Public opinion about the risks of technology varies over a wide range because of different levels of technical education and misinformation from the media. These preformed opinions, fear, and concern often turn discussion over each issues into a heated debate. The conflict over such issues in modern society is often one of risk versus indispensable benefits. For example, the recent concern with electromagnetic fields (EMFs) from electric power lines shows an example of a product of technology that must be used in everyday life despite the unknown risks (Link to ELF web page) [3].People would ideally desire that technology be risk free, but this is impractical in today's society and economy. Therefore public health officials must place risks into pe rspective in making policy decisions.

In addition, public concerns increase when there is uncertain or conflicting scientific data. In particular, the word "radiation" carries the concern of ionizing radiation into non-ionizing radiofrequency (RF) radiation, unnecessarily increasing fear and concern. It is thus imperative that public awareness be increased by distributing clear information on these important issues.

It is unfortunate that public policy decisions must be made in an age of scientific uncertainty, where public perceptions influence decisions. Public opinion influences decisions in Congress, which then decides on funding scientific institutions such as the EPA should receive. Scientists usually desire that information is conclusive before making decisions, whereas policy makers often take action based on inconclusive findings. Others believe that unless something is absolutely proven safe, it should be assumed dangerous. As a result of these competing factors, policy decisions are not always based on science.

For example, uncertainties in risk assessment are especially large in areas where precise health effects are unknown, particularly in low-level exposure to RF radiation. Policy measures tend to be conservative when dealing with uncertain areas, and safety factors add another conservative bias to the estimate of risk, with the combined result that the calculated risk may be completely improbable.

It is often very difficult to come to a conclusive decision because of the enormous amount of conflicting data, and the lack of thorough testing done at this point. The way in which information is made available to the public often results in a skewing of the evidence. Negative studies are often not published or repeated. On the other hand, one positive study serves to refute the null hypothesis which can never be completely proven.

Comparison of risks is difficult because risk estimates are often formulated with different kinds of data, so that comparing the risk based on conservative assumptions, to one based on liberal assumptions, would not give a reliable comparison [3].
It is important that we keep these factors in mind when discussing such controversial issues. The information given here is intended to serve as an unbiased informational resource for those interested in the health effects of radiofrequency radiation.

The word "radiation" encompasses the entire range of frequencies in the electromagnetic spectrum. These include visible light, the high-energy (link) UV rays emitted by the sun, and the low-frequency (link to definition of frequency) waves that transmit your favorite TV or radio program. What distinguishes these "waves" from each other? The properties of the waves depend on their frequency. In particular, the distinction between ionizing and non-ionizing radiation is crucial to understanding the issue at hand. The radiofrequency range of the electromagnetic spectrum is typically defined as being between the frequencies of 0 and 3000 GHz (see electromagnetic spectrum below). In this report we are in particular concerned with frequencies in the cellular telephone and PCS ranges of 800-900 MHz and 1800-2000 MHz respectively.

Read further to find out more about biological effects of RF radiation.

The energy of electromagnetic waves is quantized, meaning it is divided into small but measurable packets, as e = hv, where e is energy, h is Planck's constant, and v is the frequency. This energy can also be expressed in units of kinetic energy for electrons, the electronvolt. This is the energy acquired by an electron accelerated through a potential difference of 1 V: 1 eV = 1.6 x 10-19 J.

Quantized energy can "excite" molecules (by causing increased vibrations and rotations), and can "ionize", or remove, an electron from an atom, but only if the energy "packet" is large enough. The minimum energy required to ionize an electron from an atom is known as the ionization potential, and is the amount of energy required to remove one electron from the highest energy orbit of an element. Ionization potentials are typically on the order of 10 eV. Even the highest frequency radiofrequency waves do not have enough quantum energy to ionize any chemical substance. Electromagnetic waves only become ionizing at the frequency of UV light and above. Hence RF radiation is non-ionizing. Unlike ionizing radiation, RF EM radiation must be specified in terms of carrier frequency, modulation, electric field and magnetic field strengths, and zone of irradiation.

The distinction between ionizing and non-ionizing radiation is particularly important in the difference of effects of non-ionizing and ionizing radiation on biological systems. The crucial question about electric and magnetic fields is whether they can in any way affect biologically important chemical reactions. Ionizing radiation can cause serious irreversible chemical changes because removing an electron can break chemical bonds in compounds crucial to a living system. X-rays and UV radiation are ionizing, so exposure to this kind of radiation should be limited. Non-ionizing radiation cannot break chemical bonds, so it cannot cause this kind of damage. Non-ionizing radiation, and hence radiofreqeuncy radiation, in general can only cause tissue heating by exciting molecules in vibrational and rotational modes. Other biological effects that could occur at non-ionizing levels include: dielectrophoresis, depolarization of cell membranes, mechanical stress due to piezoelectric transduction, or dielectric saturation resulting in the orientation of the polar sidechains of macromolecules leading to the breaking of hydrogen bonds [1]. The rates at which energy must be delivered in order to produce these effects are very high. In general, the only important effect is tissue heating.

Heating occurs when a molecule is excited by an incident electromagnetic wave which causes it to move rapidly. RF radiation at high enough levels excites molecules, which in combination with friction forces, heats the tissue. This is the way a microwave oven works to heat food (although a microwave oven cannot heat humans because the amount of energy absorption is dependent on the size of the object). Heat ing is the only well-known health effect of RF radiation, and exposure limits are made based on this. Heating is generally of concern only in very high-strength fields, greater than 100mW/cm² [6]. The increase in body temperature that results is similar to the increase resulting from exercise. Levels that cause this kind of heating are not ordinarily encountered by the general public.

Exposure is defined as some specified combination of field intensity or power flux and the duration of time during which an animal or person is subjected to that field or power flux. The field is averaged over the whole body unless otherwise specified.

It is generally accepted that there is a threshold level of exposure, before which the body has not begun to compensate for the increased energy input. Therefore during this time, the specific absorption, or absorbed energy, is constant with time. The time constant, T, denotes the delay time before the body initiates compensation processes, such as energy loss and transfer (through means described above). After these processes have begun, the body comes to an equilibrium temperature. The body now has a constant SAR or specific absorption rate.

For lower power densities, the time constant, T, is larger, which is consistent with the fact that sensation of RF radiation is quicker at higher levels. The thermal time constant for humans under whole-body irradiation at frequencies near resonance (~70MHz) is about one hour [5].

Safety factors can be derived by knowledge of the time constant. The ANSI guidelines essentially divide the time constant of one hour by a safety factor of 10 to obtain 6-minute time constant. The averaging-time seen in all current guidelines is essentially T, the time constant. (see regulations section).

It should be emphasized that environmental levels of RF radiation routinely encountered by the public are far below the levels necessary to produce significant heating and increased body temperature. In fact, a national study of RF radiation fields conducted by the Environmental Protection Agency within US metropolitan areas has estimated that 99% of the population is exposed to less than 0.001 mW/cm² [3]. These measurements include all frequencies, not just cellular or PCS. The remaining one percent that experiences higher exposure is generally in residences very near high power broadcast stations. There may also be situations, particularly workplace environments, where RF safety standards are exceeded and people could be exposed to potentially harmful levels of RF radiation.

Other studies have found RFR levels up to 0.1 mW/cm2 in tall buildings near major broadcast facilities, and levels in the 1-10 mW/cm² range in the region immediately at the base of broadcast towers, which are accessible to the public [3].

The contribution to the background radiation expected from new cellular and PCS antennas will most likely be insignificant in comparison to the contributions from TV and AM/FM radio.

Cellular telephone antennas use relatively low effective radiated powers (about 100 W per channel) and therefore produce very weak ground-level RF radiation power densities, much lower than the exposure standards. [3].Our sample measurements taken in Newton and Arlington confirmed that the power densities of cellular antennas are insignificant when compared to the those of TV and radio towers.(Examples of field measurements from Newton and Arlington, MA.) Other environmental measurements have also shown that RF field levels are generally of greatest magnitude in the adult-body resonance range of 70-100 MHz, where absorption is greater than at other frequencies [2].

In addition, radiofrequency radiation from cellular and PCS antennas is at frequencies at which the body does not absorb radiation as well. Much of the radiation from TV and AM/FM transmitters is within th is resonance range, and is much more readily absorbed by the human body. It is also present at much higher power densities. It thus seems that there should be little concern over new PCS and cellular antenna sites, in considering the high power densities present at much more significant frequencies for human absorption.

Many studies on animals have shown that RF irradiation that results in a rise of body core temperature to 43 or 44°C (109.4 or 111.2°F) from the normal 37°C (98.6°F) is lethal to the organism [4].However, the amount of energy that needs to be absorbed to achieve this temperature change is very large (over 100 mW/cm² for an extended period of time) , and would never be encountered by the public.