Evidence of Biological Effects of RF Exposure Relevant to PAVE PAWS Radar System
Biological studies to determine the plausibility of an environmental exposure having either detrimental or beneficial consequences take many forms. However, the primary goal in most of these studies is to establish a reproducible biological effect from the exposure under well-controlled conditions. Such studies utilize animal cell cultures and embryo cultures, as well as plant-growth cultures and field studies. Exposure conditions for these studies may represent those that human populations might be exposed to, or alternatively those that are expected to produce an observable biological effect in a reasonable period of time. For example, it is common research practice to use exposure levels that are much higher than those encountered in the environment to obtain a rapid and robust experimental effect. Such studies may lead to subsequent investigations of possible human health effects in animal systems or epidemiological studies. Cell-culture experiments are easy to reproduce, but the behavior of cells in culture is never exactly the same as within an organism due to the fact that cells have been isolated from their usual environment, which includes contact with a variety of other cell types, exposure to intercellular factors, and a tissue architecture. In vitro experiments, therefore, can be, in comparison to whole organism in vivo experiments, sometimes more and sometimes less likely to demonstrate a response to an environmental exposure. Cell-culture experiments are also of limited value if one wants to undertake very long-term exposure experiments (months to years). Embryonic development studies can provide greater insight into potential health effects; however, there are a limited number of established embryo models that provide well-accepted, quantifiable endpoints for study. Plant growth studies per-
mit very long-term exposures to be studied under well-controlled conditions, but are only remotely connected to potential human health issues.
Tremendous advances in our understanding of biological systems have occurred over the 25 years since the previous review of in vitro studies of RF exposure effects, which was a part of the 1979 NRC review of the PAVE PAWS installation (NRC 1979). Those advances have had profound effects on our understanding of biology, greatly enabling the scientific community in its efforts to determine if and how the RF radiation generated by the PAVE PAWS system could influence biological systems. Our ability to design experiments and collect data from culture studies has been enhanced as a result of numerous technical advances, as well as significant advances in modeling the inherent complexity of biological systems, which provides a theoretical foundation for interpreting data from such experiments.
At the time of the initial NRC PAVE PAWS report (1979), cell/tissue-culture techniques were well-developed approaches but their analysis involved predominantly simple biochemical assays and single-molecule detection approaches. Protein biochemistry was also a developed field, but few specific signal-transduction pathways had been identified in cells. The techniques of molecular biology were only in the early stages of development. Today, three-dimensional tissue-culture systems are being developed to permit the study of differentiating cell systems in a native tissue architecture, and polymerase chain reaction technology permits DNA amplification from samples as small as a single cell. Differential display techniques and cDNA microarray approaches permit studies of gene expression of large numbers of genes at one time, and high performance liquid chromatography (HPLC), mass spectroscopy of “protein chips,” and yeast two-hybrid systems permit studies of protein distributions, protein dynamics, and protein-protein interactions. Similarly, developments in microscopic techniques (such as atomic force, confocal fluorescent, real-time fluorescent, and micromanipulation techniques [laser capture microscopy] have significantly advanced our abilities to undertake studies of processes such as cell dynamics and intra- and inter-cellular interactions.
Of equal importance has been the development of computational approaches for modeling biological systems and responses based on concepts from complexity theory. Fuzzy logic, neural-network analysis, genetic algorithms, and clustering techniques are modern bioinformatic tools that permit the large datasets obtained by molecular biological techniques to be analyzed. These new approaches are tools that allow scientists to understand how complex systems (i.e. systems with many highly interactive components) are influenced by alterations to their environment. The computational modeling of biological processes, therefore, may help us to predict under which situations perturbations in the environment may influence biological systems. Whereas all complex systems are robustly stable to acute environmental insult, even slight perturbations in the environment can influence the self-organization of such systems if imposed for a sufficient period of
time. All cells and organisms are potentially sensitive to fluctuations in the environment; however, the influence of a specific environmental perturbation on cells and organisms may not necessarily be observed in studies of a single model, but could require that a class of models be used to capture the potential set of outcomes of a given environmental perturbation. Application of these concepts to the review of biological studies of RF exposure suggests that studies that focus on the self-organization in a system (e.g., differentiation and development) and involve long-term exposures may eventually be best positioned to identify the influence of an environmental perturbation.
In order to provide a maximal representation of different cells, tissues, and “general” experimental conditions, and still remain in the realm of experimental conditions relevant to the PAVE PAWS system, this review emphasizes experimental designs from the following types of systems:
A large ensemble of cells,
An RF exposure similar to that generated by the PAVE PAWS system, and
A long-term exposure to the radiation (similar to the circumstances associated with the PAVE PAWS installation).
We have also reviewed responses in cells based on stress responses that have been identified in the literature as being important for cellular recovery to acute toxicity and injury. Life on earth has evolved in an environment associated with a variety of stressors including radiation, heat, chemicals, and other toxic insults. As a consequence, cells and animals have evolved defense mechanisms to cope with these acute stresses including anti-oxidants, apoptosis (cell death to avoid replication of damaged cells), DNA repair, refolding of damaged proteins, and other mechanisms. These defense pathways work to prevent the continued expansion and use of damaged biomolecules in the cell. Much acute cellular damage can be compensated by these different damage-response pathways and so, correspondingly, these pathways represent important targets to consider in the context of detrimental biological responses to an environmental exposure. The presence of these pathways may also explain how biological responses may occur but not result in adverse health effects.
The effects of exposure to external stimuli can be categorized into:
Direct molecular effects
Protein function alterations
Indirect molecular effects
Cell signal transduction
Cell cycle perturbation
Differentiation and development
Direct Molecular Effects
DNA damage is induced by a wide variety of different stimuli including radiation, chemicals (such as chemotherapeutic drugs), and oxidative damage (including the damage that results as a normal consequence of cellular respiration). Elaborate pathways exist within cells that serve to repair damage to DNA, thereby maintaining genetic integrity and normal cellular function. Incomplete or faulty repair can lead to the production of abnormal proteins or the dysregulation of specific protein syntheses. While the overall resiliency of the cell may compensate for this dysregulation, a disruption of certain specific DNA repair processes can result in diseases such as cancer, immunodeficiency, and others. DNA damage is a normal consequence of cellular function, and it is estimated that mammalian cells encounter 104 DNA strand breaks/cell/day, which are usually repaired without adverse effects.
Several studies have examined possible effects of exposures to radar and cell-phone RF energies on DNA damage in mammalian cells following acute exposures (hours). The results have been contradictory and controversial (Lai and Singh 1995; McNamee and others 2002; Tice and others 2002; Bisht and others 2002; Malyapa and others 1997; Lai and Singh 1996). While Lai and Singh have detected strand breaks after RF exposures, several groups which have also used very sensitive alkaline comet assays detect no DNA break increase at pulsed RF frequencies of 1.9 GHz, 835.62 MHz, or 847.74 MHz (cell-phone frequencies) at 0.6 W/kg SAR (McNamee and others 2002; Malyapa and others 1997). Additional recent studies from Roti-Roti’s laboratory have demonstrated an absence of DNA damage in brain cells, fibroblasts, and lymphoid cells following exposure to pulsed-wave microwaves and radiofrequency (Lagroye and others 2004a; Lagroye and others 2004b; Hook and others 2004). The validity of such studies depends on the sensitivity of the assay system in any particular laboratory, the types and times of exposures, and the possible sources of error. Recent studies by Dimitroglou and others (2003) have shown using single-cell gel electrophoresis
higher levels of DNA strand-breaks in people who have been psychologically stressed, suggesting a role for hormonal and biochemical factors in the response, a consideration that was not previously addressed in the above reports and may be one source of error. For a review of controversial cytogenetic observations in mammalian somatic cells see Vijayalaxmi and Obe (2004).
It should be noted that the ability of an agent to cause single- or double-strand breaks (ssb or dsb) in DNA does not necessarily mean that the agent is dangerous or even capable of inducing mutations. Chemicals such as hydrogen peroxide are known to cause breaks in DNA but cause few adverse health effects. Likewise, low doses of ionizing radiation or UV light well within the limits of the permissible exposure also cause DNA strand breaks. Exposure to very low doses of ionizing radiation (1 cGy) can be detected to cause DNA strand breaks (for example, Buatti and others, 1992 find that the rate of strand breaks per cell is 1815/Gy). UV-radiation exposure, analogous to the exposure from sunlight, causes 0.07 ssb/1010 Da/kJ/m2 for UVA; and 1.9 ssb/1010 Da/kJ/m2 for UVB (Wenczl and others 1997).
Direct damage to cellular membranes has been associated with exposure to a variety of chemicals and to ionizing radiation. These stresses often lead to differences in lipid and protein composition of cellular membranes, altering the membrane fluidity, ion transport, and surface properties of the membrane.
As in the studies with DNA damage, changes in membrane fluidity or ion transport are associated with a large variety of normal states, and these changes in and of themselves are not necessarily associated with pathogenic states or with a progression toward pathogenesis. For example, chemicals known as ionophores cause a change in membrane permeability and permit ions that are usually outside the cell to rapidly influx. Nevertheless, there are very few dangerous consequences associated with exposure to ionophores, and in general they are used to mimic natural ionophoric processes that occur in mammalian cells.
Some isolated reports of changes in membranes and ion transport have been reported to be associated with exposure of cells to modulated cell-phone and radar radiation. The reported effects in the literature come largely from one laboratory, and include both changes in Ca++ ion flux in cells in monolayer culture and efflux from ex vivo tissue slices (Dutta and others, 1989; Dutta and others, 1984; Blackman and others 1985; Joines and Blackman, 1980). Subsequent studies (Cranfield and others 2001; Wolke and others 1996) have documented no or marginal effects of RF exposure on Ca++ flux in cell-culture systems. Taken together, these experiments provide some support for the suggestion that modulated RF exposures may be more capable of causing biological effects than unmodulated RF fields.
Clustering of membrane proteins (called membrane capping) occurs on a
variety of cell types including lymphocytes and is usually a measure of membrane perturbations and membrane responses in mammalian cells. Sultan and others (1983) performed studies to determine whether or not modulated RF exposure caused changes in the ability of B-lymphocytes to cap following exposure to antigen; these studies showed no difference in the capping responses of unexposed and exposed cells in culture.
Protein Function (Folding, Protein-Protein Interactions, Translations)
Proteins are responsible for carrying out most of the cellular maintenance functions within mammalian cells. Changes in DNA are considered dangerous primarily because they lead to changes in the expression of proteins. However, cellular stress-inducing agents have been shown to affect proteins in several different ways. Changes in the ways in which proteins fold have been found predominantly following exposure to heat-shock, while changes in protein-protein interactions and in protein translation have been associated with almost all types of cellular stress. Because of the resiliency of biological systems, such damage to proteins is not usually sufficient to harm a cell unless it has occurred with a large number of proteins resulting in protein aggregation and large-scale dysfunction in a cell. In addition, cells have evolved complex systems for managing this type of damage. Chaperone systems and proteosomes are proteins that function to refold damaged proteins, clear unrepairable proteins from the cell, and disassociate aggregates created following exposure to heat-shock stress. This damage-response pathway permits heat-damaged cells to repair their proteins and resume normal function in the body. This pathway is generally induced whenever the body is experiencing fever or thermal dysregulation, although there have been a few reports in the literature of heat-like responses following exposure to ionizing radiation, UV, or other forms of stress. Numerous studies have examined the thermal effects of radar, and these effects have been well-characterized in the literature. However, such thermal effects cannot occur at the radar power densities experienced by the Cape Cod population and are not considered here.
Several recent reports have documented induction of chaperone-like heat-shock protein responses in mammalian cells following exposure to cell-phone frequencies below the thermal range. In particular, DiCarlo and others (2002), and studies by Kwee and others (1998, 2001), have documented induction of several heat-shock proteins (hsp70) in mammalian cells, as well as increased binding of heat-shock elements to their DNA-binding sequence. Replication of those findings have not been reported in the literature but are suggested by other studies showing increases in hsp70 following RF exposure (cell-phone frequencies) of fruit flys (Weisbrot and others 2003). Related studies by dePomerai and others (2000a, 2000b, 2002) have demonstrated that non-thermal microwaves can induce hsp70 in the nematode Caenorhabditis elegans. Similar induction of hsp70 has been observed following exposure to very low doses of ionizing radiation
(Calini and others 2003). The implications of this non-thermal induction of heat-shock proteins are not clear however they do suggest the induction of a cellular mechanism to protect proteins from degradation/denaturation. Whether this is a direct consequence of radar exposure is also not clear, but levels of induction are very low, far below the threshold of a small fever response. On the other hand, other studies have suggested that stress proteins are not induced following exposure to radiofrequency or microwave radiation (Cleary and others 1997).
INDIRECT MOLECULAR EFFECTS
Cell Signal Transduction
Extracellular signals (for growth, differentiation, apoptosis) are transmitted to the cell via a cell signal-transduction cascade that usually involves stimulation of a surface receptor, alterations in intracellular ionic concentrations, a variety of phosphorylation events, amplification of the signal, transmission of the signal into the nucleus, and alterations in gene expression. Transient changes in cell signal-transduction cascades have been associated with most cellular stress-inducing agents; these changes can lead to more permanent expressions of cellular changes such as those reflected in terminally differentiated cells.
Studies of changes in cell signal transduction following radiofrequency exposure have been limited to an examination of production of extracellular factors following exposure to RF. The most significant changes that have been reported in the literature are in the transient release of cellular growth factors and other cell signal-inducing agents that might alter cellular functions temporarily (Mausset and others 2001; George and others 2002). Other studies, however, have reported no changes in levels of such extracellular modulators as melatonin or cortisol (Radon and others 2001; Stark and others 1997). While there are numerous studies in the literature of the effects of other cell stressing agents on kinase activation or intracellular phosphorylation events, Pacini and others (2002) is the only report of changes in mitogen-activated protein kinase (MAPK) phosphorylation pathways affected by exposure to RF. Leszczynski and others (2002) reported activation of MAPK stress pathway in human endothelial cells using mobile-phone exposures.
Time-series data provide an exceptional means for characterizing cell system dynamics, and fluorescent microscopy provides a well-established technique for monitoring the activity of cell ensembles. Specifically, calcium signaling has played a major role in discussions of the influence of RF exposure on biological systems, dating to the early calcium-efflux studies of Adey and others as reported in the 1979 NRC report. Modern techniques permit the real-time monitoring of calcium activity in cell ensembles. Cranfield and others (2001) monitored calcium activity (using Fluo-3 dye) in monolayers of Jurkat E6-1 cells exposed to a 915 MHz RF waveform pulsed at 217 Hz and designed to simulate a GSM tele-
phone signal. SAR varied from 1 to 2.1 W/kg with a weighted average of 1.5 W/ kg. Mean calcium levels and calcium spike height were not affected by the RF exposure; however, a significant shift in calcium spike frequency was observed, consistent with an affect on cell ensemble activity.
Changes in gene expression encompass events from activation of genes (promoter activation), through the changes in mRNA availability, to changes in protein stability/quantity, all of them finally leading to the changes in quantity of the protein product of the gene in question. Moderate changes in gene expression have been associated with mild or moderate exposures to cellular stressing agents including mild heat-shock or very low doses of ionizing radiation.
Several groups have examined changes in gene expression following exposure to RF. For the majority of genes examined for changes in expression to date, c-fos is the only transcription factor that has been shown, in multiple studies, to be modulated in response to RF exposure (Goswami and others 1999). Pacini and others (2002) reported induction of beta-transforming growth-factor and apoptosis-factor (bax) gene expression following RF exposure. Several studies of gene expression using comprehensive gene-chip arrays that can monitor the entire genome of expressed genes in a single experiment are underway and hold promise for resolving questions of gene expression changes associated with RF exposure.
Apoptosis is the process of programmed cell death induced either in natural circumstances of embryogenesis and differentiation or in states of stress following exposure to cellular damaging agents such as heat or radiation. In cell-stress responses, apoptosis can be protective because it prevents the induction of cancer cells by causing the death of cells with damaged DNA that might otherwise allow for cells bearing deleterious DNA mutations to survive.
Few studies have examined induction of apoptosis following RF exposure. As noted above, Pacini and others (2002) reported the induction of the proapoptotic gene bax following RF exposure.
The cell cycle not only marks the progression of a cell from single cell through its DNA replication and division into two daughter cells, but also can include stages of cellular preparation for proliferation, differentiation, or cell-
cycle arrest. Cell-cycle perturbations are commonly observed following exposure to cellular stressing agents. Ionizing and UV radiations are both known to cause delays in cell-cycle progression associated with an increase in DNA repair and activation of other cell-survival functions. In addition, changes in cell-cycle time are reflective of each particular cell type and its degree of differentiation.
In studies on the effects of RF exposure, George and others (2002) demonstrated an increase in proliferative potential in exposed fibroblasts and epithelial cells. Similarly, Velizarov and others (1999) demonstrated a change in cell-proliferative capacity following RF exposure that was not related to thermal effects. Pacini and others (2002) also documented an increased proliferation of normal human skin fibroblasts in culture following exposure to RF. On the other hand, Higashikubo and others (2001) observed no changes in cell-cycle progression in two different cell lines exposed to RF (Higashikubo and others, 2001). Similarly, Stagg and others, (1997) reported no effects of a modulated RF field on cell proliferation in a glioma cell line or in primary glial cells.
These differences in observations may be due to different cell systems used, different sensitivities of assays, and different experimental conditions.
Differentiation and Development
Cellular differentiation is a critical aspect of tissue and organismal development. The process of differentiation is complex and poorly understood, yet it is known to involve changes in gene expression, protein production, cell surface-marker expression, and cell signal-transduction pathways. An undermining of this process is associated with some types of tumor progression in which normal differentiated cells are replaced by de-differentiated continuously dividing tumor cells. This process is perhaps best understood in vitro when differentiating agents are added to cells in culture to induce particular phenotypic changes associated with end-stage cells. A few studies have examined the effects of RF exposure on cellular differentiation.
Koldayev and Shchepin (1997) reported a study of RF effects on early embryogenesis of sea urchins. In two studies involving 450 MHz radiation for a period of 5-20 minutes, the protocol investigated fertility associated with combinations of exposed sperm and unexposed eggs, and unexposed sperm with exposed eggs. Exposure of sea urchin eggs to 100 mW/cm2 caused a 1.2- to 1.9-fold decrease in cell fertilization. Irradiation of eggs at 200 mW/cm2 caused a 1.8- to 2.6-fold decrease in fertilization rate, with 7-11 times the control number of abnormal zygotes. Sperm irradiation had no effect on fertilization rates. However, Saito and others (1991), in a study involving 20-day exposures of chick embryos to a 428 MHz, 5.5 mW/cm2 incident field, showed severely delayed development according to the Hamburger-Hamilton staging. Ten replications using 10 eggs were completed, with developmental anomalies observed at SARs in the range of 8.6 mW/kg to 47.1 mW/kg.
Numerous studies have been undertaken to address the potential influence of RF exposure on teratogenesis (the production of non-heritable birth defects). In 1987, Lary and Conover (1987) completed a literature review of all teratogenesis studies extant to that date, including all studies with exposures from 300 to 3000 MHz, and below the ANSI exposure limit of 0.4 W/kg. They found no reports of teratogenic effects in the absence of organismal heating.
More recently, Heynick and Merritt (2003) reviewed work (and subsequent errata, including Saito and others 1991) on teratologic effects and developmental abnormalities from exposure to radiofrequency electromagnetic fields (RFEMF) in the range 3 kHz-300 GHz. A series of studies was conducted on beetles, birds, rodents, and nonhuman primates indicating that teratologic effects occur only from exposure levels that cause biologically detrimental increases in body temperature.
Effects of RF exposures on development in whole-animal mammalian systems are discussed in detail in Chapter 7.
Normal cells have the capacity to repair damage to their genetic material as a part of their evolutionary heritage. DNA-repair pathways in mammalian cells are complex, with multiple proteins regulating the reactions. Different types of repair are associated with repair of different types of DNA damage. Faulty repair of DNA damage is associated with some human hereditary diseases such as ataxia telangiectasia or xeroderma pigmentosum. In addition, abnormalities of specific DNA-repair proteins are associated with a higher incidence of particular cancers. For example, abnormalities of the Brca1 gene, part of a DNA-repair complex, are associated with a higher incidence of breast cancer among women. Abnormalities of DNA repair would be evident in several different ways including increased accumulation of DNA damage, changes in the accumulation of particular DNA-repair proteins, and alterations in other pathways controlled by DNA-repair proteins (such as cell-cycle progression and cellular transformation). To date, there have been no direct measures of DNA-repair capacity in cells exposed to RF fields. Nevertheless, the moderate to undetectable changes observed in DNA damage, cell-cycle progression, and carcinogenesis that occur following RF exposure suggest that direct effects on DNA-repair pathways are unlikely.
Carcinogenesis is a process whereby changes in the genome of a cell lead to the progression of a normal cell into a cancerous cell. This process leads to the clonal expansion of a single cell that has uncontrolled growth and progresses to a full malignancy. Genes that have been found to be mutated in cancer cells include many of those discussed above—genes that regulate gene expression, cell-signal transduction, apoptosis, DNA repair, cellular differentiation and development, and cell-cycle progression. Neoplastic transformation is tightly associated with DNA damage and mutagenesis except in a very few cases. Reports discussed
above regarding effects of RF on DNA damage relate to this issue since most DNA-damaging agents are mutagenic and also carcinogenic.
One of the most important endpoints that has been examined after RF exposures is that related to cellular transformation in vitro and induction of cancer in animals following exposure. Several types of in vitro and in vivo assays have been applied to the problem in an effort to discern whether or not RF exposure leads to an increased risk of carcinogenic transformation. Studying cells in culture, Roti Roti and others (2001) demonstrated that CDMA1 radiations cause no effect on neoplastic transformation following a seven-day exposure. In related work, Cain and others (1997) reported, in a chemical tumor-promoter study using the same cell system, that modulated RF field exposure for 28 days does not lead to increased tumor promotion or progression over that of the chemical promoter alone. Detailed discussion on the effects of RF field exposure in mammals is presented in Chapter 7.
Growth in Plant Systems
A remarkable consistency has developed in a small number of studies addressing the influence of RF radiation on tree growth and fecundity, most notably in three plant studies out of the former Soviet Union in the republic of Latvia (all conducted in the vicinity of Skrunda Radio Location Station).
In the initial study, Balodis, and others (1996) reported on the growth of trees in an exposed region for the 11 years before 1971, when the radar became active, and for the 16 years following the continuous radiation exposure. Trunk samples were obtained from 50-90-year-old Pinus sylvestris L. trees (Balodis and others 1996) growing in 29 sampling plots and the tree heights and diameters were also measured. Radial annual increments in growth were measured to a precision of 0.01 mm. Exposure was at 156-162 MHz, with a pulse duration of 0.8 msec, interpulse interval of 41 msec, and pulse power densities as high as 375 µW/cm2. Growth was significantly (p = 0.001) inhibited by exposure, with a direct linear correlation with distance from the station. Electric-field exposure levels appear to have ranged from 0.4 mV/m to 250 mV/m. Several possible sources of pollution that might have affected the ring widths were shown not to have caused the decrease in ring widths that coincided with the startup of the Skrunda radio-location system.
In a companion paper, Selga and Selga (1996) reported on Skrunda Radio Location Station EMF-induced modification of Golgi apparatus in pine needles and a switch from synthesis of predecessors of cell walls (lignins) to formation and export of resin predecessors.
In the paper by Magone (1996), effects of Skrunda Radio Location Station EMF on the duckweed Spirodela polyrhiza was observed. After 55-day exposure, various morphological and developmental abnormalities were observed in 6-10 daughter plants from 10 exposed mother plants, while only 0.1 plant with abnormalities per 10 mother plants were observed in the control condition. The same daughter fronds had a shorter life-span (67 days compared to 87 days in the control) and fewer subsequent daughters (total eight compared to 10 in the control group).
In a more recent, sham-controlled study of the effect of RF exposure on tree growth, Lerchl and others (2000) obtained a similar observation. In this study, seedlings of three conifer species (Abies alba, Abies grandis, Pinus pumila) were exposed in a radial waveguide, in a blinded fashion, and seedling height was measured each week for a six-month period. Exposure was at 383 MHz, with a 20% duty cycle Hz, at a field intensity of 131 V/m. A significant inhibition of growth was observed.
It should be noted, however, that long-term exposures in plants can be influenced by a variety of different factors including micro-environmental changes.
SUMMARY AND CONCLUSIONS
The biological studies that most closely reflect a PAVE PAWS type of radiation exposure are the tree-growth studies. In those studies, a significant dose-dependent response was observed. In addition, some embryo development studies and a few in vitro studies have also suggested the possibility of ELF-modulated microwave-frequency RF exposures producing significant biological effects.
The consideration that the modulation frequency of the PAVE PAWS may play a significant role in understanding the potential for this radar to influence biological systems was also raised by the first NAS review committee in 1979. PAVE PAWS has an ELF-modulation envelope that gives rise to spectral characteristics in the 10-100 Hz frequency range. This is due to diagnostic and calibration sequences, where a pulse is removed, but many other radar systems use these sequences. Substantial research has been undertaken in this area over the last decade, with the specific intent of establishing field-intensity thresholds under well-controlled conditions. As a result of those efforts, reproducible biological effects of electric-field exposures in the ELF-frequency range have been demonstrated for induced electric-field intensities of less than 1 µ/centimeter (e.g., see the work of Rosenspire and others 2001; McLeod and Collazo 2000). Indeed, the NIEHS has concluded in a recent report that ELF electric fields below 10 µ/cm can produce reproducible biological effects (NIEHS 1998).
Responses at the cell level that are traditionally associated with carcinogenesis, such as DNA damage and mutation induction, have been observed in only one study, while several studies have documented no DNA damage associated with RF exposure. While further studies are required to clarify this issue, the
evidence supporting DNA damaging events following RF exposures is weak. Other biological events that would contribute to non-DNA damage responses, and whole-organism responses, are better reported in the literature.
To clarify these conclusions, additional studies would be required. Specifically, long-term studies of complex biological responses following exposure to PAVE PAWS type radiation, as described in the U.S. Air Force Phase IV time-domain studies, would be capable of directly confirming previous reports of cell-level effects, particularly those that utilize modern large-scale data generation and analysis techniques (i.e., protein- and genomic-array-based studies). In addition, studies addressing the rectification properties of living tissue in the microwave region, most importantly, living skin, which is the predominant human organ exposed to the pulsed radiation associated with PAVE PAWS, would provide a firm foundation on which to calculate the magnitude of any induced-ELF field in the body due to exposure to ELF-modulated microwave radiation. If significant demodulation in living tissue were to be demonstrated, much of the literature regarding ELF-field interactions with tissue would be relevant to understanding the potential of PAVE PAWS exposure to influence biological systems. Similarly, due to the fact that long-term studies have demonstrated effects on plant growth from radar exposure, consideration should be given to examining plant growth around the PAVE PAWS facility.
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