In the previous section, we looked at some of the different types of electromagnetic radiation that are around in every day life, and we saw that one of the most important types is microwave radiation, as we use that to cook our food and for our mobile communications.  The principal cause of health effects from microwaves can be deduced if we just think about how we use our microwave oven.  We use it to heat things, and indeed if we are exposed to microwaves at a high enough level, then the cells and organs in our body will be subject to a temperature increase.

The heating effect arises as follows.  The human body is composed of molecules that, when subject to the effects of electromagnetic radiation, are made to vibrate.  Bearing in mind that a typical microwave frequency is 2,400 MHz (2,400,00,00 Hz), the rate of vibration is very rapid, and generates a lot of friction within the area of the body being irradiated, and hence heat.  The effect is rather like rubbing your hands together to warm them up.

Biological effects that arise from heating in this way tend to occur at electromagnetic radiation power levels of 10 milli-Watts per square centimetre or greater.  To put this in context, we need to note that a Watt is a unit of power, equal to a joule per second.  It is therefore a measure of energy input per unit time.  To put this further into context, consider heating 1 kg of water in a kettle.  To raise the temperature of this water by one degree Celsius requires 4,200 joules of energy.  The human body has a cross-sectional area of about 9,000 square centimetres.  So a whole-body exposure at 10 milli-Watts per square centimetre equates to about 90 Watts, or joules per second, of irradiation.  At this rate of power radiation, the water in the kettle would need about 50 seconds of exposure to raise the temperature by one degree Celsius.  Not a particularly high power rate, then, when compared with conventional heat sources.

Two quantities are of interest in considering health effects from electromagnetic radiation.  The first is called the "power density", and is the quantity that we were considering in the previous paragraph.  The other is called the "specific absorption rate".  This is a measure of how much electromagnetic radiation is actually absorbed in the body, and is measured per unit mass of the region that is being irradiated.  For example, if the specific absorption rate is equal to 1 milli-Watt per gram, this means that every gram of the part of the body being irradiated is subject to an energy absorption of 1 milli-joule per second.

Note that it is possible to induce biological effects from electromagnetic radiation that are not thermal in origin.  These arise for power densities lower than 10 milli-Watts per square centimetre.  The mechanisms by which these arise are not well understood.  However, they are clearly important for exposures at low levels of electromagnetic radiation, such as from using cell phones and other communication devices.

In terms of heating effects, the eyes and testicles (sorry guys!) are particularly vulnerable.  This essentially is because the eyes and the testicles are not subject to high levels of blood flow.  Thus, when heat is generated through irradiation in these organs, there is no mechanism for dissipating the heat (e.g. flow of heated blood away from the eyes and testicles).

Experiments have been carried out to quantify the heating effect.  According to Cember, in his 1996 book called Health Physics, animal studies have shown that if the received radiation is sufficient to raise the body temperature by more than about 5 degrees Celsius, then the radiation received is lethal.  To understand this, it is necessary to know that body temperature is homeostatically controlled.  This means that if the body temperature changes from normal, then the body takes steps to control that temperature variation.  For example, when we get hot, we sweat to lose heat energy.  When we are too cold, we shiver - the body motion during shivering being an attempt to generate body heat.  An increase of around 5 degrees Celsius is beyond the homeostatic control of the body, and death results.

Cell Phone Radiation

Cell phones emit microwaves at a power density several orders of magnitude below the limit of 10 milli-Watts per square centimetre.  (I must confess that, in trying to research for this article, I tried hard to find some figures quoted by manufacturers, and didn't have much luck - so my previous statement is a guess rather than a proven fact).  If there are any health effects from using cell phones, then they don't come under the category of heating effects.

The arguments about whether cell phone use has associated risks is a difficult one.  In general, there are three sides to stories such as this.  These are:

1.  The manufacturers, who will (for obvious reasons) play down any possibility of harmful effects from their products.

2.  Campaign groups, among whom there may be members who have suffered a loss that is believed to be attributable to cell phone use.

3.  Regulatory authorities, who have to be very careful about giving undue weight to one side or the other, and who very often take a neutral stance.

For example, the US Food and Drug Administration, in its very useful website (here), had the following to say about the risks from cell phone use:

The amount of [radio frequency] radiation routinely encountered by the general public is too low to produce significant heating or increased body temperature. Still, some people have questions about the possible health effects of low levels of [radio frequency] energy. It is generally agreed that further research is needed to determine what effects actually occur and whether they are dangerous to people. In the meantime, standards-setting organizations and government agencies are continuing to monitor the latest scientific findings to determine whether changes in safety limits are needed to protect human health.

While this is not "copping out", it is failing to draw any definitive conclusions from the evidence that is already available.  It is saying that more research is required.  (Since I work for a consultancy that undertakes this type of research, perhaps I should not be too distressed to read this type of wording).  Nevertheless, if the current research fails to identify any definitive conclusions, then maybe it is better simply to say so in more direct terms.

On the other hand, campaign groups can look at the same research and data and say something slightly different.  They can say something along the lines of:

Your research has so far failed to find any evidence of health effects from cell phone use.  But, by the same token, you have failed to demonstrate conclusively that there are NO health effects.

This is subtly different from what the Food and Drug Administration has to say.  But, in my opinion, it is equally valid.  The fact is, we don't know at this stage whether there are health effects.  In my opinion, the wording of the Food and Drug Administration is designed to give the impression that no health effects are expected, and even if they are, then they are not expected to be dangerous to people.

I have some sympathy with this point of view, even though I'm not an expert on cell phone radiation and its effects.  My own line of work is in ionising radiation (nuclear radiation, gamma rays, etc), and in that field it is held that there is no "threshold" below which ionising radiation can be considered to have no effect.  However, at very low levels of radiation exposure, the risks are sufficiently small that the probability that they will lead to a health effect - over a person's lifetime - are also very small.  In other words, low level ionising radiation may not be enough to kill you.  It may just be that exposure to cell phone radiation does indeed lead to an increased probability of a health effect, but the probability is sufficiently small that an individual is more likely than not to feel no ill effects over a life time.

I also have some sympathy with the research workers who attempt to determine what the health effects are.  The problem lies in trying to separate out the effects that are definitely caused by cell phone radiation from those that arise from other sources.  Take the induction of cancer, for example.  There are many causes of cancer.  These include smoking, exposure to carcinogenic agents, and sometimes just a "malfunction" within the cell structure in the body.  In my own field, there are various cases where the induction of cancer can be directly attributed to a radiation source.  The atomic bombs that were dropped on Japan during World war 2 are notable examples.  However, these arose from very high levels of exposure.  As the level of exposure drops, it becomes progressively more difficult to determine that the cause of the cancer was exposure to radiation.

The same is likely to apply in studies of cell phone radiation.  The effects that a particular patient may exhibit may be difficult to attribute to any particular cause, because of the lack of knowledge about the other exposures that the patient may have suffered.

Finally, it is worth stating that there are very few beneficial activities in life that do not engender some form of risk to the individual.  Driving our cars is one such risk that we take.  We know that there is some small risk that we might not complete our journeys, because we may be involved in a fatal crash along the way.  Nevertheless, we don't stop driving because of this.  Maybe a similar line of thinking should apply to the use of cell phones.  The ability to have contact at all times with our families and business colleagues is undoubtedly a good thing.  Maybe the small risk of a health effect is worth it - just as the risk is worth it to drive on the roads in order to get where we want to go?

Perhaps, after all, the Food and Drug Administration got it right when they said that more research is required before we draw any definitive conclusions about safe levels of cell phone radiation.

THE END