Evaluation of Specific Absorption Rate as a Dosimetric Quantity for Electromagnetic Fields Bioeffects

Carlo GL (2013) Evaluation of Specific Absorption Rate as a Dosimetric Quantity for Electromagnetic Fields Bioeffects. PLoS ONE 8(6): e62663. doi:10.1371/journal.pone.0062663 Evaluation of Specific Absorption Rate as a Dosimetric Quantity for Electromagnetic Fields Bioeffects Dimitris J. Panagopoulos 0 Olle Johansson 0 George L. Carlo 0 Nils Cordes, Dresden University of Technology, Germany 0 1 Department of Biology, University of Athens , Athens , Greece , 2 Radiation and Environmental Biophysics Research Centre , Athens , Greece , 3 Experimental Dermatology Unit, Department of Neuroscience, Karolinska Institute, Stockholm, Sweden, 4 The Science and Public Policy Institute, Institute for Healthful Adaptation , Washington, D.C. , United States of America Purpose: To evaluate SAR as a dosimetric quantity for EMF bioeffects, and identify ways for increasing the precision in EMF dosimetry and bioactivity assessment. Methods: We discuss the interaction of man-made electromagnetic waves with biological matter and calculate the energy transferred to a single free ion within a cell. We analyze the physics and biology of SAR and evaluate the methods of its estimation. We discuss the experimentally observed non-linearity between electromagnetic exposure and biological effect. Results: We find that: a) The energy absorbed by living matter during exposure to environmentally accounted EMFs is normally well below the thermal level. b) All existing methods for SAR estimation, especially those based upon tissue conductivity and internal electric field, have serious deficiencies. c) The only method to estimate SAR without large error is by measuring temperature increases within biological tissue, which normally are negligible for environmental EMF intensities, and thus cannot be measured. Conclusions: SAR actually refers to thermal effects, while the vast majority of the recorded biological effects from man-made non-ionizing environmental radiation are non-thermal. Even if SAR could be accurately estimated for a whole tissue, organ, or body, the biological/health effect is determined by tiny amounts of energy/power absorbed by specific biomolecules, which cannot be calculated. Moreover, it depends upon field parameters not taken into account in SAR calculation. Thus, SAR should not be used as the primary dosimetric quantity, but used only as a complementary measure, always reporting the estimating method and the corresponding error. Radiation/field intensity along with additional physical parameters (such as frequency, modulation etc) which can be directly and in any case more accurately measured on the surface of biological tissues, should constitute the primary measure for EMF exposures, in spite of similar uncertainty to predict the biological effect due to non-linearity. - Specific Absorption Rate (SAR) is defined as the amount of absorbed non-ionizing radiation power (or rate of absorbed energy) by unit mass of biological tissue. The reason for the introduction of SAR as a non-ionizing radiation Radio Frequency (RF) Electromagnetic Field (EMF) dosimetric quantity, was as with the rate of absorbed dose in the ionizing case to describe the amount of absorbed energy and the rate by which it is absorbed within an exposed tissue and not just the radiation/field intensity on its surface. This derives from the fact that when radiation exposes matter, most usually, it does not interact completely with it and in such a case only a part of its energy gets absorbed. The remainder just passes through without affecting the medium. The amount of absorbed energy by a certain amount of matter (within a certain time interval) will determine the degree of interaction. But in the case of biological matter this is not as simple. Biological tissue is a much more complicated and organized form of matter compared to inanimate. The degree of interaction does not necessarily determine the biological effect because that depends on which specific bio-molecule or set of bio-molecules from a whole tissue or organ will interact with the radiation. Some bio-molecules may get damaged while others may not by the same amount of radiation energy absorbed within the same time-interval. Interaction between man-made electromagnetic radiation and living matter Man-made electromagnetic waves are produced by electromagnetic oscillation circuits (Thomson circuits), not by atomic events (as in the case of natural electromagnetic radiation infrared, visible, ultraviolet, x-rays, c), and for this they are polarized in contrast to natural electromagnetic radiation that is not. The plane of polarization is determined by the geometry of the circuit. Polarized electromagnetic waves (in contrast to nonpolarized) can produce interference effects and induce coherent forced-vibrations on charged/polar molecules within a medium. When a polarized, non-ionizing electromagnetic oscillation wave passes through a mass of polar and charged molecules, such as those composing biological tissue induces a forcedoscillation on each of these particles that it meets and transfers to each of them a tiny part of its energy. This induced oscillation will be most intense on the free particles which carry a net electric charge such as the free (mobile) ions that exist in large concentrations in all types of cells or extracellular biological tissue determining practically all cellular/biological functions [1,2]. The induced oscillation will be much weaker or even totally negligible on the polar biological macromolecules and the water molecules that do not have a net charge and additionally are usually bound chemically to other molecules. After each such event of interaction between the wave and a charged or polar particle, the remaining wave continues on its way through the tissue possibly scattered by a tiny angle and reduced by a tiny amount in its amplitude/intensity. After large numbers of such events, depending on the tissues mass, density, and the number of polar/charged molecules, the remaining wave, if any, leaves the tissue as a scattered wave of reduced amplitude/ intensity. When the amplitude/intensity E of the oscillating field or wave is decreasing after interaction with the charged/polar molecules of a medium, its energy density decreases as well, according to the equation for the energy density of a plane, harmonic electromagnetic wave (as those usually produced by Thomson circuits): Wem is the total energy per unit volume of the electromagnetic wave, and E the intensity of the electric component of the wave within a medium with relative permittivity e. eo = 8.854610212 C2/N?m2 is the vacuum permittivity. That means that a part of its energy per unit volume is transferred to the charged/polar molecules of the medium. The amount of energy absorbed by a single free ion within biological tissue will manifest itself as kinetic energy of the forcedoscillation induced on that particle. The maximum kinetic energy of the f (...truncated)