Absorption of microwave radiation by the anesthetized rat: electromagnetic and thermal hotspots in body and tail

Anatomic variability in the deposition of radiofrequency electromagnetic energy in mammals has been well documented. A recent study [D'Andrea et al., 1985] reported specific absorption rate (SAR) hotspots in the brain, rectum and tail of rat carcasses exposed to 360- and to 2,450-MHz microwave radiation. Regions of intense energy absorption are generally thought to be of little consequence when predicting thermal effects of microwave irradiation because it is presumed that heat transfer via the circulatory system promptly redistributes localized heat to equilibrate tissue temperature within the body. Experiments on anesthetized, male Long-Evans rats (200-260 g) irradiated for 10 or 16 min with 2,450, 700, or 360 MHz radiation at SARs of 2 W/kg, 6 W/kg, or 10 W/kg indicated that postirradiation localized temperatures in regions previously shown to exhibit high SARs were appreciably above temperatures at body sites with lower SARs. The postirradiation temperatures in the rectum and tail were significantly higher in rats irradiated at 360 MHz and higher in the tail at 2,450 MHz than temperatures resulting from exposure to 700 MHz. This effect was found for whole-body-averaged SARs as low as 6 W/kg at 360 MHz and 10 W/kg at 2,450 MHz. In contrast, brain temperatures in the anesthetized rats were not different from those measured in the rest of the body following microwave exposure.     

Physiological interaction processes and radio-frequency energy absorption.

Because exposure to microwave fields at the resonant frequency may generate heat deep in the body, hyperthermia may result. This problem has been examined in an animal model to determine both the thresholds for response change and the steady-state thermoregulatory compensation for body heating during exposure at resonant (450 MHz) and supra-resonant (2,450 MHz) frequencies. Adult male squirrel monkeys, held in the far field of an antenna within an anechoic chamber, were exposed (10 min or 90 min) to either 450-MHz or 2,450-MHz CW fields (E polarization) in cool environments. Whole-body SARs ranged from 0-6 W/kg (450 MHz) and 0-9 W/kg (2,450 MHz). Colonic and several skin temperatures, metabolic heat production, and evaporative heat loss were monitored continuously. During brief RF exposures in the cold, the reduction of metabolic heat production was directly proportional to the SAR, but 2,450-MHz energy was a more efficient stimulus than was the resonant frequency. In the steady state, a regulated increase in deep body temperature accompanied exposure at resonance, not unlike that which occurs during exercise. Detailed analyses of the data indicate that temperature changes in the skin are the primary source of the neural signal for a change in physiological interaction processes during RF exposure in the cold.     

Viability and phagocytosis of neutrophils exposed in vitro to 100-MHz radiofrequency radiation

Rabbit polymorphonuclear leucocytes (PMN, neutrophils) obtained from peritoneal exudate were exposed in vitro for one-half or one hour to continuous wave or amplitude-modulated (20-Hz) 100-MHz RF radiation in a temperature-controlled coaxial exposure chamber at field strengths from 2.5 to 4.1 V/cm (SARs of 120 to 341 W/kg). RF exposure at 37 +/- 0.2 degrees C had no detectable effect on PMN viability or phagocytosis compared to sham-exposed cells simultaneously subjected to the same time-temperature regime. Temperature control studies indicated that at 37 degrees C no effect on PMN viability would be expected but phagocytosis would be reduced by approximately 6%/degrees C temperature increase. The absence of an effect of RF exposure suggests that there was minimal undetected intrasample heating and that phagocytosis was not affected by 100-MHz RF radiation under the conditions of this study.     

In vitro lymphocyte proliferation induced by radio-frequency electromagnetic radiation under isothermal conditions

Whole human blood was exposed or sham-exposed in vitro for 2 h to 27 or 2,450 MHz radio-frequency electromagnetic (RF) radiation under isothermal conditions (i.e., 37 +/- 0.2 degrees C). Immediately after exposure, mononuclear cells were separated from blood by Ficoll density-gradient centrifugation and cultured for 3 days at 37 degrees C with or without mitogenic stimulation by phytohemagglutinin (PHA). Lymphocyte proliferation was assayed at the end of the culture period by 6 h of pulse labeling with 3H-thymidine (3H-TdR). Exposure to radiation at either frequency at specific absorption rates (SARs) below 50 W/kg resulted in a dose-dependent, statistically significant increase of 3H-TdR uptake in PHA-activated or unstimulated lymphocytes. Exposure at 50 W/kg or higher suppressed 3H-TdR uptake relative to that of sham-exposed cells. There were no detectable effects of RF radiation on lymphocyte morphology or viability. Notwithstanding the characteristic temperature dependence of lymphocyte activation in vitro, the isothermal exposure conditions of this study warrant the conclusion that the biphasic, dose-dependent effects of the radiation on lymphocyte proliferation were not dependent on heating.     

Effects of continuous and pulsed 2450-MHz radiation on spontaneous lymphoblastoid transformation of human lymphocytes in vitro.

Normal human lymphocytes were isolated from the peripheral blood of healthy donors. One-ml samples containing (10(6)) cells in chromosome medium 1A were exposed for 5 days to conventional heating or to continuous wave (CW) or pulsed wave (PW) 2450-MHz radiation at non-heating (37 degrees C) and various heating levels (temperature increases of 0.5, 1.0, 1.5, and 2 degrees C). The pulsed exposures involved 1-microsecond pulses at pulse repetition frequencies from 100 to 1,000 pulses per second at the same average SAR levels as the CW exposures. Actual average SARs ranged to 12.3 W/kg. Following termination of the incubation period, spontaneous lymphoblastoid transformation was determined with an image analysis system. The results were compared among each of the experimental conditions and with sham-exposed cultures. At non-heating levels, CW exposure did not affect transformation. At heating levels both conventional and CW heating enhanced transformation to the same extent and correlate with the increases in incubation temperature. PW exposure enhanced transformation at non-heating levels. This finding is significant (P less than .002). At heating levels PW exposure enhanced transformation to a greater extent than did conventional or CW heating. This finding is significant at the .02 level. We conclude that PW 2450-MHz radiation acts differently on the process of lymphoblastoid transformation in vitro compared with CW 2450-MHz radiation at the same average SARs.     

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.     

Glioma proliferation modulated in vitro by isothermal radiofrequency radiation exposure

Isothermal (37 +/- 0.2 degrees C) exposure of glioma cells (LN71) for 2 h to 27 or 2450 MHz continuous-wave radiofrequency (RF) radiation in vitro modulated the rates of DNA and RNA synthesis 1, 3, and 5 days after exposure. The alterations indicate effects on cell proliferation and were not caused by RF-induced cell heating. The dose response for either frequency of the radiation was biphasic. Exposure to specific absorption rates (SARs) of 50 W/kg or less stimulated incorporation rates of tritiated thymidine (3H-TdR) and tritiated uridine (3H-UdR), whereas higher SARs suppressed DNA and RNA synthesis. Statistically significant time-dependent alterations were detected for up to 5 days postexposure, suggesting a kinetic cellular response to RF radiation and the possibility of cumulative effects on cell proliferation. General mechanisms of effects are discussed.     

Mobile phone base station-emitted radiation does not induce phosphorylation of Hsp27

An in vitro study focusing on the effects of low-level radiofrequency (RF) fields from mobile radio base stations employing the International Mobile Telecommunication 2000 (IMT-2000) cellular system was conducted to test the hypothesis that modulated RF fields act to induce phosphorylation and overexpression of heat shock protein hsp27. First, we evaluated the responses of human cells to microwave exposure at a specific absorption rate (SAR) of 80 mW/kg, which corresponds to the limit of the average whole-body SAR for general public exposure defined as a basic restriction in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. Second, we investigated whether continuous wave (CW) and Wideband Code Division Multiple Access (W-CDMA) modulated signal RF fields at 2.1425 GHz induced activation or gene expression of hsp27 and other heat shock proteins (hsps). Human glioblastoma A172 cells were exposed to W-CDMA radiation at SARs of 80 and 800 mW/kg for 2-48 h, and CW radiation at 80 mW/kg for 24 h. Human IMR-90 fibroblasts from fetal lungs were exposed to W-CDMA at 80 and 800 mW/kg for 2 or 28 h, and CW at 80 mW/kg for 28 h. Under the RF field exposure conditions described above, no significant differences in the expression levels of phosphorylated hsp27 at serine 82 (hsp27[pS82]) were observed between the test groups exposed to W-CDMA or CW signal and the sham-exposed negative controls, as evaluated immediately after the exposure periods by bead-based multiplex assays. Moreover, no noticeable differences in the gene expression of hsps were observed between the test groups and the negative controls by DNA Chip analysis. Our results confirm that exposure to low-level RF field up to 800 mW/kg does not induce phosphorylation of hsp27 or expression of hsp gene family.     

Erythrocyte hemolysis by radiofrequency fields

A field-strength-dependent hemolytic effect of continuous-wave radiofrequency (RF) exposure in vitro has been demonstrated. Erythrocytes in whole heparinized rabbit blood were hemolyzed by a 2-h exposure to 50- or 100-MHz RF fields at field strengths of greater than 4 V/cm. An effect of comparable magnitude resulted from exposure to 10-MHz RF at a field strength of 9 V/cm. Sample temperatures were maintained at 22.5 degrees +/- 0.2 degrees C. There was no apparent involvement of heating or temperature gradients, nor were there any RF exposure effects on cellular K+ or Na+ concentration, nor on pH. The mechanism of the hemolytic effect is not known. Since the percentage of lysed erythrocytes was less than 1% and there was an absence of effects on cellular cation concentrations, RF radiation may have irreversibly altered the plasma membrane permeability of a sensitive subpopulation of red cells (possibly aged cells) leading to osmotic lysis. RF radiation at these frequencies appears to affect red cells in a manner that is qualitatively and quantitatively different from microwave radiation.     

Acute radio frequency irradiation does not affect cell cycle, cellular migration, and invasion

Although in vitro studies have been previously conducted to determine the biological effects of radio frequency (RF) radiation, it has not yet been determined whether or not RF radiation poses a potential hazard. This study was conducted to determine whether RF radiation exposure exerts detectable effects on cell cycle distribution, cellular invasion, and migration. NIH3T3 mouse fibroblasts were exposed to 849 MHz of RF radiation at average SAR values of 2 or 10 W/kg for either 1 h, or for 1 h per day for 3 days. During the exposure period, the temperature in the exposure chamber was maintained isothermally by circulating water throughout the cavity. Cell cycle distribution was analyzed at 24 and 48 h after exposure, by flow cytometry. We detected no statistically significant differences between the sham-exposed and RF radiation-exposed cells. Cellular invasion and migration were assessed by in vitro Matrigel invasion and Transwell migration assays. The RF radiation-exposed groups evidenced no significant changes in motility and invasiveness compared to the sham-exposed group. However, the ionizing radiation-exposed cells, used as a positive control group, manifested dramatic alterations in their cell cycle distribution, cellular invasiveness, and migration characteristics. Our results show that 849 MHz RF radiation exposure exerts no detectable effects on cell cycle distribution, cellular migration, or invasion at average SAR values of 2 or 10 W/kg.     

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.     

Growth and development of mice offspring after irradiation in utero with 2,450-MHz microwaves

Mice offspring irradiated in utero with 2,450-MHz radio-frequency (RF) radiation at 0 or 28 mW/cm2 (whole-body averaged specific absorption rate = 0 or 16.5 W/kg) for 100 minutes daily on days 6 through 17 of gestation were evaluated for maturation and development on days 1, 5, 10, 12, 15, and 17 of age. The tests used to determine differences in developmental age in the two treatment groups were body weight, urine concentrating ability, brain weight, tolerance to ouabain, and bone lengths. Fifteen sham-irradiated and 26 RF-irradiated litters, normalized to eight pups/litter, were used in this study. Mean body weight of the microwave-irradiated offspring were significantly (p = .0003) decreased only on day 1 of age. Brain weight on days 10, 12, and 17 were significantly lower in microwave-irradiated pups (p = .01). There were no significant differences in the two groups in urine concentrating ability on day 5, ouabain tolerance on day 15, or bone length on days 5, 10, 12, and 17. It is concluded that there is a persistent delay in postnatal development of the brain after RF irradiation with 16.5 W/kg during gestation.     

Effects of exposure to a 1950 MHz radio frequency field on expression of Hsp70 and Hsp27 in human glioma cells

Human glioma MO54 cells were used to investigate whether radio frequency (RF) field exposure could activate stress response genes. Cells were exposed to continuous wave 1950 MHz or sham conditions for up to 2 h. Specific absorption rates (SARs) were 1, 2, and 10 W/kg. For the cell growth experiment, cell numbers were counted at 0-4 days after exposure. Expression of Hsp27 and Hsp70, as well as the level of phosphorylated Hsp27 (78Ser) protein, was determined by Western blotting. It was found that sham exposed and RF exposed cells demonstrated a similar growth pattern up to 4 days after RF field exposure. RF field exposure at both 2 and 10 W/kg did not affect the growth of MO54 cells. In addition, there were no significant differences in protein expression of Hsp27 and Hsp70 between sham exposed and RF exposed cells at a SAR of 1, 2, or 10 W/kg for 1 and 2 h. However, exposure to RF field at a SAR of 10 W/kg for 1 and 2 h decreased the protein level of phosphorylated Hsp27 (78Ser) significantly. Our results suggest that although exposure to a 1950 MHz RF field has no effect on cell proliferation and expression of Hsp 27 and Hsp70, it may inhibit the phosphorylation of Hsp27 at Serine 78 in MO54 cells.     

Influence of microwaves on the beating rate of isolated rat hearts

Previous reports have shown that microwave exposure can decrease the beating rate of isolated rat hearts. These experiments were conducted at room temperature and with the hearts exposed to air. We observed arrhythmia frequently at room temperature, and the variation of heart beat was so large that it makes the results difficult to reproduce. Therefore, we employed a double-circulating system to provide perfusion through the coronary artery and around the outside of the heart to maintain the rat hearts at 37.7 degrees C. No arrhythmias were observed in our experiments, and the hearts were beating for at least 1 h. The effects of 16-Hz modulated 2,450-MHz pulsed microwaves (10 microseconds, 100 pps) on the beating rate of 50 isolated rat hearts were studied. Results showed no statistically significant changes of heart rate in exposed groups at SARs of 2 and 10 W/kg compared with the control group. The effect seen at 200 W/kg was shown to be similar to that resulting from heating the heart.     

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.     

Long-term exposure of E-mu-Pim1 transgenic mice to 898.4 MHz microwaves does not increase lymphoma incidence

A total of 120 E mu-Pim1 heterozygous mice and 120 wild-type mice were exposed for 1 h/day 5 days/week at each of the four exposure levels in "Ferris-wheel" exposure systems for up to 104 weeks to GSM-modulated 898.4 MHz radiation at SARs of 0.25, 1.0, 2.0 and 4.0 W/kg. In addition, 120 heterozygous and 120 wild-type mice were sham-exposed; there was also an unrestrained negative control group. Four exposure levels were used to investigate whether a dose-response effect could be detected. Independent verification confirmed that the exposures in the current study were nonthermal. There was no significant difference in the incidence of lymphomas between exposed and sham-exposed groups at any of the exposure levels. A dose-response effect was not detected. The findings showed that long-term exposures of lymphoma-prone mice to 898.4 MHz GSM radiofrequency (RF) radiation at SARs of 0.25, 1.0, 2.0 and 4.0 W/kg had no significant effects when compared to sham-irradiated animals. A previous study (Repacholi et al., Radiat. Res. 147, 631-640, 1997) reported that long-term exposure of lymphoma-prone mice to one exposure level of 900 MHz RF radiation significantly increased the incidence of non-lymphoblastic lymphomas when compared to sham-irradiated animals.     

Chromosome damage and micronucleus formation in human blood lymphocytes exposed in vitro to radiofrequency radiation at a cellular telephone frequency (847.74 MHz, CDMA)

Peripheral blood samples collected from four healthy nonsmoking human volunteers were diluted with tissue culture medium and exposed in vitro for 24 h to 847.74 MHz radiofrequency (RF) radiation (continuous wave), a frequency employed for cellular telephone communications. A code division multiple access (CDMA) technology was used with a nominal net forward power of 75 W and a nominal power density of 950 W/m(2) (95 mW/cm(2)). The mean specific absorption rate (SAR) was 4.9 or 5.5 W/kg. Blood aliquots that were sham-exposed or exposed in vitro to an acute dose of 1.5 Gy of gamma radiation were included in the study as controls. The temperatures of the medium during RF-radiation and sham exposures in the Radial Transmission Line facility were controlled at 37 +/- 0.3 degrees C. Immediately after the exposures, lymphocytes were cultured at 37 +/- 1 degrees C for 48 or 72 h. The extent of genetic damage was assessed from the incidence of chromosome aberrations and micronuclei. The kinetics of cell proliferation was determined from the mitotic indices in 48-h cultures and from the incidence of binucleate cells in 72-h cultures. The data indicated no significant differences between RF-radiation-exposed and sham-exposed lymphocytes with respect to mitotic indices, frequencies of exchange aberrations, excess fragments, binucleate cells, and micronuclei. The response of gamma-irradiated lymphocytes was significantly different from that of both RF-radiation-exposed and sham-exposed cells for all of these indices. Thus there was no evidence for induction of chromosome aberrations and micronuclei in human blood lymphocytes exposed in vitro for 24 h to 847.74 MHz RF radiation (CDMA) at SARs of 4.9 or 5.5 W/kg.     

SAR in rats exposed in 2,450-MHz circularly polarized waveguides

Average specific absorption rates (SARs) for live rats exposed in 2,450-MHz circularly polarized waveguides were estimated from the total system loss determined from measurements using five power meters, and a correction factor representing actual SAR/apparent SAR. The actual SAR was measured by twin-well calorimetry and the apparent SAR by power meters. Values were obtained for carcasses of various body masses for five orientations. The average SAR with free movement in the cages changed less than threefold as the rats grew from 200 to 700 g. The ratio of peak to average SAR in the body was less than 3. These results indicate relatively constant energy disposition in rats exposed in the circularly polarized waveguide.     

Effect of 900-, 1800-, and 2100-MHz radiofrequency radiation on DNA and oxidative stress in brain

Ubiquitous and ever increasing use of mobile phones led to the growing concern about the effects of radiofrequency radiation (RFR) emitted by cell phones on biological systems. The aim of this study is to explore whether long-term RFR exposure at different frequencies affects DNA damage and oxidant-antioxidant parameters in the blood and brain tissue of rats. 28 male Sprague Dawley rats were randomly divided into four equal groups (n = 7). They were identified as Group 1: sham-control, Group 2: 900 MHz, Group 3: 1800 MHz, and Group 4: 2100 MHz. Experimental groups of rats were exposed to RFR 2 h/day for 6 months. The sham-control group of rats was subjected to the same experimental condition but generator was turned off. Specific absorption rates (SARs) at brain with 1 g average were calculated as 0.0845 W/kg, 0.04563 W/kg, and 0.03957, at 900 MHz, 1800 MHz, and 2100 MHz, respectively. Additionally, malondialdehyde (MDA), 8-hydroxydeoxyguanosine (8-OHdG), total antioxidant status (TAS), and total oxidant status (TOS) analyses were conducted in the brain tissue samples. Results of the study showed that DNA damage and oxidative stress indicators were found higher in the RFR exposure groups than in the sham-control group. In conclusion, 900-, 1800-, and 2100-MHz RFR emitted from mobile phones may cause oxidative damage, induce increase in lipid peroxidation, and increase oxidative DNA damage formation in the frontal lobe of the rat brain tissues. Furthermore, 2100-MHz RFR may cause formation of DNA single-strand breaks.     

In vitro effect of pulsed 900 MHz GSM radiation on mitochondrial membrane potential and motility of human spermatozoa

Ejaculated, density purified, human spermatozoa were exposed to pulsed 900 MHz GSM mobile phone radiation at two specific absorption rate levels (SAR 2.0 and 5.7 W/kg) and compared with controls over time. Change in sperm mitochondrial membrane potential was analysed using flow cytometry. Sperm motility was determined by computer assisted sperm analysis (CASA). There was no effect of pulsed 900 MHz GSM radiation on mitochondrial membrane potential. This was also the case for all kinematic parameters assessed at a SAR of 2.0 W/kg. However, over time, the two kinematic parameters straight line velocity (VSL) and beat-cross frequency (BCF) were significantly impaired (P < 0.05) after the exposure at SAR 5.7 W/kg and no exposure by time interaction was present. This result should not be ascribed to thermal effects, due to the cooling methods employed in the RF chamber and temperature control within the incubator.