Summary of Conclusions and Recommendations
Both phased-array antennas and reflector antennas have time delays at wide angles. Arrays and dishes of comparable size have comparable delays. PAVE PAWS is a narrow-band system (5 MHz) with significant filtering for interference reduction. This results in waveform rise and decay times that are several times the maximum delay time of 60 nsec. Effects of delay time were not observed in the extensive Phase IV measurements.
The large number of PAVE PAWS active elements (1792), and their irregular spacing, make the discrete-beam formation almost indistinguishable from a continuous formation. There is no evidence to indicate that phased-array radar effects are different from those of dish radars; the Phase IV-measured waveforms affirm this.
Precursors are portions of the signal waveform that can travel faster or slower than the main part of the signal. Those precursors may occur in dispersive media for signals with large bandwidths. 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. With respect to narrow-band PAVE PAWS radar exposure, any precursors introduced into the human body would likely be below the noise level, and are unlikely to be of consequence. Precursor formation is directly related to bandwidth (rise time) in nsec, and dispersion, but not to slope (V/m/nsec).
Extremely-low-frequency (ELF) electric fields have been shown to produce biological effects at low-field intensities. Because PAVE PAWS is modulated at ELF frequencies, it is theoretically possible that exposure to PAVE PAWS radar
could result in inducing very low levels of ELF fields in the body. To determine the possible levels of ELF energy induced by PAVE PAWS radar exposure, a Fourier analysis could be made of a representative search-pulse pattern, including the dead (maintenance) interval. This information, in combination with measurements of the non-linearities in human tissue impedance at the carrier frequency, would allow an estimation of the extent to which the sideband energy is converted to ELF energy in an exposed body and this in turn could be evaluated for possible biological effects if the ELF-exposure levels are large enough to correspond to observed effects at ELF frequencies. It should be noted that many radars employ diagnostic intervals in their waveforms that result in a small ELF modulation.
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. They show distribution patterns that are strongly influenced by site-specific local topography and intervening terrain at any given location. The available data and models of the PAVE PAWS power-density emissions adequately characterize the spatial distribution of the exposures occurring throughout the communities of Cape Cod. The modeled power densities tend to be higher than measured power-densities, perhaps due to conservative assumptions made in the modeling effort.
No biological studies have been identified that used RF exposures identical to the PAVE PAWS system. However, a variety of biological studies have been undertaken based on short-term (hours), medium-term (weeks to months), and long-term (years) RF exposures in the frequency range of PAVE PAWS.
Short Exposure Times
Many short-exposure-time studies (hours to days) have addressed the possibility of DNA damage and other cellular responses following exposure to RF. DNA damage is a normal occurrence in living cells, with estimates that mammalian cells encounter thousands of DNA strand breaks/cell/day, most of which are repaired without adverse effects. In numerous short-term exposure studies, no reproducible effects on DNA damage have been observed, as measured by a number of different methods (micronucleus formation, DNA strand-break analysis, apoptosis, and others). While some studies have shown significant effects on gene expression due to modulated RF exposure of cells in culture, these do not include endpoints traditionally associated with carcinogenesis.
Intermediate Exposure Times
In studies involving exposure times on the order of weeks to months at levels of 900/1900 MHz, and in one case, 60 Hz, there are reports of statistically significant changes in development and differentiation of tissues and organisms. In particular, studies of exposures of chick embryos have shown a delay in development and reduced fertilization. A decreased developmental stability was also observed following exposure of fruit fly eggs. The implications of this observation for human embryonic development are unknown at this time.
Perhaps of greatest interest are the studies undertaken at 435 MHz (similar to the central frequency of the PAVE PAWS system), which demonstrated a substantial and significant reduction in dopamine levels in exposed animals.
Long Exposure Times
Long-term exposure studies (multiple years) are principally two-year bioassay experiments or carcinogenesis studies in animals and studies of changes in plant growth. A wide range of carcinogenesis studies have been conducted in animals exposed to RF fields. Such studies can generally be described as those with field intensities high enough to cause an increase in temperature in tissue (thermal) and those with field intensities below that level (athermal; comparable to the PAVE PAWS signal). Review of the lower-intensity animal studies identified some potential influences of exposure, but no reproducible indications of increased cancer risk with exposure have been shown.
Tree growth studies have been undertaken with radar exposures similar to those of PAVE PAWS at an early-warning radar installation in Latvia. Those studies showed a dose- and distance-dependent decrease in tree-ring width. Plant growth-response effects have been confirmed by changes in cell-wall synthesis activity after RF exposure.
At the present time there has been no physical mechanism shown to connect electromagnetic fields at the exposure levels associated with the PAVE PAWS radar to changes in chemical reactions that would lead to biological effects.
Given the observation of long-term RF-exposure effects in plants and the several (though unreproduced) reports of effects in intermediate-duration exposures, the committee concludes certain additional studies on the biological effects of PAVE PAWS-specific RF exposures are warranted. In particular, studies using large-scale genomic screening for gene and protein expression at the cellular level
and studies of plant growth in the area around the PAVE PAWS facility would improve our understanding of possible biological effects of long-term exposures to this radar.
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. The committee concludes that there is a need for three types of studies:
Studies are recommended that include large-scale genomic and proteomic screening to identify gene- and protein-expression patterns in cell and animal studies after exposure to simulated PAVE PAWS radiation, both at levels approximating peak-exposure levels of the CAPE COD population and at higher power levels to identify potential threshold power densities for biological effects. The committee recognizes that the limitation of these 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 theoretical mechanism-related hypotheses of the possible effects of PAVE PAWS exposures.
Studies to further investigate the potential influence of PAVE PAWS exposure on neurotransmitter (e.g., dopamine) concentrations in the central nervous system are also recommended. The observation of a robust depression in dopamine levels (~50%) with an onset concurrent with the start of exposure, and lasting for the duration of the exposure, could prove to be of great importance if this effect can be replicated. Dopamine is closely involved in motor control (e.g., depressed levels of dopamine are believed to be causal in the etiology of Parkinson’s disease) and so there could be a direct link between these observations and health effects. It is recommended that these studies be undertaken utilizing modulation frequencies more representative of the PAVE PAWS system rather than the 1 kHz utilized by Toler and others, as these lower modulation frequencies are closer to dominant brainwave frequencies.
Studies of tree growth in the vicinity of the PAVE PAWS facility are also recommended. Evaluation of tree-ring width, comparing rings from trees before and after the facility became operational with similar trees in areas that provide similar growth conditions outside the beam, should be possible with minimal or no impact on the environment. 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). In addition, if the findings replicate the Latvian tree-growth results, it is anticipated that the information from these studies could lead to mechanism-generating hypotheses.
Massachusetts Department of Public Health Statistics for Upper 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 for the following cancers: colorectal (SIR 112), breast (SIR 110), prostate (SIR 130), and lung (SIR 112) (Table 9-2 in Chapter 9).
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. The observed elevated cancer-incidence rates among residents of upper Cape Cod have not been adequately explained through subsequent investigations.
A comparison of the calculated SIR for 5 categories consisting of total cancers, breast, colon, lung, and prostate cancer during 1987-1994 versus 1995-1999 for 5 towns in upper Cape Cod (see Table 9-2) demonstrated no consistent pattern of increase during the latter time period. During these two time periods, a decrease 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, thus indicating that increasing duration of exposure to the PAVE PAWS radar has not resulted in increased incidence of cancer.
Human Epidemiology of Pulsed-RF Exposures
Studies of the U.S. Embassy in Moscow, the Radiation Laboratory at MIT, and of 40,000+ U.S. Navy personal all showed no health effects ascribable to the exposure to radars. Studies of the Polish military and the populations near Skrunda in Latvia can be considered as indicative of a possible need for follow-up studies. However, the difficulties in defining possible confounders reduces the weight given to these studies by the committee until they are supported by other epidemiological studies.
Committee Analysis of PAVE PAWS and Cancer Incidence
Peak and average power-density measurements obtained by use of (1) digital elevation maps, which take into account the height and operating angle of the radar, (2) MITRE data, and (3) the BSL report, all provided similar estimates of the exposure to the PAVE PAWS beam at each census tract within upper Cape Cod (see Figure 10-1 below) with the exception that the modeled estimates are consistently higher than the measured power densities.
The analysis conducted by the NRC committee, based on 2000 data (Table 9-7 in Chapter 9), and using available information on population density, topography, and direction of the PAVE PAWS radar beam, estimated that the proportion of the population of upper Cape Cod residing (primary residence) in areas that result in direct exposure to the PAVE PAWS beam was 11.8% in 1990 and 12.4% in 2000.
The analysis conducted by the NRC committee of the occurrence of all cancers combined, as well as specific cancers, including colorectal, breast (female), prostate, and lung, did not identify any increase in cancer risk with estimated peak or average power-density exposure to the PAVE PAWS beam. Statistical adjustment for socioeconomic status, utilizing the percent of population below the poverty level, had little impact on the observed correlations (Figures 9-7 to 9-11 in Chapter 9).
The size of the population on upper Cape Cod is sufficient (with 10 years of observation) to design and conduct research, either prospective or retrospective, that could address increases in risk levels between 40% and 100% for some of the more common cancer outcomes (i.e., colo-rectal, lung, breast, prostate, bladder, and non-Hodgkin lymphoma; see Table 9-6 in Chapter 9).
Because of the limitations of exposure estimates, confounders, and range of health outcomes it is recommended that future investigations integrate (1) exposure assessment and health at the census-block level; (2) personal exposure char-