24/04/2007 - Dispelling the Wireless Myths
With all of the recent coverage of WiFi networks and mobile phone base stations, it seems appropriate to address some of the common microwave radiation exposure myths that get frequently promulgated by the pseudo-scientific, pseudo-intellectual technical community online.
It is good to see that there are some other impartial voices of precaution on this issue, as Kathleen Sibley writes on the IT Business news site.
Myth 1: We've been exposed to this radiation for years, it must be safe
From the Sun
Yes, we had heard quite a few people saying that standard cosmic background radiation has enough microwaves in it that we should already be being affected even before the appearance of TV and radio, let alone mobile phones. The background microwave radiation (by which we refer to frequencies ranging from 300 MHz to 30 GHz) from the Sun was almost non-existent, millionths of what can be found in your local wireless cafe. So even if the signals themselves were the same, this claim is nonsense.
Background on Radiation Frequencies
It is generally accepted now that X-rays can cause health problems via known mechanisms (e.g. DNA strand breaks). It is also generally accepted that visible light does not cause much harm (with the possible exception of eye-damage if the intensity is too great) during the daytime (caveat here as night-time visible light may cause health problems such as breast cancer indirectly by melatonin suppression). As any physicist could tell you, whilst both naturally occurring forms of radiation, they consist of very different wavelengths and are not comparable.
From Radio and TV
FM Radio tranmissions are at about 100 MHz, considerably lower than the 900 MHz and 1800 MHz of GSM mobile phone communications. Moreover, and we believe this is of critical importance, radio transmissions are continuous wave transmissions, and do not rely on pulsed signals to transmit data. Likewise, whilst the transmission frequency of TV is much closer (approximately 450 to 850 MHz), this is again close to continuous wave, and does not have anything like the amplitude modulation that mobile phone carriers do.
This is crucial, not because it guarantees that there must therefore be a risk, but because it highlights that this exposure is new. We are now being surrounded and bombarded by radiation that is unlike anything we have been exposed to previously. It may be safe, it may not be, but we cannot use the argument that it has been around for years as this is not the case.
Myth 2: People only got affected when the scare stories started, it must be psychosomatic
Again, this is a quickly dispelled myth (often also referred to as a 'nocebo' effect -- basically a negative 'placebo' effect). A quick look at some of the science:
Cell death induced by GSM 900-MHz and DCS 1800-MHz mobile telephony radiation
Panagopoulus DJ et al, January 2007 [View on Pubmed]
This study from the University of Athens in Greece found that DNA fragmentation of egg chamber cells could be created in fruit flies when exposed to a simulated phone call from a real digital mobile phone. Yes, this is not damaging human tissue, but it is clearly not a psychological response.
Effects of electromagnetic radiation from a cellular phone on human sperm motility: an in vitro study
Erogol O et al, October 2006 [View on Pubmed]
This study from Turkey found examined the sperm motility (a measure of fertility) in 27 male human subjects. They found that after exposure from a standard GSM 900-MHz mobile phone sperm motility was measurably decreased, and that this decrease was statistically signifcant. Again, not a psychological response.
Gene expression changes in human cells after exposure to mobile phone microwaves
Remondini D et al, September 2006 [View on Pubmed]
This in vitro study from the University of Bologna in Italy found that some (but not all) of the tested cell lines would react to 900 and 1800 MHz microwave radiation. This is again evidence that a non-thermal reaction can be found that is not psychological, and again can be replicated in lab conditions.
Possible Effects of Electromagnetic Fields from Phone Masts on a Population of White Stork (Ciconia ciconia)
Balmori A, October 2005 [View full paper on our site]
This time a study on animal populations in Spain, Balmori looked at the nesting and behavioural patterns of white storks located around a mobile phone base station near Valladolid. Some very startling results, such as the storks failing to start or half building their nests. It was also found that the number of storks without young rose from a consistent average of 5-10% before the mast was built up to 40% after the mast was built. Again this is not looking at humans, but it is also therefore not feasible to put this down to some form of psychosomatic phenomena.
Myth 3: Being on a phone for 20 minutes is equivalent to 1 year in a wifi classroom
This statement, very unhelpfully publicised by Mike Clark, senior spokesperson for the Health Protection Agency, is both factually incorrect and highly misleading.
Whist Mike Clark is right that a mobile phone, working on full power and with you talking continuously (not listening) can technically expose you up to about 50% of the SAR limits. In normal use, with a good number of signal strength bars showing on the display (say 75% signal level), the phone will be working at somewhere between one-thousandth and one-twentieth of this level. Let's average this at about one fiftieth as a reasonable level for the phone to be operating at most of the time. Then, if you are talking 50% of the time, this would reduce the transmitted pulses (using DTX) by another factor of 2. So, a typical exposure would not be 50% of the SAR limit but more like 0.5% of the SAR limit which we should assume to be 0.5% of the the ICNIRP limit (for a typical call).
11/10/2007 - This has been updated to more accurately reflect expected real life power outputs from Wireless access points in use.
Now we come to a slightly different exposure regime in the classroom in that you are not holding the wLAN card to your head. 2.4 GHz wLANs (most common in the UK) operate at 0.03 watts output power (5-6 GHz ones can use up to 20 times this). So we have one wLAN node in the classroom (0.03 W) and, say, 20 laptops all at 0.03 W. However, they are only transmitting much power when actually transferring files. So, let's say that we have the equivalent of one laptop operating absolutely continuously (actually the combined output of 20 may well be more that this), and that we are on average 2 metres from the antennas. This seems reasonable based on the fact that there are 20 in the room. So E = (sq.root (30*0.03*2))/2 = 0.67 V/m equivalent continuous. Now the ICNIRP guidance at 2.4 GHz is 61.5 V/m. So the signal strength is about 1/100th of what is allowed. Power is proportional to signal strength squared so that would be around 1/10000th of the ICNIRP power level.
So, we have a mobile phone call next to head typically 0.5% (1/200th) of the ICNIRP guidance. We also have being in a 20 PC wLAN classroom being something in the order of 0.01% (or 1/10000th) of ICNIRP guidance, about a 50-fold difference.
Therefore 20 minutes on a mobile phone running at typical power levels would be equivalent to about 16 hours in a classroom with 20 wLAN PCs, approximately eight standard school days.
There are other differences. In the phone call situation, almost all the energy goes into the user's head and hand. In a classroom situation the whole body aborbs this lower level of power, so the "total body burden" if we were to compare it with ionising radiation (for example), would actually be very similar.
We have no idea how Mike Clark can feel justified in claiming this completely unsubstantiated and unsupportable statistic.
The above calculations are based on absorbed power levels, which is based on the idea that the only thing that microwaves do is heat you. As we are looking at non-thermal effects we believe that signal strength is likely to be a more appropriate metric (measured in volts per metre). This has the advantage of not being averaged over time, and we can therefore tell the difference between exposure from a continuous wave signal and one where the signal consists of a number of short pulses with gaps.
Myth 4: The WHO factsheet says there is no cause for concern, and they should know
Whilst it would be great if this was true, it also appears that they have become quite the beaurocracy when it comes to actually keeping on top of the science. The wonderful factsheet that keeps getting quoted as evidence that there is no problem can be found here, and was last updated in June 2000, over 6 and a half years ago! They have not taken into account any of Hardell's work showing an increase in brain cancer from mobile phone usage, the INTERPHONE studies, nor did they assess any of the papers shown in the rebuttal of myth 2 (which, incidentally, is just the tip of the iceberg anyway). This factsheet is so hopelessly out of date with regards to the current state of science on this issue that it should now be simply ignored.
Important Update - 07/06/2007: Actually, this section is incorrect, the latest WHO factsheet on electromagnetic fields and health is Factsheet 304, from May 2006. So whilst it would still have ignored all 4 references in Myth 2, it is much more relevant. Sadly, some points made in the document are factually incorrect, such as "To date, the only health effect from RF fields identified in scientific reviews has been related to an increase in body temperature (> 1 °C) from exposure at very high field intensity found only in certain industrial facilities, such as RF heaters". The factsheet also states "Over the past 15 years, studies examining a potential relationship between RF transmitters and cancer have been published. These studies have not provided evidence that RF exposure from the transmitters increases the risk of cancer." So whilst it is a more recent report, I can only assume that this review also didn't look at the Hardell work that found a clear and statistically significant increase in some forms of brain cancer from extended mobile and cordless phone use.
The problem is that the sentences themselves are "enhanced" by the usage of highly subjective terminology. For example, the conclusions state "Considering the very low exposure levels and research results collected to date, there is no convincing scientific evidence that the weak RF signals from base stations and wireless networks cause adverse health effects." Everything in this sentence hinges around the word "convincing", without which the statement would be factually incorrect. However, convincing is both entirely subjective and also not justified in either the document itself nor the linked documents. It would be interesting to understand exactly what constituted "convincing", and in the meantime it would be better to have a less ambiguous description of what the currect scientific actually says.
This page has links to content that requires a .pdf reader such as Adobe Acrobat Reader