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New look at prolonged radiation exposure: at low dose-rate,radiation poses little risk to dna, stud by ferujkll sdff
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New look at prolonged radiation exposure: at low dose-rate,radiation poses little risk to dna, stud by FERUJKLL SDFF
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| Article Posted: 11/09/2013 |
| Article Views: 74 |
| Articles Written: 2023 - MORE ARTICLES FROM THIS AUTHOR |
| Word Count: 1021 |
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New look at prolonged radiation exposure: at low dose-rate,radiation poses little risk to dna, stud |
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The study, led by Bevin Engelward and Jacquelyn Yanch and publishedin the journal Environmental Health Perspectives , found that when mice were exposed to radiation doses about 400times greater than background levels for five weeks, no DNA damagecould be detected. Current U.S. regulations require that residents of any area thatreaches radiation levels eight times higher than background shouldbe evacuated. However, the financial and emotional cost of suchrelocation 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 NuclearScience and Engineering. "This paper shows that you could go400 times higher than average background levels and you're stillnot detecting genetic damage. It could potentially have a bigimpact on tens if not hundreds of thousands of people in thevicinity of a nuclear powerplant accident or a nuclear bombdetonation, if we figure out just when we should evacuate and whenit's OK to stay where we are." Until now, very few studies have measured the effects of low dosesof radiation delivered over a long period of time. This study isthe first to measure the genetic damage seen at a level as low as400 times background (0.0002 centigray per minute, or 105 cGy in ayear). "Almost all radiation studies are done with one quick hit ofradiation.
That would cause a totally different biological outcomecompared to long-term conditions," says Engelward, anassociate professor of biological engineering at MIT. How much is too much? Background radiation comes from cosmic radiation and naturalradioactive isotopes in the environment. These sources add up toabout 0.3 cGy per year per person, on average. "Exposure to low-dose-rate radiation is natural, and somepeople may even say essential for life. The question is, how highdoes the rate need to get before we need to worry about ill effectson our health?" Yanch says.
Previous studies have shown that a radiation level of 10.5 cGy, thetotal dose used in this study, does produce DNA damage if given allat once. However, for this study, the researchers spread the doseout over five weeks, using radioactive iodine as a source. Theradiation emitted by the radioactive iodine is similar to thatemitted by the damaged Fukushima reactor in Japan. At the end of five weeks, the researchers tested for several typesof DNA damage, using the most sensitive techniques available. Thosetypes of damage fall into two major classes: base lesions, in whichthe structure of the DNA base (nucleotide) is altered, and breaksin the DNA strand.
They found no significant increases in eithertype. DNA damage occurs spontaneously even at background radiationlevels, conservatively at a rate of about 10,000 changes per cellper day. Most of that damage is fixed by DNA repair systems withineach cell. The researchers estimate that the amount of radiationused in this study produces an additional dozen lesions per cellper day, all of which appear to have been repaired. Though the study ended after five weeks, Engelward believes theresults would be the same for longer exposures.
"My take onthis is that this amount of radiation is not creating very manylesions to begin with, and you already have good DNA repairsystems. My guess is that you could probably leave the mice thereindefinitely and the damage wouldn't be significant," shesays. Doug Boreham, a professor of medical physics and applied radiationsciences at McMaster University, says the study adds to growingevidence that low doses of radiation are not as harmful as peopleoften fear. "Now, it's believed that all radiation is bad for you, and anytime you get a little bit of radiation, it adds up and your risk ofcancer goes up," says Boreham, who was not involved in thisstudy. "There's now evidence building that that is not thecase." Conservative estimates Most of the radiation studies on which evacuation guidelines havebeen based were originally done to establish safe levels forradiation in the workplace, Yanch says -- meaning they are veryconservative.
In workplace cases, this makes sense because theemployer can pay for shielding for all of their employees at once,which lowers the cost, she says. However, "when you've got a contaminated environment, then thesource is no longer controlled, and every citizen has to pay fortheir own dose avoidance," Yanch says. "They have toleave their home or their community, maybe even forever. They oftenlose their jobs, like you saw in Fukushima.
And there you reallywant to call into question how conservative in your analysis of theradiation effect you want to be. Instead of being conservative, itmakes more sense to look at a best estimate of how hazardousradiation really is." Those conservative estimates are based on acute radiationexposures, and then extrapolating what might happen at lower dosesand lower dose-rates, Engelward says. "Basically you're usinga data set collected based on an acute high dose exposure to makepredictions about what's happening at very low doses over a longperiod of time, and you don't really have any direct data. It'sguesswork," she says. "People argue constantly about howto predict what is happening at lower doses and lowerdose-rates." However, the researchers say that more studies are needed beforeevacuation guidelines can be revised.
"Clearly these studies had to be done in animals rather thanpeople, but many studies show that mice and humans share similarresponses to radiation. This work therefore provides a frameworkfor additional research and careful evaluation of our currentguidelines," Engelward says. "It is interesting that, despite the evacuation of roughly100,000 residents, the Japanese government was criticized for notimposing evacuations for even more people. From our studies, wewould predict that the population that was left behind would notshow excess DNA damage -- this is something we can test usingtechnologies recently developed in our laboratory," she adds. The first author on these studies is former MIT postdoc WernerOlipitz, and the work was done in collaboration with Department ofBiological Engineering faculty Leona Samson and Peter Dedon.
Thesestudies were supported by the DOE and by MIT's Center forEnvironmental Health Sciences. I am an expert from Business Bags & Cases, usually analyzes all kind of industries situation, such as cheap fireplace mantels , bathroom granite countertop.
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