1) radiation is cumulative (and the implication that effects on humans is cumulative) 2) the amount of radiation, no matter how low, carries risk
1) Theoretically, yes, but in the real world, cells are constantly being bombarded by background radiation and, most often, repair themselves. Empirical studies to prove impact of very low doses is difficult if not impossible. Also, in cases where radiation is high enough to kill the cell, then the impact is not cumulative - e.g. radioiodine treatment for thyroid cancer.
2) While it's true that the NAS agrees with the linear no-threshold model (LNT), and most use this model when estimating risk, not all universally agree. The UN's UNSCEAR, the Health Physics Society and the French (because they're French) either urge caveats or disagree with it. After all it's a model, and it's not easily testable when exposure doses are below background level. Even the EPA, which endorses LNT, warns:
"Estimates [of cancers caused by low-level radiation] include uncertainty, because of major challenges in making the estimates:
- Developing an exposure history can be extremely difficult.
- Separating the effects from exposure levels that are tens or hundreds
of times smaller than exposures due to background is extremely difficult.
- Determining whether radiation exposure is the cause of a particular
occurrence of a health effect, such as cancer. Many chemicals are also
carcinoge
Here's a good example (involving Chernobyl) of why the impact of minuscule doses of radiation are difficult to estimate (from American Physical Society):
" Dr. Wolfe is correct: the deaths *attributable* to the Chernobyl accident are only about 40. But he is incomplete and, to this extent, misleading because, as Garwin points out, the number of deaths worldwide that are calculated may be 20,000. It is important to say "maybe" because the calculation is based on a linear no threshold theory and most of the deaths (if they come) will come from very low levels that are indistinguishable from the variable background. Neither scientist made the important point that the general arguments for a linear no threshold theory apply to a vast number of other situations in society where society conventionally ignores the effects of low exposures. Air pollution is the most well known example but only one of many. Many scientists believe air that pollution is causing the (delayed) deaths of tens of thousands of people in the USA *every year.*
"Unless this or a similar comparison is made (as Dr. Garwin did not do and has not done on many other occasions) the discussion of the large number of calculated deaths from Chernobyl can be highly misleading."
http://www.aps.org/units/fps/newsletters/1999/april/lapr99.html "It has been difficult to estimate cancer induction risks, because most of the radiation exposures that humans receive are very close to background levels. At low dose levels of millirems to tens of rems, the risk of radiation-induced cancers is so low, that *if* the risk exists, it is not readily distinguishable from normal levels of cancer occurrence. In addition, leukemia or solid tumors induced by radiation are indistinguishable from those that result from other causes." http://web.princeton.edu/sites/ehs/osradtraining/biologicaleffects/page.htm
On Thu, Mar 17, 2011 at 4:15 PM, Gar Lipow <gar.lipow at gmail.com> wrote:
> There is not such thing as a "threshold". And amount of radiation, no
> matter how low carries risk. Radiation is cumulative. So short term
> damage might be the same, adjusting for population, but the same
> methodology incorporating just that one change would give larger long
> term estimates.
>
>
-- Peter Fay http://theclearview.wordpress.com