РАДИАЦИОННАЯ БИОЛОГИЯ. РАДИОЭКОЛОГИЯ, 2007, том 47, № 6, с. 727-732
НЕИОНИЗИРУЮЩИЕ ^^^^^^^^^^^^ ИЗЛУЧЕНИЯ
УДК 614.7:612.014.423
PROBLEMS IN ASSESSMENT OF RISKS FROM EXPOSURES TO MICROWAVES OF MOBILE COMMUNICATION
© 2007 г. I. Ya. Belyaev1' 2' 3*, Yu. G. Grigoriev3
Stockholm University, Stockholm, Sweden 2lnstitute of General Physics, Russian Academy of Science, Moscow, Russia 3Russian National Committee on Non-Ionizing Radiation Protection, Moscow, Russia
Since pioneering investigations published in the beginning of 1970th, various biological responses to nonthermal (NT) microwaves (MW), including adverse health effects, have been described by many research groups all over the world. There is strong evidence that the NT MW biological effects depend on several physical parameters and biological variables, which must be controlled in replication studies. Apart from the fundamental importance, the development of comprehensive mechanisms for the NT MW effects is socially important. The effects of MW of mobile communications are of major concern because of the increased exposure in many countries. It has been shown that adverse effects of NT MW from GSM/UMTS mobile phones on human lymphocytes from healthy and hypersensitive to EMF persons depend on carrier frequency and modulation. Further investigations with human primary cells, animals and volunteers are needed to elucidate possible adverse effects of MW signals that are used in wireless communication. Identification of those types and frequency channels/bands for mobile communication, which do not affect human cells, is urgently needed as the high priority task for the development of safe mobile communication. Numerous data on the NT MW effects clearly indicate that the SAR-concept alone cannot underlie the safety guidelines for chronic exposures to MW from mobile communication and other approaches are needed. However, there is not enough research information to set exposure MW standards. Various genetic and epigenetic effects of signals used in mobile communication should be studied. It has been shown that NT MW affect cells of various types including stem cells and reproductive organs. Stem cells represent especially important cellular model because recent data suggest that different cancer types, including leukemia, have a fundamentally common basis that is grounded on epigenetic changes in stem cells.
Key words: Microwaves, health risk, non-thermal effects, chronic exposure.
Numerous sources of mobile communication result in chronic exposure of general population to microwaves at the non-thermal levels (specific absorption rate, SAR, <2 W/kg). In the following text this exposure condition is named "NT MW" as abbreviation for non-thermal microwave exposure.
Reports on the non-thermal effects started appearing in the 1970s and have previously been reviewed [114]. Numerous experimental data have provided strong evidence for the NT MW effects and have also indicated dependence of these effects on several physical parameters and biological variables [15]: dependence on carrier frequency of "resonance-type" within specific frequency windows; dependence on modulation and polarization; non-linear dependence on intensity within specific intensity windows including super-low power densities (PD) down to 10-15 W/cm2 that are comparable with intensities from base stations; narrowing of the frequency windows with decreasing intensity; high sensitivity of the NT MW effects to the duration and in-
*Corresponding author: Belyaev I.Ya., Department of Genetics, Microbiology and Toxicology, Stockholm University, S-106 91 Stockholm, Sweden; Tel: +46-8-16 4108; fax: +46-8-16 4315; e-mail: Igor.Belyaev@gmt.su.se.
termittence of exposure; dependence on stray electromagnetic field (EMF) of extremely low frequency (ELF); dependence on cell density that suggests cell-to-cell interaction during response to NT MW; dependence on genetic background, physiological variables during exposure and a potential of radical scaven-gers/antioxidants to minimize the MW effects. Most of these regularities clearly indicate that the MW effects at low intensities cannot be accounted for any type of thermal effects.
There are not yet confirmed observations that gender, individual traits, oxygen concentration, and static magnetic field during exposure may be of importance for the effects of NT MW [15].
Despite of considerable body of studies with NT MW in biology, only few studies were performed to replicate the original data on the NT MW effects. It should be noted that the "replications" are usually not comparable with the original studies because of either missing description of important parameters of exposure or significant differences in these parameters between original study and replication.
RISK ASSESSMENT OF SIGNALS USED IN MOBILE COMMUNICATION
The safety recommendations of International Commission on Non-Ionizing Radiation Protection (ICNIRP) [16], 2 W/kg for workers and 0.8 W/kg for general population, are based on thermal effects in acute exposures and cannot protect from eventual risks of chronic exposures to the NT MW from mobile communication. Some national authorities such as Russian National Committee on Non-Ionizing Radiation Protection (RNCNIRP) have established significantly lower safety recommendations, 1 W/cm2 for workers [17] and 10 ^W/cm2 for general population, that are based on studies with chronic exposures and acceptance of non-thermal effects [18].
It should be pointed out that before introduction of radar and microwave ovens in the 1950th and microwave links in the 1960th there was no significant microwave exposure of the population. The present generations are the first human beings being chronically exposed to NT MW from different types of mobile communication including GSM and UMTS/3G phones/base stations, WLAN (Wireless Local Area Networks), WPAN (Wireless Personal Area Networks such as Bluetooth), DECT (Digital Enhanced (former European) Cordless Telecommunications) wireless phones. The microwave links at the frequencies >6 GHz and the general broadband development in this frequency region provide rapidly increasing input to the NT MW exposure of general population.
RNCNIRP admits that the established safety standards do not correspond to the present situation when general population is exposed to variety of MW signals with durations of exposure comparable with the lifespan. Except for the inevitable exposure to MW from base stations, most part of population including children expose themselves to mobile-phone MW voluntarily [19].
So far, most of the real MW signals that are in use in mobile communication have not been tested for adverse effects. Very little research has been done with real signals and for durations and intermittences of exposure that are relevant to chronic exposures from mobile communication. In some studies, so-called "mobile communication-like" signals were investigated that in fact were different from the real exposures in such important parameters as carrier frequency, modulation, polarization, duration and intermittence. To what degree such studies are relevant to evaluation of health risks from MW of mobile communication, is not known. For example, GSM users are exposed to MW at different carrier frequencies during their talks. There are 124 different channels/frequencies, which are used in Europe for GSM900. They differ by 0.2 MHz in the frequency range from 890 MHz to 915 MHz. Mobile phone users are supplied by various frequencies from the base stations depending on number of connected users. The base station can change the frequency during
the same call. It has been shown that adverse effects of NT MW from GSM mobile phones depend on carrier frequency [20, 21]. Frequency-dependent effects of GSM MW on the 53BP1/y-H2AX DNA repair foci in human lymphocytes from healthy and hypersensitive to EMF persons, human fibroblasts and human stem cells were observed in replicated studies [20, 21].
In a Dutch study, the group of persons recruited based on their experience of being hypersensitive to MW and the healthy control group reported reduced well-being during exposure to MW of Universal Global Telecommunications System (UMTS) [22]. GSM uses GMSK modulation (Gaussian Minimum Shift Keying). Contrary to GSM phones, UMTS mobile phones of the 3rd generation (3G) use essentially QPSK (Quadrature Phase Shift Keying) modulation and irradiate wideband signals with the bandwidth of 5 MHz. UMTS MW may hypothetically result in a higher biological effect as compared to monochromatic GSM MW because of eventual "effective" frequency windows within the UMTS bands. Frequency window effects have not been studied in the UMTS frequency range. However, frequency dependences were reported for GSM900 frequency range [20] and in numerous studies using microwaves at the frequency range of 30-100 GHz [1, 7, 14, 23, 24]. Therefore, it is reasonable to expect frequency-dependent effects in the UMTS region. UMTS MW induced significant adverse effects in human lymphocytes, fibroblasts and stem cells that were more pronounced as compared to GSM effects [21].
URGENT NEEDS AND FURTHER PERSPECTIVES IN RISK ASSESSMENT
It should be anticipated that some part of population, such as children, pregnant women and groups of hypersensitive persons, may be especially sensitive to the NT MW exposures. It is becoming more and more clear that the SAR-concept that has been widely adopted for safety standards may not be useful alone for the evaluation of health risks from MW of mobile communication. How the role of other exposure parameters such as carrier frequency, modulation, polarization, duration, and intermittence of exposure should be taken into account is an urgent problem to solve. Solution of this problem would greatly benefit from the knowledge of the biophysical mechanisms of the NT MW effects. The understanding of mechanisms for the NT MW effects is currently
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