Radio frequency radiation exposure standards: considerations for harmonization

Radio frequency radiation exposure standards vary in origin, development process, legal status, and in the actual exposure limits. To identify the sources of differences in limits, we evaluated technical aspects of eight standards that included supporting information on the scientific data and rationale. Comparisons were made among the standards by examining the scope of the underlying database, the rationales for safety factors and other issues underlying exposure limits in the energy-deposition range (0.1 MHz to 10.0 GHz) and in the surface-heating range (about 10 or 15 GHz to 300 GHz). The framework for this assessment was based on the methods recommended by the scientific and regulatory organizations for developing health-based exposure limits. General guidelines for performing risk assessments for threshold acting agents have been developed by the U.S. Environmental Protection Agency, Health Canada's Environmental Health Directorate, and the International Program on Chemical Safety of the World Health Organization. This general methodology was applied to radiofrequency radiation for this assessment. Because these methods strive to identify scientific issues and separate them from risk management or policy, they provide a basis for evaluation of standards in this paper. This distinction can provide a foundation for the longer-term goal of global harmonization of radio frequency radiation standards. Each of the standards evaluated in the energy-deposition range was found to use the same basic restriction, based on biological data and a 10-fold safety factor, yet explanations reflect different interpretations of the underlying biological data. Rationales differ for the magnitude of the safety factor, for the circumstances of exposure, for the nature of sensitive populations, and for the presumed health status of the individuals for whom the basic restriction is applicable. In the surface-heating range, broad variability in exposure limits are seen in the limit itself, as well as in the approach to time averaging and frequency dependence. Averaging times differ among standards, as do tissue geometries for defining partial-body exposures. The differences in approaches to develop the standards do not completely explain differences among the exposure limits, and methods for computing exposure limits from basic restrictions are not always defined. This analysis suggests harmonization of standards will require more detailed review and coordination of biological and engineering data and of policy options.