Background on the LNT (linear no-threshold) radiation model
By: Gordon Edwards
Dear Friends and colleagues:
Because of the importance of the debate that continues to rage over the harmful effects of low-level radioactivity, I am sending out a copy of my recent exchanges on this topic in the context of the Canadian Pugwash Group. As you know, nuclear proponents have been for many years eagerly pushing the idea that there is a safe threshold of exposure and that exposures below this threshold are either completely harmless or actually beneficial. The latter claim is called “hormesis”.
Robin Collins, a well-known activist working to abolish nuclear weapons, is strongly inclined to a pro-nuclear-energy position, despite his assertion that he is “neutral” on the subject. He started a discussion on the Canadian Pugwash Website by posting some fairly extreme points of view on the industry’s support of “hormesis” — health benefits resulting from low-level radiation exposure – to the CPG members. I felt it important to respond.
Jeremy Whitlock is an avidly pro-nuclear physicist, ex-AECL from Chalk River, now working for IAEA in Vienna. He regularly challenges people who are cititcal of Canada’s nuclear enterprise, and he weighs in on this discussion.
Gordon Edwards.
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Background explanation of the linear no-threshold (LNT) model of radiation carcinogenesis.
Linearity is the same thing as proportionality. The LNT model states that the number of radiation-induced cancers that occur in a given exposed population is proportional to the total radiation dose received by that same population. Thus if the dose is doubled, the number of radiation-induced cancers will also double. If the dose is reduced by a factor of 10, the number of radiogenic cancers is also reduced by 10. Thus as the radiation dose gets closer to zero, the number of radiation-caused cancers also gets closer to zero.
John Gofman was a celebrated nuclear physicist who later became a celebrated medical researcher. Originally he thought there was probably a safe dose of radiation exposure (i.e. a safe threshold). When he was hired by the US AEC to study the question, a job he did for 7 years at the Lawrence Radiation Lab, he began with the Navajo uranium miners on the Colorado plateau. This was a pretty homogenous group of men who were non-smokers. Radiation doses were estimated based on measurements of radon in the mine shafts and the working history of miners, how much time they spent in various parts of the underground workings. These estimates were pretty rough, but much better than nothing. Gofman then divided the mining population into 5 groups, A, B, C, D, and E, based on the level of radiation exposure experienced by each group. He found a surprisingly clear linear relationship, as the groups with the higher radiation exposures also had the higher lung cancer incidence, and the proportionality relationship was very good.
In each group, it was the NUMBER of cancers that was important, not the individual exposures of the individual men. For example, someone in the lowest exposure group may have died from lung cancer while someone from the highest dose group might never have got cancer. This is mathematically a clear indictaion of a random mechanism. It’s like throwing darts randomly at various dart boards, some will hit the biard and some will miss. The radiation dose is like the number of darts that are thrown — more darts will produce more hits, but there will still be lots of misses. Also a larger dart board (corresponding to a larger population) will get kore hits than a smaller dart board (smaller population) even though the nukber of darts (radiation dose) is the same.
This gave rise to the idea of a “population dose” as opposed to an individual dose. The population dose is the sum of all the individual doses of all the members of the population. The number of cancers in that population seems to be proportional to the population dose, but there is absolutely no way of predicting which individuals will actually get the cancer. Nor is it the. case that a person that gets cancer will necessarily have rteceived a higher dose than someone who does not get cancer. This same pattern is observed with all other carcinogens, such as asbestos, cigarette smoking, etc. So there is no absolutely safe dose, but very low doses will cause very few cancers; it is largely a matter of luck whether one cell is going to be damaged in just the “right” way to initiate a pre-cancerous growth that will develop into a full-blown cancer years or even decades later.
To summarize: The LNT model says that the number of radiation-induced cancers in an exposed population is proportional to the population dose. That being so, you cannot reach absolute zero risk without going to zero exposure. But in small populations, with very small doses, chances are good that NO one will get cancer. But it is not a sure thing.
Gordon.
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BELOW IS THE EXCHANGE FROM THE CPG LISTSERV.
Hello everyone:
(1) Jeremy Whitlock says that “radiation is probably the most well-understood and easily tracked agent in our environment”, yet as recently as 2009 there were over 500 workers at the Bruce Nuclear Refurbishment project who were exposed for almost three weeks to a work environment where they inhaled plutonium-contaminated dust on a daily basis. Now these men (mostly men) carry a body burden of plutonium that will be with them for the rest of their lives. For the most part, they are not Bruce emnployees, but local tradesmen such as plumbers, welders, pipe-fitters, etc. The nuclear authorities at Bruce Power and CNSC failed to detect the problem until long after these unnecessary alpha-radiation exposures had occurred, yet they were the ones who had assured the workers that they did not need to wear respirators because the radiation levels were too low to worry about. Later, most of the Bruce employees and managers overseeing the refurbishment confessed that they knew almost nothing about this particular kind of radiation hazard. They had not been taiught about it or warned about it, despite the fact that alpha contamination inside the pipes was well-documented years before this regrettabe incident. Nevertheless it was decided by the CNSC that no one in a position of authority at Bruce or at CNSC was in any way responsible for the gross negligence and ignorance that led to these 500-plus men having their lungs contaminated with plutonium-bearing dust.
“Bruce Power officials told a public hearing Thursday they did not anticipate or test for airborne alpha radioactivity in one of the reactors being refurbished at the Bruce A nuclear station. They said they’re always on the lookout for beta radioactivity, operating on the assumption that protecting against one will protect against the other.”
– Owen -Sound Sun-Times, Feb 18 2010,
http://www.owensoundsuntimes.
By the way, describing alpha and. beta emissions as “radiation” is scientifically unsound. These emissions consist of electrically charged particles, not electromagnetic radiation. The nuclear industry misleads the public by repeatedly describing these ionizing agents as “radiation”. In fact, per radioactive disintegration, alpha emitters are known to be from 100 to 1000 times more biologically damaging than beta- or gamma-emitters. However, due to its electrical charge and particulate nature, an alpha particle cannot penetrate through a normal sheet of paper. But inside the body it can be deadly. The most notorious radioactiuve killers of the last century — radium, radon, polonium, plutonium, thorium, uranium – are all alpha emitters.
(2) Decades earlier, a similar incident involving a totally different radioactive contaminant — this time a beta-emitter — plagued workers during the Pickering nuclear plant retubing. In that eerily similar case, the authorities did not test for airborne beta activity because they “did not expect it”. [Ridiculous!] After weeks of failing to detect the presence of radioactive carbon-14 dust on worker’s bodies, because the regular radiation monitors did not give off any alarms, these men tracked radioactive contamination from the work site into their homes. In this case it is not alpha “radiation”, but beta “radiation” that is involved. Eventually, when the “blameless” nuclear authorities finally figured out what was going on, they had to go and confiscate contaminated furniture and bedclothes from workers’ homes to be disposed of as radioactive waste. The men were not so treated, but were dutifully reassured that they had nothing to worry about….
(3) The man who murdered Alexander Litvinenko with a small quantity of polonium-210 could have easily carried the murderous agent in a sealed package without any fear whatsoever of detection by any external radiation monitor. Polonium-210 is a “pure” alpha emitter, giving little or no gamma radiation. In any sealed container, the alpha particles will not penetrate through the walls of the container and so cannot trigger any alarms. Something similar can be said for small quantities of weapons-grade uranium or plutonium; such material can be transported safely and smuggled across borders with very little chance of detection. My point is: To say that “alpha radiation” is easily detected and tracked is simply untrue, and is part of a larger disinformation campaign that the nuclear establishment in Canada and elsewhere has always pursued in order to keep journalists, politicians and the public in the dark about radioactive emissions – many of which are in fact not radiation at all. Alpha particles and beta particles and neutrons are not in any sense “radiation”. You may search for them in vain along the electromagnetic spectrum : they are nowhere to be found.
(4) The fact of the matter is that debates over low-level radiation are not merely academic. Such exposures affect the lives of large numbers of people. It also affects the public relations efforts of the nuclear industry and their bottom line in terms of dollars and cents. Arguing that low levels of radiation exposure are harmless or beneficial allows nuclear operators to avoid responsibility, shun blame, avoid compensating workers and others for allowing preventable radioactive exposures, cut costs on safety measures, obtain permission to dump “low-level” radioactive waste into landfills or allow it to be incorporated in scrap metal for unrestricted use in manufacturing commercial products of all kinds, or to weaken the “overly stringent” radiation protection standards advocated by scientists outside the nuclear establishment (something that is happening right now under the Trump administration.)
For example, Ontario commissioned two separate independent scientific agencies to examine the radiation exposure standards for tritium (radioactive hydrogen) in drinking water. The first panel, called ACES (Advisory Committee on Environmental Standards), issued its report in 1994; the sceond was ODWAC (Ontario Drinking Water Advisory Committee); it reported in 2009. There was no overlap between the two committees, but they both came to the same conclusion : that to be consistent with health standards that are routinely imposed on chemical contamimants, the permissible level for tritium in drinking water should be lowered to 20 becquerels per litre. That’s 350 times lower than the current Canadian standard of 7000 becquerels per litre, already down from 40,000 becquerels per litre a few decades earlier. Spokespersons from CNSC have stated on the public record that tritium contamination would not cause them any concern unless it were measured in the millions of becquerels per litre. Each CANDU reactor routinely emits about 100 trillion becquerels of tritium per year into the environment.
(5) During the BC Royal Commission on Uranium Mining, way back in 1980, two medical doctors carefully monitored the hearings (Dr. Robert Woollard and Dr. Eric Young) and published a 350 page report under the auspices of the BC Medical Association (BCMA) entitled “Health Hazards of Uranium Mining”. At that time the permissible level of radon exposure for uranium miners, over a working lifetime, was set by the Atomic Energy Control Board at 120 WLM (“working-level-months”). The BCMA report cited several independent scientific studies indicating that 120 WLM of radon exposure would approximately dopubtle the normal expected incidence of lung cancer in the affected mining population. However, the Atomic Energy Control Board (AECB) – the precursor of the Canadian Nuclear Safety Commission (CNSC) – had a totally different perspective:
“The AECB [Atomic Energy Control Board] policy regarding a lifetime exposure limit for uranium miners [February 1978] is based on one study [published in 1969] , which is not only 11 years out of date, but which has been revised several times by the authors. The AECB notes in passing that in Ontario,
“only 20 of the 81 lung cancer victims who had worked in uranium mines had accumulated as much as 120 WLM (the exposures of the other 61 victims being 0 to 99 WLM, or 35 WLM on average).”
“Ignoring this and using the 1969 study (which seems to be the extent of their literature review as no other references are cited) AECB states:
“If one had to choose a WLM value that had some special significance 840 WLM would be a more logical choice [than 120 WLM] because it marks the level above which lung cancer incidence appears to increase with increasing exposure; (i.e. although an excess of lung cancer is evident in each of the exposure categories, the excess appears to be independent of exposure below 840 WLM.)”
“Such a policy statement, based on antiquated data and inadequate literature review, would be irresponsible coming from the nuclear industry, let alone the regulatory agency of that industry. However, as will become clear, it is difficult to ascertain where one ends and the other begins.” See www.ccnr.org/bcma/html .
It should be noted that the 81 lung cancer deaths in Ontario uranium miners mentioned above had been identified by Dr. James Hamm, author of the Royal Commission Report on the Health and Safety of Workers in Mines (1976) as a clear demonstration of radiation carcinogenesis at work, even though most of the cancer victims were under the 120 WLM “threshold”. (Since that time the number of lung cancer deaths in the populations of Ontario uranium miners has conmtinued to grow; the BCMA report refers to it as “a gradually-flowering crop of radiation-induced cancers”.)
(6) Pharmaceutical companies have taken pains to tell doctors that opioids are generally safe to prescribe. The tobacco execs has worked hard to support the notion that cigarette smoking is pretty harmless. It is not surpising that nuclear proponents have been working for decades to “prove” that low levels of radiation are harmless or beneficial. Every time a specific number has been promoted as a “safe” level of exposure, evidence has confirmed that that level is not safe. For example, both the Canadian Nuclear Safety Commission and Jeremy Whitlock have stated that “below approximately 100 mSv of exposure (roughly 50 times the average natural background dose in Canada), we don’t see any solid evidence of an effect”. However, ALL of the evidence of biologcal harm cited by the US National Academy of Scioences’ BEIR VII Report is based on exposures BELOW 100 millisieverts [“The study committee defined low doses as those ranging from nearly zero to about 100 millisievert (mSv)”] . Based on that evidence, BEIR VII says that the evidence in favor of the LNT model is stronger than ever, and specifically rejects the notion of hormesis (that small doses of radiation are beneficial).
(7) Here is a link to a paper that I wrote in 1978 entitled “Estimating Lung Cancers”, which is a summary of testimony I gave to the Ontario Inquiry into Radon Gas Standards for new homes under construction in Elliot Lake Ontario. I argued in that hearing that residents subjected to the maximum level of exposure considered “acceptable” would
See. www.ccnr.org/lung_cancer_1.
www.ccnr.org/thomas_report.
(8) I could continue but I will not do so. The notion that the well-established linear relationship between population exposure and excess cancer incidence must fail at some point, without any evidence as to what that point may be, is based on little more than wishful thinking backed by inconclusive arguments and pseudo-scientific “principles” that have never been verified or accepted by independent scientific bodies. The BEIR VII Report investigated these claims and specifically rejected them as unsubstantiated. To put the LNT model and the “hormesis theory” on an equal acientific footing is like putting evolution and creationism on the same footing, or putting global warming on an equal footing with the views of climate change deniers. It is theoretically possible that in some distant future time or in some parallel universe hormesis may turn out to have some basis, but at the present time it is not able to gain acceptance because the case is far too weak, whereas the evidence on the other side is very strong and getting stronger than ever. To call the LNT model a “hypothesis” is, to my mind, similar to calling evolution a “hypothesis”.
Moreover Jeremy Whitlock’s statement that LNT was never intended to predict consequences is utterly untrue.
Gordon Edwards.
P.S. This debate has nothing whatever to do with nuclear medicine, except to reinforce the wise principle that all unnecessary exposure should be avoided. But if radiation therapy can extend the life of a cancer patient by shrinking or killing a cancerous growth, great! If perchance another cancer is caused by that same radiation exposure, we know that the radiogenic cancer will not appear for 5, 10 or even 20 years — or more! — after exposure. This is a clear benefit to the individual, as it extends his or her life by years. And of course, with any luck, there probably will not be a radiogenic cancer produced in that particular case. So much the better.
It is quite different when you are considering the exposure of tens of millions of people to small doses of ionizing alpha beta and gamma emitters following a major nuclear reactor accident as in the case of the Chernobyl and Fukushima Daiichi disasters. In that case the LNT model clearly indicates that hundreds of thousands of cancers will ultimately result from such large population doses, even though the individual exposures may be small.
GE
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On Oct 22, 2017, at 10:44 AM, Jeremy Whitlock wrote:
Dear all,
I have often noted the particular irony that radiation, while probably the most well-understood and easily tracked agent in our environment, is also the most feared and misunderstood by the public. Although this misunderstanding is constantly exploited by the media, we can’t blame them too much for doing their job; the root of the issue is the manner in which radiation was first introduced to the public at large (i.e. its initial and continuing association with nuclear bombs), the cultural stereotype that inevitably evolved from this, and the seeming inability of the nuclear and medical profession to mitigate any of this through communication.
Scientists, while adept at talking to each other, are typically not great at public relations. One of the key reasons for this is that scientists seldom talk in black and white terms, being trained to consider all possibilities, recognize bias and uncertainty, and change one’s mind in the face of new evidence. That many of the public think of scientists as exactly the opposite (think Sheldon of Big Bang Theory), is another communication failure.
Low level radiation – the kind that’s all around us in nature, inside our bodies, in the food we eat, and augmented by human activity – falls victim to this professional circumspection in a huge way, because – despite radiation being the most well-understood and easily-tracked agent in the environment, we just don’t see enough effects from it (positive or negative) at low levels to be able to draw conclusions. About all we can say is that below approximately 100 mSv of exposure (roughly 50 times the average natural background dose in Canada), we don’t see any solid evidence of an effect.
This isn’t to say that there isn’t an effect: what it says is that whatever effect there is – good or bad – it can’t be detected. This also isn’t to say that there isn’t evidence in both directions – including a growing body of scientific research that suggests that low levels of radiation exposure are good for you (in the same way that many environmental agents, like sunlight, are good for you at low exposure levels but dangerous at high levels – these agents have typically been in our environment throughout our species’ evolution, and sometimes – as the case of background radiation – at levels much higher than they are today). All it says is that IF there is an effect, it’s too small to be seen through the standard scientific processes for investigating health effects on populations – largely based on epidemiology. And it’s not for lack of looking – along with the other superlatives used above we can probably say it’s the most looked-for effect of any in our environment.
When you think about it, this isn’t necessarily a bad thing: any effect from low-level radiation, whether good or bad, is too small to be detected against the background “noise”. Society is typically comfortable with such assurances – for example, when your doctor says it’s safe to take 2 Tylenol every 6 hours, that’s not because it’s been unequivocally shown that this dose is safe; it’s been unequivocally shown that this dose doesn’t have a detectable adverse effect on test populations, therefore delivering a net positive heath effect.
Against this lack of knowledge in the case of low-level radiation, the precautionary principle is applied: we assume a negative effect, and make the prudent assumption that the upper limit of this effect can be defined by extrapolating a straight line down from high doses (mostly drawing from data obtained from the Hiroshima and Nagasaki survivor study). In other words, we know that the dose-risk relationship is unequivocally linear at high doses (>>100 mSv), and we assume this to be the case all the way to zero dose. This is the so-called Linear No-Threshold (LNT) model that forms the basis of radiation regulation in Canada and around the world.
It is important to keep in mind that the LNT model is not just a “best guess” at low dose levels, but an UPPER LIMIT on our best guess – i.e. the LNT model completely encompasses the notion that the dose effect is less than the value it predicts, or zero, or even negative (predicting a positive health effect, or “hormesis”). Furthermore, the LNT model was never intended as a predictive tool for calculating the health impact on large population due to small doses of radiation, but as convenient generic model for administrating both public and occupational radiation protection policy.
Unfortunately, the only time that the public generally hears about radiation risk is when an event has occurred (Three Mile Island, Chernobyl, Fukushima) or in warnings about radon or medical radiation exposure, when someone (usually a gov’t agency) is using the LNT exactly as it was never intended – to predict large numbers of fatalities from small levels of individual radiation exposure (and seldom, if never, pointing out the academic nature of the model used to calculate the numbers, nor the fact that the numbers are an upper limit, for which the corresponding lower limit is potentially zero).
It works this way: If you were to move from, say, Ottawa to Winnipeg, you would double your natural background exposure, from roughly 2 mSv/year to 4 mSv/year. Although this increase of radiation dose may not have any effect whatsoever, we can predict using the LNT model that it may increase your probability of dying of cancer by 0.01% per year. In other words, if your probability of dying from cancer was 30% while living in Ottawa (the national average), it would now be 30.01% after the first year. This increased risk would of course never have a real impact on your lifespan, and certainly would not be a detectable statistic – even if it were real. However, if we take the population of Winnipeg to be 700,000, then this means about 70 more Canadians per year will die from background radiation Winnipeg, compared to Ottawa. This is not how the LNT was meant to be used, but we see headlines generated from this kind of calculation all the time – for example following the Fukushima accident in 2011, and in warnings from groups opposed to nuclear diagnostic medical imaging
Why does any of this matter, especially since it’s all just precautionary anyway? Because people do strange and sometimes dangerous things when scared, and radiation scares people like few other things can. They refuse proven medical diagnosis and treatment, and they abandon patients in their care to perish (in the case of Fukushima) while they run for the hills. I often contend that the biggest safety risk of radiation stems from its miscommunication.
It is for this reason that groups like the Health Physics Society, the American Association of Physicists in Medicine, and the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) recently came out with statements that warn against the use of LNT to predict the consequences to large populations from small amounts of radiation exposure (at least without sufficient caveats so that people are aware of the shaky basis behind these predictions).
Personally I don’t hold out much hope that this perception issue will change since it is so firmly rooted in the fabric of society – but the truth is often worth communicating, even when inconvenient.
Cheers,
Jeremy Whitlock
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On Oct 19, 2017, at 4:35 PM, Robin Collins wrote:Thanks Gordon, for your comments.A couple of quick responses. No, my posting of the link to the video by Jerry Cuttler was my idea, and not at the prodding of our Pugwash colleague Jeremy Whitlock. I have no idea what his current opinion is on the LNT hypothesis.Unlike the abolition listserv, which is focussed entirely on the abolition of nuclear weapons, the CPG and its list has no such restriction. Indeed, the subject of nuclear energy and other non weapon nuclear issues has popped up on occasion (and by yourself most recently) and is in my view most appropriate as a subject of study.Putting aside what our biases might be about nuclear power (I am ambivalent; you are strongly opposed), I think the challenge to the LNT hypothesis is fascinating and I have been following it for maybe a half dozen years. To be clear, one could be opposed to nuclear power but support the use of low level radiation for medical purposes.I hope others on the CPG list are similarly interested in watching the video (I suggest you watch it, and then you can better assess whether the challenge to LNT has merit.)Incidentally, I emailed Jerry about his topic and I think he might be interested in making a presentation on this subject in Toronto to a joint CPG-Science for Peace group. Please consider.Cheers,Robin=============================
On Thu, Oct 19, 2017 at 4:22 PM, Gordon Edwards <ccnr@web.ca> wrote:Dear CPG collleagues:I have refrained from entering into the debate about low-level radiation and the LNT (linear no-threshold) model of radiation carcinogenesis on this list-serv, becase I feel it is off-topic for CPG. Robin has previously reproached me for raising such matters on another list-serv that is focussed on the abolition of nuclear weapons.Perhaps Robin is moved to circulate this material to the CPG list-serv at the urging of his old friend Jeremy Whitlock of AECL (Atomic Enegy of Canada Limited) who is an avid promoter and defender of all things nuclear. I do not know how much research Robin has done on his own in this very controversial and highly politicized area of study. At any rate, the views being circulated by him are highly suspect and not at all balanced by any reference to the overwhelming evidence to the contrary.It should be noted that the LNT model applies in virtually all cases of carcinogenic and mutagenic agents, be they chemicals or radioactive materals or other sources of ionizing radiation such as x-rays. There are mountains of scientific evidence indicating that there is generally no safe threshold of exposure when it comes to carcinogenesis/mutagenesis of any kind. That’s why people do not speak of a permissible level of asbestos exposure, or argue for a recommended number of cigarettes that one can safely smoke per day, or insist on the existence of a harmless level of second-hand cigarette smoke. Deniers of all kinds — deniers of evolution, denials of climate change, deniers of LNT — can always mount arguments and cherry-pick data to support those denials. But that is not serious science. Of course one can and should pursue one’s own research on such matters, and keep an open mind too, but in the final analysis one has to persuade other scientists who are not like-minded.The papers that Robin has circulated on this subject have not been subjectedt to peer-review. They orginate from within the nuclear etsbaiishment, and are authored by individuals who are dedicated promoters of nuclear energy. Jerry Cutter for example has been arguing for decades that too much money is being spent on nuclear safety and that nuclear energy is unfairly put at a financial disadvantage due to the “exaggerated” concern about the health effects of low-level and/or chronic exposures to radioactivity released by nuclear plants, whether purposely or accidentally. Similarly, although it has been given the look of a serious publication in a reputable scientific journal, the previous article on this subject that Robin circulated to the list [ Current Radiation Protection Limits: An Urgent Need for Change http://www.ans.org/pubs/magazines/download/a_1081 ] is really just an article in a nuclear industry magazine that is published by the American Nuclear Society. Because of repeated claims of the existence of a “safe threshold” of radiation exposure emanating from within the nuclear establishment — manly from nuclear energy promoters and nuclear weapons testers – the National Academy of Sciences specifically instructed the BEIR VII Committee (BEIR = Biological Effects of Ionizing Radiation) to examine the reputability of the science behind industry claims of a safe threshold and/or “hormesis”. In a series of six previous studies, published as the BEIR-I to BEIR-VI Reports, carried out in each case by a separately constituted committee of scientists, in each case balancing those from within the nuclear energy and nuclear weapons establishments with others from outside that sphere of influence, the BEIR Reports had consistenly found that the linear relationship was the best fit to the existing data, and that there is no reliable evidence to support the existence of a safe threshold when it comes to carcinogenesis/mutagenesis. The BEIR-VII report re-examined all the evidence and found that the case for a no-threshold linear moidel was stronger than ever before, given new supporting data sets that had been acquired since the publication of BEIR-VI. Of course there is the caveat that it is not possible to prove beyond any doubt that such a threshold might exist somewhere, but every time a specific threshold has been proposed it has suibsequently been proven to be erroneous. The 1974 Report on the Ontario Royal Commission on the Health and Safety of Workers in Mines, by Dr James Ham, included a special appendix showing very clearly that the “protective standards” of radiation exposure for uranium miners propsed by the Atomic Energy Control Board at that time were clearly NOT protective of health as the excess of radiation-induced canbcers in the Ontario uranium mining population was undeniable at those levels of exposure. Of course it would be convenient for the industry if the evidence had tilted the other way, but alas it did not, and it still does not.In a press release issued by the BEIR-VII Committee on the release of the BEIR-VII Report we read:WASHINGTON (June 2007) — A preponderance of scientific evidenceshows that even low doses of ionizing radiation, such as gamma raysand X-rays, are likely to pose some risk of adverse health effects, saysa new report from the National Academies’ National Research Council.The report’s focus is low-dose, low-LET — “linear energy transfer” —ionizing radiation that is energetic enough to break biomolecularbonds. In living organisms, such radiation can cause DNA damagethat eventually leads to cancers. However, more research is needed todetermine whether low doses of radiation may also cause other healthproblems, such as heart disease and stroke, which are now seen withhigh doses of low-LET radiation.The study committee defined low doses as those ranging from nearlyzero to about 100 millisievert (mSv) — units that measure radiationenergy deposited in living tissue. The radiation dose from a chest Xrayis about 0.1 mSv. In the United States, people are exposed toaverage annual background radiation levels of about 3 mSv.The committee’s report develops the most up-to-date andcomprehensive risk estimates for cancer and other health effects fromexposure to low-level ionizing radiation. In general, the reportsupports previously reported risk estimates for solid cancer andleukemia, but the availability of new and more extensive data havestrengthened confidence in these estimates.Specifically, the committee’s thorough review of available biologicaland biophysical data supports a “linear, no-threshold” (LNT) riskmodel, which says that the smallest dose of low-level ionizingradiation has the potential to cause a small increase in health risks tohumans. In the past, some researchers have argued that the LNTmodel exaggerates adverse health effects, while others have said that itunderestimates the harm. The preponderance of evidence supportsthe LNT model, this new report says.“The scientific research base shows that there is no threshold ofexposure below which low levels of ionizing radiation can bedemonstrated to be harmless or beneficial,” said committee chairRichard R. Monson, associate dean for professional education andprofessor of epidemiology, Harvard School of Public Health, Boston.“The health risks – particularly the development of solid cancers inorgans – rise proportionally with exposure. At low doses of radiation,the risk of inducing solid cancers is very small. As the overall lifetimeexposure increases, so does the risk.” The report is the seventh in aseries on the biological effects of ionizing radiation.Incidentally, you may observe that the harmful effects of radioactive exposures studied by the BEIR-VII Committee were all based on doses BELOW 100 millisieverts — yet the Canadian Nuclear Safety Commission (CNSC), the modern incarnation of the Atomic Energy Control Board [AECB] — has stated repeatedly that there is “no evidence” of harmful effects of such exposure to radioactive emitters below 100 millisieverts. They too, apparently, base their “science” on only those documents that are produced by the very industry that it is suppsoed to be regulating.Gordon.=======================On Oct 19, 2017, at 10:34 AM, Robin Collins wrote:[CPG] challenging the LNT radiation hypothesisJerry Cutler posted this on a Cdn nuclear listserv, his presentation to the Michigan House committee looking at the topic of low level radiation. It is a fascinating — but certainly controversial — look at the fallacy of LNT (linear, no threshold) radiation regulation. The LNT hypothesis states than any level of radiation exposure in dangerous. The contrary argument is while high levels will kill you, low level radiation is actually beneficial. I encourage you to listen through the full presentation, much of which looks at old data reassessed.
Jerry Cutler’s presentation starts at 11:14. I suggest skipping to that point.==========================On Sep 30, 2017, at 8:53 AM, Robin Collins wrote:
[CPG] Changing radiation safety limits: challenge to LNTFYIThis has been an ongoing debate.
R.
