H-FIELD CONTRIBUTION TO THE ELECTROMAGNETIC ENERGY DEPOSITION IN TISSUES SIMILAR TO THE BRAIN BUT CONTAINING FERRIMAGNETIC PARTICLES, DURING USE OF FACE-HELD RADIO TRANSCEIVERS

A portable radio transceiver with rubber ducky antenna emitting at 446 MHz with an output power of 5W was considered as near-field source of electric (E) and magnetic (H) field components when being used in the proximity of the user’s face. By taking into account the significant content of ferrimagnetic nanoparticles recently identified to reside in the human brain, we assessed the specific absorption rate (SAR) of energy deposition due to H-component penetrating a presumptive forebrain. H-component SAR contribution to the total SAR is for the first time estimated in such a case, based on an original idea inspired from knowledge on magnetic fluids hyperthermia. 1. MAGNETIC PROPERTIES OF BRAIN TISSUE AND THE APPROACH OF ELECTROMAGNETIC DOSIMETRY In 1992 Kirschvink and colleagues reported, for the first time, the presence of magnetic material in the human brain in the form of tiny crystals of magnetite, which were hypothesized to have biogenic origin [1]. Some other human organs were later proved to contain biogenic ferrimagnetic materials: liver, spleen, pancreas, heart and lungs. Recently, all these tissues were carefully investigated by Sant’Ovaia et al. [2] who reported presence of magnetic biominerals in various proportions and locations in human body tissues and classified them taking into account their mean magnetic susceptibility and their saturation isothermal remanent magnetization. In the present, scientific evidence indicates the presence of six iron oxides in human brain tissue [3], and oxides are well characterized. However, the exact role of magnetic minerals in tissues remains unclear after decades of study. In the case of the brain, a few hypotheses exist — it seems that magnetite crystals are located in neurons, and they might be involved in the storage of memory. A very recent hypothesis [4] sustains that magnetite deposited in the outer membranes of the brain could even act as a shield against external electromagnetic radiation. Up to the end of 2014, the knowledge about magnetite distribution in the brain indicated that piaand dura-mater outer layers of human brain contain 108 magnetite nanocrystals per gram, organized in clusters, while other brain tissues contain about 5 × 106 nanocrystals per gram [4]. Dimensions of biogenic magnetite crystals are in the range of 30–70 nm, and their shapes are angular, cubo-octahedral or prismatic. In September 2016, a surprising discovery was reported by Maher and coworkers [5]. They identified a very high quantity of magnetic crystals in human brain tissues — which had an external, environmental origin. It seems that anthropogenic magnetic particles, which can be generated by some professional activities, are able to penetrate in the head by respiratory tract and to store in the brain, adding to the Received 1 January 2017, Accepted 12 February 2017, Scheduled 1 March 2017 * Corresponding author: Simona Miclaus (simo.miclaus@gmail.com). 1 Department of Technical Sciences, “Nicolae Balcescu” Land Forces Academy, Sibiu, Romania. 2 Department of Environmental Sciences and Physics, Faculty of Sciences, “Lucian Blaga” University of Sibiu, Romania. 50 Miclaus, Racuciu, and Bechet afore-discovered biogenic magnetite. The shape of exogenous magnetite particles discovered in human brains is different — being rounded, and the “nanospheres” may present fused surface textures. The concentrations are in the range 0.2–12 μg of magnetic material per gram of dry tissue, and the diameters are spread between 10–150 nm. Moreover, in December 2016, the authors of [6] have shown that a combination of two specific methods offers a unique possibility to study and properly characterize the iron accumulation in the human brain. They also formulated the observation that magnetic moments of magnetite/maghemite nanoparticles are blocked for sizes exceeding 40–50 nm at the room temperature. Back in 1996, Kirschvink formulated a hypothesis on the mechanism of transduction of the nonthermal electromagnetic energy by magnetite and underlined the need of a cellular-level dosimetric investigation in the very proximity of magnetite crystals in the brain [7]. The first ones to raise the question about a possible connection between “environmental levels” of magnetic (H) field strength (arising from mobile phones radiation) and some possible deleterious biological effects were the group of Cranfield in 2003 [8]. However, in a second paper of the same group published soon after their first one [9], they reported that the magnetite-containing bacteria used as a target were not affected by H field of the radiofrequency (RF) radiation emitted by mobile phone. A second wave of concern, connected to effects of H-component of “environmental levels” of electromagnetic fields, was signaled by the publication in 2014 of a paper by Engels et al. [10] who reported that a species of migratory birds, European robins (Erithacus rubecula), when being exposed to the background electromagnetic noise in the frequency range 50 kHz–5 MHz, were not able to orient anymore based on their magnetic compass in the brain. The study, which was completely doubleblinded, also demonstrated that the effect of anthropogenic electromagnetic noise on the behavior of birds was reproducible. In 2009, Milham even raised the hypothesis that there was a connection between firemen cancers cases and the use of portable radio transceivers used in front of the face [11]. With aforementioned gathered biological data, it becomes evident that H-field component needs a more careful consideration, especially when RF dosimetry is applied in tissues containing magnetic materials. An early but rare approach in the direction of H-field RF dosimetry was made by Kuster and Balzano in 1992 [12], who analyzed electromagnetic energy deposition generated by H-field component. The idea was re-launched in 2015 by Rubtsova et al. [13] in connection to exposure assessments in the near field of personal wireless telecommunication devices. Present approach proposes that in some specific exposure cases, to express specific absorption rate (SAR) of energy deposition in human tissues (heating) by taking into account both contributions: the one due to the electric (E) field, (SAR E), and the one due to H-field, (SAR H). Presently, the general rule is to report only SAR E value, because human tissues are considered as dielectric materials, without having magnetic properties. Consequently, experimental RF dosimetry makes use of only E-field probes, but not H-field probes. SAR E can be calculated by the formula [14]: