CSIRO - June 1994 BIOLOGICAL EFFECTS AND SAFETY OF EMR |
9.2 INTERPRETATION OF DATAThere are some problems in accepting some of the reports of biological effects of EMR due to: a. absence of accepted mechanisms to explain the observed effects b. absence of a dose response in many studies c. absence of independently verified results because of inconsistencies in methodology and choice of experimental endpoints d. proposed theories of nonlinear mechanisms, without threshold values, are contrary to established, conventional biological concepts e. extrapolation of cell responses when grown in culture to a potential health effect in organised human tissue f. so-called 'windows' effects at specified frequency or intensity In terms of assessing human safety, it requires a quantum leap in philosophy to make a direct extrapolation of events occurring in a very simple biological system, such as yeast cell colonies, to the complex system of organised, differentiated adult tissue. Simple cell systems grown under controlled laboratory conditions provide a convenient and accepted method for studying fundamental processes in respiration, growth and behaviour, development and reproduction. The level of detail has extended to develop an understanding of molecular/biochemical pathways essential for normal cell growth. Thus, these systems are proven as useful test objects to establish interactive mechanisms, and many simple systems, including bacteria are routinely used in testing for toxicology and potential mutagenicity of environmental physical and chemical agents. The difficulty in extrapolation is primarily due to uncertainties about EMR exposure within the human body. The absence of an established mechanism for some of the non-thermal effects reported in cell systems creates difficulties in estimating its effect in organised tissue. Gradients in electric and magnetic fields, as well as in temperature, are quite different in cell culture (with single cell layer thickness or free cells in suspension) compared to large volumes of tissue in body organs. The cell biology approaches involve standardised procedures to control variables as strictly as possible to allow detection of subtle effects. In this environment cell division is a constant and continuing process and the rate of growth is clearly defined for each species and strain. The rapid proliferation allows optimal opportunity to express developmental abnormalities through many generations on the way to produce neoplastic pathologies. It is not necessarily the case that cells in developed human organs will be in active states of division when EMR exposure occurs. Thus, it is likely that an organ such as the adult human brain would be less sensitive to insult than cells growing in culture. The attenuation of microwave energy by the scalp and skull increases as a function of frequency and is difficult to relate to exposure of cells in a highly absorbing liquid medium. It has even been suggested that the human head might act as some sort of a lens that concentrates radiated energy at certain frequencies, related to wavelength. The resonance frequency for the rat head is on the order of 5.0 GHz, while the human head is approximately two orders of magnitude larger with an equivalent difference in its resonant frequency. It is clearly essential that dosimetry is accurately characterised for experiments (in vitro cells in liquid, and animals head volume) and human exposures before meaningful evaluation of human health implications can be achieved. In the meantime, data from cellular and animal studies should be seriously considered whether or not currently accepted and demonstrated mechanisms of action exist.
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