DNA And The Microwave
Effect
Penn State University
January 20, 2001
Can microwaves disrupt the
covalent bonds of DNA? The fundamentals of thermodynamics and physics indicate
this is impossible. Numerous studies have concluded that there is no evidence
to support the existence of the 'Microwave Effect', and yet, some recent
studies have demonstrated that microwaves are capable of breaking the covalent
bonds of DNA. The exact nature of this phenomenon is not well understood, and
no theory currently exists to explain it. This report summarizes the history
of the controversy surrounding the microwave effect, and the latest research
results.
The effectiveness of
microwaves for sterilization has been well established by numerous studies
over the previous decades (Latimer 1977, Sanborn 1982, Brown 1978, Goldblith
1967). The exact nature of the sterilization effect and whether it is due
solely to thermal effects or to the 'microwave effect' has been a matter of
controversy for decades.
The dielectric effect on
polar molecules has been known since 1912 (DeBye 1929). Polar molecules are
those which possess an uneven charge distribution and respond to an
electromagnetic field by rotating. The angular momentum developed by these
molecules results in friction with neighboring molecules and converts thereby
to linear momentum, the definition of heat in liquids and gases. Because the
molecules are forced to rotate first, there is a slight delay between the
absorption of microwave energy and the development of linear momentum, or
heat. There are some minor secondary effects of microwaves, including ionic
conduction, which are negligible in external heating. Microwave heating is,
therefore, not identical to external heating, at least at the molecular level,
and the existence of a microwave effect is not precluded simply because the
macroscopic heating effects of microwaves are indistinguishable from those of
external heating.
During the 1930s the effects
of low frequency electromagnetic waves on biological materials were studied in
depth by physicists, engineers and biologists. Studies of the effects of
microwaves on bacteria, viruses and DNA were performed in the 1960s and
included research on heating, biocidal effects, dielectric dispersion,
mutagenic effects and induced sonic resonance. Some of the early biophysicists
investigating microwave absorption claimed evidence of a 'microwave effect'
which was distinct in its biocidal effects from the effects of external
heating (Barnes 1977, Cope 1976, Furia 1986). Most biologists in turn claimed
there was no evidence of a microwave effect and that the biocidal effects of
microwaves were either due entirely to heating or were indistinguishable from
external heating (Goldblith 1967, Lechowich 1969, Vela 1978, Jeng 1987,
Fujikawa 1991, Welt 1994). These experiments were repeated with increased
sophistication right up to the present with the majority consensus being that
the microwave effect did not exist.
These experiments typically
fell into two categories, 'controlled temperature' experiments and 'dry'
experiments. In the controlled temperature experiments the researchers
controlled the temperature of the irradiated specimen through various timing,
pulsing or cooling techniques (Welt 1994, Lechowich 1968).
For example, Welt (1994)
investigated the effects of microwave irradiation on Clostridium spores and
found no additional lethality caused by microwaves that could not be accounted
for by conventional heating. However, spores may not be representative of
microwave irradiation effects on active growing bacterial cells. The results
of this and other experiments showed that controlling the temperature
prevented biocidal effects, and this was taken as conclusive evidence that the
microwave effect did not exist. However, the assumption that the microwave
effect is independent of, and separable from, temperature was always implicit
in these studies, but was never acknowledged.
The second type of
experiment, the dry experiment, also contains unacknowledged assumptions.
Studies have shown that in the absence of water or moisture, biocidal effects
of microwaves are severely diminished, or require considerably longer
exposures (Jeng 1987, Vela 1979). This was typically taken as evidence that
nonthermal microwave effects did not exist, however, since water is the
primary medium by which microwaves are converted to heat, the absence of
biocidal effects in the absence of water would only indicate that water is
necessary for sterilization whether or not heating is the cause. Furthermore,
the possibility that the specific frequency used, 2450 MHz, only affects water
and not bacteria or spores was overlooked. DNA has a dielectric dispersion,
where microwaves are readily absorbed, at much lower frequencies than water
(Takashima 1984). The experiments may simply be indicating that the wrong
frequency is being used for targeting 'dry' bacteria and spores.
Most of the studies mentioned
above concluded that the microwave effect, if it existed, was
indistinguishable from the effects of external heating. However, it was
recently demonstrated (Kakita 1995) that the microwave effect is
distinguishable from external heating by the fact that it is capable of
extensively fragmenting viral DNA, something that heating to the same
temperature did not accomplish. This experiment consisted of irradiating a
bacteriophage PL-1 culture at 2450 MHz and comparing this with a separate
culture heated to the same temperature. The DNA was mostly destroyed, a
result that does not occur from heating alone. These photos are borrowed from
Kakita et al (1995), permission pending.
In the Kakita experiment the
survival percentage was approximately the same whether the samples were heated
or irradiated with microwaves, but evaluation by electrophoresis and electron
microscopy showed that the DNA of the microwaved samples had mostly
disappeared. In spite of the evolving complexity of all the previous
experiments, electrophoresis had not been used to compare irradiated and
externally heated samples prior to this. Electron microscopy had been used to
study the bacteriocidal effects of microwaves (Rosaspina 1993, 1994) and these
results also showed that microwaves had effects that were distinguishable from
those of external heating.
The energy level of a
microwave photon is only 10-5 eV, whereas the energy required to break a
covalent bond is 10 eV, or a million times greater. Based on this fact, it has
been stated in the literature that "microwaves are incapable of breaking
the covalent bonds of DNA" (Fujikawa 1992, Jeng 1987), but this has
apparently occurred in the Kakita experiment, even though this may be only an
indirect effect of the microwaves.
There is, in fact, plenty of
evidence to indicate that there are alternate mechanisms for causing DNA
covalent bond breakage without invoking the energy levels of ionizing
radiation (Watanabe 1985, 1989, Ishibashi 1982, Kakita 1995, Kashige 1995,
Kashige 1990, 1994). Still, no theory currently exists to explain the
phenomenon of DNA fragmentation by microwaves although research is ongoing
which may elucidate the mechanism (Watanabe 1996).
The results of microwave
irradiation affected two bacteria, S. aureus and E. coli. The death curves
exhibited classic exponential decay with ab appararent shoulder, as well as a
possible second stage. These curves are based on data from Kakita etal (1999).
The microwave frequency used
in the Kakita study was the standard 2450 MHz used in conventional microwave
ovens. This is the same frequency that was used in essentially all prior
studies, except for the earliest studies (which looked at lower frequencies),
and sonic resonant studies, which looked at much higher frequencies. The early
studies showed that DNA tended to absorb microwave radiation "in the
kilocycle range" (Takashima 1963, 1966, Grant 1978, Grandolfo 1983), but
no biocidal effects in the range of 1 MHz to 60 MHz were observed.
One notable exception,
however, was an early experiment which found that frequencies between 11 and
350 MHz had lethal effects on bacteria, with a peak at 60 MHz (Fleming 1944).
As far as could be determined, the contradiction between the results of
Fleming and those of Takashima has never been resolved or re-addressed. In any
event, there is no evidence in these studies to indicate any undue attention
was paid to control the actual absorbed dose or the precise geometry of the
irradiation cell, and therefore the differences in the results of these
investigators may reflect differences in their cell geometries, among other
things.
In summary, it
would seem there is reason to believe that the microwave effect does indeed
exist, even if it cannot yet be adequately explained. What we know at present
is somewhat limited, but there may be enough information already available to
form a viable hypothesis. The possibility that electromagnetic radiation in
the non-ionizing frequency range can cause genetic damage may have profound
implications on the current controversy involving EM antennae, power lines,
and cell phones.
A Theory of
Microwave Induced DNA Covalent Bond BreakageA review of the data from the
various referenced experiments shows a common pattern -- for the first few
minutes of irradiation there is no pronounced effect, and then a cascade of
microbial destruction occurs. The data pattern greatly resembles the dynamics
of a capacitor; first there is an accumulation of energy, and then a
catastrophic release. It may simply indicate a threshhold temperature has been
reached, or it may indicate a two-stage process is at work.
The second stage of this
process may very well be the accumulation of oxygen radicals, which would
certainly seem to be primary suspects as they have a considerable propensity
for dissociating the covalent bonds of DNA. Oxygen radicals can be generated
by the disruption of a hydrogen bond on a water molecule. Water molecules
exist alongside DNA molecules as "bound" water, two or three layers
thick. These water molecules share a hydrogen bond with component atoms of the
DNA backbone, including carbon, nitrogen and other oxygen atoms. At any given
point in time one of the hydrogen atoms may be primarilly bonded to either an
oxygen atom on the water molecule, or to an oxygen (or other) atom on the DNA
backbone.
The fluctuating character of
these shared and exchanged bonds is enhanced by temperature and by the
dynamics induced by microwaves. Although the amount of oxygen radicals which
may be produced by this process cannot presently be determined, the production
of some number of oxygen radicals is inevitable in these circumstances. It
must be noted here though, that most of the oxygen radicals produced in this
manner would exist only briefly, as they would almost immediately bond to the
nearest available site. If this site is an oxygen atom on the DNA backbone, we
get a covalent bond break, albeit probably only a brief one. Although DNA
tends to repair itself naturally, the simultaneous breakage of a sufficient
number of covalent bonds would lead to a catastrophic failure of the entire
DNA molecule.
Due to the exceedingly large
number of bonds involved, the matter boils down to a reproducible function of
pure probabilities. In other words, after a set and reproducible amount of
time determined by probability functions, you would expect to see DNA
disintegration. And so, what we have is a two-stage process of DNA covalent
bond breakage resulting from oxygen radicals generated by microwave
irradiation. This is one theory, and it awaits experimental verification.
An alternate theory comes
from investigators at Fukuoka University in Japan. In a series of studies not
specifically involving microwaves, these investigators established that
certain ions can stimulate DNA breakage and OH radical production (Kashige eta
al 1990, Kashige et al 1994). They also determined that amino sugars and
derivatives could induce DNA strand breakage (Kashige et al 1991). It is
possible that microwaves may be causing generation of cupric ions and hydroxyl
radicals, and that auto-oxidation of aminosugars in solution are involved in
DNA strand breakage (Watanabe et al 1990, Watanabe et al 1986). The link
between microwaves and these secondary products remains to be established.
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