xpost Very Important paper Environment Health Publication - Study by MIT
says that they found undetected DNA damage even when radiation was much higher..This study may surprise most of people here.
Integrated Molecular Analysis Indicates Undetectable DNA Damage in Mice after Continuous Irradiation at ~400-fold Natural Background Radiation
Abstract:
ACKGROUND: In the event of a nuclear accident, people are exposed to elevated levels of continuous low dose-rate radiation. Nevertheless, most of the literature describes the biological effects of acute radiation. Our major aim is to reveal potential genotoxic effects of low dose-rate radiation.
OBJECTIVES: DNA damage and mutations are well established for their carcinogenic effects. Here, we assessed several key markers of DNA damage and DNA damage responses in mice exposed to low dose-rate radiation.
METHODS: We studied low dose-rate radiation using a variable low dose-rate irradiator consisting of flood phantoms filled with 125Iodine-containing buffer. Mice were exposed to 0.0002 cGy/min (~400X background radiation) continuously over the course of 5 weeks. We assessed base lesions, micronuclei, homologous recombination (using fluorescent yellow direct repeat [FYDR] mice), and transcript levels for several radiation-sensitive genes.
RESULTS: Under low dose-rate conditions, we did not observe any changes in the levels of the DNA nucleobase damage products hypoxanthine, 8-oxo-7,8-dihydroguanine, 1,N6-ethenoadenine or 3,N4-ethenocytosine above background. The micronucleus assay revealed no evidence that low dose-rate radiation induced DNA fragmentation. Furthermore, there was no evidence of double strand break-induced homologous recombination. Finally, low dose-rate radiation did not induce Cdkn1a, Gadd45a, Mdm2, Atm, or Dbd2. Importantly, the same total dose, when delivered acutely, induced micronuclei and transcriptional responses.
CONCLUSIONS: Together, these results demonstrate in an in vivo animal model that lowering the dose-rate suppresses the potentially deleterious impact of radiation, and
calls attention to the need for a deeper understanding of the biological impact of low dose-rate radiation.
Citation: Olipitz W, Wiktor-Brown D, Shuga J, Pang B, McFaline J, Lonkar P, et al. 2012. Integrated Molecular Analysis Indicates Undetectable DNA Damage in Mice after Continuous Irradiation at ~400-fold Natural Background Radiation. Environ Health Perspect :-. http://dx.doi.org/10.1289/ehp.1104294
This is also a main MIT news
http://web.mit.edu/newsoffice/2012/prol ... -0515.html
A new look at prolonged radiation exposure
MIT study suggests that at low dose-rate, radiation poses little risk to DNA.
Worth reading in full.. posting some excerpts..
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, 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.
“There are no data that say that’s a dangerous level,” says Yanch, a senior lecturer in MIT’s Department of Nuclear Science and Engineering. “This paper shows that you could go 400 times higher than average background levels and you’re still not detecting genetic damage. It could potentially have a big impact on tens if not hundreds of thousands of people in the vicinity of a nuclear powerplant accident or a nuclear bomb detonation, if we figure out just when we should evacuate and when it’s OK to stay where we are.”
Until now, very few studies have measured the effects of low doses of radiation delivered over a long period of time. This study is the first to measure the genetic damage seen at a level as low as 400 times background (0.0002 centigray per minute, or 105 cGy in a year). { for perceptive, this is about 1000 mSV /Yr = 10000000 bed /yr - about 1000 times 1mSV insisted by some.. about 50 times the current limit when one is forced to evacuate .. about 4 times the limit allowable (which they increased to 250 mSV) for emergency workers in Japan..Amber G notes }
“Almost all radiation studies are done with one quick hit of radiation. That would cause a totally different biological outcome compared to long-term conditions,” says Engelward, an associate professor of biological engineering at MIT.
<snip:
(Background radiation . add up to about 3 mSV per year in US)
“Exposure to low-dose-rate radiation is natural, and some people may even say essential for life. The question is, how high does the rate need to get before we need to worry about ill effects on our health?” Yanch says.
Previous studies have shown that a radiation level of 10.5 cGy, the total dose used in this study, does produce DNA damage if given all at once. { This is what I said in one of VERY early message - I said that below this one does not see any symptoms ... LNT predicts about 4% increased risk of cancer in life time } However, for this study, the researchers spread the dose out over five weeks, using radioactive iodine as a source. The radiation emitted by the radioactive iodine is similar to that emitted by the damaged Fukushima reactor in Japan.
At the end of five weeks, the researchers tested for several types of DNA damage, using the most sensitive techniques available. Those types of damage fall into two major classes: base lesions, in which the structure of the DNA base (nucleotide) is altered, and breaks in the DNA strand. They found no significant increases in either type.
<snip - Technical details about DNA damage >
... “My take on this is that this amount of radiation is not creating very many lesions to begin with, and you already have good DNA repair systems.
Doug Boreham, a professor of medical physics and applied radiation sciences at McMaster University, says the study adds to growing evidence that low doses of radiation are not as harmful as people often fear.
“Now, it’s believed that all radiation is bad for you, and any time you get a little bit of radiation, it adds up and your risk of cancer goes up,” says Boreham, who was not involved in this study. “There’s now evidence building that that is not the case.”
Most of the radiation studies on which evacuation guidelines have been based were originally done to establish safe levels for radiation in the workplace,.....
....“when you’ve got a contaminated environment, then the source is no longer controlled, and every citizen has to pay for their own dose avoidance,” Yanch says. “They have to leave their home or their community, maybe even forever. They often lose their jobs, like you saw in Fukushima. And there you really want to call into question how conservative in your analysis of the radiation effect you want to be. Instead of being conservative, it makes more sense to look at a best estimate of how hazardous radiation really is.”
Those conservative estimates are based on acute radiation exposures, and then extrapolating what might happen at lower doses and lower dose-rates, Engelward says. “Basically you’re using a data set collected based on an acute high dose exposure to make predictions about what’s happening at very low doses over a long period of time, and you don’t really have any direct data. It’s guesswork,” she says. “People argue constantly about how to predict what is happening at lower doses and lower dose-rates.”
....
“It is interesting that, despite the evacuation of roughly 100,000 residents, the Japanese government was criticized for not imposing evacuations for even more people. From our studies, we would predict that the population that was left behind would not show excess DNA damage — this is something we can test using technologies recently developed in our laboratory,” she adds.
<snip>
Pay attention to the following quote from Jacqueline Yanch, MIT
"Instead of being conservative, it makes more sense to look at a best estimate of how hazardous radiation really is."
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(I have some thoughts on this... will post later in physics dhaga...)
