Methodology of detailed dosimetry and treatment of uncertainty and variations for in vivo studies

Detailed and accurate dosimetric information is a basic precondition for acquiring adequate interpretations and valuations of in vivo studies testing radiofrequency (RF) electromagnetic fields (EMF). Instantaneous locally induced fields depend on many parameters, for example, orientation of the animal with respect to the incident field, animal size and posture, and tissue distribution. These parameters are often constrained, resulting in significant uncertainties in the dosimetric assessment of the exposure, averaged over all animals and the entire experimental phase, as well as in significant variations of the local exposures during the experiment. A sufficient analysis should therefore include (1) average and peak spatial specific absorption rate (SAR) values for the whole body and specific organs, (2) the uncertainty of each assessed SAR value, and (3) the short term and long term SAR variations between the tissues of individual animals. A methodology to obtain this pertinent information is developed and proposed in this paper. Using this methodology the dosimetry of a rat exposure apparatus operating at the carrier frequency of 1747 MHz, previously developed for a 2-year bioassay study within the European Union project PERFORM, was obtained. We have demonstrated that comprehensive dosimetric data can be obtained with reasonable effort using the proposed method, providing that the exposure setup is soundly formulated.     

A study of absorption of energy of the extremely high frequency electromagnetic radiation in the rat skin by various dosimetric methods and approaches

Using experimental and theoretical methods of dosimetry, the energy absorption of extremely high-frequency electromagnetic radiation (EHF EMR) in the skin of laboratory rats was analyzed. Specific absorption rate (SAR) in the skin was determined on the basis of both microthermometric measurements of initial rates of temperature rise in rat skin induced by the exposure and microcalorimetric measurements of specific heat of the skin. Theoretical calculations of SAR in the skin were performed with consideration for dielectric parameters of rat skin obtained from the measurements of the standing wave ratio upon reflection of electromagnetic waves from the skin surface and for the effective area of stationary overheating measured by infrared thermography. A numerical method was developed to determine electromagnetic wave energy reflected, absorbed, and transmitted in the model of flat layers. The algorithm of the method was realized in a computer program and used to calculate SAR in the skin on the basis of the complex dielectric constant of rat skin. The SAR values obtained from experimental measurements, theoretical calculations and numerical analysis are in good mutual correspondence and make about 220-280 W/kg at a frequency of 42.25 GHz and a power of 20 mW at the radiator output. The results obtained can be used for dosimetric supply of biomedical experiments on studying the physicochemical mechanisms of the biological effects of EHF EMR.     

Effect of pierced metallic objects on SAR distributions at 900 MHz

A study of the interaction between mobile phone antennas and a human head in the presence of different types of metallic objects, attached and pierced to the compressed ear, is presented in this article. Computed and measured results have been performed by considering a quasi-half-wavelength dipole as the radiating source and measurements with the DASY4 dosimetric assessment system. Two different human head models have been implemented: a homogeneously shaped sphere and a three-level head model with four different kinds of tissue. Antenna input impedance, reflection coefficient, radiation patterns, SAR distribution, absorbed power, and peak SAR values have been computed and measured for diverse scenarios, electromagnetic simulators, and organs. Despite the measuring accuracy limitations of the study, both simulated and measured results suggest that special attention has to be paid to peak SAR averaged values when wearing metallic objects close to the radiation source, since some increment of peak SAR averaged values is expected.     

Wireless Wearables and Implants: A Dosimetry Review

Wireless wearable and implantable devices are continuing to grow in popularity, and as this growth occurs, so too does the need to consider the safety of such devices. Wearable and implantable devices require the transmitting and receiving of electromagnetic waves near and through the body, which at high enough exposure levels may damage proximate tissues. The specific absorption rate (SAR) is the quantity commonly used to enumerate exposure levels, and various national and international organizations have defined regulations limiting exposure to ensure safe operation. In this paper, we comprehensively review dosimetric studies reported in the literature up to the year 2019 for wearables and implants. We discuss antenna designs for wearables and implants as they relate to SAR values and field and thermal distributions in tissue, present designs that have made steps to reduce SAR, and then review SAR considerations as they relate to applied devices. As compared with previous review papers, this paper is the first review to focus on dosimetry aspects relative to wearable and implantable devices. Bioelectromagnetics. 2020;41:3–20 © 2019 The Authors. Bioelectromagnetics published by Wiley Periodicals, Inc.     

Exposure of human peripheral blood lymphocytes to electromagnetic fields associated with cellular phones leads to chromosomal instability

Whether exposure to radiation emitted from cellular phones poses a health hazard is at the focus of current debate. We have examined whether in vitro exposure of human peripheral blood lymphocytes (PBL) to continuous 830 MHz electromagnetic fields causes losses and gains of chromosomes (aneuploidy), a major "somatic mutation" leading to genomic instability and thereby to cancer. PBL were irradiated at different average absorption rates (SAR) in the range of 1.6-8.8 W/kg for 72 hr in an exposure system based on a parallel plate resonator at temperatures ranging from 34.5-37.5 degrees C. The averaged SAR and its distribution in the exposed tissue culture flask were determined by combining measurements and numerical analysis based on a finite element simulation code. A linear increase in chromosome 17 aneuploidy was observed as a function of the SAR value, demonstrating that this radiation has a genotoxic effect. The SAR dependent aneuploidy was accompanied by an abnormal mode of replication of the chromosome 17 region engaged in segregation (repetitive DNA arrays associated with the centromere), suggesting that epigenetic alterations are involved in the SAR dependent genetic toxicity. Control experiments (i.e., without any RF radiation) carried out in the temperature range of 34.5-38.5 degrees C showed that elevated temperature is not associated with either the genetic or epigenetic alterations observed following RF radiation-the increased levels of aneuploidy and the modification in replication of the centromeric DNA arrays. These findings indicate that the genotoxic effect of the electromagnetic radiation is elicited via a non-thermal pathway. Moreover, the fact that aneuploidy is a phenomenon known to increase the risk for cancer, should be taken into consideration in future evaluation of exposure guidelines.     

Large scale in vitro experiment system for 2 GHz exposure

A beam formed radiofrequency (RF) exposure-incubator employing a horn antenna, a dielectric lens, and a culture case in an anechoic chamber is developed for large scale in vitro studies. The combination of an open type RF exposure source and a culture case through which RF is transmitted realizes a uniform electric field (+/-1.5 dB) in a 300 x 300 mm area that accommodates 49 35 mm diameter culture dishes. This large culture dish area enables simultaneous RF exposure of a large number of cells or various cell lines. The RF exposure source operates at 2142.5 MHz corresponding to the middle frequency of the downlink band of the International Mobile Telecommunication 2000 (IMT-2000) cellular system. The dielectric lens, which has a gain of 7 dB, focuses RF energy in the direction of the culture case and provides a uniform electric field. The culture case is sealed and connected to the main unit for environmental control, located outside the anechoic chamber, via ducts. The temperature at the center of the tray, which contains the culture dishes in the culture room, is maintained at 37.0 +/- 0.2 degrees C by air circulation. In addition, the appropriate CO2 density and humidity supplied to the culture case realizes stable long-term culture conditions. Specific absorption rate (SAR) dosimetry is performed using an electric field measurement technique and the Finite Difference Time Domain (FDTD) calculation method. The results indicate that the mean SAR of the culture fluid at the bottom of the 49 (7 x 7 array) culture dishes used in the in vitro experiments is 0.175 W/kg for an antenna input power of 1 W and the standard deviation of the SAR distribution is 59%. When only 25 culture dishes (5 x 5 array) are evaluated, the mean SAR is 0.139 W/kg for the same antenna input power and the standard deviation of the SAR distribution is 47%. The proliferation of the H4 cell line in 72 h in a pair of RF exposure-incubators reveals that the culture conditions are equivalent to those of a common CO2 incubator.     

Postresonance electromagnetic absorption by man and animals

A surface integral equation (SIE) method is used to calculate the specific absorption rate (SAR) in spherically capped cylindrical models irradiated by an axially incident electromagnetic plane wave (K polarization) in a frequency range for which calculations previously have not been available (80–400 MHz for man models). In the SIE method, the electromagnetic (EM) field relations are formulated in terms of electric and magnetic currents on the surface of the model. The average SAR is calculated from the far scattered EM fields by means of the forward scattering theorem. SAR data calculated by the SIE method agree with data calculated by the extended boundary condition method (EBCM) for frequencies up to 80 MHz (the upper frequency limit of the EBCM) for man models. For rat models exposed to 1–3 GHz radiation, reasonable agreement was also obtained with the limited experimental data available.     

Absorption of electromagnetic surface waves by electrons in a transition layer between the plasma and dielectric

The effect of the Debye layer on the absorption of an electromagnetic surface wave propagating along the plasma-dielectric interface is considered. The electric field distribution in the Debye layer and the energy absorbed by the plasma electrons in this layer are determined. It is shown that the ratio of the rate at which surface waves are damped due to Cherenkov absorption by the electrons reflected from the electric field potential in the transition layer to their frequency is on the order of the ratio of the electron thermal velocity to the wave phase velocity.     

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

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.     

Effects of a brain tumor in a dispersive human head on SAR and temperature rise distributions due to RF sources at 4G and 5G frequencies

In this paper, effects of a brain tumor located in a dispersive human head model on specific absorption rate (SAR) and temperature rise distributions due to different types of RF sources at 4G and 5G cellular frequencies are investigated with the use of a multiphysics model. This multiphysics model analyzes the dispersive human head with the brain tumor and provides the SAR and temperature rise distributions in the head due to the RF source operated at 4G and 5G cellular frequencies in a single finite-difference time-domain simulation. An adjacent antenna operated at 4G and 5G cellular frequencies to the human head is considered as the RF source for near-field exposure, while a plane wave field radiated by base stations operated at 4G and 5G cellular frequencies is considered as the RF source for far-field exposure. Numerical results show that the brain tumor in the head slightly affects the SAR and temperature rise distributions due to different RF sources at 4G and 5G cellular frequencies.     

Systems for exposing mice to 2,450-MHz electromagnetic fields

Two systems for exposing mice to 2,450-MHz electromagnetic fields are described. In a waveguide system, four mice were placed in a Styrofoam cage and exposed dorsally to circularly polarized electromagnetic fields. The temperature and humidity in the mouse holder were kept constant by forced-air ventilation. For 1-W input power to the waveguide, the average specific absorption rate (SAR) was determined by twin-well calorimetry to be 3.60 ± 0.11 (SE) W/kg in 27-g mice. The maximum SAR at the skin surface determined thermographically was 8.36 W/kg in the head of the mouse. The second system was a miniature anechoic chamber. Six mice were irradiated dorsally to far field plane waves. Copper shielding and high-temperature absorbing material were lined inside the chamber to accommodate the high input power. The air ventilation at the location of the mice was separately controlled so that any heating in the absorber would not affect the animals. For 1-W input power, the average SAR was 0.17 ± 0.01 W/kg and the maximum SAR at the skin surface was 0.41 W/kg in the animal when irradiated with body axis parallel to the E field; the SARs were 0.11 ± 0.01 W/kg and 0.64 W/kg, respectively, when irradiated perpendicular to the E field.     

RF Energy Absorption in Human Bodies Due to Wearable Antennas in the 2.4 GHz Frequency Band

Human exposure to electromagnetic fields produced by two wearable antennas operating in the 2.4 GHz frequency band was assessed by computational tools. Both antennas were designed to be attached to the skin, but they were intended for different applications. The first antenna was designed for off-body applications, i.e. to communicate with a device placed outside the body, while the second antenna model was optimized to communicate with a device located inside the body. The power absorption in human tissues was determined at several locations of adult male and female body models. The maximum specific absorption rate (SAR) value obtained with the off-body antenna was found on the torso of the woman model and was equal to 0.037 W/kg at 2.45 GHz. SAR levels increased significantly for the antenna transmitting inside the body. In this case, SAR values ranged between 0.23 and 0.45 W/kg at the same body location. The power absorbed in different body tissues and total power absorbed in the body were also calculated; the maximum total power absorbed was equal to 5.2 mW for an antenna input power equal to 10 mW. Bioelectromagnetics. 2020;41:73–79 © 2019 Wiley Periodicals, Inc.     

Dielectric properties of muscle and liver from 500 MHz–40 GHz

Dielectric properties are the most important parameters determining energy deposition when biological tissues are exposed to radio frequency and microwave fields. Energy absorption is determined by the specific absorption rate (SAR). SAR distributions can be computed accurately only if the complex relative permittivity of the target tissue is known to a sufficiently high accuracy, and currently there is a lack of data on the dielectric properties of biological tissues at high frequencies. In this study, tissue dielectric properties are measured using an open-ended coaxial probe technique from 500 MHz up to 40 GHz. We present dielectric data for ex vivo bovine and porcine muscle and liver tissues at 37 °C. One-pole Cole–Cole model is used to fit the measured data as a function of frequency and the dispersion parameters are presented. This data is supported by an accurate study on reference liquids such as methanol and ethanediol.     

Influence of a 902.4 MHz GSM signal on the human visual system: investigation of the discrimination threshold

The proximity of a mobile phone to the human eye raises the question as to whether radiofrequency (RF) electromagnetic fields (EMF) affect the visual system. A basic characteristic of the human eye is its light sensitivity, making the visual discrimination threshold (VDThr) a suitable parameter for the investigation of potential effects of RF exposure on the eye. The VDThr was measured for 33 subjects under standardized conditions. Each subject took part in two experiments (RF-exposure and sham-exposure experiment) on different days. In each experiment, the VDThr was measured continuously in time intervals of about 10 s for two periods of 30 min, having a break of 5 min in between. The sequence of the two experiments was randomized, and the study was single blinded. During the RF exposure, a GSM signal of 902.4 MHz (pulsed with 217 Hz) was applied to the subjects. The power flux density of the electromagnetic field at the subject location (in the absence of the subject) was 1 W/m(2), and numerical dosimetry calculations determined corresponding maximum local averaged specific absorption rate (SAR) values in the retina of SAR(1 g) = 0.007 W/kg and SAR(10 g) = 0.003 W/kg. No statistically significant differences in the VDThr were found in comparing the data obtained for RF exposure with those for sham exposure.     

Effects of 171 MHz Low‐Intensity Electromagnetic Field on Glucocorticoid and Mineral Corticoid Activity of the Adrenal Glands of Rats

A sub‐acute electromagnetic field (EMF) biological effect study was carried out on rats exposed in the Transverse ElectroMagnetic exposure chamber at 171 MHz Continuous Wave (CW). The experiments involved three exposure levels (15, 25, and 35 V/m) for 15 days with triplicate parallel sham‐exposed controls in each series. All exposure conditions were simulated for the evaluation of the electromagnetic energy distribution and specific absorption rate (SAR) in the rat phantoms. Studies have shown a biphasic biological response depending on time and absorbed electromagnetic energy. Under low SAR, approximately 0.006 W/kg, EMF exposure leads to the stimulation of adrenal gland activity. This process is accompanied by an initial increase of daily excretion of corticosterone and Na⁺, which is seen as a higher Na⁺/K⁺ ratio, followed by a decrease of these parameters over time. It is possible that EMF exposure causes a stress response in animals, which is seen as an increased adrenal activity. Bioelectromagnetics. 2019;40:578–587. © 2019 Bioelectromagnetics Society.     

Harmful effects of 41 and 202 MHz radiations on some body parts and tissues

Many types of invisible electromagnetic waves are produced in our atmosphere. When these radiations penetrate our body, electric fields are induced inside the body, resulting in the absorption of power, which is different for different body parts and also depends on the frequency of radiations. Higher power absorption may result into health problems. In this communication, effects of electromagnetic waves (EMW) of 41 and 202 MHz frequencies transmitted by the TV tower have been studied on skin, muscles, bone and fat of human. Using international standards for safe exposure limits of specific absorption rate (SAR), we have found the safe distance from TV transmission towers for two frequencies. It is suggested that transmission towers should be located away from the thickly populated areas and people should keep away from the transmission towers, as they radiate electromagnetic radiations that are harmful to some parts/tissues of body.     

Biological effects of high-frequency electromagnetic fields on Salmonella typhimurium and Drosophila melanogaster

Salmonella typhimurium and Drosophila melanogaster were exposed to continuous wave (CW) 2.45-GHz electromagnetic radiation, pulsed 3.10-GHz electromagnetic radiation, CW 27.12-MHz magnetic fields, or CW 27.12-MHz electric fields (only Drosophila). The temperatures of the treated sample and the nonexposed control sample were kept constant. The temperature difference between exposed and control samples was less than +/- 0.3 degrees C. Ames' assays were made on bacteria that had been exposed to microwaves (SAR 60-130 W/kg) or RF fields (SAR up to 20 W/kg) when growing exponentially in nutrient broth. Survival and number of induced revertants to histidine prototrophy were determined by common plating techniques on rich and minimal agar plates. The Drosophila test consisted of a sensitive somatic system where the mutagenicity was measured by means of mutations in a gene-controlling eye pigmentation. In none of these test systems did microwave or radiofrequency fields induce an elevated mutation frequency. However, a significantly higher concentration of cells was found in the bacterial cultures exposed to the 27-MHz magnetic field or 2.45-GHz CW and 3.10-GHz pulsed microwave radiation.     

Effects of continuous and intermittent exposure to RF fields with a wide range of SARs on cell growth, survival, and cell cycle distribution

To examine the biological effects of radio frequency (RF) electromagnetic fields in vitro, we have examined the fundamental cellular responses, such as cell growth, survival, and cell cycle distribution, following exposure to a wide range of specific absorption rates (SAR). Furthermore, we compared the effects of continuous and intermittent exposure at high SARs. An RF electromagnetic field exposure unit operating at a frequency of 2.45 GHz was used to expose cells to SARs from 0.05 to 1500 W/kg. When cells were exposed to a continuous RF field at SARs from 0.05 to 100 W/kg for 2 h, cellular growth rate, survival, and cell cycle distribution were not affected. At 200 W/kg, the cell growth rate was suppressed and cell survival decreased. When the cells were exposed to an intermittent RF field at 300 W/kg(pk), 900 W/kg(pk) and 1500 W/kg(pk) (100 W/kg(mean)), no significant differences were observed between these conditions and intermittent wave exposure at 100 W/kg. When cells were exposed to a SAR of 50 W/kg for 2 h, the temperature of the medium around cells rose to 39.1 degrees C, 100 W/kg exposure increased the temperature to 41.0 degrees C, and 200 W/kg exposure increased the temperature to 44.1 degrees C. Exposure to RF radiation results in heating of the medium, and the thermal effect depends on the mean SAR. Hence, these results suggest that the proliferation disorder is caused by the thermal effect.     

Animal death after exposure to ultra-high frequency waves in the dependence of power flux density and specific absorption rate

A comparative analysis and mathematical modeling of laboratory animal sensitivity (mice, rats, rabbits and dogs) to microwave exposure in the dependence of the power flux density (PFD) and the specific absorption rate (SAR) were carried out. The results obtained in our laboratory and some data published by other authors were presented as the dependence of the survival time of various animals during exposure both on PFD and SAR of microwave radiation (0.46; 2.4 and 7 GHz). It is shown that if PFD is used as a dosimetric parameter, the animal sensitivity to nonionizing electromagnetic ultrahigh frequency radiation increased with animal mass. If SAR was used as a dosimetric parameter, the arrangement of animals in accordance with their sensitivity to microwave became quite opposite. Mathematical equations describing the dependence of the survival time of laboratory animals on the duration and the intensity of microwave radiation were obtained. These equations describe the published experimental data and can be used to predict the animal death during the process of microwave irradiation.