Biological effects and health of Electromagnetic Field

The effects of electromagnetic fields have been studied since the 1950s. Currently, the database of the International Electromagnetic Field Project (updated to August 2006) indicates a total of 2,462 studies of different types, of which 2,346 pertain to radiofrequency, including 1,137 on mobile telephony.

Table 02. Summary of study of radiofrequency electromagnetic fields

The above data was taken from the following World Health Organization web page:

http://www.who.int/peh-emf/emfstudies/studychart_criteria.cfm

From the outset, it is advisable to distinguish clearly between biological effects and health effects.  Biological effects are measurable physiological responses to exposure to electromagnetic fields that are not necessarily dangerous to health; whereas adverse health effects are biological effects outside the body’s normal range of physiological compensation that are detrimental to human health or well-being.

Non-thermal effects

The energy quanta of radiofrequencies, including mobile telephony, are extremely small, from 4 to 7 µeV, and are not capable of altering molecular structure or breaking molecular bonds.  The maximum energy of a quantum at 300 GHz is 1.2 millielectron volts (meV).  By comparison, the energy for thermal movement at 30° C is 26 meV.  To disrupt the weakest hydrogen link requires 80 meV; and to break the weakest links of DNA molecules, 1 eV is required (Durney, C., Massoudi, H., Iskander, M., 1982; IEGMP, 2000).

Biological effects rarely occur at average levels of exposure to RF well below thermal levels, but current evidence does not enable possible biological effects to be ruled out at levels below the international permissible maximum limits.  However, this will not necessarily imply health effects. (ICNIRP, 98; IEGMP, 2000).

Radiofrequencies can produce other effects that would only be detectable if the effects of internal electrical fields are not masked by thermal noise resulting from random movement and vibration of components of biological issue as a result of the thermal energy above absolute zero possessed by all bodies.

Among non-thermal effects investigated are those derived from movement of ions resulting from the action of internal electrical fields, it being found that both movement and energy are much less those caused by thermal movement.  Therefore, it can safely be concluded that movement of ions resulting from electrical fields below thermal levels cannot produce biological effects.

Another possible mechanism is that associated with the passage of current through cell membranes, which act as rectifiers which, with the passage of alternating current, would give rise to net potential over the membrane.  However, as the rectifiers of ions are much slower than mobile telephony frequencies for internal field levels associated with real exposures, the change in membrane potential would be negligible. 

Carcinogenesis

The results of the scientific evidence of cell and animal studies show that neither acute nor chronic exposure to radiofrequency, including mobile telephony, fields – when maintained within thermoregulatory limits – can increase the frequency of chromosomal aberration or mutation, but may cause a slight increase in levels and activity of ornithine decarboxylase.  Generally speaking, changes are too small to give rise to or promote the development of cancer (ICNIRP, 1998; IEGMP, 2000).

Neurophysiological effects

Cell, animal, and human studies show that pulsating signals, such as those corresponding to mobile telephony, can cause changes in neuronal excitability, neurotransmitter function, and innate and learned behavior if the temperature of internal or local organs increases by about 1°C.  Otherwise, evidence is general inconsistent and unconvincing.

There is also evidence of slight modifications in cerebral electrical activity (changes in EEG rate) or evoked visual and auditory potentials in waking persons, disturbance of some stages of sleep of sleeping persons, memory loss, and changes in attention and in blood pressure.  These biological effects would occur at lower than thermal levels.  However, they do not compromise human health, disappearing when exposure ceases (IEGMP, 2000).

Effects on the hematopoietic and immunological systems and on longevity

At low levels of exposure to mobile telephony signals, related studies do not report effects on blood formation and circulation-related cells (e.g., changes in the number of bone marrow cells, lymphocytes, or erythrocytes, or in the number of hematocytes. 

Exposure at thermal levels implies stimulation or inhibitory immunological system responses, but such effects are generally temporary, and return to normal levels when exposure has ended.  The results of exposure at low levels are inconsistent.

Studies of the effect on longevity of exposure to RF signals show no influence on human length of life (IEGMP, 2000).

Reproductive and developmental effects

Animal studies provide no evidence that exposure to radiofrequency signals, including from mobile telephony, constitutes a risk to fetuses or to male fertility (ICNIRP, 1998).

Effects on the cardiovascular system and blood pressure

Animal and human studies show no effect whatsoever on the heart, circulation, or blood pressure.  Effects at high intensities appear to be due to thermal effect (ICNIRP, 1998; IEGMP, 2000).

Hypersensitivity

Studies of the high incidence of headaches, anxiety, or stinging or heat sensations among mobile telephone users are on the whole inconclusive.  The symptoms are real and there are indications that their causes may lie in pre-existing psychiatric conditions and stress, rather than in electromagnetic fields (IEGMP, 2000; OMS, 2005).   

Thermal effects

These are caused by increases in body temperature produced by absorption of time variable electromagnetic fields.  Such absorption is due to the force exerted by an electrical field on charged bodies, such as free ions within the body, which cause their movement, resulting in electrical currents which, on interacting with the electrical resistances of the biological matter of the body, produce heat.

With regard to thermal effects on the head, in a recently published study (Van Leuven et al., 1999), the distribution of heat within the head was calculated by adjusting a finite difference model in the time domain for SAR to a new thermal model.  The thermal model includes the convective effects of discrete blood vessels whose anatomies were determined using the magnetic resonance angiography of a healthy volunteer.  For a bipolar antenna at 915 MHz with time average power of 0.25 W (equivalent to a typical mobile telephone), this study produced an SAR of nearly 1.6 W/kg and predicts a maximum steady state increase in brain temperature of 0.11° C.

Available experimental evidence indicates that exposure to EMF by resting humans for approximately 30 minutes producing an SAR throughout the body of between 1 and 4W kg-1 results in an increase in body temperature of less than 1° C.  Animal data indicate an SAR threshold in the same range.  For behavioral responses, exposure to stronger fields that produce SAR values above 4 W kg-1, the body’s thermoregulatory capacity may break down and produce harmful levels of tissue warming.  Many non-human laboratory studies with rodents and primates have demonstrated the broad spectrum of tissue damage resulting from partial or total warming of the body produced by temperature increases above 1-2° C.  Sensitivity to thermal damage of the different tissue types varies widely, but the threshold for irreversible effects on more sensitive tissue is 4 W kg-1 and above, under normal environmental conditions.  Such data constitutes the basis for occupational exposure limits of 0.4 W kg-1, which provides a large margin of safety for other limiting factors, such as ambient temperature, humidity, or levels of physical activity.

Laboratory data and the results of a small number of human studies (Michaelson and Elson 1996) make evident that enervating thermal environments and the use of drugs or alcohol may compromise the body’s thermoregulatory ability.  In such conditions, safety factors should be introduced to provide adequate protection to exposed individuals.  

To summarize, it may be said that of the research conducted: 

It is known that exposure to radiofrequency fields causes health effects above 4 W/kg, causing changes in behavior and reducing resistance as a result of heat.  That is, thermal effect is the only established effect for radiofrequency waves.

The organs most sensitive to heat are the least irrigated, i.e., the eyes and gonads.

Thermal effect is the basis for international standards, and no effect has been established below these limits.

Use of mobile terminals by children

Some important documents (IEGMP, 2000; Direction Générale de la Santé de France, 2001; NRPB, 2004) recommend precaution in regard to mobile telephone use, suggesting that mobile telephony operators not encourage the use of mobile telephones by children under the age of 16, as they might be more vulnerable to potential future health effects for the following reasons:

• Development of children’s nervous systems is fully under way

• Absorption in the head is greater in children than in adults as children’s skull bones are weaker

• As the diameter of the head is smaller, radiation can more easily reach the most vital organs

• Lifetime exposure would be greater than it is for persons who begin mobile telephone use in adolescence or adulthood.

Victor Cruz
Advisor
International Electromagnetic Fields Project
National Institute for Telecommunication Research and Training (INICTEL-UNI)