No abstract

Since the 1990's, use of mobile phones has augmented worldwide generating a public concern as to whether frequent utilization of such devices is unsafe. This provoked EMF researchers to find suitable techniques of assessing radiation blueprint and exposure hazards if any. Most research groups focused on two techniques: experimental measurements and finite-difference time-domain (FDTD) computations. Computation of the specific absorption rate (SAR) generated by cellular phones inside two models of the human head is presented in this paper. Two models of mobile phones were considered working at 900 and 1800 MHz bands according to the Global System for Mobile Communication. Radiated energy distributions and averaged SAR values in 1 g and 10 g of tissue were computed inside the models of head using FDTD. Computations were compared with a realistic head model constructed with the MRI scans. The distribution of the local SAR in the head was similar to that of the simplified head models. The maximum local SAR calculated was 53.43 W/kg and the maximum SAR(10 g) was 2.96 W/kg, both for 1 W output power from the antenna. The results indicated the area of the maximum local SAR was situated in outer layer of skull, where muscle and skin were. The important parameters in absorbed energy in the head were the type of antenna, current distribution and the distance between head and antenna. The head models used for simulation proved as insignificant parameter in the calculations.

The majority of the results indicated no significant effect of exposure on cognition. However, verbal recall of a list of 15 words after an interference (the different list) was significantly impaired in the 'field on' condition. This is indicative of a reduction in short-term memory of words. The mean baseline score was somewhat higher in the 'field on' condition. However, this difference is within the parameters of normal variation. The other significant result occurred during performance of a trail-making task (alternating 1-A-2-B-3-C, etc.), with a decrease in performance as a result of exposure to the 50 Hz field. This task requires executive functioning with a working memory load, involving parietal spatial processing coordinated by prefrontal executive processing. In summary, the data are suggestive of detrimental effects on cognitive processes, particularly short-term learning and executive functioning. However, larger sample sizes are required to demonstrate statistically a more specific pattern of cognitive effects.

Studies of the biological effects and any health related consequences of extremely low frequency (ELF) electromagnetic fields (EMF) have been going on for over half a century however with contradictory outcomes. Hence, it is now necessary to stress on standardizing the EMF-health research experiment procedures in order to enable such experiments become replicable and results comparable. In 1998, a review of several of the ELF EMF human biological interaction mechanisms regarding field intensities and frequencies was presented to the Australian Radiation Laboratory of Commonwealth Department of Community Services and Health in 1988 by Andrew W. Wood. Wood's 1988 assertion of the importance of understanding the interaction mechanisms did not alter even after a decade when the NIEHS RAPID (http://www.niehs.nih.gov/) gathering of world experts produced their statement, in which quoted, there have been experiments on possible mechanism/s in support or refutation of the various proposals however none were replicated. Valberg (Valberg et al., 1997) also summed up some but failed to include all the claimed proposed mechanisms at the time. This paper is to present a complete list of the allegedly possible interaction mechanisms to date. This paper will also report on an academic research on computer modeling of biological effects of ELF EMF using one of the proposed mechanisms. The research reported here has generally aimed at modeling the proposals using computer. The initial phase of this effort has concentrated on Ca effect as the number of publications referencing that was considerable. Calcium is a key element in the biological performance of every organ in the human body. Thus it deemed imperative to study the effect of EMF on Ca channels of a living cell. Furthermore, considerations for setting standards in EMF experimental research protocols are recommended. Developing a standard protocol allows results of future experiments to be comparable; and, the chance of replicability in EMF-health improve, which this aspect has indisputably been absent in EMF research projects thus far. Replication is desirable mainly because it eliminates bias, artifact and systematic errors. Replication is almost impossible in the case of epidemiological studies however in experimentation is possible if the details are specified in full. To authenticate any effect of MF, it is not satisfactory to present experimental results without reporting the experimental settings in their entirety.

In order to assess the possible effects of occupational levels of 50 Hz magnetic fields (MF) on human performance it is preferable to monitor performance during rather than subsequent to MF exposure. We previously reported studies of heart rate and cognitive behaviour where the issue of contamination was not a serious one. Our present study involves electrophysiological measures, which have a greater capacity to identify the effects and assist in localising them. The contamination of EEG signal by the MF exposure is clearly a problem in this type of study. Previous investigators have not reported these types of measurement concurrent with MF exposure due to the contamination difficulty; but this paper reports means of accomplishing this. Overall a combination of 12 methods for reducing pickup were employed. These were: 1) Distancing recording instruments from the MF source; 2) Shielding the devices and wiring; 3) Appropriate choice of cables; 4) Grounding the instrumentation; 5) Orientation of conduits; 6) Isolation of electrical mains power supplies; 7) Balancing the input impedances; 8) Applying a driven shield technique; 9) Improved electronics design incorporating pre-amplification and circuit impedance level control; 10) Analogue filtering; 11) Signal Averaging; and 12) Post acquisition digital filtering using frequency and time domain techniques.