:5, Informative)
Maybe you, and the mods, might want to familiarize yourself with lab mice. They are precisely breed.
We know pretty much everything about them. For example, you can get mice that will get a specific cancer at 2 months, and it happens every time. 'only' 99.9% guarantee, but I have never seen one in a control not get cancer at the expected time
SO, for this test, 5 weeks is fine. But with ALL STUDIES, one isn't enough. DO several, control different variables, move to different species.
Re:As opposed to... (Score:4, Informative)
The amounts were tiny, but randomly sized/distributed particulates are notoriously hard to measure and map.
Re:5 weeks = long term? (Score:4, Informative)
Spoken like someone who knows nothing about radioactive materials and how they interact biologically.
Few radioactive elements stay in the body permanently. Most of them like Cs137 and I131 cycle through the body in days to couple of months. Plutonium is one of the few that has a biological half life of significant length, and it is one of the lesser radioactive isotopes. The most likely isotope you'd encounter after a nuclear accident that has a long biological half-life is Strontium-90.
The effective half-life of an isotope is measured by taking into account the physical half-life of the isotope and the biological half-life of an isotope. Thus, an element like Strontium 90 has an effective half-life of about 18 years while plutonium has an effective half-life of about 50 years (due to their propensity for gather in bone). Cesium has an effective half-life of about 70 days, and iodine has an effective half-life of about 7.6 days.
With that in mind, chronic long term exposure can only occur if they are taking in enough radioactive materials to replace those that are expelled from the body. To accumulate, you'd need to be taking in more.
Re:As opposed to... (Score:4, Informative)
Funny, but "no detectable DNA damage" is not the same as "no DNA damage or other side effects". This study would need to be much longer term and need to look for more than obvious DNA damage for me to trust it, personally. It was only 5 weeks!
Not that much longer, a mouse goes from infancy to maturity in about 6 to 10 weeks, a year can get you a generation or two. A mouse can have 5 - 10 litters in a year and their lifespan is 9 to 12 months; 5 weeks for a mouse is like 20 years for a human.
Re:As opposed to... (Score:4, Informative)
Sophisticated molecular and genetic analyses were not available in 1950s - 70s when many experiments investigating the effects of radiation on plants and animals took place; most were crude LD50 and cancer frequency tests conducted at moderate to very high doses, few were conducted at low doses (0.1 Gy) where cells could potentially repair the damage caused. This has all changed in the last ~20 years.
Sophisticated laboratory techniques now detect and observe the defence & repair mechanisms that operate in cells and whole organisms at low doses (100 mSv, ~0.8% increased risk of cancer in humans). For example, healthy people's cells repair all radiation induced DNA Double Strand Breaks (DSBs) within 24-hours after a CAT scan, indicating little or no additional risk of cancer. It is clear from resent experiments that living organisms are not passive accumulators of radiation damage but they actively combat and repair the damage done. After all, life involved with radiation and 3.5-3.8 billion years ago radiation levels were many times greater then now, it was necessary to evolve sophisticated error correction mechanisms. Indeed, it is likely that radiation is far less harmful or harmless below a certain threshold, possibly ~ 20 mSv year.
Crump, K. S. et al. 2012. A Meta-Analysis of Evidence for Hormesis in Animal Radiation Carcinogenesis, Including a Discussion of Potential Pitfalls in Statistical Analyses to Detect Hormesis. Journal of Toxicology and Environmental Health, Part B 15, 210–231.
Neumaier, T. et al. 2012. Evidence for Formation of DNA Repair Centers and Dose-Response Nonlinearity in Human Cells. PNAS 109, 443–448.
Löbrich, M. et al., 2005. In vivo formation and repair of DNA double-strand breaks after computed tomography examinations. Proceedings of the National Academy of Sciences of the United States of America 102, 8984 –8989
Tubiana, M., Feinendegen, L. E., Yang, C. & Kaminski, J. M., 2009. The Linear No-Threshold Relationship Is Inconsistent with Radiation Biologic and Experimental Data. Radiology 251, 13–22. (Paper available without subscription).