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DNA And The Microwave
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 Breakage
A 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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