Electrical stimulation vs thermal effects in a complex electromagnetic environment

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Abstract

Studies linking exposure to low levels of radiofrequencies with adverse health effects, notwithstanding their present apparent inconsistency, have contributed to a steady improvement in the quality of evaluating that exposure. In complex electromagnetic environments, with a multitude of emissions of different frequencies acting simultaneously, knowledge of the spectral content is fundamental to evaluating human exposure to non-ionizing radiation. In the present work, we quantify the most significant spectral components in the frequency band 0.5–2200 MHz in an urban area. The measurements were made with a spectrum analyzer and monopole, biconical, and log-periodic antennas. Power density levels were calculated separately for the medium wave, short wave, and frequency modulation radio broadcasting bands, and for the television and GSM, DCS, and UMTS mobile telephony bands. The measured levels were compared with the ICNIRP reference levels for exposure to multiple frequency sources for thermal effects and electrical stimulation. The results showed the criterion limiting exposure on the basis of preventing electrical stimulation of peripheral nerves and muscles to be stricter (exposure quotient 24.7 10 4) than that based on thermal considerations (exposure quotient 0.16 10 4). The bands that contribute most to the latter are short wave, with 46.2%, and mobile telephony with 32.6% of the total exposure.

In a complex electromagnetic environment, knowledge of the radiofrequency spectrum is essential in order to quantify the contribution of each type of emission to the public's exposure. It is also necessary to evaluate the electrical effects as well as the thermal effects because the criterion to limit exposure on the basis of the effect of the electrical stimulation of tissues is stricter than that based on thermal effects.

Introduction

Environmental levels of electromagnetic radiation have been constantly increasing due to the continual implementation of new telecommunications systems. The technical evolution of mobile telephony, and the appearance of wifi and wireless systems, have generated radiofrequency (RF) emissions in addition to those that had existed for decades from radio and television broadcasting antennas.

The sudden implementation of all these telecommunication devices, together with the constant stream of studies linking electromagnetic fields with adverse health effects, have led to concern among the public at large over the possible risks of exposure to non-ionizing radiation. As a result, various national and international agencies, such as the International Commission on Non-ionizing Radiation Protection (ICNIRP), the Federal Communications Commission (FFC), and the Institute of Electrical and Electronics Engineers (IEEE), have prepared regulatory guidelines to limit exposure to electromagnetic fields (FCC (Federal Communications Commission), 1999, ICNIRP (International Commission on Non-Ionising Radiation Protection), 1998, IEEE (Institute of Electrical and Electronics Engineers), 2006) based primarily on criteria of thermal effects.

There have been studies, however, that have detected other non-thermal effects. For example, Croft et al. (2008) in studies performed on volunteers find effects caused by cell-phones on the alpha rhythm in electroencephalograms. Kolodynski and Kolodynska (1996) find reduced development of memory, attention, and motor functions in children living near a radio station. And other studies report increased incidence of various types of cancer in people living near television towers (Hocking et al., 1996), TV and FM radio transmitters (Dolk et al., 1997), medium and short wave radio transmitters (Michelozzi et al., 2002), and mobile telephony antennas (Wolf and Wolf, 2004). A exhaustive review of epidemiological studies of the effects of RF fields on human health was published by Ahlbom et al. (2004), with reports of high rates of cancer in some cases. Those same authors indicate, however, that the results of epidemiological studies do not as yet provide consistent or convincing evidence of a causal relationship between RF exposure and adverse health effects, and furthermore that those studies have too many deficiencies for it to be possible to establish any association (Ahlbom et al., 2004).

A key aspect in all studies of this type is the quality of the evaluation of RF exposure. There are often situations in which the determination of the degree of compliance with standards for protection against electromagnetic fields is difficult and cannot always be done directly. The spectral content, spatial and temporal patterns, and polarization are some of the factors in the electromagnetic environment that may be important in evaluating a biological effect. Despite the rapid growth of the new technologies, little is known about public exposure to radiofrequencies and even less about the relative importance of different sources. This is particularly relevant in complex electromagnetic environments in which a multitude of emissions of different frequencies are acting simultaneously.

It is therefore necessary to improve the methods of measurement so that the spectral components can be quantified, and hence the measured field levels compared with the reference levels for different frequencies, since the potential effects on the organism will be different for different frequencies. Equally important is to use criteria for calculating exposure levels that take into account the possible additivity of the effects. For example, in its regulatory guidelines, ICNIRP (ICNIRP, 1998) states that additivity should be examined separately to limit electrical stimulation and thermal effects. The effects of electrical stimulation predominate over other possible effects in the low frequency region, up to 10 MHz, where the current density J is the dosimetry parameter that is applied. For frequencies between 100 kHz and 300 GHz, thermal effects predominate, and from 10 MHz to 10 GHz the specific absorption rate, SAR, and from 10 GHz to 300 GHz the incident power density are the most appropriate dosimetry parameters.

In the present work, we evaluated the relative importance of different RF sources in the range 0.5–2200 MHz for the exposure of the population in an urban area. We used as reference levels the regulatory guidelines published by ICNIRP (ICNIRP, 1998) for exposure to multiple frequencies based on criteria for limiting electrical stimulation and thermal effects.

The study was conducted in the city of Merida, capital of the Region of Extremadura in western Spain. The sources of electromagnetic radiation emissions that could potentially affect the city's inhabitants are mobile telephony antennas within the city limits, and radio and television transmitters at different distances outside the city. Measurements were made with a spectrum analyzer and monopole, biconical, and log-periodic antennas, determining the most significant spectral components of the medium wave, short wave, and frequency modulation broadcasting bands, and of the television and GSM, DCS, and UMTS mobile telephony frequency bands. The signal measurements were converted to electric field strengths using the appropriate antenna calibration equation, and the magnetic field strengths and equivalent plane-wave power densities were calculated assuming a far-field regime. The electric and magnetic field intensities were used together with the reference levels to determine the exposure quotients corresponding to electrical stimulation and thermal effects.

Section snippets

Site description

The study was conducted in the city of Merida, capital of the Autonomous Region of Extremadura and seat of its government institutions. In 1993 the city was declared a UNESCO World Heritage Site because of its historical monuments and archaeological importance. It is the third centre of population in size in Extremadura, with 53 915 inhabitants according to the 2007 census. It is located approximately in the geographic centre of the region (see Fig. 1), with geographic coordinates 38° 54′ N and

Radiation levels

In the Methods section, it was indicated that seven spectra were collected at each sampling point, with the three antennas covering different frequency ranges. These spectra were merged to form a single spectrum in the range 0.5–2.2 MHz, and thus allow the display of all the emissions simultaneously so as to evaluate their relative importance. Fig. 2 shows by way of example one of these spectra for the electric field taken at a point in the urban centre of Mérida. In this figure, we have

Conclusions

We have described a spectral analysis of the levels of electromagnetic radiation in an urban environment. The mobile telephony antennas located within the city, and the radio and television broadcasting antennas outside, were found to be major sources of non-ionizing radiation that could potentially affect the city's inhabitants. This environment could be described as one of low-level electromagnetic radiation, since the more powerful transmitters are not sufficiently close to the city to

References (21)

  • KolodynskiA. et al.

    Motor and psychological functions of school children living in the area of the Skrunda radio location station in Latvia

    Sci Total Environ

    (1996)
  • AhlbomA. et al.

    Epidemiology of health effects of radiofrequency exposure

    Environ Health Perspect

    (2004)
  • Al-RuwaisA.S.

    Measurements of RF radiation near MW and SW radio broadcast stations

    IEEE Trans Broadcast

    (1998)
  • BergqvistU. et al.

    Mobile telecommunication base stations — exposure to electromagnetic fields

  • BurchJ. et al.

    Radio frequency nonionizing radiation in a community exposed to radio and television broadcasting

    Environ Health Perspect

    (2006)
  • CroftR.J. et al.

    The effect of mobile phone electromagnetic fields on the alpha rhythm of human electroencephalogram

    Bioelectromagnetics

    (2008)
  • DolkH. et al.

    Cancer incidence near radio and television transmitters in Great Britain

    Am J Epidemiol

    (1997)
  • ECC (Electronic Communication Committee). Recommendation (02)04: Measuring non-ionising electromagnetic radiation...
  • FCC (Federal Communications Commission)
  • HockingB. et al.

    Cancer incidence and mortality and proximity to TV towers

    Med J Aust

    (1996)
There are more references available in the full text version of this article.

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