1.4 STATE OF KNOWLEDGE The presence of microwave radiation in the environment was negligible prior to World War II. Since then, electromagnetic emissions from microwave frequency generators for communications, radio-navigation, military applications, diathermy, food ovens, and other industrial purposes have increased dramatically. In 1970, the First Task Force on Research Planning in Environmental Health Science (NIEHS, 1970) conservatively estimated that nearly one-half of our population lived in a measurable microwave environment. Since 1970, the number of microwave sources has increased as new and broader domestic, medical, industrial and military applications have been found. However, U.S. research programs to determine and evaluate biologic effects of nonionizing radiation have not as yet generated a data base upon which quantitatively sound and scientifically valid population exposure standards for microwave radiation (Ref. 1.8.3) can be established. Research during the past five years has led to significant advances, both in research methodology and in knowledge of the effects of microwave radiation on living systems. This work has indicated that some biological systems exhibit responses to microwave radiation at intensities that were previously considered to be too low to produce detectable alterations, i.e., in the range of 1-10 mW/cm^ (Ref. 1.8.12-15). At frequencies below 10 GHz, the full extent to which perturbations impact on living systems has not been determined nor are the conditions necessary to produce an observed alteration well defined. Even less is known about biological effects of microwaves at frequencies greater than 10 GHz. Major difficulties in reliably evaluating consequences of exposure of humans to microwaves are the paucity of human data, difficulty in establishing dose distribution within a body, insufficiency of valid data on experimental animals, and the usual problems of extrapolating data from animals to humans. The current lack of understanding of basic mechanisms of how low-intensity fields interact with biological systems compounds the problem. Research to date has not resolved these difficulties, but it has helped to define the nature and scope of the problem and has provided directions for continuing research (Ref. 1.8.4). Only intensive experimental study of continuous wave (CW) radiation at the proposed frequency of 2.45 GHz can reveal whether the SPS concept can be implemented safely (Ref. 1.8.1).
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