Executive Summary

INTRODUCTION

This report, prepared by the National Academies Committee to Assess Potential Health Effects from Exposures to PAVE PAWS Low-Level Phased-Array Radiofrequency Energy is the fifth Academies report on the PAVE PAWS radar located at the Massachusetts Military Reservation in Cape Cod, Massachusetts. Two previous reports evaluated the engineering and potential for population exposure associated with the PAVE PAWS radar in 1979, just prior to the radar becoming operational.1 Two recent letter reports by this committee provided advice on the Phase IV waveform measurement effort and evaluated the status of information available to the committee.2

Individuals in the Cape Cod community have raised concerns that exposure to PAVE PAWS radiation represents a unique type of radiation exposure due to the possibility that there are:

1  

NRC (National Research Council). 1979a. Analysis of the Exposure Levels and Potential Biologic Effects of the PAVE PAWS Radar System. Washington, DC: National Academy Press; NRC. 1979b. Radiation Intensity of the PAVE PAWS Radar System, Engineering Panel on the PAVE PAWS Radar System, Final Report. Washington, DC: National Academy Press.

2  

NRC. 2002. Letter Report to the Department of the Air Force from the Committee to Assess Potential Health Effects from Exposure to PAVE PAWS Low-Level Phased-Array Radiofrequency Energy: Recommendations for Phase IV Measurements. Washington, DC; NRC. 2002. Interim Letter Report to the Department of the Air Force from the Committee to Assess Potential Health Effects from Exposure to PAVE PAWS Low-Level Phased-Array Radiofrequency Energy: Adequacy of Available Research Data (see Appendix A of this report). Washington, DC.



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An Assessment of Potential Health Effects from Exposure to Pave Paws Low-Level Phased-Array Radiofrequency Energy Executive Summary INTRODUCTION This report, prepared by the National Academies Committee to Assess Potential Health Effects from Exposures to PAVE PAWS Low-Level Phased-Array Radiofrequency Energy is the fifth Academies report on the PAVE PAWS radar located at the Massachusetts Military Reservation in Cape Cod, Massachusetts. Two previous reports evaluated the engineering and potential for population exposure associated with the PAVE PAWS radar in 1979, just prior to the radar becoming operational.1 Two recent letter reports by this committee provided advice on the Phase IV waveform measurement effort and evaluated the status of information available to the committee.2 Individuals in the Cape Cod community have raised concerns that exposure to PAVE PAWS radiation represents a unique type of radiation exposure due to the possibility that there are: 1   NRC (National Research Council). 1979a. Analysis of the Exposure Levels and Potential Biologic Effects of the PAVE PAWS Radar System. Washington, DC: National Academy Press; NRC. 1979b. Radiation Intensity of the PAVE PAWS Radar System, Engineering Panel on the PAVE PAWS Radar System, Final Report. Washington, DC: National Academy Press. 2   NRC. 2002. Letter Report to the Department of the Air Force from the Committee to Assess Potential Health Effects from Exposure to PAVE PAWS Low-Level Phased-Array Radiofrequency Energy: Recommendations for Phase IV Measurements. Washington, DC; NRC. 2002. Interim Letter Report to the Department of the Air Force from the Committee to Assess Potential Health Effects from Exposure to PAVE PAWS Low-Level Phased-Array Radiofrequency Energy: Adequacy of Available Research Data (see Appendix A of this report). Washington, DC.

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An Assessment of Potential Health Effects from Exposure to Pave Paws Low-Level Phased-Array Radiofrequency Energy Particularly “steep” rise-times associated with the PAVE PAWS waveform, and Overlapping wave fronts originating from multiple antennas on the PAVE PAWS radar. It has been suggested that if those temporal characteristics exist, then the PAVE PAWS radar signal could give rise to precursor formation that might result in greater exposure to biological tissue. TASK FOR THE REPORT This committee has been tasked to provide an update of the 1979 Academy report that includes a discussion of: The applicability of, and the level of uncertainty associated with, using data derived from cell, animal, and epidemiological studies employing continuous-wave exposure for evaluation of potential adverse health effects following phased-array exposures; The extent of the exposure of the public to electromagnetic energy from the PAVE PAWS system; Potential biological and health effects of the PAVE PAWS radar system, and Recommendations for appropriate follow-on study-design issues, including the strengths and limitations of the approaches suggested and the potential value of the proposed work. The Executive Summary addresses the task items in order of appearance above. 1. The applicability of, and the level of uncertainty associated with, using data derived from cell, animal, and epidemiological studies employing continuous-wave exposure for evaluation of potential adverse health effects following phased-array exposures. APPLICABILITY OF USING NON-PHASED-ARRAY DATA Because there were essentially no PAVE PAWS data provided to or discovered by the committee that specifically addressed PAVE PAWS health effects, the first task of the committee was to determine whether continuous and pulsed radiofrequency (RF) energy research are adequate for determining the biological and potential health effects of the PAVE PAWS phased-array system. As stated in our interim report, the committee concluded that certain waveforms and power-density levels are applicable in the evaluation of biological effects and their rel-

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An Assessment of Potential Health Effects from Exposure to Pave Paws Low-Level Phased-Array Radiofrequency Energy evance to potential health effects. For the purposes of this study the committee has reviewed cell, plant, animal, and epidemiological data derived from pulse-modulation RF exposures. A major focus of the committee was a review of data with exposure characteristics defined in the committee’s interim report (for a description of these exposure characteristics, see the committee’s interim report in Appendix A). The conclusions above were based in part on the committee’s understanding of the PAVE PAWS radar characteristics as noted below. RADAR CHARACTERISTICS While minor differences have been measured in sidelobe energy characteristics, phased-array radar characteristics are substantially equivalent to those of dish radars. That observation is based on the following results of measurements made during the Phase IV waveform measurement investigation carried out by the Air Force Research Laboratory: PAVE PAWS is a narrow-band system (5 MHz) consistent with its theory of operation. Phased-array antennas and reflector antennas have measurable time delays at wide angles. Both arrays and dishes of comparable size have comparable delays. The large number of PAVE PAWS active elements (1792) and their irregular spacing make the discrete beam formation almost indistinguishable from a continuous formation and thus, the role of individual elements is usually not evident. Precursors are additions to a signal waveform, and may occur before, during, or after the signal waveform. They have been calculated and measured, but only for wideband signals—typically, 10,000 MHz bandwidth in dispersive media. They may decay slowly, but only after significant attenuation in the cellular media. For the narrow-band PAVE PAWS radar, any precursors would be extremely small and probably not measurable. Precursor formation is directly related to bandwidth (rise time), and dispersion, but not to electric field slope (V/m/nsec). UNCERTAINTIES INVOLVED IN USING NON-PHASED-ARRAY DATA FOR EVALUATION OF POTENTIAL ADVERSE HEALTH EFFECTS FOLLOWING PHASED-ARRAY EXPOSURES. There are a number of uncertainties associated with using data derived from cell, animal, and epidemiological studies employing continuous-wave and pulsed RF exposures for evaluation of potential adverse health effects in humans following phased-array exposures. Those uncertainties relate to the significance of

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An Assessment of Potential Health Effects from Exposure to Pave Paws Low-Level Phased-Array Radiofrequency Energy the waveforms, their repetition rates and power levels on the biological systems, and the significance of induced biological responses as a predictor of human-health effects. Those uncertainties are summarized at the end of Chapter 1. 2. The extent of the exposure of the public to electromagnetic energy from the PAVE PAWS system. Various measurements of PAVE PAWS power-density levels in the Cape Cod community have been made by the Air Force and by citizen groups. PAVE PAWS power-densities were also modeled by Mitre Corporation, a contractor to the Air Force. A recent analysis by Broadcast Signal Labs included measured and modeled power-density information. After evaluating the information, the committee concludes that: The measured data show that average power densities are consistently below 0.1 µW/cm2 and generally in the 0.001-0.01 µW/cm2 range at locations where the public would be expected to be exposed. Measured peak levels are generally less than 1 µW/cm2, although values as high as 15 µW/cm2 have been found at elevated locations near the radar. Power-density measurements recorded by different groups at different times within the communities surrounding the Cape Cod PAVE PAWS radar are generally consistent with each other and with modeled results. The measurements show distribution patterns that are strongly influenced by site-specific local topography and intervening terrain at any given location. The modeled data are generally consistent with the measured data with the exception that the modeling results are higher overall than the measured results. However, this is to be expected from the approximations that were made in setting up the simulations that do not include scattering and other losses. The available measurement data and models of the PAVE PAWS power-density emissions provide a good first-order characterization of the spatial distribution of the exposures occurring throughout the communities of Cape Cod. In spite of the measurements and estimates of the PAVE PAWS waveforms and power densities, currently there are no data for estimating personal exposure at the level of an individual. Using information on population density, topography, and direction of the PAVE PAWS radar beam, the committee estimated that the proportion of the population of upper Cape Cod whose primary residence is in direct line of sight3 to the PAVE PAWS beam was 11.8% in 1990 and 12.4% in 2000. 3   Line of sight means that there are no hills between the resident and the radar that would block the radar emissions. The main beam is aimed above the population and residents in the line of sight are exposed to the sidelobes of the main beam.

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An Assessment of Potential Health Effects from Exposure to Pave Paws Low-Level Phased-Array Radiofrequency Energy 3. Potential biological and health effects of the PAVE PAWS radar system. After a review of the information available to this committee at this time, the committee concludes that there is no health hazard from exposure to the PAVE PAWS radiation. There are however, a few statistically significant biological responses that have been reported. Since biological effects do not necessarily translate into adverse health effects, the implications of the biological observations are not known. At this time it is not known which characteristics of RF radiation, at the power levels associated with the exposures to the general public from the PAVE PAWS radar, are biologically significant, if any. The committee’s conclusions from its review of biology and epidemiology relevant to the PAVE PAWS radar are outlined below. BIOLOGY Mechanisms There are a number of physical mechanisms by which electric and magnetic fields of radiofrequencies are known to lead to biological changes. There are no known physical mechanisms that predict a physical interaction with tissue resulting in a biological response at power densities, on the order of 1 µW/cm2, that are associated with the PAVE PAWS radar. Animal Studies Evidence from animal studies does not provide a case for an increase in cancer risk with low-level RF exposure. There is no evidence of adverse effects on mammalian reproduction and development during exposure of animals to RF at levels that do not produce a significant temperature rise in tissues. There is some evidence of low-level RF exposure being capable of significantly reducing dopamine (a neurotransmitter in the brain involved in the control of movement) levels. Given the magnitude of the reduction observed, and the extended duration of the effect, we believe these studies merit replication. Alteration of behaviors, both learned and unlearned, can occur at exposure levels as low as 1 mW/cm2 (a thousandfold higher than PAVE PAWS exposures); however, those changes appear to be reversible with no long-term or permanent effects.

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An Assessment of Potential Health Effects from Exposure to Pave Paws Low-Level Phased-Array Radiofrequency Energy Other Biological Studies Few biological studies have been completed using RF exposures whose physical characteristics are similar to the PAVE PAWS system; however, a wide variety of biological studies have been undertaken based on RF exposures in the frequency range of PAVE PAWS. No biological experiments have employed the exposure durations that some Cape Cod residents have experienced. No endpoints traditionally associated with carcinogenesis have been found to be reproducibly affected by RF exposure in cell systems. Long-term exposure (multiple-year) studies on plant growth undertaken with radar exposures very similar to that of PAVE PAWS showed a dose- and distance-dependent decrease in tree growth, but there is currently no means for extrapolating from the biological responses reported in these studies to any health effect in humans. EPIDEMIOLOGY Epidemiology of Radiofrequency Exposures Other than PAVE PAWS Studies reported in the peer-reviewed scientific literature describing health outcomes among human populations exposed to pulsed or continuous-wave radiofrequency exposures vary in scientific quality and provide conflicting results. The methodological issues associated with those investigations primarily relate to the lack of precision in the exposure assessments, which seriously limits the use of the data in making a determination of the potential impact of radar exposure on human health. Epidemiology of the Cape Cod Population General Cancer Incidence Rates on Cape Cod Using the upper Cape Cod cancer-incidence review of 1986-1994 from the Massachusetts Department of Public Health, statistically significant increases in the standardized incidence ratio (SIR) are seen on Cape Cod for the following cancers: colorectal (SIR 112), breast (SIR 110), prostate (SIR 130), and lung (SIR 112). The observed elevated cancer-incidence rates among residents of upper Cape Cod have not been adequately explained through subsequent investigations. As an overall measure of health for the upper Cape Cod towns, premature mortality before age 75 is a useful indicator. Based on 2001 data, Barnstable, Falmouth, Mashpee, and Sandwich have lower mortality than the Massachusetts state average, while Bourne has elevated mortality.

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An Assessment of Potential Health Effects from Exposure to Pave Paws Low-Level Phased-Array Radiofrequency Energy Contrasting the calculated SIRs for 5 categories (total cancers, breast, colon, lung, and prostate cancer) during 1987-1994 versus 1995-1999 for 5 towns in upper Cape Cod demonstrated no consistent pattern of increase. During those two time periods, a decrease in SIR was observed in 15 out of 25 SIRs, no change in 4 out of 25 SIRs, and an increase in 6 out of 25 SIRs, suggesting that increasing duration of the presence of the PAVE PAWS radar has not resulted in increased incidence of cancer. Analyses covering longer durations may be required to confirm this initial observation. Committee Analysis of Cancer Incidence and the PAVE PAWS Radar Health-outcome data on cancers in the population surrounding the PAVE PAWS radar have been published in the upper Cape Cod cancer-incidence review of 1986-1994. A statistical analysis was conducted by this committee using the 1986-1994 data and peak and average power density as the measure of residential exposure. The committee evaluated the occurrence of all cancers combined, as well as specific cancers, including colorectal, breast (female), prostate, and lung, and did not identify any increase in cancer risk with exposure to the PAVE PAWS radar. Adjustment for socioeconomic status (utilizing the percent of population below the poverty level) had little impact on the observed lack of correlation between the radar and health outcomes evaluated. The population size of upper Cape Cod places limits on the ability to conduct well-designed and well-conducted research to evaluate health outcomes associated with PAVE PAWS; however, moderately low levels of increased risk ranging between 40% and 100% (i.e., relative risks between 1.4 and 2.0) could be investigated, with acceptable statistical power, for some of the more common forms of cancer. 4. Recommendations for appropriate follow-on study-design issues, including the strengths and limitations of the approaches suggested and the potential value of the proposed work. RECOMMENDATIONS Because of the limitations of human-exposure assessment, confounders, and range of health outcomes, the committee does not recommend that further PAVE PAWS health investigations be conducted unless they integrate: (1) exposure assessment and health outcomes at the census-block level; (2) strategies to quantify personal exposure in addition to residential location; and (3) appropriate considerations of potential confounders. In addition, it is recommended that future geographical correlation studies should be carried out for age-specific strata

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An Assessment of Potential Health Effects from Exposure to Pave Paws Low-Level Phased-Array Radiofrequency Energy that address early age of exposure and/or early age at onset of adverse health outcomes. To determine the levels of extremely low-frequency (ELF) sideband energy in the PAVE PAWS radar signal, a Fourier analysis should be made of a representative search pulse pattern, including the dead (maintenance) interval. Non-linearities in tissue impedance (which need to be determined) might convert the sideband energy to ELF energy that may have biological effects. This relatively simple analysis could identify or rule out potential effects from ELF that may be generated by the PAVE PAWS RF exposure. Many other radar systems employ diagnostic and calibration pulse sequences and it should be noted that many radars may have small ELF sideband energy; the possible ELF is due to the waveform characteristics, not to the phased-array antenna. Theoretical work is needed to establish connections between the physics of the electromagnetic fields and changes in chemical reaction rates and the binding of molecules to membranes. Such investigations would lend insight into possible mechanisms of biological effects of RF exposures. The strength of such theoretical investigations is that they can help determine which of a large number of possible experiments are likely to identify changes that lead to biological effects and how such effects are a function of parameters such as the field strengths, frequency, and exposure times. The limitation of such theoretical work is that the models that are analyzed may not accurately describe the problems of interest and may miss some important parameters. Selected studies on the biological effects of RF exposures are warranted, particularly those that build upon existing studies demonstrating statistically significant responses to RF exposure. While biological responses do not necessarily translate into health effects, it is important to follow up on known biological effects to determine if they relate to an identifiable health effect. Therefore, we suggest two types of biological studies: Studies are recommended that should include large-scale genomic and proteomic screening to identify gene and protein expression patterns in cells and animals after exposure to simulated PAVE PAWS radiation, both at levels approximating peak exposure levels to the Cape Cod population and at higher power levels to identify potential threshold power densities for biological effects. The committee recognizes that the limitation to these in vitro and animal studies is that they may have limited applicability to the human situation. However, the strength of these studies is that they will provide information covering a wide range of cellular activity in a limited number of experiments and the information gained may be useful in generating mechanism-related hypotheses of the effects of PAVE PAWS exposures in cell and animal systems. Studies of plant growth in the vicinity of the PAVE PAWS facility, such as tree ring width before and after the facility became operational, are also recom-

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An Assessment of Potential Health Effects from Exposure to Pave Paws Low-Level Phased-Array Radiofrequency Energy mended. While these studies have the limitation of not being directly applicable to human health, they have the specific strength of involving long-term exposures (years) under very similar conditions as the human exposures. In addition, it is anticipated that the information from these studies could relate to mechanism-generating hypotheses, particularly if initial plant investigations are followed up with more detailed analytical studies that investigate the mechanism of effect.