Mobile Health Hazard

Mobile Health Hazard: Reality or Myth? Manish Das DGM (New Services) For many people worldwide, Mobile phones have become part of their way of life. In countries like us too, the number of Mobile phone users is increasing at a very high rate. Plummeting cost of the Mobile handsets as well as call charges have fuelled this growth. Mobile phones are basically low power devices that emit and receive radio waves. It is radio waves that connect each phone to a network of base stations, so that users can make and receive calls. Base stations (BTS) are also basically radio transmitters and receivers. They have antennas, mounted either on roof top masts or towers, which transmit and receive radio signals. Each BTS has its own areas of coverage , known as cells. Cells usually have a radius of few kilometers. However, more base stations are needed where mobile phone usage is high. So, in rural areas cells can have a radius of 4-6 km, while in towns and cities their radius may be as low as a few hundred meters. They overlap at the edges to ensure that mobile phone users remain within range of a base station. Without sufficient base stations in the right locations, mobile phones will not work. Due to the licensing policy of government, each city in India is supposed to have four GSM operators. Most of the cities are already having two operators, few are having three. Very soon all the cities will have at least three operators beaming radio waves from base stations. City like Calcutta will have no less than 400 base stations in near future. This unprecedented growth in use of radio signals has led to a public debate all over world, specially in western countries, about possible impact on health due to use of mobile phones. Is it safe? One of the first allegations regarding ill effects of mobile phone on health came in public in 1992 in a U.S. court. A lawsuit filed in Florida by David Reynard alleged that the use of a cell phone had caused his wife's fatal brain cancer. A Federal court dismissed the suit for lack of valid scientific evidence, and similar suits since have been treated almost in similar way. But at that time the question was also raised whether do we have entirely satisfactory answers on this issue. Driven in by these disturbing allegations, a new wave of research in the United States and elsewhere is exploring possible links between cell phone radiation and cancer. Radiations from sources like X-rays can knock electrons from atoms in living tissue causing serious biological damage. But GSM in our country operates in 900MHz frequency range. Energy in this frequency range is called non-ionizing because the photon energy is insufficient to knock electrons from atoms in living tissue. The most commonly appreciated biological effects of RF energy at cell phone frequencies may be due to heating. Quantity of absorption of radiation energy in body mass is measured by a unit called Specific Absorption Rate (SAR). It is expressed as watts per kilogram (W/kg). The SAR is given by the following formula: SAR = [E]² / where E is Electrical field intensity (V/m),  is the electrical conductivity of the medium (in Siemens per meter) and  the density of the medium ( in kg/m³). Radio waves emitted above a certain level can cause heating effects in the body. On the basis of scientific data obtained from laboratory animals and volunteers, it has been established that if the increase in body temperature does not exceed 1°C, this does not lead 1

to health problems even in the case of long-term exposure. It is assumed in all the guidelines that, if the average SAR in the body does not exceed 4 W/kg, body temperature does not rise by more than 1°C. International guidelines seek to ensure that exposure is kept below that level. These values pertain to total body exposure.

Now, let us see whether mobile phones and BTSs exceed the maximum SAR value of 4 W/kg. The maximum transmission power of a GSM-900 telephone is 2 W. But the mobile radiates only during the one of the eight available timeslots it is allotted during a call. So the effective transmission power is, by application of the time slots, one eighth of this: 250mW.

Fig 1. Radiation from Mobile phone.

Some amounts of electromagnetic energy are only absorbed in the head when making calls on a mobile phone, during which time it is held against the head. This does not occur in any other situation. If the telephone is in use, but is not held to the head (when using a hands free set, for example) the level of electromagnetic energy absorbed by the body and the region of the body affected will depend on the position of the device relative to the body. When sending or receiving SMS messages, energy absorption is negligible due to its very short duration, which is no more than a few seconds. Composition or reading of a message takes place in standby mode. Moreover, in this situation the telephone is held at some distance from the body. If the telephone is on standby, it regularly emits short (1-2 s) pulses for the purpose of Location Update (LU) within the network. The intervals between such pulses vary – depending on the network settings – from 20 minutes to several hours. The pulse is initially broadcasted at full power, but the power is then reduced. This reduction will depend on the phone’s position relative to the nearest base station and the setting of that base station. This determines the maximum transmission power of the GSM telephone. If a call takes place, a link is established and the telephone transmits continuously. Here, too, this process takes place initially for a very short time on full power, with the power then being reduced to the minimum level required for a good link.

A mobile would require a power density of 20-100 mW/cm-sq to achieve a SAR as high as 4 W/kg. If we see from BTS point of view, signal is constantly transmitted in the control time slot only, normally time slot 0. During other time slots, radiation occurs only whenever telephone calls are in progress, one time slot for each call.

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Fig 2. Radiation from Base Stations.

The consensus of the scientific community is that the power from these base station antennas is far too low to produce health hazards as long as people are kept away from direct access to the antennas and they are not within few tens of meters from the base station antenna. Base station antennas do not create "hot spots" (unless you are standing directly in front of one), so the potential safety issues concerning the phones have no real applicability to the base station antennas. Under worst-case assumptions, the SAR of a human in publicly accessible locations near a base station would be less than 0.01 W/kg. Under realistic conditions the SAR to a human near such a base station would be less than 0.0005 W/kg. But it is possible that use of cell phones causes headaches. It has been found that users of cell phones commonly report having headaches. A study reported that headaches and other symptoms were higher in users of analog (NMT 900) phones than users of digital (GSM) phones. Headache prevalence increase significantly with duration of use, and the use of hands free equipment eliminated the increase. But again, no one has claimed that there is scientific evidence that base stations cause headaches, and there are no biophysical or physiological bases for expecting such an effect. There are still significant gaps in our scientific knowledge. It is recommended that “a precautionary approach” to the use of mobile phones should be followed until more research findings become available. If one uses a mobile phone, he can choose to minimize your exposure to radio waves. These are ways to do so: • keeping calls short • use of hands free kit, though the level of effectiveness of hands free kit to reduce SAR is still uncertain. Further research is being carried out to investigate SAR levels when using phones with hands free kit .

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