I agree with Michael, that the idea that cancer is caused by breaking DNA bonds is way out of date. 

But the more fundamental point that Chandler is addressing is interesting and important: is the making and breaking of covalent bonds the only way to affect a biological system?  Our knowledge of biophysics tells us that this is not the case.  Proteins are held together in their 3D structure by hundreds and thousands of interactions with energies that are on the order of thermal energy (kT), water molecules inside cells bind to other water molecules and to cytoplasmic macromolecules by hydrogen bonds whose energies are also at the order of thermal energy, proteins bind to other proteins and to DNA with weak non-covalent bonds, proteins have vibrational modes that are often essential in their function, oscillations of ion concentrations are an indispensable part of physiology and development, etc, etc.  All these processes could be affected by electromagnetic radiation whose energy is not sufficient to break covalent bonds of DNA.


But there is a more fundamental point
On May 31, 2011, at 8:18 PM, Chandler Davis wrote:

> Will some physical scientist help me clarify the question
> of whether microwave radiation COULD cause cancer?  Robert
> L. Park, to whom I am grateful for much enlightenment on
> many matters, tirelessly reiterates that the only known
> way for electromagnetic radiation to cause cancer is by
> breaking a bond in DNA, and this requires a photon of
> much higher frequency than microwaves have.  This seems
> to me to be relevant but incomplete, for reasons I will
> give, but Park didn't reply to my query on the point
> (probably misidentifying me as a microwave-alarmist), so
> I'm looking for help from others.
> 	What we must talk about is a high-amplitude wave
> at a frequency too low to break organic bonds, by a factor
> of a few million.  Right?  Park says it doesn't matter how
> high the amplitude is: strengthening the microwave signal
> is (in his metaphor) just increasing the number of rocks
> you try to throw across the Potomac, this doesn't get any
> of them across the river because EACH ROCK has too low an
> energy.  I object that this isn't the whole story, because
> a periodic wave is not exactly sinusoidal, the sine wave at
> its fundamental frequency comes accompanied by harmonics at
> multiples thereof.  In quantum terms, that means that the
> electromagnetic signal consists of photons at the energy
> belonging to the fundamental frequency, accompanied by a
> cloud of photons at multiples of that energy.  Now (as I
> have explained to many undergraduate classes) the higher
> the harmonic the lower the amplitude: for the n-th
> harmonic, the amplitude goes down like 1/n, meaning that
> the power goes down like 1/n^2.  By the time n is around
> a million, this factor is around a trillion.  But not zero.
> (True, a very smooth wave has weaker higher harmonics.)
> In order to be sure a very very strong microwave signal
> could not break a chemical bond, I would have to know
> quantitatively HOW strong.
> 	Maybe somebody here will tell me the numbers on
> this, I haven't looked them up.  It seems evident even
> without having the numbers that putting a mobile phone to
> my ear will not endanger me.  Thus I am as mystified as
> Park by the new, more credible study pointing to some
> correlation with cancer.  But it also seems to me that
> further discussion of the matter ought to include the
> little wrinkle of HIGHER HARMONICS.
> 			Chandler