Hotting Up

There is so much confusion nowadays about the pros and cons of radiation I thought it best to try and clarify it as best I could. People are exposed to non-ionising radiation through natural sources such as the sun as well as human-generated sources like computers, microwave ovens, mobile phones, radar systems and power lines. From the sun, UV radiation is a major concern related to sunburn, skin damage and skin cancer. Too much sun can have a negative effect on one's immune system. On the other hand, without enough exposure to the sun, the body does not produce Vitamin D. But more on that at a later date.

Microwave radiation or microwaves are extremely high frequency radio waves on the electromagnetic radiation spectrum. While some microwaves and radiofrequency radiation occur naturally - the sun, the earth and the ionosphere create natural sources of low-level RF and MW radiation fields - the incidence of non-naturally occurring radiation has increased dramatically with the advance of technology. Microwaves can be used to carry satellite signals for communication in televisions, AM and FM radio, computers, global positioning systems and mobile phones. Microwaves can also be used to generate heat through the extremely rapid reversal in the polarity of electrons affected by magnetic and electric fields via a tube called a magnetron - this occurs in almost every kitchen and restaurant throughout the industrialised world, with the ubiquitous microwave oven.

Microwaves and radiofrequencies represent one of the most common and fastest growing environmental influences about which anxiety and speculation are spreading. Yet very little is known about the results of exposure to microwaves; even less is known about the relative dangers of different sources of microwaves. We do, however, know that microwaves can be reflected, transmitted or absorbed by matter in their path. Absorption occurs in matter that contains moisture, including human beings.

Living organisms absorb microwaves and radiofrequency energy at the molecular, cellular, tissue and whole body levels. Heating of internal organs is a consequence of the absorption of energy. The energy is absorbed by water within the tissue; so tissues with high water density and low blood density, such as the eyes and testes, are particularly vulnerable.

Scientists have known for a long time about the capacity of RF radiation to cause this type of heating and have discovered that prolonged exposure to RF radiation can lead to health problems such as fatigue, reduced mental concentration and, in the case of very high levels, cataracts. These effects are similar to subjecting a person to an extremely warm environment. Other possible thermal effects include foetal abnormalities, decreased thyroid function, cardiovascular mortality, impaired ability to perform complex tasks and the suppression of behavioural responses, gonadal function and natural killer cell activity. Studies have shown that environmental levels of microwaves and radiofrequency energy routinely encountered by the general public are far below levels necessary to produce significant heating and increased body temperature. But there is concern for whole body heating among the elderly and those on specific medications that affect thermoregulatory function. Also of concern are people with cardiac and circulatory problems, those with implanted medical electronic devices (eg heart pacemakers), fever sufferers, infants and pregnant women.

Most studies in this area are concerned with cataracts, arguably the major hazard associated with microwave radiation. A cataract is a clouding of the lens within the eye. Authorities concerned with producing safety standards agree that little is known with any real certainty about the effects of microwave radiation beyond its thermal effects. But microwave studies contain too many shortcomings to rule out the possibility that microwaves cause adverse health effects.

The recognition of non-thermal effects has been highly controversial, due to conflicting and inconclusive studies. Studies are complex, investigating possible effects of microwave radiation - from cancer to effects on the operation of all systems and parts of the human body. Cancer studies have examined cancers of the breasts, lungs, testicles and brain, as well as ocular melanoma and leukaemia. Other studies have included assessments of the relationships between radiation and cardiovascular disease, birth defects and hormone secretion rates. Research has also shown the effect of microwaves on reducing a cell's ability to perform apoptosis that is when the cell terminates its own life as a part of the life cycle of the cell, increasing the risk of spontaneous mutations, including cancer.

An example of the controversy surrounding microwaves occurred with a 1990 leaked draft EPA report in the USA , recommending that radiofrequency microwave radiation be considered a "possible human carcinogen". The White House moved quickly to suppress the draft and commissioned another report, which stated that there was no EMF cancer risk. Unfortunately, politics has its influence in too many places it should not.

Power lines and electrical devices

The ever-increasing use of electrical appliances, along with the consequent demand for electric power, has greatly increased awareness of possible risks from electric and magnetic fields at extremely low frequencies. In particular, concern has been raised about power lines. This concern has, in some cases, led to strong opposition to the installation of transmission facilities, which has delayed or even prevented their licensing. The proximity to power lines in suburbs usually means less demand for the properties and lower real estate values due to concerns about raising families near these powerful sources of electromagnetic radiation.

The idea that such fields might be deleterious has been seriously considered only since 1979, when researchers suggested, on the basis of a case control study conducted in Colorado , that the fields associated with power lines and domestic electric wiring might cause cancer in children.

At the time the idea seemed bizarre - power lines were such a normal part of everyday life and they had not been shown in laboratory experiments to have any effect that appeared to be even remotely connected with the development of cancer. During the past 25 years, however, numerous epidemiological studies have suggested a link between leukaemia and brain cancer in adults and exposure to similar and higher frequency fields at work. Residential-based studies have found similar links. The findings are, however, difficult to interpret. One reason for this is that neither leukaemia nor brain cancer is a single entity; each consists of a variety of conditions that differ in childhood and adult life and may - and in some cases definitely do - have complex causes.

Residential studies do not always directly measure exposure, but frequently use surrogates. These surrogates might include the distance of the residence from overhead power lines or electrical transmission stations or the wiring configurations in the vicinity of the residence, which could be classified as "high" or "low" according to the presence or absence of transformers and the characteristics of the local electricity supply cables.

However, in three Scandinavian studies in 1993, children who lived in houses within broad corridors around power lines had higher than normal rates of leukaemia and brain cancer. Other studies have shown similar results: the incidence of leukaemia with residential exposure equal to or greater than 0.2 (T (or 0.25 (T in the Danish series) was 2.1 times that in the unexposed population. A recent study in Canada , in which participants wore personal monitoring devices, supports a link between magnetic field exposure and an increased risk of childhood leukaemia. Evidence of a carcinogenic effect in adults has been supported by studies that have suggested occupational hazards for leukaemia and cancer of the brain.

In a three year study of some 570 people in Auckland, New Zealand researchers found that people living within 20 metres of high tension power lines were three times as likely to have asthma, twice as likely to experience major depression, twice as likely to suffer from immune deficiencies (including allergies and dermatitis) and more likely to have diabetes than those who did not live within such proximity to power lines.

Researchers have also found significant evidence that occupational exposure to electromagnetic fields may reduce melatonin levels. Melatonin levels appear to be affected by the intensity and length of exposure. as well as time of day it occurred; levels did not return to normal when workers were away on weekends. Melatonin, produced by the body, regulates sleep cycles and is a potent antioxidant that protects us from cancer.

The magnetic field strength produced by overhead lines depends mainly on the current flowing and distance from the line. Unlike the voltage, the current may change considerably during the day according to the demand for energy and, therefore, the magnetic field from power lines will be highly variable, reaching its maximum values when the load is highest - that is, when many people are using electrical appliances. Objects and buildings provide little or no screening for the magnetic field. In other words, even though it is safer to be farther from power lines, buildings don't block out the magnetic field.

Exposure to electromagnetic radiation from appliances in buildings is also an area of growing concern. The results from measurements in some offices show that magnetic induction levels are within the range 0.2-3.2 (T close to typical office devices such as personal computers and photocopiers, while at the writing desks and in usual conditions the mean value is equal to 0.37 (T, with a maximum value of 1.4 (T. Most new computers have a screening device on the front but unfortunately not behind the computers, so don't sit behind a computer. In a few buildings I have investigated, wiring ran inside internal columns in the buildings, with people working right next to the columns. The exposure was extremely high and resulted in many health complaints. Devices to measure electromagnetic radiation are relatively cheap and can be obtained from some electrical stores.

In the home environment, the most significant exposure is likely to come from electrical equipment, clocks and lights in the bed head or near where people sleep. In addition, exposure can be considerable if the bed backs onto a wall that has a circuit board behind it. In general the bedroom should not have too many electrical devices in it and none near the area where one's head is during sleep.

Peter Dingle is an environmental and nutritional toxicologist and Associate Professor in Health and the Environment at Murdoch University .