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 said.
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 doesn’t have to be a cell-phone user to become exposed to the radiation. You could be living near a base-station that’s 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.
Hondou’s 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.
|Box 1How 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 wave’s 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 that’s 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.
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.
|Box 2In vitro nonthermal effects of microwaves|
|Box 3In vivo non-thermal effects of microwaves|
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 dopamine–opiate 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.