Physical Models of the Interaction of Mobile Phone Radiation with Cells

At low power levels where thermal effects are unimportant, EMR still maintains the ability to affect cells. Radiation in the very high-energy gamma-ray frequency range, for example, can directly induce ionisation and lead to radical formation. While this has clear implications for biology, the energy associated with the visible region and down to the radio frequency is not sufficient to remove electrons from atomic or molecular orbitals, i.e. they are not ionising radiations. For example, radiofrequency EMR, at the gigahertz frequencies used in mobile phone communications, can be considered to be a stream of particles, or photons, with energies one million times less than the energies required to directly alter the chemistry of molecules.

Several hypotheses exist which may explain the interaction of RF-EMR with biology, including the male reproductive system and spermatozoa. The difficulty comes in identifying a physical mechanism by which RF radiation at low levels, 106 times lower than required to directly ionise molecules, can cause biochemical effects. Indeed, as summarised by Phillips et al. [9] "we are at the stage of having inconsistent results and no proven mechanism to explain RF-induced effects on DNA damage". This is in spite of the fact that there are structures in the body that are extremely sensitive to EMR. For example, a single photon of visible light can cause a change in rhodopsin causing a polarisation in a rod cell in the retina [1]. Different authors have surveyed the range of physical mechanisms which may result in RF-induced biochemical effects. Sheppard et al. [2] argue that possible mechanisms including coherence, resonance, signal averaging, field non-uniformity in inhomogeneous dielectric structures and nonlinear effects all produce effects far below the levels of the electric fields associated with normal bodily processes of wound healing and excitation of muscles and the nervous system. Challis [10] identified one possible non-thermal process—free radical generation in biomolecules with large hyperfine splittings and fast relaxation. In this process, if the EM frequency is resonant with the difference between energy levels in a molecule, then the energy from the external signal can be concentrated, leading to an amplified response at the driving frequency. However, the degree of amplification decreases with the losses in the system. Since most ions are associated with water, the energy dissipation by collisions of water molecules increases the loss of the system at RF frequencies and limits the degree of amplification which can be achieved in resonant systems.

Two other processes commonly used to justify RF effects on cells are the development of additional potentials across membranes which lead to a change in ion transport [11-15] and alteration of normal vibrations of molecular bonds, perhaps affecting proteins and the activities and interactions [16, 17] through alterations in protein conformation. An alteration of ion transport across cell membranes is possible, but only for fields of several hundreds of millivolts, much higher than the resting voltages across membranes, even of organelles such as the mitochondria. Modelling of transient voltages across organelle structures show that if the organelle membrane is thicker than the cell membrane and the organelle contains a high ion concentration, it is possible at RF frequencies for the voltage across the organelle membrane to be larger than that across the cell membrane [15]. Indeed, the change in voltage is of the order of ER [18], where E is external field and R is cell radius in the direction parallel to the field—changes may give rise to 100 mV changes in membrane potential. However, if a voltage is applied across a tissue, most of the voltage drop appears across the membrane at low frequencies. At gigahertz frequencies, the capacitance of the membrane effectively shorts out the membrane resistance at gigahertz frequencies, so the above effects are unlikely in that frequency range.

Cotgreave [19] argues that cellular proteins have different structures and would be expected to behave differently when exposed to RF. In addition, many proteins are in electrostatic contact, so RF-EMR may affect organisation of proteins within the cell. Studies have shown denaturation, aggregation and stability of proteins are affected by RF exposure [20, 21]. Indeed, the efficiency of a protein as an enzyme depends on its conformation. Several side chains of amino acids in proteins are polar and so will behave differently in EM fields. Experiments at high irradiation levels (3 h of 1.95 GHz irradiation at 51 W kg-1) have been shown to affect protein folding [22], Soa possible physical model suggests that resonances with charges and dipoles in each protein conformation change the barrier heights for intermediate processes in the refolding pathways [22] , However, dissipative effects discussed previously would reduce the effect of resonant excitation of dynamic excitations, making it difficult to imagine a mechanism at gigahertz frequencies.

In summary, even though several hypotheses exist for effects of non-ionising, mobile phone range EMR on biology, there is no clear proven mechanism. This is a key point to which much of the debate about the reported detrimental effects of EMR are based. Nonetheless, because there is no known mechanism at this point does not prove there is no effect. With this unknown and the many conflicting reports in the literature over the past decade, this field remains controversial.

Pregnancy Guide

Pregnancy Guide

A Beginner's Guide to Healthy Pregnancy. If you suspect, or know, that you are pregnant, we ho pe you have already visited your doctor. Presuming that you have confirmed your suspicions and that this is your first child, or that you wish to take better care of yourself d uring pregnancy than you did during your other pregnancies; you have come to the right place.

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