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For the last hvo to three decades there has been public concern regarding possible health effects from exposure to EMFs. Epidemiological reports have suggested a

link between exposure to power frequency EMFs and the occurrence of cancers

such as leukaemias and breast cancer (Wertheirner and Leeper, 1979; 1982, 1995).

A need existed to identify possible biological mechanisms to explain such a link. In

1987, Stevens proposed his melatonin hypothesis which suggested that melatonin

production may be suppressed by exposure to EMFs in the same manner as

natural light suppresses melatonin production. As melatonin is a free radical

scavenger, if such a suppression occurred, it could theoretically result in an

increase in malignancies.

There have been several occupational or environmental studies reporting suppression of melatonin levels consequential to chronic exposure to ELF E11Fs (Wilson, 1990, Burch et al, 1998; Juutilainen et al, 2000, Hong, 2001). However, the possibility exists that the results in occupational studies may have been due to other factors in the environment, such as high light intensity or the use of chemical solvents.

There is a substantial body of laboratory research reporting reductions in the levels of the brain hormone, melatonin, in rodents exposed to EtviFs (lviartinez et al., 1992; Kato et al., 1993, Loscher et al., 1994; Selmaoui et al, 1995; Mevissen, 1996; Rosen et al, 1998). Although, other studies on rodents have failed to find effects (Grota et al., 1994; Bakos et al., 1995 & 2002; John et al., 1998). Studies on other animals, such as sheep and baboons, have also failed to find effects (Lee et al. 1995; Rogers et al., 1995). Field intensities have often been higher than would occur in a normal environment. Exposure times tend to have been for periods of several weeks.

TI1ere have been few laboratory studies on humans. Wilson et al. (1990) reported a decrease in the urinary metabolite of melatonin during a chronic (8 week) exposure to electric blankets, but only for the group on a type of blanket that switches on and off frequently. Other studies have reported no effects on

melatonin levels (Selmaoui et al., 1996; Graham et al., 1997, 2000;) but these studies used low intensity fields of 10 ,uT to 28.3 �JT. Two studies, (Graham et al. 1996;

Crasson et al. 2001) reported effects, but only in people with naturally low levels of melatonin. The study by Gral1an1 (1996) had found that effect using a 1 11T continuous, or 20 11T intermittent field, overnight. It may be that those subjects were more susceptible to the effects of EIYIF exposure. This raises the question as to whether a higher flux density may have produced an effect in the other

subjects. A follow-up study by Graham (1997) failed to replicate this result but the field used in the follow-up was continuous rather than intermittent. Findings have suggested that frequent switching on and off may be an important factor

mitigating response to an EMF (Lerchl et al., 1991; Wilson et al. 1990; Cook et al.,

1992).

All the above mentioned studies used only male subjects, ostensibly to avoid possible confounders produced by variations in the female menstrual cycle. Though studies have not been done to assess whether this is, in fact, a problem. Confining subjects to males only, excluded half the population and it can not be assumed that male data can be extrapolated to include the female population. If hom1onal differences can be considered important enough to be a confounder then such differences could also be a potential coagent in any possible effects from exposure to EMFs. Just as subjects with low naturally occurring levels of

melatonin may be more susceptible to the effects of EMFs (Graham et al., 1996)

then females may by more susceptible at times in the menstrual cycle when melatonin levels are lower.

Tests of attention and working memory are a central focus of neuropsychological assessment as they are sensitive to disruption by brain injury (Cordon et al. 1997).

Consequently, they may be the most likely cognitive parameters in which to find effects from exposure to EiviFs.

Tests on attention and memory were included in this study because the literature contained little research on possible effects on these parameters in humans. An

vigilance, numerical memory and digit symbol (which is a task of executive functioning) in workers exposed to a 400 kV power line. Cook et al. (1992)

reported no effect on vigilance, addition and numerical memory but had found a decrease in errors on a choice reaction time task on exposure to a 50 Hz, 20J,LT E11F. Several other studies had been carried out on possible effects on reaction time (Lyskov, 1993; Graham et al., 1994; Cook et al.,1992, Whittington et al., 1996a). vVhilst the current study was underway three papers were published. Beale et al (1997) found no effect on attention and memory but did find a decrease in digit symbol in people living under high voltage transmission lines. Preece et al. (1998) found significant field effects for numerical working memory, delayed word recall and choice reaction time in subjects exposed to a 0.6 mT E11F ( length of exposure not stated). Trimmel et al. (1998) reported a reduction in visual attention, perception and memory as a consequence of exposure to a 50 Hz, 1 mT E11F. The subjects were also exposed to a 45 dB noise which will have made the task more difficult.

It has been suggested that EMF effects may be found only on relatively difficult tasks (Cook et al., 1992; Graham et al. 1994; Whittington et al., 1996a). For

example, vVhittington et al. (1996a) found a decrease in reaction time only on the hardest level of a visual discrimination task during exposure to a 50 Hz, 100J,LT E11F. Consequently, it is important to ascertain if possible effects from an E11F increased with the difficulty of the task. It is also possible that this effect may be further magnified by circadian effects. This possibility has not been explored.

If an E11F does effect attention or working memory then there could be

important safety consequences. For example, the ability to discriminate between letters presented in morse code is a vital skill for pilots as navigational aids are identified by their morse code ident. A task similar to the working memory task presented to the subjects in this experiment. Disturbances in attention could have serious consequences for operators of machinery.

Experiment One was carried out in 1997 I 1 998. The aim was to investigate possible acute effects from a 50 Hz, 100 J,LT pulsed EMF on the dependant variables of melatonin levels, attention and working memory.

Fifty hertz was chosen as it is the frequency used by most domestic and office appliances and hence the frequency to which the public is most commonly exposed. The flux density of 100 J.LT was chosen as the aim was to ascertain

77 whether the partial effect found by Graham et al. (1996) using 20 �LT could be expanded using a higher field intensity. It is also the recommended maximum

continuous public exposure permitted under National Radiation Laboratory (1996)

guidelines and is a common level of exposure when using appliances, such as hairdryers.

Two times of day were chosen, midday and midnight, to allow for possible circadian effects on the susceptibility to an E11F. The use of midday and midnight allowed investigation of the possibility that effects of the E11F may be greater when melatonin levels are naturally low as well as the possibility of the E:NIF suppressing or delaying the evening melatonin rise. The design allowed for the possibility of E�1F exposure enhancing melatonin production, though this has not been reported in the literature. It also allowed for possible circadian effects on

attention and memory. It may be that an EMF may be more likely to show an effect at night, when a person is tired and working closer to their limits.

The E11F was pulsed as it may be the change in field condition that produced effects. Wilson (1990) had attributed the significant effects found in that study to the electric blankets frequently switching on and off. The one second on/ off timing of the pulse was chosen as it had previously been associated with field effects (Lyskov, 1993).

The length of exposure was 30 minutes. Lewy et al. (1980) had reported that the change in melatonin levels as a response to changing light intensity is quite rapid, within 30 minutes. If EtvfF exposure effects melatonin levels by the same

mechanism as light does then an exposure time of 30 minutes should be enough to produce an effect.

A primary aim of the study was to examine the effects of an E11F on melatonin

levels at night when levels are high and in the daytime when they are low. The possibility that those with naturally low levels of melatonin form a subgroup of people who may be susceptible to an E11F, was investigated. Possible differences in gender responses to exposure were also investigated.

Neuropsychological studies have suggested that "deficits in memory are

secondary to attentional and problem solving deficits" (Eichenbamn and Cohen p.475, 2001) . Consequently it was considered important to include a simple attention test in this study. The attention task was similar to that subsequently used by Beale et al. (1997) and Crasson et al., (1999) and was a test of attention

and visual scanning.

The aural memory task wa'3 a discrimination task with three levels of difficulty. Using the same task but varying the difficulty was done to reduce the possibility of adding confounders by changing the task. The current study was carried out to add to the research in the important areas of attention and memory adding a circadian factor not present in the above studies.