Statistical determination of whole-body average SARs in a 2 GHz whole-body exposure system for unrestrained pregnant and newborn rats

A 2 GHz whole-body exposure to rats over a multigeneration has been conducted as part of bio-effect research in Japan. In this study, the rats moved freely in the cage inside the exposure system. From observation of the activity of rats in the cage, we found that the rats do not stay in each position with uniform possibility. In order to determine the specific absorption rate (SAR) during the entire exposure period with high accuracy, we present a new approach to statistically determine the SAR level in an exposure system. First, we divided the rat cage in the exposure system into several small areas, and derived the fraction of time the rats spent in each small area based on the classification of the documentary photos of rat activity. Then, using the fraction of time spent in each small area as a weighting factor, we calculated the statistical characteristics of the whole-body average SAR for pregnant rats and young rats during the entire exposure period. As a result, this approach gave the statistical distribution as well as the corresponding mean value, median value and mode value for the whole-body SAR so that we can reasonably clarify the relationship between the exposure level and possible biological effect.

Analysis of three-dimensional SAR distributions emitted by mobile phones in an epidemiological perspective

The three-dimensional distribution of the specific absorption rate of energy (SAR) in phantom models was analysed to detect clusters of mobile phones producing similar spatial deposition of energy in the head. The clusters' characteristics were described from the phones external features, frequency band and communication protocol. Compliance measurements with phones in cheek and tilt positions, and on the left and right side of a physical phantom were used. Phones used the Personal Digital Cellular (PDC), Code division multiple access One (CdmaOne), Global System for Mobile Communications (GSM) and Nordic Mobile Telephony (NMT) communication systems, in the 800, 900, 1500 and 1800 MHz bands. Each phone's measurements were summarised by the half-ellipsoid in which the SAR values were above half the maximum value. Cluster analysis used the Partitioning Around Medoids algorithm. The dissimilarity measure was based on the overlap of the ellipsoids, and the Manhattan distance was used for robustness analysis. Within the 800 MHz frequency band, and in part within the 900 MHz and the 1800 MHz frequency bands, weak clustering was obtained for the handset shape (bar phone, flip with top and flip with central antennas), but only in specific positions (tilt or cheek). On measurements of 120 phones, the three-dimensional distribution of SAR in phantom models did not appear to be related to particular external phone characteristics or measurement characteristics, which could be used for refining the assessment of exposure to radiofrequency energy within the brain in epidemiological studies such as the Interphone.

Estimation of RF energy absorbed in the brain from mobile phones in the Interphone Study

Objectives

The objective of this study was to develop an estimate of a radio frequency (RF) dose as the amount of mobile phone RF energy absorbed at the location of a brain tumour, for use in the Interphone Epidemiological Study.

Methods

We systematically evaluated and quantified all the main parameters thought to influence the amount of specific RF energy absorbed in the brain from mobile telephone use. For this, we identified the likely important determinants of RF specific energy absorption rate during protocol and questionnaire design, we collected information from study subjects, network operators and laboratories involved in specific energy absorption rate measurements and we studied potential modifiers of phone output through the use of software-modified phones. Data collected were analysed to assess the relative importance of the different factors, leading to the development of an algorithm to evaluate the total cumulative specific RF energy (in joules per kilogram), or dose, absorbed at a particular location in the brain. This algorithm was applied to Interphone Study subjects in five countries.

Results

The main determinants of total cumulative specific RF energy from mobile phones were communication system and frequency band, location in the brain and amount and duration of mobile phone use. Though there was substantial agreement between categorisation of subjects by cumulative specific RF energy and cumulative call time, misclassification was non-negligible, particularly at higher frequency bands. Factors such as adaptive power control (except in Code Division Multiple Access networks), discontinuous transmission and conditions of phone use were found to have a relatively minor influence on total cumulative specific RF energy.

Conclusions

While amount and duration of use are important determinants of RF dose in the brain, their impact can be substantially modified by communication system, frequency band and location in the brain. It is important to take these into account in analyses of risk of brain tumours from RF exposure from mobile phones.

Short-term exposure to a 1439-MHz TDMA signal exerts no estrogenic effect in rats

The aim of this study was to elucidate the possible effects of short-term exposure to a 1439-MHz electromagnetic field (EMF) employing time division multiple access (TDMA), which is the basis of the Japanese Personal Digital Cellular system, on estrogenic activity in rats. Sixty-four ovariectomized female Sprague-Dawley rats were divided into four groups: EMF exposure (EM), sham exposure, cage control, and 17 beta-estradiol injected (E2). The EM group was exposed, for 4 h per day on three consecutive days, to the 1439-MHz TDMA signal that produced 5.5-6.1 and 0.88-0.99 W/kg average specific absorption rates in the brain and the whole body, respectively. The uterine wet mass and serum estradiol level significantly increased in the E2 group, while there were no differences among the other three groups. Although negative effects of long-term EMF exposure must be thoroughly investigated before a final conclusion can be reached, our results do not support the assumption that the high frequency EMF used in cellular phones exerts estrogenic activity.

Local exposure system for rats head using a figure-8 loop antenna in 1500-MHz band

Cellular phones are used in the vicinity of the human head, resulting in localized exposure to this part of the body. To simulate exposure during cellular phone use, microwave energy absorption should be focused within the head region of laboratory animals. In this paper, we developed an exposure system using a figure-8 loop antenna to permit localized exposure of a rat head to 1500-MHz microwave fields, simulating human head exposure to cellular phones. We have numerically estimated the specific absorption rate (SAR) in a rat exposed to microwave fields via our new exposure system. The high ratio of SAR averaged over the target tissue (i.e., the brain) to that averaged over the whole body suggests that the figure-8 antenna can realize greater localized exposure than the previously used exposure system. We have also confirmed the effectiveness of our proposed system experimentally.

Local exposure of the rat cortex to radiofrequency electromagnetic fields increases local cerebral blood flow along with temperature

Few studies have shown that local exposure to radiofrequency electromagnetic fields (RF) induces intensity-dependent physiological changes, especially in the brain. The aim of the present study was to detect reproducible responses to local RF exposure in the parietal cortex of anesthetized rats and to determine their dependence on RF intensity. The target cortex tissue was locally exposed to 2-GHz RF using a figure-eight loop antenna within a range of averaged specific absorption rates (10.5, 40.3, 130, and 263 W/kg averaged over 4.04 mg) in the target area. Local cerebral blood flow (CBF) and temperatures in three regions (target area, rectum, and calf hypodermis) were measured using optical fiber blood flow meters and thermometers during RF exposure. All parameters except for the calf hypodermis temperature increased significantly in exposed animals compared with sham-exposed ones during 18-min exposures. Dependence of parameter values on exposure intensity was analyzed using linear regression models. The elevation of local CBF was correlated with temperature rise in both target and rectum at the end of RF exposure. However, the local CBF elevation seemed to be elevated by the rise in target temperature, but not by that of the rectal temperature, in the early part of RF exposure or at low-intensity RF exposure. These findings suggest that local RF exposure of the rat cortex drives a regulation of CBF accompanied by a local temperature rise, and our findings may be helpful for discussing physiological changes in the local cortex region, which is locally exposed to RF.

Intercomparison of induced fields in Japanese male model for ELF magnetic field exposures: effect of different computational methods and codes

The present study provides an intercomparison of the induced quantities in a human model for uniform magnetic field exposures at extremely low frequency. A total of six research groups have cooperated in this joint intercomparison study. The computational conditions and numeric human phantom including the conductivity of tissue were set identically to focus on the uncertainty in computed fields. Differences in the maximal and 99th percentile value of the in situ electric field were less than 30 and 10 % except for the results of one group. Differences in the current density averaged over 1 cm(2) of the central nerve tissue are 10 % or less except for the results of one group. This comparison suggests that the computational uncertainty of the in situ electric field/current density due to different methods and coding is smaller than that caused by different human phantoms and the conductivitys of tissue, which was reported in a previous study.

In-situ electric field and current density in Japanese male and female models for uniform magnetic field exposures

The present study quantified the in situ electric field and induced current density in anatomically based numeric Japanese male and female models for exposure to extremely low-frequency magnetic fields. A quasi-static FDTD method was applied to analyse this problem. The computational results obtained herein reveal that the 99 th percentile value of the in situ electric field in the nerve tissue and the current density averaged over an area of 1 cm(2) of the nerve tissue (excluding non-nerve tissues in the averaging region) in the female models were less than 35 and 25 %, respectively. These induced quantities in the Japanese models were smaller than those for European models reported in a previous study, which is mainly due to the difference in cross-sectional area of the body.

Distribution of RF energy emitted by mobile phones in anatomical structures of the brain

The rapid worldwide increase in mobile phone use in the last decade has generated considerable interest in possible carcinogenic effects of radio frequency (RF). Because exposure to RF from phones is localized, if a risk exists it is likely to be greatest for tumours in regions with greatest energy absorption. The objective of the current paper was to characterize the spatial distribution of RF energy in the brain, using results of measurements made in two laboratories on 110 phones used in Europe or Japan. Most (97-99% depending on frequency) appears to be absorbed in the brain hemisphere on the side where the phone is used, mainly (50-60%) in the temporal lobe. The average relative SAR is highest in the temporal lobe (6-15%, depending on frequency, of the spatial peak SAR in the most exposed region of the brain) and the cerebellum (2-10%) and decreases very rapidly with increasing depth, particularly at higher frequencies. The SAR distribution appears to be fairly similar across phone models, between older and newer phones and between phones with different antenna types and positions. Analyses of risk by location of tumour are therefore important for the interpretation of results of studies of brain tumours in relation to mobile phone use.

Mobile phone use, exposure to radiofrequency electromagnetic field, and brain tumour: a case-control study

In a case–control study in Japan of brain tumours in relation to mobile phone use, we used a novel approach for estimating the specific absorption rate (SAR) inside the tumour, taking account of spatial relationships between tumour localisation and intracranial radiofrequency distribution. Personal interviews were carried out with 88 patients with glioma, 132 with meningioma, and 102 with pituitary adenoma (322 cases in total), and with 683 individually matched controls. All maximal SAR values were below 0.1 W kg⁻¹, far lower than the level at which thermal effects may occur, the adjusted odds ratios (ORs) for regular mobile phone users being 1.22 (95% confidence interval (CI): 0.63–2.37) for glioma and 0.70 (0.42–1.16) for meningioma. When the maximal SAR value inside the tumour tissue was accounted for in the exposure indices, the overall OR was again not increased and there was no significant trend towards an increasing OR in relation to SAR-derived exposure indices. A non-significant increase in OR among glioma patients in the heavily exposed group may reflect recall bias.

Effects of subchronic exposure to a 1439 MHz electromagnetic field on the microcirculatory parameters in rat brain

THE AIM of this study was to investigate whether repeated exposure to radio frequency electromagnetic field (RF-EMF) of 1439 MHz affects the cerebral microcirculation, including blood-brain barrier function, in a rat brain.

MATERIALS AND METHODS

The head of the rat was exposed for four weeks (60 min/day, 5 days/week) to RF-EMF at 2.4 W/kg of brain averaged specific absorption rate (BASAR). Three microcirculatory parameters: blood-brain barrier permeability, leukocyte behavior and plasma velocity were measured before and after RF-EMF exposure using a closed cranial window method.

RESULTS

No extravasation of intravenously injected dyes from pial venules was found at any BASAR level. No significant changes in the number of endothelial-adhering leukocytes after exposure were found. The plasma velocity remained constant within the physiological range through each exposure.

CONCLUSION

These findings suggest that there were no effects on the cerebral microcirculation under the given RF-EMF exposure conditions.

Effects of acute exposure to a 1439 MHz electromagnetic field on the microcirculatory parameters in rat brain

THE AIM of this study was to determine the potential of radio-frequency electromagnetic fields (RF-EMF) to affect cerebral microcirculation, including blood-brain barrier function, in rat brain.

MATERIALS AND METHODS

The head of the rat was exposed for 10 min to 1439 MHz RF-EMF having three intensity doses: 0.6, 2.4, 4.8 W/kg of brain averaged specific absorption rate (BASAR). Four microcirculatory parameters: blood-brain barrier permeability, leukocyte behavior, plasma velocity, and vessel diameter were measured before and after RF-EMF exposure using a closed cranial window method.

RESULTS

No extravasation of intravenously injected dyes from pial venules was found at any BASAR level. No significant changes in the number of endothelial-adhering leukocytes after exposure were found. The hemodynamics indicated that the plasma velocities and vessel diameters remained constant within the physiological range throughout each exposure.

CONCLUSION

These findings suggest that there were no effects on the cerebral microcirculation under the given RF-EMF exposure conditions.

Lack of promoting effects of chronic exposure to 1.95-GHz W-CDMA signals for IMT-2000 cellular system on development of N-ethylnitrosourea-induced central nervous system tumors in F344 rats

The present study was performed to evaluate effects of a 2-year exposure to an electromagnetic near-field (EMF) equivalent to that generated by cellular phones on tumor development in the central nervous system (CNS) of rats. For this purpose, pregnant F344 rats were given a single administration of N-ethylnitrosourea (ENU) on gestational day 18. A total of 500 pups were divided into five groups, each composed of 50 males and 50 females: Group 1, untreated controls; Group 2, ENU alone; Groups 3 to 5, ENU + EMF (sham exposure and two exposure levels). A 1.95-GHz wide-band code division multiple access (W-CDMA) signal, which is a feature of the International Mobile Telecommunication 2000 (IMT-2000) cellular system was employed for exposure of the rat head starting from 5 weeks of age, 90 min a day, 5 days a week, for 104 weeks. Brain average specific absorption rates (SARs) were designed to be .67 and 2.0 W/kg for low and high exposures, respectively. The incidence and numbers of brain tumors in female rats exposed to 1.95-GHz W-CDMA signals showed tendencies to increase but without statistical significance. Overall, no significant increase in incidences or numbers, either in the males or females, was detected in the EMF-exposed groups. In addition, no clear changes in tumor types in the brain were evident. Thus, under the present experimental conditions, exposure of heads of rats to 1.95-GHz W-CDMA signals for IMT-2000 for a 2-year period was not demonstrated to accelerate or otherwise affect ENU-initiated brain tumorigenesis.

Mobile phone use and acoustic neuroma risk in Japan

OBJECTIVES

The rapid increase of mobile phone use has increased public concern about its possible health effects in Japan, where the mobile phone system is unique in the characteristics of its signal transmission. To examine the relation between mobile phone use and acoustic neuroma, a case-control study was initiated.

METHODS

The study followed the common, core protocol of the international collaborative study, INTERPHONE. A prospective case recruitment was done in Japan for 2000-04. One hundred and one acoustic neuroma cases, who were 30-69 years of age and resided in the Tokyo area, and 339 age, sex, and residency matched controls were interviewed using a common computer assisted personal interview system. Education and marital status adjusted odds ratio was calculated with a conditional logistic regression analysis.

RESULTS

Fifty one cases (52.6%) and 192 controls (58.2%) were regular mobile phone users on the reference date, which was set as one year before the diagnosis, and no significant increase of acoustic neuroma risk was observed, with the odds ratio (OR) being 0.73 (95% CI 0.43 to 1.23). No exposure related increase in the risk of acoustic neuroma was observed when the cumulative length of use (<4 years, 4-8 years, >8 years) or cumulative call time (<300 hours, 300-900 hours, >900 hours) was used as an exposure index. The OR was 1.09 (95% CI 0.58 to 2.06) when the reference date was set as five years before the diagnosis. Further, laterality of mobile phone use was not associated with tumours.

CONCLUSIONS

These results suggest that there is no significant increase in the risk of acoustic neuroma in association with mobile phone use in Japan.

Computational verification of anesthesia effect on temperature variations in rabbit eyes exposed to 2.45 GHz microwave energy

This paper computationally verifies the effect of anesthesia on temperature variations in the rabbit eye due to microwave energy. The main reason for this investigation is that our previous paper suggested a reduction in blood flow due to the administration of anesthesia, resulting in an overestimated temperature increase. However, no quantitative investigation has yet been conducted. The finite-difference time-domain (FDTD) method is used for calculating power absorption and temperature variation in rabbits. For this purpose, we used a computational rabbit phantom, which is comprised of 12 tissues (including 6 eye tissues) with a resolution of 1 mm. Thermal constants of the rabbit were derived by comparing measured and calculated temperatures. For intense microwave exposure to the rabbit eye, time courses of calculated and measured temperatures were in good agreement for cases both with and without the administration of anesthesia. The point to be stressed is that under anesthesia the thermoregulatory response was inactivated and blood flow and basal metabolism was reduced.

Chronic exposure to a 1.439 GHz electromagnetic field used for cellular phones does not promote N-ethylnitrosourea induced central nervous system tumors in F344 rats

The present study was designed to evaluate whether a 2 year exposure to an electromagnetic field (EMF) equivalent to that generated by cellular phones can accelerate tumor development in the central nervous system (CNS) of rats. Brain tumorigenesis was initiated by an intrauterine exposure to N-ethylnitrosourea (ENU) on gestational day 18. A total of 500 pups were divided into five groups, each composed of 50 males and 50 females: Group 1, untreated control; Group 2, ENU alone; Groups 3-5, ENU + EMF (sham exposure and 2 exposure levels). A 1.439 GHz time division multiple access (TDMA) signal for the Personal Digital Cellular (PDC), Japanese standard cellular system was used for the exposure of the rat head starting from 5 weeks of age, 90 min a day, 5 days a week, for 104 weeks. Brain average specific absorption rate (SAR) was 0.67 and 2.0 W/kg for low and high exposures, respectively: whole body average SAR was less than 0.4 W/kg. There were no inter-group differences in body weights, food consumption, and survival rates. No increase in the incidences or numbers per group of brain and/or spinal cord tumors, either in the males or females, was detected in the EMF exposed groups. In addition, no clear changes in tumor types were evident. Thus, under the present experimental conditions, 1.439 GHz EMF exposure to the heads of rats for a 2 year period was not demonstrated to accelerate or affect ENU initiated brain tumorigenesis.