MAPPING OF RADIOFREQUENCY EXPOSURE AND ASSESSMENT OF POTENTIAL HEALTH HAZARD FROM BASE TRANSCEIVING STATIONS AND COMMON MOBILE PHONES IN SELECTED CITIES IN NIGERIA

Abstract

The proliferation of mobile telecommunication devices and radio transmitting antennas has precipitated global concern over possible health hazards associated with exposure to the generated electromagnetic radiations.Global System of Mobile (GSM) communications in Nigeria is enabled byover 30,000 Base Transceiving Stations (BTS) servicing over 140 million mobile subscribers. Data on the spectral analyses of Radiofrequency (RF) signals and the energyabsorbed by the human brainfrom mobile phones in Nigeria are scarce. This has made it impossible for GSM risk assessments in the Nigerian environment. The objectives of this work were to delineate the energy contribution of each RF component, estimate energy absorbed in the brain from BTS and mobile phones to ascertain possible health risk to the public. Lagos,Ibadan and Abuja were purposively selected for the study. A calibrated spectrum analyser coupled with an isotropic antennawas used to identify prominent RF signals within 900-2500 MHz band and to determine their exposure levels from 40 BTS in each city.The mean distances of maximum human exposure from theseBTS were determined.The analyser, which measures specific bands, and a broadband Electrosmog meter for measuring total RF band were used to acquire RF spectra at the points of maximum exposure from 120, 100 and 80 BTS in Lagos,Ibadan and Abuja, respectively. The spectra were analysed to determine the power density of the various signals observed. The energy fractions transmitted to the brain tissue from 60 common mobile phones in active mode were computed in terms of Specific Absorption Rate (SAR), using a multi-layered model of the human head.The obtained level of exposure was compared to the standard prescribed by the International Commission on Non Ionizing Radiation Protection (ICNIRP). Data were analysed using descriptive statistics. The distances of maximum exposure were 183±58, 195±19and 190±63 m,in Lagos, Ibadan and Abuja, respectively. Nine major RF signals were identified at each point in the three cities. Five of these signals were satellite signals, within band 960-1700 MHz and producing a highest power density overall of 9.6 μW/m2 in Lagos. The remaining four (within 935-960 MHz and 1805-2290 MHz) were from BTS, producing a highest power density overall of 5411 μW/m2 in Abuja. The total power densities in the cities ranged from 10-27500,1-8430 and 108-90900μW/m2, with only 23, 26 and 46% being from BTS inLagos, Ibadanand Abuja, respectively. The SAR in brain tissue from BTS ranged from 8.0x10-9– 7.3x10-5 W/kg. The SAR due to all emissions in the near field of the mobile phones ranged from 1–150mW/kg. This showed that the energy absorption in the brain from mobile phones was higher than from the base stations. The highest SAR obtained was lower than the 2.0 W/kg exposure limit set by the ICNIRP. Exposures to radiofrequency radiation are from nine major communication signals in most environments, with global system of mobile communications producing the highest. The currently obtained exposure level is within limits, indicating low health risk to the public.