Is the LNT accurate?

[starcanuck64]

The question is to a large extent moot as the threshold would be below the naturally occurring level of radiation from radioactive potassium in the body, which fits quite comfortably on the linear part of the model.

There may be a level below which all damage might theoretically be repaired, but the body's natural radioactivity is already above that level, so it's really quite pointless to consider it for risk assessment.

As for the question about large vs small animals and cancer for exposure, note that the unit for exposure is energy absorbed per body mass.
And that there are no known animals that are free of cancer (yes, sharks can get cancer too).

Cancer itself takes place as part of a complex chain of events, the initial break in DNA just being one, and there are different degrees of damage that can lead to cancer. From what I understand a double break in DNA is much more likely to produce the kind of mutation that can lead to a cancerous cell than a single strand break. And cancer is also age dependent to a large degree which would indicate a systemic decline that contributes to the growth of tumor cells.

If cancer itself isn't a simple linear process and radiation exposure is a constant that all life has evolved with over several billion years then why does increased radiation levels get so much play in the public forum. Especially since we really don't know at a fine detail what the real effect is of LLR?

The amount of toxic exposure from the "artificial" radiation introduced into our lives is a tiny fraction of the toxic effect of producing and consuming billions of tons of fossil fuels a year. We probably know with a lot more certainty the negative effects of mercury, arsenic, lead, some hydrocarbons and yet they're widely broadcast into the environment with little thought.

It just seems truly bizarre to me people spend so much time pulling their hair out over a risk factor that in real world terms is insignificant while actively embracing an energy and economic model that often puts them in intimate contact with all sorts of serious toxins.

The LNT is meant to capture the risk involved in introducing a potentially harmful condition(radiation) into our lives, countries like Germany and Japan are moving back to using coal for baseload power because of the political resistance to nuclear power, and yet any sensible examination of the physical risk involved(before you even get to climate change) would indicate that fossil fuels are much more of a health risk.

[starcanuck64]

I need to read up on this subject, the more this discussion goes on the less I understand it.

Does anyone have any good articles or books to recommend?

edit- Already I have serious questions about how representative the LNT can be, it was created before the DNA molecule was even identified. Just a small amount of reading shows how complex and resilient cellular function and repair has to be.

http://en.wikipedia.org/wiki/DNA_repair

DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1 million individual molecular lesions per cell per day.[1] Many of these lesions cause structural damage to the DNA molecule and can alter or eliminate the cell's ability to transcribe the gene that the affected DNA encodes.

Another article is dealing with how some areas with high levels of natural background radiation can have lower rates of cancer than neighbouring areas such as Ramsar Iran.

http://en.wikipedia.org/wiki/Linear_no-threshold_model

A 2005 study[13] of Ramsar, Iran (a region with very high levels of natural background radiation) showed that lung cancer incidence was lower in the high-radiation area than in seven surrounding regions with lower levels of natural background radiation. A fuller epidemiological study[14] of the same region showed no difference in mortality for males, and a statistically insignificant increase for females.

I really need to sit down with a good book on the subject to get a grasp of it.

[Van Rijn]

I don't have time right now to discuss this, but I'm adding a couple of links before I lose them:

http://www.physics.harvard.edu/~wils...ppaper644.html

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2647823/

They're discussing assumptions about the linear model which is also used to evaluate chemical carcinogens. There's some interesting background on how the linear model argument got started, and some possible alternatives, at least on the chemical side.

[starcanuck64]

Since that time, physicists have tended to accept Crowther's suggestion that cancer incidence is linear with exposure to radiation, but biologists and physicians have often continued to believe in thresholds.

An interesting division.

Thanks for the articles, they should really help.

[starcanuck64]

I'm starting to realize that this is a political issue more than a technical one.

[starcanuck64]

http://www.pnas.org/content/109/2/443.full

Single time or single dose measurements are snapshots and might not capture the complexity of the IR response of DNA damage-sensing proteins. Here, we present a methodology and a mathematical kinetic model that can characterize the DNA damage response simultaneously across both time and dose levels. Our results provide a more accurate model of RIF dose response, and underscore fundamental concerns about static image data analysis in the dynamic environment of the living cell. We observe that as the number of DSB increases in a cell, the number of RIF does not increase proportionally and the kinetics of RIF formation/disappearance is altered; RIF appear faster but remain longer in the cells as dose levels increase. These nonlinear processes cast considerable doubts on the general assumption that risk to IR is proportional to dose and could be interpreted as the consequence of DNA repair centers in human cells.

Impact of Results for Regulating Risk of IR on Human Populations. The current literature has assumed the linear-no-threshold hypothesis (LNT), which implies that any amounts of IR are harmful. LNT is used to set dose limits for radiation occupational workers or the general public. The LNT is based mainly on data from the Japanese atomic bomb survivors and secondarily on arguments involving the dose-response of surrogate endpoints. Gene mutations are thought to be the initiating events of cancer and they can occur via misrejoining of two DNA DSBs or via point mutation. Physical laws lead us to believe DSB frequencies are proportional to dose. Therefore, it is well accepted that point mutations are linear with dose because it requires only one DSB, whereas DSB misrejoinings are dependent to the dose squared (39). In the dose range of radiation cancer epidemiology, the quadratic term is almost always negligible, especially at low dose rates, as the first lesion is probably repaired before the second mutation occurs (40). However, the amount of DSB clustering at 1 Gy suggests a much higher quadratic term for DSB misrejoining than expected. Therefore, extrapolating risk linearly from high dose as done with the LNT could lead to overestimation of cancer risk at low doses.

http://junksciencecom.files.wordpres...e-muller-1.pdf

Abstract In his Nobel Prize Lecture of December 12,
1946, Hermann J. Muller argued that the dose–response for
radiation-induced germ cell mutations was linear and that
there was ‘‘no escape from the conclusion that there is no
threshold’’. However, assessment of correspondence
between Muller and Curt Stern 1 month prior to his Nobel
Prize Lecture reveals that Muller knew the results and
implications of a recently completed study at the University of Rochester under the direction of Stern, which
directly contradicted his Nobel Prize Lecture. This finding
is of historical importance since Muller’s Nobel Lecture
gained considerable international attention and is a turning
point in the acceptance of the linearity model in risk
assessment for germ cell mutations and carcinogens.

I need to go over this in more detail, but the evidence does point to the model much of the policies regarding radiation exposure are based on is inaccurate.

[starcanuck64]

Some interesting preliminary findings on the effect of very low levels of radiation(below background levels) on cells.

http://www.wipp.energy.gov/pr/2011/L...%20Release.pdf

Results so far, as reported in the Health Physics article, indicate that the cell growth of the
bacteria in the WIPP underground, exposed to less background radiation than the control group,
is hampered.

“Initial results from June 2010 show … the growth of ‘radiation starved’ cells are (sic) inhibited
compared to cells grown in the presence of background radiation levels,” the researchers
reported.

“The noise in the data is still fairly high,” Smith clarified. “It’s preliminary, and we still need more
data to show it as statistically different.”

[HenrikOlsen]

It's interesting to note here that some chemical reactions are catalyzed by radiation (just look at UV-hardening of dental polymer fillings), I wonder if that is part of the effect,

[quotation]

I'm starting to realize that this is a political issue more than a technical one.

ya think?
http://www.nucleartownhall.com/blog/...-ted-rockwell/
From Ted Rockwell:

I’m really frustrated! I’ve been involved with radiation protection since I edited The Shielding Manual in 1956. And with radiation, since I wrote “Frontier Life Among the Atom Splitters” for the SatEvePost (Dec 1, 1945). Continuously since then, I’ve been told that we should never mention hormesis, never try to tell people that radiation behaves like everything else in the world: a little is beneficial, too much is harmful. Like sunshine, like exercise, like all those nasty poisons in our daily vitamins. I’ve been writing, and lecturing, and talking to the person next to me on the airplane. And I’ve never met anyone who had trouble understanding or believing that simple concept. Yet “the experts” keep proclaiming that, although we all understand and believe it ourselves (how can you deny the data?), we shouldn’t try to tell it to the public or the Congress or the media. It’s time to knock off that destructive behavior. Its only function is to protect persons who believe their job depends on scaring people. Radiation protection is an honorable function, and done right, it can help us find ways to operate more profitably, not less. But we in the nuclear community have continually bad-mouthed ourselves and our profession. It’s time to stop it. There is a vast body of good scientific evidence that in the dose range of interest, more radiation is beneficial. But a great deal of effort has gone into hiding that fact. The relevant policy-setting reports like NCRP-136 and -121 concede that the data demonstrate hormesis, but they recommend it would be “prudent” to assume the opposite. It’s not science, but a strange sense of prudence, that leads people to want to hide hormesis.

[starcanuck64]

It's interesting to note here that some chemical reactions are catalyzed by radiation (just look at UV-hardening of dental polymer fillings), I wonder if that is part of the effect,

I was wondering if it could be the lack of ionizing radiation stimulus on the DNA "repair center" that would result in more genetic damage and less expression of dysfunctional genes.