It's the old debate, that of mobile phones and their harmful effects. The Indian government recently decided to adopt the guidelines issued by ICNIRP, an international science body, writes M S S Murthy 

Mobile phones and cancer: the debate has been on for over a decade now without any definite conclusion. While studies show an association, albeit weak, with some types of brain tumors, an equal number of studies have failed to substantiate that claim. The latest is the warning given by Dr Ronald Herberman, Director of the University of Pittsburg Cancer Institute, USA, about excessive use of mobile phones, particularly by children. 

Mobile phones and personal communications systems are low-power radio devices that transmit and receive signals in the radio frequency (RF) range 900 and/or 1800 megahertz through a network of base stations. Most countries have brought in regulations to limit public exposure to RF radiation. 

These are based on the recommendations of International Commission for Non-ionizing Radiation Protection (ICNIRP), an independent science organisation. It evaluates the hazards of electromagnetic radiation, of which RF is a part, and develops guidelines. Recently, the Indian government also decided to adopt these guidelines. 

RF radiation
Exposure to RF radiation can occur from the base station, and mobile phones. A base station has a tower mounted on a building at heights between 15 and 30 metres. 

The tower carries three-directional antennae separated by 120 degrees to cover the phones in a given geographical area (cell) managed by a particular service provider.  At the base of the tower is the instrument room housing low power radio transmitters and receivers. Generally, a base station will have over one transmitter, depending upon the number of phones in the cell. The outputs from these transmitters are combined and fed to the antennae. Most base stations radiate about 20 to 40 watts of RF power. 

The intensity of the radiation decreases beyond a few meters from the antenna. Because base stations are located in populated areas, those living in the path of the beam are exposed to radiation.

The mobile phone also has a radio transmitter and an antenna. The transmitter generates RF energy of one to two watts, radiated through the antenna. Because the phone is held close to the head, much of this energy is absorbed by the brain.

What are the possible effects of RF radiation exposure? The ICNIRP says the only established effect of RF energy absorption by the human body is the rise in tissue temperature. In fact, this is the mechanism of microwave cooking. The RF energy absorbed is expressed in terms of “specific absorption rate” (SAR), measured in units of watts per kg (W/kg) of tissue. If the heat generated is small, the body’s thermoregulatory mechanism can dissipate it without causing adverse effects. If the temperature exceeds this capacity, (about 1 to 2 degree celsius), tissue damage may occur. Penetration of the blood-brain barrier, disturbed neuromuscular functions, lens opacity and reduced sperm production are effects observed in animal experiments and human volunteers exposed to high RF radiation levels, known as 'thermal effects'. 

This increase occurs when whole-body energy absorption exceeds a SAR of  4 W/kg. Taking this value as threshold for harmful effects, ICNIRP applies a safety factor of 50 to derive safe limits for exposure to general public. If only a part of the body is exposed, a higher value of SAR can be permitted. The ICNIRP has recommended RF exposure levels for general public, in terms of power densities, as 4.5 W/m2 and 9.0 W/m2 respectively for the 900 and 1800 MHZ frequency radiations. Exposures below these levels are harmless.

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