In October, 2002, cell biologist Fiorenzo Marinelli and his team at the National Research Council in Bologna, Italy, reported that radio waves from mobile phones could promote the growth of cancer cells.
The team exposed leukaemia cells to 900-megahertz radio waves at a power density level of 1 milliwatt per squared centimetre (mW/cm2).
After 24 hours of continuous exposure to the radio waves, the researchers found that certain suicide genes were turned on in far more leukaemia cells than in a control cell population that had not been exposed, and 20 per cent more exposed cells had died than in the controls.
But after 48 hours exposure to the radio waves, the apparently lethal effect of the radiation went into reverse. Instead of more cells dying, the exposed cells were replicating furiously compared to the controls. Three genes that trigger cells to multiply were turned on in a high proportion
of the cells. The cancer, although briefly beaten back, had become more aggressive.
Marinelli presented the results at the International Workshop on Biological Effects of Electromagnetic Fields on the Greek island of Rhodes.
He suspects that the radiation may initially damage DNA, and that this interferes with the biochemical signals in a way that ultimately triggers the cells to multiply more rapidly.
Meanwhile, a research team in the University of Florence reported that normal human skin fibroblasts, placed over an active cell phone for 1 h, also showed significant changes. The fibroblasts shrivelled up, and several genes indicative of stress response became expressed, that are involved
in cell proliferation, growth inhibition and cell death. There was a significant increase in DNA synthesis and in key molecules that signal cell division. These findings are similar to those reported earlier from yet another laboratory.
Dariusz Leszczynski at the Radiation and Nuclear Safety Authority in Helsinki found that one-hour exposure to mobile phone radiation caused cultured human cells to shrink.
Leszczynski believes this happens when a cell is damaged. In a person, such changes could destroy the blood-brain barrier that normally prevents harmful substances in the bloodstream from entering the brain and damaging it.
Radiation-induced changes in the cells could also interfere with normal cell death when the cell is damaged. If cells that are marked to die do not, tumours can form.
This research is particularly important, Leszczynski said, because it demonstrates that mobile phone radiation too weak to heat up the cells can still affect them.
David de Pomerai, molecular toxicologist at the University of Nottingham, provided the first clear evidence on such non-thermal effects of mobile phone radiation. He found that nematode worms exposed to radio waves had an increase in fertility - the opposite effect from what would be
expected from heating.
De Pomerai also insisted that a consensus is emerging that electromagnetic waves such as those used in mobile phones can indirectly damage DNA by affecting its repair system without heating the cell. "Cells with unrepaired DNA damage are likely to be far more aggressively cancerous," he
Non-thermal effects due to weak electromagnetic radiation are at the heart of the debate on the health hazards of mobile phones and other electrical installations in the environment.
These recent results should be seen in the light of the report released in March 2002 by the National Radiological Protection Board (NRPB), which concluded that children exposed to high levels of electromagnetic radiation in the home could be doubling their risk of leukaemia (see
"Electromagnetic fields double leukaemia risk". This series).
One doesnt have to be a cell-phone user to become exposed to the radiation. You could be living near a base-station thats beaming the radio waves at you (see Box 1). Or you could be exposed as a passenger on a crowded train full of mobile phone users.
Tsuyoshi Hondou, a physicist from Tohoku University in Sendai, Japan, currently working at the Curie Institute in Paris, calculated that in a typical Japanese railway carriage with mobile phone users surfing the net, the radio waves rebounding from the metal wall of the carriage would give
an electromagnetic field that could exceed the maximum exposure level recommended by the International Committee for Non-Ionising Radiation (ICNIRP), even when the train is not crowded.
Hondous calculations show that it is possible to exceed ICNIRP exposure limit if 30 people, each with a mobile phone that emits radio waves at a power of 0.4 watts, all use their phones at the same time.
The ICNIRP limits have already been severely criticised for being set far too high, and are aimed at protecting people from acute heating effects only, and take no account of non-thermal effects.
An inquiry in April 2000 by the British government found no evidence of any health risks from mobile phones. But the report nevertheless recommended a precautionary approach until further evidence emerged. In particular, it suggested children should not use mobile phones excessively.
How do mobile phones work?
Mobile telephony is based on radio communication between a portable handset and the nearest base-station. Every base-station serves a cell, varying in radius from hundreds of metres in densely populated areas to kilometres in rural areas, and is connected both to the
conventional landline telephone network, and by tightly focused microwave links to neighbouring stations. As the mobile-phone user moves from cell to cell, the call is transferred from one base-station to the next without interruption.
The radio communication depends on microwaves at 900 or 1800 megahertz (MHz) (a million cycles per second) to carry voice information via small modulations of the waves frequency. A base-station antenna typically radiates 60W and a handset between 1 and 2 W (peak). The antenna
of a handset radiates equally in all directions, but a base-station produces a beam that is much more directional. In addition, the stations have subsidiary beams called side-lobes, into which a small fraction of the emitted power is channelled. Unlike the main beam, the side-lobes are located in
the immediate vicinity of the mast, and, despite their low power, the power density can be comparable with that of the main beam much further away from the mast. At 150 to 200m, the power density in the main beam near the ground level is typically tenths of microWatt/cm2.
A handset in operation also has a low-frequency magnetic field associated, not with the emitted microwaves, but with surges of electric current from the battery thats necessary to implement time division multiple access, the system used to increase the number of
people who can simultaneously communicate with the base-station. Every communication channel has 8 time slots (thus the average power of a handset is 1/8 of the peak values, ie, beween 0.125 and 0.25W), which are transmitted as 576 microsecond bursts. Together, the 8 slots define a frame, the
repetition of which is 217 Hz. The frames transmitted by both handsets and base-stations are groups into multi-frames of 25 by the absence of every 26th frame. This results in an additional low frequency pulsing of the signal at 8.34Hz, which, unlike that at 217 Hz, is
unaffected by call density, and is thus a permanent feature of the emission. With handsets that have an energy-saving discontinuous transmission mode (DTX), there is an even lower frequency pulsing at 2 Hz, which occurs when the user is listening but not speaking.
Thus, the fields to which users are exposed can be quite complex.
A review published in The Lancet the same year by Gerard Hyland, physicist at Warwick University, listed numerous studies over the past 30 years that showed microwaves do have a range of non-thermal effects (see Box 1 and Box 2).
Some of the findings, such as increases in chromosome aberrations, DNA single- and double-strand breaks, promotion of cancer in cells, and in transgenic mice, are all consistent with the recent reports. Hyland is extremely critical of the current exposure limits set by the ICNIRP.
In vitro nonthermal effects of microwaves
Elicits epileptic activity in rat brain slices in conjunction with certain drugs.
Affects cell division of yeast and on the genome conformation of E. coli.
Synchronises cell division in yeast, S. carisbergenis.
Switches on l-phage and colicin synthesis in bacteria.
Alters ornithine decarboxylase activity in cultured cell line.
Reduces T lymphocyte cytotoxicity.
Increases permeability of red blood cell membrane.
Affects calcium efflux in brain cells.
Increases chromosome aberrations and micronuclei in human blood lymphocytes.
Promotes cancer synergistically with cancer-promoting drugs such as phorbol esters.
In vivo non-thermal effects of microwaves
Causes epileptic activity in rats, in conjunction with certain drugs.
Depresses chicken immune systems (melatonin, corticosterone and IgG levels).
Increases DNA single- and double-strand breaks in rat brain.
Promotes lymphomas in transgenic mice.
Synergeistic effects with certain psychoactive drugs.
A delayed increase in spectral power density (particularly in the alpha band) corroborated in the awake EEG of adults exposed to mobile phone radiation. Influences on the asleep EEG include a shortening of rem sleep during which the power density in the alpha band increases, and
effects on non-REM sleep.
Exposure to mobile phone radiation also decreases the preparatory slow potentials in certain regions of the brain and affects memory tasks.
Resting blood pressure was found to increase during exposure to radiofrequencies.
Dr Zenon Sienkiewicz, a radiation biologist at the National Radiological Protection Board (NRPB), told BBC News Online that there was still no hard evidence that showed mobile phones causing harm in real humans, rather than human cells in a test tube.
He said: "The bottom line is there are no known mechanisms by which mobile phone radiation can increase the risk of cancer."
Hyland disagrees. He points out that mobile phone radiation has been found to affect a wide variety of brain functions - such as electrical activity (EEG) electrochemistry and the permeability of the blood/brain barrier - and to undermine the immune system.
Although the precise mechanisms are unclear, Hyland pointed to an "undeniable consistency between some of these non-thermal influences and the nature of many of the health problems reported", such as headache, sleep disruption, impairment of short term memory, increases in the
frequency of seizures in some epileptic children when exposed to Base-station radiation, and of brain tumours amongst users of mobile phones.
Thus, reports of headache are consistent with the effect observed on the dopamineopiate system of the brain, and the increase in permeability of the blood-brain barrier, both of which have been medically connected with headache. The reports of sleep disruption are consistent with the
observed effect of the radiation on rapid eye movement (REM) sleep and on melatonin levels; whilst memory impairment is consistent with the finding that microwave radiation targets the hippocampus. Epileptic seizures are known to be induced by visible light flashing at a certain low
frequency, and there is no reason to suppose that microwave radiation, which can access the brain directly through the skull, flashing at a similar frequency, cannot cause the effect. Indeed, exposure to such microwave radiation is known to induce epileptic activity in certain animals; and
there have been reports of increased seizures in some children suffering from epilepsy that were exposed to base-station radiation.
Finally, mobile phone users show statistically significant increase (by a factor of between 2 and 3) in the incidence of a rather rare kind of tumour (epithelial neuroma) on the side of the brain nearest the mobile phone.
What then is the appropriate exposure limit? Hyland points out that some experiments are indicating non-thermal thresholds for biological effects of the order of microwatt/cm2. Adverse effects have been reported, however, at power densities a few tenths of that value
at distances of 150-200m from a typical 15m high Base-station mast and within the range of the more localised side-lobes in the immediate vicinity of a mast. Incorporating a further safety factor of 10 to allow for the possibility of long-term exposure, the power densities should not exceed 10
nanoW (billionth of a Watt)/cm2.