The World Health Organization, based upon the consensus view of the scientific and medical communities, that health effects (e.g. headaches) are very unlikely to be caused by cellular phones or their base stations, and expects to make recommendations about mobile phones in 2009–10.
Electromagnetic radiation can be classified into ionizing radiation and non-ionizing radiation, based on whether it is capable of ionizing atoms and breaking chemical bonds. Ultraviolet and higher frequencies, such as X-rays or gamma rays are ionizing. These pose their own special hazards.
Non-ionizing radiation is associated with two major potential hazards: electrical and biological. Additionally, induced electric current caused by radiation can generate sparks and create a fire or explosive hazard.
Non-ionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules — that is, to completely remove an electron from an atom or molecule. Instead of producing charged ions when passing through matter, the electromagnetic radiation has sufficient energy only for excitation, the movement of an electron to a higher energy state. Nevertheless, different biological effects are observed for different types of non-ionizing radiation.
Near ultraviolet, visible light, infrared, microwave, radio waves, low frequency RF and static fields are all examples of non-ionizing radiation. Visible and near ultraviolet may induce photochemical reactions, ionize some molecules or accelerate radical reactions, such as photochemical aging of varnishes or the breakdown of flavoring compounds in beer to produce the 'lightstruck flavor'. The light from the Sun that reaches the earth is largely composed of non-ionizing radiation, with the notable exception of some ultraviolet rays.
Ultraviolet radiation
Ultraviolet light can cause burns to skin and cataracts to the eyes. Ultraviolet is classified into near, medium and far UV according to energy, where near ultraviolet is non-ionizing. Ultraviolet light produces free radicals that induce cellular damage, which can be carcinogenic. Ultraviolet light also induces melanin production from melanocyte cells to cause sun tanning of skin. Vitamin D is produced on the skin by a radical reaction initiated by UV radiation.
Health hazards of handsets
Part of the radio waves emitted by a mobile telephone handset are absorbed by the human head. The radio waves emitted by a GSM handset, can have a peak power of 2 watts, and a US analogue phone had a maximum transmit power of 3.6 watts. Other digital mobile technologies, such as CDMA and TDMA, use lower output power, typically below 1 watt. The maximum power output from a mobile phone is regulated by the mobile phone standard it is following and by the regulatory agencies in each country. In most systems the cellphone and the base station check reception quality and signal strength and the power level is increased or decreased automatically, within a certain span, to accommodate for different situations such as inside or outside of buildings and vehicles.
The rate at which radiation is absorbed by the human body is measured by the Specific Absorption Rate (SAR), and its maximum levels for modern handsets have been set by governmental regulating agencies in many countries. In the USA, the FCC has set a SAR limit of 1.6 W/kg, averaged over a volume of 1 gram of tissue, for the head. In Europe, the limit is 2 W/kg, averaged over a volume of 10 grams of tissue. SAR values are heavily dependent on the size of the averaging volume. Without information about the averaging volume used comparisons between different measurements can not be made. Thus, the European 10-gram ratings should be compared among themselves, and the American 1-gram ratings should only be compared among themselves.
Specific absorption rate (SAR) is a measure of the maximum rate at which radio frequency (RF) energy is absorbed by the body when exposed to radio-frequency electromagnetic field. It is used for exposure to fields between 100kHz and 10 GHz. The SAR value will depend heavily on the geometry of the part of the body that is exposed to the RF energy and on the exact location and geometry of the source of the RF energy. Thus tests must be made with each specific source, such as a mobile phone model, and at the intended position of use. The value cited for a specific model is then the maximum level measured in the body part studied. The most common use is in relation to mobile phones, and here the mobile phone is placed at the head in a talk position. The SAR value measured is then value measured in the place that has the highest absorption rate in the entire head, which for a mobile phone often is as close to the phone as possible. Various governments have defined safety limits for exposure to RF energy produced by mobile devices that mainly exposes the head or a limb for the RF energy:
Thermal effects
One well-understood and well known effect of microwave radiation is dielectric heating, in which any dielectric material (such as living tissue) is heated by rotations of polar molecules induced by the electromagnetic field. In the case of a person using a cell phone, most of the heating effect will occur at the surface of the head, causing its temperature to increase by a fraction of a degree which is less than that obtained during the exposure of the head to direct sunlight. The brain's blood circulation is capable of disposing of excess heat by increasing local blood flow. However, the cornea of the eye does not have this temperature regulation mechanism and exposure of 2-3 hours' duration has been reported to produce cataracts in rabbits' eyes at SAR values from 100-140W/kg, which produced lenticular temperatures of 41-41°C[12]. Premature cataracts have not been linked with cell phone use, possibly because of the lower power output of mobile phones. Thus we see that lens protein is far more sensitive to mobile phone radiation than the human head which is, in most of the cases, is directly exposed to the radiation.
Non-thermal effects
Some researchers have argued that so-called "non-thermal effects" could be reinterpreted as a normal cellular response to an increase in temperature. There may be several thermoreceptor molecules in cells, and that they activate a cascade of second and third messenger systems, gene expression mechanisms and production of heat shock proteins in order to defend the cell against metabolic cell stress caused by heat.
Proponents of another school of thought disagree with the thermal hypothesis, citing evidence of different pathways for the synthesis of stress proteins in cells subject to EMF radiation versus heat shock. These pathways involve different DNA segments of the same gene. They postulate instead a non-thermal mechanism whereby EMF rearranges the electron configuration on DNA molecules. This charge accumulation could overcome the hydrogen bonds joining the DNA strands.
Blood Brain Barrier effects
Swedish researchers have found a leakage of albumin into the brain via a permeated blood-brain barrier.
Electrical sensitivity
Some users of mobile handsets have reported feeling several unspecific symptoms during and after its use; ranging from burning and tingling sensations in the skin of the head and extremities, fatigue, sleep disturbances, dizziness, loss of mental attention, reaction times and memory retentiveness, headaches, malaise, tachycardia (heart palpitations), to disturbances of the digestive system. All of these symptoms can also be attributed to stress and it is impossible to put the blame on cell phone use only.
Genotoxic effects
Research published in 2004 by a team at the University of Athens had a reduction in reproductive capacity in fruit flies exposed to 6 minutes of 900 MHz pulsed radiation for five days. Subsequent research, again conducted on fruit flies, was published in 2007, with the same exposure pattern but conducted at both 900 MHz and 1800 MHz, and had similar changes in reproductive capacity with no significant difference between the two frequencies. These effects could be due to degeneration of large numbers of egg chambers after DNA fragmentation of their constituent cells.
In 1995, Lai and Singh reported damaged DNA after two hours of microwave radiation at levels deemed safe according to government standards in the journal Bioelectromagnetics. Later, in December 2004, a pan-European study named REFLEX (Risk Evaluation of Potential Environmental Hazards from Low Energy Electromagnetic Field (EMF) Exposure Using Sensitive in vitro Methods), involving 12 collaborating laboratories in several countries showed some compelling evidence of DNA damage of cells in in-vitro cultures, when exposed between 0.3 to 2 watts/kg, whole-sample average. There were indications, but not rigorous evidence of other cell changes, including damage to chromosomes, alterations in the activity of certain genes and a boosted rate of cell division. Reviews of in vitro genotoxicity studies have generally concluded that RF is not genotoxic and that studies reporting positive effects had experimental deficiencies.
Mobile phones and cancer
In 2006 a large Danish study about the connection between mobile phone use and cancer incidence was published. It followed over 420,000 Danish citizens over 20 years and showed no increased risk of cancer.
In order to investigate the risk of cancer for the mobile phone user, a cooperative project between 13 countries has been launched called INTERPHONE. The idea is that cancers need time to develop so only studies over 10 years are of interest.
The following studies of long time exposure have been published:
• A Danish study (2004) that took place over 10 years and found no evidence to support a link. – negative
• A Swedish study (2005) that draws the conclusion that "the data do not support the hypothesis that mobile phone use is related to an increased risk of glioma or meningioma. - negative
• A British study (2005) that draws the conclusion that "The study suggests that there is no substantial risk of acoustic neuroma in the first decade after starting mobile phone use. However, an increase in risk after longer term use or after a longer lag period could not be ruled out. – negative with word of caution
• A German study (2006) that states "In conclusion, no overall increased risk of glioma or meningioma was observed among these cellular phone users; however, for long-term cellular phone users, results need to be confirmed before firm conclusions can be drawn. – negative with word of caution
• A joint study conducted in northern Europe that draws the conclusion that "Although our results overall do not indicate an increased risk of glioma in relation to mobile phone use, the possible risk in the most heavily exposed part of the brain with long-term use needs to be explored further before firm conclusions can be drawn. – negative with word of caution
Other studies on cancer and mobile phones are:
• A Swedish scientific team at the Karolinska Institute conducted an epidemiological study (2004) that suggested that regular use of a mobile phone over a decade or more was associated with an increased risk of acoustic neuroma. The increase was not noted in those who had used phones for fewer than 10 years.[34]
• The INTERPHONE study group from Japan published the results of a study of brain tumour risk and mobile phone use. They used a new approach: determining the SAR inside a tumour by calculating the radiofrequency field absorption in the exact tumour location. Cases examined included glioma, meninigioma, and pituitary adenoma. They reported that the overall odds ratio (OR) was not increased and that there was no significant trend towards an increasing OR in relation to SAR-derived exposure. In a February 2008 update on the status of the INTERPHONE study IARC stated that the long term findings ‘…could either be causal or artifactual, related to differential recall between cases and controls.’
Sleep and EEG effects
Some studies have claimed to show that mobile phone signals affect sleep patterns and possibly delay sleep onset during exposure. In another clinical study, carried out by Sweden's Karolinska Institute and Wayne State University in the US, the authors concluded their research suggested an association between RF exposure and adverse effects on sleep quality within certain sleep stages, though participants were unable to determine better than chance if they had been exposed to actual radiation or sham exposure. The UK National Health Service criticized the research because of
• the small sample size used, and
• because of the 53% of participants who reported sensitivity to mobile use, a proportion unlikely to be representative of the general population.
Health hazards of base stations
Another area of worry about effects on the population's health have been the radiation emitted by base stations, because, in contrast to mobile handsets, it is emitted continuously and is more powerful at close quarters. On the other hand due to the attenuation of power with the square of distance, field intensities drop rapidly with distance away from the base of the antenna. Base station emissions must comply with ICNIRP guidelines of a maximum power density of 4.5 W/m² (450 microwatts/cm2) for 900 MHz and 9 W/m² (900 microwatts/cm2) for 1800 MHz.
These guidelines are set for short term heating, which is the only understood mechanism of electromagnetic fields on biological tissue.
Several surveys have found increases of symptoms depending upon proximity to electromagnetic sources such as mobile phone base stations.
• A 2002 survey study by Santini et al. in France found a variety of self-reported symptoms for people who reported that they were living within 300 metres (984 ft) of GSM cell towers in rural areas, or within 100 m (328 ft) of base stations in urban areas. Fatigue, headache, sleep disruption and loss of memory were among the symptoms reported. Similar results have been obtained with GSM cell towers in Spain, Egypt, Poland and Austria. It is, however, important to note that these surveys do not show statistically significant clustering or causality and those complaining of adverse symptoms may be displaying the nocebo effect, unless this is controlled in the study.
• However, a study conducted at the University of Essex and another in Switzerland concluded that mobile phone masts were unlikely to be causing these short term effects in a group of volunteers who complained of such symptoms.
Occupational health hazards
A variety of studies over the past 50 years have been done on workers exposed to high RF radiation levels; studies including radar laboratory workers, military radar workers, electrical workers, and amateur radio operators. Most of these studies found no increase in cancer rates over the general population or a control group. Many positive results could have been attributed to other work environment conditions, and many negative results of reduced cancer rates also occurred.
Safety standards and licensing
In order to protect the population living around base stations and users of mobile handsets, governments and regulatory bodies adopt safety standards, which translate to limits on exposure levels below a certain value. There are many proposed national and international standards, but that of the International Commission for Non-Ionizing Radiation Protection (ICNIRP) is the most respected one, and has been adopted so far by more than 80 countries. For radio stations, ICNIRP proposes two safety levels: one for occupational exposure, another one for the general population. Currently there are efforts underway to harmonise the different standards in existence.
Evolution of Safety Standards
The following is a brief summary of the wireless safety standards, which have become stricter over time.
• 1966: The ANSI C95.1 standard adopted the standard of 10mW/cm2 (10,000 microwatts/cm2) based on thermal effects.
• 1982: The IEEE recommended further lowering this limit to 1mW/cm2 (1,000 microwatts/cm2) for certain frequencies in 1982, which became a standard ten years later in 1992 (see below).
• 1986: The NCRP recommended the exposure limit of 580 microWatts/cm2.
• 1992: The ANSI/IEEE C95.1-1992 standard based on thermal effects used the 1mW/cm2 (1,000 microwatts/cm2) safety limit. The EPA called this revised standard "seriously flawed", partly for failing to consider non-thermal effects, and called for the FCC to adopt the 1986 NCRP standard which was five times stricter.
• 1996: The FCC updated to the standard of 580 microWatts/cm2 over any 30-minute period for the 869 MHz, while still using 1mW/cm2 (1,000 microwatts/cm2) for PCS frequencies (1850-1990 MHz).[59]
• 1998: The ICNIRP standard uses the limit of 450 microwatts/cm2.
Adequacy of Current Standards
The controversial question is whether the current safety standards are adequate enough to protect the public's long-term health. A few nations have set safety limits orders lower than the ICNIRP limit. In particular, the Salzburg Resolution for Austria recommends safety limits many times lower (0.6 V/m = 0.1 microWatts/cm2 for pulsed radiation.[60]
Precautionary principle
In 2000, the World Health Organization (WHO) recommended that the precautionary principle could be voluntarily adopted in this case. It follows the recommendations of the European Community for environmental risks.
According to the WHO, the "precautionary principle" is "a risk management policy applied in circumstances with a high degree of scientific uncertainty, reflecting the need to take action for a potentially serious risk without awaiting the results of scientific research." Other less stringent recommended approaches are prudent avoidance principle and ALARA (As Low as Reasonably Achievable).
Although all of these are problematic in application, due to the widespread use and economic importance of wireless telecommunication systems in modern civilization, there is an increased popularity of such measures in the general public, though also evidence that such approaches may increase concern. They involve recommendations such as
• the minimization of cellphone usage,
• the limitation of use by at-risk population (such as children),
• the adoption of cellphones and microcells with ALARA levels of radiation,
• the wider use of hands-free and earphone technologies such as Bluetooth headsets,
• the adoption of maximal standards of exposure, RF field intensity and distance of base stations antennas from human habitations.
