Paniagua JM, Rufo M, Jiménez A, Antolín A, Sánchez M. 2009. Electrical stimulation vs thermal effects in a complex electromagnetic environment. Sci Total Environ. 407(16):4717-4722.

In complex electromagnetic environments produced by multiple sources of EMF of various frequencies it is often difficult to determine the degree of compliance with safety standards. It is necessary to improve measurement methods to be able to quantify spectral components of EMFs and hence to compare the measured levels with the reference levels for different frequencies.

The aim of this study was to evaluate relative importance of different sources in the frequency range from 0.5 to 2200 MHz for population exposure in an urban area.

The study was conducted in the city of Merida in Spain. The sources of EMF were mobile phone antennas within the city and radio and TV transmitters at different distances from the city. Measurements were conducted with a spectrum analyzer and monopole, biconical, and log-periodic antennas. Power density levels were determined for the medium wave, short wave, and frequency modulation broadcasting bands, and for the television and GSM, DCS and UMTS mobile phone frequency bands. The ICNIRP (1998) reference levels for exposure to multiple frequencies for thermal effects and electrical stimulation effect were used for comparison.

Results and interpretation
The main contributors to radiation levels were mobile telephony (34.8%), short wave (29.4%) and medium wave (28.4%) emissions. Their relative contributions to exposure levels were different due to different biological effects of EMFs of different frequencies. Based on thermal criteria, the greatest contributors to exposure levels were short wave (46.4%) and mobile telephony (32.6%). In the presence of emissions with frequencies below 10 MHz, such as AM radio, it is necessary to evaluate exposure levels for multiple-frequency sources using the criterion limiting exposure on the basis of avoidance of electrical stimulation of peripheral nerves and muscles. It was shown that this criterion was stricter than the criterion based on preventing thermal effects.

The authors have concluded that in a complex electromagnetic environment it is essential to know the frequency spectrum. Since the relative contribution of different frequency bands in the levels of radiation is different from their relative contribution in the levels of exposure, it is not enough to calculate the levels of radiation; it is necessary to calculate exposure levels. It is also necessary to evaluate not only thermal but electrical effects because the electrical stimulation criterion is stricter than the thermal criterion.

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