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Investigation of Radio-frequency Power Density Distribution around GSM Mast in Keffi Town, Nigeria

In this study, an investigation of radiofrequency power density distribution around GSM mast in Keffi town, Nigeria was determined. Radiofrequency meter (Electrosmog ED155A) was used to measure the EM radiation at 50, 70, 90,110, 130, 150, 170, and 190 m away from mobile base stations. A total of fifteen mobile base stations were randomly selected in Keffi town covering about four network providers (MTN, Globacom, Etisalat, and Airtel), according to their proximity to buildings, number of antennas mounted on their masts, how close they are to other base stations and the population density around them.The result reveal that MBS5 was found to have the highest value of average power density compared to that of the remainder, with a contribution of about 16% (2908.38 μW/m). The least contribution was recorded in MBS3 with only about 1% (173.71 μW/m 2 ). The other MBS with significant contribution are MBS6 (15%), MBS11 (15%), MBS10 (13%), MBS8 (13%) and MBS13 (11%) with average power densities of 2878.72μW/m, 2767.28μW/m, 2385.43 μW/m, 2382.70 μW/m, and 1996.36 μW/m respectively. The findings reveal that the measured values of power densities across all the sites are well below the RF radiation exposure safety limit set by International Commission on Non-ionizing Radiation Original Research Article Ibrahim et al.; AJR2P, 2(2): 1-6, 2019; Article no.AJR2P.47665 2 Protection (ICNIRP) when compared with the findings in this study. Therefore, RF radiation exposure from mobile base stations in Keffi town may pose no health risk to the people living within the area.


INTRODUCTION
Mobile communications technology are now common in Nasarawa State particularly Keffi town. The introduction of communication systems in the year 2002 in Nigeria has increased radiofrequency radiation exposure of the general public to telecommunications and mobile base stations [1].
There is widespread public concern about the potential adverse health effects of mobile phones and especially their associated base stations alongside with hundreds of apparently conflicting reports in the media about the health effects of mobile phones and base stations as reported by Zenon [2]. Studies have shown that exposure levels of about 3 kHz-5 MHz generates painful nerves impulses while 100 kHz-3 GHz leads to temperature rise of the body and frequencies of 300GHz can change the cellular DNA and initiate a carcinogenic transformation [3]. In medicine, it is used for the treatment of liver cancer, cosmetic surgery, sleep Apnea, Snoring, rapid heartbeat syndrome etc, [4].
The increased use of mobile phone has led to increased deployment of base stations. There are two sources of radiofrequency radiation exposure from the mobile telephone system: base station antenna and mobile phone. Exposure from base station antennas is continuous and it irradiates the whole body and expose an entire community in different ways according to position and separation distance. The mobile phone system works as a network containing base stations within each cell. These base stations can link with a number of handsets. The mobile phone and base stations communication with each other, sharing a number of operation frequencies [5,6].
A cellular phone transmits 1 to 2 Watt of power in the frequency range of 824-849 MHz (CDMA), 890-915 MHz (GSM900), 1710-1780 MHz and 1805-1880 MHz (GSM 1800). In Nigeria, the Specific Absorption Rate (SAR) limit for cell phones is 1.6W/kg, which is actually for 6minutes per day usage [7]. It has a safety margin of 3 to 4, so a person should not use a cell phone for more than 18 to 24 minutes per day. This information is not commonly known to most people in Nigeria, so people use cell phones for more than an hour per day without realising the related health hazards [8,9].

MATERIALS AND METHODS
Measurement of Electromagnetic radiation was carried using RF Meter (Electrosmog ED-155A). The RF meter is a frequency weighted broadband device for monitoring high frequency radiation in the specific ranges of 900 MHz, 1800 MHz, and 2.7 GHz. Measurements of power density were made by simply pointing the RF meter to the source of the RF radiation. A maximum of 190m radial distance from the foot of the base station was considered and measurement were taken at 20 m interval from each base station starting with 50 m. The proximity of residential buildings, office buildings and schools to base stations forms the bases for choosing this range of distance. A total of fifteen (15) mobile base stations were randomly selected in Keffi town covering about four (4) network providers -MTN, Globacom, Etisalat, and Airtel, according to their proximity to buildings, number of antennas mounted on their masts, how close they are to other base stations and the population density around them.
The meter was set to the tri-axial measurement mode and also to the maximum instantaneous measurement mode, to measure the maximum instantaneous power density at each point. Each measurement was made by holding the meter away from the body, at arm's length and at about 1.5m above the ground level pointing towards the mast as suggested by Victor et al. [10]. The values of the measured Electric field taken after the meter is stable (about 2 min) were recorded. We ensured that the measured values were not influenced by unwanted sources and disturbances. Such precautions taken were to avoid the movement of the meter during measurements and excessive field strength values due to electrostatic charges. We also ensured (where possible) that phone calls and movement of cars were reduced before taking measurements. Global positioning system (GPS) was used to take the geographical location of the MBS investigated as shown in Table 1.
The meter can also measure electric field E along a different axis, but readings can also be taken in all Es at the same time (Tri axial) using: Where, E x , E y and E z are the electric field in x, y and z coordinate directions.

RESULTS AND DISCUSSION
The results of the measured power density S for all the mobile base station investigated is shown in Table 2.We observed that MBS5 was found to have the highest value of average power density compared to that of the remainder, with a contribution of about 16% (2908.38 µW/m 2 ) as shown in Table 3 and Fig. 1 Significant fluctuation in data collection during measurement was observed. It is expected that the variation of the power flux density should obeys inverse-square-law (P t /4πR move farther away from the reference mobile base station. The measured power flux densities however deviated as shown in Fig. 2. This Significant fluctuation in data collection during measurement was observed. It is expected that the variation of the power flux density should /4πR 2 ) as you move farther away from the reference mobile base station. The measured power flux densities however deviated as shown in Fig. 2. This deviation could result from either of the following: obstruction constituted by immobile placed or erected within the line of sight of measurement; wave interference from other sources of electromagnetic radiation around reference base station such as radio and TV antennas, receivers etc; interference from radiation and/or noise from moving objects such as vehicles, motorcycles etc; topography (or elevation) of the land area around reference base station with respect to radial distance away from base station; and wave interference from other mobile base stations clustered around a reference base station.

Mobile Base Station
; Article no. AJR2P.47665 (%) contribution contribution (%) deviation could result from either of the following: obstruction constituted by immobile structures placed or erected within the line of sight of measurement; wave interference from other sources of electromagnetic radiation around reference base station such as radio and TV antennas, receivers etc; interference from m moving objects such as vehicles, motorcycles etc; topography (or elevation) of the land area around reference base station with respect to radial distance away from base station; and wave interference from other mobile base stations clustered around a

Fig. 2. Mean power flux density vs distance plot for all mobile base station
The graph in Fig. 2 shows that power flux density decreases exponentially with distance. That is at distance, d= 0, the power density S is maximum and ford˃ 0, the power density decreases exponentially.
The effects from excessive power density can lead to headaches, concentration difficulties and behavioral problems in children and adolescents; and sleep disturbance headaches and concentration problems in adults. Other long term effect of Power density can cause loss of memory and cancer that will be experienced after severe years of exposure. 900 mHz emission has the effect of thermal heating of body tissue.

CONCLUSION
Over the years, a lot of work has been done to understand how radiofrequency (RF) radiation interacts with matter. Different instruments have been use to study the health impact of nonionizing radiation which includes environmental health assessment and epidemiological surveys to assess the level of RF exposure in the environment. The present study was carried out to determine the RF radiation exposure from mobile base stations (MBS) in Keffi town, Nasarawa State, Nigeria. It has been observed from the findings that the measured values of power densities across all the sites are well below the RF radiation exposure safety limit set by ICNIRP for the general public and occupational exposure when compared with the findings in this study. Therefore, RF radiation exposure from mobile base stations in Keffi town may pose no health risk to the people living within the area. It is recommended that mobile network providers should site mobile base stations at least 50 m distance away from residential building areas, school buildings, office buildings and so on.